Assisted and hybrid food drying routes: Mechanisms, configurations, and implementation pathways

Abstract

Assisted and hybrid drying technologies have expanded rapidly as the food-processing literature seeks routes that accelerate moisture removal without sacrificing structural integrity and quality retention. This review synthesizes recent advances in microwave-, infrared-, ultrasound-, vacuum-, and freeze-drying combinations reported between 2021 and 2025, with emphasis on configuration logic, transport modification, kinetic behavior, and preservation-oriented outcomes. The evidence base was constructed from a Scopus-derived retrieval of 1982 records and narrowed to 640 retained articles and reviews through document-type, drying-centrality, target-technology, assisted/hybrid relevance, title-centrality, and off-scope exclusion criteria. Instead of treating microwave, infrared, ultrasound, vacuum, and freeze-drying as isolated dryer labels, this review synthesizes the corpus through four configuration classes: assisted primary-route systems, structural hybrid systems, integrated multi-stage systems, and pretreatment-linked enhancement pathways. The resulting synthesis shows that microwave-centered combinations primarily contribute internalized energy delivery, infrared-centered combinations intensify surface and boundary-zone heat transfer, ultrasound-assisted routes modify matrix permeability and water mobility, vacuum-integrated systems promote pressure-mediated moisture escape under reduced thermal burden, and freeze-drying combinations preserve porous structure while seeking process shortening. These mechanisms explain why assisted and hybrid drying should be evaluated through process-product balance, including kinetic improvement, structural retention, rehydration behavior, bioactive preservation, energy implications, and implementation readiness, rather than through drying-time reduction alone. Despite strong progress, the literature remains constrained by terminological inconsistency, fragmented endpoint selection, uneven mechanistic depth, limited system-wide energy evaluation, and incomplete scale-up validation. Future progress will depend on configuration-based reporting, mechanism-centered interpretation, balanced multi-criteria evaluation, and implementation-aware route design.