Non-thermal grape juice and preparation method thereof

Abstract

The invention provides non-thermal grape juice and a preparation method thereof, and belongs to the technical field of food processing. The method comprises the following steps: crushing grape particles to obtain grape paste; mixing the grape paste with pectinase, and performing enzymolysis to obtain grape pulp; squeezing the grape pulp, and then standing to remove tartar precipitate to obtain fruit juice; performing high-pressure homogenization treatment on the fruit juice to obtain the non-hot grape fruit juice; the pressure of the high-pressure homogenization treatment is 100 to 300 MPa. HPH is a non-thermal processing technology, in the preparation process, HPH can remarkably improve the turbidity stability and nutritional quality of fruit juice, reduce the number of microorganisms and inactivate spoilage microorganisms and prolong the shelf life under the condition that the damage to the quality of the fruit juice is reduced, and in combination with limiting of the pressure of high-pressure homogenization treatment, the quality of the fruit juice is improved. The original flavor and nutritional value of the grape juice can be reserved to the greatest extent, and continuous production is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of food processing, and particularly relates to a non-thermal grape juice and a preparation method thereof. Background Art

[0002] Grape juice is a healthy drink with a rich taste and contains a variety of nutrients. It is also a rich source of antioxidants. The traditional processing methods of grape juice are heat extraction, enzyme impregnation, and high-temperature sterilization. However, heat has a negative impact on the quality of the juice, especially in terms of sensory and nutritional aspects. For example, grape juice stored at room temperature needs to go through a high-temperature sterilization process, which easily causes the degradation of heat-sensitive components (such as polyphenols and vitamin C), reduces the nutritional value, and loses some of the original fresh flavor of the grapes. Modern non-thermal processing technologies can be used to preserve food with little quality decline, meeting the growing demand of consumers for fresh-like products. For example, high-pressure processing (HPP) is used for the sterilization treatment of food, but it is a batch-type discontinuous production. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a non-thermal grape juice and a preparation method thereof. The preparation method of the present invention can not only improve the sterilization effect while maintaining the flavor and nutrients of the grape juice, but also achieve continuous production and significantly extend the shelf life of refrigerated juices.

[0004] To achieve the above-mentioned invention purpose, the present invention provides the following technical solutions:

[0005] The present invention provides a preparation method of non-thermal grape juice, comprising the following steps:

[0006] Crush grape grains to obtain grape puree;

[0007] Mix the grape puree with pectinase for enzymatic hydrolysis to obtain grape pulp;

[0008] Press the grape pulp, and then let it stand to obtain juice;

[0009] Perform high-pressure homogenization treatment (HPH) on the juice to obtain the non-thermal grape juice; the pressure of the high-pressure homogenization treatment is 100 - 300 MPa.

[0010] Preferably, the pressure of the high-pressure homogenization treatment is 100, 200, or 300 MPa.

[0011] Preferably, the number of times of the high-pressure homogenization treatment is 1 - 3 times.

[0012] Preferably, the temperatures of the inlet and outlet of the high-pressure homogenization treatment do not exceed 25°C.

[0013] Preferably, the temperature of the enzymatic hydrolysis is 45-65°C and the time is 1-3 h.

[0014] Preferably, for every 0.45 kg of grape puree, the dosage of the pectinase is 0.1-0.5 mL.

[0015] Preferably, the temperature of the static settlement is 2-5°C and the time is 1-2 weeks.

[0016] Preferably, after the high-pressure homogenization treatment, it also includes storage at 2-10°C.

[0017] Preferably, the grape particles are Ci'ao grape particles.

[0018] The present invention also provides a non-thermal grape juice prepared by the preparation method described in the above technical solution.

[0019] The present invention provides a method for preparing a non-thermal grape juice, comprising the following steps: crushing grape particles to obtain grape puree; mixing the grape puree with pectinase for enzymatic hydrolysis to obtain grape pulp; pressing the grape pulp, and then performing static settlement (the function of the static settlement is to remove tartrate precipitation) to obtain juice; performing high-pressure homogenization treatment on the juice to obtain the non-thermal grape juice; the pressure of the high-pressure homogenization treatment is 100-300 MPa.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] In the present invention, HPH is a non-thermal processing technology. During the preparation process, HPH can significantly improve the turbidity stability and nutritional quality of the juice, reduce the number of microorganisms, inactivate spoilage microorganisms and extend the shelf life while reducing the damage to the juice quality, and by combining the limitation of the pressure of the high-pressure homogenization treatment, the original flavor and nutritional value of the grape juice can be retained to the greatest extent, and continuous production is achieved.

