CN115736079A

CN115736079A - Processing method and application of berries

Info

Publication number: CN115736079A
Application number: CN202211486371.6A
Authority: CN
Inventors: 刘帮迪; 张敏; 冯欣欣; 孙静; 周新群; 孙洁; 郭淑珍; 庞中伟; 刘瑜; 郭雪霞; 陈�全; 李岚欣
Original assignee: Academy of Agricultural Planning and Engineering MARA
Current assignee: Academy of Agricultural Planning and Engineering MARA
Priority date: 2022-11-24
Filing date: 2022-11-24
Publication date: 2023-03-07

Abstract

The invention relates to the technical field of food processing, in particular to a processing method of berries and application thereof. The processing method of the berries comprises the following steps: (1) Punching holes on the surfaces of the berries to penetrate through the whole berries, wherein the number of the punched holes is 2-4, and the diameter of each hole is 0.2-0.35 mm; (2) And (2) dehydrating the berries treated in the step (1) to obtain a dehydration rate of 1.5-2.5%. According to the invention, the holes are punched on the surfaces of the berries, and meanwhile, after the berries are subjected to micro-dehydration treatment at a specific degree, the freezing storage quality of the berries is obviously improved, and the storage effect is obviously superior to the existing slow freezing and quick freezing effects, so that the method has important significance in the existing fields of berry transportation and berry product production.

Description

Processing method and application of berries

Technical Field

The invention relates to the technical field of food processing, in particular to a processing method of berries and application thereof.

Background

The blueberry is a blue fruit type plant of Ericaceae and Vaccinium, has unique taste, delicate fruit, wide planting area and high yield, and is a common fruit variety. However, the blueberries are easily damaged by mechanical damage, and the storage time is short, so that about 30% of the blueberries are directly eaten in fresh, and about 70% of the blueberries are made into different types of processed products for sale or export. In addition, the mature period of the blueberries is usually 6-8 months, the seasonality is strong, the blueberries are influenced by high-temperature rainy seasonality, the picked blueberries are breathed vigorously, water remains on the surface skins of the fruits, and the growth and the reproduction of microorganisms are caused, the storage period is very short, the storage time in a laboratory is only 14 days at most, however, the processing of the blueberries needs to be continuously carried out all year round, and in order to realize annual supply, most of the blueberries are frozen and stored after primary freezing processing, and the subsequent processing, storage and transportation and sale links are waited.

The freezing technology is the most important mode for prolonging the storage period of the blueberries, can inhibit the growth and the propagation of microorganisms, the activity of fruit enzymes and the oxidation reaction of vulnerable nutrient substances, and greatly keeps the sensory, edible, selling and processable quality of the blueberries. The normal slow freezing at the temperature of minus 10 to minus 20 ℃ belongs to slow freezing, large ice crystals formed when the freezing speed is too slow enable cell membranes to be expanded continuously until the cell membranes are broken, so that water is migrated continuously, nutrient loss is serious after cell walls are broken, and the large ice crystals formed in the fruit and vegetable freezing process can damage plant cells irreversibly; the structure and the characteristics of the enzyme cannot be damaged by freezing, and only the activity of the enzyme and the speed of biochemical reaction in the fruit and vegetable tissues can be reduced, so that quality deterioration phenomena such as browning, nutrient loss and the like can be caused after freezing and thawing, and the processing and the commodity quality are influenced. In industrial processing, the blueberries are mostly frozen in a common slow freezing (-18 to-10 ℃), but the blueberries are typical large-cell berries, the water content in cell tissues is high, the proportion of free water is correspondingly high, and water in a cell solution is condensed into ice crystals in the freezing process, so that the quality, color, nutrition and flavor of the frozen and thawed fruits are deteriorated, and the processing standard and the eating requirements cannot be met. Similarly, the quick-freezing technology also has certain shortcoming, for example when freezing speed is higher, the phenomenon that the ice crystal leads to low temperature fracture to the mechanical damage that blueberry cell caused and the thermal stress that temperature gradient brought appears, further promotes the enzymatic activity in the cell tissue, the increase of the juice loss rate after thawing, in addition, still have an urgent problem that power consumption is big, the power consumption is with high costs that awaits solution in quick-freezing technology in the industrial application process to be solved.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a processing method of berries and application thereof. Through the processing of punching on the berry fruit surface, can also improve its quality after the refrigeration is stored when improving berry fruit infiltration dehydration efficiency.

