A method and system for automatic determination of digestion endpoint of food based on electrical signal gradient

Abstract

The present application relates to the technical field of food detection pretreatment, and discloses a food digestion endpoint automatic determination method and system based on an electric signal gradient. The method comprises: obtaining an electric signal time sequence and digestion temperature data of a digestion system during food sample digestion; performing temperature compensation on the electric signal time sequence based on the digestion temperature data, and performing baseline correction in combination with a blank digestion liquid baseline to obtain a compensated electric signal sequence; dividing the compensated electric signal sequence into sampling windows and removing transient disturbance windows; calculating a first-order gradient feature and a fluctuation stability feature based on the retained sampling windows; when a plurality of consecutive sampling windows meet gradient stability conditions, window stability conditions and temperature stability conditions, determining that the food sample reaches a digestion endpoint, and outputting a digestion control instruction. The present application can reduce the influence of temperature, reagent background and transient disturbance on endpoint determination, and improve the automation degree and reliability of food digestion endpoint determination.

Description

Technical Field

[0001] This invention relates to the field of food pretreatment technology, and in particular to an automatic method and system for determining the endpoint of food digestion based on electrical signal gradient. Background Technology

[0002] In food testing, when detecting heavy metals, inorganic elements, or other analytes in food samples, it is usually necessary to digest the samples first. This process thoroughly breaks down the organic matrix in the food sample and allows the analytes to enter a solution system suitable for subsequent instrumental analysis. The effectiveness of food sample digestion directly affects the accuracy, repeatability, and stability of subsequent test results.

[0003] Current food sample digestion processes are typically controlled by fixed temperatures, fixed times, or preset heating programs. The completion of digestion is determined manually by observing the color, clarity, and state of remaining particles in the digestate. While automated digestion equipment can usually perform automatic heating, heat preservation, liquid replenishment, acid removal, or cooling, the determination of the digestion endpoint still largely relies on preset process parameters or human experience.

[0004] However, the matrix composition of different types of food samples varies considerably, with differences in the content of proteins, fats, carbohydrates, salts, moisture, and other additives. This can lead to significant differences in reaction rates, foam states, solution electrochemical properties, and digestion completion times during the digestion process. Using a uniform, fixed digestion time can easily result in some samples being under-digested or over-digested. Under-digestion leads to insufficient destruction of the sample matrix, affecting subsequent testing results; over-digestion increases digestion time, reagent consumption, and energy consumption, and may increase the risk of sample loss or contamination.

[0005] Meanwhile, during the digestion process, electrical signals such as conductivity, impedance, potential, and current response of the digestion solution change as the digestion reaction progresses. However, these electrical signals are also easily affected by factors such as digestion temperature, background of digestion reagents, addition of reagents, boiling of the digestion solution, bubble adhesion, electrode contamination, and switching of heating power. If the digestion endpoint is determined solely based on a single electrical signal value or a simple trend, misjudgment is likely to occur, making it difficult to meet the stability and consistency requirements of food pretreatment processes.

[0006] Therefore, there is an urgent need to provide a technical solution that can automatically determine the digestion endpoint by combining digestion temperature, electrical signal baseline, and electrical signal gradient change status during the digestion process of food samples, so as to improve the accuracy and automation of food digestion endpoint determination. Summary of the Invention

[0007] The purpose of this invention is to provide an automatic method and system for determining the endpoint of food digestion based on electrical signal gradient, which solves the technical problem that existing food digestion processes mainly rely on fixed digestion procedures or manual experience to determine the digestion endpoint, making it difficult to adapt to differences in different food matrices and easily causing under-digestion or over-digestion.

[0008] To achieve the above objectives, the present invention provides an automatic method for determining the endpoint of food digestion based on electrical signal gradient, comprising: During the food sample digestion process, the time series of electrical signals and digestion temperature data of the digestion system are acquired; Temperature compensation is performed on the electrical signal time series based on the digestion temperature data, and baseline correction is performed on the temperature-compensated electrical signal time series in combination with the blank digestion solution baseline to obtain the compensated electrical signal series. The compensation electrical signal sequence is divided into sampling windows, and transient disturbance windows are removed based on the electrical signal change state within the sampling window; Based on the sampling window retained after removing the transient disturbance window, the electrical signal gradient features are calculated. The electrical signal gradient features include the first-order gradient features between adjacent sampling windows and the fluctuation stability features within the sampling window. When the first-order gradient features of multiple consecutive sampling windows satisfy the first gradient stability condition, the fluctuation stability features satisfy the window stability condition, and the corresponding digestion temperature data satisfy the temperature stability condition, the food sample is determined to have reached the digestion endpoint. Output the digestion control command based on the digestion endpoint.

[0009] Optionally, the electrical signal time series includes at least one of the following: conductance signal time series, impedance signal time series, current response signal time series, voltage response signal time series, potential signal time series, and electrochemical impedance spectroscopy characteristic time series. By acquiring one or more electrical signals, changes in the food sample digestion process can be characterized from aspects such as changes in ion concentration, charge transport state, interfacial response characteristics, or electrochemical response state of the digestion system.

[0010] Optionally, the electrical signal time series is acquired using an acid-resistant electrode assembly. The acid-resistant electrode assembly can be placed inside the digestion container, in the digestion solution circulation pipeline, or in the digestion solution detection tank. The acid-resistant electrode assembly is connected to an electrical signal acquisition circuit, which applies an AC excitation signal to the acid-resistant electrode assembly and acquires the corresponding response signal of the digestion system. Thus, the changes in the electrical response of the digestion system can be acquired in real-time or near real-time during the digestion process.

[0011] Optionally, temperature compensation is performed on the electrical signal time series based on the digestion temperature data, including: determining the temperature compensation coefficient corresponding to each sampling time according to the digestion temperature data; and converting the electrical signal time series into an equivalent electrical signal time series at a reference temperature based on the temperature compensation coefficient. The reference temperature can be a preset temperature or a reference temperature after the digestion process enters the stable heating stage. Through temperature compensation, the influence of digestion temperature changes on the electrical signal can be reduced, making the compensated electrical signal better reflect the digestion reaction process.