[0022] Furthermore, the present invention combines the limitation of the pressure and number of times of the high-pressure homogenization treatment, further improves the killing effect on Escherichia coli and Saccharomyces cerevisiae, extends the shelf life under refrigeration conditions to 4 months, and significantly extends the shelf life of refrigerated juice.

[0023] The present invention also provides a non-thermal grape juice prepared by the preparation method described in the above technical solution. The non-thermal grape juice of the present invention is sterilized by the combined action of various forces and pressures of high-speed homogenization generated by high-pressure homogenization, retains various flavors and nutrients of the original grapes, and the produced grape juice has good quality in terms of fragrance, original taste, flavor, nutrition and color, retains the original flavor of the grape juice to the greatest extent, and meets the needs of consumers for the fresh flavor and original taste of juice products. Description of the Drawings

[0024] Figure 1 The bactericidal effect diagrams of different treatment groups on Escherichia coli;

[0025] Figure 2 The bactericidal effect diagrams of different treatment groups on Saccharomyces cerevisiae;

[0026] Figure 3 The total colony number diagrams during storage (4°C) of different treatment groups. Specific implementation manners

[0027] The present invention provides a method for preparing non-thermal grape juice, comprising the following steps:

[0028] Crush grape grains to obtain grape puree;

[0029] Mix the grape puree with pectinase for enzymatic hydrolysis to obtain grape pulp;

[0030] Press the grape pulp, and then let it stand to obtain juice;

[0031] Perform high-pressure homogenization treatment on the juice to obtain the non-thermal grape juice; the pressure of the high-pressure homogenization treatment is 100-300 MPa.

[0032] In the present invention, unless otherwise specified, the raw materials and equipment used are all commercially available products in the art.

[0033] The present invention crushes grape grains to obtain grape puree.

[0034] In the present invention, the grape grains are preferably organic thorn grape grains, and more preferably Fu'an thorn grape (Vitis davidii (Rom. Caill.) )

[0035] The present invention preferably selects mature, fresh, and pest-free grapes, washes them and stores them at 4±1°C for 1 day, then removes the branches to obtain the grape grains, and then crushes the grape grains to obtain grape puree.

[0036] In the present invention, the crushing is preferably carried out in a crusher.

[0037] After obtaining the grape puree, the present invention mixes the grape puree with pectinase for enzymatic hydrolysis to obtain grape pulp.

[0038] In the present invention, the temperature of the enzymatic hydrolysis is preferably 45-65°C, specifically can be 45, 50, 55, 60 or 65°C, and the time is preferably 1-3 h, specifically can be 1, 2 or 3 h.

[0039] In the present invention, for every 0.45 kg of grape puree, the dosage of the pectinase is preferably 0.1 - 0.5 mL, specifically it can be 0.1, 0.2, 0.3, 0.4 or 0.5 mL. In a specific embodiment of the present invention, the dosage of the pectinase is 0.2 mL / kg of grape puree.

[0040] After obtaining the grape pulp, the present invention presses the grape pulp and then allows it to stand to obtain the fruit juice.

[0041] In the present invention, the pressing is preferably carried out using a hydraulic press.

[0042] In the present invention, the temperature for standing is preferably 2 - 5 °C, specifically it can be 2, 3, 4 or 5 °C, and the time is preferably 1 - 2 weeks.

[0043] The present invention stores the sample obtained after pressing the grape pulp in a glass container, then allows it to stand at 2 - 5 °C for 1 week, discards the precipitate and changes the bottle to obtain the fruit juice.

[0044] After obtaining the fruit juice, the present invention performs high-pressure homogenization treatment on the fruit juice to obtain the non-thermal grape juice; the pressure for the high-pressure homogenization treatment is 100 - 300 MPa.

[0045] In the present invention, the pressure for the high-pressure homogenization treatment is preferably 100, 200 or 300 MPa.

[0046] In the present invention, the number of times for the high-pressure homogenization treatment is preferably 1 - 3 times, specifically it can be 1, 2 or 3 times.

[0047] In the present invention, the temperatures of the inlet and outlet ports for the high-pressure homogenization treatment are both preferably not exceeding 25 °C.

[0048] In the present invention, the high-pressure homogenization treatment is preferably carried out in a high-pressure homogenizer. The high-pressure homogenizer utilizes the bactericidal effect generated by high-pressure driving, cavitation effect, shear force, impact force and turbulence action when high-pressure liquid fluid passes through a narrow orifice at high speed to achieve continuous bactericidal production, solves the discontinuity of batch production of ultra-high pressure equipment, and at the same time overcomes the damage to nutrients and flavor substances in continuous liquid thermal sterilization treatment, maximally retaining the original flavor of the product and meeting the needs of consumers for the fresh flavor and authenticity of fruit juice products.

