CN113545457A

CN113545457A - Method for softening shrimp shell, soft-shell dried shrimp product and preparation method thereof

Info

Publication number: CN113545457A
Application number: CN202110822552.0A
Authority: CN
Inventors: 毛伟杰; 杨冠茹; 周高慧; 任惠峰
Original assignee: Guangdong Ocean University
Current assignee: Guangdong Ocean University
Priority date: 2021-07-21
Filing date: 2021-07-21
Publication date: 2021-10-26

Abstract

The invention discloses a method for softening shrimp shells, a dried soft-shell shrimp product and a preparation method thereof, belonging to the field of food processing and comprising the following steps: (1) pre-treating; (2) soaking and softening shrimp shells in the soaking solution; wherein the soaking solution comprises chitinase and an acetic acid buffer solution; the soft-shell shrimp prepared by the method is scalded with brine, dried and cooled to obtain a dry soft-shell shrimp product. The method of the invention softens the shrimp shell, the decalcification rate of the shrimp shell reaches 63.5 +/-1.0 percent, the loss rate of the protein of the shrimp meat is 4.0 +/-0.2 percent (wet basis), the hardness of the shrimp is obviously reduced, the structural damage of the shrimp meat is light, the shrimp meat has enough taste elasticity, good chewiness and more bright color, and has better quality of the shrimp.

Description

Method for softening shrimp shell, soft-shell dried shrimp product and preparation method thereof

Technical Field

The invention relates to the field of food processing, in particular to a method for softening shrimp shells, a soft-shell dried shrimp product and a preparation method thereof.

Background

The litopenaeus vannamei is the shrimp species with the highest single yield in three cultured prawns in the world at present and is an excellent variety for intensive high-yield culture. The hardness of the litopenaeus vannamei shells is higher for direct eating, and the litopenaeus vannamei shells are often processed into shelled shrimp products which are convenient to eat, and part of the litopenaeus vannamei products with shells are also often shelled for eating in daily life. However, the shrimp shell is rich in nutrient components such as chitin, minerals, proteins and the like. The removal of the shrimp heads and shells is a huge waste from the nutrition point of view, and the waste of the shrimp shells generated also puts pressure on the environmental problems. The hardness of the shrimp shells is reduced and the original nutritional state is kept through the softening treatment of the shrimp shells, and the method is an effective way for solving the problem of resource waste caused by shelling and eating of the litopenaeus vannamei.

The exoskeleton of crustaceans is mainly divided into three layers, wherein the outer layer consists of calcium carbonate and protein, the middle layer consists of chitin and mineral substances, and the inner layer consists of chitin and protein. Therefore, the current shrimp shell softening research is mainly to decalcify the shrimp shell and decompose the chitin cut-in of the shrimp shell. The existing shrimp shell softening treatment methods mainly comprise an acid method, an enzyme method and an enzyme-acid combination method. The acid method mainly refers to acid hydrolysis decalcification, and the effect of the scarlet gold on the shrimp shell softening of four organic acids is researched, and the result shows that the shrimp shell softening effect of 6-8% of citric acid and acetic acid buffer solution is optimal. The influence of factors such as citric acid malic acid proportion on the decalcification efficiency of the shrimp shells is analyzed by the Chenhong, and the byproduct calcium malate solution is obtained while the shrimp shells are softened. Liulisa discusses the shrimp shell treatment by compounding organic acid, and the softening effect is better than that of the shrimp shell treated by single organic acid. The enzyme method mainly uses protease, and the combination of acid and protease for the catalytic macrobotium proves that the shrimp shell softening effect is better than the former two under the combined action of 5 percent of acetic acid and 3 percent of papain. However, this method requires a softening treatment for 6 hours, and has a problem that it takes too long. In addition, the shrimp shells are softened by the method of adopting organic acid and chitin decomposition enzyme in two steps under the condition of low temperature by the stem and the like, which proves that the shrimp shells have obvious softening effect, particularly the shrimps, and the taste and the freshness do not generate adverse effects. The dry basis content of the chitin in the litopenaeus vannamei shell powder reaches 20 percent, and the polysaccharide is the biological polysaccharide with the largest storage capacity in nature except cellulose. The current common method for extracting chitin from shrimp shells is an acid-base method, which mainly comprises the steps of removing protein by using concentrated alkali liquor, and removing calcium in shrimp heads and shrimp shells by using hydrochloric acid. The method consumes a large amount of acid and alkali, and has high energy consumption and great environmental pollution.

