Dorota Witrowa-Rajchert

Effect of ultrasound treatment on the water state in kiwifruit during osmotic dehydration

The present work investigates how ultrasound pretreatment modulates the effects of osmotic dehydration (OD) on the water state and microstructure of kiwifruit. Kiwifruit slices (10mm thick) were subjected to ultrasonic waves in a water bath at a frequency of 35 kHz for 10, 20 and 30 min. OD process was then carried out by immersing the samples in 61.5% sucrose solution equilibrated at 25°C for a contact period of 0, 10, 20, 30, 60 and 120 min. The partition of water into the cellular tissue structures (vacuole, cytoplasm, extracellular spaces and cell wall) was investigated by Time Domain Nuclear Magnetic Resonance (TD-NMR). In parallel, the microstructure of kiwifruits slices was examined using a Scanning Electron Microscope. The results showed that US pretreatment performed for more than 10 min had a positive effect on the mass exchange caused by osmotic dehydration. A creation of microchannels and an increase of the average cross-section area of cells were observed when the samples were pretreated with US before OD. TD-NMR showed a slight redistribution of water through the substructures of the cells, as a function of the length of the US pretreatment applied.

Effect of Drying Method on the Microstructure and Physical Properties of Dried Apples

The purpose of this study was to determine the influence of the internal structure of dried apples on such physical properties as density, porosity, or shrinkage. Apple slices were dried using convection, microwave-convection, and infrared-convection methods. The apple slices dried by means of the microwave and infrared methods showed between 11 to 12% lower shrinkage, 30–34% lower volume, 18–23% lower density, and porosity of 25–28% higher than the slices dried exclusively by the convection method. Considerable differences in the density and porosity of the apple slices dried using the above methods were confirmed by analyzing the tissue images made with the help of scanning electron microscopy. Convective drying caused significant changes in the actual size and distribution of the apple cells. The cells dried using both the microwave and infrared methods had a larger cross-sectional area compared with the convective-dried material.

Spray-Drying of α-Amylase—The Effect of Process Variables on the Enzyme Inactivation

ABSTRACT The objective of this work was to investigate the effect of spray-drying conditions on the activity of enzyme and the process development. Several experiments were performed to determine the influence of the following variables: feed ratio speed and inlet and outlet drying air temperature. Fungal α-amylase was dissolved in a maltodextrin solution and spray-dried in a laboratory drier Anhydro. Water concentration and residual enzyme activity were determined in obtained powders as a function of the drying conditions. It was found that both temperature and feed ratio speed affected the activity retention of enzyme after drying. Higher value of feed ratio speed should be used in order to obtain high active dried α-amylase. Low outlet air temperature should be kept in order to obtain high active dried α-amylase.

Selected Emerging Technologies to Enhance the Drying Process: A Review

According to the U.S. Energy Information Association (EIA), world energy consumption will increase by 56% in 2040. Therefore, a lot of effort is being dedicated to maintaining economic development with minor impact on the environment. This can be done altering existing technologies or introducing completely new technologies. Due to the fact that drying can be considered one of the most energy-consuming processes, researchers have focused on ways to save energy while minimally changing the physicochemical properties of food, which shape its quality. Additionally, the increasing growth of consumer expectations and their nutritional knowledge have further stimulated efforts to seek new solutions. Non-thermal technologies such as pulsed electric field (PEF), ultrasound (US), and high hydrostatic pressure (HHP) seem to meet the expectations of both producers and consumers. This article reviews the impact of PEF, US, and HHP on drying kinetics and the quality attributes of dried food.

Drying Kinetics of Apple Tissue Treated by Pulsed Electric Field

The aim of this work was to study the influence of pulsed electric field (PEF) on the drying kinetics of apple tissue. Therefore, mathematical models that are commonly used in the literature were applied to describe the process. PEF treatment of the samples was carried out at an intensity of E = 5–10 kV/cm and 10–50 pulse numbers. Subsequently, the apples were convectively dried at 70°C and air velocity of 2 m/s. Based on electrical conductivity measurement, the cell disintegration index Z p was computed. Midilli et al.s(Drying Technology, Vol. 20, pp. 1503–1513, 2001) model was evaluated as the most adequate to describe the moisture transfer in PEF-treated and intact samples. PEF pretreatment induced a reduction in drying time of up to 12% when 10 kV/cm and 50 pulses were applied. For instance, after 60 min of drying, the dimensionless moisture ratio for PEF-treated (10 kV/cm, 50 pulses) samples was 0.18 compared to 0.26 for the untreated apples. The effective moisture diffusivity, calculated on the basis of the Ficks second law, was 1.04 × 10−9 m/s for intact samples and from 1.09 × 10−9 to 1.25 × 10−9 m2/s for PEF-treated samples at 10 pulses at 5 kV/cm and 50 pulses at 10 kV/cm, respectively.

