High Hydrostatic Pressure Pretreatments Regulating Drying Characteristics, Texture Quality, and Pectin Fractions Content of Yam Slices

In order to investigate the effects of high hydrostatic pressure (HHP) pretreatments on the drying characteristics and qualities of yam slices, HHP (100~600 MPa) pretreatments were employed prior to drying process. The drying characteristics, texture quality, microstructure and pectin content of the dried yam slices were evaluated, and the relevant analysis was conducted. The results indicated that the HHP pretreatment significantly influenced both drying process and water state of yam slices. Specifically, when the pressure ≥300 MPa, both the free degree of water in yam slices and the drying rate during the pre-drying period increased. After drying, the proportion of immobile water in yam slices increased and reached 41.77% at 600 MPa. Furthermore, the hardness and ∆E values of dried yam slices increased by 362.06~760.06 g and 0.62~9.83, respectively, after HHP pretreatment. In contrast, the fracturability, fracture energy, and rehydration ratio of dried yam slices decreased by 0.33~0.94 mm, 80.17~356.30 g·sec, and 0.30~0.84, respectively, after HHP pretreated. Scanning electron microscopy (SEM) results revealed that, when the pressure was ≥300 MPa, the surfaces of starch granules in HHP pretreated and dried yam slices exhibited a squeezed depression, coupled with ruptured cell wall, adhered starch granules, and reduced tissue voids. Pectin fractions analysis showed that the contents of water-soluble (WSP), CDTA-soluble (CSP) and Na₂CO₃-soluble (NSP) pectin in yam slices were reduced by 24.73, 3.34 and 3.37 mg/g, respectively, after 600 MPa HHP pretreatment and drying. Correlation analysis demonstrated a significant negative correlation between pectin fraction and hardness (P<0.05). These findings provide both technical and theoretical reference for the preparation of high-quality yam slices through HHP regulation.