Disclosure of Invention

The invention aims to provide a method for softening shrimp shells, a soft-shell dried shrimp product and a preparation method thereof, which are used for solving the problems in the prior art.

In order to achieve the purpose, the invention provides the following scheme:

the invention provides a method for softening shrimp shells, which comprises the following steps:

(1) pre-treating;

(2) soaking and softening shrimp shells in a soaking solution:

the soaking solution comprises chitinase and an acetic acid buffer solution.

Further, in step (1), the pre-processing comprises: selecting shrimps, removing impurities, cleaning, and blanching with boiling water; wherein the blanching temperature of the boiling water is 100 ℃, and the time is 1-2 min. .

Furthermore, in the soaking solution, the mass concentration of chitinase is 2-6%, the concentration of acetic acid buffer solution is 0.1-0.25mol/L, and the pH value is 4-6.

Furthermore, in the soaking solution, the mass concentration of chitinase is 5%, the concentration of acetic acid buffer solution is 0.2mol/L, and the pH value is 4.5.

Further, in the step (2), the feed-liquid ratio of the shrimps to the soaking solution is 1 g: 4 mL.

The invention also provides a preparation method of the soft-shell dried shrimp product, which is characterized in that the shrimp shell softening method is adopted to soften the shrimp shell to obtain the soft-shell shrimp; and (3) blanching the soft-shell shrimp salt water, drying and cooling to obtain a dry soft-shell shrimp product.

Further, the drying is sectional drying, which comprises drying at 60-70 ℃ for 0.5-1.5h, cooling, and drying at 85-95 ℃ for 1.5-2.5 h.

Further, the brine blanching is to blanch the soft-shelled shrimps in a NaCl solution with the mass concentration of 2-4% for 1-3min, and the temperature of the brine is 100 ℃.

The invention also provides a soft-shell dried shrimp product prepared by the preparation method of the soft-shell dried shrimp product.

The invention also provides the application of the method for softening the shrimp shell or the preparation method of the dried soft-shell shrimp product in food processing.

The invention discloses the following technical effects:

the invention optimizes the shrimp shell softening process through a single-factor experiment and an orthogonal experiment, and finally determines the optimal shrimp shell softening treatment conditions as follows through a drying research experiment of the soft-shell shrimp products under the optimal softening conditions: 5% of chitinase, the concentration of 0.2mol/L acetic acid buffer solution with pH 4.0, the temperature is 55 ℃, and the processing time is 60 min; under the condition, the decalcification rate of the shrimp shells reaches 63.5 +/-1.0 percent, the loss rate of shrimp meat protein is 4.0 +/-0.2 percent (wet basis), the hardness of the shrimps is obviously reduced, the damage to the tissue structure of the shrimp meat is light, the shrimp meat has enough elasticity in taste, good chewiness and more bright color, and has better quality of the shrimps; then the soft-shell dried shrimp product obtained under the optimal softening treatment condition is taken as a raw material, and the soft-shell dried shrimp product is dried at 65 ℃ and 90 ℃ in a segmented manner, so that the hardness of the dried product is reduced when the moisture content of the dried product is 35 percent, which is the most direct expression of the softening of the shrimp shell, the chewiness is reduced but still in a better level, and the mouthfeel, the flavor and the color are better than those of the soft-shell dried shrimp product with the moisture content of 40 percent.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is a graph showing the effect of treatment time on the decalcification rate of soft-shelled shrimp products;

FIG. 2 is a graph showing the effect of the amount of the treatment enzyme on the decalcification rate of the soft-shelled shrimp product;

FIG. 3 is a graph of the effect of pH treatment on the decalcification rate of soft-shelled shrimp products;

FIG. 4 is a graph showing the effect of treatment temperature on the decalcification rate of soft-shelled shrimp products;

FIG. 5 is a graph showing the effect of treatment buffer concentration on the decalcification rate of soft-shelled shrimp products;

FIG. 6 shows the quality index of the decalcification rate and protein loss rate of shrimp shells of group 1 and group 2;

FIG. 7 is a graph showing the effect of softening treatment on the texture of prawns;

FIG. 8 is a graph of the effect of hot air drying on the moisture characteristics of a soft-shelled shrimp product;

FIG. 9 is a graph showing the effect of hot air drying on the texture characteristics of a soft-shelled shrimp product;

FIG. 10 is a graph of the hardness of dried soft shell shrimp products at different moisture levels;

FIG. 11 is a graph of the chewiness of dried soft shell shrimp products at different moisture levels;

FIG. 12 is the effect of weight loss rate of softened dried prawn product;

FIG. 13 shows non-softened and softened prawns before drying;

FIG. 14 shows non-softened and softened prawns after drying;

figure 15 is a sensory score of dried soft shell shrimp products at different moisture levels.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The description and examples are intended to be illustrative only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.