[0012] Optionally, baseline correction is performed on the temperature-compensated electrical signal time series based on the blank digestion solution baseline. This includes: obtaining the baseline electrical signal sequence of the blank digestion solution without food sample added under the corresponding digestion program; and subtracting and correcting the equivalent electrical signal time series based on the baseline electrical signal sequence to obtain the compensated electrical signal sequence. The baseline electrical signal sequence is used to characterize the background changes in electrical signals of the digestion reagent itself as a function of digestion temperature and / or digestion time. This reduces the interference of changes in the acid system itself on the identification of the digestion status of the food sample.

[0013] Optionally, transient disturbance windows are eliminated based on the electrical signal change state within the sampling window, including: calculating the abrupt change amplitude and / or window fluctuation amplitude of the compensated electrical signal within the current sampling window; when the abrupt change amplitude is greater than a preset abrupt change threshold, and / or the window fluctuation amplitude is greater than a preset fluctuation threshold, the current sampling window is determined as a candidate disturbance window; the digestion process state corresponding to the candidate disturbance window is obtained; if the digestion process state corresponds to a preset disturbance state, the candidate disturbance window is determined as a transient disturbance window, and the transient disturbance window is eliminated when determining the digestion endpoint. The preset disturbance state includes at least one of the following: addition of digestion reagent, boiling of digestion solution, bubble adhesion, electrode contamination, and switching of heating power. This avoids misjudging electrical signal abrupt changes not caused by the digestion process itself as changes at the digestion endpoint.

[0014] Optionally, calculating the electrical signal gradient characteristics based on the sampling windows retained after removing the transient disturbance window includes: calculating the window statistics of the compensated electrical signal within each retained sampling window; determining the first-order gradient characteristics based on the difference between the window statistics of adjacent sampling windows and the sampling window time interval; and determining the fluctuation stability characteristics based on the standard deviation, range, or coefficient of variation of the compensated electrical signal within the current sampling window. The window statistics can be the mean, median, weighted mean, or filtered representative value of the compensated electrical signal within the sampling window.

[0015] Optionally, the electrical signal gradient feature further includes a second-order gradient feature. The second-order gradient feature is determined based on the change between adjacent first-order gradient features. When the first-order gradient features of multiple consecutive sampling windows satisfy the first gradient stability condition, the second-order gradient features satisfy the second gradient stability condition, the fluctuation stability feature satisfies the window stability condition, and the corresponding digestion temperature data satisfies the temperature stability condition, the food sample is determined to have reached the digestion endpoint. This allows for further determination of whether the rate of change of the electrical signal tends to level off, improving the stability of endpoint determination.

[0016] Optionally, the first gradient stabilization condition, the window stabilization condition, and / or the temperature stabilization condition are determined based on at least one of the following: the matrix type of the food sample, the initial electrical signal level, the type of digestion reagent, the sample mass, and the digestion temperature range. By determining the judgment criteria based on the food sample and digestion conditions, the applicability among different food samples can be improved.

[0017] Optionally, when the food sample has not been determined to have reached the digestion endpoint, the digestion equipment is controlled to maintain heating, extend the digestion time, adjust the heating power, or output a prompt to add digestion reagent. When the food sample is determined to have reached the digestion endpoint, the digestion control command includes at least one of the following: a stop heating command, an acid removal control command, a cooling control command, a volume adjustment prompt command, and a digestion completion prompt command. Thus, the endpoint determination result can be linked with the digestion equipment control process, improving the automation level of food pre-digestion processing.

[0018] The present invention also provides an automatic food digestion endpoint determination system based on electrical signal gradient, comprising: The digestion unit is used to digest food samples. Acid-resistant electrode assembly for use in contact digestion systems; An electrical signal acquisition unit, connected to the acid-resistant electrode assembly, is used to acquire the electrical signal time series of the digestion system during the food sample digestion process; Temperature acquisition unit, used to acquire digestion temperature data of the digestion system; The compensation processing unit is used to perform temperature compensation on the electrical signal time series based on the digestion temperature data, and to perform baseline correction on the temperature-compensated electrical signal time series in combination with the blank digestion solution baseline, so as to obtain the compensated electrical signal series. The disturbance removal unit is used to divide the compensation electrical signal sequence into sampling windows and remove transient disturbance windows according to the electrical signal change state within the sampling window. The gradient calculation unit is used to calculate the gradient features of the electrical signal based on the sampling window retained after removing the transient disturbance window. The gradient features of the electrical signal include the first-order gradient features between adjacent sampling windows and the fluctuation stability features within the sampling window. The endpoint determination unit is used to determine that the food sample has reached the digestion endpoint when the first-order gradient features of multiple consecutive sampling windows meet the first gradient stability condition, the fluctuation stability features meet the window stability condition, and the corresponding digestion temperature data meet the temperature stability condition. A control output unit is used to output a digestion control command according to the digestion endpoint.

[0019] Through the above technical solutions, the beneficial effects of the present invention are as follows: During the digestion of food samples, the electrical signal time series of the digestion system is collected, and the digestion endpoint is determined based on the electrical signal gradient characteristics. This eliminates the reliance on fixed digestion times or manual observation results, and more directly reflects the state changes of the digestion system as the digestion reaction progresses, thereby reducing the risk of under-digestion and over-digestion. Furthermore, by dividing the compensation electrical signal sequence into sampling windows and eliminating transient disturbance windows based on the electrical signal change state within the sampling windows, the influence of transient disturbances caused by factors such as the addition of digestion reagents, boiling of the digestion solution, bubble adhesion, electrode contamination, or switching of heating power on the endpoint determination results can be reduced, thus improving the reliability of the digestion endpoint determination. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention, and the embodiments in the accompanying drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A flowchart illustrating an automatic food digestion endpoint determination method based on electrical signal gradient provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of an automatic food digestion endpoint determination system based on electrical signal gradient, provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of the continuous change curve of electrical conductivity during the digestion process of a food sample provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the continuous impedance change curve during the food sample digestion process provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the continuous potential change curve during the digestion of a food sample, provided in an embodiment of the present invention. Figure 6 This is a schematic diagram of the electrical signal gradient stability characteristics provided in an embodiment of the present invention; Figure 7 A flowchart illustrating the transient disturbance window removal process provided in an embodiment of the present invention; Figure 8 A logical diagram illustrating the process of determining the digestion endpoint and controlling digestion according to an embodiment of the present invention; The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the following embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Where there is no conflict, the technical features in the following embodiments can be combined with each other.

