Fast sugar infusion method for instant solid fruit and instant solid fruit

Abstract

The invention discloses an instant solid fruit rapid sugar permeation method and an instant solid fruit, and belongs to the technical field of food processing. The method aims at solving the problems that an existing sugar permeation technology is low in efficiency, uneven in product quality, dependent on food additives and difficult to meet the label cleaning requirement. According to the technical scheme, the method is characterized in that pretreated fruits are subjected to low-temperature plasma treatment so as to form microscopic permeation channels on the surfaces and superficial layers of the fruits, then the fruits are immersed in a high-concentration sugar solution, and an ultrasonic wave field generated by an upper ultrasonic plate and a rising microbubble flow field formed by introducing nitrogen into a bottom bubbling device are synchronously applied; the two components are coupled in a three-dimensional space to form a three-dimensional mass transfer power system without mechanical contact, so that high-efficiency and uniform permeation of sugar is realized within 20-30 minutes, and the whole sugar degree of fruits stably reaches over 20-degree Brix. The method is mainly used for rapidly preparing the high-quality and high-sweetness ready-to-eat solid fruit product with the clean label and without sweetening agents and preservatives.

Description

Technical Field

[0001] This invention relates to the field of food processing technology. More specifically, this invention relates to a method for rapid sugar infusion into ready-to-eat solid fruit products and the ready-to-eat solid fruit products themselves. Background Technology

[0002] In the modern processing system of ready-to-eat solid fruits, osmosis dehydration (sugar infiltration) is a core process that imparts a pleasant sweetness, improves texture, and extends shelf life. Consumers' demand for high-quality, healthy ready-to-eat fruits is growing, requiring not only excellent sensory qualities but also natural ingredients and clean labels (i.e., clean labeling). However, existing mainstream sugar infiltration technologies face a series of interconnected and long-standing technical bottlenecks in terms of efficiency, quality, and the alignment with the clean labeling concept, severely hindering the development of high-end products and industrial upgrading.

[0003] First, the fundamental flaws of classic methods, such as traditional boiling and prolonged soaking under normal pressure, lie in the coexistence of inefficiency and quality damage. Boiling accelerates sugar infusion by increasing molecular motion at high temperatures, but the intense heat inevitably leads to softening and discoloration of the fruit, as well as significant loss of heat-sensitive nutrients like vitamin C, greatly diminishing the product's taste and nutritional value. Meanwhile, soaking under normal pressure is extremely time-consuming, often requiring several hours or even tens of hours. This not only results in low production efficiency but also increases the risk of microbial contamination due to the long processing window, forcing producers to rely on preservatives for safety, contradicting the principle of reduced additives on clean labels. Both methods rely on concentration gradient-driven natural diffusion, resulting in weak mass transfer dynamics, which is the root cause of their long processing times.

[0004] To improve efficiency, non-thermal or weakly thermal auxiliary technologies have been introduced. Vacuum sugar penetration promotes sugar syrup entry by reducing internal gas pressure and widening intercellular spaces through negative pressure, while ultrasonic-assisted technology utilizes microjets and disturbances generated by cavitation to enhance interfacial mass transfer. These methods shorten processing time and reduce heat damage to some extent. However, each faces new limitations. Vacuum treatment requires sophisticated equipment and has limited effectiveness for dense or large fruit pieces. When ultrasonic technology is applied to high-viscosity, high-concentration sugar syrups, energy attenuation is significant, and the cavitation effect weakens, resulting in a ceiling on the increase in penetration efficiency. More importantly, if the mechanical vibrations generated are not properly controlled, or if power is increased to compensate for energy attenuation, collisions and friction between fruit pieces can easily occur, causing visible mechanical damage or microstructural disruption. This results in uneven texture, inconsistent taste, and difficulty in ensuring quality stability within the same batch of products.

[0005] Secondly, while pursuing efficiency, the aforementioned technologies often struggle to maintain product uniformity and meet clean labeling requirements. Whether through heat cooking or assisted physical field treatment, the migration path and rate of sugar within the fruit are difficult to control precisely, easily leading to an uneven sweetness or blandness on the inside. To address insufficient sweetness or taste variations, many processing methods have to resort to adding artificial sweeteners, flavor enhancers, or stabilizers to the formula for post-processing adjustments. While this approach can improve sensory scores in the short term, it directly introduces food additives that consumers are increasingly wary of, making the product ingredient list less clean and deviating from the market's core demand for natural and healthy products. Furthermore, consistently and uniformly increasing the soluble solids content of the product to above the critical flavor threshold of 20 °Brix (below this value, the sweetness is insufficient, market acceptance is low, and relying solely on additives does not conform to the clean labeling principle) may become a goal that current technologies cannot reliably achieve in the short term.

[0006] In summary, existing sugar infiltration technologies generally face a dilemma of balancing multiple objectives: pursuing high efficiency often comes with high damage or high energy consumption; pursuing high quality and uniformity may sacrifice efficiency or rely on chemical additives; and meeting clean label requirements poses almost stringent challenges to the technology's gentleness, precision, and zero-additive reliability. Overcoming these technological barriers and developing a new sugar infiltration process that can achieve efficient and uniform sugar penetration in a very short time with near-zero physical damage, and without relying on any non-natural additives, has become a core technological challenge that urgently needs to be overcome to promote industrial upgrading and meet the demands of the high-end market. Summary of the Invention

[0007] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0008] Another objective of this invention is to provide a method for rapid sugar penetration into ready-to-eat solid fruits. This method achieves efficient and uniform sugar penetration within 20-30 minutes by coupling plasma treatment with an ultrasonic-bubbling three-dimensional mass transfer field, significantly increasing the sugar content of the fruit to above 20°Brix. The entire process is carried out without mechanical damage, and the texture and nutrients of the fruit are fully preserved.