1 materials and methods

1.1 materials and reagents

Experiment raw materials: litopenaeus vannamei purchased from the happy ocean market in Xixia mountain area, Zhanjiang province, Guangdong province, and the water bag is transported to a laboratory in vivo;

experimental reagent: chitinase (food grade) purchased from Shanghai-Town Biotech, and having an enzyme activity of 1762U/g as determined by using an endo-chitin kit from Kurthi Biotech, Suzhou; glacial acetic acid (food grade) was purchased from Guangzhou kang Biotech limited; sodium acetate, sodium chloride, sodium hydroxide, disodium Ethylenediaminetetraacetate (EDTA), copper sulfate, potassium sulfate were all chemically pure and purchased from west longa science ltd; absolute ethyl alcohol, absolute formaldehyde, acetylacetone, calcium carboxylic acid indicator and p-nitrophenol are all chemical analytical purifiers and purchased from Aladdin reagent Co.Ltd; concentrated hydrochloric acid and concentrated sulfuric acid are chemically pure and purchased from national drug group chemical reagent limited company.

1.2 instruments and devices

HH-6 DIGITAL DISPLAY CONSTANT TEMPERATURE WATER BATH, AUDIO-KILOWAY INSTRUMENTS GmbH

PL2002 electronic balance Mettler-Torledo instruments (Shanghai) Ltd

Science instruments Co, Ltd for PB-10 acidimeter Sadolis

DK-98-II electronic temperature-regulating Universal electric furnace Tenst instruments Co., Tianjin, Ltd

101-3-BS-II electrothermal blowing dry box Shanghai leap-in medical instruments Co Ltd

V-5100 visible light spectrophotometer Shanghai chromatography Instrument Co., Ltd

XT Plus texture analyzer British Stable Micro Systems

CR-20 color difference meter Nika minolta

1.3 Experimental methods

1.3.1 shrimp Shell softening Process

Litopenaeus vannamei → washing → blanching in boiling water → softening by enzyme and acid combination → washing and cooling

1.3.2 determination of shrimp Shell softening Process

1.3.2.1 Single factor experiment

36 litopenaeus vannamei were taken and randomly divided into 4 groups (3 per group, 3 replicates). Under the condition that the feed-liquid ratio is 1:4(g: mL), soaking the shrimp shells in 0.2mol/L acetic acid buffer solution with 5% enzyme content, 55 ℃ and pH 4.5 for 30min, 40min, 50min and 60min respectively, taking out, washing the soaking solution with distilled water, draining, measuring the decalcification rate of the shrimp shells of each group respectively, and determining the optimal softening time of the shrimp shells by using sensory evaluation of the soft-shell shrimp products under different time treatment conditions as an auxiliary.

Taking 108 shrimps, applying the shrimps to 3 single factor groups (36 shrimps in each group, performing parallel test for 3 times) on average, determining the optimal condition of the enzyme action through two indexes of the shrimp shell decalcification rate and the whole shrimp sensory evaluation, respectively researching the influence of the added chitinase amount (2%, 4%, 5%, 6%), the pH (4.5, 5.0, 5.5, 6.0), the temperature (40 ℃, 45 ℃, 50 ℃, 55 ℃) on the shrimp shell softening decalcification rate in a single factor variable experiment under the condition that the feed-liquid ratio (g: mL) is 1:4, researching the influence of other factors of the temperature 55 ℃, the time 60min, the concentration of the acetic acid buffer solution of 0.2mol/L and the pH of 4.5 under the condition of observing one factor, determining the condition of the optimal softening effect of the enzyme, then researching the influence of the acetic acid buffer solution of different concentrations (0.1, 0.15, 0.2, 0.25mol/L) under the optimal pH action condition on the effect of the shrimp shell softening, determining the concentration of the optimal acetic acid buffer solution, the effect of softening the shrimp shells also takes the decalcification rate of the shrimp shells and the sensory condition of the whole shrimps as evaluation indexes.

