The South American white prawn, scientific name Vannah prawn, is commonly known as white prawn. It is loved by people because of its thin shell, fat body, delicious meat, and rich nutrition. However, South American white prawns are perishable foods. They are very susceptible to bacterial invasion and spoilage during fishing, transportation, processing and storage, resulting in a shorter shelf life, which seriously affects the sales and circulation of products.

At present, Tap water ice (TW ice) is an ideal method commonly used to maintain food freshness. It is widely used in the preservation of fruits, vegetables, especially aquatic products and other foods because it can provide lower temperatures and higher humidity. During the shrimp preservation process, TW ice can effectively slow down bacterial growth but cannot inactivate it. When the shrimp is exposed to the environment, the bacteria will reproduce rapidly, causing the shrimp to rot. Acidic electrolyzed water ice (AEW ice) is a new high-efficiency sterilization and preservation technology, attracting more and more attention.

Zhao Aijing and others from Shanghai Ocean University studied the bactericidal and fresh preservation effect of acidic electrolytic water ice on South American whitening shrimp. The experimental process and results are as follows:

The AEW ice used in the study refers to transferring the prepared acidic electrolytic water to -20 ℃ for 24 hours to make ice, and then knocking the ice into crushed ice cubes of about 2.0 cm×1.5 cm×1.0 cm. AEW ice not only has the advantages of TW ice, but also can use its higher redox potential, lower pH value and higher effective chlorine concentration to effectively sterilize. It has the advantages of no pollution, no residue, safety for the human body, easy to produce, and low price. In recent years, research on electrolytic water ice has mainly involved food preservation and microbial killing. The experiment uses fresh South American whitening shrimp in summer as the research object, and explores the influence of AEW ice and TW ice on sensory, physical, chemical and microbial indicators during their refrigeration process, in order to provide a reference basis for the sterilization and preservation mechanism of AEW ice. The South American white prawns were randomly divided into two batches and placed on AEW ice and TW ice, and covered with a layer of ice above to ensure that the shrimp samples were completely covered with ice and stored at room temperature of air conditioning (20±2 °C) for 8 days. Change ice every 8 hours, and random samples were taken every day for various indicators. The control group was fresh untreated shrimp samples, and all assays were performed in three parallels.

Assessment of sensory quality during storage of South American white shrimp

① The sensory scoring standards for sensory assessment are shown in Table 1. The total score is divided into freshness level 1 between 8 and 10, 6 and 8 are divided into freshness level 2, 5 and 6 are divided into freshness level 3, and 5 and 5 are the corruption level.

② Determination of color difference The color difference value is obtained by measuring shrimp heads by a color difference meter. The color difference value is expressed as the average value of the six measurements. The calculation formula of ΔE is:

Results and Analysis

① Effect of AEW ice on the sensory quality of South American white shrimp
      

The sensory assessment results of South American white shrimp treated by AEW ice and TW ice are shown in Figure 2. As can be seen from Fig. 2a, as the storage time increases, the quality of the shrimp decreases, so the sensory score decreases. On the 6th day, the sensory scores of South American white shrimp treated with AEW ice and TW ice were 5.58 and 6.30, respectively, and were still in the third level of freshness, but on the 7th day, the sensory scores were both below 5 points, with a large change in color (red or black), the inherent smell of the shrimp disappeared, the shrimp head and shrimp body fell off slightly, the shell was loose, the meat was not tight, the elasticity was poor, and the quality was unacceptable, indicating that the shrimp body had entered the stage of rot. Among them, although the sensory scores of the South American whitening shrimp treated by AEW ice were lower than those of the TW ice treatment group, the difference between the two was not significant (p > 0.05), indicating that the AEW ice treatment would not have an adverse effect on the sensory quality of the South American whitening shrimp. Figure 2b shows the changes in the △E value of South American white shrimp under the storage conditions of AEW ice and TW ice. The results show that the change range of the AEW ice treatment group △E is 0~8.67, and the change range of the TW ice treatment group △E is 0~12.27. Whether it is AEW ice or TW ice treatment, the △E value of shrimps showed a gradual upward trend, mainly because the shrimps are rich in astaxanthin and hemocyanin. As the protein decomposes, the properties of astaxanthin are unstable and decompose and oxidize, resulting in the fading of shrimp meat. In addition, polyphenol oxidase (PPO) catalyzes the biochemical reaction in the shrimp's body to produce melanin, causing the body color to gradually darken after death, and the shrimp's body eventually turns black or red. Statistical analysis results show that during the storage period, compared with TW ice, AEW ice significantly inhibited the increase of △E in shrimps (p < 0.05). AEW ice is a mixture with higher ORP, lower pH and higher ACC (such as HCl, HOCl, OCl- ), where HOCl has strong oxidation and bleaching properties. It may play a bleaching role in the storage process of shrimps and inhibit chromatic aberration changes. To sum up, under the synergy of these factors, AEW ice significantly inhibits the change in color difference value during shrimp storage, which is conducive to the maintenance of sensory quality during South American white shrimp storage. ②The influence of AEW ice on the physicalization index of prawns in South American whitening