[0023] This invention provides an automatic method and system for determining the endpoint of food digestion based on electrical signal gradients. It is applicable to wet digestion, electrothermal digestion, graphite digestion, microwave digestion, or other digestion processes in the pretreatment of food for testing. The food sample can be a grain sample, meat product sample, dairy product sample, vegetable sample, aquatic product sample, condiment sample, beverage sample, or other food sample to be tested. The food testing items can be heavy metal element detection, inorganic element detection, or other detection items that require the release of the analyte through pretreatment before digestion.

[0024] During food sample digestion, organic matter, salts, and analytes are gradually released, causing changes in the ionic composition, redox environment, and electrode interface response of the digestion solution. Consequently, electrical signals such as conductivity, impedance, current response, voltage response, potential, and electrochemical impedance spectroscopy characteristics of the digestion system also undergo continuous changes. Typically, in the initial stages of digestion, the reaction is more vigorous, resulting in a higher rate of change in electrical signals. As the organic matrix in the food sample is gradually destroyed, the number of newly released ions and reactive components decreases, leading to a slower rate of change in electrical signals and a gradual entry into a relatively stable plateau region. Therefore, the stability of the electrical signal gradient can be used to characterize whether the food sample has reached the digestion endpoint.

[0025] Meanwhile, the electrical signals during the digestion process are easily affected by factors such as digestion temperature, background of digestion reagents, addition of digestion reagents, boiling of the digestion solution, bubble adhesion, electrode contamination, and switching of heating power. If the endpoint is determined directly based on the original electrical signals, temperature drift, changes in acid background, or transient disturbances may be mistaken for changes in the digestion reaction state. Therefore, this embodiment performs temperature compensation and blank digestion solution baseline correction on the collected electrical signals, removes transient disturbance windows, and then determines the endpoint based on the first-order gradient characteristics, fluctuation stability characteristics, and digestion temperature data from multiple consecutive sampling windows.

[0026] like Figure 1As shown in the figure, the automatic determination method for the endpoint of food digestion based on electrical signal gradient provided in this embodiment includes the following steps.

[0027] S101, during the food sample digestion process, acquire the electrical signal time series and digestion temperature data of the digestion system.

[0028] Specifically, the food sample to be digested and the digestion reagent are added to the digestion container, and the digestion program is started. The digestion reagent may include one or more of nitric acid, hydrogen peroxide, hydrochloric acid, and perchloric acid, or other digestion reagents commonly used in the field of food testing pretreatment. The digestion equipment heats the digestion container according to a preset heating program, heat preservation program, or heating power control program, causing the organic matrix in the food sample to be oxidized, decomposed, or destroyed.

[0029] During the digestion process, the time series of electrical signals of the digestion system is acquired using an acid-resistant electrode assembly. The acid-resistant electrode assembly can be placed inside the digestion container, within the digestion solution circulation pipeline, or in the digestion solution detection tank. The acid-resistant electrode assembly may include platinum electrodes, titanium-coated electrodes, graphite electrodes, glassy carbon electrodes, or other acid- and temperature-resistant electrodes. The electrical signal acquisition circuit can apply an AC excitation signal to the acid-resistant electrode assembly and acquire the corresponding response signal of the digestion system, thereby obtaining at least one of the following: conductivity signal, impedance signal, current response signal, voltage response signal, potential signal, or electrochemical impedance spectroscopy characteristics. The time series of electrical signals can be expressed as E(t), where t is the sampling time.

[0030] Among them, conductivity signals can be used to characterize changes in ion concentration and ion migration ability in the digestion solution; impedance signals can be used to characterize changes in the overall conductivity of the digestion solution and the response state of the electrode-solution interface; and potential signals can be used to characterize changes in the redox environment of the digestion system. In practical applications, one of the electrical signals can be selected as the main criterion for judgment, or multiple electrical signals can be combined for judgment.

[0031] Simultaneously, the digestion temperature data of the digestion system is acquired through temperature sensors. These sensors can be placed inside the digestion vessel, on its outer wall, near the heating module, or in the digestion solution detection tank. The digestion temperature data can be represented as T(t). This data is not only used for subsequent temperature compensation but also to determine whether the current digestion process is within a stable temperature range, avoiding misjudgment of the digestion endpoint during rapid heating phases.

[0032] S102, temperature compensation is performed on the electrical signal time series based on the digestion temperature data, and baseline correction is performed on the temperature-compensated electrical signal time series in combination with the blank digestion solution baseline to obtain the compensated electrical signal series.

[0033] Specifically, since the electrical signal of the digestion system changes with temperature, it is necessary to perform temperature compensation on the electrical signal time series based on the digestion temperature data. For example, under similar conditions, conductivity usually increases with increasing temperature, impedance usually decreases with increasing temperature, and the potential signal may also drift due to temperature changes. Without temperature compensation, some changes in the electrical signal curve may originate from temperature changes rather than the digestion reaction of the food sample itself.

[0034] In one implementation, the temperature compensation coefficient K(T) corresponding to each sampling time can be determined based on the digestion temperature data T(t). For conductivity signals, temperature compensation can be performed as follows: Ec1(t)=E(t) / [1+α(T(t)-Tref)]; Where Ec1(t) is the equivalent electrical signal after temperature compensation, E(t) is the acquired electrical signal, α is the temperature compensation coefficient, and Tref is the reference temperature. The reference temperature can be a preset temperature, such as 25℃, or it can be the reference temperature after the digestion process enters the stable heating stage.

[0035] For impedance or potential signals, compensation can also be performed using a pre-calibrated temperature-electrical signal compensation model or temperature compensation lookup table. For example, a temperature compensation model can be established based on the impedance change curves or potential drift curves of the blank digestion solution at different temperatures, and the collected impedance or potential signals can be converted into equivalent signals at a reference temperature. This embodiment does not limit the specific form of the temperature compensation model, as long as it can reduce the influence of digestion temperature changes on the electrical signal.

[0036] Further, the baseline electrical signal sequence B(t) of the blank digestion solution without the addition of food samples is obtained under the corresponding digestion program. The blank digestion solution can be the same type and amount of digestion reagent added as in the food sample digestion experiment, but without the addition of food samples. Under the same or similar temperature, holding, and sampling conditions, the baseline electrical signal sequence corresponding to the blank digestion solution is collected. This baseline electrical signal sequence is used to characterize the background changes in electrical signals of the digestion reagent itself as a function of digestion temperature and / or digestion time.