[0009] To achieve these objectives and other advantages according to the present invention, a method for rapid sugar infusion into ready-to-eat solid fruit is provided, comprising: S1. The pretreated fruit is subjected to low-temperature plasma treatment for 100-200 seconds to form micro-permeation channels on its surface and shallow layer. S2. Immerse the fruit treated in step S1 in a sugar solution with a mass concentration of 60-70%, and simultaneously apply two physical fields to the sugar solution for permeation treatment: apply an ultrasonic field above the sugar solution through the ultrasonic plate of the ultrasonic device, and introduce nitrogen gas through the lower plate bubbling device of the ultrasonic device at the bottom of the sugar solution to form a rising microbubble flow field. S3. Rinse and quick-freeze the fruit after the permeation treatment in step S2 to obtain the ready-to-eat solid fruit. The ultrasonic field and the rising microbubble flow field form a three-dimensional, non-mechanically contactless mass transfer force in three-dimensional space, so that the overall sugar content of the fruit can be stably increased to above 20°Brix within 20-30 minutes.

[0010] Preferably, the preprocessing in step S1 includes: S01. Select fresh, pest-free, and mechanically undamaged fruit raw materials for washing, cutting, or leaving them uncut. S02. Pre-freeze the fruit treated in S01 at a temperature of -20 to -40 ℃ for 4 to 6 hours. S03. Thaw the fruit that has been pre-frozen by S02 at a temperature of 30-40 ℃ for 5-20 minutes.

[0011] Preferably, the radio frequency power of the low-temperature plasma generator used in the low-temperature plasma treatment in step S1 is 200-400 W, the working gas is pure oxygen, and the gas flow rate is 10-30 NL / min.

[0012] Preferably, in step S2, the conditions for applying the ultrasonic field are: ultrasonic frequency 20-40 kHz, ultrasonic power 80-100 W, and permeation dehydration treatment time 20-30 min; during the formation of the rising microbubble flow field, the flow rate of nitrogen gas introduced is 0.5-3 VVM.

[0013] Preferably, the sugar in the sugar solution in step S2 is selected from sucrose, fructose syrup, or maltitol.

[0014] Preferably, the temperature of the quick-freezing treatment in step S3 is -30 to -40 °C.

[0015] Preferably, in step S2, while applying the two physical fields for permeation treatment, the sugar solution is circulated under controlled temperature to maintain the sugar solution temperature at 35~40℃. The nitrogen gas introduced by the lower plate bubbling device of the ultrasonic equipment is pretreated saturated wet nitrogen gas, and the difference between its dew point temperature and the sugar solution temperature is ≤5℃.

[0016] Preferably, after rinsing in step S3 and before quick-freezing, a partial dehydration and shaping step is also included: the rinsed fruit is placed in a circulating hot air condition with a humidity of ≤30% and a temperature of 35~40℃ for 3~8 minutes to form a soft, non-hard shell semi-dry sugar gum layer on its surface.

[0017] Preferably, in step S2, 0.1% to 1.0% of nanocellulose crystals by mass of the sugar solution are added to the sugar solution. The nanocellulose crystals have a particle size of 20 to 100 nm and an aspect ratio greater than 10. Under the action of mass transfer, the nanocellulose crystals can partially penetrate into the micro-channels of the fruit and adhere to it. Finally, the content of nanocellulose crystals in the ready-to-eat solid fruit is 0.01% to 0.1% of the dry weight of the fruit.

[0018] The present invention further claims protection for a ready-to-eat solid fruit product, which is prepared by a rapid sugar infiltration method.

[0019] The present invention has at least the following beneficial effects: Firstly, this invention constructs microscopic permeation channels through low-temperature plasma treatment and couples them with a three-dimensional non-contact mass transfer dynamic system consisting of upper ultrasound and lower bubbling. This fundamentally overcomes the technical bottleneck of uneven mass transfer in high-viscosity sugar solutions. It can stabilize the overall sugar content of various fruits to above 20°Brix within 20-30 minutes. The sugar permeation efficiency is significantly improved compared to traditional processes, and the sugar content distribution of products within a batch is highly uniform. This successfully solves the problem of the difficulty in achieving both high efficiency and uniformity. Secondly, the partial dehydration and shaping step provided by this invention involves short-term, gentle hot air treatment of the candied fruit before quick-freezing, which precisely controls the moisture content on the surface of the fruit, forming a soft, semi-dry sugar syrup layer. This not only effectively prevents the fruit from sticking together after quick-freezing, but more importantly, while retaining the juicy and tender texture inside, it also gives the surface of the product a moderate chewiness and a dry flavor, significantly improving the taste and consumer experience of ready-to-eat fruit. Thirdly, this invention adds nanocellulose crystals to the sugar solution and utilizes the three-dimensional mass transfer dynamics of this process to partially introduce and anchor them inside the fruit, so that the final product not only achieves high sweetness but also naturally and simultaneously increases the dietary fiber content (0.01%-0.1% on a dry basis). Furthermore, the presence of nanocellulose in the microstructure can also enhance cell wall support and improve the overall crispness and chewiness of the product, achieving multiple positive interventions in flavor, nutrition, and texture through a single process.

