Pyrodextrinization of yam (Dioscorea sp.) starch isolated from tubers grown in Brazil and physicochemical characterization of yellow pyrodextrins.

This study optimizes the pyrodextrinization of yam (Dioscorea sp.) starch isolated from tubers grown in Brazil to produce a yellow pyrodextrin with the lowest enzymatically available starch (AS) content and color difference (ΔE) index. At 140 °C (fixed heating temperature), the effects of acid concentration (0.65 - 2.99 g of HCl/kg of starch) and incubation time (53 - 307 min) on the response variables were evaluated using a response surface methodology. Some physicochemical characteristics were also determined on pyrodextrins. Both factors negatively affected the AS content, although positively influenced the ΔE (P < 0.05). The yellow pyrodextrin produced with 1.82 g/kg and heating for 307 min, presented physicochemical properties similar to the commercial pyrodextrins from potato starch, with 46.6 % of AS, 24.5 of ΔE, high solubility and very low viscosity. The pyrodextrinization caused a decrease of 30 - 54 % in AS content (P < 0.05), making these yam pyrodextrins a promising material for water-soluble and very low viscous dietary fiber.

Digestibility of starches isolated from stem and root tubers of arracacha, cassava, cush-cush yam, potato and taro.

Digestibility of arracacha, cassava, cush-cush yam, potato and taro starches was evaluated. In vitro (potentially-available starch and total resistant starch) and in vivo digestibility in the rice weevil (Sitophilus oryzae) bioassay (survival, weight variation, α-amylase like activity [ALA], and uric acid excretion [UAE] as biomarkers) were estimated. In in vitro assays, all starches presented high resistant starch content (14-56%, dry basis), except for cassava starch. In in vivo assays, cush-cush yam and potato starches promoted higher ALA (>3 times) and UAE (>4 times) compare to a reference diet (cornstarch), in agreement to their low digestibility. These two biomarkers were related with resistant starch (r>0.81) and could be used to predict the starch bioavailability. This study demonstrates that the use of both in vitro and in vivo assays allows a better evaluation of starch digestibility, and may help to elucidate the final metabolic fate of starch digestion products.