Quantitative Analysis of Natural Antioxidant Remaining in Various Natural Rubber Types.

Various natural rubber types i.e. air dried sheet (ADS), ribbed smoked sheet No.3 (RSS3) and Standard Thai Rubber 20 (STR20) were collected during early period of yearly tapping season. All samples were analyzed for their total phenolic content (TPC), free radical scavenging assays namely a 2,2 -azinobis-(3-ethylbenzothiazoline)-6-sulphonic acid (ABTS) and oxygen radical absorbance capacity (ORAC). The plasticity retention index (PRI) was also determined. It was found that TPC values calculated as mg gallic acid equivalent (GAE)/100 g ranged from 200.04 to 291.39, 247.09 to 294.95, and 287.32 to 378.90 for ADS, RSS3 and STR20, respectively. The ABTS values calculated as mg trolox equivalent (TE)/100 g rubber were found to be in the range of 44.31 to 93.36, 69.71 to 77.81, and 73.32 to 95.39 for ADS, RSS3 and STR20, respectively. ORAC values calculated as µmol trolox equivalent (TE)/100 g rubber were found to be in a range of 1,559 to 2,173, 2,724 to 3,827, and 2,616 to 4,265 for ADS, RSS3 and STR20, respectively. TPC, ABTS and ORAC values showed high correlation. PRI of ADS, RSS3 and STR20 were in the range of 97.16 to 99.22, 97.77 to 98.91, and 70.31 to 84.60, respectively. PRI values of ADS and RSS3 were not significantly different (confidence, P 0.05), but both were higher than that of STR20. Moreover, it was found that PRI of STR20 from different sources showed slightly different values and a similar trend was observed for antioxidant obtained in natural rubber. [ABSTRACT FROM AUTHOR]