Preparation Of Nano-silver Coating Solution And Application In The Low-temperature Dried Products Of Sea Cucumbers

Sea cucumber (S. japonicus) belong to the Holothurioidea of phyum Echinodermata and are extremely rich in nutrition, but its transport and storage are very difficult, because the sea cucumbers can autolyze after leaving sea water in a few hours. As a result, most sea cucumbers in the market are dehydrated products with various dry means. The traditional method of processing is salt dry and the main component of the body wall of sea cucumber is collagen. Vacuum freeze-drying can preserve the rich nutrition and bioactive substances of the sea cucumbers, so it is considered the best current processing methods. But during the process of freeze-drying, the killing of microorganisms is little because of the low-temperature. For the moisture absorption of freeze-drying product, the microorganisms were hard to control in the process of storage. To ensure the security of products, the relevant measures should be taken to control of microorganisms. In the paper, to control the microbial within the scope of security, the sea cucumbers were coated by nano-silver firstly, and then microwave freeze-dried.In this paper, the silver colloids were prepared by the chemical reduction in liquid phase using silver nitrate, sodium hypophosphite (as reducer), sodium hexametaphosphate (as disperser), and polyvinylpyrrolidone (as protective agent). Through controlling reaction condition, the dispersible and the stable silver colloids were prepared in size between 50 ~ 60 nm. In the security measures, it is difficult to control microorganisms in a safe range only with nano-silver water solution coating. To control the microorganisms within a safe area of the freeze-dried sea cucumbers, the nano-silver starch film was prepared for special. To research the relation between the sterilization effects of nano-silver and the microbial species, the dominant bacteria was isolated from the corrupt sea cucumbers and treated with silver nanoparticles alone. The effects of sterilization are about 80 percent both of the total and the dominant bacteria with treatment of nano-silver of 0.044 mg/L.The microbial of freeze-dried sea cucumber products is hard to control. After the sea cucumbers coated with the nano-silver starch membrane solution of 0.3 mg/L, and then dried with microwave freeze-drying, the mortality rate of microorganisms was 99.1 %. Detecting with the non-flame atomic absorption, the content of silver was 0.177 mg/kg on the sea cucumber with nano-silver starch film. The content accords with the relevant food standards in domestic and international.To determine the storage conditions of sea cucumber, and the impact of nano-silver on sea cucumber microbial in the storage period, the sorption isotherms of the sea cucumber were determined at different temperatures; the sea cucumber microbial changes were detected at hot and humid environment. The microbes of the sea cucumber coated nano-silver had a certain decrease for one month storage in the environment of 92.31 percent humidity, temperature of 30℃, on in the control group, the microorganisms had a certain degree of increase.