Effect of Pretreatment Methods using Citric Acid and Sodium Metabisulfite on Browning Prevention of Yacon (Smallanthus sonchifolius)

Yacon (Smallanthus sonchifolius) is a highly nutritious tuber rich in fructooligosaccharides (FOS), which possesses prebiotic properties and provides various health benefits. During processing, the freshly cut surface of yacon slices turns brown rapidly owing to the activity of polyphenol oxidase (PPO) and peroxidase (POD) enzymes. Therefore, controlling enzymatic browning is essential to preserve the desirable properties of yacon during processing. This research aimed to evaluate the effects of individual and combined treatments of anti-browning agents (citric acid and sodium metabisulfite (Na2S2O5)) on color stability and enzyme inhibition. After peeling and slicing, yacon slices were immersed in the prepared solutions at a solid-to-liquid ratio of 1:2 (w/v). Yacon tubers treated with the mixture of Na2S2O5 (0.5%) and citric acid (0.15%) for 15 min showed the most effective pretreatment results. Under this condition, the PPO and POD activities decreased by 89% and 90%, respectively, and the browning index (BI) reached the lowest (30.75 ± 0.34). Moreover, the lightness (L*) reached the highest (43.30 ± 0.16) compared to the other methods examined, indicating that the method retained the characteristic color of the fresh tubers. This study contributes to the development of appropriate preservation techniques to extend the shelf life of yacon and enhance its potential applications in further product processing.