1.3.2.2 orthogonal experiments

On the basis of a shrimp shell softening single-factor experiment, the temperature (A), the time (B), the concentration (C) of an acetic acid buffer solution and the pH (D) are selected as research factors, 3 levels are selected, a 4-factor 3-level orthogonal experiment is carried out, the optimal shrimp shell softening process condition is determined by taking the shrimp shell decalcification rate as a main research index, and the levels of all factors are shown in table 1.

TABLE 1 orthogonal experiment factor horizon

According to the orthogonal experiment result, the screened process conditions are verified, and meanwhile, the quality indexes such as protein loss, texture characteristics and the like are detected for the soft shrimp shell products under the conditions, so that the optimal softening process is determined, and the soft shrimp shell products with higher quality and total edible acceptance are obtained.

1.3.3 determination of the decalcification Rate of shrimp Shell

Shearing cleaned shrimp shell to less than 1cm²The small pieces are dried in an oven at 105 ℃, the weight is constant, the weight is weighed and recorded after the small pieces are cooled, then the crushed shrimp shells are soaked in 1mol/L hydrochloric acid solution with the material-liquid ratio of 1:10(g: mL), the solution is kept stand for 12 hours at room temperature, the decalcification solution is transferred to a 100mL volumetric flask, the shrimp shells are washed by distilled water, and the washing solution is transferred to the volumetric flask together for constant volume. Adding 10.0mL of decalcifying solution into a 250mL conical flask, adding 2mL of 4mol/L sodium hydroxide solution and 0.4g of calcium carboxylate indicator, immediately titrating with an EDTA standard solution, taking the titration end point when the to-be-detected decalcifying solution is changed from mauve to blue, and recording the dosage of the EDTA standard solution consumed by titration for 3 times in parallel.

(1) Calculating the calcium content (mg/L) in the decalcifying liquid:

(2) and (3) calculating the decalcification rate:

C_EDTA: EDTA standard solution molar concentration; v_EDTA: the volume of EDTA standard solution, mL, is consumed during titration; m_Ca: relative atomic mass of calcium, g/mol; v₁: volume fixing, mL; v₂: transferring the volume of the titration sample solution, mL; c_Ca: calcium concentration in decalcifying liquid, g/mL

1.3.4 sensory evaluation of Soft shelled shrimp products

The sensory evaluation group consisted of 6 food professional students, and the specific evaluation criteria are shown in table 2. And boiling the prawn to be detected in water for 3min, cooling to room temperature, and evaluating sensory quality indexes such as appearance, shrimp shell softness, shrimp meat texture and the like.

TABLE 2 sensory evaluation criteria for soft shell shrimp products

1.3.5 determination of protein loss ratio of Soft-shelled shrimp product

Shearing the first and second abdominal muscles of the shelled prawn, beating to form meat paste, measuring protein content, and calculating protein content for 2 times. The protein content is determined by reference to GB5009.5-2016, and the spectrophotometry is selected in the experiment.

(1) Calculating the content of protein in the sample:

x: the content of protein in the sample, g/100 g; c: the content of nitrogen in the sample measuring solution is mug;

C₀: measuring the content of nitrogen in the reagent blank measuring solution, namely mu g; v₁: the volume of the sample digestive juice is determined to be mL;

V₂: preparing a digestive juice volume, mL, of the sample solution; v₃: total volume of sample solution, mL;

V₄: volume of sample solution for measurement, mL; m: sample mass, g;

f: coefficient of nitrogen conversion to protein 6.25

(2) The protein loss rate was calculated as follows:

1.3.6 measurement of texture Properties of Soft-shelled shrimp products

And (4) performing quality characteristic determination on the prawns in the non-softened group and the screened group treated under the better softening condition to obtain data such as hardness, elasticity, chewiness and the like. The measurement position is the third abdominal node of the shrimp body. The texture analyzer test parameters are set as follows, the probe selects a P0.5 flat-bottom cylindrical probe, the mode is TPA, the probe speed before measurement is 2mm/s, the speed during measurement is 1mm/s, the speed after measurement is 2mm/s, the trigger force is 5g, the interval time is 5s, and the deformation amount is 30%.

1.4 Dry processing of Soft shelled shrimp products

1.4.1 Process for processing dried shrimps with soft shell

Soft shell shrimp product → washing → salt water blanching → segment drying → cooling

3% salt solution is scalded 2min, is to carrying out the seasoning of certain degree to soft shell shrimp product on the one hand, is favorable to promoting the texture of the dry back shrimp meat in later stage simultaneously, and on the other hand can reach the effect of enzyme deactivation to chitinase, prevents that chitinase from causing harmful effects to soft shell shrimp product. The soft-shelled shrimp product is dried in a sectional drying mode at 65 ℃ and 90 ℃, the drying curve characteristic is followed, the phenomenon of uneven hardness of the shrimp meat is favorably reduced, the internal and external water is uniformly distributed, and better edible mouthfeel is obtained.

