A method for evaluating the sensory quality of milk odor based on key flavor components

Abstract

The application discloses a method for establishing a standard product for training evaluation of key sensory characteristics in finished milk. Based on research on key sensory properties of milk and key flavor components in milk, the method analyzes the correlation between volatile flavor components in milk and corresponding sensory quality by a statistical analysis method, determines three standard products corresponding to key sensory properties of milk, and can train evaluators, so that the evaluators can better objectively and quantitatively describe the sensory quality of milk.

Description

Technical Field

[0001] This invention belongs to the field of food quality, and relates to methods for sensory evaluation of milk and methods for detecting flavor substances, as well as the correlation between the sensory quality of milk and volatile compounds. Background Technology

[0002] Milk is a complex latex primarily composed of water, fat, protein, lactose, minerals, and vitamins. It contains abundant bioactive proteins such as α-lactalbumin, β-lactoglobulin, lactoferrin, and immunoglobulins. Milk possesses a wide range of physiological functions, including regulating immunity, inhibiting bacteria, and controlling lactose absorption. Furthermore, its rich nutritional content, suitable composition, and ease of digestion and absorption make it vital for human health.

[0003] The sensory quality of milk is the most direct factor influencing consumer preference, and the flavor characteristics of milk must meet consumer demands. The sensory quality of milk varies significantly between different pastures, and factors such as pasture feed, environment, and season directly affect the flavor of the milk. Furthermore, different sterilization methods have a certain impact on the flavor components and protein denaturation in milk, thus also affecting its sensory quality.

[0004] Flavor compounds in milk are chemical substances that give milk its unique flavor. They mainly include free fatty acids, ketones, aldehydes, alcohols, sulfur-containing compounds, and other organic compounds. Short-chain fatty acids such as butyric acid and hexanoic acid, within a suitable concentration range, contribute to the aroma of milk fat; 2-heptanone and 2-nonanone impart a unique warm milk aroma; aldehydes give milk a unique nutty and fatty flavor; and sulfur-containing compounds such as methanethiol, dimethyl sulfide, and dimethyl trisulfide contribute to the cooked flavor of milk.

[0005] Numerous studies both domestically and internationally have conducted sensory evaluations of milk aroma. These evaluations mostly focus on overall scores of milk's sensory characteristics or scores of specific sensory attributes, such as the cooked taste, milky smell, and milky aroma. They are largely descriptive and lack reference standards for specific sensory attributes. The RHB101-2004 "Detailed Rules for Sensory Quality Evaluation of Pasteurized Milk" published by the China Dairy Industry Association has overly abstract sensory evaluation standards, only scoring the overall flavor characteristics of milk without evaluating individual indicators. This results in significant subjective influence on the evaluators and places high demands on sensory personnel. In their paper, "Sensory Evaluation Analysis of Five Famous Whole Milks from Domestic and International Sources and a Preliminary Study on Electronic Nose and Electronic Tongue Discrimination," Liu Li et al. conducted a sensory evaluation analysis of five different commercially available brands of milk, providing descriptive analyses of color, texture, flavor, and aftertaste. Regarding flavor, none of the five milks showed obvious off-flavors, while the imported milk had a richer milky aroma and sweetness than the domestic milk. This paper did not conduct a quantitative analysis of sensory attributes, nor did it combine the sensory evaluation results with volatile flavor compounds. Y. Jo et al., in their paper "Flavor and flavor chemistry differences among milks processed by high-temperature, short-time pasteurization or ultra-pasteurization," trained six sensory evaluators and scored seven sensory attributes of five different types of milk listed in Table 1. However, the article did not specify the training content, nor did it provide training on standardized samples for the sensory attributes of milk. Currently, domestic and international milk sensory evaluation mainly relies on the sensory experience of evaluators, and descriptions of milk sensory attributes tend to be subjective, lacking standardized samples for training in sensory characteristics.

[0006] Table 1 Sensory rating results of different milks

[0007] Summary of the Invention

[0008] This invention addresses the lack of current quantitative evaluation methods for the sensory characteristics of milk by combining the results of milk sensory evaluation with the quantitative results of volatile flavor compounds. This establishes a standard for milk sensory attributes and develops a relatively complete and unified system for milk sensory evaluation. Furthermore, it provides training for evaluators to avoid errors caused by the subjectivity of evaluators in sensory evaluation.