[0020] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can implement it based on the description.

[0022] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0023] Example 1 S0. Select fresh, pest-free, and mechanically undamaged yellow peaches, wash them, peel them, remove the pits, and cut them into 8 pieces; further pre-freeze them at -40 ℃ for 5 hours; thaw the pre-frozen yellow peaches at 40 ℃ for 20 minutes. S1. Low-temperature plasma treatment: The yellow peaches obtained in step S0 are placed in a low-temperature plasma generator with a radio frequency of 300 W, pure oxygen as the medium, a working gas flow rate of 20 NL / min, and a treatment time of 150 s. S2. Two physical field permeation treatment: The yellow peaches treated in step S1 were immersed in a 70% sucrose solution, and two physical fields were applied to the solution simultaneously for permeation treatment: an ultrasonic field was applied above the solution through the ultrasonic plate of an ultrasonic device, with an ultrasonic frequency of 40 kHz, an ultrasonic power of 100 W, and a permeation dehydration treatment time of 20 min; nitrogen gas was introduced into the bottom of the solution through the lower plate bubbling device of the ultrasonic device to form a rising microbubble flow field, with a nitrogen gas flow rate of 1.8 VVM. S3. Rinse the yellow peaches treated in step S2 with water 1-2 times; place them at -40℃ for rapid freezing to obtain the ready-to-eat solid yellow peaches.

[0024] Example 2 S0. Select fresh strawberries that are free from pests and mechanical damage, wash them and set them aside; further pre-freeze them at -40 ℃ for 4 hours; thaw the pre-frozen strawberries at 35 ℃ for 10 minutes. S1. Low-temperature plasma treatment: The strawberries obtained in step S0 are placed in a low-temperature plasma generator with a radio frequency of 350 W, pure oxygen as the medium, a working gas flow rate of 30 NL / min, and a treatment time of 180 s. S2. Two physical field permeation treatment: The strawberries treated in step S1 were immersed in a 70% maltitol solution, and two physical fields were applied to the sugar solution simultaneously for permeation treatment: an ultrasonic field was applied above the sugar solution through the ultrasonic plate of an ultrasonic device, with an ultrasonic frequency of 40 kHz, an ultrasonic power of 100 W, and a permeation dehydration treatment time of 30 min; nitrogen gas was introduced into the bottom of the sugar solution through the lower plate bubbling device of the ultrasonic device to form a rising microbubble flow field, and the flow rate of nitrogen gas was 1.9 VVM. S3. Rinse the strawberries treated in step S2 with water 1-2 times; then freeze them quickly at -40℃ to obtain the ready-to-eat solid strawberries.

[0025] Example 3 S0. Select fresh apricots that are free from pests and mechanical damage, wash them, remove the pits, and cut them in half for later use; further pre-freeze them at -40 ℃ for 5 h; thaw the pre-frozen apricots at 40 ℃ for 5 min. S1. Low-temperature plasma treatment: The apricot obtained in step S0 is placed in a low-temperature plasma generator with a radio frequency of 200 W, pure oxygen as the medium, a working gas flow rate of 20 NL / min, and a treatment time of 120 s. S2. Two physical field permeation treatment: The apricots treated in step S1 were immersed in a 60% sucrose solution, and two physical fields were applied to the sugar solution simultaneously for permeation treatment: an ultrasonic field was applied above the sugar solution through the ultrasonic plate of an ultrasonic device, with an ultrasonic frequency of 30 kHz, an ultrasonic power of 90 W, and a permeation dehydration treatment time of 28 min; nitrogen gas was introduced into the bottom of the sugar solution through the lower plate bubbling device of the ultrasonic device to form a rising microbubble flow field, and the flow rate of nitrogen gas was 2.1 VVM. S3. Rinse the apricots treated in step S2 with water 1-2 times; then freeze them quickly at -30℃ to obtain the ready-to-eat solid apricots.

[0026] Example 4 S0. Select fresh apples that are free from pests and mechanical damage. After washing, peel and core them, and cut them into 8 pieces. Further pre-freeze them at -40 ℃ for 6 hours. Thaw the pre-frozen apples at 40 ℃ for 15 minutes. S1. Low-temperature plasma treatment: The apples obtained in step S0 are placed in a low-temperature plasma generator with a radio frequency of 400 W, pure oxygen as the medium, a working gas flow rate of 30 NL / min, and a treatment time of 180 s. S2. Two physical field permeation treatment: The apples treated in step S1 were immersed in a 70% fructose syrup solution, and two physical fields were applied to the syrup simultaneously for permeation treatment: an ultrasonic field was applied above the syrup through the ultrasonic plate of an ultrasonic device, with an ultrasonic frequency of 40 kHz, an ultrasonic power of 100 W, and a permeation dehydration treatment time of 25 min; nitrogen gas was introduced into the bottom of the syrup through the lower plate bubbling device of the ultrasonic device to form a rising microbubble flow field, and the flow rate of nitrogen gas was 2.1 VVM. S3. Rinse the apples treated in step S2 with water 1-2 times; then freeze them quickly at -40℃ to obtain the ready-to-eat solid apples.