[0049] In the present invention, after the high-pressure homogenization treatment, it is preferably further stored at 2 - 10 °C, specifically it can be stored at 2, 3, 4, 5 or 6 °C.

[0050] The present invention also provides a non-thermal grape juice prepared by the preparation method described in the above technical solution.

[0051] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the protection scope of the present invention.

[0052] Example 1

[0053] Prepare non-thermal grape juice, including the following steps:

[0054] Pretreatment: (1) Select mature, fresh, and pest-free organic wild grape (Vitis davidii (Rom. Caill.) ), wash it and place it at 4°C; (2) After removing the branches of the grapes, put them into a grape crusher to obtain grape pulp; (3) Add pectinase to the grape pulp at a ratio of 0.2 mL / kg of grape pulp, and heat it at 45°C for 1 h; (4) The sample obtained by pressing the grape pulp with a hydraulic press is stored in a glass container and stored at 2°C for 1 week; (5) After refrigerated storage, discard the tartar precipitate and change the bottle to obtain the juice;

[0055] Experimental group: Use a high-pressure homogenizer to process the juice. The pressures for high-pressure homogenization are 100 (HPH-100), 200 (HPH-200), and 300 (HPH-300) MPa respectively. The number of high-pressure homogenization treatments is 1 time. The temperatures at the inlet and outlet are both 25°C to obtain non-thermal grape juice, and then store it at 2°C.

[0056] Heat treatment group: Conduct heat treatment. The juice is sterilized at 90°C for 1 min in a heat exchanger, and then stored at 2°C.

[0057] Test methods and results

[0058] (1) To verify the effect of HPH on pathogenic and spoilage microorganisms, inoculate the original culture solution of Escherichia coli ATCC 25922 into 5 mL of tryptic soy broth and incubate it at 37°C for 24 h; Propagate Saccharomyces cerevisiae (low-temperature fermenting Saccharomyces cerevisiae) in MRS broth and incubate it at 32°C for 40 h. Add the subculture to the flask containing the juice obtained by pretreatment respectively, and mix them by manual stirring. Randomly collect the inoculated juice samples to determine the initial microbial population number, which is 7-8 log CFU / mL. Collect the juice samples before and after HPH treatment to study the microbial count to determine the bactericidal effect of HPH.

[0059] Total viable count: Analysis was performed using total plate count (TPC) to observe the reduction of microbial counts in different groups over 15 weeks. The specific steps were as follows: 1 mL of the juice sample was poured onto plate count agar and then incubated at 30 °C for 48 to 72 h. The results were expressed as log CFU / mL.

[0060] (2) Physicochemical property analysis:

[0061] Color was determined by a colorimeter. The color difference (ΔE) was calculated from the measured L*, a*, and b* values using the following formula:

[0062]

[0063] L*, a*, and b* represent the positions on the lightness, red-green, and yellow-blue axes of the treated groups (high-pressure homogenization group and heat treatment group), respectively; L0*, a0*, and b0* represent the positions on the lightness, red-green, and yellow-blue axes of the untreated (control) juice, respectively. The larger the values of L*, a*, and b*, the greater the tendency for the juice color to be lighter, redder, and yellower, respectively.

[0064] Total soluble solids content was determined using a refractometer.

[0065] The pH value was measured using a pH meter at ambient temperature.

[0066] (3) Content and antioxidant activity of phenolic compounds

[0067] Total phenolic content (PC): All results were expressed as mg gallic acid equivalents (GAE) per L of extract (mg / L).

[0068] Total anthocyanin content (AC): Expressed as cyanidin-3-glucoside (cyd-3-glu) equivalents (CGE) per L of extract (mg / L).

[0069] In vitro antioxidant activity (free radical scavenging activity ABTS): The free radical scavenging ability was calculated as Trolox equivalent antioxidant capacity (TEAC value, μm / L).

[0070] (4) Sensory evaluation: A sensory evaluation panel consisting of 95 people evaluated the appearance preference (including extremely like, relatively like, and like), color appropriateness (the color depth is just right), grape flavor (the juice is close to the flavor of grapes), original grape freshness (close to the original taste of fresh grapes), juice sweetness (the juice sweetness is just right), and aroma preference (aroma concentration perception) of the HPH-300 and heat-processed juices. The sensory differences were compared based on the proportion of people with the best evaluation.

[0071] Table 1 shows the test results of different treatment groups. It can be seen that there are no significant changes in the total soluble solid content, total phenolic content, and antioxidant activity of the HPH-treated and heat-treated samples (p<0.05). The total anthocyanin content is higher after HPH treatment, realizing continuous non-thermal processing and maximizing the retention of flavor substances in the juice.

