Preparation method of low-sugar recombinant preserved blueberries

Abstract

The preparation method comprises the following steps: mixing and pulping cerasus humilis pulp and water to obtain cerasus humilis pulp, and independently pulping the blueberry pulp; mixing the two kinds of fruit pulp according to the mass ratio of (1-2): 10 to form compound fruit pulp; oligosaccharide or sugar alcohol accounting for 1%-10% of the mass of the composite fruit pulp is added into the composite fruit pulp; performing ultrasonic treatment on the mixed fruit pulp for 8-12 minutes at the frequency of 40-60 kHz and the power of 400-500 W; concentrating until the solid content is greater than or equal to 45%, molding into a green body, and drying to obtain a finished product. Through cooperation of ultrasonic treatment and a low-sugar formula, active ingredients are effectively reserved while the sugar content is reduced, and finally the low-sugar preserved blueberry which is uniform in texture and meets the health requirement is obtained and is suitable for the field of leisure food and functional food development.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of food processing. More particularly, the present application relates to a preparation method of low-sugar recombined blueberry preserved fruit. BACKGROUND

[0002] In the field of preserved fruit processing, traditional methods generally rely on high concentrations of sucrose (usually 30-50%) to achieve preservation, shape retention, and texture control. Although this high-sugar formula can extend the shelf life and maintain the product form, it significantly increases the sugar content of the final product, which is contrary to the current consumer demand for low-sugar healthy food. Simply reducing the amount of sucrose can cause multiple problems: first, insufficient osmotic pressure leads to decreased microbial stability, and the product is prone to mold; second, the role of sugar as a shaping medium is weakened, and the fruit pulp shrinks more during drying, resulting in defects such as dryness, cracking, or deformation in the finished product; third, in a low-sugar environment, natural colloids such as pectin cannot be fully dissolved and cross-linked, resulting in loose texture and poor chewiness of the preserved fruit.

[0003] Blueberry pulp has particularly prominent problems when processed alone due to its low fiber content, low pectin content, and dense cell wall structure. Conventional pulping and hot cooking processes cannot effectively destroy the cell wall to release bound pectin, and additional thickeners or increased sugar content are needed to compensate for texture defects, further deviating from the low-sugar goal. In addition, blueberries are rich in anthocyanins and other heat-sensitive active substances, which are prone to degradation and browning during traditional high-temperature concentration (85-95°C) and long drying processes. Studies have shown that heat treatment above 60°C can result in a loss of blueberry anthocyanins of over 50%, while low-temperature processing, although it can reduce losses, faces the risk of low efficiency and microbial control.

[0004] To solve the problem of high sugar, the industry has tried to use oligosaccharides or sugar alcohols as alternative sweeteners. However, these substances have different molecular weights, solubilities, and osmotic pressure characteristics from sucrose, and direct replacement often leads to the following consequences: first, the osmotic dehydration efficiency is insufficient, and the water activity (Aw) after drying is difficult to drop below the safety threshold (≤0.65); second, sugar alcohols are prone to crystallization during concentration, which destroys the texture uniformity of the preserved fruit; third, the lack of glass transition properties of sucrose makes it impossible to form a stable skeletal structure during drying, and the product is prone to moisture absorption and sanding. At the same time, the introduction of exogenous colloids or starches to compensate for texture defects often masks the natural flavor of the fruit and does not meet the clean label trend.

[0005] At the level of processing technology, there is a contradiction between efficiency and active ingredient retention in traditional thermal concentration and atmospheric drying: increasing temperature can accelerate water evaporation, but intensify the decomposition of heat-sensitive substances; reducing temperature is beneficial to ingredient retention, but significantly prolongs processing time and increases the risk of oxidation. Vacuum concentration can reduce operating temperature, but high-viscosity fruit pulp has poor flowability at low temperature, which easily leads to uneven heat transfer, local overheating and coking, and high energy consumption. If single hot air drying is used in the drying stage, water gradient stress easily causes the surface of preserved fruit to harden and crack; while freeze-drying can better retain active substances, but the equipment investment is large, the cycle is long, and it is difficult to apply on a large scale.

[0006] Therefore, it is still necessary to overcome multiple technical obstacles such as material characteristics, functional limitations of sugar substitutes, and process adaptability to develop a blueberry preserved fruit processing method that can simultaneously achieve a significant reduction in sugar content, effective improvement in texture, high retention of active ingredients, and suitability for industrial production. SUMMARY

[0007] An object of the present application is to solve at least the above problems and to provide at least the advantages described later.

[0008] Another object of the present application is to provide a method for preparing low-sugar reconstituted blueberry preserved fruit, which solves the problems of health risks caused by high sugar content in traditional preserved fruit and easy loss of active ingredients during processing.

[0009] In order to achieve these objects and other advantages according to the present application, a method for preparing low-sugar reconstituted blueberry preserved fruit is provided, which comprises the following steps: Step one, mixing aronia pulp and water at a mass ratio of 3-5:1 to obtain aronia fruit pulp; and mixing blueberry pulp to obtain blueberry fruit pulp; Step two, mixing the obtained aronia fruit pulp and the obtained blueberry fruit pulp at a mass ratio of 1-2:10 to form a composite fruit pulp; Step three, adding oligosaccharides or sugar alcohols to the composite fruit pulp of step two to obtain a mixed fruit pulp; the mass ratio of the composite fruit pulp to oligosaccharides or sugar alcohols is 100:1-10; Step four, treating the mixed fruit pulp obtained in step three by a slit-type ultrasonic device; the ultrasonic frequency is 40-60 kHz, the ultrasonic power is 400-500 W, and the ultrasonic time is 8-12 min; Step five, concentrating the composite fruit pulp treated in step four to a solid content of ≥45%, pouring it into a mold to obtain a preserved fruit blank, and drying the preserved fruit blank to obtain a low-sugar reconstituted preserved fruit.

