Study On The Browning Inhibition Activity Of Onion Extract

The browning of fresh-cut vegetables remains a problem today and seriously deteriorates their quality during storage. In this paper, components from onion were extracted by common solvent extraction method and CO2 super critical fluid (SCF) extraction method, and their activity on inhibiting enzymatic browning of fresh-cut vegetables during storage was evaluated with the inhibiting mechanism discussed.Optimal extraction conditions of common solvent extraction method, which was the solvent (pH 6.8 phosphatic buffer), the ratio of material and extract solvent (1:1, w/v), extraction temperature (40℃), extraction time (3hr), were obtained by employing orthogonal experiment, and RSA (Response Surface Analysis) was employed with the optimal conditions of SCF extraction method: extraction pressure 14.6~15.9MPa, temperature 33.3~36.6℃, flow rate of CO2 1.83~2.171Vmin.Two methods was respectively adopted to evaluate the enzymatic-browning-inhibition-activity of the two extracts mentioned above on three fresh-cut vegetables (lotus root, potato, lettuce), which was evaluated by Hue angle, Rigidity, activity of polyphenol oxidation enzyme (PPO) and pectin enzyme. And the content change of soluble solid materials, starch, reductive sugar, Vitamin C, Fe was detected at the same time for further studies on inhibition mechanism. Results indicate that extract by phosphatic buffer remarkably effects Hue angle, Rigidity, activity of PPO (P<0.05) and so did the extract by SCF on Hue angle (P<0.05).Besides, with the existence of onion phosphatic buffer extract, the effect of temperature and package on the browning of lotus root was investigated and proved to be remarkable respectively with P value of less than 0.01 and 0.05. Glucose, Alpinia Officinarum Hance, liquorice was added in phosphatic buffer extract to test the co-effect with the result that addition of citric acidremarkably inhibited browning.Onion extract by phosphatic buffer and the extract added citric acid exhibited good browning-inhibition activity. The 3 fresh-cut vegetables could be extended to 12 days after treatment of onion extract by phosphatic buffer and 16 days after treatment of onion extract with citric acid added. Onion extract by SCF could extended the fresh-cut vegetables by 1~2 days.As microorganisms are centered in the fresh-cut vegetables storage, the bacterial inhibition effect of onion phosphatic buffer extraction was investigated with the result that it can inhibit growth of staphylococcus and 5. dysenteriae.The mechanisms of enzymatic-browning-inhibition-activity of both onion extracts were studied and discussed. The relationship between Browning Degree and activity of PPO revealed that onion extract by phosphatic buffer might not only inhibit activity of PPO, but also react with intermedias produced during enzymatic browning and form stable, non-color compound, and thus break secondary oxidation and polymerization. Onion extract by SCF exhibited browning-inhibition effect even without direct contact with fresh-cut vegetable pieces, which suggested that it is the volatile that took effect.Conclusively, onion extract exhibited good enzymatic-browning-inhibition activity during storage of fresh-cut vegetables and thus extended their storage period.