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.