In a first aspect, the present invention provides a method for processing berries, comprising:

(1) Punching holes on the surfaces of the berries to penetrate through the whole berries, wherein the number of the punched holes is 2-4, and the diameter of each hole is 0.2-0.35 mm;

(2) And (2) dehydrating the berries treated in the step (1) to obtain a dehydration rate of 1.5-2.5%.

The method provided by the invention has the advantages that the punching treatment is carried out on the surfaces of the berries, the osmotic dehydration efficiency is improved, the required time is reduced, meanwhile, the micromolecular fructose and glucose components can be more efficiently wrapped on the surfaces of the berries during the osmotic dehydration, the damage of ice crystals to the berries during the freezing process is more favorably reduced, and the stability of the berries during the storage process is improved. But the perforation is not suitable to be too large or too small, and the perforation is too small (when the diameter of the puncture pore is less than 0.2 mm), the dewatering rate and the consolidation rate can not be increased; when the perforation is too large (when the diameter of the perforation pore is more than 0.35 mm), the small berry epidermal cells can be damaged greatly, and the phenomenon that the texture collapses because the small berry epidermal cells are damaged from the pore during osmotic dehydration and freeze thawing can be caused.

The punched berries can be dehydrated in a short time under the condition that the dehydration rate is 1.5-2.5%, so that the shapes and nutritional ingredients of the berries are better preserved.

In the prior art, the higher the dehydration rate is, the more beneficial the fruit is to preserve (becomes more difficult to rot after dehydration), so the current osmotic dehydration treatment of berries and fruits generally has higher dehydration rate. However, the research of the invention finds that the method is not the same for the berries, and the berries have better quality after being frozen and stored under the condition that the dehydration rate is 1.5-2.5%.

Further, the dehydration process comprises:

processing the berries processed in the step (1) in sugar liquor until the dehydration rate reaches 1.5-2.5%;

the mass percentage of sugar components in the sugar liquid is 60-75%;

the mass ratio of the berries to the sugar solution is 1: (2-4).

Further, the sugar solution comprises the following components in parts by weight: 3 to 5 parts of fructose, 3 to 5 parts of glucose syrup, 0.8 to 1.2 parts of sucrose and 0.8 to 1.2 parts of maltose syrup.

Further, the sugar solution comprises the following components in parts by weight: 4 parts of fructose, 4 parts of glucose syrup, 1 part of sucrose and 1 part of maltose syrup.

The conventional dried berries are usually treated by sugar soaking to improve the flavor, but the sugar soaking treatment is usually accompanied by high-temperature and long-time processing, so that on one hand, the berries subjected to the sugar soaking treatment are not suitable for being processed into other products, and are generally processed into finished products immediately after the sugar soaking treatment; on the other hand, the loss of the bioactive nutritional values of the ascorbic acid, the phenolic acid, the flavone, the anthocyanin and the like of the berries can be caused by high-temperature treatment, and the high-temperature sugar boiling process is a very energy-consuming link, so that the cost of processing enterprises is greatly increased, and the current policy of electricity utilization and environmental protection can be limited, thereby causing unscheduled shutdown and production halt. The invention adopts specific sugar solution component combination, has proper osmotic pressure after combination through multiple considerations and screens, and completes dehydration in a shorter time; meanwhile, the molecular weight of the sugar is small, so that the sugar can naturally enter fruit cells by utilizing the principle of membrane exchange in the permeation process; in addition, the used sugar combination is matched according to the sugar components of the small berry fruits, so that better edible flavor can be ensured; finally, the sugar can be effectively combined with anthocyanin, polyphenol and other substances after entering the small berry cells, so that the stability of the small berry active substance in the processes of freezing, thawing and processing is protected. Therefore, the sugar solution combination provided by the invention can dehydrate rapidly, and simultaneously, the berries and fruits can still have higher flavor and nutritive value after being frozen and stored.

Further, the method also comprises the following steps: and drying the berries to ensure that the water content is 15-25%.

Further, the berries are: berries with a waxy layer; preferably: one or more of blueberry, medlar, blackcurrant, black medlar, cranberry or gooseberry.

