Influence of different pre-treatments on flavor quality of freeze-dried carrots mediated by carotenoids and metabolites during 120-day storage

Changes in carotenoids and volatiles (including β-carotene-metabolites) of freeze-dried carrots (FDC) treated by thermal/nonthermal-ultrasound (40 KHz, 10 min) and ascorbic (2%, w/v)-CaCl2 (1%, w/v) solution ((H)UAA-CaCl2) during a 120-day storage period were investigated. The results of HS-SPME/GC-MS showed that caryophyllene was the dominant volatile compound (70.80 ∼ 275.74 µg/g, d.b) in FDC, and 144 volatile compounds were detected in 6 samples. Besides, 23 volatile compounds were significantly correlated with β-carotene content (p < 0.05), and β-carotene degraded to off-flavor compounds (β-ionone: 22.85 ∼ 117.26 µg/g, β-cyclocitral: 0 ∼ 113.84 µg/g and dihydroactindiolide: 4.04 ∼ 128.37 µg/g) that had adverse effects on FDC flavor. However, UAA-CaCl2 effectively preserved the total carotenoid content (793.37 µg/g), and HUAA-CaCl2 reduced the off-odors (such as β-cyclocitral and isothymol) formation at the end of storage. These results indicated that (H)UAA-CaCl2 treatments were conducive to the maintenance of carotenoids and the flavor quality of FDC.