Effect of thermal processing of Sweet potato chips on drying kinetics and quality retention

Abstract

Sweet potatoes are a significant crop and are popular among consumers. Preserving fresh sweet potatoes by making of sweet potatoes chips is a common practice in the northern and eastern (Teso) regions of Uganda.The quality of sweet potato chips after drying is undesirable.Also, heat treatment has proven to retain quality when applied to fruits and vegetables. Therefore,this study was aimed at assessing the effect of thermal processing of sweet potato chips on drying kinetics and quality retention (physical and biochemical properties). Sweet potato variety of cream skin that is yellow fleshed when cooked was used and sized to 3mm and 6mm under peeled and unpeeled samples during experimentation. These were subjected to heat treatment by hot water blanching maintained at a temperature of 1000C using a thermometer, at different blanching times of 1 min and 3 min and dried under the sun. Moisture content, drying rate, drying time and different levels of nutrients in fresh and dried sweet potato slices were assessed using standard methods of analysis. Moisture content and drying rate were observed to decrease with increase in drying time. After drying blanched sweet potato chips, the protein and carbohydrate contents increased by 10.585% and 84.26% respectively. Beta carotene (provitamin A) content decreased especially in the 3 mm size chips due to leaching of the soluble nutrients during hot water blanching process. Contents of protein, carbohydrate and betacarotene (provitamin A) in dried chips were found significant at P < 0.05 when compared to fresh sweet potato sample nutrients. However, moisture content, drying rate and drying time were not significant at 5% significance. Yellow colour was maintained in dried peeled chips, blanched at 3 min in 3 mm and 6 mm while browning occurred at 1 min blanched chips of 6 mm and on blanched unpeeled outer flesh chips. Peeled sweet potatoes blanched at 3min retained most of their nutrients as compared to unpeeled and control. Therefore, farmers should be educated and encouraged to apply heat treatment on sweet potato slices in order retain the quality of sweet potato chips after drying.