[0009] Specifically, this invention, based on data analysis of the flavor compound content and sensory evaluation results of milk, determines the correlation between the sensory quality of milk and its flavor compounds, aiming to accurately and objectively quantitatively describe and analyze the sensory quality of milk. This invention improves the standards for milk sensory evaluation, avoiding subjective factors from sensory evaluators by accurately and objectively quantitatively analyzing the sensory quality of milk using the types and contents of flavor compounds. After sensory evaluators determine the sensory descriptors for milk, they need to score the intensity of different sensory attributes for each type of milk. When the sensory attributes of milk are defined by standard samples, all evaluators can have the same scoring criteria, making the sensory evaluation data more objective and accurate. Simultaneously, combining the sensory evaluation results with the results of gas chromatography-mass spectrometry (GC-MS) allows for the determination of the standard sample content in the sensory attributes of milk using objective data measured by instruments, thereby avoiding the subjective influence that may be brought by untrained sensory evaluators.

[0010] Therefore, a method for establishing a training standard for evaluating key sensory characteristics in finished milk is characterized by the following steps:

[0011] (1) Take the milk sample to be tested and extract volatile flavor substances from all samples in the milk sample group by solid phase microextraction.

[0012] (2) Then, gas chromatography-mass spectrometry was used to quantitatively analyze the volatile flavor compounds in all milk samples;

[0013] (3) Statistical analysis methods were applied to analyze the correlation between volatile flavor components in milk and their corresponding sensory qualities, thereby determining the corresponding standard for the sensory attributes of milk used for training.

[0014] In one specific embodiment, the solid-phase microextraction analysis method described in step (1) refers to the following: 10g of milk sample is weighed into a headspace vial, 1g of sodium chloride is added, and 1μl of 0.816mg / ml internal standard 2-methyl-3-heptanone is injected into the headspace vial using a microsyringe. The water bath temperature is set to 45℃, and after the sealed headspace vial is placed in the water bath and heated to equilibrium for 20min, the extraction head is inserted into the headspace vial, and the extraction fiber is extended. After headspace adsorption for 30min, the extraction fiber is retracted, and the extraction head is pulled out, awaiting GC injection.

[0015] Further, the gas chromatography-mass spectrometry (GC-MS) method described in step (1) is as follows: the extraction head is inserted into the gas chromatography vaporization chamber, desorbed at 250°C for 5 min, the capillary column is a 60m×0.25mm, 0.25μm DB-WAX column, helium is used as the carrier gas, and a constant flow rate of 1.2 ml / min is set. The column temperature program is as follows: the initial column temperature is 40°C, increased to 75°C at 7°C / min; then increased to 150°C at 2°C / min; finally increased to 230°C at 5°C / min and maintained for 2 min. Splitless mode is used. Mass spectrometry conditions: electron ionization source, electron energy 70 eV; injection port temperature 250°C, ion source temperature 230°C, quadrupole temperature 150°C; full scan mode, mass scan range is m / z 35-350.

[0016] Furthermore, the quantitative analysis described in step (1) adopts a semi-quantitative analysis, which uses an internal standard semi-quantitative method. The calculation formula is Ax / Ai=Cx / Ci, where Ax and Ai represent the peak area of ​​the target compound and the peak area of ​​the internal standard, respectively, and Cx and Ci represent the concentration of the target compound and the concentration of the internal standard, respectively. Preferably, the internal standard is 2-methyl-3-heptanone.

[0017] The present invention provides a standard for training sensory trainers to determine the milky aroma of milk, characterized in that it is composed of the following components: hexanoic acid (50±10μg / kg) + octanoic acid (200±40μg / kg) + nonanoic acid (20±4μg / kg) + decanoic acid (400±80μg / kg) + 9-decenoic acid (50±10μg / kg) + dodecanoic acid (200±40μg / kg), preferably prepared in a 3% concentrated milk protein solution;

[0018] The present invention provides a training standard for sensory trainers to determine the boiled flavor of milk, characterized in that it is composed of the following components: dimethyl sulfone (1000±200μg / kg) + dimethyl trisulfide (1±0.2μg / kg), preferably, in a 3% concentrated milk protein solution;

[0019] The present invention provides a training standard for sensory trainers to determine the milky smell of milk, characterized in that it is composed of the following components: hexanal (10±2 μg / kg) + decanal (10±2 μg / kg) + 1-octen-3-ol (10±2 μg / kg), preferably prepared in a 3% concentrated milk protein solution.

[0020] This invention also provides the application of the above three training standards in training milk flavor sensory evaluators.

[0021] This invention innovatively utilizes statistical correlation analysis to analyze the correlation between volatile components and sensory attributes based on the variation patterns of volatile component content obtained from gas chromatography-mass spectrometry, in order to identify characteristic volatile components that conform to milk quality. Specifically, a database of milk-identifying characteristic flavor components has been established for the volatile flavor components and sensory quality of milk samples. Based on this database, combined with statistical analysis methods, evaluators can receive standard training on the sensory attributes of milk samples, thereby establishing a complete sensory evaluation system for milk.

