Identification of new strawberry sulfur volatiles and changes during maturation

Two Florida strawberry cultivars, 'Strawberry Festival' and 'Florida Radiance', were harvested at five fruit developmental stages (white, half red, three-quarter red, full ripe, and overripe) at four harvest dates. A static headspace solid-phase microextraction (SPME) sampling technique coupled with gas chromatography (GC) using pulsed flame photometric detection (PFPD) was employed to measure 16 sulfur volatiles in these strawberries. A total of 7 sulfur volatiles have been previously reported, and 9 are reported for the first time in strawberries. Newly identified sulfur volatiles include methyl thiopropionate, ethyl thiobutanoate, methyl thiohexanoate, methyl (methylthio)acetate, ethyl (methylthio)acetate, methyl 2-(methylthio)butyrate, methyl 3-(methylthio)propionate, ethyl 3-(methylthio)propionate, and methyl thiooctanoate. Identifications were based on matching sulfur peak linear retention indexes (LRIs) of unknowns with authentic standards and gas chromatography-mass spectrometry (GC-MS) data. Concentrations were determined using both internal and external standards. Most sulfur volatiles increased with increasing maturity, with only concentrations of hydrogen sulfide and methanethiol remaining relatively consistent at all five stages. At the white and half red stages, most sulfur volatiles consisted of various alkyl sulfides. At three-quarter red (commercial ripe), full ripe, and overripe stages, the majority of sulfur volatiles consisted of sulfur esters. Most sulfur volatiles increased dramatically between the commercial ripe, full ripe, and overripe stages, increasing as much as 100% between full ripe and overripe. Principal component analysis indicated that sulfur volatiles could be used to distinguish overripe from full ripe and commercial ripe berries.