关键词: 荔枝果实, 采后品质, 熏硫, 脱硫, 亚硫酸盐降解

Abstract: The effect of desulfurization on the postharvest quality, sulfite residue and sulfite degradation of sulfurfumigated ‘Heiye’ litchi fruit was investigated. The color, browning index, decay incidence, sulfite residue of litchi fruit, and the activities and gene expression of sulfite oxidase (SO), adenosine 5’-phosphosulfatezoline reductase (APR), sulfite reductase (SiR), serine acetyltransferase (SAT) and O-acetylserine (thiol) lyase (OAS-TL) in pulp were measured in the control (treated with prochloraz), sulfur-fumigated and desulfurized fruits during storage at 4 ℃. Our results showed that the desulfurized fruit turned red earlier than the sulfur-fumigated fruit during storage. The browning index and decay incidence of the treated fruits were significantly lower than those of the control fruit. Desulfurized fruit showed a greater reduction in the moisture content and a greater increase in the relative conductivity of pericarp than did sulfur-fumigated fruit, whereas both treatments were similarly effective against respiration. After desulphurization, sulfite content in pericarp decreased significantly, and sulfite content in desulfurized litchi pulp decreased to a level comparable to that of the control on the 16th day of storage. During storage, the activities of all enzymes investigated except for APR increased in sulfur-fumigated and desulfurized fruits when compared with the control; the activities of SO and SAT in the treated fruits increased by 2.0 and 8.6–26.7 times, respectively. On day 0 of storage, SAT activity in desulfurized litchi increased by 11.1 times in comparison with the control, and then it decreased rapidly, reaching a level not significantly different from that of the control on Day 32. The gene expression of all five enzymes in sulfur-fumigated and desulfurized fruits was higher than that in the control at the middle and late stages of storage. This study indicated that desulfurization accelerated color recovery in the pericarp of sulfur-fumigated litchi fruit with achieving a preservation effect comparable to sulphur-fumigation, and dramatically reduced sulfite residue, thereby ensuring its safety for consumption. The increasing activity of SO and SAT in sulfur-fumigated and desulfurized fruit pulp indicated that oxidative degradation of sulfite catalyzed by SO was dominant and was the most stable way, which may be complemented by the reduction pathway controlled by SAT and SiR.

Key words: litchi fruit, postharvest quality, sulphur fumigation, desulfurization, sulfite metabolism