[0022] This invention utilizes gas chromatography-mass spectrometry (GC-MS) to analyze volatile components, thereby revealing the variation patterns of volatile flavor compound content in different milk samples. Statistical correlation analysis is then used to analyze the correlation between volatile components and sensory attributes, aiming to identify characteristic volatile components that contribute to the sensory quality of milk. However, obtaining volatile components is crucial in the initial steps; therefore, this invention employs solid-phase microextraction (SPE) to extract volatile compounds from milk. In subsequent steps, statistical correlation analysis is conducted to determine which components influence the sensory quality of milk.

[0023] This study utilizes gas chromatography-mass spectrometry (GC-MS) to explore the characteristic flavor components and their content variations in different milk samples. By linking these findings with sensory evaluation results, the relationship between milk sensory quality and the content of these characteristic components is explored, thereby identifying standard samples that meet the sensory characteristics of milk. Training evaluators on these standard samples will further enhance the objectivity and accuracy of milk sensory evaluations. Detailed Implementation

[0024] The present invention will be further described below through specific embodiments to provide a clearer understanding of the invention, but these are merely exemplary and do not constitute any limitation on the invention.

[0025] 1. Preliminary preparations

[0026] 1) Sample preparation

[0027] To ensure that the milk reaches the best sensory conditions, all milk samples need to be placed in a constant temperature environment of 15°C before sensory evaluation.

[0028] Once the required temperature is reached, take 10-15 ml of each type of milk and place it in a sensory evaluation cup. Number the milk samples using a three-digit random number. To prevent photo-oxidation and other reactions in the milk, it should be prepared in the dark.

[0029] After tasting each milk sample, the team members were provided with mouthwash and unsalted biscuits to rinse and cleanse their taste buds.

[0030] 2) Principles for selecting evaluators

[0031] In quantitative descriptive analysis, a sensory evaluation team is required to determine the sensory attributes of milk samples and the intensity of these attributes. Members of this team should be familiar with dairy products and possess relevant expertise. The sensory evaluation team is then trained to use their senses of sight, touch, taste, and smell to accurately evaluate the color, aroma, flavor, and texture of dairy products, enabling them to precisely perceive the sensory attributes of milk and assess their intensity. The sensory descriptors generated by the team should also closely align with consumer needs.

[0032] Descriptive analysis sensory evaluation teams typically consist of 6-12 people, the level of training of whom depends on the complexity of the sensory attributes being analyzed. If experienced expert team members are well-trained and can obtain consistent results on the sensory attributes of milk, their results can be used as analytical instruments to determine the grade and position of milk products in the market.

[0033] To be a milk sensory evaluator, the following requirements must be met: Must possess professional knowledge in dairy processing and inspection; must have passed sensory analysis tests and possess excellent sensory analysis skills; should be in good health and not suffer from color blindness, rhinitis, dental caries, stomatitis, or other diseases; possess excellent communication skills, able to accurately and appropriately describe the sensory characteristics of samples; have the ability to concentrate and remain unaffected by external influences, and be passionate about the evaluation work; have no bias or aversion towards samples, and be able to evaluate samples objectively and impartially; must not use perfume or cosmetics or wash hands with soap before work; must not conduct evaluation work within one hour after eating; and must not smoke within 30 minutes before the start of the evaluation.

[0034] This study selected 12 personnel from dairy companies who specialize in sensory quality evaluation of dairy products. The selected evaluators have strong professional skills and rich experience in sensory evaluation, and they have relatively unified sensory evaluation standards.

[0035] 2. Sensory evaluation experiment

[0036] 1) Establishment of a sensory evaluation form

[0037] By combining sensory descriptions provided by milk consumers and professional sensory evaluators, this study selected three common milk aromas—milky aroma, steamed aroma, and milky smell—as the research content.

[0038] Please have the evaluators taste the milk sample following these steps and score its sensory attributes.

[0039] Odor: Gently shake the milk, place your nose directly over it, and inhale the air above the sample thoroughly. This will allow you to detect any possible off-odors.

[0040] Taste: After pouring in the sample, the evaluator should take a big sip of the sample, roll it in their mouth, keep each sample in their mouth for about 4-6 seconds, pay attention to the taste, and then spit it out.

[0041] Fill in the corresponding number below the flavor in Table 2 to indicate the intensity of the flavor: 0 - none, 1 - slightly, 2 - distinct, 3 - strong flavor.

