荔枝、龙眼采后酶促褐变反应化学机理研究进展

荔枝、龙眼采后果皮极易褐变，主要是果皮细胞中多酚氧化酶（PPO）与酚类底物的酶促反应所致。文章系统综述了荔枝与龙眼果实采后PPO酶促褐变机理、褐变底物种类确定与化学结构鉴定、外界条件对酚类底物性质的影响及贮藏期间底物含量变化规律等方面的研究进展，发现除花色素苷类物质外，有关荔枝、龙眼果皮中其他酚类褐变底物理化性质的研究鲜见报道。今后需进一步研究探讨有关酶促褐变底物种类及其化学结构鉴定、外界环境因素如何影响PPO底物性质和酶活性变化、外界环境因素与不同品种褐变过程差异的关系、贮运期间PPO底物含量的变化规律等，为控制荔枝、龙眼果实采后贮运过程中果皮酶促褐变提供理论依据。

Chemical mechanism advances of enzymatic browning reaction in postharvest lychee and longan fruits

The pericarp tissues of lychee （Litchi chinensis Sonn.） and longan （Dimocarpus longan Lour.） turns brown easily immediately after harvesting， which greatly affects the storage and commercial values of two fruits. The postharvest browning of lychee and longan fruits was mainly due to the enzyme-catalyzed oxidation of polyphenol oxidase （PPO） and phenolic substrates in pericarp cells. Basing off of recent relevant researches， this paper comprehensively reviewed the enzymatic browning mechanism， composition， and chemical structure identification of enzymatic browning substrates， effects of storage， and transportation conditions， on substrate properties and changes in substrate contents during storage. It was discovered that except for anthocyanin， the properties of other phenols browning substrates in pericarp of lychee and longan were seldom reported； hence， the types and chemical structure identification of enzymatic browning substrates， effects of environmental factors on changes in PPO substrates and enzyme activity， relationship between environmental factors， differences in browning process in different varieties， and changes in PPO substrates content during storage and transportation still need to be further studied in order to provide bases for controlling pericarp enzymatic browning during storage and transportation of postharvest lychee and longan.