1.4.2 quality characterization of dried Soft shelled shrimp products

The quality characteristics of the prawns in the non-softened group and the group treated under the better softening condition are measured after the prawns are dried by hot air. The texture characteristics are determined by setting other test parameters to be the same as those of the soft-shell shrimp product except that the deformation amount is 40 percent; measuring the moisture content, namely a 105 ℃ normal pressure drying method, according to the GB 50093-2010 food safety national standard for measuring the moisture in the food.

1.4.3 dehydration Rate

(1) And (3) calculating the dehydration rate of the dried prawns according to a formula:

1.4.4 color difference analysis of dried Soft shelled shrimp products

The color of dried shrimp was measured using a CR-20 colorimeter, and a was measured on a standard white board (a-0.1, b-4.1, L-94.9)^*、b^*And L^*Value, repeat 3 trials. Calculating the saturation C of the dried prawn^*。

a^*The value represents red and green; b^*The values represent yellow blue; l is^*The value represents luminance.

1.4.5 determination of weight loss ratio of dried Soft shelled shrimp product

And (3) calculating the weight loss rate of the prawns in the drying process according to a formula:

1.4.6 sensory evaluation of dried Soft shelled shrimp products

After the dried prawns to be tested are cooled to room temperature, sensory quality indexes such as appearance, flavor, taste and the like of the dried prawns are evaluated, and the standard is shown in table 3.

TABLE 3 sensory evaluation criteria for dried soft shelled shrimp products

1.5 data processing and statistics

The data analysis determined by the experiment is processed by adopting SPSS.25 and Excel software, the influence of each factor of the single-factor experiment on the decalcification rate is analyzed by adopting one-factor ANOVA, and the analysis of variance of the orthogonal experiment is analyzed by adopting variance univariate analysis to carry out the effect test between subjects. Drawing is performed by using Excel and origon.2019b software.

2 results

2.1 Effect of treatment time on shrimp Shell softening Effect

The decalcification rate of the shrimp shells treated by softening at different times is shown in FIG. 1 (note: different lower case letters indicate that the difference between treatments is significant (P <0.05), the same applies hereinafter). After the treatment time is more than 40min, the decalcification rate is increased along with the extension of the treatment time. The reason is that the acetic acid buffer solution acts on the shrimp shell in the early softening stage, the acetic acid buffer solution acts on the surface layer of the shrimp shell, the outer layer consisting of calcium carbonate and protein is gradually destroyed, the middle layer consisting of chitin and mineral substances is exposed, the action point of chitinase is increased, the calcium in the shrimp shell is more exposed due to the destruction of the middle layer and is converted into soluble organic acid calcium under the action of the acetic acid buffer solution, the phenomenon that the decalcification amount is greatly increased occurs in the late softening stage, at the moment, the shrimp shell loses brittleness and is in a thin and soft state, and the back of the shrimp and the tail of the shrimp are slightly damaged.

As can be seen in Table 4, the shrimp after 60min softening still has a good level of food acceptance, and the shrimp meat has flexibility, elasticity, good taste and good quality.

TABLE 4 Effect of treatment time on organoleptic quality of Soft shelled shrimp products

2.2 Effect of conditions of the enzyme-acid Complex treatment solution on the softening Effect of shrimp Shell

2.2.1 Effect of enzyme dosage on shrimp Shell softening Effect

The effect of different enzyme addition amounts on the shrimp shell softening effect can be seen from fig. 2, and there is a significant difference (P <0.05) between the four enzyme addition amounts. When the enzyme dosage is 5%, the decalcification rate of the shrimp shell can reach more than 50%, the softening effect is better, and the damage condition of the muscle tissue of the prawn is less than 6% (see table 5).

TABLE 5 Effect of treatment enzyme amount on sensory quality of Soft shelled shrimp products

2.2.2 Effect of pH treatment on shrimp Shell softening Effect

The influence of different treatment pH values on the shrimp shell softening effect can be seen from figure 3, the decalcification rate of the shrimp shells is greatly reduced along with the increase of the pH value, the pH value is an important influence factor influencing the shrimp shell softening effect, and the four treatment pH values have a significant difference (P is less than 0.05). When the pH value is 4.5, the decalcification rate of the shrimp shells is more than 50%, and meanwhile, as can be seen from the table 6, the shrimp shells are soft in sense, the shrimp meat keeps the original toughness, and the total edible acceptance is better.

