| Conjugated linoleic acid(CLA)refers to a mixture of conjugated positional and geometric isomers of linoleic acid. It has received great attention for their beneficial health properties. CLA has been reported to prevent carcinogenesis and atherosclerosis, modulate immune response and reduce body fat. At present, the production of CLA is mainly produced by chemical synthesis, but there are many unsafe factors in chemical synthesis production. Thus, people pay more attention to biosynthesis of CLA.Immobilization methods have been used for a considerable time and have become significantly interesting in the area of biotechnology over the past few years. The main advantage of immobilized cells which used in the food industry is can protect cells from the outside adverse conditions such as acids, alkalis and toxicion effects, in addition to play a continuous production purposes.That biology isomerization of LA into CLA with the use of food-grade microorganisms like Lactobacillus acidophilus (La) and Streptococcus thermophilus (St) finds a new way for CLA-fortified foods. Ultraviolet spectrophotometry was used to analyze the content of CLA. To increase the function of dairy and decrease the cost, ultraviolet light and DES were used to create CLA-hyperbiosynthesis mutant. The conditions of fermentation and immobilization of the mutant with CLA-producting strain were also optimized in this study.The fermental conditions which were optimized on Lactobacillus acidophilus and Streptococcus thermophilus were summarized as follows:inoculum volume4%, proportion of La and St was1:1, substrate concentration4%, culture temperature40℃, initial pH5.5, culture time60h, the concentration of CLA reached the maximum biosynthesis151.88μg/mL.It was proved that UV inducement and DES to induce Lactobacillus acidophilus and Streptococcus thermophilus produced two mutants with higher ability to transform LA to CLA than those of original strains. The screened two mutants La-1and St-1formed the maximum CLA with62.71μg/mL and80.41μg/mL respectively, whereas the original strains only produced CLA of75.71%for La-1or105.39%for St-1.The fermental conditions were optimized on La-1and St-1by response surface design method. The optimal conditions were that:culture temperature43℃, substrate concentration5%, inoculum volume4%(proportion of La and St was1:1), initial pH6.5, the concentration of CLA reached the maximum biosynthesis220.63μg/mL after culture time48h.Increase in CLA production than the original strains of45.27%.The optimal condition for mutants La-1and St-1to immobilize is summarized as follows: calcium chloride of3%, sodium alginate of4%, ratio of embedded strains volume of60%, the size of colloid particle of3mm, immobilized time of1h, culture temperature of40℃, culture time36h, the concentration of CLA reached the maximum biosynthesis291.70μg/mL. Mutant strains than the free mutant strains CLA production increased by32.21%, than the original production increased by92.06%. |
