Post-storage changes of volatile compounds in air- and sun-dried raisins with different packaging materials using HS-SPME with GC/MS

Free- and bound-form volatiles in sun-dried raisins (SDRs) and air-dried raisins (ADRs) of 'Thompson Seedless' were analyzed by gas chromatography-mass spectrometry (GC/MS) for 0, 3, 6, 9 and 12 months of storage. The compounds originating from glycosidically bound (GB) volatiles were significantly more abundant in boundform than their free-form. A total of 89 and 88 free-form compounds were identified in ADRs and SDRs, respectively. Overall, higher concentration of unsaturated fatty-acid-oxidation (UFAO) and Maillard reaction (MR) compounds were observed in the SDRs. The plastic and woven bags have an insignificant effect on the volatiles in the raisins. The main characteristics of ADR aroma were floral and fruity, while fatty, roasted, and chemical aromas were prominent in SDRs. With the exception of chemical aroma, the aromatic series (fruity, floral, herbaceous and roasted) increased during the storage duration and become more compelling in 12 month. The packaging materials have similar effect on aromatic series, except fruity note, which was higher in woven bag. The main floral and fruity aroma contributors were decanal, beta-ionone, ethyl hexanoate, beta-damascenone, and 1-octen-3-ol. Herein we identified UFAO and MR compounds as the main contributors of raisin aromas.