Research On The Factors Affecting Litchi Fruit And Litchi Wine Enzymatic Browning And Browning Controling

Litchi wine is a kind of health wine which made from high quality fresh litchi, with a wide prospect of market. The process involves washing, drain, peeling, denucleating, juicing and low temperature fermentation. However, due to the browning characteristic of litchi, the raw material is prone to oxidation. As a result, litchi wine products usually have short shelf life and poor product quality, which seriously affected the sales and promotion of litchi wine. This research took the lychee as raw material, investigated the variation of browning factors of litchi wine during fermentation and storage, studied the the three kinds of enzymes related to browning in litchi pulp of enzymology properties and studied inhibiting browning process conditions of litchi wine. The results were made as follows:1. On the premise of no browning inhibitors were added, during the litchi wine fermentation and 60d-storage, litchi wine browning degree, polyphenol oxidase(PPO) activity, peroxidase(POD) activity and 5-hydroxymethyl furfural(5-HMF) have been increasing. The phenylalanine ammonia enzyme(PAL) activity, total phenols content and total flavonoids content in litchi wine have been decreasing during the whole procedure. Pearson correlation analysis showed that the factors which highly significant correlated to the degree of litchi wine browning during the period of fermentation and storage were PPO, POD, total phenol and flavonoids. The factor that significantly correlated to the degree of litchi wine browning was 5-HMF.2. The optimum substrate of litchi pulp PPO and POD were catechol and guaiacol, respectively. PPO and POD both had combination capacity with other phenolic compounds. The optimum pH value of PPO and POD were 7.0 and 6.2, respectively. PPO and POD were not resistant to acid and base. The optimum temperature of PPO and POD were 55 ℃and 45℃, respectively. PPO and POD had a high thermostability. Glutathione, cysteine, ascorbic acid, citric acid, EDTA, CaCl2 had inhibitory effect both on litchi PPO and POD activity. The optimum substrate of litchi pulp PAL was L-phenylalanine with 2mmol/L. The optimum reaction pH value was 8.7. Litchi PAL did not resistant to acid and alkali. The optimum reaction temperature was 45℃. L-tyrosine and L-cysteine had significant inhibitory effect on Litchi PAL.3. To prevent litchi wine from browning, single factor experiments were carried out to confirm the best concentration of six inhibitors added to the litchi wine. Based on the results, orthogonal experiments with six factors and two levels were made to determine the effect order of inhibitors on inhibition rate, using L8(27) orthogonal table. The four inhibitors with the greatest effect on browning inhibition were: L-cysteine, Glutathione(GSH), EDTA-Na2 and citric acid. The results were optimized and analyzed by response surface regression using Design-expert 8.0. The results show that the best compound browning inhibitors were as follows: L-cysteine dosage 8.46mmol/L, GSH dosage 1.16mmol/L, EDTA-Na2 dosage 1.87mmol/L, citric acid dosage 1.89mmol/L. The browning inhibition rate under this condition was 47.89%, and the actual value was 50.18%. The match degree between actual value and predicted value reached 95.44%.