CN101539561A - Method for predicting storage quality changes of penaeus vannmei in cold chain - Google Patents

Abstract

The invention discloses a method for predicting changes in the storage quality of Penaeus vannamei in a cold storage chain, and studies the total number of colonies, volatile base nitrogen TVB-N, K values, and sensory changes of Penaeus vannamei stored at different temperatures , and finally establish a quality change dynamics model according to the Arrhenius equation. Beneficial effect of the present invention: applying the prediction formula of shelf life to Penaeus vannamei, the kinetic model is conducive to accurately predicting the shelf life of Penaeus vannamei and dynamically judging its quality during storage.

Description

A method for predicting storage quality changes of Penaeus vannamei in the cold chain

technical field

The invention relates to a method for predicting the storage quality change of Penaeus vannamei in cold storage chain.

Background technique

The food cold chain refers to all links of food circulation from producers to consumers, that is, all links from raw material procurement, production and processing, storage, distribution, sales to consumer tables, etc., can be maintained at a moderately low temperature. The main reason for the spoilage of aquatic products is that the microorganisms contained in the aquatic products themselves or polluted during storage and transportation grow and reproduce under suitable conditions, decompose proteins, amino acids, fats and other components to produce odor and toxic substances, resulting in spoilage of aquatic products; On the one hand, the enzymes contained in aquatic products can promote their spoilage under certain environmental conditions. In the process of storage and transportation, ambient temperature is an important condition for the growth and reproduction of microorganisms, and the action of enzymes is also closely related to temperature, so temperature has a direct relationship with the quality of aquatic products.

The scientific name of Penaeus vannamei is Penaeus vannamei, also known as white-legged shrimp and Penaeus vannamei. It has the characteristics of fast growth, long reproductive cycle, delicious taste, and good nutrition. It is one of the large and high-quality shrimp species, and it is also the shrimp species with the highest yield among the three major cultured prawns. Due to the continuous improvement of domestic and foreign markets for the freshness of aquatic products and the increase in the circulation volume and distribution distance of fresh aquatic products, it is very important to quickly evaluate the freshness of aquatic products and accurately predict the remaining shelf life.

During the low-temperature storage of Penaeus vannamei, the total number of colonies, TVB-N value of volatile basic nitrogen, K value and sensory quality will change. By studying the dynamic characteristics of each index change during low-temperature storage, a dynamic model of quality change can be established, so that the quality of Penaeus vannamei can be dynamically evaluated and the shelf life can be predicted.

Contents of the invention

A method for predicting changes in the storage quality of Penaeus vannamei in the cold storage chain. The present invention studies the total number of colonies, volatile base nitrogen TVB-N value, K value, and sensory evaluation changes of Penaeus vannamei under different storage temperature conditions. The change of each index value establishes the dynamic model of quality change, which provides experimental and theoretical basis for dynamic monitoring and control of the quality of Penaeus vannamei during storage.

The realization of the technical solution of the present invention, a method for predicting the storage quality change of Penaeus vannamei in the cold chain, is characterized in that the method steps are:

1) The vannamei shrimp stored in the constant temperature environment of -5°C, 0°C, 5°C, 10°C, and 20°C were sampled every day, and the total number of microbial index colonies, physical and chemical indexes (volatile basic nitrogen TVB-N value and K value), measurement and evaluation of sensory value.

2) To establish the kinetic model form of the total bacterial count and volatile base nitrogen (TVB-N) value of Penaeus vannamei changing with storage temperature. The selected model is a first-order chemical reaction kinetic model.

3) Through regression analysis and calculation, establish a dynamic mathematical model of the total number of bacterial colonies, volatile basic nitrogen (TVB-N) value, and K value change.

4) Verification and evaluation of quality dynamics model. Penaeus vannamei was stored under specific temperature conditions. The measured value of the quality change of the sample was compared with the predicted value obtained by the kinetic model, and the relative error between the predicted value and the measured value was calculated to verify the accuracy of the model.

Description of drawings

Figure 1 Changes in the total bacterial count of Penaeus vannamei under different storage temperatures.

Fig. 2 Changes of TVB-N value of volatile basic nitrogen of Penaeus vannamei under different storage temperatures.

Figure 3 Changes in K value of Penaeus vannamei under different storage temperatures.

Figure 4 Sensory evaluation values of Penaeus vannamei at different storage temperatures.

Detailed ways

The specific implementation of the invention will be further described in conjunction with the description, but the scope of protection required by the present invention is not limited to the scope described in the examples.

1 Materials and methods

1.1 Raw material

Shrimp used as raw material was purchased from Yangpu Market, Tumen Road, Shanghai. The whole batch of shrimp was clean and had no peculiar smell. After removing dead shrimp and old shelled shrimp, fresh Penaeus vannamei shrimp with large size and bright color were selected as experimental raw materials.

