Preparation method of dried blueberries

Abstract

The embodiment of the invention discloses a preparation method of dried blueberries. The method comprises the following steps: selecting blueberries without plant diseases and insect pests and mechanical damage, cleaning and screening, sequentially blanching, pricking, performing high-voltage pulse electric field treatment and sugar solution permeation treatment, draining, and performing hot air drying. By controlling the high-voltage pulse time, the pulse intensity, the sugar infusion temperature and the sugar liquid concentration in the high-voltage pulse electric field assisted sugar infusion process, the hot air drying time of the blueberries is greatly shortened, meanwhile, the texture and the sense of the prepared dried blueberries are improved, and the production cost and the energy consumption are reduced.

Description

Technical Field

[0001] The embodiment of the invention relates to the technical field of deep processing of blueberries, and in particular to a method for preparing dried blueberries. Background Art

[0002] Blueberries have a short storage period and are susceptible to mechanical damage. The development of dried blueberry products can effectively solve the problem of their preservation. However, the traditional processing method of dried blueberries has defects such as osmotic dehydration and long drying time, serious damage to blueberries, and a large loss of nutrients. Traditional blueberry drying requires a series of thermal processing steps such as high-temperature cooking and drying in sugar solution, which causes a large loss of most water-soluble and heat-sensitive functional components (such as polyphenols). Therefore, the processing of dried blueberries is pretreated and intervened in different drying forms in order to effectively solve the problems of long drying time and reduced functional quality. Summary of the invention

[0003] To this end, an embodiment of the present invention provides a method for preparing dried blueberries.

[0004] In order to achieve the above purpose, the embodiment of the present invention provides the following technical solutions:

[0005] A method for preparing dried blueberries, the method comprising:

[0006] Blueberries that are free of pests and diseases and mechanical damage are selected. After washing and screening, they are blanched, pierced, treated with high-voltage pulse electric fields and infiltrated with sugar solution in sequence. After draining, they are dried with hot air.

[0007] Furthermore, the blanching method is: blanching the blueberries in 50-70°C hot water for 10-20s, and then rinsing and cooling with 10-20°C cold water.

[0008] Furthermore, the puncturing method is: using a needle to puncture a single fresh blueberry, puncturing 3 holes in each blueberry, with a depth of 2-3 mm, and the model of the needle is No. 4.5.

[0009] Furthermore, the conditions of the high-voltage pulse electric field treatment are: pulse electric field intensity 10-30Kv, pulse time 1-10min.

[0010] Furthermore, the sugar solution is a sucrose aqueous solution with a mass concentration of 30%-50%;

[0011] The conditions for the sugar solution penetration treatment are: temperature 25-45°C, penetration 3h.

[0012] Furthermore, the hot air drying condition is: drying in a hot air drying oven at 70° C. until the wet basis moisture content of the blueberry sample is 28-32%.

[0013] The embodiments of the present invention have the following advantages:

[0014] 1. The present invention is based on the currently commonly used hot air drying technology. Due to the problems of long drying time and high energy consumption, a high-voltage pulse electric field combined with osmotic dehydration is used to shorten the hot air drying time of blueberries.

[0015] 2. The traditional single-stage sugar solution penetration was improved and changed to multi-stage incremental sugar solution penetration, which can avoid damaging the blueberry plasmolysin cells and shorten the time to reach the penetration endpoint.

[0016] 3. The pre-treatment method of high-voltage pulse electric field combined with osmotic dehydration is adopted to shorten the drying time of blueberries.

