Guyot or pergola for dehydration of Rondinella grape

Abstract

AIM: Pergola veronese is the most important vine training system in Valpolicella area but Guyot in the last decades is diffusing. Rondinella is one of the three most important varieties to make Amarone wine. In this study we compared the response of Rondinella grape during postharvest dehydration from vines trained with Guyot or Pergola.

METHODS: Grapes were harvested at the same ripening stage but the grape production of Guyot and Pergola was quite different, higher in Pergola vines. Grape bunches were placed in commercial fruttaio and left to dehydrate with close-open system until reaching a weight loss of 30%. Samplings were done at 10, 20, and 30% weight loss. Berry juice enochemical analyses were performed with WineScanTM (Foss Italia) whereas the analyses of specific polyphenol compounds such as trans-resveratrol, quercetin-glucoside, and the monoglucoside anthocyanins were carried out by HPLC. Electronic nose was used to measure the juice headspace gas and GC/MS to analyze the specific VOCs (volatile organic compounds).

RESULTS: Not significant difference in the grape characteristics between the two samples were observed during dehydration; sugars increased at the same extent, about 30% in proportion with the weight loss. The acidity did not change and was similar between the two samples but malic acid initially decreased and then increased. FAN was much higher in Guyot sample at harvest and the difference was kept during dehydration, probably due to higher yield of Pergola. Guyot sample had a higher content in quercetin and monoglucoside anthocyanins while Pergola grapes had higher content in total polyphenols and total anthocyanins and specifically in trans-resveratrol and complexed anthocyanins. Electronic nose revealed a significant difference in grape must volatiles between the two samples which was validated by different concentration in VOCs. 

CONCLUSIONS

Guyot provide grapes with high content of free anthocyanins and quercetin while Pergola grapes have high content in trans-resveratrol and total anthocyanins that increased greater in Pergola than in Guyot. A significant difference in VOCs were measured which was validated by electronic nose