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[Display omitted] • TCC influenced the color and flavor of FDC during the 120-day storage. • The nonenzymatic browning index was positively related to moisture content and Aw. • UACT increased the redness (29.60%) and chroma (16.59%) of FDC. • UACT improved carotenoid's extraction ratio (11.41%–13.40%) during storage. • Carrots treated by UACT and then preserved at 25 °C facilitated the storage of FDC. Discoloration and unpleasant flavor were observed in freeze-dried carrots (FDC) during shelf life. This study aimed to investigate the effects of thermal/non-thermal pre-treatments and storage temperatures on the color and flavor of FDC during the 120-day storage. Results showed that terpenes and sulfur-containing organics were the main volatiles sensitive to the 60 °C treatment (p < 0.05). Nonenzymatic browning of FDC happened during storage, which was significantly positively related to moisture content (r = 0.63) and water activity (r = 0.84), while negatively correlated with total carotenoid content (TCC, r = -0.62). However, redness (29.66%), chroma (16.59%) and TCC (3.40%) of FDC at 120-day (25 °C) was effectively improved after the combination treatment of ultrasound (40 kHz, 100 W, 10 min) and ascorbic acid (2%, w/v)-CaCl 2 (1%, w/v) solution (UAA-CaCl 2), showing that carrots pre-treated with UAA-CaCl 2 and preserved at 25 °C facilitated the FDC storage. [ABSTRACT FROM AUTHOR]

Non-enzymatic browning (NEB) reduced the colour quality of hot-air dried peppers, but the specific mechanism remains unclear. This may be related to the degradation of chlorophyll, ascorbic acid, and polyphenols. The findings revealed that the surface of pepper gradually browned during hot-air drying, with the Δ E ⁎ value and browning degree (BD) significantly increasing by 119.4 % and 62.9 %, respectively. However, the total phenol content (TPC) and ascorbic acid content decreased by 74.2 % and 84.3 %, respectively. TPC was negatively correlated with BD (R = −0.86), and its value (31.7 %) was 300 times higher than that of other colour-related components (ascorbic acid, chlorophyll). UPLC-MS/MS analysis further identified 345 polyphenols, among which 1, 3-dicaffeoylquinic acid and 5,7-dihydroxy-3′, 4′, 5′-trimethoxyflavone were the two key monophenols influencing NEB (R = −0.87). The results suggested that NEB pathways involve chlorophyll a nd ascorbic acid degradation, the Maillard reaction, and polyphenol degradation, with the latter playing a major role. [Display omitted] • Phenols, chlorophyll, and ascorbic acid contribute to the browning of dried peppers. • Total phenol content in peppers inversely correlated with browning degree. • Metabolomics analysis revealed the non-enzymatic browning in hot-air dried peppers. • Polyphenol degradation pathways primarily drive non-enzymatic browning in peppers. [ABSTRACT FROM AUTHOR]