[0037] In one implementation, the baseline electrical signal sequence of the blank digest can be subjected to the same temperature compensation to obtain a temperature-compensated baseline electrical signal sequence Bc1(t). Then, the equivalent electrical signal Ec1(t) after temperature compensation is baseline corrected to obtain a compensated electrical signal sequence Ec(t). For example, the subtraction correction can be performed as follows: Ec(t) = Ec1(t) - Bc1(t).

[0038] In other implementations, the compensated electrical signal sequence can be obtained using ratio correction, normalization correction, differential correction, or correction based on a fitting function. For impedance signals, correction can also be performed using a relative rate of change, depending on the detection requirements. Through temperature compensation and blank digestion baseline correction, the compensated electrical signal sequence can better reflect the digestion state changes of the food sample itself.

[0039] S103, the sampling window of the compensation electrical signal sequence is divided, and transient disturbance windows are removed according to the change state of the electrical signal within the sampling window.

[0040] Specifically, the compensation electrical signal sequence Ec(t) is divided into multiple sampling windows according to a preset time length. Each sampling window can be a fixed time window, such as 30s, 60s, 120s, or other time lengths. Adjacent sampling windows can be non-overlapping or partially overlapping. The i-th sampling window can be represented as Wi.

[0041] During digestion, factors such as the addition of digestion reagents, boiling of the digestion solution, bubble adhesion, electrode contamination, and switching of heating power may cause transient abrupt changes or short-term abnormal fluctuations in the electrical signal. These abnormal fluctuations do not necessarily indicate a change in the digestion process of the food sample itself. Directly using such windows for endpoint determination may lead to misjudgment. Therefore, this embodiment identifies and eliminates transient disturbance windows based on the changes in the electrical signal within the sampling window.

[0042] like Figure 7 As shown, in one implementation, the abrupt change amplitude and / or window fluctuation amplitude of the compensated electrical signal within the current sampling window Wi are calculated. The abrupt change amplitude can be determined based on the maximum difference between adjacent sampling points within the current window, or based on the difference between the current window statistics and the previous window statistics. The window fluctuation amplitude can be determined based on the range, standard deviation, or coefficient of variation of the compensated electrical signal within the current window.

[0043] When the mutation amplitude exceeds a preset mutation threshold, and / or the window fluctuation amplitude exceeds a preset fluctuation threshold, the current sampling window is determined as a candidate perturbation window. Subsequently, the digestion process status corresponding to this candidate perturbation window is obtained. The digestion process status can be derived from the digestion equipment's control log, heating power change records, liquid replenishment records, temperature change rate, abnormal electrical signal patterns, or operator input information.

[0044] If the digestion process state corresponding to a candidate perturbation window corresponds to a preset perturbation state, then the candidate perturbation window is identified as a transient perturbation window and is removed during the digestion endpoint determination. The preset perturbation state may include at least one of the following: addition of digestion reagent, boiling of the digestion solution, bubble adhesion, electrode contamination, and switching of heating power. It should be noted that removing a transient perturbation window does not mean deleting the original collected data, but rather that when calculating the continuous stable window required for endpoint determination, the transient perturbation window is not included as a valid stable window in the determination.

[0045] S104: Calculate the gradient characteristics of the electrical signal based on the sampling window retained after removing the transient disturbance window.

[0046] Specifically, the electrical signal gradient features are calculated based on the retained sampling windows. These electrical signal gradient features include first-order gradient features between adjacent sampling windows and fluctuation stability features within the sampling window. In other embodiments, the electrical signal gradient features may also include second-order gradient features.

[0047] In one implementation, the window statistics Xi of the compensated electrical signal within each retained sampling window Wi is first calculated. The window statistics Xi can be the mean, median, weighted mean, filtered representative value, or other statistical values ​​that characterize the current window's electrical signal level. For example, the window mean can be calculated as follows: Xi = mean{Ec(t), t∈Wi}.

[0048] Then, based on the difference between the window statistics of adjacent sampling windows and the sampling window time interval, the first-order gradient feature Gi is determined. For example: Gi = (Xi - Xi-1) / (ti - ti-1); Where Xi is the window statistics corresponding to the i-th sampling window, Xi-1 is the window statistics corresponding to the (i-1)-th sampling window, and ti and ti-1 are the center time or end time of the corresponding sampling window, respectively.

[0049] The first-order gradient feature Gi is used to characterize the rate of change of the electrical signal between adjacent sampling windows. For conductance signals, Gi is usually a large positive value in the early stages of digestion, indicating a rapid increase in conductivity; as the digestion system stabilizes, Gi gradually approaches zero. For impedance signals, Gi can be a large negative value in the early stages of digestion, indicating a rapid decrease in impedance; as the digestion system stabilizes, its absolute value gradually decreases and approaches zero. For potential signals, Gi can exhibit a significant positive or negative drift in the early stages of digestion; as the digestion system stabilizes, its absolute value gradually decreases.

[0050] Further, the fluctuation stability feature Si is determined according to the standard deviation, range or coefficient of variation of the compensated electrical signal in the current sampling window. For example, the coefficient of variation may be calculated in the following manner: Si=std{Ec(t), t∈Wi} / (|Xi|+ε); Herein, std represents the standard deviation, and ε is a constant for preventing the denominator from being zero. The fluctuation stability feature Si is used to characterize the fluctuation degree of the electrical signal in the current sampling window. A smaller Si indicates that the electrical signal in the current window is more stable.

[0051] In a further embodiment, a second-order gradient feature Hi may also be calculated. The second-order gradient feature Hi may be determined according to the variation between adjacent first-order gradient features, for example: Hi=(Gi-Gi-1) / (ti-ti-1).

[0052] The second-order gradient feature Hi is used to characterize whether the change rate of the electrical signal itself tends to be gentle. If both the first-order gradient feature and the second-order gradient feature tend to be stable, it indicates that the compensated electrical signal sequence has a high possibility of entering a continuous plateau region.

[0053] S105: When the first-order gradient features of a plurality of consecutive sampling windows satisfy a first gradient stability condition, the fluctuation stability features satisfy a window stability condition, and the corresponding digestion temperature data satisfy a temperature stability condition, it is determined that the food sample reaches the digestion end point.