[0010] Preferably, in the method for preparing low-sugar reconstituted blueberry preserved fruit, the fruit pulp is pretreated as follows before pulp beating operation: Blueberry pulp is immersed in hot water at 72-75℃ for 90-120 seconds, and then cooled rapidly to below 25℃; Cot fruit pulp is treated in steam at 88-90℃ for 45-60 seconds, and then cooled rapidly to below 25℃; During pulping, the pulp is placed in a closed environment filled with food-grade nitrogen, and the pulp temperature is controlled at ≤35℃. The pulping time is 3.0±0.5 minutes at a rotation speed of 5000±200 r / min.

[0011] Preferably, in the preparation method of the low-sugar reconstituted blueberry fruit preserve, the concentration in step five is carried out under three-stage gradient vacuum-rotation speed coupling conditions: )First stage: vacuum degree 0.06-0.08 MPa, temperature 68-72℃, rotation speed 150 r / min, concentration to solid content 25-30%; )Second stage: vacuum degree 0.04-0.05 MPa, temperature 58-62℃, rotation speed 120 r / min, concentration to solid content 35-40%; )Third stage: vacuum degree 0.08-0.09 MPa, temperature 50-52℃, rotation speed 90 r / min, concentration to solid content ≥45%; During the concentration process, deoxygenated food-grade nitrogen (oxygen content ≤0.5 ppm) is continuously introduced, and the solid content is monitored in real time using an online near-infrared sensor.

[0012] Preferably, in the preparation method of the low-sugar reconstituted blueberry fruit preserve, the drying process of the fruit preserve blank body in step five is pulse negative pressure-microwave assisted heat pump drying, which specifically includes: a) First stage drying: when the fruit preserve blank body water activity Aw>0.85, dry to Aw≤0.85 under normal pressure, temperature 60-65℃, and wind speed 2.0-2.5 m / s; b) Second stage drying: when the fruit preserve blank body water activity Aw is between 0.85 and 0.75, dry under pulse negative pressure and intermittent microwave assistance, the vacuum degree is between 0.04 and 0.08 MPa, and the pulse changes at a frequency of 1-2 min / time, while intermittent microwave is applied, the microwave power density is 0.5-1.0 W / g, the microwave on time / off time is 10 s / 50 s-20 s / 40 s, the drying temperature is 55-60℃, the wind speed is 1.5-2.0 m / s, and the drying is carried out to Aw≤0.75; c) Third stage drying: when the fruit preserve blank body water activity Aw≤0.75, stop the microwave, maintain the vacuum degree at 0.04-0.06 MPa, the drying temperature at 50-55℃, and the wind speed at 1.0-1.5 m / s, and dry to Aw≤0.65.

[0013] Preferably, in the preparation method of the low-sugar recombined blueberry preserved fruit, before the step of adding oligosaccharides or sugar alcohols to the compound fruit pulp, a compound enzyme preparation is added to the compound fruit pulp, the compound enzyme preparation comprising pectin esterase (PME) and cellulase, the total amount of the compound enzyme preparation being 0.01-0.05% of the mass of the compound fruit pulp, and the activity units of the pectin esterase and the cellulase being in a ratio of 1:2-3; the compound fruit pulp to which the compound enzyme preparation is added is incubated at 40-50°C for 15-30 min for enzymatic hydrolysis, and then is subjected to ultrasonic treatment in a slit-type ultrasonic device, the ultrasonic frequency being 40-60 kHz, the power being 700-800 W, and the time being 8-12 min.

[0014] Preferably, in the preparation method of the low-sugar recombined blueberry preserved fruit, when the oligosaccharides or sugar alcohols are added in step three, a microcapsule system with dual functions of antioxidation and nutritional strengthening is synchronously added, the microcapsule system comprising a core material and a wall material for covering the core material, the mass ratio of the core material to the wall material being 1:3-5; the core material being composed of tea polyphenols and blueberry anthocyanin extract in a mass ratio of 1.5-2:1, and the wall material being a sodium alginate-chitosan compound; and the amount of the microcapsule system added being 0.5-1.2% of the mass of the compound fruit pulp.

[0015] Preferably, in the preparation method of the low-sugar recombined blueberry preserved fruit, the microcapsule system is prepared by the following steps: S1. Dissolving tea polyphenols and blueberry anthocyanin extract in a mass ratio of 1.5-2:1 in a citric acid buffer solution with a pH of 5.0-5.5 to form a uniform solution with a core material mass concentration of 8-12%, under the condition of light shielding at 25-30°C; S2. Dissolving sodium alginate and chitosan in a mass ratio of 2:1-3:1 in deionized water, adjusting the pH to 4.5-5.0, and stirring in a water bath at 45-50°C until complete dissolution to form a compound solution with a total wall material mass concentration of 3-5%; S3. Injecting the core material solution obtained in step S1 into the wall material solution obtained in step S2 at a rate of 0.8-1.2 mL / min, and simultaneously performing high-speed shearing emulsification at a speed of 400-600 r / min to form an O / W emulsion; S4. Gradient solidification: S41. Dropping the emulsion obtained in step S3 into a 0.1-0.3 mol / L CaCl2 solution, and crosslinking and solidifying at 25-30°C for 20-30 min; S42. Transferring to a 0.5-1.0 wt%, pH 5.5-6.0 chitosan acetic acid solution, and performing secondary solidification at 35-40°C for 40-60 min to obtain a solidified product; S43, after the curing product is washed by deionized water, pulse negative pressure-low temperature combined drying is adopted, drying is carried out under the conditions of vacuum degree 0.06-0.08 MPa and temperature 35-40 DEG C to obtain a microcapsule system with moisture content ≤5%.