[0072] Table 1 Test results of different treatment groups

[0073]

[0074]

[0075]

[0076] Table 2 shows the results of sensory evaluation. It can be seen that both the heat-treated group and the HPH-300 treatment group show good consumer acceptance in terms of appearance and aroma preference; on the other hand, HPH-300 has a better scoring proportion of people in terms of color appropriateness, grape flavor, and natural grape flavor, and a lower scoring proportion in terms of juice sweetness, meeting consumers' pursuit of reduced sugar taste and retention of natural flavor in fruit juice products, indicating that non-thermal treatment with HPH can better maintain the natural fresh flavor of fruit juice and meet market demands.

[0077] Table 2 Results of sensory evaluation

[0078] Scoring item \ Processing HPH-300 Heat treatment Appearance preference 82％ 82％ Color moderation 83％ 75％ Grape flavor 68％ 63％ Original fresh taste of grapes 54％ 47％ Sweetness of juice 59％ 63％ Aroma preference 54％ 54％

[0079] Figure 1 is the bactericidal effect diagram of different treatment groups on Escherichia coli, Figure 2 is the bactericidal effect diagram of different treatment groups on Saccharomyces cerevisiae, Figure 3 is the total colony count diagram of different treatment groups during storage (4°C). Visible mold filaments appeared in the HPH-; 100 and HPH-200 groups after 1 month of storage, and the shelf life ended. It can be seen that a pressure level of 300 MPa can reduce Escherichia coli by more than 5 log, while HPH-300 can reduce Saccharomyces cerevisiae by more than 4 log. The shelf life of the juice treated with HPH-300 was significantly extended from a few days to more than three months compared to traditional refrigerated juice.

[0080] In summary, the present invention proposes a method for continuously producing a safe, refrigerated, and high-quality non-thermal grape juice by high-pressure homogenization. The low-temperature continuous sterilization process of high-pressure homogenization is used to produce non-thermal grape juice with high stability and high nutrient retention, aiming to solve the problems of flavor loss and nutrient degradation caused by traditional thermal sterilization, as well as the discontinuous production problem of ultra-high-pressure non-thermal sterilization. The sterilization is carried out by the combined action of various forces and pressures of high-speed homogenization generated by high-pressure homogenization, retaining various flavors and nutrients of the original grapes. The produced grape juice has good quality in terms of fragrance, original taste, flavor, nutrition, and color. A comparison of HPH-treated and heat-treated juices was made in terms of safety, quality, and shelf life, showing that HPH-300 can extend the shelf life under refrigerated conditions to more than 3 months (about 15 weeks), and its quality is comparable to that of heat-treated juice. On the other hand, the non-thermal treatment of HPH can better maintain the natural fresh flavor of the juice. However, the heat-treated juice loses some of the original grape flavor, and it is observed that the volatile flavor substances decrease significantly during storage. The grape juice treated with HPH is closer to the original flavor of fresh grapes in terms of flavor and can significantly retain volatile flavor substances during storage, making the flavor last longer.

[0081] The above are only the preferred embodiments of the present invention and do not impose any formal restrictions on the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of non-thermal grape juice, characterized in that Comprising the following steps: Crush grape grains to obtain grape puree; Mix the grape puree with pectinase for enzymatic hydrolysis to obtain grape pulp; Press the grape pulp and then let it stand to obtain fruit juice; Perform high-pressure homogenization treatment on the fruit juice to obtain the non-thermal grape juice; the pressure of the high-pressure homogenization treatment is 100 - 300 MPa.

2. The preparation method according to claim 1, characterized in that, The pressure of the high-pressure homogenization treatment is 100, 200 or 300 MPa.

3. The preparation method according to claim 1 or 2, characterized in that, The number of times of the high-pressure homogenization treatment is 1 - 3 times.

4. The preparation method according to claim 1, characterized in that, The temperatures of the inlet and outlet of the high-pressure homogenization treatment do not exceed 25°C.

5. The preparation method according to claim 1, wherein, The temperature of the enzymatic hydrolysis is 45 - 65°C and the time is 1 - 3 h.

6. The preparation method according to claim 1 or 5, characterized in that For every 0.45 kg of grape puree, the dosage of pectinase is 0.1 - 0.5 mL.

7. The preparation method according to claim 1, characterized in that, The temperature for standing is 2 - 5°C and the time is 1 - 2 weeks.

8. The preparation method according to claim 1, characterized in that After the high-pressure homogenization treatment, it further includes storage at 2 - 10°C.

9. The preparation method according to claim 1, characterized in that, The grape grains are vitis davidii foex grains.

10. The non-thermal grape juice prepared by the preparation method according to any one of claims 1 - 9.

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