[0054] Specifically, the first gradient stability condition may include: the absolute values of the first-order gradient features of M consecutive sampling windows are all less than a first gradient threshold Gth, that is, |Gi|<Gth.

[0055] The window stability condition may include: the fluctuation stability features of M consecutive sampling windows are all less than a stability threshold Sth, that is, Si<Sth.

[0056] The temperature stability condition may include: the digestion temperatures corresponding to M consecutive sampling windows are within a preset digestion temperature interval, and / or the temperature change rate is less than a preset temperature change threshold. For example, the average temperature in the current window is within a preset stable temperature interval, and the temperature change between adjacent windows is less than the preset temperature change threshold. M is an integer greater than or equal to 2, for example, may be 3, 4 or 5.

[0057] In one embodiment, when M consecutive sampling windows simultaneously satisfy |Gi|<Gth, Si<Sth and the temperature stability condition, it is determined that the food sample reaches the digestion end point. In another embodiment, it may be further required that the second-order gradient feature Hi satisfies a second gradient stability condition, for example, |Hi|<Hth, so as to improve the reliability of end point determination.

[0058] The first gradient threshold Gth, stability threshold Sth, second gradient threshold Hth, and temperature stabilization conditions can be determined based on at least one of the following: matrix type of the food sample, initial electrical signal level, type of digestion reagent, sample mass, and digestion temperature range. For example, for food samples with high salt content, the first gradient threshold can be normalized and adjusted based on its initial conductivity level; for food samples with high fat or protein content, the number of consecutive windows M or the sampling window length can be appropriately increased to avoid misjudgment caused by early local stabilization.

[0059] S106, outputs a digestion control command based on the digestion endpoint.

[0060] like Figure 8 As shown, when the food sample is determined to have reached the digestion endpoint, the controller can output a digestion control command. The digestion control command may include at least one of the following: a stop heating command, an acid removal control command, a cooling control command, a volume adjustment prompt command, and a digestion completion prompt command. For example, after the digestion endpoint is determined, the digestion equipment can stop the main digestion heating and enter the acid removal stage; after acid removal is completed, it can enter the cooling stage or prompt the operator to perform volume adjustment.

[0061] When the food sample has not been determined to have reached the digestion endpoint, the controller can control the digestion equipment to maintain heating, extend the digestion time, adjust the heating power, or output a prompt to add digestion reagent. For example, if the electrical signal is still in a rapidly changing phase, the current digestion program will continue; if the electrical signal has not reached a stable state for a long time and the temperature has reached the preset digestion temperature, a prompt to add digestion reagent or a sample abnormality can be issued; if there are continuous and violent fluctuations, a prompt to check the electrode status or the boiling status of the digestion solution can be issued.

[0062] like Figures 3 to 5 As shown, different types of electrical signals can exhibit different continuous change curves during the digestion of food samples. Figure 3 The diagram illustrates the continuous change in conductivity. In the initial stage of digestion, salts, analytes, and some soluble components in the food sample are gradually released, causing rapid changes in ion concentration and migration capacity in the digestate, resulting in a rapid increase in conductivity. As the organic matrix in the food sample is sufficiently destroyed, the number of newly released ions gradually decreases, the rate of change in conductivity slows down, and the sample enters a relatively stable plateau region.

[0063] Figure 4 The diagram schematically illustrates the continuous impedance variation curve. In the initial stage of digestion, the impedance signal can decrease rapidly as the conductivity of the digestate increases and the interfacial charge transport state changes. As the digestion reaction gradually completes, the impedance decrease rate gradually decreases and enters a relatively stable plateau region.

[0064] Figure 5The diagram illustrates the continuous potential change curve. In the initial stage of digestion, the organic matter in the food sample is gradually destroyed by the strongly oxidizing digestion system, resulting in a significant change in the redox environment of the digestion solution, and the potential signal exhibits a clear drift trend. As the reactive components gradually decrease, the potential drift rate decreases, and the digestion enters a relatively stable state.

[0065] Figure 6 The diagram illustrates the gradient stability characteristics of an electrical signal. After dividing the compensation electrical signal curve into sampling windows, the first-order gradient characteristics between adjacent sampling windows and the fluctuation stability characteristics within the current sampling window can be calculated. During the rapid change phase of the electrical signal, the absolute value of the first-order gradient characteristic is relatively large, and the fluctuation within the window may also be large; after the electrical signal enters the continuous plateau region, the absolute value of the first-order gradient characteristic gradually approaches zero, and the fluctuation stability characteristics within the window decrease. Therefore, the first-order gradient stability state and the window fluctuation stability state of multiple consecutive sampling windows can be used as the criteria for determining the elimination endpoint.

[0066] To further illustrate the correspondence between the continuous change curve of an electrical signal and the gradient stability characteristics of the electrical signal, the following example data will be used for illustration.

[0067] In a specific data example, taking the digestion process of a food sample as an example, the conductivity, impedance, and potential data of the digestion system were collected every 5 minutes during the digestion process, and the corresponding digestion stages were recorded simultaneously. After temperature compensation and baseline correction of the blank digestion solution, the following continuous change data of electrical signals were obtained. It should be noted that the data in the table below is only used to illustrate the trend of electrical signal changes during the digestion process and does not constitute a limitation on the scope of protection of this invention.

[0068] Table 1 Examples of continuous changes in electrical signals during food sample digestion.

[0069] As shown in Table 1, in the initial stage of digestion, from 0 min to 25 min, the conductivity increased from 2.20 mS·cm^-1 to 8.96 mS·cm^-1, the impedance decreased from 205.0 Ω to 79.1 Ω, and the potential changed from 315.0 mV to 259.4 mV. This indicates that organic matter, salts, and analyte elements in the food sample were continuously released, and the ionic composition and redox environment of the digestion solution were in a state of rapid change.

[0070] Between 30 and 55 minutes, the conductivity continued to increase, but the rate of increase decreased significantly; the impedance continued to decrease, but the rate of decrease decreased significantly; and the potential drift amplitude also gradually decreased. This indicates that the main digestion reaction of the food sample gradually slowed down, and the digestion system gradually transitioned from the reaction-dominated stage to the stable stage.

