| The production of fermented dairy products is becoming large-scale and centralized; industrial production is dependent on the starter-manufacturing technology. Whether natural starter, traditional starter, or highly concentrated straight starter, they can only be used for intermittent production, bur not for continuous fermentation, limiting the further improvement of production efficiency. Immobilization of biological micro-capsule technology, especially biological capsule provides a new continuous way. In our strdy the characteristics of liquid-core capsule were surveyed comprehensivly.Capsule with good performance was selected then for the highly-density culture of lactic acid bacterea and finally wsa used for continuous production of lactic acid bacteria yogurt. The main result was given as follows:1. The four factors, the concentration of chitosan, calcium chloride respectively for hardening and making membrane, and sodium alginate, which had effects on the compression intensity of liquid-core capsule, were investigated. According to the resuly of single factor experiment and orthogonal experiment, the optimum concentration conditions for the compression intensity of liquid-core microcapsule were 0.30% chitsan, 6.00% calcium chloride for hardening,6.00% calcium chloride for making membrane and 0.90% sodium alginate. Diffusivities from the solution into the liquid-core of four small molecular substrates, such as glucose, PEG2000, lycozyme, bovine serum album were investigated. The results showed that all of four substrates can diffuse into the capsule. The diffuse rate of glucose was higher than that of PEG2000, lysozyme and bovine serum album had a lower diffuse rate. The four small molecular substrates can diffuse into the capsuleⅢ, but hardly into the capsuleⅡand capsuleⅠ.The effects of calcium chloride, sodium alginate, corn starch, xanthan on growth of Streptococcus. thermophilus were studied. The result showed that calcium chloride restrained and sodium alginate, corn starch, xanthan promoted the growth of Streptococcus. thermophilus.2. Encapsulated Streptococcus. thermophilus was cultivated in the capsuleⅢto get a higher cell density. The results showed that capsuleⅢhad a good property for continuous inoculation. Plackett-Burman Design and Central Composite Design was for research the seven factors related to the growth of Streptococcus. thermophilus. The results showed that the significant factors were whey power, yeast extract and MgSO4. Optimizated formula obout culture medium is:Y=354.00+30.75X1+7.62X2-1.63X6-47.37X12-61.63X22-53.13X62-7.00X1X2+0.50X1X6-4.75X2X6, where X1=(whey power-80)/10, X2= (yeast extract -4.5)/0.5, X6=(MgSO4-0.15)/0.05. The optimized composition for the culture of S.thermophilus liquid-core capsule is whey power 83.20 g/L, yeast extract 4.54g/L, tomato juice 90mL/L, K2HPO4 1g/L, MgSO40.16g/L, MnSO40.15g/L, CaCO33g/L, and the cell density in the liquid-core capsule attained 3.58×109cfu/g.3. Encapsulated S. thermophilus in liquid-core capsule was cultivated in a stirred tank reactor using the optimized medium. Changes of glucose content were measured. After the cultivation, liquid-core capsule with LAB was transferred to a container with the shape of slender column. Response surface methodology was used to evaluate process of continuous inoculation with liquid-core LAB capsule. The result showed that the dilute rate was affected by the volume of capsule, temperature and pH. The dilute ratio of 12.71/h was obtained when volume of capsule was 1.25L, temperature was 43.49℃and pH was 5.89. Pasteurized milk was led in through the column with liquid-core capsule to inoculate continuously. The result showed that the capsule has a good stability in the 18 days. After 18 days, the capsule broken. Physical and chemical index of yogurt came up to national standard. The dilution ratio of two liters of liquid-core capsule with LAB came up to 12.71/h and the output of yogurt was 10.59L/h.Yogurt can be produced by continuous inoculation. |
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