Leaf removal at veraison stage differentially affects qualitative attributes and bioactive composition of fresh and dehydrated grapes of two indigenous Cypriot cultivars

The beneficial effect of leaf removal during fruit set on physiological, biochemical, and qualitative indices and volatile organic compound profile of the Cypriot reference cultivar 'Xynisteri'

BACKGROUND

'Xynisteri' is the reference Cypriot white cultivar that, despite its significant societal and economic impact, is poorly characterized regarding its qualitative properties, while scarce information exists regarding its aroma profile. In the current study, the effect of leaf removal during fruit set (BBCH 71) on 6-year cordon-trained, spur-pruned grapevines was assessed and an array of physiological, biochemical, and qualitative indices were monitored during successive developmental stages (BBCH 75, BBCH 85, BBCH 87, and BBCH 89). Grapes were additionally monitored for the volatile organic compounds (VOCs) profile during the advanced on-vine developmental stages (BBCH 85-BBCH 89) with the employment of gas chromatography-mass spectrometry (GC-MS), Fourier-transform near infrared (FT-NIR) spectra and electronic nose (E-nose) techniques.

RESULTS

Grape berries from the vines subjected to leaf removal were characterized by higher solid soluble sugars (SSC), titratable acidity (TA), tartaric acid, and ammonium nitrogen contents, while this was not the case for assimilable amino nitrogen (primary amino nitrogen). A total of 75 compounds were identified and quantified, including aliphatic alcohols, benzenic compounds, phenols, vanillins, monoterpenes, and C₁₃ -norisoprenoids. Leaf removal led to enhanced amounts of glycosylated aroma compounds, mainly monoterpenes, and C₁₃ -norisoprenoids. Chemometric analysis, used through FT-NIR and E-nose, showed that the aromatic patterns detected were well associated to the grape ripening trend and differences between leaf removal-treated and control grapes were detectable during fully ripe stage.

CONCLUSION

Leaf removal at fruit set resulted in an overall induction of secondary metabolism, with special reference to glycosylated aroma compounds, namely monoterpenes and C₁₃ -norisoprenoids. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Effects of leaf removal on hexose accumulation and the expression of sugar unloading-related genes in syrah grapes

Leaf removal (LR) around the cluster zone is a common practice for regulating grape quality. The purpose of this study was to assess the effects of cluster-zone leaf removal, applied at the pea-size stage of berry development, on berry soluble sugar, organic acid and phenolic compound, sugar unloading-related gene expression of Vitis. vinifera L. Syrah. Four different severities of leaf removal were applied: no leaf removal (Control), removing 2 leaves above the cluster (LR1), removing 4 leaves above the cluster (LR2), and removing 6 leaves above the cluster (LR3). The three leaf removal treatments (LR), especially removing 4 leaves (LR2), resulted in significantly higher reducing sugar, soluble sugar (glucose, fructose and sucrose), total anthocyanin and citric acid contents as compared to the control group during ripening for both vintages. At harvest, the LR treatments increased the transcript abundance of most sugar unloading-related genes. In addition, VvHT3, VvHT5, VvSUC11, VvSUC12, VvSS and VvcwINV were positively correlated with both reducing sugar contents and soluble sugar contents. Our results suggest that removing 4 leaves above the cluster is useful for improving the quality of Syrah (Vitis vinifera L.) grapes in cool climate regions with excessive leaves. These findings provide insights into the molecular basis of the relationship between leaf removing and hexose (glucose and fructose) accumulation in the grape berries.

Postharvest Water Loss of Wine Grape: When, What and Why

In postharvest science, water loss is always considered a negative factor threatening fruit and vegetable quality, but in the wine field, this physical process is employed to provide high-quality wine, such as Amarone and Passito wines. The main reason for this is the significant metabolic changes occurring during wine grape water loss, changes that are highly dependent on the specific water loss rate and level, as well as the ambient conditions under which grapes are kept to achieve dehydration. In this review, hints on the main techniques used to induce postharvest wine grape water loss and information on the most important metabolic changes occurring in grape berries during water loss are reported. The quality of wines produced from dried/dehydrated/withered grapes is also discussed, together with an update on the application of innovative non-destructive techniques in the wine sector. A wide survey of the scientific papers published all over the world on the topic has been carried out.