Characterization of Key Aroma Compounds of Apple Slices Dried by Hot-air at Different Temperatures by GC-MS and Electronic Nose

To clarify the key aroma compounds of Fuji apples and the influence of drying temperatures, the volatile compounds of Fuji apple slices dried by hot-air at 50, 60, 70 and 80 ℃ were characterized by head space solid-phase micro-extraction gas chromatography-mass spectrometer (HS-SPME-GC-MS) combined with electronic nose. The results showed that 64 volatile compounds were identified in fresh and four kinds of dried apple samples, including 23 esters, 18 alcohols, 8 aldehydes, 2 alkenes, 2 ketones, 3 lactones, 1 acid, 3 sulfur-containing compounds and 4 heterocyclic compounds. The differences between types and contents of volatile compounds in different samples were great. The content of aroma compounds in fresh samples was 397.059 mg/kg. Total volatile compounds contents in four hot-air dried samples from high to low were 64.189 mg/kg at 50 ℃, 57.703 mg/kg at 80 ℃, 32.124 mg/kg at 70 ℃ and 32.020 mg/kg at 60 ℃, respectively. Odor-active value (OAV) analysis showed that there were 8 key aroma compounds both in fresh apple sample and hot-air dried apple samples. They were α-farnesene (12746.11~1597.75), hexyl 2-methylbutyrate (755.62~6.90), hexanol (2988.00~168.54), 1-octene-3-ol (53.12~12.08), nonanal (1534.99~47.36), trans-2-nonenal (1202.98~189.38), linalool (1264.30~212.75) and 6-methy-5-hepten-2-one (11.27~3.90). The key aroma compounds identified in hot-air dried samples included 2-methyl-1-butanol (32.26~7.16), 3-methyl-4-heptanol (14.39~6.90), phenylethanol (11.11~4.67), octanal (211.25~84.36), 3-hydroxy-2-butanone (64.57~21.86), 3-methylthiopropanol (13.52~5.88) and 2-pentylfuran (26.44~14.88). Electronic nose analysis showed that there were differences in aroma profiles between fresh apple and apple slices dried by hot-air at different temperatures. The fresh samples and dried apple slices could be effectively distinguished by principle component analysis (PCA). Considering aroma and energy consumption, 80 ℃ hot air dehydration apple slices had better characteristic aroma than 50 ℃ hot air treatments. Therefore, 80 ℃ hot air drying was the optimal drying condition.