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The effect of low frequency ultrasound (LFU) pretreatment prior to intermediate-wave infrared radiation (IW-IR) drying on water migration and quality attributes of carrot slices was investigated in this study. Results showed that the vacuole water of LFU pretreated carrot samples decreased, while the cytoplasm and intercellular space water increased by low-field nuclear magnetic resonance analysis. In addition, LFU pretreatment caused the disruption of cell structures and formation of micro-channels, resulting in significant (p<0.05) decrease of drying time required. The IW-IR dried carrot slices with LFU pretreatment showed higher β-carotene content and rehydration ratio in comparison with control samples. The color parameters of ultrasound pretreated dried carrot slices after dehydration were closer to the raw carrot samples. The results of electronic nose showed that the aromatic and volatile organic compounds of dried carrot increased by sonicated pretreatment, while the nitrogen oxides decreased, indicating that LFU can improve the flavor of dried carrot slices.
Wang et al. (Sat,) studied this question.