Abstract
Terpenes contribute to the desirable flavour and aroma of grapes and wine. The biosynthesis of these plant secondary metabolites is influenced by both physiological and environmental factors, such as grapevine phenological stage and sunlight exposure. In this study, we investigated the influence of ultraviolet (UV) at different grapevine phenological stages on free terpenes in grape at harvest. Two types of transparent polymer films were applied to grape bunches to eliminate both UV-A and UV-B or only eliminate UV-B, followed by the identification and quantification of terpenes using headspace solid-phase microextraction with gas chromatography–mass spectrometry (HS–SPME–GC–MS) analysis. In all, 27 free terpenes were identified, including eight monoterpenes/monoterpenoids, four norisoprenoids and fifteen sesquiterpenes. Higher concentrations of γ-terpinene, linalool and β-damascenone were observed in grapes with UV-B attenuation compared to the naturally exposed grape bunches. Elevated α-muurolene was observed in UV-attenuated grapes from pre-veraison to harvest, while higher concentrations of γ-cadinene were observed in naturally exposed grapes. The impacts of UV exclusion on grape terpenes at harvest were specific to phenological stages, where applying UV films from veraison to intermediate ripeness reduced the concentrations of key terpenes in grape harvest and UV attenuation from intermediate ripeness to harvest promoted the accumulation of α-muurolene and γ-cadinene. This study provides information for viticulturists to better manage grape terpene composition through UV shading.
Highlights
Terpenes are secondary metabolites naturally produced by plants, and can be classified as monoterpenes, sesquiterpenes, diterpenes, triterpenes and carotenes, based on the isoprene structure [1].Terpenes and their oxygenated derivatives, terpenoids, present in wine mostly originate from grape.Up to now, there are approximately 200 terpenes and terpenoids reported in grapes and wine [2,3].Terpenes present either as glycosidic precursors or as unbound free volatiles in grapes, where bound terpenes are more abundant, especially toward harvest [4]
This study aimed to investigate the influences of UV attenuation at different phenological stages of grape ripening on the free terpenes produced in grapes
This research investigated the impacts of UV attenuation at different phenological stages on the concentration of free terpenes in Shiraz grapes at harvest
Summary
Terpenes are secondary metabolites naturally produced by plants, and can be classified as monoterpenes, sesquiterpenes, diterpenes, triterpenes and carotenes, based on the isoprene structure [1].Terpenes and their oxygenated derivatives, terpenoids, present in wine mostly originate from grape.Up to now, there are approximately 200 terpenes and terpenoids reported in grapes and wine [2,3].Terpenes present either as glycosidic precursors or as unbound free volatiles in grapes, where bound terpenes are more abundant, especially toward harvest [4]. Terpenes are secondary metabolites naturally produced by plants, and can be classified as monoterpenes, sesquiterpenes, diterpenes, triterpenes and carotenes, based on the isoprene structure [1] Terpenes and their oxygenated derivatives, terpenoids, present in wine mostly originate from grape. Especially free terpenes, are responsible for attracting insect pollinators and acting as plant defence [5], and importantly contribute to the distinctive flavours and aroma of grapes and wine [6] Many terpenes, such as D-limonene, β-caryophyllene and carnosol, have been reported to have anticancer, antioxidant and antimicrobial properties [7,8,9], which may enhance the health benefits of consumers
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