Wash the selected fresh live shrimp with ice water, cool the shrimp to shock, then put the whole shrimp into a tight bag, and store them in the environment of -5°C, 0°C, 5°C, 10°C, and 20°C for different indicators. determination.

1.2 Determination method of quality index

Samples stored at different temperatures were taken on time every day for sensory evaluation, analysis and determination of microbes and physicochemical indicators, and if the samples began to be sensory unacceptable, the test was stopped.

1.2.1 Evaluation of sensory analysis

According to GB 2741-94 "Sea Shrimp Hygienic Standard", the sensory evaluation standard of Penaeus vannamei was formulated. Evaluation is based on comprehensive indicators such as the color and luster, smell, compactness of the flesh of the shrimp body, and the connection between the head and the abdomen. A 10-point scale is used for scoring. If the comprehensive score is below 6, it indicates that the raw material is inedible in terms of sensory perception.

1.2.2 Determination of the total number of bacterial colonies

Operate according to GB/T 4789.2-2003.

1.2.3 Determination of TVB-N value of volatile base nitrogen

Automatic azotometer (Switzerland, FOSS-KEJET 2300). Instrument settings: absorption liquid is 30ml, automatic distilled water is 50ml, alkali addition is 0, delay mode, and the result is expressed in mg N/100g.

1.2.4 Determination of K value

In the early stage of aquatic product death, the action of its own enzymes has not stopped. At this time, nucleotides are gradually decomposed with the energy substance adenosine triphosphate (ATP). The ratio of the total amount is defined as the K value. The K value can effectively reflect the internal changes of aquatic products and can be used as a quality indicator of the freshness of aquatic products. Extraction and determination of ATP-related substances The present invention refers to the method of Yokoyama and Ryder after modification.

Use high-performance liquid chromatography (Japan, Shimadzu LC-10AD) to measure; Chromatographic column: OD-2 (150 * 4.66mm, Shinwa Chemical Industries), mobile phase: 0.05mol/L KH2PO4: 0.05mol/LK2HPO4 (1: 1 , V/V, pH6.78), flow rate: 1mL/min, detection wavelength: 254nm, injection volume 20μL, external standard method for quantification. Calculated according to the following formula:

1.3 Data collation and analysis

Using Excel-2003 and SPSS 10.0 to analyze and organize the experimental data.

2 Results and Analysis

2.1 Changes of total bacterial colonies of Penaeus vannamei with storage temperature and time

According to the GB18406.4-2001 standard, it can be known that the total number of colonies of seawater shrimp with second-grade freshness should be ≤10 ⁶ cfu/g. The experimental results of the total number of colonies of Penaeus vannamei stored under different temperature conditions are shown in Figure 1. It can be seen from Figure 1 that the whiteleg shrimp stored at 5°C, 10°C, and 20°C exceeded the national standard after 6 days, 4 days, and 2 days, respectively. However, the total number of bacterial colonies in the samples of Penaeus vannamei stored at -5°C and 0°C remained at a low level at the end of the experiment, which shows that low temperature can effectively inhibit the activity of microorganisms.

2.2 Changes of TVB-N of Penaeus vannamei with storage temperature and time

Volatile basic nitrogen content has been used as one of the indicators to identify the degree of corruption of meat and aquatic products in my country and most countries in the world. There is a fairly high correlation between TVB-N levels and sensory evaluation in many aquatic products, so it is widely used as an indicator of freshness of seafood foods. The lower the volatile basic nitrogen content, the higher the freshness of the product.

Figure 2 shows the determination results of TVB-N content in Penaeus vannamei during storage at different temperatures. It can be seen from the figure that the TVB-N value of the samples increases gradually with the prolongation of storage time, and the higher the storage temperature, the faster the growth rate. This is mainly because the low temperature inhibits the reproduction of microorganisms and the activity of enzymes, thereby inhibiting or slowing down the degradation and spoilage of proteins by microorganisms. According to GB18406.4-2001, the TVBN value of general freshness should be ≤30mg/100g. At 5°C, the TVB-N value (27.3407 mg/100g) was close to the upper limit on the 6th day of storage; when stored at 20°C, the TVB-N value increased very rapidly, and after 1 day of storage, the TVB-N value was as high as 21.9638mg/100g, seriously exceeded the standard on the second day; when stored at -5°C, the TVB-N value of Penaeus white shrimp changed slowly, and the measured value in the first 7 days of storage did not change much, but gradually increased in the later period, which further verified Inhibitory effects of low temperature on mesophilic microorganisms and enzyme activities in aquatic products.

