Enzymatic browning and chemical composition of whole yacon [Smallanthus sonchifolius (Poepp.) H. Rob.] tubers as affected by blanching

Abstract

Browning is the major problem associated with yacon [Smallanthus sonchifolius (Poepp.) H. Rob.] processing as it takes place rapidly and intensely after tissue damage. This study investigated the effects of different blanching conditions on the browning parameters and some chemical components of yacon. Whole yacon tubers were blanched in hot water under different temperature and time conditions and immediately cooled in ice water. Increasing blanching temperature and time significantly reduced the polyphenol oxidase (PPO) activity but resulted in an undesirable change in firmness; lightness (L*) decreased approaching to a black color flesh of yacon, and the a* and b* values decreased representing a tendency to a green and blue colors, respectively. Blanching the whole yacon at 60⁰C for 20 mins was found to be the most effective and can be used as preprocessing treatment to reduce browning of the product. At this condition, PPO activity was reduced to 70%, firmness was retained, and further browning was decelerated when the cut surface of yacon was allowed to stand at room temperature. Moreover, the total phenolic content (TPC), antioxidant activity, glucose, sucrose and fructose were not significantly different from unblanched yacon but fructooligosaccharide (FOS) content was reduced from 51.36 to 36.29% on dry weight basis