[0027] Example 5 S0. Select fresh, pest-free, and mechanically undamaged pears, wash them, peel them, remove the cores, and cut them into 8 wedges; further pre-freeze them at -30 ℃ for 5 hours; thaw the pre-frozen pears at 40 ℃ for 10 minutes. S1. Low-temperature plasma treatment: The pear obtained in step S0 is placed in a low-temperature plasma generator with a radio frequency of 400 W, pure oxygen as the medium, a working gas flow rate of 30 NL / min, and a treatment time of 200 s. S2. Two physical field permeation treatment: The pears treated in step S1 were immersed in a 70% fructose syrup solution, and two physical fields were applied to the sugar solution simultaneously for permeation treatment: an ultrasonic field was applied above the sugar solution through the ultrasonic plate of an ultrasonic device, with an ultrasonic frequency of 20 kHz, an ultrasonic power of 80 W, and a permeation dehydration treatment time of 30 min; nitrogen gas was introduced into the bottom of the sugar solution through the lower plate bubbling device of the ultrasonic device to form a rising microbubble flow field, and the flow rate of nitrogen gas was 3.0 VVM. S3. Rinse the pears treated in step S2 with water 1-2 times; then freeze them quickly at -40℃ to obtain the ready-to-eat solid pears.

[0028] Example 6 S0. Select fresh, pest-free, and mechanically undamaged pears, wash them, peel them, remove the cores, and cut them into 8 wedges; further pre-freeze them at -30 ℃ for 5 hours; thaw the pre-frozen pears at 40 ℃ for 10 minutes. S1. Low-temperature plasma treatment: The pear obtained in step S0 is placed in a low-temperature plasma generator with a radio frequency of 400 W, pure oxygen as the medium, a working gas flow rate of 30 NL / min, and a treatment time of 200 s. S2. Two physical field permeation treatment: The pears treated in step S1 were immersed in a 70% fructose syrup solution. Two physical fields were applied to the sugar solution simultaneously for permeation treatment, maintaining the sugar solution temperature at 40℃. An ultrasonic field was applied above the sugar solution through the ultrasonic plate of an ultrasonic device with an ultrasonic frequency of 20 kHz and an ultrasonic power of 80 W for 30 min of permeation and dehydration treatment. At the bottom of the sugar solution, nitrogen gas was introduced through the lower plate bubbling device of the ultrasonic device to form a rising microbubble flow field. The flow rate of the introduced nitrogen gas was 3.0 VVM, and the introduced nitrogen gas was pretreated saturated wet nitrogen gas with a dew point temperature ≤5℃ difference from the sugar solution temperature. S3. Rinse the pears treated in step S2 with water 1-2 times; then freeze them quickly at -40℃ to obtain the ready-to-eat solid pears.

[0029] Example 7 S0. Select fresh, pest-free, and mechanically undamaged pears, wash them, peel them, remove the cores, and cut them into 8 wedges; further pre-freeze them at -30 ℃ for 5 hours; thaw the pre-frozen pears at 40 ℃ for 10 minutes. S1. Low-temperature plasma treatment: The pear obtained in step S0 is placed in a low-temperature plasma generator with a radio frequency of 400 W, pure oxygen as the medium, a working gas flow rate of 30 NL / min, and a treatment time of 200 s. S2. Two physical field permeation treatment: The pears treated in step S1 were immersed in a 70% fructose syrup solution. Two physical fields were applied to the sugar solution simultaneously for permeation treatment, maintaining the sugar solution temperature at 40℃. An ultrasonic field was applied above the sugar solution through the ultrasonic plate of an ultrasonic device with an ultrasonic frequency of 20 kHz and an ultrasonic power of 80 W for 30 min of permeation and dehydration treatment. At the bottom of the sugar solution, nitrogen gas was introduced through the lower plate bubbling device of the ultrasonic device to form a rising microbubble flow field. The flow rate of the introduced nitrogen gas was 3.0 VVM, and the introduced nitrogen gas was pretreated saturated wet nitrogen gas with a dew point temperature ≤5℃ difference from the sugar solution temperature. S3. Rinse the pears treated in step S2 with water 1-2 times; place the rinsed fruit under circulating hot air conditions with humidity ≤30% and temperature 40℃ for 5 minutes to form a soft, non-hard shell semi-dry sugar gum layer on its surface, and then quickly freeze it at -40℃ to obtain the ready-to-eat solid pear.

[0030] Example 8 S0. Select fresh, pest-free, and mechanically undamaged pears, wash them, peel them, remove the cores, and cut them into 8 wedges; further pre-freeze them at -30 ℃ for 5 hours; thaw the pre-frozen pears at 40 ℃ for 10 minutes. S1. Low-temperature plasma treatment: The pear obtained in step S0 is placed in a low-temperature plasma generator with a radio frequency of 400 W, pure oxygen as the medium, a working gas flow rate of 30 NL / min, and a treatment time of 200 s. S2. Two physical field permeation treatment: The pears treated in step S1 are immersed in a 70% fructose syrup solution. 1.0% of nanocellulose crystals (60 nm in diameter, aspect ratio greater than 10) are added to the syrup. Two physical fields are simultaneously applied to the syrup for permeation treatment, maintaining the syrup temperature at 40°C. An ultrasonic field is applied above the syrup using an ultrasonic plate with a frequency of 20 kHz and a power of 80 W, for a permeation dehydration treatment time of 30 min. Nitrogen gas is introduced into the syrup at the bottom using a lower plate bubbling device of the ultrasonic equipment to form a rising microbubble flow field. The flow rate of the introduced nitrogen gas is 3.0 VVM, and the introduced nitrogen gas is pretreated saturated wet nitrogen gas with a dew point temperature ≤ 5°C difference from the syrup temperature. S3. Rinse the pears treated in step S2 with water 1-2 times; place the rinsed fruit under circulating hot air conditions with humidity ≤30% and temperature 40℃ for 5 minutes to form a soft, non-hard shell semi-dry sugar gum layer on its surface; then quickly freeze it at -40℃. Finally, the content of nanocellulose crystals in the ready-to-eat solid fruit is 0.06% of the dry weight of the fruit, thus obtaining the ready-to-eat solid pear.