2.3K value changes with storage temperature and time

Many scholars have studied the relationship between K value and freshness, and think that it is more appropriate to use K value to evaluate the freshness of most aquatic products in the early storage period. K value is used as an index to evaluate the freshness of aquatic products. The smaller the value, the better the freshness, otherwise, the worse the freshness. Ozogul Y, a foreign scholar, found that for general ready-to-kill fish, the K value is below 10%; for fresh fish as sashimi, the K value is required to be below 20%; the general freshness is about 40%. The K value calculated from the experimental measurement results is shown in Figure 3. It can be seen that with the prolongation of storage time, the K values of Penaeus vannamei at different storage temperatures showed an upward trend, and the vannamei stored at 10°C The K value (45.435%) of prawns has exceeded the general freshness after storage to the 5th day. However, the K value increased slowly at the lower temperature of -5°C, and remained at a low level at the end of the experiment (12.381%). From Figure 2 and Figure 3, it is easy to see that the variation of K value of Penaeus vannamei under the same storage temperature is basically consistent with the variation of TVB-N.

2.4 Sensory evaluation

Sensory morphology is the most intuitive way to judge the degree of corruption of aquatic products. The experiment found that vannamei shrimp was stored at 20°C. On the first day, the shrimp meat was soft, with turbid body fluid on the surface, and the appearance lost its normal blue luster and turned black. In 2 days, the body of the shrimp turned red and had a strong fishy smell, which was already unacceptable to the senses. However, when stored at a temperature of -5°C, the sensory evaluation value on the 6th day was still 8 points, and there was no obvious corruption. As can be seen from Figure 4, the sensory evaluation of fresh Penaeus vannamei was 10 points on day 0. With the prolongation of storage time, the sensory level of Penaeus vannamei stored at various temperatures showed a downward trend. The higher the temperature, the earlier the sensory corruption phenomenon appeared, and the microbial indicators, physical and chemical indicators (TVB -N and K values) have the same trend.

3 Establishment of quality dynamics model of Penaeus vannamei

Predicting the shelf life of food by studying the dynamics of food quality loss has attracted the attention of many scholars. Labuza wrote that during food processing and storage, most food quality changes follow zero-order or first-order patterns. After testing, the freshness quality function of Penaeus vannamei is a first-order reaction kinetic model. Its equation form is:

$\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}{\mathrm{<span\; class="notranslate">\; e</span>}}^{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula: t-storage time, d;

[A ₀ ]-Initial quality index of food;

[A] - The quality index of the food after storage for t days;

Kn-n (n=0, 1) order reaction rate constant.

Collect the reaction rate constant values in the quality function at different temperatures, through the Arrhenius first-order reaction relationship:

$\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="k"\; filenames="A20091004990800111.png,A20091004990800112.png"\; state="\{\{state\}\}">k</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}}{\mathrm{<span\; class="notranslate">\; RT</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula, k ₀ - pre-exponential factor

E _A - activation energy, J/mol;

R-gas constant, 8.314J/(mol K);

T - thermodynamic temperature, K.

Take the logarithmic equation to (2), after obtaining the reaction rate constants at different temperatures, use lnk to plot the reciprocal (1/T) of the thermodynamic temperature to obtain a straight line whose slope is (-E _A /R), From this, the activation energy E _A in the Arrhenius equation can be obtained.

After obtaining the value of each parameter in the reaction kinetic model, the time at the end of shelf life and the quality of the product after a certain temperature history can be calculated, and the storage time when the quality reaches any specific value can also be calculated. In this experiment, exponential regression analysis was performed on different freshness index values of Penaeus vannamei stored at -5°C, 0°C, 5°C, 10°C, and 20°C to determine the reaction order and calculate the reaction constant to obtain different See Table 1 for the activation energy E _A and Arrhenius equation of the quality change of the freshness index.

Table 1 Kinetic model parameters of quality change of Penaeus vannamei at different storage temperatures

It can be seen from Table 1 that the exponential regression equation at each temperature has a high fitting accuracy (R ² >0.9), and as the storage temperature increases, the rate constant k increases significantly, and the time to reach the national quality standard is The shelf life time is gradually shortened.

After regression analysis, the activation energies of each freshness indicator (total number of colonies: code A; TVB-N value: code B; K value: code C) are E _A =5.9863×10 ⁴ J/mol, E _B = 4.8471×10 ⁴ J/mol, E _C =5.4346×10 ⁴ J/mol. K ₀ is determined by regression of the functional relationship between the calculated activation energy and the reaction rate constant at different temperatures, that is, formula (2), and finally a shelf life prediction model for various indicators is established. The specific form is shown in Table 2 .

