Revealing quality formation in turmeric (Curcuma longa L.) during pulse-spouted microwave vacuum drying: Insights...

Changes in pore structure significantly impact heat-mass transfer and quality, yet their mechanisms have not been systematically elucidated. This study evaluated the changes in drying characteristics, physicochemical properties, and microstructure of turmeric during pulse-spouted microwave vacuum drying (PSMVD) process, in comparison with hot air drying (AD) and vacuum drying (VD). A shrinkage-collapse model was established to predict the porosity and illustrate the mechanisms underlying quality changes. The results indicated that the Page model provided the most accurate fit to the drying curves, with R² of 0.99896 (AD), 0.99922 (VD), and 0.99909 (PSMVD). The shrinkage-collapse model exhibited good fitting performance (R² = 0.96895). Shrinkage and collapse simultaneously occurred and their contributions in porosity differed during the PSMVD process, resulting in a trend of porosity characterized by an increase-decrease-increase pattern. At stage III, the porosity of PSMVD samples increased by 40.15% and 37.33%, respectively, compared with AD and VD samples. Notably, the cell walls ruptured and reaggregated at the end of drying, leading to the formation of larger pores and decrease in the number of micropores. This porous and loose structure significantly enhanced the T₂ and drying rate, thereby reducing the relative crystallinity and temperature uniformity index, with lower hardness and chewiness (P < 0.05). The shorter drying time significantly contributed to reducing the total color difference (ΔE) and enhancing the retention of phenolic compounds, leading to higher antioxidant activity (P < 0.05). This study provides a theoretical basis for the precise quality control during drying and industrial application of PSMVD.