[0042] Table 2 Sensory Evaluation Table

[0043] Milk flavor Steamed or boiled flavor milky smell Sample 1 Sample 2 Sample 3 ……

[0044] 2) Sensory evaluation results

[0045] This study selected six batches of milk and evaluated them for three sensory attributes. To reduce the influence between sensory attributes, only one sensory attribute was evaluated for each batch of milk. The results are shown in Table 3, where the data represents the average scores given by 12 evaluators.

[0046] Table 3 Sensory evaluation results

[0047]

[0048] 3. Determination of volatile flavor compounds

[0049] 1) Experimental apparatus:

[0050] 7890B-5977A gas chromatograph-mass spectrometer, Agilent Technologies, USA; DB-WAX capillary column (60m × 0.25mm, 0.25μm), Agilent Technologies, USA; solid-phase microextraction (SPME), Agilent Technologies, USA, was used for extraction.

[0051] 2) Solid-phase microextraction

[0052] Weigh 10g of sample milk into a headspace vial, add 1g of sodium chloride, and inject 1μl of 0.816mg / ml internal standard 2-methyl-3-heptanone into the headspace vial using a microsyringe. Set the water bath temperature to 45℃, place the sealed headspace vial in the water bath and heat for equilibration for 20min. Then, insert the extraction head into the headspace vial and extend the extraction fiber. After headspace adsorption for 30min, retract the extraction fiber and remove the extraction head, awaiting GC injection.

[0053] 3) GC-MS analysis method

[0054] GC conditions: A 60m × 0.25mm, 0.25μm DB-WAX capillary column was used, with helium as the carrier gas, and a constant flow rate of 1.2 ml / min was set. The column temperature program was as follows: initial column temperature 40℃, increased to 75℃ at 7℃ / min; then increased to 150℃ at 2℃ / min; finally increased to 230℃ at 5℃ / min and held for 2 minutes. Splitless mode was used.

[0055] MS conditions: electron ionization (EI) source, electron energy 70 eV; injection port temperature 250℃, ion source temperature 230℃, quadrupole temperature 150℃; full scan mode, mass scan range m / z 35~350.

[0056] 4) Qualitative and quantitative analysis

[0057] Qualitative analysis:

[0058] Two methods were used to qualitatively identify the compounds: first, compounds were searched and compared in the NIST14 spectral library; then, the retention index of the compounds was calculated and compared with retention indices in the literature. The retention index was calculated by obtaining the GC retention times of n-alkanes (C7-C40) and milk samples under the same chromatographic conditions, and then calculating the retention index (t) of the analyte compound i according to the formula. n <t i <t n+1 ).

[0059]

[0060] In the formula: RI—retention index; ti—retention time of sample i; n—number of carbon atoms; tn+1—retention time of n-alkanes with n+1 carbon atoms; tn—retention time of n-alkanes with n carbon atoms.

[0061] Quantitative analysis:

[0062] The content of each volatile flavor compound was calculated using the internal standard semi-quantitative method, based on the peak area ratio of the compound to the internal standard.

[0063] The calculation formula is A x / A i =C x / C i A x A i C represents the peak area of ​​the target compound and the peak area of ​​the internal standard, respectively. x C i These represent the concentrations of the target compound and the internal standard, respectively.

[0064] 5) Temperament results

[0065] The types and contents of volatile flavor compounds in the selected 6 batches of milk were determined by the above gas chromatography-mass spectrometry method, so that different milk samples could be compared and analyzed. The contents of some flavor substances in milk are shown in Table 16.

[0066] Table 16 Flavor Compound Content of Milk

[0067]

[0068] 4. Statistical correlation analysis

[0069] 1) Partial Least Squares Regression Model

[0070] Partial Least Squares (PLS) regression is a multivariate technique used for dimensionality reduction. It reduces the number of explanatory variables in a regression problem, aiming to remove multicollinearity from the set of explanatory variables X (flavor compounds) and ensure that the resulting subset of explanatory variables is optimal for predicting the dependent variable Y (flavor compound content in milk samples). Variable Importance in Projection (VIP) screening is a variable selection method based on PLS. VIP screening describes the importance of independent variable X to dependent variable Y through principal components. If independent variable X has a large effect on its extracted principal components, and these principal components have a strong explanatory power for dependent variable Y, then independent variable X can be considered to have a strong explanatory power for dependent variable Y. Independent variables X are then selected based on their explanatory power. This design uses PLS, a statistical regression method, combined with VIP, an index-based screening method, i.e., the PLS-VIP method, to analyze milk samples. The theoretical basis of the PLS model is as follows:

[0071] X = TP T +E (1)

[0072] Y = UC T +F (2)

[0073] In the formula: X is the independent variable matrix; Y is the dependent variable matrix; T and U represent the score matrix; P and C represent the loading matrix; E and F represent the residual matrix; the superscript T represents the transpose.

