The Color Attribute Improvement of Dried Longans

Abstract

The objective of this research was to study the effect of chemical reagents on colorattribute of dried longans. The experimental design used was completely randomized designwith 3 replications. Longans were pretreated by 5 different chemical solution which were 1)0.02%w/v potassium metabisulfite (KMS); 2) 0.5%w/v ascorbic acid; 3) 0.5%w/v citric acid;4) mixed solution of 0.02%w/v KMS, 0.5%w/v ascorbic acid and 0.5%w/v citric acid and5) water (control). After soaking for 10 minutes, the samples were dried in tray dryer at60 oC for 15 hrs. L, a, b value, moisture content, ash content, pH, total soluble solid (TSS),total sulfurdioxide content, total viable count and yeast and mold of the samples weredetermined. The sensory evaluation of dried longan products were evaluated by 50 untrainedpanelists. The result showed that using sulfite solution (only type or more of chemicalreagent) to soak fresh longan for 10 mins before drying could improve the color attribute ofdried long products because the products had more lightness and golden-yellow appearance.At the same time, they could reduce a value (red color) that occured from browning reactionbetter than using only citric and ascorbic solutions. Five conditions used in the research werenon-significantly different from moisture content and TSS (P>0.05). However, ash, pH andtotal sulfurdioxide of products were significantly different (P???0.05). The residual quantity ofsulfurdioxide in finished products did not standard limit. In addition, sulfite solution could beinhibit morn microbial growth than water and other acid solutions. Finally, the researchfound that the color attribute was a more important factor on a preference score than otherattribute.

Keywords: dried longans, color attribute, improvement