TABLE 6 Effect of pH treatment on organoleptic qualities of Soft shelled shrimp products

2.2.3 Effect of treatment temperature on shrimp Shell softening Effect

The decalcification rate of the shrimp shells treated by softening at different temperatures is shown in FIG. 4. When the four treatment temperatures have significant difference (P <0.05) and the temperature is more than 50 ℃, the shrimp shell softening effect and the sensory edible effect are both in better level. On one hand, the temperature reaches the temperature near the optimal temperature of the chitinase, which is beneficial to the chitinase to decompose the chitin, and simultaneously, the temperature is improved, which is also beneficial to the decalcification efficiency of the acetic acid buffer solution. Although the prawn quality is reduced with increasing temperature (see table 7), the prawn quality is still acceptable, and the temperature has a more important influence on the decalcification of the prawn shells.

TABLE 7 Effect of treatment temperature on organoleptic qualities of Soft shelled shrimp products

2.2.4 Effect of acetic acid buffer concentration on shrimp Shell softening Effect

The decalcification rate of the shrimp shells treated by softening with different concentrations of the acetic acid buffer is shown in FIG. 5. The concentrations of the four buffer solutions are significantly different (P is less than 0.05), when the concentration of the buffer solution is more than 0.15mol/L, the decalcification rate of the shrimp shells can reach 50%, and when the concentration of the buffer solution is 0.25mol/L, the decalcification rate is greatly improved, and the quality of the shrimps is obviously reduced (see table 8).

TABLE 8 Effect of treatment buffer concentration on organoleptic qualities of Soft shelled shrimp products

2.3 orthogonal experiments on shrimp Shell softening

As can be seen from Table 9, R_D>R_A>R_C>R_BI.e. the pH has the greatest influence on the softening effect of the shrimp shell, and the temperature and the buffer solution are sequentially usedConcentration, time. The optimum softening condition combination is A₃B₃C₃D₁Namely, the enzyme adding amount of the chitinase is 5 percent; the temperature is 55 ℃; the treatment time is 60 min; the concentration of the acetic acid buffer solution is 0.25 mol/L; pH 4.0.

To further verify the results of the orthogonal experiments, analysis of variance was performed. As can be seen from Table 10, the factors temperature and pH reached significant levels (P <0.1), indicating that these two factors have a significant effect on the shrimp shell softening effect. Factor time and buffer concentration do not reach obvious levels, but have certain influence on the shrimp shell softening effect.

TABLE 9 orthogonal experimental results table

TABLE 10 analysis of variance results

Note: indicates significant differences between treatments (P < 0.1).

2.4 shrimp Shell softening Process verification

According to the orthogonal experiment result and in combination with the actual softening effect requirement, two groups of softening condition combinations are selected, namely the No. 1 group: t is 50 ℃; t is 50 min; the concentration of the buffer solution is 0.25 mol/L; pH 4.0; group 2: t is 55 ℃; t is 60 min; the concentration of the buffer solution is 0.2 mol/L; pH 4.0; and (3) carrying out parallel verification on the dried shrimp shells, detecting the protein loss rate, the texture characteristics and the sensory evaluation of the product, and finally determining the optimal shrimp shell softening process conditions by comparing the dehydration condition and the texture characteristics of the dried product through hot air drying.

As shown in fig. 6, comparing the two verification indexes, the decalcification rate of the shrimp shell of group 2 is higher than that of group 1, and the protein loss rate is lower than that of group 1, because the protein loss is positively correlated with the concentration of the acetic acid buffer, and the protein loss rate is higher when the acetic acid is used in the acetic acid buffer. It can be seen that the group 2 softening conditions performed better in the overall effect. In sensory evaluation (see table 11), the meat quality of the shrimp meat of the two groups can keep the original toughness, but the shrimp shell of the No. 2 group is softer and more suitable for direct eating, meanwhile, the damage condition of the shrimp quality is lighter than that of the shrimp shell of the No. 1 group, the eating taste is better, and the total acceptance is higher.

As shown in fig. 7, hardness of the softened prawns is obviously reduced, which is the most visual index of the shrimp shell softening effect, and this also directly indicates that the softening treatment has a relatively obvious effect, and meanwhile, chewiness is reduced to some extent, which is reflected by that the shrimp meat tissues are damaged, but the chewiness of the group 2 is higher than that of the group 1, so that the damage to the groups is relatively light, and the groups are more suitable for processing dry products.

