Abstract
Proper postharvest storage preserves horticultural products, including tea, until they can be processed. However, few studies have focused on the physiology of ripening and senescence during postharvest storage, which affects the flavor and quality of tea. In this study, physiological and biochemical indexes of the leaves of tea cultivar ‘Yinghong 9′ preserved at a low temperature and high relative humidity (15–18 °C and 85–95%, PTL) were compared to those of leaves stored at ambient conditions (24 ± 2 °C and relative humidity of 65% ± 5%, UTL). Water content, chromatism, chlorophyll fluorescence, and key metabolites (caffeine, theanine, and catechins) were analyzed over a period of 24 h, and volatilized compounds were determined after 24 h. In addition, the expression of key biosynthesis genes for catechin, caffeine, theanine, and terpene were quantified. The results showed that water content, chromatism, and chlorophyll fluorescence of preserved leaves were more similar to fresh tea leaves than unpreserved tea leaves. After 24 h, the content of aroma volatiles and caffeine significantly increased, while theanine decreased in both groups. Multiple catechin monomers showed distinct changes within 24 h, and EGCG was significantly higher in preserved tea. The expression levels of CsFAS and CsTSI were consistent with the content of farnesene and theanine, respectively, but TCS1 and TCS2 expression did not correlate with caffeine content. Principal component analysis considered results from multiple indexes and suggested that the freshness of PTL was superior to that of UTL. Taken together, preservation conditions in postharvest storage caused a series of physiological and metabolic variations of tea leaves, which were different from those of unpreserved tea leaves. Comprehensive evaluation showed that the preservation conditions used in this study were effective at maintaining the freshness of tea leaves for 2–6 h. This study illustrates the metabolic changes that occur in postharvest tea leaves, which will provide a foundation for improvements to postharvest practices for tea leaves.
Highlights
Tea from Camellia sinensis is among the world’s three most popular beverages
Throughout the 24 h monitoring period, preserved tea leaves (PTL) maintained a water content level closer to that of FTL than unpreserved tea leaves (UTL), and the difference between UTL and PTL was significantly different at 24 h (p < 0.05)
After 24 h, the water content of UTL decreased to 75.77%, and PTL fluctuated between 77.15% to 78.57% water
Summary
Tea from Camellia sinensis is among the world’s three most popular beverages. Tea is rich in polyphenols, caffeine, theanine, and terpenoids, which collectively provide a wealth of benefits to humans and contribute to its unique taste and aroma [1]. Anti-aging, cancer prevention, and other health benefits continue to be uncovered, boosting tea consumption and demand [2]. Tea is a processed food produced from the tender leaves of Camellia sinensis. The chemical components of fresh tea leaves are essential for their market value. As with other agricultural products, proper postharvest storage is critical for tea [4]. Oxidization reactions change the overall phytochemical composition of tea leaves and alter the organoleptic profile of the final tea product, decreasing its commercial value [5]. Practices adopted by enterprises typically include chilled temperature storage to preserve sensory and quality components [5]
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