The processing method provided by the invention can be suitable for various fruits with waxy layers, because the fruits contain the waxy layers, the dehydration difficulty is higher, and a large amount of time is usually spent during dehydration, the flavor is improved and the micro-dehydration is realized in one step through the perforation and the specific dehydration process, the efficiency is higher, the berries still have better shape and nutritive value after being frozen, and the freezing preservation effect is better than the modes of slow freezing, quick freezing and the like.

In a second aspect, the present invention provides a method of berry fruit storage comprising:

the berry is directly stored at the temperature of minus 20 ℃ after being processed by the processing method.

The invention has the following beneficial effects:

according to the method, through the punching treatment on the surfaces of the berries, the osmotic dehydration efficiency is improved, the required time is reduced, and meanwhile, micromolecular fructose and glucose components can be coated on the surfaces of the berries cells more efficiently during the osmotic dehydration, so that the damage of ice crystals to the berries in the freezing process can be reduced, the stability of the berries in the storage process is improved, and the berries still have excellent flavor and nutritional value after being frozen.

Drawings

FIG. 1 shows the comparison result of anthocyanin content determination of blueberry preserved fruit provided by test example 1 of the invention.

Fig. 2 is a comparison result of the total antioxidant capacity of the blueberry preserved fruit provided by the test example 1 of the invention.

Fig. 3 is a comparison of juice loss rates of osmotically dehydrated frozen blueberries of different dehydration degrees provided in test example 2 of the present invention.

Fig. 4 is a comparison of hardness of osmotically dehydrated frozen blueberries of different dehydration levels provided in test example 2 of the present invention.

Fig. 5 is a comparison of anthocyanin content of osmotically dehydrated frozen blueberries of different dehydration degrees provided in test example 2 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

The embodiment provides a blueberry processing and storing method, which comprises the following specific processes:

(1) Selecting and cleaning: selecting blueberry fruits with consistent sizes and no physical damage on the appearance, cleaning with clear water, and draining for later use.

(2) Puncturing: a needle is used for puncturing a single fresh blueberry, each blueberry punctures 3 holes and penetrates the blueberry (the type of the needle is No. 4.5, the diameter of the obtained hole is 0.2-0.35 mm, and the hole diameter can be kept within the range in the actual implementation process due to the fact that the hole diameter is difficult to be accurate to the specific diameter).

(3) Preparing sugar liquor: fructose, glucose syrup, sucrose and maltose syrup are prepared into sugar solution respectively according to the mass fraction of 26%, 6.5% and 6.5%.

(4) Micro-infiltration dehydration: placing the blueberries and the high fructose corn syrup in a plastic container, wherein the mass ratio of the treated feed liquid of the blueberries to the high fructose corn syrup is 1.

(5) Freezing: and (4) putting the blueberry sample subjected to osmotic dehydration into a polyethylene packaging bag, sealing, and storing in a refrigerator at the temperature of-20 ℃.

(6) And (3) unfreezing: taking out a blueberry sample, thawing at room temperature (25 +/-0.5 ℃) for 4 hours, and then determining each index.

(7) Leaching and draining raw materials: the flowing water washes the blueberries, the juice loss caused by the damage of the fruit peels is avoided as much as possible in the washing process, and then the water on the surfaces of the fruits is naturally drained.

(8) Drying the preserved fruits by hot air: and (3) placing the blueberries in a tray for hot air drying at the drying temperature of 60 ℃ until the water content of the blueberries is 15-25%, thus obtaining the finished product of the blueberry preserved fruit.

Comparative example 1

The comparison example provides a conventional common blueberry processing method, and the specific flow is as follows:

washing blueberries: selecting complete blueberries without rotting, and cleaning silt and the like on the surfaces of the blueberries until the blueberries are cleaned;

freezing: putting the blueberry sample into a polyethylene packaging bag, sealing, and freezing in a refrigerator at-40 ℃ for 24h;

unfreezing: unfreezing for 4 hours at room temperature until the blueberries are completely thawed;

color protection and hardening: putting blueberries into a 1.5% citric acid-ascorbic acid solution for color protection for 1 hour, taking out the blueberries, and soaking the blueberries in a 1.5% calcium chloride-gluconolactone solution for 3.5 hours;

heating and sugar permeation: carrying out sugar permeation on blueberries for 20 hours under the experimental conditions of water bath temperature of 70 ℃ and sucrose syrup with mass fraction of 65%;

leaching and draining raw materials: the flowing water is used for washing, the blueberry peel is prevented from being damaged during washing, juice loss is avoided, and then the water on the surface of the blueberry fruit is naturally drained.

