NUTRIENT CONTENT, TOXICOLOGICAL CHARACTERIZATION AND BIOTECHNOLOGICAL POTENTIAL OF PEELS FROM COLOCASIA ESCULENTA (INHAME) AND DIOSCOREA CAYANENSIS (CARÁ)

Colocasia esculenta and Dioscorea cayanensis ("inhame" and "cará" in Portuguese, respectively) are popular edible tubers largely consumed in Brazil. Peels are rich in nutrients and several uses have been proposed in both nutrition and pharmacological areas. Nevertheless, they are not commonly consumed, due to their hard texture, difficult digestion, unpleasant taste or some reported cases of allergy and intolerance, so they are largely discarded, generating big amounts of solid domestic and industrial wastes that could be used for biotechnological purposes. This work is aimed to characterize nutrient content of peels from inhame and cará, as well as the presence of toxic compounds and their fermentation potential. Nutrient analysis was performed assessing total carbohydrate concentration (Dubois), reducing sugars (ADNS), total protein (Bradford) and total phosphates (Jacintho), and the presence of bioactive or toxic compounds was determined using the bioassay with Artemia salina nauplia. The biotechnological potential of both inhame and cará peel samples was evaluated in 100 mL flask fermentation process using a Saccharomyces cerevisiae strain with high ethanol tolerance, substituting the carbohydrate source in regular fermentation broth by the studied peels and running the fermentation for 72 hours, when substrate consumption, cell growth and ethanol production were determined. Biochemical characterization showed low protein concentration in both inhame and cará samples, while total carbohydrates showed the highest concentration in the inhame peels (74.8 mg/g). Reducing sugars concentration was higher in cará peels (25.3 mg/g) and the highest phosphate concentrations were also found in inhame samples (39.9 mg/g). No toxicity was observed in any of the inhame or cará samples, which displayed survival values above 87% in all Artemia salina cultures, even when added at the highest extract concentrations. Fermentation process showed cell growth values of 14,000,000 cells/mL (cará) and 19,000,000 cells/mL (inhame), while ethanol yield values ranged between 7.9% and 5.9% (w/v) respectively. These results confirm the biotechnological potential of inhame and cará wastes as a rich nutrient sources in fermentation processes for alternative biofuels production, as well as the possibility to reduce waste volumes generated during both manufacturing and domestic consumption.