[0031] Comparative Example 1 S0. Select fresh, pest-free, and mechanically undamaged yellow peaches, wash them, peel them, remove the pits, and cut them into 8 pieces; further pre-freeze them at -40 ℃ for 5 hours; thaw the pre-frozen yellow peaches at 40 ℃ for 20 minutes. S1. Immerse the yellow peaches treated in step S0 in a 70% sucrose solution; introduce nitrogen gas into the bottom of the sugar solution through the lower plate bubbling device of an ultrasonic device to form a rising microbubble flow field, and perform permeation dehydration treatment for 20 minutes. The flow rate of nitrogen gas introduced is 1.8 VVM. S2. Rinse the yellow peaches treated in step S2 with water 1-2 times; place them at -40℃ for rapid freezing to obtain the ready-to-eat solid yellow peaches.

[0032] Comparative Example 2 S0. Select fresh strawberries that are free from pests and mechanical damage, wash them and set them aside; further pre-freeze them at -40 ℃ for 4 hours; thaw the pre-frozen strawberries at 35 ℃ for 10 minutes. S1. Low-temperature plasma treatment: The strawberries obtained in step S0 are placed in a low-temperature plasma generator with a radio frequency of 350 W, pure oxygen as the medium, a working gas flow rate of 30 NL / min, and a treatment time of 180 s. S2. Immerse the strawberries treated in step S1 in a 70% maltitol solution. At the bottom of the sugar solution, nitrogen gas is introduced through the lower plate bubbling device of an ultrasonic device to form a rising microbubble flow field. The permeation dehydration treatment time is 30 min, and the flow rate of nitrogen gas introduced is 1.9 VVM. S3. Rinse the strawberries treated in step S2 with water 1-2 times; then freeze them quickly at -40℃ to obtain the ready-to-eat solid strawberries.

[0033] Comparative Example 3 S0. Select fresh apricots that are free from pests and mechanical damage, wash them, remove the pits, and cut them in half for later use; further pre-freeze them at -40 ℃ for 5 h; thaw the pre-frozen apricots at 40 ℃ for 5 min. S1. Immerse the apricots treated in step S0 in a sucrose solution with a mass concentration of 60%. Apply an ultrasonic field above the sugar solution through the ultrasonic plate of an ultrasonic device. The ultrasonic frequency is 30 kHz, the ultrasonic power is 90 W, and the permeation dehydration treatment time is 28 min. S2. Rinse the apricots treated in step S1 with water 1-2 times; then freeze them quickly at -30℃ to obtain the ready-to-eat solid apricots.

[0034] Comparative Example 4 S0. Select fresh apples that are free from pests and mechanical damage. After washing, peel and core them, and cut them into 8 pieces. Further pre-freeze them at -40 ℃ for 6 hours. Thaw the pre-frozen apples at 40 ℃ for 15 minutes. S1. Immerse the apples treated in step S0 in a 70% fructose syrup solution for 25 min to allow them to dehydrate. S2. Rinse the apples treated in step S1 with water 1-2 times; place them at -40℃ for rapid freezing to obtain the ready-to-eat solid apples.

[0035] Comparative Example 5 S0. Select fresh, pest-free, and mechanically undamaged pears, wash them, peel them, remove the cores, and cut them into 8 wedges; further pre-freeze them at -30 ℃ for 5 hours; thaw the pre-frozen pears at 40 ℃ for 10 minutes. S1. Low-temperature plasma treatment: The pear obtained in step S0 is placed in a low-temperature plasma generator with a radio frequency of 400 W, pure oxygen as the medium, a working gas flow rate of 30 NL / min, and a treatment time of 200 s. S2. Immerse the pears treated in step S1 in a 70% fructose syrup solution. Apply an ultrasonic field above the sugar solution through the ultrasonic plate of an ultrasonic device. The ultrasonic frequency is 20 kHz, the ultrasonic power is 80 W, and the permeation dehydration treatment time is 30 min. S3. Rinse the pears treated in step S2 with water 1-2 times; then freeze them quickly at -40℃ to obtain the ready-to-eat solid pears.

[0036] Soluble solids content and preference were evaluated for Examples 1-8 and Comparative Examples 1-5. The indicators tested included: Soluble Solids (SSC): After ultrasonic dehydration, the fruit was rinsed 1-2 times with clean water and then pulped. The SSC of the fruit before and after dehydration was measured using a handheld digital saccharimeter (DLX-SDJ1530, Delixi Electric Co., Ltd.). Ten measurements were taken for each sample group, and the average value was calculated. Ascorbic Acid Content Determination: The vitamin C content of the product was tested according to the method specified in GB 5009.86-2016 "National Food Safety Standard - Determination of Ascorbic Acid in Food" (2,4-dinitrophenylhydrazine method). Ten measurements were taken for each sample group, and the average value was calculated. Sensory Evaluation: Thirty professionals conducted a sensory evaluation of the frozen product. Liked: A, Moderate: B, Disliked: C.

