Identification of the Cooked Off-flavor in Heat-sterilized Lychee (Litchi Chinensis Sonn.) Juice by Means of Molecular Sensory Science

The main contributors to the cooked off-flavor in heat-sterilized lychee juice (HLJ) were studied by means of molecular sensory science. The HLJ which elicited cooked cabbage/potato and onion/garlic off-flavor was compared with fresh lychee juice (FLJ) having desired sensory attributes via chemical analysis and sensory evaluation. Aroma extract dilution analysis, quantitative analysis and calculation of odor activity values (OAVs) were conducted on both FLJ and HLJ. The results showed that compared with FLJ, 15 compounds had increased OAVs in HLJ, among which, dimethyl sulfide (DMS), methional, dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS) and 2,4-dithiapentane presented cooked cabbage/potato, garlic/onion and sulfurous impression. The omission experiment proved that DMS, methional, DMTS, DMDS, 3-methylbutanal and 2,4-dithiapentane had significantly negative effects on the overall aroma of HLJ. Further studies on HLJs from other varieties of lychee confirmed that DMS, methional, DMTS, DMDS and 3-methylbutanal were responsible for the cooked off-flavor of HLJ in general.