Effect of Pre-Gelatinization Conditions on the Total Oxalate Content and Techno-Functional Properties of Taro ( Colocasia esculenta) Flour

Abstract

Like most roots and tubers, taro (Colocasia esculenta) corms have a short shelf-life due to the high moisture content, which aggravates their post-harvest losses. They also contain high amounts of calcium oxalates, limiting their use in food applications. To help add value and diversify the use of taro corms as well as curb food losses, various strategies have been proposed, such processing of the corms into flour. This study aimed at evaluating the total oxalate content and techno-functional properties of taro flour as affected by the pre-gelatinization conditions (i.e., method and time). Pre-gelatinized taro flour was prepared by subjecting peeled and cleaned taro corms to roasting (190˚C), boiling (100˚C), and steaming (100˚C) for 10 min, 20 min and 30 min, respectively, for each method, followed by drying at 55˚C and milling. Generally, all the properties of flour were significantly affected by the pre-gelatinization conditions (P < 0.05). The total oxalate content of the pre-gelatinized taro flour ranged from 33.26 to 76.90 mg/100g. Pre-gelatinization by boiling significantly reduced the oxalate content (56.7%), while roasting resulted in the least reduction (36.2%). The flour colour i.e. L*, hue, and chroma ranged from 38.47˚ - 70.30˚, 42.64˚ - 69.43˚, and 7.78˚ - 10.58˚, respectively. Roasting resulted in flour with the largest L* (70.30˚) and hue angle (69.43˚). Boiling also resulted in flour with the highest bulk density (BD) (0.86 g/cm3) and the lowest water solubility index (WSI) (9.39%). Steamed flour had the highest water absorption index (WAI) (3.81 g/g), water holding capacity (WHC) (4.59 g/g), and swelling capacity (SC) (4.86 g/g). This study shows that pre-gelatinization (i.e. by boiling, steaming or roasting) significantly affects the total oxalate content and techno-functional properties of taro flour, which in turn influences its use in other food applications thus increasing the utilization and production of taro simultaneously.