Abstract
The residual sulfite caused by sulfur fumigation (SF) is a hazard to health and influenced the export trade of litchi. Desulfurization (DS) is a valid chemical method to reduce the residual sulfite. However, the effect of DS on fumigated litchi has not been studied at physiological and molecular level. This study was aimed to evaluate the effect of DS (SF plus 3% desulfurizer) on the postharvest quality, sulfite residue, and the sulfite metabolism in sulfitated “Feizixiao” litchi during the 4°C storage. Results indicated that the DS promoted the color recovery of sulfitated litchi and achieved an effect similar to SF on controlling rot and browning. DS recovered the water content and respiration rate of sulfitated litchi pericarp. Thus, DS improves commodity properties of sulfitated litchi. Moreover, DS greatly reduced sulfite residue especially in pulp and ensured the edible safety of sulfitated litchi. The activities of sulfite oxidase, sulfite reductase, serine acetyltransferase, and O‐acetylserine(thiol) lyase in pulp increased after SF but fell down after DS while the expressions of their encoding genes decreased after SF but then rallied after DS. These results indicated the key role of these enzymes in sulfite metabolism after SF and DS changed the sulfite metabolism at both enzymatic and transcriptional level. It could be concluded that DS used in this study was an effective method for improving the color recovery and ensuring the edible safety of sulfitated litchi by not only chemical reaction but also both of enzymatic and transcriptional regulation.
Highlights
Litchi (Litchi chinensis Sonn.) fruits were nonclimacteric subtropical fruits which were originated in China and prized on the world market for their flavor, semitranslucent white pulp, and attractive red skin (Yun et al, 2016)
The red pigmentation of “Feizixiao” litchi fruits immediately disappeared and turned to be yellowish green after the sulfur fumigation, but it quickly restored after the desulfurization (0 days after storage (DAS), AF; Figure 1a)
These results indicated that desulfurization treatment effectively restored the pigmentation, and performed a significantly inhibitory effect on the pericarp browning and decay
Summary
Litchi (Litchi chinensis Sonn.) fruits were nonclimacteric subtropical fruits which were originated in China and prized on the world market for their flavor, semitranslucent white pulp, and attractive red skin (Yun et al, 2016). Decay and pericarp browning are the main causes of postharvest loss of litchi fruits Pathogenic microorganisms such as Peronophythora litchii, Geotrichum candidum Link, Colletotrichum gloeosporioides Penz., and Aspergillus niger are the mainly biotic stresses leading to postharvest rot of litchi fruits (Wu et al, 2017). Storage under controlled atmosphere (Jiang & Fu, 1999), pure oxygen (Duan et al, 2004), NO (Duan et al, 2007), or O3 (Whangchai, Saengnil, & Uthaibutra, 2006), treatments with chitosan (Zhang & Quantick, 1997), edible coatings, plastic film (Scott, Brown, Chaplin, Wilcox, & Bain, 1982), hydrothermal dipping (Trevor, Nacey, Wiltshire, & O'Brien, 2003), gamma irradiation (Mishra et al, 2012), ultraviolet or ultrasonic have been reported to be effective to inhibit pericarp browning. Over the past three decades, SO2 fumigation (or dipping with sodium metabisulfite or other SO2‐donor) was the most effectively and widely used technology to control the loss the of litchi fruits during long distance transportation and export
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