[0037] The changes in soluble solids before and after sugar infusion in Examples 1-5 and Comparative Examples 1-5 are shown in Table 1. The ascorbic acid content of the products in Examples 1-5 and Comparative Examples 1-5 is shown in Table 2. The preference evaluation of the products in Examples 1-5 and Comparative Examples 1-5 is shown in Table 3.

[0038] Table 1. Changes in soluble solids content before and after sugar infusion. As shown in Table 1, Examples 1-5 increased the soluble solids content of various fruits by more than 200% within 20-30 minutes, reaching a maximum of 292.31%, and the final sugar content consistently exceeded 20°Brix, significantly better than all comparative examples. This demonstrates the advantages of ultra-efficient sugar penetration. This is because the present invention constructs a two-stage synergistic mass transfer system of channel creation and dynamic enhancement. First, the low-temperature plasma pretreatment is not a simple surface etching. It utilizes high-energy active particles (such as oxygen free radicals and excited-state particles) to selectively oxidize and break molecular bonds in the waxy epidermis, cuticle, and intercellular matrix of fruits and vegetables, precisely weakening the mechanical strength of the tissue structure. Without destroying the integrity of the overall cells, it creates a nano- to micron-scale, hydrophilic, directional permeation microchannel network, significantly reducing the initial activation energy barrier for sugar molecule diffusion. Second, the three-dimensional physical field formed by the upper immersion ultrasound and the lower microbubble bubbling has a synergistic effect far exceeding functional superposition. The cavitation effect generated by the ultrasonic field in high-concentration sugar solution not only directly impacts the fruit surface through microjets, enhancing local disturbance, but also induces the existing microchannels to undergo periodic expansion and contraction in a breathing-like manner, thereby pumping the sugar solution deeper. Simultaneously, the continuously injected microbubble flow from the bottom acts as numerous micro-stirring agents, creating a gentle yet efficient laminar shearing and convection circulation throughout the sugar solution, completely eliminating the mass transfer boundary layer stagnation problem caused by viscosity. Furthermore, the coupling of the bubbles with the ultrasonic field during collapse or rise further excites and stabilizes the cavitation effect, forming a synergistically amplified fluid dynamic. These two physical fields intertwine and couple in three-dimensional space, jointly constructing a dynamic, forced, three-dimensional osmotic pressure environment, enabling sugar molecules to migrate rapidly and uniformly into the fruit interior along pre-opened plasma channels at rates far exceeding those achievable through natural diffusion and single-aid techniques.

[0039] Table 2 Ascorbic Acid Content of Products Table 2 shows that the ascorbic acid (vitamin C) retention rate of fruits treated with this invention is as high as 85%-91.2%, generally superior to the comparative examples lacking certain technical steps. The high nutrient retention rate is due to the fact that this invention forms a three-in-one nutrient preservation system integrating active temperature control, oxygen isolation protection, and zero physical contact. First, in terms of temperature, the low-temperature plasma treatment is carried out in a gas discharge close to room temperature. Its energy selectively acts on the molecular bonds of the epidermis, producing almost no macroscopic thermal effect. Although the ultrasonic-bubbling synergistic field generates localized cavitation heat, the overall system temperature is far lower than the mild range of traditional hot cooking (usually >60℃), fundamentally avoiding the covalent bond breakage, isomerization, or volatilization loss of heat-sensitive nutrients (such as vitamin C and polyphenols) caused by high temperatures. Second, in terms of anti-oxidation, the low-temperature plasma treatment uses pure oxygen as a medium. Its short-term, controllable oxidation mainly targets the epidermal structure, rather than overall penetration, and the treated product immediately enters the sugar solution immersion environment. Nitrogen bubbling, with the continuous introduction of inert gas into the sugar solution, effectively displaces and replaces dissolved oxygen, creating a low-oxygen or even near-oxygen-free liquid environment throughout the core sugar infiltration stage. This strongly inhibits the non-enzymatic oxidation of easily oxidized substances such as vitamin C. Finally, in terms of physical preservation, the non-mechanical contact three-dimensional mass transfer dynamics are key. The force field generated by upper ultrasound and lower bubbling is a uniform fluid shear and pressure wave, keeping the fruit in a controlled suspended state, completely avoiding shear damage such as collision and compression caused by mechanical stirring. This maximizes the preservation of cell wall integrity, preventing leakage of contents (including nutrients and flavor substances) due to cell damage, as well as enzymatic browning and nutrient degradation caused by enzyme-substrate contact.

[0040] Table 3 Product Preference Evaluation Table 3 clearly shows that all products from the embodiments received the highest rating of A, while the comparative examples mostly received B or C. This directly reflects the comprehensive advantages of this invention in terms of efficiency, homogeneity, and mildness. Efficient and uniform sugar infiltration ensures a full-bodied sweetness that is consistent throughout; the non-thermal physical field treatment perfectly preserves the original color, shape, and inherent texture of the fruit; and the collision-free processing avoids a soft or rough texture. These factors combined result in the product's excellent visual appeal, taste, and flavor, meeting the core demands of the high-end market for ready-to-eat fruit.

[0041] The changes in soluble solids before and after sugar infusion in Examples 5-8 are shown in Table 4, and the ascorbic acid content of the products in Examples 5-8 is shown in Table 5.

