Study On Freshness Preservation Technique For Oyster

Oyster , known as white oyster, because it contains high protein, also known as the" ocean of milk " . It is a kind of shellfish seafood of edible and medicinal, At present, in the domestic oyster is used with fresh and made of dried meat products, a small amount of processing into oyster sauce or other condiments. In recent years, with the rapid development of aquaculture of oysters, oyster preservation issues gradually aroused people’s attention.In this experiment, means of freshness preservation for oyster such as biological preservatives, coating, modified atmospheric environment and combinations between them have been studied under storage temperatures of 0℃,-3℃and -20℃. During the storage, evolution of oyster’s freshness index such as pH, Ca²⁺-ATPase, thibabituric acid （TBA）, total volatile basic nitrogen （TVBN）, free fatty acid （FFA） and total bacterial count were analysed to evaluate preservation effect.Content and conclusion of the study are as follows:1. Oyster is used biological preservative , controlled atmosphere , coating preservation ,combined with biological preservation and controlled atmosphere, combined with biological preservative and coating preservation , in the storage process ,Determine the pH, ATP-enzyme activity, TBA , TVBN , FFA ,the total number of colonies and other fresh degree indexs. the freshness of Oyster during the process has been assessed. The study provides freshness preservation for Oyster and other shellfish with theory and technical guidance.2. The results of biological preservatives tests show that complex biological preservative（mainly comprised of lysozyme, Nisin, glycine, Vc, potassium sorbate, NaCl） has good freshness preservation effect for oyster. Under temperature of 0℃, the sample of oyster treated with biological preservatives kept fresh for 12 days, 6 days longer than control sample which only kept fresh for 6 days, the TVBN of the latter, exceeds 15 mg/100g the tolerance threshhold of the National Standard; Under light frozen of -3℃, the sample of oyster treated with biological preservatives kept relatively fresh status after 30 days.,the samples still keep good organoleptic characters, the flesh was elastic and no decay odour was perceived, pH was 5.76, TVBN was 14.00 mg/100g, which was within 15 mg/100g, the tolerance threshhold of the National Standard; one year later. Under temperature of -20℃, the sample of oyster treated with biological preservatives was still acceptable in terms of freshness, its pH was 6.46 at most, TVBN was 14.32mg/100g.3. The results of modified atmosphere with N₂ and CO₂ tests show that modified atmosphere environment combined with biological preservatives is superior to control sample in terms of freshness index such as pH, TBA, FFA, TVBN and Ca²⁺-ATPase. Under mild frozen condition of -3℃, the results show that after 25 days storage, TVBN of modified sample nearly reach the limit of 15 mg/100g . TVBN of control sample is over the limit of 15 mg/100g after 18 days storage. Applying modified-atmosphere of N₂ and CO₂ combined with biological preservatives obviously outmatch solely application of modified-atmosphere in effect of preservation of oyster4. The results of coating tests show that coating preservation has good freshness preservation effect, especially the coating ingredient has alginate composition. Under temperature of 0℃, TVBN of control sample exceeded the tolerance threshhold of 15 mg/100g after 6 days storage. While the sample of oyster treated with coating had TVBN value of 14.95 mg/100g after 12 days storage, nearly reached the tolerance threshhold; Under light frozen of -3℃, the sample of oyster treated with coating looked good appearance after 25 days, and its flesh was elastic, no decay odour was perceived, pH was 5.62, its TVBN was 13.00 mg/100g; one year later under temperature of -20℃, the sample of oyster treated with coating was still acceptable in terms of freshness, its pH was 6.43 at most, TVBN was 14.93mg/100g.5. According to the national hygienic standard of sea shellfish seafood, provisions of TVBN≤15 mg/100g is acceptable limit. Different temperatures on the fresh keeping effects the results show, temperature on the fresh keeping effect remarkable. TVBN and ATP enzyme activity of numerical changes over time showed a correlation between each other, are reflecting the protein a trend, TBA value and FFA value changes over time showed a correlation between each other. Only according to an index to judge the oyster shelf life will produce deviation, if the integrated use of indicators will be better. After comprehensive analysis: biological preservative on preservation effect of oyster plays an obvious.