Michael Bantle

Parametric Study of High-Intensity Ultrasound in the Atmospheric Freeze Drying of Peas

Atmospheric freeze drying (AFD) is a dehydration process that can be used to produce high-end products for the food, pharmaceutical, and biological industries. Evaporation or sublimation at the drying temperatures used for these processes is generally low. Airborne ultrasound can be used to increase drying rates. This parametric study investigates the influence of the drying temperature, drying time, and ultrasonic power for atmospheric freeze drying in the presence of an airborne ultrasonic field. Accelerated effective diffusion of up to 14.8% was obtained for atmospheric freeze drying with a fluid bed. The faster drying in ultrasonic-assisted atmospheric freeze drying is assumed to be due to a higher mass transfer rate at the solid-gas interface, caused by a reduced boundary layer due to a higher turbulent interface. Thus high intensity, airborne ultrasound used with modern drying systems has great potential to accelerate drying, reduce investment and production costs, and improve product quality.

Modification of the Weibull Distribution for Modeling Atmospheric Freeze-Drying of Food

An empirical physical model was derived from the Weibull distribution and investigated for its ability to describe the moisture content for common atmospheric (or convective) freeze-drying processes (AFD). A set of experiments was performed for different products: peas, apple, pineapple, cod, and zooplankton. The effect of drying temperatures (−6°C, −3°C, 0°C, 10°C and 20°C), approach velocities (1 m sec−1, 1.8 m sec−1, 2.6 m sec−1, 3.1 m sec−1, and 4.7 m sec−1), and particle sizes (8.7 mm, 15.7 mm, and 28.8 mm) was investigated using the selected products. Non-linear regression analyses showed good agreement between the model and experimental data. The coefficient of determination was at least 99.9% (R2 > 0.999) and the chi-square lower than 0.0001 (χ2 < 0.0001) for all investigations. The shape parameter β in the modified Weibull model varied in a narrow range from 0.661 to 0.937, which indicates that AFD is controlled by internal mass transfer (=diffusivity). The diffusivity (Dcalc) ranged from 1.554 to 8.681 10−9 m2 sec−1, depending on the product and drying conditions. The modification of the Weibull distribution can be used to describe AFD processes based on a simple empirical but highly accurate model and for the determination of the effective diffusion (Ficks law).

Ultrasonic Convective Drying Kinetics of Clipfish During the Initial Drying Period

A hybrid drying system for high-intensity airborne ultrasound applied in convective drying was investigated for the drying of salted codfish (clipfish). Convective drying with ultrasonic assistance at 10, 20, and 30°C was compared to the same process without ultrasound. The Weibull model was used to model and investigate the drying behavior, and the effective diffusion in Ficks law was determined. The ultrasound decreased the drying time more at lower drying temperatures. The drying time was reduced by over 90% at a drying temperature of 10°C. For an industrial drying process at a temperature of 20°C, the drying time was reduced by 32.2%. The ultrasonic, convective drying of clipfish at a temperature of 20°C was faster than the same process without ultrasound at 30°C. The investigations showed a thermal effect for all products when ultrasound was applied. The specific moisture extraction ratio (SMER) in the investigated system was improved by 0.2 kgwater kWh−1. The heat transfer coefficient in the system used was increased by 32.6% for a heating process in a separate investigation, whereas for a cooling process no increased heat transfer coefficient was determined. The thermal effect might (at least partially) explain the faster drying of ultrasonic-assisted convective drying. The results obtained demonstrate the potential of airborne ultrasound in convective drying with regard to drying time, energy consumption, and product quality. Documentation of the thermal effect should be included in future R&D on this topic.

