Abstract
The postharvest dehydration of grape berries allows the concentration of sugars and other solutes and promotes the synthesis of metabolites and aroma compounds unique to high-quality raisin wines such as the passito wines made in Italy. These dynamic changes are dependent on environmental parameters such as temperature and relative humidity, as well as endogenous factors such as berry morphology and genotype, but the contribution of each variable is not well understood. Here, we compared berries subjected to natural or accelerated dehydration, the latter driven by forced air flow. We followed the evolution of transcript and metabolite profiles and found that accelerated dehydration clearly dampened the natural transcriptomic and metabolomic programs of postharvest berries. We found that slow dehydration over a prolonged duration is necessary to induce gene expression and metabolite accumulation associated with the final quality traits of dehydrated berries. The accumulation of key metabolites (particularly stilbenoids) during postharvest dehydration is inhibited by rapid dehydration conditions that shorten the berry life time.
Highlights
Most of the physical and chemical quality traits sought by grape growers and winemakers are acquired by the berries during ripening, which for wine grapes may last 30–60 days or more, depending on the cultivar, agronomic/environmental factors, and winemaker choice
Bunches were subjected to intense ventilation by forced air (FR), significantly reducing the relative humidity compared with the first room, without changes in temperature (Fig. 1a, b)
In climacteric fruits like tomato and apple, ripening and senescence processes may occur after harvest and are associated to a marked increase in ethylene synthesis and respiration, and to metabolisms controlling changes in color, texture, aroma, and nutritional components[15]
Summary
Most of the physical and chemical quality traits sought by grape growers and winemakers are acquired by the berries during ripening, which for wine grapes may last 30–60 days or more, depending on the cultivar, agronomic/environmental factors, and winemaker choice. Genome-wide gene expression analysis has been used to study grape berry development and has provided a comprehensive and detailed overview of the molecular program controlling the physical and biochemical changes during berry formation and ripening The application of such large-scale analytical methods to postharvest life has revealed that a new transcriptomic program emerges following the detachment of grape clusters from the vine, driving the metabolic changes that determine the final quality traits of dehydrated berries[5,6,7]. The key Zenoni et al Horticulture Research (2020)7:141 features of this transcriptomic program include the massive induction of genes controlling stilbenoid and terpenoid biosynthesis, the oxidative polymerization of phenol compounds, and the modification of the cell wall pectin fraction These processes are induced in part by the osmotic stress caused by progressive water loss[8]
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