[0042] Table 4. Changes in soluble solids content before and after sugar infusion. As shown in Table 4, Example 6, based on Example 5, adds temperature control and saturated moist nitrogen bubbling, resulting in a more stable sugar solution mass transfer environment and a slight increase in sugar penetration efficiency. Example 7, based on Example 6, further adds a partial dehydration and shaping step. Moderate surface dehydration leads to a slight change in osmotic pressure, which in turn promotes further fixation and optimized distribution of internal sugars, thus further increasing SSC. Example 8, based on Example 7, adds nanocellulose crystals. Nanocellulose crystals with specific particle size and aspect ratio, driven by three-dimensional mass transfer dynamics, can not only partially enter the microchannels, but their unique nanofiber network structure can also form a skeletal support and flow guiding effect inside the fruit. On the one hand, it may assist sugar solution transport through capillary action; on the other hand, it can reduce the slight shrinkage of tissues caused by water migration after sugar penetration, thereby facilitating more complete and stable sugar retention, achieving a synergistic enhancement of functional addition and core sugar penetration efficiency.

[0043] Table 5 Ascorbic Acid Content of Products As shown in Table 5, the application of temperature control and saturated moist nitrogen in Example 6 significantly improved the ascorbic acid retention rate. This is because temperature control and moist nitrogen created a more precise low-temperature, low-oxygen environment. The brief, mild hot air treatment in Example 7 did not cause nutrient loss, and the rapid formation of the surface glycogum layer may have provided slight insulation and protection for the interior, further improving the retention rate. Example 8 achieved the highest nutrient retention rate. Its superiority lies in the successful introduction and anchoring of nanocellulose crystals in the microstructure. Nanocellulose is not only a dietary fiber, but its large specific surface area and hydrophilic functional groups may also have a certain physical adsorption and protective effect on some water-soluble nutrients, including vitamin C, reducing their migration or loss during subsequent rinsing and quick-freezing. Simultaneously, the strengthening effect of nanocellulose on the cell wall further stabilizes the cell structure and reduces leakage of contents. This allows Example 8 to achieve peak nutrient retention after integrating all the process advantages.

[0044] To verify the effects of temperature-controlled cycling and humid saturated nitrogen bubbling on the stability of sugar solution concentration and batch-to-batch consistency of the product, in the processing of Examples 5 and 6, this application used a digital refractometer (such as the ATGO PAL series) to sample and measure the sugar solution concentration every 5 minutes, and calculated the sugar solution concentration fluctuation rate. The sugar solution concentration rate was expressed as the percentage of the maximum positive or negative deviation relative to the initial set concentration. Simultaneously, the sugar content of three independent batches of products from Examples 5 and 6 was measured, and the batch-to-batch sugar content variation coefficient (CV) was calculated. The CV was obtained by preparing three independent batches of products, randomly selecting at least 10 samples from each batch, measuring the overall sugar content using a digital saccharimeter, and calculating the mean and standard deviation. The ratio of the standard deviation to the mean was used as the batch-to-batch sugar content variation coefficient (CV), and the results are shown in Table 6.

[0045] Table 6. Range of sugar concentration fluctuation and coefficient of variation (CV) of sugar content between batches As shown in Table 6, the temperature-controlled circulation (maintaining 35~40℃) used in the example effectively reduced local viscosity and temperature unevenness, while saturated wet nitrogen (dew point matching) completely avoided evaporation of sugar solution moisture caused by bubbling. The combined effect of these two factors ensured a highly stable main sugar solution concentration during treatment, fundamentally guaranteeing the consistency of the permeation environment for each batch and each fruit, thus ensuring the uniformity of product sweetness. A low coefficient of variation implies extremely high reliability for industrial production. The precise control of process parameters (stable temperature and gas fields) directly translates into high repeatability of the product's core quality indicator (sugar content).

[0046] This application further determined the surface water activity and adhesion rate of the products obtained in Examples 6 and 7, and the results are shown in Table 7. The surface water activity was measured using a calibrated water activity meter (such as the Aqualab series) at 25°C. The adhesion rate after quick-freezing was determined as follows: 100g of fruit that had undergone sugar infiltration and shaping treatment was evenly spread on a quick-freezing tray, and after quick-freezing at -40°C, the tray was gently shaken. Fruit pieces that could not be naturally separated due to adhesion were collected and weighed. Adhesion rate (%) = (weight of adhered fruit pieces / total weight) × 100%.

[0047] Table 7 Product surface water activity and quick-freezing adhesion rate Table 7 data shows that the partial dehydration and shaping in Example 7 actively regulated the surface texture and ease of consumption of the product. The short-term mild hot air treatment in Example 7 reduced the surface water activity of the fruit from a high level close to pure water to about 0.85. This not only almost eliminated the problem of products sticking together during quick-freezing (improving post-processing and packaging efficiency), but more importantly, this non-hard-shell semi-dry sugar gum layer endowed the product with a unique double-layer texture that is slightly tough on the outside and juicy on the inside.

[0048] This application further determines the total dietary fiber (TDF) content of the products obtained in Examples 7 and 8, specifically according to the enzymatic gravimetric method specified in the National Food Safety Standard for Determination of Dietary Fiber in Food (GB 5009.88). After drying, pulverizing, and defatting the samples, they were sequentially enzymatically hydrolyzed using amylase, protease, and glucosidase to remove protein and digestible starch. Ethanol was then added to precipitate the total dietary fiber. The samples were filtered, washed, dried, and weighed to calculate the total dietary fiber content on a dry basis. The hardness and chewiness of the products obtained in Examples 7 and 8 were determined using a texture analyzer: a texture profile analysis (TPA) test was performed using a texture analyzer (such as a StableMicro Systems TA.XT series). A cylindrical flat-bottom probe (such as P / 36) was used to compress the sample twice to 50% of its original height. The speed before, during, and after the test was 1.0 mm / s, and the trigger force was 5 g. Hardness was directly taken from the maximum peak force of the first compression curve (unit: N), and chewiness was automatically calculated by the instrument software based on hardness, cohesion, and elasticity parameters (unit: mJ). The results are shown in Table 8.