[0074] X = T P P P T +T O P O T +E (3)

[0075] After improvement, PLS provides model interpretation by dividing the system variations contained in the X data matrix into two parts: a prediction part related to Y and an unrelated orthogonal part. The X matrix is ​​decomposed according to equation (3), where the superscript T denotes transpose, the subscripts p and o denote prediction and orthogonality, T is the score matrix, P is the load matrix, and E is the residual matrix.

[0076]

[0077] Equation (4) is the formula for calculating VIP for the j-th independent variable, where: Y is the dependent variable; k is the number of independent variables; c h Principal components extracted from relevant independent variables; m is the number of principal components extracted; r(Y,c h ) is the dependent variable matrix Y and the principal component c h The correlation coefficient between the principal components represents the explanatory power of Y for Y; w hj The independent variable is x j In principal component c h Weighting on.

[0078] Because the independent variable x j The effect on the dependent variable Y is through the principal component c h This is achieved through [the means], therefore if c h The influence on Y is relatively large and x j With c h If the correlation is strong, then x j The greater the contribution of the independent variable to the dependent variable, the more significant the explanation of Y. Therefore, the VIP value can explain the importance of the independent variable to the dependent variable and can rank and score them according to the contribution of the independent variable. If the VIP... j If the value is greater than 1, then the independent variable can explain the dependent variable well. j If the value is less than 1, then the independent variable is insufficient to explain the dependent variable.

[0079] 2) Partial Least Squares Regression Analysis

[0080] Statistical correlation analysis was performed between the sensory score results and the volatile flavor compound content results for each batch to obtain the PLS-VIP diagram.

[0081] Table 4: PLS-VIP values ​​of milk aroma and flavor compounds in the first batch of milk samples

[0082] Flavor compounds Lactosolic acid nonanoic acid bitter Acetophenone Octyl alcohol 1-Octen-3-one VIP value 1.32475 1.27405 1.25285 1.2441 1.2269 1.2269 2,3-Octanedione Decanoic acid 9-Decanonic acid Hexanal hexanoic acid 1.2269 1.21768 1.19785 1.18604 1.17007

[0083] Table 5: PLS-VIP values ​​of milk aroma and flavor compounds in the second batch of milk samples

[0084]

[0085] Milk aroma, a sensory attribute, has the greatest impact on the sensory quality of milk. Generally, milk with a strong milk aroma is more popular with consumers. Therefore, the intensity of milk aroma is one of the most important criteria for sensory evaluation of milk. This experiment selected a series of milk samples with different milk aromas as milk samples, scored the milk aroma, and determined the flavor compounds in the milk samples. Tables 4 and 5 show the results of statistical correlation analysis of the scores of the milk aroma sensory attribute and the content of flavor compounds. It can be seen that various milks were well distinguished based on both sensory attributes and volatile compounds. By summarizing the PLS-VIP results of the two batches of milk, flavor compounds with PLS-VIP values ​​>1 are important factors in distinguishing milk samples. It can be seen that the compounds affecting milk aroma are: hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, 9-decenoic acid, and dodecanoic acid. Generally, in the same batch of milk, the stronger the milk aroma, the higher the content of these key flavor compounds.

[0086] Table 6: PLS-VIP values ​​of cooking flavor and flavor compounds in the third batch of milk samples

[0087] Flavor compounds dimethyl sulfide 2-Ethyl-1-hexanol Hexanal dimethyl sulfone Ethylbenzene p-xylene Nononal VIP value 1.42584 1.35796 1.34474 1.33674 1.31305 1.27552 1.22443 Octal 2-Hepagonal 2-Undecone styrene 2-Tetane 2-Nonone 1.22002 1.22002 1.22002 1.22002 1.15966 1.04427

[0088] Table 7: PLS-VIP values ​​of cooking flavor and flavor compounds in the fourth batch of milk samples

[0089] Flavor compounds 2-Tetane dimethyl sulfone δ-octyl lactone hexanoic acid 2-Undecone Dimethyl trisulfide VIP value 1.6487 1.64644 1.60047 1.55257 1.45983 1.42798 2-Hepagonal Toluene furfural δ-decanolide Decanoic acid styrene 1.39039 1.35252 1.34393 1.29371 1.14356 1.10303

[0090] The cooked flavor is a common sensory characteristic of milk. Generally, milk processed using ultra-high temperature (UHT) sterilization, which involves strong pasteurization, will have a more pronounced cooked flavor. Milk with a strong cooked flavor typically provides a negative sensory experience for consumers and is not easily accepted by the general public. Two batches of milk samples with significantly different cooked flavors were selected, and statistical correlation analysis was performed between the content of flavor compounds and the sensory evaluation results, yielding the results shown in Tables 6 and 7. The compounds that significantly influence the cooked flavor are mainly sulfur-containing compounds such as dimethyl sulfone and dimethyl trisulfide.