Drying the preserved fruits by hot air: and (3) placing the dried fruit peels in a constant-temperature air-blast drying oven at 60 ℃ for drying until the water content is 15% -25%, and in order to ensure that the dried fruit peels can be dried uniformly, turning over the fruit peels and replacing the position of a drying pan on time in the drying process. And finishing the operation, namely finishing the preparation of the blueberry preserved fruit finished product.

Test example 1

The test example analyzes various attributes of the dried blueberry preserved fruits processed in the example 1, the comparative example 1 and each control group, and relates to sensory score, texture characteristics, color, anthocyanin content, antioxidant capacity, raw material storage and energy consumption cost of dried blueberry processing.

In addition to example 1 and comparative example 1, the following control groups were set up:

control group 1: the processing flow of control 1 was the same as that of example 1, except that the puncturing flow (2) was not performed, the dehydration degree was not changed, and the dehydration time was changed to 8.5 hours accordingly because the puncturing flow was not performed.

Control group 2: the processing procedure of control group 2 was the same as that of example 1, except that the number of perforations was increased to 6 in the puncturing procedure, the dehydration degree was not changed, and the dehydration time was changed to 2 hours.

Control group 3: the comparative group 3 was identical in processing procedure to example 1 except that 65 mass% sucrose syrup was used as the sugar solution, and the dehydration degree was not changed, so that the dehydration time was changed to 8 hours.

Control group 4: the process flow of the control group 4 is the same as that of the example 1, except that the sugar solution adopts high fructose syrup with the mass fraction of 65 percent, the dehydration degree is not changed, and the dehydration time is correspondingly changed to 6.5h.

Control group 5: the comparative example 5 was conducted in the same manner as in example 1 except that 65 mass% maltose syrup was used as the sugar solution, and the dehydration degree was not changed, so that the dehydration time was changed to 7 hours.

1. The detection methods and results were as follows:

(1) Dried blueberry sensory score

Sensory evaluation of blueberry preserved fruits comprises an evaluation group consisting of 10 students in food profession, performs sensory evaluation on the blueberry preserved fruits, and selects percentage to evaluate the blueberry preserved fruits according to the mode in GB14884-2016 national standard preserved fruits for food safety, wherein the form is 30 minutes, the taste and flavor are 50 minutes, and the color is 20 minutes. The mean of the scores of 10 panelists was calculated.

The evaluation criteria are shown in table 1 below:

TABLE 1 sensory Scoring criteria for dried blueberry

The results are shown in the following table, the sensory scores of the preserved blueberries of the examples and the comparative examples are 85.46 and 72.20 respectively, and the sensory score of the examples is 18.36 percent higher than that of the comparative example. The blueberry preserved fruits in the embodiment have no damage, moderate hardness, good sour-sweet degree and uniform and bright color, while the blueberry preserved fruits in the comparative example have dry shrinkage and general brightness, and the eating quality of the blueberry preserved fruits can be improved by adjusting the processing process sequence and changing the process parameters of the blueberry preserved fruits in the embodiment.

Meanwhile, compared with the control group 1 without perforation and the control groups 3, 4 and 5 using three different sugar solutions, due to extremely long dehydration time, the blueberry is subjected to browning, pigment degradation, pectin degradation and the like in the dehydration process, and the final form and color index sensory score is low.

In addition, since the osmotic pressure was lower in the case of osmotic dehydration using a single sugar in the control groups 3, 4, and 5 than in example 1 of the present invention, the permeation time was greatly prolonged. And the single sugar does not accord with the natural sugar component composition principle of the fruit, so that the taste is single, the taste score is lower, and the situation of more greasy taste is shown.