[0017] The present invention controls the high-voltage pulse time, pulse intensity, sugar infiltration temperature and sugar solution concentration in the high-voltage pulse electric field-assisted sugar infiltration process, so that the hot air drying time of blueberries is greatly shortened, and the texture and sensory perception of the prepared dried blueberries are improved, thereby reducing production costs and energy consumption. DETAILED DESCRIPTION

[0018] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] (1) Sources of raw materials and instruments

[0020] Blueberries were purchased from Beilu Blueberry in Bajiazi Fruit Wholesale Market in Shenyang; reagents used: sucrose (analytical grade) was purchased from Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd.; citric acid, anhydrous sodium carbonate, and anhydrous sodium acetate (analytical grade) were purchased from Shandong Keyuan Biochemical Co., Ltd. Instruments used: FA2004 electronic balance (sensitivity 0.001g), Shanghai Sunyu Hengping Scientific Instrument Co., Ltd.; BMT-GYMCSJ500 high-voltage pulse electric field sterilizer, Shandong Bomet Electric Technology Co., Ltd.; SCIENTZ-10N hot air dryer, Ningbo Xinzhi Biotechnology Co., Ltd.; BCD-520WDPD refrigerator, Haier Smart Home Co., Ltd.; UV-1800BPC ultraviolet-visible spectrophotometer, Shanghai Meipuda Instrument Co., Ltd.; electric constant temperature water bath DK-98-ⅡA, Tianjin Test Instrument Co., Ltd.

[0021] (2) Index measurement method

[0022] Determination of color difference

[0023] A handheld colorimeter was used to measure the chromaticity (L*, a*, b* values) of the sample surface. The color difference value ΔE was calculated from the L* value (brightness value), a* value (red value) and b* value (yellow value). Ten samples were randomly selected and the middle part of the surface was tested. The results were averaged. Fresh blueberries were used as standard samples, and L0* = 30.32, a0* = 0.213, and b0* = -3.55 were measured. The chromaticity value was calculated according to formula (1):

[0024]

[0025] Where: L*—brightness value of blueberries after drying;

[0026] a*—redness value of blueberries after drying;

[0027] b*—yellowness value of blueberries after drying.

[0028] Physical property index determination

[0029] Texture measurement: The probe speed before the test was 2 mm / s, the test process speed was 0.5 mm / s, the compression deformation of the test was 40%, and the trigger value was 0.5 N. Ten preserved fruits were randomly selected for each treatment for measurement, and five evaluation parameters representing the texture of the fruit were obtained based on the force-displacement curve, namely hardness, elasticity, chewiness, cohesion, and stickiness.

[0030] Determination of rehydration rate: Take 2g of sample and place it in a 100mL beaker, add 50mL of distilled water, soak at room temperature, weigh the sample every 30min for a total of 6 times. Calculate the rehydration rate according to formula (2):

[0031]

[0032] Where: W is the rehydration rate, %;

[0033] m1 is the mass before rehydration, g;

[0034] m2 is the mass after rehydration, g.

[0035] The water loss rate (WL) and solid gain rate (SG) were used to evaluate the mass transfer effect of blueberry osmotic dehydration. The calculation results are shown in equations (3) and (4).

[0036]

[0037]

[0038] Where: M0 is the initial mass of raw materials, g;

[0039] M is the sample mass after each cycle of single-stage or multi-stage osmotic dehydration of raw materials, g;

[0040] m0 is the initial dry mass of the raw material, g;

[0041] m is the dry mass of the sample after each cycle of single-stage or multi-stage osmotic dehydration of the raw material, g.

[0042] Drying characteristic index measurement

[0043] After the high-voltage pulse electric field and sugar infiltration treatment, the blueberry sample was taken out, rinsed with 210 ml of distilled water for 10 seconds, and the surface moisture was wiped off with a paper towel. The sample was weighed with an electronic balance, and then placed in an electric blast constant temperature drying oven at a temperature of 70°C for hot air drying with an air flow rate of 1 m / s. The sample was weighed once every 60 minutes with an electronic balance until its moisture content was ≤30% (wet basis moisture content) and the drying was stopped to determine the weight change during the drying process. The experiment was measured in triplicate.

[0044] Moisture content determination

[0045] The moisture ratio (MR) indicates the residual moisture content of the blueberry sample under drying conditions, reflecting the drying rate of the blueberry. The moisture ratio is calculated according to formula (5):

[0046]

[0047] Where: M is the dry basis moisture content of blueberries at any time;

[0048] M e The dry basis moisture content of blueberries at equilibrium;

[0049] M0 is the initial dry basis moisture content of blueberries.