[0016] The present application at least includes the following beneficial effects: 1, the present application is based on the concept of full utilization of fruit pulp and food recombination, using the natural pectin content in blueberry, PME enzyme activity is high and easy to gel characteristics, compound with high calcium content of the plum fruit pulp, through the slit ultrasonic technology, give full play to the interaction between the components in the mixed fruit pulp system, prepare blueberry low sugar recombination preserved fruit, conform to the development concept of modern food "big health". Using blueberry fruit pulp and plum fruit pulp as main raw materials supplemented with natural polysaccharide, a new type of low sugar preserved fruit is prepared through the recombination interaction between components, realizing the green upgrading of preserved fruit industry; 2, the present application carries out directional processing on the composite fruit pulp containing oligosaccharide / sugar alcohol by slit ultrasonic wave (40-60 kHz, 400-500 W), and multiple synergistic mechanisms are formed at the molecular level: cavitation effect promotes efficient crosslinking of pectin molecules and oligosaccharide chains, while reducing the total sugar content (1-10% of the mass of the composite fruit pulp), a stable gel network is constructed, and the loose texture defect of traditional low sugar preserved fruit is avoided; the transient microjet effect accelerates water penetration and sugar alcohol dispersion, and inhibits the risk of crystallization during the concentration stage; high-frequency mechanical vibration simultaneously realizes non-thermal inactivation of microorganisms, creating conditions for subsequent low-temperature processing. The process innovatively integrates sugar reduction, texture improvement and processing safety into a single physical treatment step, laying the foundation for the industrialization of low sugar preserved fruit.

[0017] 3, the present application adopts pulse negative pressure-microwave assisted heat pump drying mode, which dynamically regulates the water migration path in three stages: in the initial stage, the free water content is rapidly reduced to a safe threshold (Aw≤0.85) under normal pressure hot air; in the middle stage, the pulse negative pressure (0.04-0.08 MPa) intermittently expands the fruit pores, combined with precise time control of microwave energy (0.5-1.0 W / g, 10-50 s interval) to selectively stimulate bound water molecule movement, and crack the cracking problem caused by drying stress; in the final stage, low-temperature constant-pressure drying avoids the decomposition of heat-sensitive components. The technology makes the preserved fruit maintain flexible texture under low water activity (Aw≤0.65), and the energy consumption is lower than that of traditional hot air drying.

[0018] 4、The application adopts sodium alginate-chitosan composite wall material to form a pH-responsive protective layer in an acidic fruit pulp environment, and the dense network effectively isolates oxygen permeation; tea polyphenols and blueberry anthocyanins (1.5-2:1) in the core material establish an oxidation priority transfer chain - tea polyphenols preferentially quench free radicals, reducing the oxidation loss of anthocyanins. The microcapsule system (addition amount 0.5-1.2%) releases part of chitosan during ultrasonic treatment, and the cationic property spontaneously crosslinks with the anionic pectin, further strengthening the gel strength, realizing the dual gain of nutrition fortification and texture optimization.

[0019] 5、The three-stage gradient vacuum-rotation speed coupled concentration of the application matches the fruit pulp viscosity variation law by gradually reducing the operating pressure (0.06→0.04→0.08 MPa) and stirring intensity (150→120→90 r / min): free water is quickly removed in the high vacuum stage; pectin is induced to dissolve in the medium vacuum slow-speed stage; the end stage of rising vacuum cooperates with low temperature (50-52℃) to inhibit the Maillard reaction. Continuous introduction of deoxygenated nitrogen gas (oxygen content ≤0.5 ppm) blocks the oxidation path, and near-infrared real-time monitoring ensures that the solid content accurately meets the standard (≥45%), avoiding the loss of active ingredients caused by local overheating.

[0020] Other advantages, objects, and features of the application will be apparent from the following specification, and will be appreciated by those skilled in the art. DETAILED DESCRIPTION

[0021] The application will be further described in detail below with reference to the examples, so that those skilled in the art can implement it according to the description.

[0022] It should be understood that the terms such as "have", "contain" and "include" used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0023] It should be noted that the experimental methods in the following embodiments are all conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0024] <Embodiment 1> The application provides a preparation method of low-sugar recombinant blueberry fruit preserves, which comprises the following steps: Step one, mix the aronia flesh and water at a mass ratio of 3:1 to pulp (5000 r / min, 3 min) to obtain aronia fruit pulp; Step two, directly pulp the blueberry flesh (5000 r / min, 3 min) to obtain blueberry fruit pulp; Step three, mix the aronia fruit pulp and blueberry fruit pulp at a mass ratio of 1:5 (20:100) to form a composite fruit pulp; Step four, erythritol is added to the compound fruit pulp (the mass ratio of the compound fruit pulp to the erythritol is 10:1, that is, the addition amount of the erythritol is 10%), and the mixture is uniformly dispersed at high speed to obtain a mixed fruit pulp; Step five, the mixed fruit pulp is subjected to slit type ultrasonic treatment (50 kHz, 450 W, 10 min); Step six, concentration (vacuum degree 0.05 Mpa, 65℃, 120 r / min, 40 min) to solid ≥45%, pour into the mold to obtain dried fruit body, and the dried fruit body is dried (drying machine drying for 14 h, the temperature is set to 65℃, and the wind speed is 1.5 m / s) to obtain low-sugar recombined dried fruit.