Table 2 The shelf life model of vannamei based on different freshness indicators

Note: In the formula, t-storage time, d; A, B, C-determination value of freshness quality; A ₀ , B ₀ , C ₀ -determination value of initial freshness quality.

According to the above research results, the extrapolation method can be used to predict the shelf life of Penaeus vannamei stored at a certain temperature, that is, as long as the environmental temperature of Penaeus vannamei, the initial value of the freshness index and the limit of the end of the shelf life are known value, the shelf life under the temperature condition can be obtained from the obtained shelf life prediction model; in addition, the storage environment temperature, the initial value of the freshness index of Penaeus vannamei and the storage time can also be used to infer the storage temperature. The quality status of Penaeus vannamei after a certain period of storage.

4 Verification and evaluation of kinetic prediction model

The theoretical shelf life obtained by the prediction model can be calculated by taking the freshness limit value of each index stipulated in the national standard as the judging standard. Table 3 lists the theoretical shelf life under the conditions of -5°C, 0°C, and 5°C and the actual shelf life obtained by sensory evaluation. After comparison, it is found that the relative error between the predicted value and the measured value is small, showing that the established model can quickly Reliable prediction of freshness and remaining shelf life of Penaeus vannamei.

Table 3 The shelf life of different temperature conditions obtained by the shelf life prediction model

Note: The data in brackets in the table is the relative error (%) between the predicted value and the real value

5 Conclusion

By measuring the freshness index and sensory evaluation of Penaeus vannamei under different storage temperature conditions, it was found that storage temperature has a significant impact on the quality and shelf life of Penaeus vannamei. The changes of the total bacterial count, TVB-N value, and K value of Penaeus vannamei stored at different temperatures with the prolongation of storage time are basically consistent with the sensory evaluation, and they all conform to the first-order kinetic model. The higher the storage temperature, the greater the value of the reaction rate constant k of the total number of bacterial colonies, TVB-N value and K value; the growth rate of each index is the smallest at -5°C, and the rest of the temperature is proportional to the growth of the reaction rate constant; the temperature and the reaction rate constant The relationship can be described by the Arrhenius equation, and has a high fitting accuracy. According to this method of predicting the dynamic change of the quality of Penaeus vannamei, the edible safety of Penaeus vannamei can be accurately identified and monitored.

Claims (5)

1. A method for predicting changes in the storage quality of Penaeus vannamei in the cold chain, characterized in that: by carrying out a constant temperature test to Penaeus vannamei under different storage temperatures and checking the total number of colonies of Penaeus vannamei and the volatile base nitrogen TVB- N, K value and other physical and chemical indicators are tested, combined with the study of sensory changes, and a shelf life kinetic prediction model is established. Proceed as follows: 1) Wash the caught fresh live shrimp with ice water, and cool the shrimp to shock. 2) Pack the washed vannamei separately and refrigerate. Samples were taken regularly to determine the total number of colonies, TVB-N value, and K value, and sensory evaluation was carried out at the same time. 3) Establish the mathematical form of the dynamic model of the above-mentioned quality indicators changing with the storage temperature. 4) Calculation and analysis of reaction rate constants. 5) Establish a dynamic model of the total number of colonies, TVB-N value, K value change. 6) Predict the shelf life of Penaeus vannamei according to the initially determined dynamic model of quality change, and compare the accuracy of the model with the measured value. 2. The method for predicting changes in storage quality of Penaeus vannamei in the cold storage chain as claimed in claim 1, characterized in that: live shrimps after fishing are put into crushed ice, cooled with ice water to shock the shrimps and clean them. Store the whole cleaned Penaeus vannamei in tight bags. 3. The method for predicting changes in the storage quality of Penaeus vannamei in the cold storage chain according to claim 1, wherein the samples of Penaeus vannamei are stored in constant temperature environments of -5°C, 0°C, 5°C, 10°C, and 20°C respectively middle. 4. the method for predicting the storage quality change of Penaeus vannamei in the cold storage chain as claimed in claim 1 is characterized in that: the total number of colonies, the volatile base nitrogen TVB-N Regression analysis was carried out on the changes of indicators such as K value and K value, and the influence of temperature on the reaction rate constant was calculated and analyzed according to the form of Arrhenius equation. 5. The method for predicting changes in the storage quality of Penaeus vannamei in the cold chain as claimed in claim 1, characterized in that: as long as the ambient temperature of Penaeus vannamei is known, the initial value of the freshness index and the limit value of the end of the shelf life , the shelf life under this temperature condition can be obtained from the obtained shelf life prediction model; in addition, it can also be deduced from the storage environment temperature, the initial value of the freshness index of Penaeus vannamei and the storage time, and the storage time under the storage temperature condition can be inferred. The quality status of vannamei after a certain period of time.

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