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

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.

Research progress on properties of pre-gelatinized starch and its application in wheat flour products

Starch is the most abundant organic compound in nature,second only to cellulose.However,the conserved structure of native starches limits their properties and applications.Therefore,it is often necessary to modify them to obtain specific properties.As a common green and safe physical modification method,pre-gelatinization can improve the cold water solubility and swelling power of starch.The typical preparation methods of pre-gelatinized starch include spray drying,extrusion,and drum drying.Spray-dried pre-gelatinized starch still had good granule shape,but the increase of cold water solubility and cold paste viscosity was relatively small.Extruded and drum-dried pre-gelatinized starch showed serious structure destruction,significant increases in cold water solubility and cold paste viscosity,but relatively low hot paste viscosity.The properties of pre-gelatinized starch obtained by different methods are different,so do their effects on the quality of flour products.Wheat flour products,as one of the leading staple food for the people all over the world,play a vital role in people's daily life.With the improvement of people's living standards,more and more special flour products with unique features have received attentions of consumers and researchers.However,the sensory characteristics of special flour products are often inferior to traditional flour products,which limits its development.The unique functional characteristics of pre-gelatinized starch make it expected to play an essential role in the quality improvement of featured flour products.In this paper,the granule morphology,crystal structure,hydration and gelatinization properties of pre-gelatinized starch prepared by three common methods and their application in flour products were reviewed,which provides a theoretical basis for the application of pre-gelatinized starch in food industry.