[0025] <Example 2> The application provides a preparation method of low-sugar recombined dried blueberry fruit. Step one, mix the aronia flesh and water at a mass ratio of 3:1 to obtain aronia pulp (5000 r / min, 3 min); Step two, directly beat the blueberry flesh to obtain blueberry pulp (5000 r / min, 3 min); Step three, mix the aronia pulp and the blueberry pulp at a mass ratio of 1:10 (10:100) to form a compound fruit pulp; Step four, the compound fruit pulp is subjected to slit type ultrasonic treatment (40 kHz, 300 W, 10 min); Step five, concentration (vacuum degree 0.05 Mpa, 65℃, 120 r / min, 40 min) to solid ≥45%, pour into the mold to obtain dried fruit body, and the dried fruit body is dried (drying machine drying for 14 h, the temperature is set to 65℃, and the wind speed is 1.5 m / s) to obtain low-sugar recombined dried fruit.

[0026] <Example 3> The application provides a preparation method of low-sugar recombined dried blueberry fruit. Step one, mix the aronia flesh and water at a mass ratio of 3:1 to obtain aronia pulp (5000 r / min, 3 min); Step two, directly beat the blueberry flesh to obtain blueberry pulp (5000 r / min, 3 min); Step three, mix the aronia pulp and the blueberry pulp at a mass ratio of 3:20 (15:100) to form a compound fruit pulp; Step four, erythritol is added to the compound fruit pulp (the mass ratio of the compound fruit pulp to the erythritol is 20:1), and the mixture is uniformly dispersed at high speed to obtain a mixed fruit pulp; Step five, the mixed fruit pulp is subjected to slit type ultrasonic treatment (50 kHz, 450 W, 10 min); Step six, concentration (vacuum degree 0.05 MPa, 70℃, 120r / min, 40min) to solid ≥45%, pour into the mold to get dried fruit body, dry the dried fruit body (dry in the drying machine for 17h, the temperature is set to 60℃, the wind speed is 1.5m / s), get low-sugar recombined dried fruit.

[0027] <Example 4> The application provides a preparation method of low-sugar recombined dried blueberry, which is different from example 3 in that: In step three, the plum fruit pulp and the blueberry fruit pulp are mixed according to a mass ratio of 1:20 (5:100); In step four, erythritol is replaced by an equal amount of isomaltooligosaccharide; In step five, the ultrasonic frequency is set to 100 kHz, the power is 900 W, and the ultrasonic treatment is performed for 10 min; In step six, the concentration is performed for 30 min, the vacuum degree is 0.05 MPa, the temperature is 65℃, the rotating speed is 140r / min, the drying time in the drying machine is 18h, and the remaining conditions and parameters are the same as those in example 3.

[0028] <Example 5> The application provides a preparation method of low-sugar recombined dried blueberry, which is different from example 3 in that: In step four, erythritol is replaced by polydextrose, and the compound fruit pulp and the polydextrose are mixed according to a mass ratio of 100:10; In step five, the ultrasonic frequency is set to 80 kHz, the power is 600 W, and the ultrasonic treatment is performed for 16 min; In step six, the concentration is performed for 30 min, the vacuum degree is 0.05 MPa, the temperature is 85℃, the rotating speed is 100r / min, the drying time in the drying machine is 18h, the temperature is set to 70℃, and the wind speed is 2.0m / s; the remaining conditions and parameters are the same as those in example 3.

[0029] <Example 6> The application provides a preparation method of low-sugar recombined dried blueberry, which is different from example 3 in that: In step one, before the pulp beating operation, the pulp is pretreated in the following mode: The blueberry pulp is soaked in hot water at 74℃ for 100 seconds and quickly cooled to below 25℃; The plum pulp is treated in steam at 89℃ for 54 seconds and quickly cooled to below 25℃; During the beating, the pulp is placed in a closed environment filled with food-grade nitrogen, the pulp temperature is controlled to be 32℃, and the beating is performed at a rotating speed of 5000r / min for 3.0 minutes.

[0030] The remaining conditions and parameters are the same as those in example 3.

[0031] <Example 7> The present application provides a method for preparing low-sugar recombined blueberry preserved fruit, which is different from example 3 in that the concentration in step five is carried out under three-stage gradient vacuum-rotation speed coupling conditions: i) first stage: vacuum degree 0.07 MPa, temperature 70℃, rotation speed 150 r / min, concentration to solid content 28%; ii) second stage: vacuum degree 0.045 MPa, temperature 60℃, rotation speed 120 r / min, concentration to solid content 38%; iii) third stage: vacuum degree 0.085 MPa, temperature 51℃, rotation speed 90 r / min, concentration to solid content 46%; Deoxygenated food-grade nitrogen gas (oxygen content ≤0.5 ppm) is continuously introduced during the concentration process, and the solid content is monitored in real time by using an online near-infrared sensor. The total concentration time is about 55 minutes, and the end point of each stage is adjusted in real time by the near-infrared sensor.

[0032] The remaining conditions and parameters are the same as those in example 3.