[0050] The drying rate (DR) indicates how fast the water is released from the sample to the environment during the drying process. The drying rate is calculated according to formula (6):

[0051]

[0052] Where: DR—drying rate of sample, g / g·h;

[0053] M t1 —The moisture content of the sample at time t1, g / g;

[0054] M t2 —The moisture content of the sample at time t2, g / g.

[0055] Example 1

[0056] This embodiment provides a method for preparing dried blueberries:

[0057] Screening: Collect blueberries of similar size, uniform maturity, free of pests and diseases, and mechanical damage;

[0058] Blanching: Blanch the blueberries in 60℃ hot water for 20s, then rinse and cool with 15℃ cold water, and drain;

[0059] Puncture: Use a needle to puncture a single fresh blueberry, puncture 3 holes in each blueberry, with a depth of 2-3mm (the needle model is No. 4.5);

[0060] High voltage pulse: blueberries were treated at a pulse intensity of 20Kv and a pulse time of 1min;

[0061] Drying: Place the pretreated blueberries in a 70°C hot air drying oven and dry them. The drying is completed when the wet basis moisture content of the blueberry sample is about 30%, and then take them out.

[0062] Embodiment 2-5

[0063] The difference between Examples 2-5 and Example 1 is only the high-voltage pulse time. The pulse time of Examples 1-5 is 1 min, 3 min, 5 min, 7 min, and 10 min, respectively.

[0064] The results of Examples 1-5 are shown in Table 1.

[0065] Table 1 Effect of high pressure pulse time on drying rate

[0066]

[0067] It can be seen from Table 2 combined with the experimental process that when the pulse time in Example 3 is 5 minutes, the drying rate is the largest, which is 8.26 g / g·h. The results show that compared with other examples, the drying rate of Example 3 is significantly improved, and the difference is significant (p < 0.05);

[0068] Example 6

[0069] This embodiment provides a method for preparing dried blueberries:

[0070] Screening: Collect blueberries of similar size, uniform maturity, free of pests and diseases, and mechanical damage;

[0071] Blanching: Blanch the blueberries in 60℃ hot water for 20s, then rinse and cool with 15℃ cold water, and drain;

[0072] Puncture: Use a needle to puncture a single fresh blueberry, puncture 3 holes in each blueberry, with a depth of 2-3mm (the needle model is No. 4.5);

[0073] High voltage pulse: blueberries were treated at a pulse time of 5 min and a pulse intensity of 10 KV;

[0074] Drying: Take out the pretreated blueberries and drain them, place them in a 70°C hot air drying oven to dry, and take them out when the blueberry sample wet basis moisture content is about 30%.

[0075] Examples 7-10

[0076] The difference between Examples 7-10 and Example 6 is only the high-voltage pulse intensity. Examples 6-10 are processed at pulse intensities of 10Kv, 15Kv, 20Kv, 25Kv, and 30Kv, respectively.

[0077] The results of Examples 6-10 are shown in Table 2.

[0078] Table 2 Effect of high pressure pulse intensity on drying rate

[0079]

[0080] It can be seen from Table 2 combined with the experimental process that as the pulse intensity increases, the drying rate of hot air drying first decreases and then increases. When the pulse intensity is 25Kv, the drying rate is 12.61g / g·h. When the pulse intensity is lower than 20Kv or higher than 30Kv, the cell membrane changes unstable and the drying rate is affected, and the drying time increases slightly. Therefore, from the perspective of product optimization, the pulse electric field intensity of the present invention can effectively improve the drying rate within the range of 20Kv-30 Kv.

[0081] Embodiment 11

[0082] This embodiment provides a method for preparing dried blueberries:

[0083] Screening: Collect blueberries of similar size, uniform maturity, free of pests and diseases, and mechanical damage;

[0084] Blanching: Blanch the blueberry slices in 60℃ hot water for 20s, then rinse and cool with 15℃ cold water, and drain;

[0085] Puncture: Use a needle to puncture a single fresh blueberry, puncture 3 holes in each blueberry, with a depth of 2-3mm (the needle model is No. 4.5);

[0086] Osmotic dehydration: Blueberries were osmotically treated at 25°C in 30% osmotic solution (sucrose aqueous solution) for 3 h;

[0087] Drying: Take out the pretreated blueberries and drain them, place them in a 70°C hot air drying oven to dry, and take them out when the blueberry sample wet basis moisture content is about 30%.

