Effect of vacuum microwave drying pretreatment on the quality characteristics and textural structure of new paocai raw materials

Abstract

Suitable storage of the fresh raw vegetables used in the naturally fermented Sichuan pickle, paocai, poses a challenge for commercial producers. The objective of this study was to investigate the effects of microwave–vacuum drying at different water loss rates (30%, 35%, 40%, 45%, 50% and 55%) on the quality preservation of new-paocai raw materials. The results showed that as the rate of water loss increased with this technique, the rehydration rate increased and the hardness, chewiness and viscosity of the raw vegetables tended to decrease. At the maximum water loss rate of 55%, the hardness, chewiness and viscosity of the radish slices decreased to 339.75 g, 238.84 g and 263.53 g, respectively; the highest rehydration ratio was 1.96% and, in comparison with the untreated samples (61.51 μg g⁻¹), the vitamin C content decreased to 9.83 μg g⁻¹ corresponding to a loss rate of 84.02%. When water loss exceeded 45% in the radish slices, the color change and destruction of the shape structure were obvious, the sensory properties showed a downward trend, and the springiness reached a maximum value of 0.91 g, exceeding the untreated sample′s value of 0.85 g. These experimental results ascertained that paocai raw materials display high rehydration rates, excellent texture, nutrient retention and optimal quality at a microwave–vacuum drying water loss rate of 45%. The findings of this study provide a foundation for subsequent experiments and a theoretical basis for improvements to the industrial production of paocai.