[0033] <Example 8> The present application provides a method for preparing low-sugar recombined blueberry preserved fruit, which is different from example 3 in that: The dried preserved fruit body in step five is subjected to pulse negative pressure-microwave assisted heat pump drying, which specifically includes: a) first stage drying: when the water activity Aw of the preserved fruit body is >0.85, dry it to Aw≤0.85 under normal pressure, temperature 63℃, and air speed 2.3 m / s; b) second stage drying: when the water activity Aw of the preserved fruit body is 0.8, dry it under pulse negative pressure and intermittent microwave assistance, with the vacuum degree changing between 0.06 MPa at a frequency of 1.5 min / time, and intermittent microwave being applied, the microwave power density being 0.8 W / g, the microwave on / off time being 20 s / 40 s, the drying temperature being 58℃, and the air speed being 1.8 m / s, to dry it to Aw≤0.75; c) third stage drying: when the water activity Aw of the preserved fruit body is ≤0.75, stop the microwave, maintain the vacuum degree at 0.05 MPa, the drying temperature at 50~55℃, and the air speed at 1.3 m / s, to dry it to Aw≤0.65.

[0034] The remaining conditions and parameters are the same as those in example 3.

[0035] <Example 9> The present application provides a method for preparing low-sugar recombined blueberry preserved fruit, which is different from example 3 in that: In step three, before adding oligosaccharides or sugar alcohols to the compound fruit pulp, a complex enzyme preparation is added to the compound fruit pulp, the complex enzyme preparation comprises pectin esterase and cellulase, the total amount of the complex enzyme preparation added is 0.03% of the mass of the compound fruit pulp, and the activity units of the pectin esterase and the cellulase are in a ratio of 1:2.5; the compound fruit pulp to which the complex enzyme preparation is added is incubated at 45 DEG C for 23 min for enzymolysis, and then is subjected to ultrasonic treatment in a slit-type ultrasonic device, the ultrasonic frequency is 50 kHz, the power is 750 W, and the time is 10 min.

[0036] The remaining conditions and parameters are the same as in Example 3.

[0037] <Example 10> The application provides a preparation method of low-sugar recombined blueberry preserved fruit, which is different from Example 3 in that: In step three, when the oligosaccharides or sugar alcohols are added, a microcapsule system with dual functions of antioxidation and nutrition strengthening is synchronously added, the microcapsule system comprises core materials and wall materials for covering the core materials, and the mass ratio of the core materials to the wall materials is 1:4; the core materials are composed of tea polyphenols and blueberry anthocyanin extracts in a mass ratio of 1.8:1, and the wall materials are sodium alginate-chitosan complexes; and the amount of the microcapsule system added is 0.9% of the mass of the compound fruit pulp.

[0038] The microcapsule system is prepared through the following steps: S1, the tea polyphenols and the blueberry anthocyanin extracts are dissolved in a citric acid buffer solution with a pH of 5.3 in a mass ratio of 1.8:1, and are mixed under light-proof conditions at 28 DEG C to form a uniform solution with a core material mass concentration of 10%; S2, the sodium alginate and the chitosan are dissolved in deionized water in a mass ratio of 2.5:1, the pH is adjusted to 4.8, and the mixture is stirred in a water bath at 48 DEG C until completely dissolved to form a complex solution with a total wall material mass concentration of 4%; S3, the core material solution obtained in step S1 is injected into the wall material solution obtained in step S2 at a rate of 1.0 mL / min, and is subjected to high-speed shearing emulsification at a speed of 500 r / min to form an O / W type emulsion; S4, gradient solidification: S41, the emulsion obtained in step S3 is added dropwise into a 0.2 mol / L CaCl2 solution, and is crosslinked and solidified at 28 DEG C for 25 min; S42, the solidified product is transferred into a 0.8wt%, pH 5.8 chitosan acetic acid solution, and is subjected to secondary solidification at 38 DEG C for 50 min to obtain a solidified product; S43, after the solidified product is washed with deionized water, pulse negative pressure-low temperature combined drying is adopted, the vacuum degree is 0.07 MPa, the temperature is 38 DEG C, and the solidified product is dried until the water content is less than or equal to 5% to obtain the microcapsule system.

[0039] The remaining conditions and parameters are the same as in Example 3.

[0040] <Comparative Example 1> (blueberry pulp + 20% erythritol + 15% medlar pulp)

Compared with Example 3, the proportion of sugar is increased - the texture is hard - erythritol is precipitated, the surface is white, the sensory evaluation is low, and it is slightly sweet

[0041] <Comparative Example 2> (blueberry pulp + 5% erythritol + 15% medlar pulp)

Compared with Example 3, no narrow-gap ultrasonic treatment, not formed

[0042] <Comparative Example 3> (blueberry pulp + 5% erythritol + 15% medlar pulp)

compared with Example 3, narrow slit ultrasonic intensity is small, not shaped

[0043] <Comparative Example 4> (blueberry pulp + 5% erythritol + 15% medlar pulp)

compared with Example 3, narrow slit ultrasonic time is long, taste is hard

[0044] <Comparative Example 5> (blueberry fruit pulp + 5% erythritol + 15% medlar fruit pulp)

compared with Example 3, high drying temperature, hard texture

[0045] <Comparative Example 6> (blueberry fruit pulp + 10% sucrose + 15% medlar fruit pulp)

sucrose is used instead, high sugar content

[0046] <Comparative Example 7> (blueberry pulp + 5% sucrose)

without plum pulp, no shaping

[0047] <Comparative Example 8> (100% blueberry)

without sugar and plum pulp, moderate slit ultrasonic, poor shaping effect, poor taste and flavor

[0048] <Experimental Example 1> The products prepared according to Examples 1-10 and Comparative Examples 1-8 of the present application were detected, and the detection results are shown in Table 1.

[0049] Detection method: The soluble sugar content was detected according to the Agricultural Industry Standard NY / T 2742-2015 "Determination of soluble sugar in fruits and products 3,5-dinitrosalicylic acid colorimetric method".

[0050] Hardness detection: TA.XT2i / 50 texture analyzer was used, the probe type was P6, and the detection conditions were as follows: pre-test speed 1 mm / s, test speed 1 mm / s, post-test speed 1 mm / s, trigger force 5 gf, and compression distance 50% of the sample height.

