Physical field pretreatments enhance drying efficiency and quality of goji berry

Abstract

Physical field pretreatments offer promising solutions for enhancing drying efficiency and quality. This study evaluated four innovative physical pretreatments—freezing-thawing (FT), ultrasound (US), pulsed electric field (PEF), and dielectric barrier discharge (DBD) plasma—on goji berries, focusing on their effects on tissue microstructure, moisture transfer, energy consumption, and post-drying quality during hot air drying at 55 °C. FT, US, PEF and DBD pretreatment shortened the drying time by 15 %, 29 %, 20 % and 49 % respectively and reduced the energy consumption accordingly. Among these methods, DBD plasma pretreatment emerged as the best method in terms of comprehensive ability, offering the highest drying efficiency and post-drying quality. DBD produced the highest kinetic model coefficients. FT caused rapid shrinkage, which hindered moisture transfer during subsequent drying, leading to nutrient loss and surface browning. Both US and PEF showed moderate improvements, though less effective than DBD, with US posing a risk of nutrient loss. US, PEF, and DBD reduced browning, with PEF and DBD inhibiting browning enzymes. All pretreatments changed the microstructure within goji berries, promoted the transformation of vacuolar to interstitial water, and affected the drying efficiency. DBD treatment uniquely caused a reduction in bound water and a destruction of the surface structure bringing mass transfer benefits.