The use of sulfur dioxide and low pH treatment to control lychee (Litchi chinensis Sonn.) pericarp browning. [Workshop paper]
1994
Underhill, S.J.R. | Gardiner, S. | Prasad, A. (Queensland Dept. of Primary Industries, Hamilton (Australia). Horticulture Postharvest Group)
Browning has been attributed to the by-products of phenolic degradation by polyphenol oxidase activity (PPO, EC, 1.10.3.2). Fumigation of lychee fruit with 1.2 percent sulfur dioxide has previously been reported to inhibit PPO activity. This treatment also causes a rapid bleaching of the pericarp, due to the formation of a colourless anthocyanin-SO3H complex. The results show that acidification of the fruit with 1N HCl results in an immediate improvement in pericarp colour of sulfur dioxide-treated fruit. Acidification is suggested to reverse the bleaching effect by promoting sulfur dioxide disassociation from the pigment complex. Increased pigment stability caused by acid-induced structural changes and possible Cl-ion inhibition of PPO activity may also contribute to colour improvement. Acidification did not reduce eating quality of the aril. Total titratable acid and pH levels were consistent with little penetration of HCl into the aril. Pericarp colour recovery was very stable, with no deterioration observed after 12 weeks storage.
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