[0071] After 60 minutes, the conductivity remained relatively stable within the range of 10.37 mS·cm⁻¹ to 10.40 mS·cm⁻¹, the impedance remained relatively stable within the range of 68.1 Ω to 68.3 Ω, and the potential remained relatively stable within the range of 240.9 mV to 241.3 mV. At this point, the conductivity, impedance, and potential all entered a continuous plateau region, indicating that the number of newly released release ions and reactive components in the digestion system was significantly reduced, and the electrical response of the digestion system tended to stabilize. Combined with the reference endpoint state, it can be seen that the electrical signal plateau region after 60 minutes corresponds to the state where the food sample has reached the completion of digestion.

[0072] Furthermore, the compensated electrical signal sequences in Table 1 are processed using a fixed sampling window. In this example, the interval between adjacent sampling time points is used as a sampling window, and the first-order gradient of conductivity, first-order gradient of impedance, first-order gradient of potential, and standard deviation of conductivity window are calculated for each sampling window. Specific data are as follows.

[0073] Table 2 Examples of window gradient characteristic data during food sample digestion

[0074] In this example, the first-order gradient threshold Gth for conductivity is set to 0.010 mS·cm^-1·min^-1, the window stability threshold Sth is set to 0.060 mS·cm^-1, and the number of consecutive stable windows M is set to 3. That is, when three consecutive sampling windows satisfy the condition that the absolute value of the first-order gradient of conductivity is less than 0.010 mS·cm^-1·min^-1, and the standard deviation of the conductivity window is less than 0.060 mS·cm^-1, the compensated conductivity curve is considered to have entered a continuous plateau region.

[0075] As shown in Table 2, from 5 min to 40 min, the first-order conductivity gradient gradually decreased from 0.410 mS·cm^-1·min^-1 to 0.052 mS·cm^-1·min^-1, but it was still greater than the preset first-order conductivity gradient threshold, indicating that the digestion system was still in a significant change phase. From 45 min to 55 min, the first-order conductivity gradient further decreased to 0.022 mS·cm^-1·min^-1, 0.016 mS·cm^-1·min^-1, and 0.008 mS·cm^-1·min^-1, indicating that the digestion reaction gradually slowed down. However, since the window stability characteristics did not continuously meet the stability conditions, this stage can be identified as the transition stage.

[0076] Within the three consecutive sampling windows of 60 min, 65 min, and 70 min, the first-order gradients of conductivity were 0.004 mS·cm^-1·min^-1, 0.002 mS·cm^-1·min^-1, and 0.002 mS·cm^-1·min^-1, respectively, all less than the preset first-order gradient threshold Gth. Simultaneously, the standard deviations of the conductivity windows were 0.05 mS·cm^-1, 0.04 mS·cm^-1, and 0.04 mS·cm^-1, respectively, all less than the window stability threshold Sth. Therefore, it can be determined that the compensated conductivity curve enters a gradient stable state within the consecutive sampling windows corresponding to 60 min to 70 min, and the time corresponding to 70 min or the completion time of the third consecutive stable window can be determined as the endpoint determination time. It should be noted that the reference endpoint status is used to characterize the digestion completion status determined manually or by standard methods; this method is based on automatic determination through M consecutive stable sampling windows, so the digestion endpoint determination result can be output when the third consecutive stable window is completed.

[0077] In another embodiment, the first-order impedance gradient and the first-order potential gradient can be combined for joint determination. For example, the first-order impedance gradient threshold Zth can be set to 0.10 Ω·min^-1, and the first-order potential gradient threshold Pth can be set to 0.15 mV·min^-1. When multiple consecutive sampling windows simultaneously meet the conditions that the absolute value of the first-order conductivity gradient is less than Gth, the absolute value of the first-order impedance gradient is less than Zth, the absolute value of the first-order potential gradient is less than Pth, the window stability characteristic is less than Sth, and the temperature is stable, the food sample is determined to have reached the digestion endpoint.

[0078] Taking Table 2 as an example, in the three consecutive sampling windows of 60 min, 65 min, and 70 min, the absolute values ​​of the first-order impedance gradient are 0.02 Ω·min^-1, 0.02 Ω·min^-1, and 0.00 Ω·min^-1, respectively, all less than the first-order impedance gradient threshold Zth; the absolute values ​​of the first-order potential gradient are 0.12 mV·min^-1, 0.04 mV·min^-1, and 0.02 mV·min^-1, respectively, all less than the first-order potential gradient threshold Pth. Therefore, the conductivity, impedance, and potential signals all indicate that the digestion system enters a stable state within this continuous window period.

[0079] In another embodiment, a comprehensive gradient stability index Q can be constructed based on different electrical signals. The comprehensive gradient stability index Q can be obtained by weighting the first-order gradient of conductivity, the first-order gradient of impedance, the first-order gradient of potential, and window fluctuation stability characteristics. For example: Q=w1·|Gc| / Gth+w2·|Gz| / Zth+w3·|Gp| / Pth+w4·S / Sth; Where Gc is the first-order gradient of conductivity, Gz is the first-order gradient of impedance, Gp is ​​the first-order gradient of potential, S is the window fluctuation stability characteristic, and w1, w2, w3, and w4 are weighting coefficients, with w1+w2+w3+w4=1. When the comprehensive gradient stability index Q corresponding to multiple consecutive sampling windows is less than the preset comprehensive threshold, the food sample can also be determined to have reached the digestion endpoint.

[0080] Tables 1 and 2 above demonstrate that the continuous change curve of the electrical signal during the digestion process can reflect the changes in the food sample from the rapid digestion stage, the reaction slowing stage, to the endpoint stabilization stage. Based on the first-order gradient characteristics and fluctuation stability characteristics calculated using the sampling window, this continuous change process can be quantified into an automatically identifiable endpoint determination condition. Compared to determining the digestion endpoint solely based on a fixed digestion time or manual observation, this embodiment can determine the digestion endpoint based on the electrical response changes of the digestion system itself, thereby improving the consistency and reliability of endpoint determination under different food matrix conditions.

[0081] In one specific embodiment, the digestion device is an electrothermal digestion device or a graphite digestion device, and an acid-resistant electrode assembly and a temperature sensor are installed inside the digestion container. An electrical signal acquisition unit applies an AC excitation signal to the acid-resistant electrode assembly and acquires the corresponding response voltage and response current of the digestion system. The controller calculates the equivalent impedance or equivalent conductance of the digestion system based on the response voltage and response current, and forms an electrical signal time series. The temperature sensor synchronously acquires digestion temperature data. The controller performs temperature compensation and blank digestion liquid baseline correction on the electrical signal time series to obtain a compensated electrical signal sequence. Subsequently, the controller divides the compensated electrical signal sequence according to a preset sampling window, eliminates transient disturbance windows, calculates the first-order gradient characteristics and fluctuation stability characteristics, and outputs digestion control commands based on whether multiple consecutive sampling windows meet the endpoint determination conditions.

