Influence of storage conditions on the physico-chemical and sensory characteristics of sun-dried sweetpotato chips

Abstract

This study was designed to establish the stability of the dried sweetpotato chips on storage under different conditions of temperature and relative humidity. Roots from an orange fleshed variety of sweetpotato, SPK-004, were peeled by hand, dipped in solution of 2% sodium metabisulphite for 30 minutes, then chipped using a manual chipper. The chips were spread on drying tables at a loading density of about lkg/rn ' then sun-dried to moisture content of between 6 and 7%. The dried chips wert': . packaged in 300-gauge polyethylene bags at the rate of 250g per bag and then stored at 22°C, 30°C and 37°C and relative humidity of 40%, 68% and 95% for each storage temperature for a total period of six months. These conditions represent the average conditions typically found in Kenya. Initially and every month during storage, the samples were analyzed for moisture content, total titratable acidity, extent of browning, reduced ascorbic acid, ~-carotene content and sensory characteristics, The proximate composition of the fresh and dried chips before storage was also determined. Finally, data were subjected to multiple linear regression analysis in order to develop models for predicting Ascorbic acid and ~-carotene in the stored chips for various temperature and relative humidity regimes. The chips lost 31.2% reduced ascorbic acid and 36.9% ~-carotene during sun drying. During storage studies losses in reduced ascorbic acid and ~-carotene ranged between 34.9% and 60.9 and 49.5 and 93.4% respectively. There was a significant increase in moisture content during storage, the highest being experienced under storage at 37°C and 95% relative humidity: It increased from 6.55% to 15.50%. Likewise, increases in extent of browning and total titratable acidity were highest under conditions of high -: IX temperature and high relative humidity. Extent of browning increased from 0.08 to 0.38 at 37°C and 95% relative humidity while total titratable acidity increased from 0.6% to 1.55% % under the same conditions. Changes in appearance, colour, aroma and overall acceptability became critical to the panelists after six, five and four months of storage under 22, 30 and 37°C respectively. Temperature, relative humidity and time had a significant effect on all the parameters.Rate of loss of S-carotene and ascorbic acid and development of browning and acidity increased with increase in temperature. High relative humidity appeared to have a protective role on S-carotene while increasing loss of ascorbic acid, moisture gain and development of browning and acidity in the chips. The study showed that in order to ensure at least six months of shelf-stability of the chips and good retention of S-carotene and reduced ascorbic acid, storage at less than 22°C would be recommended.