[0088] Examples 12-15

[0089] The only difference between Examples 12-15 and Example 11 is the infiltration solutions. The infiltration solutions used in Examples 11-15 are 30%, 40%, 50%, three-stage infiltration (30%-40%-50%) (each stage is treated for 1 hour), and four-stage infiltration (30%-40%-45%-50%) (each stage is treated for 45 minutes).

[0090] The results of Examples 11-15 are shown in Table 3.

[0091] Table 3 Effect of different infiltration solutions on drying rate

[0092]

[0093] It can be seen from Table 3 combined with the experimental process that as the sugar solution concentration increases, the drying rate first increases and then tends to stabilize. When the osmotic solution is a four-stage osmotic solution (30%-40%-45%-50%), the drying rate is the largest, which is 5.46g / g·h. Compared with Examples 11-12, the drying rates of Examples 13-15 are significantly increased, and the difference is significant (p < 0.05).

[0094] Example 16

[0095] This embodiment provides a method for preparing dried blueberries:

[0096] Screening: Collect blueberries of similar size, uniform maturity, free of pests and diseases, and mechanical damage;

[0097] Blanching: Blanch the blueberry slices in 60℃ hot water for 20s, then rinse and cool with 15℃ cold water, and drain;

[0098] Puncture: Use a needle to puncture a single fresh blueberry, puncture 3 holes in each blueberry, with a depth of 2-3mm (the needle model is No. 4.5);

[0099] Drying: Take out the pretreated blueberries and drain them, place them in a 70°C hot air drying oven to dry, and take them out when the blueberry sample wet basis moisture content is about 30%.

[0100] Embodiment 17

[0101] This embodiment provides a method for preparing dried blueberries:

[0102] Screening: Collect blueberries of similar size, uniform maturity, free of pests and diseases, and mechanical damage;

[0103] Blanching: Blanch the blueberry slices in 60℃ hot water for 20s, then rinse and cool with 15℃ cold water, and drain;

[0104] Puncture: Use a needle to puncture a single fresh blueberry, puncture 3 holes in each blueberry, with a depth of 2-3mm (the needle model is No. 4.5);

[0105] High voltage pulse: blueberries were treated at a pulse time of 5 min and a pulse intensity of 25 KV;

[0106] Drying: Take out the pretreated blueberries and drain them, place them in a 70°C hot air drying oven to dry, and take them out when the blueberry sample wet basis moisture content is about 30%.

[0107] Embodiment 18

[0108] This embodiment provides a method for preparing dried blueberries:

[0109] Screening: Collect blueberries of similar size, uniform maturity, free of pests and diseases, and mechanical damage;

[0110] Blanching: Blanch the blueberry slices in 60℃ hot water for 20s, then rinse and cool with 15℃ cold water, and drain;

[0111] Puncture: Use a needle to puncture a single fresh blueberry, puncture 3 holes in each blueberry, with a depth of 2-3mm (the needle model is No. 4.5);

[0112] Osmotic dehydration: blueberries were subjected to three-stage osmotic dehydration (30%-40%-50%) at 35°C (each stage for 1 h);

[0113] Drying: Take out the pretreated blueberries and drain them, place them in a 70°C hot air drying oven to dry, and take them out when the blueberry sample wet basis moisture content is about 30%.