[0082] like Figure 2 As shown, this embodiment also provides an automatic food digestion endpoint determination system based on electrical signal gradient. The system includes a digestion unit, an acid-resistant electrode assembly, an electrical signal acquisition unit, a temperature acquisition unit, a compensation processing unit, a disturbance rejection unit, a gradient calculation unit, an endpoint determination unit, and a control output unit.

[0083] The digestion unit is used to digest food samples. The digestion unit may include one or more of the following: a digestion container, a heating module, a temperature control module, a reagent addition module, an acid removal module, and a cooling module. The digestion unit can operate according to a preset digestion program, or its operating status can be adjusted according to digestion control commands sent by the control output unit.

[0084] Acid-resistant electrode assemblies are used in contact digestion systems. These assemblies can be two-electrode, three-electrode, or multi-electrode structures. They can be installed inside the digestion container, within the digestion solution circulation pipeline, or in the digestion solution detection tank. To minimize the impact of strong acids and high temperatures on the electrodes, the acid-resistant electrode assemblies can be made of acid-resistant materials and feature a corrosion-resistant, insulating, and sealed structure.

[0085] The electrical signal acquisition unit is connected to the acid-resistant electrode assembly and is used to acquire the time series of electrical signals of the digestion system during the food sample digestion process. The electrical signal acquisition unit may include an excitation signal generation circuit, a response signal acquisition circuit, a filtering circuit, an analog-to-digital conversion circuit, and a data transmission circuit. The excitation signal can be an AC excitation signal to reduce the influence of electrode polarization on the detection results.

[0086] The temperature acquisition unit is used to collect digestion temperature data of the digestion system. The temperature acquisition unit may include thermocouples, resistance temperature detectors (RTDs), infrared temperature sensors, or other temperature detection elements. The digestion temperature data collected by the temperature acquisition unit is used for electrical signal temperature compensation and for determining temperature stability conditions.

[0087] The compensation processing unit is used to perform temperature compensation on the electrical signal time series based on the digestion temperature data, and to perform baseline correction on the temperature-compensated electrical signal time series in combination with the blank digestion solution baseline, so as to obtain the compensated electrical signal series.

[0088] The disturbance rejection unit is used to divide the sampling window of the compensation electrical signal sequence and reject transient disturbance windows based on the change state of the electrical signal within the sampling window. The disturbance rejection unit can identify transient disturbance windows by combining the abrupt change amplitude, window fluctuation amplitude, digestion equipment control log, liquid replenishment record, heating power change record, or temperature change rate.

[0089] The gradient calculation unit is used to calculate the gradient characteristics of the electrical signal based on the sampling window retained after removing the transient disturbance window. The gradient characteristics of the electrical signal include the first-order gradient characteristics between adjacent sampling windows and the fluctuation stability characteristics within the sampling window, and may also include the second-order gradient characteristics.

[0090] The endpoint determination unit is used to determine that a food sample has reached the digestion endpoint when the first-order gradient characteristics of multiple consecutive sampling windows meet the first gradient stability condition, the fluctuation stability characteristics meet the window stability condition, and the corresponding digestion temperature data meet the temperature stability condition.

[0091] The control output unit is used to output digestion control commands based on the digestion endpoint. The control output unit can be connected to the heating module, acid removal module, cooling module, liquid replenishment module, human-machine interface module, or data recording module of the digestion unit to control the digestion equipment to stop heating, enter acid removal, enter cooling, indicate volume adjustment, or generate a digestion completion record.

[0092] In one verification implementation, a manually determined endpoint or a standard digestion endpoint can be set as a reference endpoint. The reference endpoint may include at least one of the following: the digestion solution is clear and transparent, with no visible residue, and stable after acid removal and volume adjustment; it may also include a target element recovery rate reaching a preset recovery rate range and the relative standard deviation of parallel samples meeting the requirements of the detection method when using inductively coupled plasma atomic emission spectrometry, inductively coupled plasma mass spectrometry, or atomic absorption spectrometry to detect the target element. The preset recovery rate range can be from 95% to 105%.

[0093] During the validation process, digestion experiments were conducted on different food matrix samples. These food matrix samples could include at least one of the following: grain samples, meat product samples, dairy product samples, vegetable samples, and aquatic product samples. During the digestion of each food matrix sample, the conductivity, impedance, or potential signals of the digestion system were recorded simultaneously, and digestion temperature data were acquired. After temperature compensation and blank digest baseline correction were applied to the acquired electrical signals, window statistics, first-order gradient characteristics, and window fluctuation stability characteristics were calculated according to a preset sampling window.

[0094] Furthermore, the time points at which M consecutive sampling windows meet the preset endpoint determination conditions are compared with the reference endpoint. The preset endpoint determination conditions include: the absolute value of the first-order gradient feature is less than a preset gradient threshold, and the window fluctuation stability feature is less than a preset stability threshold. When, in multiple batches of food samples, the time difference between the digestion endpoint determined based on the electrical signal gradient stability and the reference endpoint is within the allowable time range, and there is no significant difference in the target element detection results obtained after continued digestion after the digestion endpoint, it indicates that the electrical signal gradient stability state corresponds to the food sample digestion completion state. The allowable time range can be ±3 min or ±5 min.

[0095] Experimental results show that when the compensated electrical signal curve enters the continuous plateau region, the first-order gradient characteristic of adjacent sampling windows approaches zero, and the fluctuation amplitude within the window is significantly reduced. This state is consistent with the digestion completion state, characterized by clear digestate, disappearance of residue, and stable recovery rate of target elements. Therefore, the criterion based on the stability of the electrical signal gradient can be used for the automatic determination of the digestion endpoint of food samples.

