Evaluation of the usefulness of serial combination processes for drying of apples

Abstract

: Serial combination drying processes are currently studied as alternatives to conventional drying processes. Compared to freeze-drying (FD), serial combination drying appears to be faster and less expensive, while providing better product quality than hot-air drying (HAD) and microwave-vacuum drying (MVD) as previously demonstrated for carrots. Using the example of carrots, it has also been shown that the drying front moves radially outwards over the course of FD. This unexpected behaviour was suggested to originate from the carrots´ heterogeneous structure. It was hypothesized that apple pieces behave differently. Here, this hypothesis was proven by using micro-computed tomography (micro-CT) measurements of partly freeze-dried apple pieces. In order to improve the drying process of apple pieces, several single and combination drying processes were carried out. Processes were evaluated by using drying time and sample quality as relevant parameters. Sample quality was determined by analyzing the 3Dstructure, rehydration behaviour, colour and ingredient retention. Results showed that single MVD is a well suitable drying technique for apple pieces, producing dried products of equal quality to FD. Different from carrots, serial combinations are not necessary to improve the quality of dried apple pieces. Nonetheless, especially a combination of HAD and MVD was useful to obtain specific structures such as puffed pores that did not result from single MVD.

High Moisture Extrusion of Soy Protein: Investigations on the Formation of Anisotropic Product Structure

“…To confirm the hypothesis that a water-rich and a water-poor (i.e., protein-rich) phase were created, the sample extruded at 124 °C was investigated before and after freeze-drying via X-ray scanning. Different to other drying methods, freeze-drying has been shown to preserve structural features of biological samples very well [ 87 ] and to reveal anisotropic structures of extrudates from HME [ 86 , 88 ]. Through X-ray measurement, local density differences can be visualized, as the X-rays are absorbed differently.…”

Supercritical CO2 for the drying and microbial inactivation of apple’s slices

“…It is worth to point it out that also sensorial and chemical stability over time are possible [19] making the Sc-CO2 drying promising for the production of safe and good quality products. However proper design of experiments should be carried out to determine the best set of process variable able to induce high product quality as well as the investigation of combined treatment [24,25]. Nevertheless, economic analysis should be accomplished to demonstrate the sustainability as novel energy save technique [26].…”

Study on the Rehydration Quality Improvement of shiitake Mushroom by Combined Drying Methods

“…From previous studies, combined drying methods shows advantages in improving drying times, rehydration and sensorial qualities of vegetable products [ 19 , 20 , 21 , 22 , 23 ], which could be a promising way of obtaining “ideal” rehydrated mushrooms. Generally, there are two kinds of combined drying methods: serial and parallel drying.…”

“…This study therefore set out to investigate the proper combination of drying methods to obtain products with the desired rehydration quality. Based on the earlier experience of Siebert [ 22 , 23 ] and Mujumdar [ 21 , 29 ], we have devised the following serial combined drying strategy: one drying method (DIC or FD) is used to enhance the porous structure, while another conventional drying method is used to remove the water efficiently. The latter methods are applied either before or after the DIC or FD treatments, and they are chosen on the basis of their reported good rehydration performance and drying efficiency.…”