Effects of different color fruit bags on the coloration and quality of Xinyu grape

Abstract:【Objective】The table grape variety Xinyu was bred from a hybrid of a single Red Globe plant E-42-6 as the female parent and Rizamat as the male parent. Xinyu berries are oval in shape and have a dark red/violet skin, a mean weight of 11.6 g, a slightly crisp texture, a sour-sweet flavour, a soluble solid content of 16%-19%, and good storage, transportation and adaptability characteristics. During the fruit coloration stage, intense light can result in excessively dark coloration and affect appearance quality and commodity. Fruit bagging is effective to regulate light environment during the growth and development of grapes. Therefore, the objective of this study was to evaluate the effects of different bags on fruit-zone light environment, berry quality and anthocyanin components. The results will provide reference for selection of fruit bags for production of high quality berries of Xinyu grape in the arid area of Northwest China.【Methods】Xinyu grapevines were used as test materials, five color fruit bags (white bags, red bags, yellow bags, blue bags and green bags) were used for fruit bagging treatment, and no bagging was used as the control (CK). The transmission spectra of different color fruit bags were analyzed with UniSpec-SC single-channel portable spectrometer, and the berry quality indexes and anthocyanin components in the peel were measured during berry ripening.【Results】The total radiation in the bags decreased at different degrees compared with the control. The white bag had thehighest total radiation and transmittance, followed by the red bag, the yellow bag, the blue bag, and the green bag. The light radiation intensity of each wavelength in the different bags was reduced compared with that in the control, and the red light and infrared light had the largest reduction, with more than 50%. The proportion of red light significantly decreased in the blue bag and the green bag. The berry mass in the treatment with green bag significantly decreased by 15.59%, and berry mass in the other treatments had no significant difference compared with the control. The soluble solids were significantly decreased by bagging with the white bag, the red bag, the yellow bag, the blue bag and the green bag compared with the control, with a reduction of 9.79%, 11.53%, 13.80%, 19.25% and 19.06%, respectively. Titratable acid (TA) was higher in the green bag than in the control, with an increase of 13.95%. The treatments with the other color fruit bags had no significant effect on TA. Compared to unbagged grape berries, The TSS/TA value of berries treated with yellow, red, blue and green bag decreased 13.79%, 16.21%, 23.54% and 29.55%, respectively. The white bag had no significant effect on TSS/TA. A total of 27, 25, 25, 24, 23 and 27 anthocyanin monomers were detected by LC-MS/MS for the white bag, the red bag, the yellow bag, the blue bag and the green bag treatments and the control, respectively. The total anthocyanins content was lower in the treatments with white bag, red bag, yellow bag, blue bag and green bag than the control, with a decrease of 16.49%, 46.96%, 64.27%, 68.59% and 79.05%, respectively. The proportion of 3’- hydroxy substituted anthocyanins for the white bag decreased by 7.49%, and the proportion of 3’, 5’-hydroxy substituted anthocyanins increased by 7.25%, compared with the control. The proportion of 3’- hydroxy substituted anthocyanins was higher in the treatments with the red bag, the yellow bag, the blue bag and the green bag than in the control, with an increase of 8.15%, 14.13%, 12.99% and 29.41%, respectively, while the proportion of 3’, 5’-hydroxy substituted anthocyanins decreased by 8.25%, 14.17%, 13.03% and 29.47%, respectively. The proportion of acylated anthocyanins was lowered by the red bag, yellow bag, blue bag and green bag compared with the control, with a decrease of 3.88%, 1.66%, 2.64% and 1.64%, respectively, and there was no significant difference between the white bag treatment and the control. The proportion of methylated anthocyanins was higher in the treatments the white bag, the red bag, the yellow bag and the blue bag than in the control, with an increase of 5.47%, 6.31%, 2.57% and 3.06%, respectively, and there was no significant difference between the green bag treatment and the control. The total proportion of acylated anthocyanins was higher in the treatments with the white bag, the red bag, the yellow bag and the green bag than in the control, with an increase of 5.17%, 2.44%, 0.92% and 1.71%, respectively, and there was no significant difference between the blue bag treatment and the control. The color index of grape (CIRG) was the highest in the control and progressively lower in the white bag, the red bag, the yellow bag, the blue bag and the green bag treatments. The color index in the control and the white bag treatment was above 6.0 and the appearance was blue black. The color index in the green bag treatment was between 2 and 4 and the berry appearance was pink. The color index for the red bag, the yellow bag and the blue bag was between 4 and 5, and appearance was red. The color index was higher for the red bag and the yellow bag treatments than the treatments with the blue bag, and berry appearance was also better. Correlation analysis showed that the intensity of orange light and red light was significantly positively correlated with the content of the 3’-hydroxy substituted anthocyanins (p＜0.001).【Conclusion】Our finding elucidates that red bag could increase anthocyanins, improve berry coloration and appearance, and enhance the berry quality. Taken together, red fruit bags are recommendable for Xinyu grape in the arid area of northwest, China.