Properties of Calanus finmarchicus biomass during frozen storage after heat inactivation of autolytic enzymes

Calanus finmarchicus is a marine zooplankton of interest for the aquaculture industry, as well as for nutraceuticals and the cosmetic industry. The chemical composition of C. finmarchicus rapidly changes postmortem due to autolytic processes; in particular phospholipids rapidly degrade to give free fatty acids. The aim of this study was to inactivate autolytic enzymes in C. finmarchicus by applying heat (72°C, 5-30min) through mixing with boiling, fresh water, and further to explore the effects of heat (70°C, 15min) combined with long time storage (-20°C, 12months) of treated and untreated material. Heat treatment (5min) inactivated all tested enzymes and maintained the initial amount of phospholipids, total lipids and crude protein. Storage of untreated material led to complete degradation of all phospholipids, whereas heat treatment resulted in a stable product containing the initial amount of phospholipids and astaxanthin.

Microwave-Assisted Atmospheric Freeze Drying of Green Peas: A Case Study

Atmospheric freeze drying (AFD) is based on the sublimation of ice due to a pressure gradient (convective drying), and is a dehydration process for temperature-sensitive products. Since the process is slow in general, microwave radiation (MW) was applied in order to increase the sublimation in fluid and fixed bed conditions at drying temperatures of −6°C, −3°C, and 0°C. The modified Weibull model was used to describe the drying behavior for all investigations. With 280 Watt power supplied to the magnetrons, it was possible to reduce drying time by approximately 50%. The drying efficiency was approximately 30%, while the SMER was increased by 0.1 to 0.3 kgwaterkWh−1, which gives better energy efficiency for the microwave drying system used in this investigation. The product quality (color reduction and particle size/porosity) was well preserved in fixed bed drying at −6°C and −3°C, while the product quality was reduced significantly in microwave AFD experiments at 0°C and in a fluid bed. The drying rates of AFD in a fluid bed condition were not as high as those in a fixed bed. MW-AFD in a fixed bed condition at temperatures of −6°C and −3°C performed best regarding product quality, drying time, and process control.

A Novel Method for Simultaneous and Continuous Determination of Thermal Properties during Phase Transition Applied to Calanus finmarchicus

The thermal properties of a product are the most important parameters for practical engineering purposes and models in food science. Calanus finmarchicus is currently being examined as a marine resource for uncommon aquatic lipids and proteins. Thermal conductivity, specific heat, enthalpy and density were measured over the temperature range from -40 to +20 degrees C. The initial freezing point was determined to be -2.3 degrees C. The thermal properties were recorded continuously on 4 samples using a new method, and the results were compared with predictive models. The accuracy of the new method is demonstrated by different calibration runs. Significant differences in the thermal conductivity of the frozen material were found between the parallel-series model and the data, whereas the model of Pham and Willix (1989) or the Maxwell-Euken adaption showed better agreement. The measured data for specific heat, enthalpy, and density agreed well with the model. Practical Application: The thermal data obtained can be used directly in food engineering and technology applications, for example, in a thin layer model for freezing food for which precise thermal data for each layer are now available, enabling the more accurate prediction of freezing times and temperature profiles. Dimensionless numbers (such as the Biot number) can also be based on measured data with minor deviations compared to more general modeled thermal properties. Future activities will include the generation of a comprehensive database for different products.

Drying and Chilling/Freezing of Perishable Foods in the Organic Sector

Abstract Organic production is often regarded as more sustainable compared with conventional production. However, in most cases only the primary production step on farm is considered while the postharvest processing is neglected. Even though the sector strives towards sustainable processing, the techniques used in dehydration and refrigeration processes for organic products are often similar to conventional processing whereby opportunities to improve product quality and environmental impact are often ignored. Thus there is a great potential for increasing sustainability. Regarding dehydration, processors of organic products often face restrictions in terms of processing temperatures that could lead to challenges regarding product quality. Big potentials to overcome this issue are increased air velocities to remove the evaporated moisture from the product surface. Even product temperature controlled drying offers big potentials for sustainable processing. Especially sensitive products such as herbs need an appropriate processing and holds several issues. The used refrigerant plays a decisive role in terms of sustainable processing, while good product quality depends mainly on the raw material and in achieving the final storage temperature as fast as possible. Innovations for the organic sector such as superchilling of animal products offer opportunities for extended shelf life under chilling temperature with reduced disadvantageous effects compared with frozen products.