Identification of Light-Induced Key Off-Flavors in Ponkan Mandarin Juice Using MDGC-MS/O and GC–MS/PFPD

Light-induced off-flavor compounds in Ponkan mandarin juice were investigated during its shelf-life by headspace solid-phase microextraction multidimensional gas chromatography–mass spectrometry/olfactometry (MDGC-MS/O) and a GC–MS/pulsed flame photometric detector (GC–MS/PFPD). A total of 34 aroma-active compounds with flavor dilution (FD) factors from 2 to 128 were tentatively identified by aroma extract dilution analysis-MDGC-MS/O. Among them, a light-induced off-flavor compound with a high FD factor, methional (cooked potato), was positively identified in the Ponkan mandarin juice at the end of the shelf-life. In addition, 11 volatile sulfur compounds (VSCs), including 6 screened shelf-markers (variable identification, VID > 0.80), were identified in Ponkan mandarin juice by a sulfur detector (PFPD). Four VSCs exhibited odor activity values exceeding 1. Three VSCs (methanethiol, dimethyl trisulfide, and methional) were confirmed as key light-induced off-flavor compounds in Ponkan mandarin juice based on addition/omission experiments. Furthermore, light irradiation accelerated the degradation of sulfur precursors (methionine and MMS) and the formation of these VSCs leading to an increase in off-flavor intensity.