[0091] Table 8: PLS-VIP values ​​of milky odor and flavor compounds in the fifth batch of milk samples

[0092] Flavor compounds Acetic acid decanal 2-Propane 2-Nonone 2-Undecone 2-Butanone 1-Octen-3-ol butyric acid 2-Tetane VIP value 1.30904 1.30502 1.30403 1.28228 1.27848 1.26506 1.26108 1.25132 1.23514 Hexanal Methanethiol Decanoic acid 2-Hexenal δ-decanolide γ-Dodecalactone styrene benzaldehyde 1.22964 1.20849 1.17518 1.12223 1.10998 1.09713 1.09282 1.01155

[0093] Table 9: PLS-VIP values ​​of milky odor and flavor compounds in the sixth batch of milk samples

[0094] Flavor compounds 4-Ethylbenzaldehyde Hexanal 1-Octen-3-ol dodecaldehyde 2-Octanone Undecaldehyde butyric acid 2-Nonone benzaldehyde VIP value 1.23508 1.22971 1.22375 1.22375 1.22133 1.21347 1.20995 1.20796 1.20185 decanal bitter Nononal dodecanol Limonene 2-Ethylhexanol Octyl alcohol Octal styrene 1.19856 1.16252 1.16178 1.1536 1.1493 1.14825 1.14825 1.11433 1.02826

[0095] A small number of milk samples exhibited a milky odor, which generally occurs in milk with high oxidation levels, resulting in a very poor sensory experience for consumers. We selected two batches of milk samples with a relatively strong milky odor and analyzed their flavor compound content and sensory evaluation results. The compounds affecting the milky odor may include aldehydes and alcohols such as hexanal, decanal, and 1-octen-3-ol.

[0096] 5. Determination of sensory attribute standards

[0097] A correlation analysis was conducted on the key flavor compounds and sensory scores of the above six batches of milk. The resulting PLS-VIP results clearly show the types and contents of flavor compounds affecting the three sensory attributes of milk aroma, milky smell, and cooked taste. Standards of key flavor substances affecting these three sensory attributes were compounded (as shown in Table 10). Using these in sensory attribute training for milk sensory evaluation allows for more accurate and objective scoring of milk sensory attributes.

[0098] Table 10 Sensory attributes, definitions, and corresponding standard samples of milk used for training.

[0099]

[0100]

[0101] Application examples of the present invention

[0102] Sensory evaluation and flavor analysis of three different milk products.

[0103] 1. Training of sensory evaluators

[0104] Sensory evaluators were selected according to the standards established in the preliminary preparation work. Before formally evaluating milk samples, sensory evaluators needed to be trained to understand the taste and intensity of milk's sensory attributes. Only in this way could the results have high credibility and allow for accurate and objective scoring of the milk. Each evaluator was required to have at least 80 hours of experience evaluating food flavor attributes and at least 40 hours of experience evaluating milk sensory attributes using specific sensory terminology. First, evaluators were trained according to the standard methods for sensory evaluation in the American Sensory Evaluation Standards Association (ADSA), with the standard samples listed in Table 11. The training requirements were met when most sensory evaluators scored the same sample consistently across all sensory attributes. Sensory scoring of the milk was conducted immediately after the training. The same group of sensory evaluators then received further training using the standard samples listed in Table 10. Evaluators needed to be proficient in the sensory attributes of milk and the intensity of their corresponding standard samples. Sensory scoring was conducted immediately after the training.

[0105] Table 11 Milk Standards Used for Training

[0106] Sensory attributes definition Standard products Milk flavor The unique milky aroma Heavy cream Steamed or boiled flavor The steamed flavor in milk Boiled eggs milky smell The milky smell wet cardboard

[0107] 2. Sensory evaluation of milk

[0108] 2.1 The organizers will send the questionnaire to the sensory evaluators, as shown in Table 12. The sensory evaluators will fill in the scores in the table according to the questionnaire requirements.

