Study On Preparation Of Fermented Oyster Beverage

Taking Crassostrea gigas as raw material, extracting the nutrients from the oyster with water, then using activated carbon for deodorization and fermenting by lactic acid bacteria, a new fermented oyster beverage was prepared, which had a refreshing taste, uniform morphology, riched in nutrients. The main results are as follows:1. The basic components of Crassostrea gigas meat had been determined. The results showed that it riched in protein, glycogen and taurine, and had a perfect amino acid composition. Meanwhile, the Crassostrea gigas meat was rich in iron, zinc, calcium, magnesium, copper and trace elements, especially in calcium, zinc, iron. But the oyster meat also contained small amounts of lead, cadmium and other heavy metals.The water-extraction process of nutritional components from Crassostrea gigas meat were studied and optimized. Using extraction rate of protein, glycogen and taurine as index, the multi-target orthogonal experiment was used for optimizing the extraction process. The optimal water-extracting conditions were: 80℃with 1:4 water-solid ratio for 4h. Under the conditions, the concentrated oyster water-extraction was yellow translucent, with a unique smell of oysters, a little fishy, no bitterness, rich in nutrient substances, which includes protein 1.10g/100mL, glycogen 4.33g/100mL, taurine 641.87mg/100mL, Zn 0.51mg/100mL, Cu 1.95 mg/100mL, Mg 2.3mg/100mL. The amino acids composition was perfect and the amino acids amount was 92.51mg/100mL.2. The deodorization of the oyster water-extraction by activated carbon andβ-cyclodextrin was studied. The results showed that the best deodorization conditions of activated carbon andβ-cyclodextrin were: 60℃for 20min with additive amount 0.75% (w/v), and 50℃for 60min with additive amount 2.5% (w/v), respectively. The deodorization effect of activated carbon was superior to that ofβ-cyclodextrin. So activated carbon was selected for deodorization treatment. After the deodorization treatment, the fishy smell of oyster extraction was mostly removal and the color changeed from yellow-green to ivory. The composition of amino acid of the oyster water-extraction before and after deodorization treatment was studied. The amino acids amount reduced 8.67%, the essential amino acids reduced 5.11%. The composition of volatile flavor compounds of the oyster water-extraction before and after deodorization treatment was studied, and the volatile flavor compounds were extracted by SPME and then detected by GC-MS. The results demonstrated that aldehydes, ketones and alcohols increased while hydrocarbons and esters decreased after deodorization. The change of the volatile components caused the oyster water-extraction more acceptable.3. The fermentation process of oyster beverage was researched. Taking titratable acidity as the main indicators, pH and total lactic acid bacteria account as secondary indicators, combining with sensory evaluation, using single factor experiment, with single factor analysis of variance (one-way ANOVE) and Least Significant Difference test, four main factors (fermentation time, fermentation temperature, inoculum size, strain ratio) which had more impact on the fermentation process from fermentation time, fermentation temperature, inoculum size, the amount of lactose, the amount of sugar added, the strain ratio were selected. Then the response surface method was used to optimize the fermentation conditions. The second empirical model (Y= -503.340 +25.490X₁ +8.121X₂ -6.753X₃ +6.396X₄ -0.319X₁2 -0.257X₂2 -0.333X₃2 -1899X₄2 -0.125X₁X₂ +0.303X₁X₃ -0.157X₁X₄ -0.0371X₂X₃ +0.981X₂X₄, model coefficients R2 was 0.9054) calculated by MINITAB 15.0 showed that the model fitted well with the actual situation, so the second empirical model could be used to analyze and forecast on the fermentation progress. Then the value of factors were calculated by the second empirical model when the titration acidity was the highest: fermentation temperature was 42.217℃, fermentation time was 9.857h, 8.534% (v/v) inoculum, strain ratio (St: Lb) was 2.819, then the titration acidity of fermentation was 48.762°T. Validation experiments showed that the actual titratable acidity were 47.34°T±0.41 in the optimum fermentation conditions. The result indicated that the model could predict the actual fermentation conditions well. 4. The deployment process of the beverage was studied. Taking viscosity, centrifugal precipitation rate as indexes and combining with sensory evaluation, results showed that high methoxy pectin was the most suitable stabilizer and the best addition level was 0.075% (w/v). In order to make the beverage more refreshing taste, added 0.02% (w/v) citric acid before fermentation to increase its acidity.The nutritional contents of the beverage were determined. The content of protein was 1.14g/100mL, carbohydrate was up to 6.27g/100ml, taurine was 601.87mg/mL, fat was 0.15 g/100mL, amino acids amount was 98.99mg/100mL, essential amino acids took 31.25% of the amino acids amount. While the beverage also contained zinc, copper, magnesium, calcium and other minerals and trace elements. After 15d storage at 4℃, the beverage had a good color, smell and taste. Meanwhile the viable count of lactic acid bacteria was more than 106cfu/mL, the health indicators of the beverage was accorded with national standards. Results of activity tests in vitro showed that the product had a high antioxidant activity and ACE inhibitory activity.The composition of volatile flavor compounds of the beverage before and after fermentation was studied. The results demonstrated that ketones, esters, organic acid and ether compounds increased while hydrocarbons and aldehydes decreased after fermentation. The change of the volatile components caused the oyster beverage with an unique fermented aroma, which made it more acceptable.