TABLE 2 sensory evaluation results of blueberry preserved fruit

Blueberry preserved fruit	Form of the composition	Taste and flavor	Color	General evaluation
					Example 1	23.35±0.14	43.25±0.26	18.86±0.31	85.46
Comparative example 1	18.87±0.34	38.98±0.09	14.35±0.13	72.2
					Control group 1	6.98±0.56	31.25±0.12	9.54±0.21	47.77
Control group 2	9.87±0.87	37.84±0.18	18.12±0.08	63.83
					Control group 3	10.14±0.24	26.98±0.26	10.21±0.11	47.33
Control group 4	14.33±0.14	28.62±0.24	11.26±0.10	54.21
					Control group 5	11.98±0.15	30.94±0.14	12.54±0.21	55.46

(2) Dried texture characteristics of blueberry preserved fruit

And measuring the hardness, elasticity, stickiness and chewiness of the prepared blueberry preserved fruit by using a texture analyzer. Testing parameters: selecting a P/10 cylindrical probe, adopting a TPA mode, testing the speed to be 1mm/s, the compression ratio to be 30 percent, and the trigger point load to be 100g, measuring 15 fruits in each group, and averaging the measuring results.

The table below shows the measurement results of the texture characteristics of the blueberry preserved fruit, in the examples, the hardness, elasticity, chewiness and adhesiveness of the blueberry preserved fruit are all reduced compared with those of the comparative example, the hardness is moderate, the toughness is good, and the hardness of the blueberry preserved fruit in the comparative example is higher, which is also the reason for poor taste. The blueberries were flaccid before freezing due to the long dehydration time in the control groups 1, 3, 4 and 5, which resulted in poor firmness, elasticity and chewiness. Therefore, the blueberry preserved fruit in the examples has better texture than the comparative examples.

TABLE 3 blueberry fruit texture characterization results

Group of	Hardness of	Elasticity	Chewiness of the product	Adhesiveness of the composition
					Example 1	517.95±16.19	0.44±0.07	101.33±4.57	201.26±10.08
Comparative example 1	1273.97±35.15	0.55±0.04	344.71±10.96	625.39±20.64
					Control group 1	225.15±15.23	0.66±0.04	26.87±6.65	154.21±12.11
Control group 2	499.51±25.61	0.39±0.02	118.92±2.65	355.61±16.87
					Control group 3	325.64±41.50	0.59±0.06	39.87±2.45	187.32±2.65
Control group 4	336.48±11.25	0.54±0.03	38.47±11.12	172.56±10.23
					Control group 5	345.24±16.58	0.57±0.05	44.14±2.11	166.58±9.87

(3) Color of dried blueberry fruit

The color measuring method comprises the following steps: and measuring color parameters L, a and b of the blueberry preserved fruit by using a colorimeter. Wherein L represents the brightness value, a represents the red-green value, and b represents the yellow-blue value.

The results are shown in the table below, the color of the blueberry preserved fruit becomes dark after being dehydrated, frozen, dried and the like, and the L value ranges from 15 to 20. Compared with the blueberry preserved fruits in the comparative examples, the blueberry preserved fruits in the examples have improved brightness values, the values of a and b are negative values, the value of a is lower than that of the comparative examples, and the value of b is higher than that of the comparative examples, namely, the color of the blueberry preserved fruits in the examples is more bright deep purple, which shows that the blueberry preserved fruits can be bright after the process conditions are changed.

The controls 1, 3, 4, 5 resulted in pigment degradation and oxidation during the permeation process due to unfavorable permeation dehydration process, with lower L and lower b values, resulting in dull final color. The control group 2 has too many punctures, so that pigment loss occurs in a certain permeation process, the L value is higher, and the b value is higher, which results in that the final blueberry preserved fruit has a weak color and is not bright.

TABLE 4 color measurement results of blueberry preserved fruit

Group of	L*	a*	b*
				Example 1	25.41±0.57	-1.57±0.14	-1.55±0.21
Comparative example 1	17.19±0.32	1.19±0.08	-2.57±0.15
				Control group 1	17.88±0.12	0.58±0.02	-2.06±0.11
Control group 2	29.45±0.11	-1.22±0.05	-1.05±0.02
				Control group 3	19.84±0.33	0.26±0.06	-1.99±0.05
Control group 4	20.11±0.25	0.35±0.03	-2.11±0.14
				Control group 5	19.12±0.18	0.22±0.04	-1.89±0.08

(4) Determination of blueberry preserved fruit dry anthocyanin content

The anthocyanin content was determined using the anthocyanin assay kit from shanghai xin sail biotechnology limited.