[0051] Anthocyanin retention rate detection method: According to GB / T 22244-2008 "Determination of anthocyanin in food High performance liquid chromatography", the specific operation is as follows: 1. Sample treatment: Raw material: 10 g of fresh blueberry pulp was taken, 30 mL of acidified methanol (containing 1% formic acid) was added, homogenized and centrifuged (8000 r / min, 10 min), and the supernatant was diluted to 50 mL; Finished product: 1.0 g of preserved fruit sample was crushed, extracted and diluted to 25 mL by the same method; 2. Chromatographic conditions: Instrument: Agilent 1260 HPLC, DAD detector; Chromatographic column: Zorbax SB-C18 (4.6x150mm, 5μm); Mobile phase: A-0.1% formic acid, B-acetonitrile; Gradient: 0 min (5%B)→10 min (15%B)→20 min (25%B)→25 min (5%B); Flow rate: 1.0 mL / min, column temperature: 30℃, detection wavelength: 520 nm; 3. Calculation Anthocyanin retention rate (%) = [total amount of anthocyanin in finished product (mg / 100g) / total amount of anthocyanin in raw material (mg / 100g)] x 100% Table 1 detection results Note: a-erythritol, fructooligosaccharide, isomaltooligosaccharide, polydextrose do not produce heat, not included) As can be seen from the comparison of Example 3 and Comparative Example 1, the proportion of sugar alcohol is increased in Comparative Example 1, so that the product has high sugar content, strong sweetness and slight hardness. As can be seen from the comparison of Example 3 and Comparative Example 1, the proportion of sugar alcohol is increased in Comparative Example 1, so that the product has high sugar content, strong sweetness and slight hardness.

[0052] As can be seen from the comparison of Example 3 and Comparative Example 2, the blueberry fruit pulp in Comparative Example 2 is not subjected to slit ultrasonic treatment, which is not conducive to the interaction between different components in the mixed fruit pulp, resulting in poor gel performance, and the product is not shaped and the organization is not full.

[0053] As can be seen from the comparison of Example 3 and Comparative Example 3, the blueberry fruit pulp in Comparative Example 3 is subjected to short-time low-intensity slit ultrasonic treatment, which is also not conducive to the interaction between different components in the mixed fruit pulp, resulting in poor gel performance, and the product is not shaped and the organization is not full.

[0054] As can be seen from the comparison of Example 3 and Comparative Example 4, the mixed fruit pulp in Comparative Example 4 is subjected to long-time high-frequency slit ultrasonic treatment, which on the one hand causes the interaction between different components in the mixed pulp to be stronger, and on the other hand causes the blueberry fruit pulp to become more delicate and uniform, resulting in increased gel capacity and increased hardness of the recombined dried fruit.

[0055] As can be seen from the comparison of Example 3 and Comparative Example 5, the temperature during drying in Comparative Example 5 is higher, and the PME enzyme activity in the blueberry fruit pulp is greatly reduced, resulting in poor product shaping and severe shrinkage, and the product is hard in texture.

[0056] As can be seen from Comparative Example 6, on the basis of Example 3, replacing erythritol with sucrose results in a product with high sugar content and a slightly sweet and hard texture.

[0057] As can be seen from Comparative Example 7, Comparative Example 7 adds 5% sucrose and does not introduce plum fruit pulp, so the calcium content is low and the gel performance of the blueberry fruit pulp cannot be improved, resulting in poor shaping before drying and a paste-like organization after drying.

[0058] As can be seen from Comparative Example 8, no sugar and plum fruit pulp are added, resulting in no shaping before drying and a surface shaping and internal paste-like organization after drying.

[0059] Example 1 (high sugar alcohol scheme): When the amount of erythritol added is 10%, the hardness of the product reaches 9.12 N, and the texture is slightly hard, proving that excessive sugar alcohol can form a product but sacrifices the texture and palatability; Example 2 (no sugar alcohol scheme): The hardness is only 6.02 N without the addition of sugar alcohol and the surface shrinks, verifying the necessity of oligosaccharides / sugar alcohols for maintaining basic texture; Example 4 (low oligomaltose): After replacing erythritol, the hardness increases to 10.57 N, indicating that different oligosaccharides need to be adapted to specific process parameters; Example 5 (polydextrose + high-temperature concentration): High addition amount (10%) and high-temperature concentration (85°C) synergistically cause a hard shell phenomenon, highlighting the critical significance of concentration temperature control.

[0060] Example 6 added pulp pretreatment (hot water soaking of blueberries + steam treatment of mountainberries) and nitrogen protection beating on the basis of Example 3. Compared with Example 3, the product of Example 6 had a smooth surface without wrinkles (compared with slight wrinkles of Example 3), better gloss (compared with good gloss of Example 3), and improved taste, being flexible and elastic (hardness 8.05 N vs 7.43 N, ↑ 8.3%). This shows that hot water soaking (74°C / 100s) effectively passivates blueberry oxidase, steam treatment (89°C / 54s) softens mountainberry fiber, and nitrogen protection beating inhibits browning and synergistically improves product appearance integrity and texture elasticity.

[0061] Example 7 added three-stage gradient vacuum-rotation concentration and nitrogen protection technology on the basis of Example 3. Compared with Example 3, the product prepared in Example 7 had uniform and bright color without browning (compared with slight browning of Example 3), uniform and delicate texture without shrinkage (compared with slight shrinkage of Example 3), and active ingredient anthocyanin retention rate 91.5% (compared with 78.5% of Example 3); this shows that gradient concentration (0.07→0.045→0.085 MPa) matches the viscosity change of fruit pulp, low temperature (51°C) in the last stage inhibits Maillard reaction, and nitrogen protection (O2≤0.5 ppm) blocks the oxidation path to achieve zero browning.

