Production Of Naringinase From Aspergillus Aculeatus And Its Effects On The Quality Of Guanxi Pomelo Juice

Naringinase play an important role in citrus juice processing due to its hydrolytic activity of the major bitter compound naringin to naringenin, which is tasteless. High production costs of naringinase and indeterminate effects of the enzymatic treatment on nutritional quality or bioactivity of juice are the main limitations for its application in citrus juice industry. A new naringinase-producing strain, JMUdb058 was identified and characterized, changes of nutritional ingrendient and antioxidant acitivity had measured in this thesis. The main results were listed as followed:(1) The macro-morphology and micro-morphology of JMUdb058 corresponded to the characteristics of Aspergillus section Nigri Gams, the 28 S rDNA sequences showed homogeneity at 100% to Aspergillus aculeatus, and it was named as Aspergillus aculeatus JMUdb058.(2) Carbon source containing rhamnose groups are able to induce the enzyme expression, and organic nitrogen resources rich in amino acid promote the production. Both submerged and solid-state fermentation are fit for yield naringinase, especially in solid-state fermentation showed an outstanding ability. After ammonium sulphate precipitation, the activities of α-L-rhamnosidase and naringinase from Aspergillus aculeatus by solid-state fermentation were 972.2 U/mL and 355.0 U/mL, with recoveries of 84.0% and 53.1%.(3) The enzymatic hydrolysis dynamic of naringin in Guanxin pomelo by naringinase from Aspergillus aculeatus JMUdb058 was corresponded to classical Michaelis-Menten equation curve, showed Vmax and Km of 56.2 U/mL and 1.78 mM. The naringenin synthetis adapt to the first order reaction. Naringin had been removed 97.5% and because of heat treatment limonin had decreased 33.6% during the enzymatic process.(4) Total acid and free amino acid were unaffected by naringinase treatment, clarity had a significant increase and pH value slightly, total sugar, ascorbic acid, total phenols, suger degree and the soluble sugar/titratable acidity were decreased, but it’s a lesser extent than resin adsorb and ultrafiltration method.(5) DPPH, OH and FRAP method were used to evaluate antioxidant capacity of Guanxi pomelo treated by heating and naringinase hydrolysis. Heating is the major cause for weaken DPPH, OH radical inhibition and ferric reducing power, although the enzymatic hydrolysis process can account for the enhanced antioxidant activity.In conclusion,it is the first time to report a stain of Aspergillus aculeatus can produce naringinase, which is a new microorganism source for high yield of naringinase, in particularly by the solid-state fermentation. The study had revealed the dynamic regulation of naringin hydrolysis by naringinase in Guanxi pomelo juice, the changes of nutritional ingrendient and antioxidant acitivity, in addition, discovered limonin can be removed by heating. These results provide the theoretic foundation for naringinase producing and its application in citrus juice industry.