Ultrasound-assisted osmotic dehydration pretreatment enhances drying kinetics, quality attributes, bioactive compounds, microstructure, FTIR profiles, and sensory properties of Litchi

Abstract

This study optimized ultrasound-assisted osmotic dehydration (USOD) as a pretreatment for convective drying of litchi quarters. Response Surface Methodology identified optimal conditions at 34.79% ultrasound amplitude, 30 min sonication, and 40% (w/w) sucrose, resulting in 23.76% predicted water loss and 3.89% solid gain, with experimental values showing less than 6% relative error. USOD pretreatment reduced drying time by 18% compared to control samples. The logarithmic model provided the best fit for drying kinetics in both USOD-pretreated and control samples, while the effective moisture diffusivity of USOD-pretreated samples increased by 39.58% compared to the control. USOD pretreated samples showed significantly (P < 0.05) higher lightness(L*:46.69), greater phenolic retention (10.72 mg GAE/g), and enhanced radical scavenging activity (56.47%). In addition, USOD pretreated samples showed significantly (P < 0.05) lower hardness (4.7 N), higher rehydration ratio (2.89), and superior sensory acceptability (7.4). Scanning electron microscopy of USOD-pretreated samples revealed noticeable microstructural alterations compared to fresh and control samples. FTIR analysis further confirmed better antioxidant preservation. Unlike previous studies that have largely focused on conventional or single-technique pretreatments, this work uniquely demonstrates the combined optimization of USOD as a novel pretreatment for litchi prior to hot air drying, while also establishing its link to microstructural modifications and FTIR-based confirmation of antioxidant preservation.