Microwave-assisted Freeze-drying Research Articles

Studies on different combined microwave drying of carrot pieces

SummaryThree different combined microwave (MW) drying methods were compared, namely microwave‐assisted vacuum drying (MWVD), microwave‐assisted freeze drying (MWFD), microwave‐enhanced spouted bed drying (MWSD), in terms of drying rate, drying uniformity, product colour, rehydration ratio, retention of β‐carotene and vitamin C, and energy consumption. The drying rate of MWVD and MWSD were much faster than that of MWFD. The largest drying rate was obtained in MWSD with 3.5 W g−1. In general, the colour of MWSD products was very uniform. Rehydration ratio of MWFD carrot pieces was almost the same as the freeze‐dried (FD) products and better than MWVD and MWSD products. In addition, the highest retention of carotene and vitamin C was observed in MWFD carrot pieces. No significant differences were observed in carotene and vitamin C between MWVD and MWSD products. However, the energy consumption in MWFD was the highest.

Trends in Microwave-Assisted Freeze Drying of Foods

Microwave-assisted freeze drying (MFD) can be accomplished in two distinct ways: freeze drying assisted concurrently with microwave application (MFD-1) and freeze drying and assisted microwave/vacuum microwave drying in two consecutive separate drying stages (MFD-2). MFD is a rapid dehydration technique that can be applied to certain foods, particularly to seafoods, solid soup, and fruits and vegetables. MFD involves much less drying time and energy consumption than conventional freeze-drying methods. Currently, this technology has been successfully used to dry many food materials and has potential in the food industry. Increasing concerns over product quality, energy savings, and production costs have motivated researchers and the industry to adopt MFD technologies. The advantages of MFD include shorter drying time, energy savings, improved product quality, and flexibility in producing a wide variety of dried products. However, current applications are limited to small categories of foods due to high startup costs and relatively complex technology compared to conventional freeze drying. This article presents a concise review of recent progress in MFD R&D and makes recommendations for future research to bridge the gap between laboratory research and industrial applications.

OPTIMIZATION OF DEHYDRATED EGG QUALITY BY MICROWAVE ASSISTED FREEZE-DRYING AND HYDROCOLLOID INCORPORATION

Enhancement of the physical and sensory properties of rehydrated egg products as a consequence of microwave assisted freeze-drying and addition of hydrocolloids to the formulation was assessed. When compared to conventional freeze-drying (CFD), microwave assisted freeze-drying (MFD) led to products with greater water-holding capacity and reduced elastic modulus. Comparisons were also made of moisture sorption rates. The addition of xanthan gum and, to a lesser extent, microcrystalline cellulose increased both water-holding capacity and elastic modulus. Magnitude estimation by a trained texture panel of critical sensory properties (chewiness, rubberiness, moistness, moisture release, and roughness) revealed that MFD samples were superior to CFD samples and that MFD samples containing xanthan were closest to the optimal for the egg products. It was concluded that the more uniform and less heat stressing process of microwave assisted freeze-drying coupled with the presence of xanthan gum leads to a rehydrated product that best retains its structural integrity and ability to bind (reabsorbed) water and that, in turn, has highly acceptable textural properties most similar to fresh eggs.