Figure 3 shows the changes in pH and TBA values ​​of South American white shrimp under the storage conditions of AEW ice and TW ice. The results of Figure 3a show that the pH value of the AEW ice treatment group varies from 6.71 to 7.42, and the pH change range of the TW ice treatment group varies from 6.71 to 7.72. Therefore, whether it is AEW ice or TW ice treatment, the pH value of shrimps is generally showing a gradual upward trend. The increase in pH of shrimp is mainly due to the decomposition of proteins in shrimp meat tissue into basic alkaline nitrogen-containing small molecule substances (such as ammonia compounds, trimethylamine, etc.), which are mainly produced by the alkalizing of microorganisms in aquatic products (fish, shrimp, etc.). Statistical analysis results show that AEW ice did not significantly inhibit the increase in pH in South American whitening shrimps compared with TW ice. However, when the storage time was extended to day 8, the pH value of the AEW ice treatment group was significantly (p < 0.05) lower than that of the TW ice treatment group. Relevant research literature shows that when the pH values ​​of pipe-whip shrimp under sterile air packaging, ice storage and air conditioning packaging reach 7.56, 7.64 and 7.55 respectively, it is believed that it has reached the end of the shelf life; when the pH value of shrimp exceeds 7.6, it is believed that it has reached the end of the shelf life. In this study, the pH values ​​of all shrimp samples stored in AEW ice at room temperature of 20±2 °C for 8 days did not exceed the unacceptable pH endpoint value of the above shrimp products. However, under TW ice storage conditions, the pH value of the 8th day of the South American white shrimp (7.72) exceeded the unacceptable range of the above values. This study shows that AEW ice can inhibit the production of alkaline compounds in shrimps and slow down pH changes. The reason for this phenomenon can be attributed to the strong bactericidal effect of AEW ice. TBA is one of the common methods to characterize the degree of fat oxidation, mainly to determine the degree of fat oxidation and decomposition into malondialdehyde. Under the storage conditions of AEW ice and TW ice, the changes in TBA values ​​of South American white shrimp are shown in Figure 3b. During storage, the TBA contents of AEW ice and TW ice treatment groups showed a gradual upward trend. After storage for 8 days, the TBA contents reached 0.80 mg/kg and 0.84 mg/kg, respectively. Statistical analysis results show that AEW ice treatment did not significantly inhibit the increase in TBA content in South American white shrimps within 2~8 days of storage (p > 0.05). Since the enzymes produced by microorganisms can cause the oxidation of shrimp fat during storage, the AEW ice treatment inhibits microbial growth to hinder fat oxidation in shrimp meat, thus maintaining the shrimp body with high freshness and a longer shelf life. The above results show that AEW ice can inhibit the growth of pH and TBA values, which is conducive to the maintenance of freshness during storage of South American white shrimp. ③AEW

The effect of AEW ice on the diversity of microbial flora during storage and preservation of South American white shrimp is shown in Figure 4 and Table 2. As can be seen from Figure 4, as the storage time is extended, the number of DGGE bands in the AEW ice treatment group is generally less than that in the TW ice treatment group, which intuitively shows that AEW ice can reduce the diversity of microbial communities in shrimps. In Table 2, the above conclusions are further proved from an objective perspective by the microbial colony diversity index H′ obtained by DGGE band calculation. AEW ice treatment group, H′ generally shows a decrease in trend as the storage time is extended, and the difference can reach 0.37 (the difference between the blank and the 8th d). However, the TW ice treatment group H′ did not show a significant change trend, both of which were above 2.27, and the maximum difference was only 0.16 (the difference between blank and 8th d), which was lower than the AEW ice treatment group. Statistical analysis results show that AEW ice (7th and 8th) significantly reduces microbial diversity compared with TW ice (p < 0.05). Compared with this laboratory's study on the bactericidal effect of AEW ice on winter whitening shrimp, AEW ice has slightly lower inhibitory effect on summer whitening shrimp microorganisms, which may be related to the shrimp growth season. Therefore, the reduction in microbial diversity in South American whitening shrimps in this study mainly attributes to the combined effect of the Cl2 content released by AEW ice and the melted AEW on microorganisms. In general, AEW ice has good sterilization effect during storage of South American white shrimp. Conclusion During the 0~8-day ice storage of South American white shrimp in summer, compared with tap water ice, acidic electrolytic water ice significantly inhibited the increase of △E (p < 0.05), which can effectively inhibit the occurrence of blackening of shrimp heads and facilitate the maintenance of sensory quality of shrimps; acidic electrolytic water ice reduces the change of pH value of shrimps, slows down the accumulation of alkaline compounds (such as ammonia compounds, trimethylamine, etc.), inhibits the formation of TBA in shrimp meat, hinders the occurrence of fat oxidation reactions, and can maintain high freshness of shrimps and prolongs its shelf life; acidic electrolytic water ice effectively reduces the diversity of microbial colonies during shrimp ice storage, which is conducive to the maintenance of freshness of shrimps and the safety of eating. In short, acidic electrolytic water ice plays a positive role in the storage and preservation process of South American whitening shrimp in summer. Its bactericidal and fresh preservation effect is better than tap water ice. It can replace traditional tap water ice to apply in aquatic products to store and preserve freshness, so as to reduce the potential pathogenic risk of microorganisms in aquatic products and ensure the edible quality and safety of aquatic products. Note: The experimental content of this article is from "Modern Food Technology" and "Research on the Effect of Acid Electrolyzed Water Ice on the Bactericidal and Fresh Preservation of South American Whitening Prawns". The content of this article is for the purpose of conveying more information and is for readers' reference only. If there is any infringement of the relevant content, please notify us. Reproduction may not be made without permission.