Fig. 1 shows anthocyanin content measurement results, anthocyanin content in the blueberry preserved fruits of the comparative example and the example is 5.98U/g and 9.83U/g respectively, anthocyanin content in the blueberry preserved fruits of the comparative example is lower than anthocyanin content in the blueberry preserved fruits of the example by about 39.16%, which shows that anthocyanin loss is serious when osmotic dehydration time is long, and the example can effectively protect anthocyanin. This conclusion can also be similarly drawn from control groups 1, 3, 4, 5, since control group 1 did not puncture, and control groups 3, 4, 5 were separately dehydrated by permeation with a single syrup for a longer time, the total anthocyanin content was significantly lower than in example 1.

(5) Determination of total antioxidant capacity of dried blueberry fruits

And (3) measuring the total antioxidant capacity by using a Nanjing constructed total antioxidant capacity detection kit.

The result of the total antioxidant capacity determination is reflected in fig. 2, and the test result shows that the total antioxidant capacity of the blueberry preserved fruit in the embodiment is 19.36U/mgprot, the comparison ratio is 24.90 percent higher, the embodiment can effectively protect the total antioxidant capacity of the blueberry preserved fruit, and the effect is obviously better than that of the comparison treatment group. In addition, control group 2 punctured too much due to the excessively long permeation time of control groups 1, 3, 4, 5, resulting in loss of reactive oxygen species with the permeation exchange process during osmotic dehydration.

(6) Determination of total processing energy consumption cost of dried blueberry fruits

The preparation of the blueberry preserved fruit is simulated under the laboratory condition, the dosage of each group of blueberry samples is 1000g, and the consumed energy consumption cost is calculated. Using an electric appliance: DHG-9070A electric heating air blowing drying box with power of 1550W; the standard power consumption of the BC/BD-300DT temperature-regulating refrigerator is 0.87 kilowatt-hour/24 hours.

The cost calculation of the test is calculated according to the average electricity price of different periods with different gradients of agricultural production electricity utilization in Beijing, namely 0.61 yuan/kilowatt hour. The formula for the cost of electricity is as follows:

cost of electricity for dehydration = actual electricity consumption time (h) × electricity consumption (kW/h) × 0.61

Freezing electricity cost = actual electricity time (h) x electricity consumption (kW/h) x 0.61

Cost of electricity for drying = actual electricity time (h) x electricity usage (kW/h) x 0.61

The results are shown in the table below, in the examples and all the control groups, the dehydration and freezing modes are changed, the original hot air drying is replaced by the permeation dehydration without energy consumption, the power cost of the final processed blueberry preserved fruit is reduced, the ultralow temperature freezing in the comparative example is changed into the ordinary freezing at the temperature of-18 ℃, the dehydration cost, the freezing cost and the drying cost are all less than those in the comparative example, so the total power consumption cost is greatly reduced, and the comparative example is about 33.17% lower. In addition, the cost calculation is calculated by taking small-scale processing in a laboratory as an example, and if in the actual processing industry, the power cost saving capability of the technology can be greatly expanded. In the actual production of the processing industry, the economic benefit is improved, and the quality of the blueberry preserved fruit is ensured on the basis of energy conservation and cost saving.

TABLE 5 determination of energy consumption cost of processing blueberry preserved fruit

Test example 2

After actual osmotic dehydration treatment, the experimental example shows that when the dehydration rate is very low, the cryopreservation effect of the blueberry material is better than that of a higher dehydration rate (10%), so that different osmotic dehydration degrees are set for further screening and optimizing the osmotic dehydration degree suitable for the blueberry material, experiments are mainly carried out on 6 gradient osmotic dehydration degrees of 0, 0.5%, 1.5%, 2.5%, 3.5%, 4.5% and 5%, and the osmotic dehydration time and the reinforcement rate are recorded. After the blueberry sample is put into a polyethylene packaging bag after permeation dehydration, the blueberry sample is placed in a refrigerator at the temperature of-20 ℃ for storage, and the blueberry sample is respectively marked as shown in the following table.