TABLE 11 Effect of different softening Condition groups on the sensory quality of Soft shelled shrimp products

After drying at 65 ℃ for 1h, standing at normal temperature to cool, and then drying at 90 ℃ for 2h, as can be seen from fig. 8 and 9, the softened prawns have faster water loss, higher dehydration rate than the un-softened group, and lower water content than the un-softened group in the dried prawns product, so that the hardness is increased compared with the un-softened group. The hardness is increased mainly due to dehydration of muscles and contraction of muscle fibers, and the softening treatment is easy to dehydrate due to certain damage of internal tissue structures of softened prawn meat. Meanwhile, in the group 1 with high protein loss rate, due to the damage of the internal structure of the shrimp meat tissue, the dehydration degree is slightly larger than that of the group 2, so that the group 2 can keep better water retention capacity under the hot air drying condition on the premise of keeping high decalcification rate and less protein loss, which also indirectly indicates that the shrimp meat tissue structure of the prawn softened under the condition of the group 2 is less damaged. The soft shell dried shrimp product of the same moisture content, group 1, was less chewy than group 2 due to greater protein loss and disruption of the internal structure of the shrimp meat tissue, consistent with the dehydration profile.

In conclusion, the softening treatment conditions of the group 2, namely the addition amount of 5% of chitinase, the concentration of 0.2mol/L acetic acid buffer solution with the pH of 4.0, the temperature of 55 ℃ and the treatment time of 60min, are the optimal softening process for the shells of the litopenaeus vannamei.

2.5 quality characteristics of semi-dried products of Soft-shelled shrimps

2.5.1 Mass Structure characteristics

Soft-shell shrimp products obtained by softening treatment under the optimal conditions are taken as raw materials and are dried by hot air at 65 ℃ and 90 ℃ in sections to obtain the dry soft-shell shrimp products with 35 percent and 40 percent of moisture content. As shown in fig. 10 and 11, the hardness of the soft-shelled dried shrimp product in the softened group is reduced compared with that in the un-softened group with the same moisture content, because the shrimp shell of the softened group is soft and thinner than that of the un-softened group, and the fiber of the meat tissue of the softened prawn has certain damage, which is consistent with the appearance of reduced chewiness. At the same time, the moisture content of the dry product is reduced, the muscle water loss is increased, and the muscle fiber is contracted, so that the hardness and the chewiness of the dry product are increased.

2.5.2 weight loss ratio

As shown in fig. 12, the dried weight loss ratio of the softened prawns is greater than that of the un-softened group because the protein of the muscle tissue of the prawns is thermally denatured under the softening condition of a higher temperature of 55 ℃, the protein structure is affected, the water holding capacity is reduced, and part of the bound water and the free water in the muscle tissue are released. The prawn powder is easier to run off in the hot air drying process, so that the weight of the prawn powder is light and the prawn powder is not softened under the same conditions.

2.5.3 color difference analysis

As shown in Table 12, L in the softened group was observed in comparison with the same moisture content of the dried prawn product^*、a^*、b^*And c^*Are all higher than the non-softened group, c^*The larger the value, the more vivid color, so that the softened dried prawn product was found to have a more vivid color than the non-softened dried prawn product. Astaxanthin is an important component for determining the appearance color of Litopenaeus vannamei, because astaxanthin and protein are combined to form a compound, and when the compound is softened at 55 ℃ for 1 hour, the protein of the Litopenaeus vannamei is gradually heated and denatured, so that the astaxanthin in the astaxanthin protein is separated out, the astaxanthin content is increased, and the red and orange of the undried prawn body is also fresherGay, this property is also exhibited in dry products (as shown in fig. 13, 14).

TABLE 12 color difference analysis of dried prawn products with different water contents

Note: "#" indicates an unsoftened group, L^*The value represents luminance; a is^*The value represents red and green; b^*The values represent yellow blue; Δ C represents the color saturation difference.

2.5.4 sensory evaluation of dried Soft shelled shrimp products

As can be seen from fig. 15, the dried soft-shelled shrimp product with 35% moisture content scored better than the dried soft-shelled shrimp product with 40% moisture content in appearance, taste and flavor, and the main sensory difference between the dried soft-shelled shrimp products with two different moisture contents was that the flavor shrimp taste was the indicator, the dried soft-shelled shrimp product with 35% moisture content had more elasticity and chewiness in the shrimp meat, and it was found that 35% moisture was more suitable for the dried soft-shelled shrimp product.