[0109] Table 12 Milk Sensory Evaluation Questionnaire

[0110] Milk Sample Sensory Evaluation Questionnaire

[0111] Name:____ Age:____ Gender:____

[0112] Please have the evaluators taste the milk sample as required, evaluate its sensory characteristics and intensity, and fill in the table below.

[0113] Smell: Gently shake the milk, place your nose directly over it, and inhale the air above the sample thoroughly.

[0114] Taste: After pouring in the sample, the evaluator should take a big sip of the sample, roll it in their mouth, keep each sample in their mouth for about 4-6 seconds, pay attention to the taste, and then spit it out.

[0115] In the table, fill in the number below the corresponding flavor to indicate its intensity: 0 - none, 1 - slightly, 2 - noticeable, 3 - strong.

[0116] Milk flavor Steamed or boiled flavor milky smell Sample 1 Sample 2 Sample 3 ……

[0117] 2.2 Sensory evaluation results

[0118] After training the evaluators according to the training content in Table 11, sensory evaluations were conducted on three commercially available milks: A, B, and C. The average scores are shown in Table 13. Similarly, after training the evaluators according to the training content in Table 10, the sensory evaluation results are shown in Table 14.

[0119] Table 13 Sensory Rating Table 1

[0120]

[0121] Table 14 Sensory Rating Table 2

[0122]

[0123] 3. Validation of Gas Chromatography-Mass Spectrometry Results

[0124] Table 15. Results of the temperament test

[0125]

[0126]

[0127] Sensory analysis and gas chromatography-mass spectrometry (GC-MS) results complement each other. Although GC-MS does not measure taste, it can be correlated with sensory data and can more clearly identify the source of taste. Volatile flavor compounds are the source of aroma in milk, and factors such as the type and content of flavor substances directly affect the sensory quality of milk. Therefore, combining sensory evaluation results with GC-MS results allows for a more objective and accurate evaluation of milk flavor.

[0128] Fatty acids are a representative class of flavor compounds in milk. They are not only flavor compounds themselves but also precursors to other flavor compounds such as methyl ketones and esters, playing a crucial role in the formation of milk flavor. Short-chain fatty acids such as butyric acid and hexanoic acid have a milky aroma at low concentrations. Table 15 shows that the total fatty acid content of the three types of milk is not significantly different, with milk C having a slightly lower total fatty acid content than milk A and milk B. Milk A and milk B have relatively similar fatty acid contents. The sensory evaluation results in Tables 13 and 14 show that milk A and milk B have similar and relatively higher scores for milk aroma, with milk C scoring last. Comparing the sensory evaluation results for milk aroma with the content of fatty acid compounds reveals a positive correlation: the higher the fatty acid content, the richer the milk aroma. The statistical correlation analysis concludes that the content of six volatile fatty acids—hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, 9-decenoic acid, and dodecanoic acid—directly affects the milk aroma of milk. The two sensory evaluation methods in Tables 10 and 11 have the same standard for milk aroma. This may be because the evaluators are familiar with the milk aroma and fat aroma contained in milk itself, and are able to give sensory scores for the milk aroma of various milks.

[0129] Sulfur compounds are a significant contributor to the cooked flavor of milk after heating, greatly influencing the flavor of dairy products. The threshold for sulfur compounds is low; even at very low levels, they play a crucial role in the overall aroma of milk. Table 15 shows that the sulfur compound content in milk B is significantly higher than in milk A and milk C. The sensory results in Table 14 indicate that milk B has the strongest cooked flavor, which is largely consistent with the anaerobic / anaerobic digestive tract (AUT) results. Table 13 shows that milk A has the strongest cooked flavor, followed by milk B, and finally milk C, which contradicts the sulfur compound content results in Table 15. This may be because the cooked egg flavor in Table 11 is insufficient to represent the cooked flavor of milk, while some sulfur compound standards in Table 10 better reflect the cooked flavor of milk.

[0130] Aldehydes mainly originate from the oxidation of unsaturated fatty acids and the microbial degradation of amino acids (decarboxylation after transamination) or through Strecker degradation, while alcohols are usually products of aldehydes. Aldehydes such as hexanal and heptanal are generally products of lipid oxidation and have a distinct lipid oxidation odor. Milk fat can also be oxidized under light to produce 1-octen-3-ol, which has a mushroom-like odor. These oxidized off-odors are mostly described as milky, oily, and metallic. As shown in Table 15, the content of aldehydes and 1-octen-3-one in milk B and milk C is significantly higher than that in milk A, which corresponds to the results of the milky odor assessment in Table 14. Similarly, the sensory assessment results in Table 13 show that the milky odor content in milk A and milk C is low and similar, which is inconsistent with the results of the milky odor compound content in Table 15.