[0062] Example 8 added pulse negative pressure-microwave assisted drying technology on the basis of Example 3. Compared with Example 3, the product prepared in Example 8 had no cracks on the surface (compared with wrinkles and hard skin of Comparative Example 5), higher drying efficiency, total time 12h (compared with 17h of Example 3, ↓ 29.4%), and energy consumption reduced by 37%, which shows that pulse negative pressure (0.06 MPa↹0.04 MPa / 90s) expands micro-pores, and intermittent microwave (0.8 W / g, 20s / 40s) targets to remove bound water, solving the problem of drying stress cracking and synchronously improving efficiency.

[0063] Example 9 added composite enzyme preparation (PME:cellulase=1:2.5) pretreatment on the basis of Example 3. Compared with Example 3, the product prepared in Example 9 had a compact gel structure (hardness 8.20 N vs 7.43 N, ↑ 10.4%), drying shrinkage was reduced by 42%, and pectin dissolution was increased by 35%, which shows that enzyme hydrolysis (45°C / 23min) synergizes with ultrasound (750W) to deeply release bound pectin, constructing a compact gel network and significantly improving the formability of low-sugar preserved fruit.

[0064] Example 10 is based on Example 3, adding a microcapsule system (tea polyphenol- anthocyanin = 1.8:1) technology, the product prepared in Example 10 has better antioxidant properties: after 30 days of storage, the anthocyanin retention rate is 82.3% (compared with 54.6% for the non-added group), the flavor is improved, and there is no oxidation taste (compared with the off-flavor of Comparative Example 5); the gel strength is increased by 28%; thus, it is shown that the sodium alginate-chitosan wall material forms a pH-responsive barrier, and tea polyphenol preferentially quenches free radicals; the ultrasonically released chitosan is crosslinked with pectin anions, achieving antioxidant- texture double reinforcement.

[0065] As can be seen from the above, the combination of prunus humilis fruit pulp + a small amount of oligosaccharide / sugar alcohol + moderate frequency slit ultrasonic treatment of blueberry fruit pulp can well maintain the texture and taste of the recombined fruit preserves; however, if oligosaccharide / sugar alcohol is not added, on the one hand, the taste and flavor of the fruit preserves will be poor, and on the other hand, the fruit preserves will not be formed; if prunus humilis fruit pulp is not added, it will also lead to poor fruit preserve formation; if the blueberry fruit pulp is not subjected to slit ultrasonic treatment, it will lead to product formation. Higher slit ultrasonic intensity can make the mixed fruit pulp more delicate and uniform, and on the other hand, it can make the interaction between different components in the mixed fruit pulp stronger, increase the gel strength, and increase the hardness of the recombined fruit preserves.

[0066] Based on the high activity of PME enzyme in blueberry fruit pulp, the present application makes full use of the interaction between different components in the mixed fruit pulp by using slit ultrasonic technology, adds prunus humilis fruit pulp with high calcium content to promote the formation of gel network structure and reduce the use of gelatin and other additives in fruit preserves, adds an appropriate amount of oligosaccharide or sugar alcohol to adjust the taste and flavor of the fruit preserves, greatly reduces the sugar content compared with traditional fruit preserves, and prepares a natural low-sugar blueberry recombined fruit preserve. Through detection, the process provided by the present application can make the anthocyanin retention rate reach 82.3~92.3% (Examples 6-10), which is more than 100% higher than that of the traditional high-sugar process (Comparative Example 6: 41.2%), and is significantly better than the basic process without nitrogen / microcapsule protection (Example 3: 78.5%).

[0067] The number of devices and the scale of processing described herein are used to simplify the description of the present application. Applications, modifications and variations of the present application will be apparent to those skilled in the art.

[0068] Although the embodiments of the present application have been disclosed as above, they are not limited to the applications and embodiments listed in the specification, and can be fully applied to various fields suitable for the present application, and additional modifications can be easily realized by those skilled in the art, and therefore the present application is not limited to specific details, without departing from the general concept defined by the claims and the equivalent scope.

Claims

1. A method of preparing a low sugar recombinant blueberry fruit leather, comprising, The method comprises the following steps: Step one, mix the aronia flesh and water at a mass ratio of 3-5:1 to obtain aronia fruit pulp; pulp the blueberry flesh to obtain blueberry fruit pulp; Step two, mix the obtained aronia fruit pulp and the obtained blueberry fruit pulp at a mass ratio of 1-2:10 to form a compound fruit pulp; Step three, add oligosaccharides or sugar alcohols to the compound fruit pulp of step two to obtain a mixed fruit pulp; the mass ratio of the compound fruit pulp to the oligosaccharides or sugar alcohols is 100:1-10; Step four, treat the mixed fruit pulp obtained in step three by a slit-type ultrasonic device; the ultrasonic frequency is 40-60 kHz, the ultrasonic power is 400-500 W, and the ultrasonic time is 8-12 min; Step five, concentrate the compound fruit pulp treated in step four to a solid content of ≥45%, pour the concentrated compound fruit pulp into a mold to obtain a preserved fruit blank, and dry the preserved fruit blank to obtain a low-sugar recombined preserved fruit.

