Effects of Blanching Conditions on the Enzyme Inhibition and Antioxidant Loss in Rambutan (<i>Nephelium lappaceum</i> L.) Seeds

Rambutan seeds – a by-product of rambutan fruit processing industry – contains various nutrients as well as phenolics and saponins with antioxidant capacities. This by-product needs to be treated before being used as a new raw material to produce value-added products. In this study, water blanching of rambutan seeds was performed and the impacts of blanching temperature and time on lipase (LP), lipoxygenase (LOX) and polyphenol oxidase (PPO) activities and antioxidant loss were investigated. At blanching temperature of 95°C, the inactivation rate constant of LP, LOX and PPO was 29.93×10 -3 , 42.80×10 -3 and 59.33×10 -3 1/min, respectively while their half-life was 23.19, 16.19 and 11.68 min, respectively. During the blanching, the total saponin content in rambutan seeds first increased and then decreased while the total phenolic content was gradually reduced. In the accelerated storage of dried rambutan seeds, the degradation rate constants of phenolics and saponins of the blanched sample were 1.7 and 1.5 times, respectively, lower than those of the unblanched counterpart; additionally, the acidic and peroxide values of oil of the blanched seeds increased more slowly and less than those of the unblanched counterpart. Blanching rambutan seeds deactivated their enzymes, resulting in lesser antioxidant loss and lipid changes in the dried seeds during the accelerated storage.