Pulsed Electric Field Pretreatment for Osmotic Dehydration of Apple Tissue: Experimental and Mathematical Modeling Studies

The aim of this study was to analyze the influence of pulsed electric field pretreatment (PEF) on the osmotic dehydration of apple tissue. Osmotic dehydration was carried out in sucrose solution at 40°C and 100 rpm in a water-bath shaker. PEF pretreatment was performed using varying field strength of 5 and 10 kV/cm and 10 and 50 pulses. On the basis of electric conductivity measurement, the cell disintegration index was calculated. The course of osmotic dehydration was described by means of water loss, solid gain, weight reduction, and water content changes. Moreover, the course of the process was described by different mathematical models that are commonly used in the literature. PEF application before osmotic dehydration significantly increased water loss after 60 minutes of the process. In turn, no significant differences were found in the case of solid gain. The highest osmotic dehydration efficiency ratio (WL/SG) was noticed for samples treated by PEF at the electric field strength of 5 kV/cm and 10 pulses. The statistical analysis of mathematical modeling of the process showed the equations utilized generally exhibit a good fit to the experimental data.

Effect of drying on respiration of apple slices

Apple tissue not pretreated before drying was subjected to convective drying and freeze-drying. Osmotic dewatering was also used as a method of water removal from the plant tissue. Respiration of apple tissue was measured in the fresh state and at different degrees of dryness. Moreover, respiration of rehydrated samples was measured. Respiration of apple tissue decreased with increasing dry matter content and at contents higher than 60% ceased completely. Rehydration led to some restoration of the respiratory activity. The degree of restoration was dependent on the amount of water removed during drying. Freeze-drying affected less respiration pathways in apple tissue than convective drying. Osmotic dewatering affected respiration in a different way than convective drying. During the initial stages of osmotic dewatering the respiration increased substantially due to the increase in substrate concentration. At later stages of osmotic treatment increased concentration of solubles and changes in cell structure caused a decrease of respiration.

Changes of structure during rehydration of dried apples

Rehydration of dried apples was carried out with continuous measurement of a cube height. It was observed that the height decreases during the early stages of rehydration and, after the minimum is reached, the cube begins to swell. It is suggested that an amorphous matrix is formed in the final stages of drying of apples. Rehydrating water plasticizes the glassy matrix and a structure collapse is observed.

Studies on drying of purple carrot roots.

The article compares kinetics of drying and properties of dried roots of purple carrot cultivars: Deep Purple F1 and Purple Haze F1 Bejo Zaden B.V., which differ in coloring of the core section of roots. Sliced carrots were dried by convective drying (CD), microwave-convective drying (MCD), infrared-convective drying (IRCD), and freeze drying (FD). An enhancement of convective drying due to the application of infrared or microwave radiation considerably reduced drying time. The lowest values of apparent density were recorded for freeze-dried carrots, whereas these values for carrots dried by other methods were approximately four times higher. Roots of carrot cv. Deep Purple dried markedly faster than those of cv. Purple Haze. Rehydration of freeze-dried carrots was higher than that dried by other methods. This was clearly manifested particularly in the initial stage of rehydration. Kinetics of rehydration were comparable for carrot dried by other methods. Cultivars did not have a noticeable effect on the analyzed physical properties apparent density and reconstitution properties. Dried carrots of cv. Deep Purple were characterized by an approximately 2.5 times higher antioxidant capacity and higher contents of anthocyanins and polyphenols than dried carrots of cv. Purple Haze.

Rehydration properties of dried onion

Abstract The effect of pretreatment preceding convective drying and the mode of drying on reconstitution properties of dried onion was investigated. Soaking in water, dipping in starch solution and osmotic dewatering were used as pre‐drying treatments. Convective drying at 60, 70, and 80°C, infrared drying and convective drying assisted with microwaves were applied to remove water from raw onion. Rehydration was done in water at room temperature and in boiling water. In general amount of absorbed water and increase in mass during rehydration, both were higher for pretreated material than those observed with dried raw onion. The mode of drying seemed to affect the course of rehydration of dried onion, and to improve its reconstitution properties. However, this was observed at room temperature rehydration only. Pre‐drying treatment followed by convection drying affected much stronger reconstitution properties of dried onion than the mode of drying.