[0049] Table 8 Total dietary fiber content, hardness, and chewiness Table 8 shows that the method in Example 8 successfully introduced and anchored exogenous nanocellulose into the fruit, increasing the total dietary fiber content of the product by approximately 26%. This signifies that the process not only efficiently infuses sugar but also simultaneously and uniformly achieves functional nutritional fortification, creating a new form of healthy product that is both high in sweetness and high in fiber. The reinforcing network formed by the nanocellulose crystals in the fruit's microstructure provides support. TPA data indicates that the product in Example 8, while maintaining good elasticity, achieved a significant and controllable improvement in hardness and chewiness. This makes the product not only sweet but also has a fuller, chewier texture, meeting the market's demand for diverse textures in ready-to-eat snacks.

[0050] The number of devices and processing scale described herein are for simplification of the invention. Applications, modifications, and variations of the present invention's rapid sugar infusion method for ready-to-eat solid fruit and the resulting ready-to-eat solid fruit will be readily apparent to those skilled in the art.

[0051] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and the specific embodiments shown and described herein.

Claims

1. A method for rapid sugar infusion into ready-to-eat solid fruit products, characterized in that, include: S1. The pretreated fruit is subjected to low-temperature plasma treatment for 100-200 s; S2. Immerse the fruit treated in step S1 in a sugar solution with a mass concentration of 60-70%, and simultaneously apply two physical fields to the sugar solution for permeation treatment: apply an ultrasonic field above the sugar solution through the ultrasonic plate of the ultrasonic device, and introduce nitrogen gas through the lower plate bubbling device of the ultrasonic device at the bottom of the sugar solution to form a rising microbubble flow field. S3. Rinse and quick-freeze the fruit after the permeation treatment in step S2 to obtain the ready-to-eat solid fruit. Among them, the synchronous ultrasonic field and the rising microbubble flow field enable the overall sugar content of the fruit to stabilize at above 20°Brix within 20~30 minutes.

2. The method for rapid sugar infusion into ready-to-eat solid fruit products as described in claim 1, characterized in that, The preprocessing in step S1 includes: S01. Select fresh, pest-free, and mechanically undamaged fruit raw materials for washing; S02. Pre-freeze the fruit treated in S01 at a temperature of -20 to -40 ℃ for 4 to 6 hours. S03. Thaw the fruit that was pre-frozen in S02 at a temperature of 30-40 ℃ for 5-20 min.

3. The method for rapid sugar infusion into ready-to-eat solid fruit products as described in claim 2, characterized in that, The low-temperature plasma generator used in step S1 has a radio frequency power of 200-400 W, uses pure oxygen as the working gas, and has a gas flow rate of 10-30 NL / min.

4. The method for rapid sugar infusion into ready-to-eat solid fruit products as described in claim 3, characterized in that, In step S2, the conditions for applying the ultrasonic field are: ultrasonic frequency 20-40 kHz, ultrasonic power 80-100 W, and permeation dehydration treatment time 20-30 min; during the formation of the rising microbubble flow field, the flow rate of nitrogen gas introduced is 0.5-3 VVM.

5. The method for rapid sugar infusion into ready-to-eat solid fruit as described in claim 1, characterized in that, The sugar in the sugar solution described in step S2 is selected from sucrose, fructose syrup, or maltitol.

6. The method for rapid sugar infusion into ready-to-eat solid fruit as described in claim 1, characterized in that, The temperature for quick-freezing in step S3 is -30 to -40 °C.

7. The method for rapid sugar infusion into ready-to-eat solid fruit as described in claim 4, characterized in that, In step S2, while applying the two physical fields for permeation treatment, the sugar solution is circulated under controlled temperature to maintain the sugar solution temperature at 35~40℃. The nitrogen gas introduced by the lower plate bubbling device of the ultrasonic equipment is pretreated saturated wet nitrogen gas with a dew point temperature ≤5℃ difference from the sugar solution temperature.

8. The method for rapid sugar infusion into ready-to-eat solid fruit products as described in claim 1, characterized in that, Step S3, after rinsing and before quick-freezing, also includes a partial dehydration and shaping step: the rinsed fruit is placed in a circulating hot air condition with a humidity of ≤30% and a temperature of 35~40℃ for 3~8 minutes to form a soft, non-hard shell semi-dry sugar gum layer on its surface.

9. The method for rapid sugar infusion into ready-to-eat solid fruit products as described in claim 1, characterized in that, In step S2, 0.1% to 1.0% of nanocellulose crystals by mass of the sugar solution are added to the sugar solution. The nanocellulose crystals have a particle size of 20 to 100 nm and an aspect ratio greater than 10. The final content of nanocellulose crystals in the ready-to-eat solid fruit product is 0.01% to 0.1% of the dry weight of the fruit product.

10. A ready-to-eat solid fruit product, characterized in that, It is prepared by the rapid sugar infiltration method for ready-to-eat solid fruit as described in any one of claims 1 to 9.

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