Multivariate comparative analysis of chemical constituent changes and antioxidant properties of polysaccharides in ribes stenocarpum maxim. at different maturity stages on the Qinghai-Tibet Plateau

Abstract

Ribes stenocarpum Maxim. (RSM) is abundant but less known in the Qinghai-Tibet Plateau, so far, it is still in the wild state and has not been effectively developed and utilized. Based on this, the fruits RSM at seven different picking time were used to quantify the contents of total polysaccharides (TP), total flavonoids (TF), titratable acids (TA), total triterpene acids (TTA), fruit oils (FO) and vitamin C (VC), and to investigate the relationship between polysaccharides structure and antioxidant activity. The relationships between the chemical constituents of the samples and meteorological factors, antioxidant activity and polysaccharide structure were investigated using multivariate comparative analysis. The results revealed that the chemical constituents content varied considerably at different stages of maturity. TF (0.660 g kg−1 dw), TA (2.280 g kg−1 dw) was abundant in immature fruits and its content decreased with fruit maturity; on the contrary, FO (0.775 g kg−1 dw), VC (0.010 g kg−1 dw) was abundant in over- mature fruits and its content increased with time. TP (1.807 g kg−1 dw), on the other hand, was abundant in mature fruits. In addition, near surface air pressure and near surface precipitation had significant effects on the accumulation of TF, near surface air temperature and near surface air specific humidity on the accumulation of TA, and surface downward shortwave radiation on the accumulation of FO. The polysaccharide structure and monosaccharide composition of RSM differed significantly depending on the picking time. Moreover, glucose and xylose had significant effects on antioxidant activity, and polysaccharides in the immature and over-mature stages had higher antioxidant activity. The study results suggested that the middle and end of September was the suitable picking period for RSM fruits. This study may provide a basis for the selection of picking period of RSM fruits.