Successfully built a process to preserve some seafood
Research on the preservation process of some marine foods
Seafood such as skipjack tuna, herring, blue crab, squid... are rich in nutrients such as protein, essential amino acids, unsaturated fatty acids, minerals... for human diet. However, this food source contains high levels of water, protein and unsaturated fatty acids, so during the preservation process, due to self-decomposition, chemical oxidation and microbial activity, secondary products with unpleasant odors are formed, reducing the quality and spoiling the product. In our country, there has not been a synchronous study on the process of preserving and storing these materials. Therefore, studying the process of decomposing substances in the storage and preservation of seafood is necessary to ensure the quality and prolong the shelf life of the product. On that basis, Dr. Pham Xuan Ky and his colleagues at the Institute of Oceanography have carried out component 2: "Developing procedures to determine toxins in some marine species in Vietnam" (code: TĐĐTB0.02/21-23, under the key science and technology project at the VAST level).
The results of 5 sampling periods in the Phu Yen - Binh Thuan sea area show that skipjack tuna, herring, squid and blue crab are rich in protein and minerals necessary for the human body. However, the water content of the species is quite large and the lipids contain mostly polyunsaturated acids with long chain double bonds ω-6, ω-3 and the pH value is quite high in the muscle. These factors easily lead to the oxidation of proteins and lipids under the influence of endogenous enzymes or microorganisms, especially occurring rapidly in unsuitable storage conditions.
Scientists have provided specific data on the activity of some enzymes, the formation of harmful volatile groups, secondary substances from protein and lipid oxidation, sensory quality and some related bacteria of raw materials of skipjack tuna, herring, squid and blue crab during storage and preservation with chemicals, natural antioxidants, and gas mixtures at 0oC. In particular, the activity of enzymes in raw material samples tends to decrease slightly under storage conditions at minus 20oC after 30 days and decreases more at 0oC after 15 days. The composition and number of bacteria in raw materials change over time. At 0oC, the number of some bacteria in normal storage samples increases faster than samples using preservation methods and normal samples at minus 20oC.
Volatile compounds (VOCs) detected in raw material samples include: Aldehydes, alcohols, ketones, furans, alkanes, sulfur and other compounds. When stored at -20oC, the VOC content decreased compared to the original material and the biogenic amine content was lower than when stored at 0 o C. The pH, PV, NH3, TVB-N indexes in raw material samples of skipjack tuna, herring, squid and blue crab increased, on the contrary, the protein, water, lipid, TBARS (thiobarbituric acid reactive substances - secondary products formed during the oxidation of fat) and SH (sulfhydryl - formed during the oxidation of protein) content gradually decreased over time. The research results showed that when raw materials were stored at deep cold temperatures and using preservation measures, harmful volatile compounds as well as biogenic amines were formed in quantity and content less. This is due to the ability to inhibit the growth of relevant microorganisms and the activity of endogenous enzymes in the preservative-treated raw materials.
Extraction and analysis of some volatile compounds in preserved products
Based on the calculation results and the effectiveness of the methods for each subject, Dr. Pham Xuan Ky and his colleagues have successfully built 4 preservation processes for skipjack tuna and herring using sodium acetate, squid using oligochitosan and blue crab using a gas mixture of CO2: N2 at 0 o C under suitable conditions. The new preservation process of the group of authors can extend the shelf life by 1.5 - 2 times compared to raw materials without preservation methods at the same temperature.
“The successful development of a suitable preservation process for the research subjects has important practical significance, helping to store and preserve seafood safely and effectively. The research can be practically applied on fishing vessels of seafood fishermen and seafood processing facilities. From the achieved results, scientists hope to continue researching the mechanism of production of harmful substances of raw materials stored at temperatures of 4oC and 10oC, different storage conditions for these subjects as well as soon applying the research into practice, contributing to improving the quality of Vietnamese seafood,” said Dr. Pham Xuan Ky.
Translated by Quoc Khanh
Link to Vietnamese version
