Ewa Gondek

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.

Active polyphenolic compounds, nutrient contents and antioxidant capacity of extruded fish feed containing purple coneflower (Echinacea purpurea (L.) Moench.)

The growth of fish is directly dependent on feed composition and quality. Medicinal plants can be added to fish feed as adjuvant therapy for the prevention of fish diseases. The purple coneflower (Echinacea purpurea (L.) Moench.) has been reported to have multiple biological effects, including immunomodulatory and antioxidant activity. The most active compounds of E. purpurea are polyphenols - caffeic acid derivatives: caftaric acid, chlorogenic acid, cynarin, echinacoside and cichoric acid. Due to a relatively limited number of studies on the use of the purple coneflower as a nutritional supplement for fish feeding, extruded fish feed with addition of Echinacea roots was produced. In the feed total phenolic content, selected polyphenol contents, the energetic value, nutrient contents and antioxidant capacity were examined. The results indicate that fish feed with addition of the Echinacea has a great potential to be a good source of natural radical scavengers, for example polyphenols, and nutritive ingredients. Antioxidant properties of feed were well correlated with the coneflower content. The study findings confirmed that high-temperature extrusion-cooking process does not deactivate phenolic antioxidant compounds, which are present both in the Echinacea roots and in the final product. Fish feed with addition of E. purpurea can be used as a nutritional supplement in the prevention of fish diseases caused by oxidative stress.

Diastase Activity Retention and Physical Properties of Honey/Arabic Gum Mixtures After Spray Drying and Storage

Abstract The effect of heat treatment (75 °C) and spray drying with the addition of Arabic gum (inlet/outlet air temperature 180/75 °C), on the diastase activity of multifloral honey (MH) and rape honey (RH) was investigated. The physical properties of the powders (particle size and morphology, water content and activity, bulk loose and tapped density, angle of repose, hygroscopicity) directly after drying and after 12 weeks of storage were studied. During heat treatment, diastase activity decreased gradually, to decline below limit values after 180 min. Diastase activity in the powders was lower than in fresh honeys, but it was concluded that temperature was not the only factor affecting this decrease. Powders were characterized by low water content and medium flowability, which was improved after storage due to particle size increase. Diastase activity in powders was stable during storage.

Mathematical Modeling of Actinidia arguta (Kiwiberry) Drying Kinetics

Abstract Consumers and scientists exhibit a growing interest in bioactive ingredients of natural origin with strong pro-health effects. Such properties have been found in fruits of of Actinidia argute, commonly known as kiwiberry (mini kiwi or hardy kiwi). Appropriate methods and parameters of the drying process enable obtaining a product with preserved high pro-health properties. The obejctive of this paper was to study the influence of the selected drying methods on the drying kinetics of actinidia. Commonly known mathematical models were used to describe the process. The kinetics of convective, microwave-convective, infrared and vacuum drying was investigated. The process was performed until samples reached dimensionless moisture ratio (MR) of 0.02. The quickest method was vacuum drying reaching moisture ratio target after 286 min, and the slowest was convective drying characterized by 1352 min of drying. In general, Midilli et al.’s model was evaluated as the most adequate for description of the moisture transfer in the fruit samples.

Mass Transfer in Osmotic Dehydration of Kiwiberry: Experimental and Mathematical Modelling Studies

The aim of this study was to analyze the impact of osmotic solutions and temperature on the osmotic dehydration (OD) of two cultivars of kiwiberry. OD was carried out in sucrose, xylitol and maltitol solutions at 30 °C and 50 °C, respectively. The process of osmotic dehydration was described by the means of water loss (WL), solid gain (SG), weight reduction (WR), and water content changes. Moreover, dehydration was described by mathematical models often used in the literature. The highest WL, WR and SG values were observed for samples treated by xylitol and maltitol at 50 °C. The statistical analysis of the mathematical modelling of the process showed that in most cases, the Peleg’s equation exhibits better fitting for the experimental data.

Effect of Processing Conditions on Microstructure and Pasting Properties of Extrusion-Cooked Starches

Abstract The aim of the work was to investigate the effect of extrusion-cooking process conditions on the structure and pasting properties of starch extrudates. In addition, the extrudates structure was observed using scanning electron microscopy (SEM) and confocal laser microscopy (CSLM). Wheat, corn and potato starch were extrusion-cooked with different process parameters (moisture content, screw speed, process temperature) in a single screw extruder. Results showed influence of the process parameters on extruded starches pasting properties. Viscosity measurements indicated that water content during starch extrusion is more important than process temperature. The extrudates structure observed with scanning electron and confocal laser microscopes showed that the main effect of extrusion-cooking was loss of the crystalline structure of the starch and the formation of a cellular structure of the extrudates. In extrudates processed at higher starch moisture content reduced the quantity and diameters of created cells was observed.