Non-thermal hybrid drying of fruits and vegetables: A review of current technologies

Abstract

Fruits and vegetables are very perishable commodities that have enormous industrial and commercial importance. To preserve its quality attributes, increase shelf life, and reduce transport weight, fruit and vegetable can be processed by drying. Over the years, conventional drying techniques have been widely applied, both industrially and commercially for the processing and preservation of fruits and vegetables. However, most of the conventional techniques are time and energy consuming, and affect important quality attributes of final products. Recently, there has been increased interest in the use of non-thermal drying methods in combination with other conventional drying techniques for preserving fruits and vegetables. These methods have been reported to enhance the quality attributes of dried products, reduce drying time and energy demand, and increase the overall drying efficiency. In this regard, the development of a cost effective non-thermal hybrid drying systems, such as combined ultrasound (US) and hot-air drying, ultraviolet (UV) and hot-air drying, and pulse electric field (PEF) and hot-air drying have recently been researched on. These drying techniques have become potential substitute for conventional industrial and commercial dryers, owing to their advantage of producing quality dried fruit and vegetable products, with reduced drying time and energy consumption. This study therefore attempts to highlight recent developments of the commonly used non-thermal combined convective hot-air drying (CHAD) techniques for fruits and vegetables, with emphasis on drying time, drying rate, quality attributes of products, and modelling approach. This study further highlights the primary constraints for industrial application of this technology as the inadequate medium of transmission for power ultrasound, cost of design and installation, and the limited study on (UV) and PEF assisted CHAD. The necessity for conducting more detailed studies on non-thermal assisted convective hot-air drying of fruits and vegetables was emphasized.

Determination of drying kinetics, some physical, and antioxidant properties of papaya seeds undergoing microwave vacuum drying

“…The shrinkage evolution of agricultural food materials during the drying process is a common phenomenon directly affecting the final product's overall quality (Onwude et al, ; Onwude, Hashim, Janius et al, 2016). Drying method, drying condition, and MC affect shrinkage and the resultant bulk density of the seeds (Koua, Koffi, & Gbaha, ; Serowik et al, ).…”

Peanut Allergy: Characteristics and Approaches for Mitigation

“…PEF employs very high voltage pulses (1 to 80 KV/cm) for fractions of a second such as millisecond or microsecond; the voltage and the treatment duration can be adjusted according to the requirements. Besides microbial inactivation, PEF is also applied for alternative purposes such as enzyme inactivation (Onwude et al, 2017), and to increase extraction yield (Puértolas & Martínez De Marañón, 2015;Yan, He, & Xi, 2017). In relation to proteins, PEF has been noted to alter the structural features of proteins; for example, a PEF treatment of 35 KV/cm for 40 μs induces vibrational changes on the bonded side of amino acid chains, altering β-sheets and β-turns suggesting the denaturation of the protein (Liu, Zeng, Deng, Yu, & Yamasaki, 2011).…”

Modern drying techniques in fruits and vegetables to overcome postharvest losses: A review

“…Various combinations were tested such as microwave added with spouted fluidized bed system of drying which improved the drying uniformity. Onwude et al () reported that combinations of nonthermal source and convective hot‐air system of drying is as efficient tool in processing (drying) as ultrasound, ultraviolet, and pulse electric field assisted with convective hot‐air drying. In result of various evaluation studies, hybrid solar system of dryers developed were found feasible and economical; such as (Pangavhane & Sawhney, ) reported hybrid solar dryer (HSD) developed for grapes drying, Boughali et al () tested HSD for slices of tomatoes, (Amer, Hossain, & Gottschalk, ) reported ripe banana drying through HSD in such a way that solar energy stored during sunshine period in water and used in cool nights when HSD operated.…”

“…Similarly, this system is more energy-efficient, reduces the duration of processing, cost effective, and easy to operate(Onwude et al, 2017). Various combinations were tested such as microwave added with spouted fluidized bed system of drying which improved the drying uniformity Onwude et al (2017). reported that combinations of nonthermal source and convective hot-air system of drying is as efficient tool in processing (drying) as ultrasound, ultraviolet, and pulse electric field assisted with convective hot-air drying.…”