[0114] Embodiment 19

[0115] This embodiment provides a method for preparing dried blueberries:

[0116] Screening: Collect blueberries of similar size, uniform maturity, free of pests and diseases, and mechanical damage;

[0117] Blanching: Blanch the blueberry slices in 60℃ hot water for 20s, then rinse and cool with 15℃ cold water, and drain;

[0118] Puncture: Use a needle to puncture a single fresh blueberry, puncture 3 holes in each blueberry, with a depth of 2-3mm (the needle model is No. 4.5);

[0119] High voltage pulse: blueberries were treated at a pulse time of 5 min and a pulse intensity of 25 KV;

[0120] Osmotic dehydration: blueberries were subjected to three-stage osmotic dehydration (30%-40%-50%) at 35°C (each stage for 1 h);

[0121] Drying: Take out the pretreated blueberries and drain them, place them in a 70°C hot air drying oven to dry, and take them out when the blueberry sample wet basis moisture content is about 30%.

[0122] Index evaluation method

[0123] Sensory evaluation: 30 trained sensory analysts were organized to evaluate the color, taste and smell, texture, mouthfeel and other qualities of the dried blueberries, and score them according to the sensory evaluation standards. The sensory evaluation standards refer to Table 4.

[0124] Table 4 Sensory scoring table for dried blueberries (scale method)

[0125]

[0126] Table 5 Effects of different treatment conditions on the texture of dried blueberries

[0127]

[0128] It can be seen from Table 5 combined with the experimental process that the changes of blueberries after drying under different treatment conditions are shown in Table 5. The hardness of dried blueberries increases after pretreatment because of water loss and hardening of the internal tissue.

[0129] Table 6 Effects of different treatment conditions on the color difference of dried blueberries

[0130]

[0131] It can be seen from Table 6 combined with the experimental process that L * Indicates the brightness of dried blueberries. The larger the absolute value, the brighter the dried fruit. As shown in Table 6, when blueberries turn brown, L * The smaller the absolute value, the more faded the color becomes, and the dark blue becomes lighter. Example 16 L of dried blueberry * The absolute value is the smallest, Example 17-19L * The absolute value of L of Example 16 is higher than that of Example 18-19. * The absolute value of the value is higher than that of Example 17, L * The values ​​were significantly different (P < 0.05). After heat treatment, the pigment was more susceptible to oxygen degradation. * The absolute value of the value is higher than that of Example 16, and the a of Example 19 is * The absolute value of the value is significantly higher than that of Examples 16-19, a * The values ​​were significantly different (P<0.05).

[0132] Table 7 Effects of different treatment conditions on sensory scores of dried blueberries

[0133]

[0134] Table 8 Effects of different treatment conditions on sensory scores of dried blueberries

[0135]

[0136] It can be seen from Tables 7 and 8 that the sensory indicators of dried blueberries after pretreatment are all improved. Example 19 has better appearance quality, and the color, glossiness, fullness and elasticity are all improved, and the differences between the treatments are significant.

[0137] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A method for preparing dried blueberries, characterized in that: The method comprises: Blueberries that are free of pests and diseases and mechanical damage are selected. After washing and screening, they are blanched, pierced, treated with high-voltage pulse electric fields and infiltrated with sugar solution. After draining, they are dried with hot air.

2. The method for preparing dried blueberries according to claim 1, characterized in that: The blanching method comprises: blanching the blueberries in 50-70° C. hot water for 10-20 seconds, and then rinsing and cooling them in 10-20° C. cold water.

3. The method for preparing dried blueberries according to claim 1, characterized in that: The piercing method is: using a needle to pierce a single fresh blueberry, piercing three holes in each blueberry, with a depth of 2-3 mm, and the model of the needle is No. 4.

5.

4. The method for preparing dried blueberries according to claim 1, characterized in that: The conditions of the high-voltage pulse electric field treatment are: pulse electric field intensity 10-30Kv, pulse time 1-10min.

5. The method for preparing dried blueberries according to claim 1, characterized in that: The sugar solution is a sucrose aqueous solution with a mass concentration of 30%-50%; The conditions of the sugar solution penetration treatment are: temperature 25-45°C, penetration 3h.

6. The method for preparing dried blueberries according to claim 1, characterized in that: The hot air drying condition is: drying in a hot air drying oven at 70° C. until the wet basis moisture content of the blueberry sample is 28-32%.

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