2. The method of claim 1, wherein the low-sugar recombinant blueberry preserve is prepared by adding 0.5 to 1.5% of the recombinant blueberry juice to 100 parts of the sugar syrup. In step one, before the pulp is pulped, the pulp is pretreated as follows: The blueberry flesh is immersed in hot water at 72-75℃ for 90-120 seconds and then quickly cooled to below 25℃; The aronia flesh is treated in steam at 88-90℃ for 45-60 seconds and then quickly cooled to below 25℃; When pulping, the pulp is placed in a sealed environment filled with food-grade nitrogen, the pulp temperature is controlled to be ≤35℃, and the pulping time is 3.0±0.5 minutes at a rotation speed of 5000±200 r / min.

3. The method of claim 1, wherein the low-sugar recombinant blueberry preserve is prepared by adding 0.5 to 1.5% of the recombinant blueberry juice to 100 parts of the sugar syrup. The concentration in step five is carried out under three-stage gradient vacuum-rotation speed coupling conditions: ) First stage: vacuum 0.06-0.08 MPa, temperature 68-72°C, rotation speed 150 r / min, concentration to 25-30% solid; ) second stage: vacuum 0.04-0.05 MPa, temperature 58-62°C, rotation speed 120 r / min, concentration to 35-40% solid content; ) Third stage: vacuum 0.08~0.09 MPa, temperature 50~52℃, rotation speed 90 r / min, concentrated to solid content ≥45%; During the concentration process, deoxygenated food-grade nitrogen is continuously introduced, and an online near-infrared sensor is used to monitor the solid content in real time.

4. The method for preparing low-sugar recombinant blueberry preserves as described in claim 1, characterized in that, The drying process of the preserved fruit blank in step five is pulse-type negative pressure-microwave-assisted heat pump drying, which specifically includes: a) First stage drying: when the water activity Aw of the preserved fruit blank is >0.85, dry it to Aw≤0.85 under normal pressure, temperature 60-65℃, and air speed 2.0-2.5 m / s; b) Second stage drying: when the water activity Aw of the preserved fruit blank is between 0.85 and 0.75, dry it under pulse negative pressure and intermittent microwave assistance, the vacuum degree is between 0.04 and 0.08 MPa, and the pulse changes at a frequency of 1-2 min / second, while intermittent microwaves are applied, the microwave power density is 0.5-1.0 W / g, the microwave on / off time is 10s / 50s-20s / 40s, the drying temperature is 55-60℃, and the air speed is 1.5-2.0 m / s, and the drying is carried out until Aw≤0.75; c) Third stage drying: when the water activity Aw of the preserved fruit blank is ≤0.75, stop the microwave, maintain the vacuum degree at 0.04-0.06 MPa, the drying temperature at 50-55℃, and the air speed at 1.0-1.5 m / s, and dry until Aw≤0.

65.

5. The method for preparing low-sugar recombinant blueberry preserves as described in claim 1, characterized in that, In step three, before adding oligosaccharides or sugar alcohols to the compound fruit pulp, a complex enzyme preparation is added to the compound fruit pulp, the complex enzyme preparation comprising pectin esterase and cellulase, the total amount of the complex enzyme preparation added being 0.01-0.05% of the mass of the compound fruit pulp, and the activity units of the pectin esterase and cellulase being in a ratio of 1:2-3; the compound fruit pulp to which the complex enzyme preparation has been added is incubated at 40-50°C for 15-30 min for enzymatic hydrolysis, and then is subjected to ultrasonic treatment in a slit-type ultrasonic device, the ultrasonic frequency being 40-60 kHz, the power being 700-800 W, and the time being 8-12 min.

6. The method of claim 1, wherein the low-sugar recombinant blueberry fruit leather is prepared by the steps of: In step three, when the oligosaccharides or sugar alcohols are added, a microcapsule system having dual functions of antioxidation and nutritional fortification is synchronously added, the microcapsule system comprising a core material and a wall material that coats the core material, the mass ratio of the core material to the wall material being 1:3-5; the core material is composed of tea polyphenols and blueberry anthocyanin extract in a mass ratio of 1.5-2:1, and the wall material is a sodium alginate-chitosan compound; the amount of the microcapsule system added is 0.5-1.2% of the mass of the compound fruit pulp.

7. The method of claim 6, wherein the low-sugar recombinant blueberry fruit leather is prepared by the steps of: The microcapsule system is prepared by the following steps: S1. Dissolve tea polyphenols and blueberry anthocyanin extract in a mass ratio of 1.5-2:1 in a citric acid buffer solution with a pH of 5.0-5.5 to form a uniform solution with a core material mass concentration of 8-12%, under light-shielded conditions at 25-30°C; S2. Dissolve sodium alginate and chitosan in a mass ratio of 2:1-3:1 in deionized water, adjust the pH to 4.5-5.0, and stir in a water bath at 45-50°C until completely dissolved to form a compound solution with a total wall material mass concentration of 3-5%; S3. Inject the core material solution obtained in step S1 into the wall material solution obtained in step S2 at a rate of 0.8-1.2 mL / min, and simultaneously perform high-speed shearing emulsification at a speed of 400-600 r / min to form an O / W emulsion; S4. Gradient solidification: S41. Add the emulsion obtained in step S3 dropwise into a 0.1-0.3 mol / L CaCl2 solution, and crosslink and solidify at 25-30°C for 20-30 min; S42. Transfer to a 0.5-1.0 wt%, pH 5.5-6.0 chitosan acetic acid solution, and perform secondary solidification at 35-40°C for 40-60 min to obtain a solidified product; S43. After washing the solidified product with deionized water, perform pulse negative pressure-low temperature combined drying at a vacuum degree of 0.06-0.08 MPa and a temperature of 35-40°C until the water content is ≤5% to obtain the microcapsule system.

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