An extensive investigation of combined freeze-drying technologies for fruit conservation

Drying is one of the oldest methods for preserving perishable foods, and protecting fruits from microbial degradation, thereby extending shelf life. However, the bland taste and hard texture affect the marketability. This has led to the development of novel drying technologies in which, freeze-drying is one such non-thermal dehydration technique that offers benefits such as maintaining structure, texture, colour, rehydration rate, and nutritional quality. Freeze-drying operates below the triple point, using temperature and pressure to remove water via vapour concentration gradients, carefully balancing critical and eutectic temperatures to preserve the structure and prevent shrinkage. Despite these advantages, freeze-drying has notable drawbacks, including high processing time, production costs, and energy consumption making the technique less feasible. Several combination drying techniques have been implemented as pre- and post-treatments to address these issues, resulting in lower power consumption, cost efficiency, and good quality retention. Techniques such as infrared, microwave, ultrasound, and pulsed electric fields have been applied as pre-treatments or to support conventional freeze-drying processes. When combined with other techniques, freeze-drying can achieve greater energy, time, and cost savings. The review presents comparative studies highlighting these benefits and discusses how these techniques can align with sustainable food processing strategies by significantly reducing energy requirements.