Effect of Infrared Blanching and Drying on Yardlong Beans (Vinga Unguiculata Ssp. Sesquipedalis)

Abstract

Yardlong bean (Vigna unguiculata ssp. sesquipedalis) belongs to the cowpea species. They are widely available in South Asian countries and known for their high protein and vitamin content. They degrade fast after harvest due to its high enzyme activity. Peroxidase enzyme is the most active enzyme present in yardlong beans. In this study near-infrared radiation was used for blanching. 90% inactivation of peroxidase occured when yardlong beans was treated for 4 min by infrared in the presence of water. The blanched sample was then dried until the moisture content reduced to less than 5% db by using near and mid-infrared radiations. The experiment were conducted at three different distances (6, 8, and 10 cm) between the infrared heat source and surface of the sample to study the effect of distance on the drying characteristics and quality of the product. Higher drying rates and colour retention was observed for the products dried by using infrared radiation. The Page model was used for describing the infrared drying of yardlong beans. The R2 values obtained showed that the Page model was fitting well to the drying data thin-layer drying of yardlong beans. The desirable conditions for yardlong beans to achieve 4.52% db moisture content within an hour were by drying using near-infrared radiation. Both the type of radiation used and the distance between the heat source and surface of the sample had a significant effect on the drying characteristic and shelf life.