Non-enzymatic Browning Of Litchi Wine

The processing of litchi wine was often accompanied with browning changes, especially non-enzymatic browning, hamful to the product qulity. With handy colour tester and visible ultraviolet spectrop hotometer, the effect of different processing conditions on litchi wine color and non-enzymatic browning degree were investigated. The processing conditions inclouded fermentation, aging and pulse electric field (PEF) treatment as well as gardenia yellow pigment addition. The optimal processing condition of producing litchi wine with little non-enzymatic browning changing, was also obtained in this research.Brewing processing conditions were gained by orthogonal test. It was showed that among the three environmental factors (inoculum concentration of yeast, fermentation temperature and primitive pH level), the most significant factor influencing the browning concentration in the product of Litchi wine was fermentation temperature, following primitive pH level, and then inoculum concentration of yeast in Litchi wine. It was demonstrated that the optimal conditons generating less browning degree during fermentation of litchi wine was as following: when inoculum concentration of yeast was 150 mg/L; fermentation temperature was 15℃; primitive pH level was 3.5. After 15 days under this brewing conditons, browning degree 0.124 of litchi fermentation liquor were obtained.During 36 days aging peried, it was explored that the browing degree of litchi wine was promoted by higher temperature level, stronger light intensity, more sugar content as well as more plentiful oxygen. It was obtainted that the best conditions for aging: full tank of litchi fermentation liquor without any external glucose additon was stored in dark refrigerated room at 4℃. Finally the wine browning degree only increased by 6.5% from 0.124 to 0.128.It was also revealed that, the litchi wine browning degree increased from 0.124 to 0.126, 6% lower than the untreated sample, when litchi juice was treated by PEF for 23 ms at 26.7 kV/cm. However, when we used intensive electric field strengths to treate litchi fermentation liquor, the level of final wine browning degree was increased. When litchi fermentation liquor was exposed to the wild PEF prosessing condition for 23 ms at 66.7 kV/cm, its final wine browning degree was 0.146, an increased of 17.7%. Meanwhile, the final wine browning degree was 0.134, with 0.001 more than counter fermentation liquor sample when the same liquor was displayed to mild PEF condition for same duration at 15.0 kV/cm. The color and medicinal value of litchi wine were significantly improved by adding suitable gardenia yellow pigment, 25 mg/L. Under this pigment content, the browning rate was 0.0036 per day, a decrease of 12.2% compared to the control sample. Moreover, the clarity of litchi wine displayed its advantage in the sensory evaluation.The optimal processing method of producing litchi wine was gained in this researth: when litchi juice was treated by PEF for 23 ms at 26.7kV/cm before 15 days fermentation, and then added gardenia yellow pigment of 25 mg/L, next exprosed to mild PEF conditions for 23 ms duration at 15 kV/cm. After 36 aging days, A420 measured as 0.151.