TABLE 6 blueberry Permeability and dehydration degree optimization and labeling

Degree of osmotic dehydration (water loss)/%	Treatment group
		0	CK
0.5	ODF-0.5
		1.5	ODF-1.5
2.5	ODF-2.5
		3.5	ODF-3.5
4.5	ODF-4.5
		5.0	ODF-5.0

And (3) measuring the juice loss rate, hardness and anthocyanin content of the frozen and unfrozen blueberries with different osmotic dehydration degrees, and finally determining the range of the osmotic dehydration degree of the blueberries to achieve a better freezing effect.

1. Dehydration curve of blueberry raw material osmotic dehydration pretreatment

When the fruits and vegetables are immersed in the hypertonic solution, osmotic pressure difference between cells and the solution is caused after the fruit and vegetable cells contact the solution, the cells begin to lose water, mass transfer of the fruits and vegetables gradually extends to the center along with the prolonging of osmotic dehydration time, the cells at the center of the fruits and vegetables lose water, cell tissue contraction and mass transfer occur simultaneously in the osmotic dehydration process, and the water loss rate and the reinforcement rate finally tend to balance.

The method for measuring the water loss rate and the solid increasing rate comprises the following steps: the water loss rate and the solid increasing rate are calculated according to the following formulas:

in the formula, WL-water loss rate,%;

m0-initial blueberry mass, g;

mt-mass of blueberry material at moment t of osmotic pre-dehydration, g;

x0-initial blueberry material wet base water content,%;

xt-moisture content of the wet base material blueberry at the moment of osmotic pre-dehydration t%;

SG-solid increase,%;

m0-blueberry initial material mass, g;

mt-mass of blueberry material at moment t of osmotic pre-dehydration, g;

s0-initial blueberry material solids content,%;

st-initial solids content of blueberry sample,%.

The research of the invention finds that the water loss rate of the blueberry material at the early stage of dehydration is high in increasing speed and then the rising trend is slow, the rising rate is remarkably slower after the water loss rate is more than 5%, similarly, the rate of increase is high at the early stage and then the rate tends to be slow, although the permeation dehydration time of the blueberry can be continuously prolonged, the characteristics of the blueberry material are different from those of fruit and vegetable materials such as purple potatoes, peaches, apricots, apples and mangos, the blueberry is difficult to dehydrate due to the obstruction of an epidermal wax layer, the water loss rate is difficult to reach more than 10% under the condition of only adopting a conventional permeation dehydration means, and meanwhile, the permeation dehydration time is too long, so that the normal substance exchange of the blueberry in the permeation process can be caused, nutrient substances, pectin and pigments flow into high-concentration permeation liquid from blueberry cells, and the phenomena of nutrient substance loss, active substance oxidation browning, cell paralysis and the like can be caused.

2. Screening and optimizing method for blueberry raw material osmotic dehydration degree

The method is the same as the step 1, and the result is shown in the following table, the solidification increasing rate is continuously increased along with the deepening of the osmotic dehydration degree when the osmotic dehydration time is prolonged, the osmotic dehydration degree is 1.5-2.5% of the osmotic dehydration degree, the solidification increasing rate and the water loss rate possibly reach a balance point in the stage, and the two osmotic dehydration treatment groups can maintain the quality of the blueberries in the subsequent freezing process by combining the osmotic dehydration time.

TABLE 7 screening of different osmotic dehydration degrees of blueberry

3. Juice loss rate of osmotic dehydration frozen blueberries with different dehydration degrees

The juice loss phenomenon is a phenomenon specific to frozen food, and refers to a phenomenon that after the food is frozen, as intracellular water is condensed into an ice crystal structure with sharp corners to damage animal and plant cells, and in the process of melting the food, intracellular free water flows out. Generally, this phenomenon is accompanied by the overflow of some soluble substances in animal and plant cells, resulting in browning of color, softening of texture, and generation of an off-flavor, which greatly reduces edibility of the frozen food. Therefore, the test in this section is to compare whether the technical method proposed in this patent reduces the phenomenon of juice loss and increases the edible feeling.

The measuring method comprises the following steps: the blueberries were weighed and recorded after removal from the refrigerator, thawed at room temperature for 4 hours, carefully wiped off for surface moisture and weighed again, and each group was tested in five replicates. The juice loss rate was calculated according to the following formula:

in the formula W ₁ -pre-thaw sample mass (g); w ₂ -sample mass after thawing (g).