[0131] In summary, the sensory evaluation criteria developed in this study are consistent with the instrumental analysis results. The standard samples can be used to train sensory personnel, and the trained evaluators can score the sensory attributes of milk relatively objectively and accurately. Therefore, this study presents a relatively complete sensory evaluation system for milk.

Claims

1. A method for establishing a standard for evaluating key sensory characteristics in finished milk products, characterized in that: Includes the following steps: (1) Take the milk sample to be tested and extract the volatile flavor substances from all samples in the milk sample group by solid phase microextraction. (2) Then, gas chromatography-mass spectrometry was used to quantitatively analyze the volatile flavor substances in all milk samples; the extraction head was inserted into the gas chromatography vaporization chamber, desorbed at 250 °C for 5 min, using a DB-WAX capillary column, with helium as the carrier gas, and a constant flow rate of 1.2 mL / min. The column temperature program is as follows: the initial column temperature is 40℃, then increased to 75℃ at 7℃ / min; then increased to 150℃ at 2℃ / min; and finally increased to 230℃ at 5℃ / min and held for 2 minutes. Adopting a non-splitting mode; (3) The correlation between the volatile flavor components in milk and their corresponding sensory qualities was analyzed by applying statistical analysis methods, thereby determining the corresponding standard for the sensory attributes of milk used for training; the sensory qualities are: milky aroma, cooking aroma and milky smell, wherein the compounds of milky aroma are: hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, 9-decenoic acid and dodecanoic acid; the compounds of cooking aroma are: dimethyl sulfone and dimethyl trisulfide; the compounds of milky smell are: hexanal, decanal and 1-octen-3-ol.

2. The method for establishing according to claim 1, characterized in that, The solid-phase microextraction analysis method described in step (1) refers to the following steps: Weigh 10g of milk sample into a headspace vial, add 1g of sodium chloride, and use a microsyringe to inject 1μL of the internal standard 2-methyl-3-heptanone with a mass concentration of 0.816mg / ml into the headspace vial; Set the temperature of the water bath to 45℃, place the sealed headspace vial in the water bath and heat it for equilibration for 20min, insert the extraction head into the headspace vial, and push out the extraction fiber; After headspace adsorption for 30min, retract the extraction fiber and pull out the extraction head, and wait for GC injection.

3. The method for establishing according to claim 1, characterized in that, The gas chromatography-mass spectrometry method described in step (2) is: Mass spectrometry conditions: electron ionization source, electron energy 70 eV; injection port temperature 250℃, ion source temperature 230℃, quadrupole temperature 150℃; full scan mode, mass scan range m / z 35~350.

4. The method for establishing according to claim 1, characterized in that, The quantitative analysis described in step (2) adopts the internal standard semi-quantitative method, and the calculation formula is Ax / Ai=Cx / Ci, where Ax and Ai represent the peak area of ​​the target compound and the peak area of ​​the internal standard, respectively, and Cx and Ci represent the concentration of the target compound and the concentration of the internal standard, respectively.

5. The method for establishing according to claim 4, characterized in that, The internal standard is 2-methyl-3-heptanone; the sensory properties include milky aroma, which is the milky aroma unique to milk itself; and steamed flavor, which is the steamed flavor contained in milk, similar to the flavor of boiled egg white; It has a milky smell, which is the milky smell of milk.

6. A standard sample for training sensory trainers to determine the aroma of milk, characterized in that, The aroma includes a milky aroma, a cooked aroma, and a milky smell, wherein the milky aroma is composed of the following components: Hexanoic acid 50±10μg / kg, octanoic acid 200±40μg / kg, nonanoic acid 20±4μg / kg, decanoic acid 400±80μg / kg, 9-decenoic acid 50±10μg / kg and dodecanoic acid 200±40μg / kg; prepared in a 3% concentrated milk protein solution; The cooked flavor is composed of the following components: 1000±200 μg / kg of dimethyl sulfone and 1±0.2 μg / kg of dimethyl trisulfide; prepared in a 3% concentrated milk protein solution; The milky odor is composed of the following components: hexanal 10±2μg / kg, decanal 10±2μg / kg and 1-octen-3-ol 10±2μg / kg, in a 3% concentrated milk protein solution.

7. The application of the training standard as described in claim 6 in training milk flavor sensory evaluators.

8. The application as described in claim 7, characterized in that, Prepare the training standard as described in claim 6, and use it to train sensory evaluators on sensory attributes and intensity.

Images