[0096] It should be noted that the threshold, sampling window length, number of consecutive windows, temperature compensation model, baseline correction method, and electrical signal type involved in the above embodiments can all be set or adjusted according to the actual food sample type, digestion equipment type, digestion reagent type, and detection items. The above formulas are merely an exemplary expression for illustrating the technical solution of the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0097] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0098] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An automatic method for determining the endpoint of food digestion based on electrical signal gradient, characterized in that, include: During the food sample digestion process, the time series of electrical signals and digestion temperature data of the digestion system are acquired; Temperature compensation is performed on the electrical signal time series based on the digestion temperature data, and baseline correction is performed on the temperature-compensated electrical signal time series in combination with the blank digestion solution baseline to obtain the compensated electrical signal series. The compensation electrical signal sequence is divided into sampling windows, and transient disturbance windows are removed based on the electrical signal change state within the sampling window; Based on the sampling window retained after removing the transient disturbance window, the electrical signal gradient features are calculated. The electrical signal gradient features include the first-order gradient features between adjacent sampling windows and the fluctuation stability features within the sampling window. When the first-order gradient features of multiple consecutive sampling windows satisfy the first gradient stability condition, the fluctuation stability features satisfy the window stability condition, and the corresponding digestion temperature data satisfy the temperature stability condition, the food sample is determined to have reached the digestion endpoint; a digestion control command is output according to the digestion endpoint.

2. The method according to claim 1, characterized in that, The electrical signal time series includes at least one of the following: conductance signal time series, impedance signal time series, current response signal time series, voltage response signal time series, potential signal time series, and electrochemical impedance spectroscopy characteristic time series.

3. The method according to claim 1, characterized in that, The electrical signal time series was acquired using an acid-resistant electrode assembly; The acid-resistant electrode assembly is disposed in the digestion container, the digestion solution circulation pipeline, or the digestion solution detection pool. The acid-resistant electrode assembly is connected to an electrical signal acquisition circuit, which is used to apply an AC excitation signal to the acid-resistant electrode assembly and acquire the corresponding response signal of the digestion system.

4. The method according to claim 1, characterized in that, The temperature compensation of the electrical signal time series based on the digestion temperature data includes: The temperature compensation coefficient corresponding to each sampling time is determined based on the digestion temperature data. Based on the temperature compensation coefficient, the electrical signal time series is converted into an equivalent electrical signal time series at the reference temperature; The reference temperature is either a preset temperature or a baseline temperature after the digestion process enters a stable heating phase.

5. The method according to claim 4, characterized in that, The baseline correction of the temperature-compensated electrical signal time series based on the blank digest baseline includes: Obtain the baseline electrical signal sequence of the blank digest without added food sample under the corresponding digestion program; The equivalent electrical signal time series is subtracted and corrected based on the baseline electrical signal sequence to obtain the compensated electrical signal sequence. The baseline electrical signal sequence is used to characterize the background changes in electrical signals generated by the digestion reagent itself as the digestion temperature and / or digestion time change.

6. The method according to claim 1, characterized in that, The step of eliminating transient disturbance windows based on the electrical signal change state within the sampling window includes: Calculate the abrupt change amplitude and / or window fluctuation amplitude of the compensated electrical signal within the current sampling window; When the mutation amplitude is greater than a preset mutation threshold, and / or the window fluctuation amplitude is greater than a preset fluctuation threshold, the current sampling window is determined as a candidate perturbation window; Obtain the resolution process status corresponding to the candidate perturbation window; If the resolution process state corresponds to the preset disturbance state, the candidate disturbance window is determined as a transient disturbance window, and the transient disturbance window is removed when the resolution endpoint is determined. The preset disturbance states include at least one of the following: adding digestion reagent, boiling of digestion solution, bubble adhesion, electrode contamination, and switching of heating power.

7. The method according to claim 1, characterized in that, The calculation of electrical signal gradient features based on the sampling window retained after removing the transient disturbance window includes: Calculate the window statistics of the compensated electrical signal within each retained sampling window; The first-order gradient feature is determined based on the difference between the window statistics of adjacent sampling windows and the sampling window time interval. The fluctuation stability characteristics are determined based on the standard deviation, range, or coefficient of variation of the compensated electrical signal within the current sampling window.

8. The method according to claim 7, characterized in that, The electrical signal gradient features also include second-order gradient features; The second-order gradient feature is determined based on the amount of change between adjacent first-order gradient features; When the first-order gradient features of multiple consecutive sampling windows satisfy the first gradient stability condition, the second-order gradient features satisfy the second gradient stability condition, the fluctuation stability features satisfy the window stability condition, and the corresponding digestion temperature data satisfy the temperature stability condition, the food sample is determined to have reached the digestion endpoint.

9. The method according to claim 1, characterized in that, The first gradient stabilization condition, the window stabilization condition, and / or the temperature stabilization condition are determined based on at least one of the following: the matrix type of the food sample, the initial electrical signal level, the type of digestion reagent, the sample mass, and the digestion temperature range. And / or, when the food sample has not been determined to have reached the digestion endpoint, control the digestion equipment to maintain heating, extend the digestion time, adjust the heating power, or output a prompt to add digestion reagent; And / or, the digestion control command includes at least one of the following: a stop heating command, an acid removal control command, a cooling control command, a volume adjustment prompt command, and a digestion completion prompt command.

10. An automatic food digestion endpoint determination system based on electrical signal gradient, characterized in that, include: The digestion unit is used to digest food samples. Acid-resistant electrode assembly for use in contact digestion systems; An electrical signal acquisition unit, connected to the acid-resistant electrode assembly, is used to acquire the electrical signal time series of the digestion system during the food sample digestion process; Temperature acquisition unit, used to acquire digestion temperature data of the digestion system; The compensation processing unit is used to perform temperature compensation on the electrical signal time series based on the digestion temperature data, and to perform baseline correction on the temperature-compensated electrical signal time series in combination with the blank digestion solution baseline, so as to obtain the compensated electrical signal series. The disturbance removal unit is used to divide the compensation electrical signal sequence into sampling windows and remove transient disturbance windows according to the electrical signal change state within the sampling window. The gradient calculation unit is used to calculate the gradient features of the electrical signal based on the sampling window retained after removing the transient disturbance window. The gradient features of the electrical signal include the first-order gradient features between adjacent sampling windows and the fluctuation stability features within the sampling window. The endpoint determination unit is used to determine that the food sample has reached the digestion endpoint when the first-order gradient features of multiple consecutive sampling windows meet the first gradient stability condition, the fluctuation stability features meet the window stability condition, and the corresponding digestion temperature data meet the temperature stability condition. A control output unit is used to output a digestion control command according to the digestion endpoint.

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