Screening Of Naringinase-producing Strain And Study On Citrus Juice Debittering

Citrus is the general name of orange, kumquat, grapefruit and trifoliate orange, which abounds in good nutrition and unique flavor. It can be eaten directly or processed to make a variety of citrus products. But the presence of bitter components in certain citrus affects the flavor of citrus juice and other citrus products, making it difficult for many consumers to accept it. Therefore, the study on debittering technology of orange juice is helpful to the developing scale of citrus and citrus products. In this paper, the orange peel powder is used as the culture substrate by making use of modern microbial technology, and naringinase producing strain is screened from rotten orange peels. Then UV and gamma-ray mutation breeding are used to improve the enzyme activity of mutant strains and fermentation conditions. Finally the naringinase enzyme is used to study debittering conditions of the orange juice.The results are as follows:1.Transparent circle method is used to screen naringinase producing strain. With orange peel powder as the culture substrate, a naringinase producing strain D7is screened from the accumulation of rotten orange peels by dilution plate method and the method of transparent circle. The colony and morphological characteristics were observed according to "description of Aspergillus niger fungi identification manual". It is identified as Aspergillus niger. By shake flask fermentation, the enzyme level reached291.41U on the strain which enjoys strong degradation ability of naringin.2. Increase the Enzyme activity. By the combined mutation of UV and gamma ray of Aspergillus niger D7, the optimal dose of UV irradiation is180s and the mortality was81.5%. The strain of high yield naringinase strain DC2is thus gained, with its enzyme activity702.27U, accounting for241%of the starting strain. The strain DC2and gamma ray induce mutation once again, with mutagenic dose800Gray and mortality80.4%. The strain of high yield naringinase mutant strain is gained, whose fermentation mutant DC2-12enzyme activity is1074.47U,1.53times the size of the ultraviolet mutation strain DC2, and3.69times the size of the original strain D7. After 10consecutive times, its fermentation performance is basically unchanged with genetic stability.3.Optimize fermentation conditions of mutant strain DC2-12. Enzyme activity of mutant strain DC2-12fermentation conditions were studied. The optimum fermentation conditions are as follows. The fermentation time is120h, the induction of rhamnose adding amount is0.05%, surface active agent Twain-80adding amount is0.2%, the initial pH is5, culture temperature is26℃, inoculation volume is10%and250mL flask liquid volume is30mL. The enzyme activity was1204U, under the optimal culture conditions of strain DC2-12, with enzyme stability.4.Study the debittering of citrus juice by using Mutant strain DC2-12crude enzyme liquid. Through the mutant strain DC2-12fermentation, crude enzyme liquid is gained and used to study the debittering of citrus juice in the preparation of citrus wine. It is identified that when lOU/mL crude enzyme is added and processed at pH4.5and55℃for lOOmin, the debittering effect is the best with removal ratio52.17%, which can effectively remove the bitter substances contained in orange juice and maintain its unique flavor.