The results are shown in FIG. 3, in which the juice loss rates of ODF-1.5 and ODF-2.5 treatment groups in the examples were lower, 2.42% and 2.30%, respectively, and were not significantly different (P < 0.05), and were significantly lower than those of the other treatment groups in the examples, indicating that this range can reduce the juice loss after freezing and thawing. The invention simultaneously adopts the method of increasing the number of blueberry puncturing holes (same as the control group 2) and combining with the vacuum permeation of 0.5 atmosphere pressure, so that the dehydration degree of the blueberries after multiple times of puncturing reaches 10 percent, the time is about 10.21 hours, the result after the same freezing and unfreezing steps shows that the juice loss rate reaches 6.33 percent, and the juice loss rate exceeds 2 times of that of ODF (ultra-low frequency) 1.5-2.5 treatment.

4. Hardness of osmotic dehydration frozen blueberries with different dehydration degrees

The hardness is the most representative quality in the quality of the fruit and vegetable products, and the hardness of the fruit and vegetable products is kept appropriate, so that the chewiness, the adhesiveness and the brittleness of the fruit and vegetable products are appropriate, and the hardness of the frozen blueberry is selected as a representative index of the texture.

The measuring method comprises the following steps: the blueberry hardness after freeze thawing is measured by a Rapid-TA texture analyzer under the following conditions: the type of the probe is a P/10 cylindrical probe; the mode is TPA; compressive strain 30%; the testing speed is 0.8mm/s; trigger point load: 100g. The results are the average of 12 fruit determinations per group of samples.

Fig. 4 shows the variation of hardness of frozen blueberries of different osmotic dehydration degrees, wherein the hardness value of the ODF-2.5 treatment group in the example is the highest and is 339.7g, the hardness value of the ODF-1.5 treatment group in the second step is 328.24g, and the difference is smaller, and the difference is higher than that of other treatment groups in the example, so that the hardness of the frozen blueberry raw material fruits is kept, and the subsequent processability of the blueberries is kept.

The blueberry with the dehydration degree of 10% in the step 3 is also adopted for the same detection, the hardness is 222.45g, and the hardness is also obviously lower than that of the group treated by ODF (ozone light fluoride) by 1.5-2.5.

5. Anthocyanin content of osmotic dehydrated frozen blueberries with different dehydration degrees

The measurement method was the same as in example 1.

The results are shown in FIG. 5, wherein the treatment groups with the highest anthocyanin content in the examples are ODF-2.5 and ODF-1.5 treatment groups, wherein the anthocyanin content of ODF-2.5 treatment group is 36.47% and 27.94% higher than that of ODF-3.5 and ODF-4.5 respectively, which indicates that the anthocyanin can be protected from damage by proper osmotic dehydration degree and the stability of the anthocyanin can be effectively maintained.

The blueberry with the dehydration degree of 10% in the step 3 is also used for the same detection, the anthocyanin content is 37.22U/g and is obviously lower than the group of ODF treatment of 1.5-2.5, and the protection of blueberry anthocyanin is not completely dependent on the unlimited reduction of water content and can be simply achieved.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. A processing method of berries is characterized by comprising the following steps:

2. The process of claim 1, wherein the dehydration treatment comprises:

the mass percentage of sugar components in the sugar liquid is 60-75%;

the mass ratio of the berries to the sugar solution is 1: (2-4).

3. The processing method according to claim 2, wherein the sugar solution comprises, in parts by weight: 3 to 5 parts of fructose, 3 to 5 parts of glucose syrup, 0.8 to 1.2 parts of cane sugar and 0.8 to 1.2 parts of maltose syrup.

4. The berry fruit processing method according to any one of claims 1 to 3, further comprising: and drying the berries to ensure that the water content is 15-25%.

5. The method of processing berries according to any one of claims 1 to 4, wherein the berries are: berries with a waxy layer; preferably: one or more of blueberry, medlar, blackcurrant, gooseberry, black medlar or cranberry.

6. A method of berry storage comprising:

directly storing the berry fruits at-20 ℃ after being processed by the processing method of the berry fruits as claimed in any one of claims 1 to 5.

7. Use of a method of processing berries according to any one of claims 1 to 6 to improve the frozen storage quality of berries.