3 summary of the invention

The invention optimizes the shrimp shell softening process through a single-factor experiment and an orthogonal experiment, and obtains the following conclusion in the drying research experiment of the soft-shell shrimp product under the optimal softening condition:

(1) the optimal shrimp shell softening treatment conditions are as follows: 5% chitinase was added at 55 ℃ for 60min at a pH of 4.0 in 0.2mol/L acetate buffer.

(2) Under the condition, the decalcification rate of the shrimp shell reaches 63.5 +/-1.0 percent, the loss rate of shrimp meat protein is 4.0 +/-0.2 percent (wet basis), the hardness of the shrimp is obviously reduced, the damage to the structure of the shrimp meat is light, the shrimp meat has enough taste elasticity, good chewiness and more bright color, and still has better quality of the shrimp.

(3) The soft-shell dried shrimp product obtained under the optimal softening treatment condition is taken as a raw material, and the soft-shell dried shrimp product is subjected to sectional drying at 65 ℃ and 90 ℃ to obtain the dried product, the hardness of the dried product is reduced when the moisture content of the dried product is 35 percent, which is the most direct expression of the softening of the shrimp shell, the chewiness is still in a better level, and the mouthfeel, the flavor and the color are better than those of the soft-shell dried shrimp product with the moisture content of 40 percent.

(4) The process of the soft-shell dried shrimp product is soft-shell dried shrimp product → washing → blanching with 3% saline water for 2min → drying at 65 ℃ for 1h → standing and cooling → drying at 90 ℃ for 2.5h → standing and cooling.

Comparative example 1

Cleaning shrimp shell, removing shrimp meat, pulverizing into fine powder with high-speed universal pulverizer, adding water (2%), and emulsifying with high-shear mixing emulsifier twice for 10 min; mu.g of enzyme (1100. mu.L of 2% emulsified shrimp shell in 2mL system, 50. mu.L of 10. mu.g/100. mu.L crude chitinase, 850. mu.L of pH5.0 acetate buffer) was added to 0.022g of emulsified shrimp shell and subjected to shake reaction at 50 ℃ and pH5.0 for 75 min.

Experiments prove that the decalcification rate of the shrimp shells reaches 36.5 +/-1.0 percent by adopting the treatment conditions of the comparative example 1.

The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.

Claims

1. A method of softening shrimp shells comprising the steps of:

(1) pre-treating;

(2) soaking and softening shrimp shells in the soaking solution;

the soaking solution comprises chitinase and an acetic acid buffer solution.

2. A method of softening shrimp shells in accordance with claim 1, wherein in step (1), the pre-treatment comprises: selecting shrimps, removing impurities, cleaning, and blanching with boiling water; wherein the blanching temperature of the boiling water is 100 ℃, and the time is 1-2 min.

3. The method for softening shrimp shells according to claim 1, wherein the soaking solution contains chitinase at a concentration of 2-6% by mass, acetic acid buffer at a concentration of 0.1-0.25mol/L and has a pH of 4-6.

4. The method for softening shrimp shells according to claim 3, wherein the soaking solution contains chitinase at a concentration of 5% by mass, an acetic acid buffer at a concentration of 0.2mol/L and has a pH of 4.5.

5. The method for softening shrimp shells according to claim 1, wherein in the step (2), the feed-liquid ratio of the shrimp to the soaking liquid is 1 g: 4 mL.

6. A method for preparing a dried shrimp product with soft shell is characterized in that the method for softening the shrimp shell of any one of claims 1 to 5 is adopted for softening the shrimp shell of the shrimp to obtain the soft shell shrimp; and (3) blanching the soft-shell shrimp salt water, drying and cooling to obtain a dry soft-shell shrimp product.

7. The method as claimed in claim 6, wherein the drying is a step drying comprising drying at 60-70 ℃ for 0.5-1.5h, cooling, and drying at 85-95 ℃ for 1.5-2.5 h.

8. The method for preparing the dried soft-shelled shrimp product as claimed in claim 6, wherein the brine blanching is blanching soft-shelled shrimps in 2-4% by mass NaCl solution for 1-3min, and the brine temperature is 100 ℃.

9. A dried soft-shelled shrimp product prepared by the method of any one of claims 6-8.

10. Use of a method of softening shrimp shells as claimed in any one of claims 1 to 5 or a method of preparing dried soft shell shrimp products as claimed in any one of claims 6 to 8 in food processing.