Volker Gaukel

Enhancement of convective drying by application of airborne ultrasound – A response surface approach

Drying is one of the oldest and most commonly used processes in the food manufacturing industry. The conventional way of drying is by forced convection at elevated temperatures. However, this process step often requires a very long treatment time, is highly energy consuming and detrimental to the product quality. Therefore, an investigation of whether the drying time and temperature can be reduced with the assistance of an airborne ultrasound intervention is of interest. Previous studies have shown that contact ultrasound can accelerate the drying process. It is assumed that mechanical vibrations, creating micro channels in the food matrix or keeping these channels from collapsing upon drying, are responsible for the faster water removal. In food samples, due to their natural origin, drying is also influenced by fluctuations in tissue structure, varying between different trials. For this reason, a model food system with thermo-physical properties and composition (water, cellulose, starch, fructose) similar to those of plant-based foods has been used in this study. The main objective was, therefore, to investigate the influence of airborne ultrasound conditions on the drying behaviour of the model food. The impact of airborne ultrasound at various power levels, drying temperature, relative humidity of the drying air, and the air speed was analysed. To examine possible interactions between these parameters, the experiments were designed with a Response Surface Method using Minitab 16 Statistical Software (Minitab Inc., State College, PA, USA). In addition, a first attempt at improving the process conditions and performance for better suitability and applicability in industrial scale processing was undertaken by non-continuous/intermittent sonication.

Characterization of the spray drying behaviour of emulsions containing oil droplets with a structured interface

The aim of this study was to characterize the process of atomization and drying of layer-by-layer emulsions containing lecithin (single layer emulsion) and lecithin/chitosan (bilayer emulsion) and the oxidative stability of the microcapsules during storage. For this purpose, the analysis of the emulsion spray droplet size during two-fluid nozzle and rotary atomization was carried out to identify suitable process parameters. The drying behaviour of single and bilayer emulsions was investigated by calculation of the volume flow density during single-droplet drying during acoustic levitation. In spray-dried solid particles, the oxidative stability in the single layer microcapsules was higher than in the bilayer microcapsules. This was partly attributed to lower microencapsulation efficiency in the bilayer microcapsules compared to the single layer microcapsules. Furthermore, it could be shown, that excess chitosan in the bulk carrier matrix affects the free volume elements and thus oxygen diffusion.

Investigating the dynamics of recombinant protein secretion from a microalgal host.

Production of recombinant proteins with microalgae represents an alternative platform over plant- or bacterial-based expression systems for certain target proteins. Secretion of recombinant proteins allows accumulation of the target product physically separate from the valuable algal biomass. To date, there has been little investigation into the dynamics of recombinant protein secretion from microalgal hosts-the culture parameters that encourage secreted product accumulation and stability, while encouraging biomass production. In this work, the efficiency of recombinant protein production was optimized by adjusting cultivation parameters for a strain of Chlamydomonas reinhardtii previously engineered to secrete a functional recombinant Lolium perenne ice binding protein (LpIBP), which has applications as a frozen food texturing and cryopreservation additive, into its culture medium. Three media and several cultivation styles were investigated for effects on secreted LpIBP titres and culture growth. A combination of acetate and carbon dioxide feeding with illumination resulted in the highest overall biomass and recombinant protein titres up to 10mgL(-1) in the culture medium. Pure photoautotrophic production was possible using two media types, with recombinant protein accumulation in all cultivations correlating to culture cell density. Two different cultivation systems were used for scale-up to 10L cultivations, one of which produced yields of secreted recombinant protein up to 12mgL(-1) within six cultivation days. Functional ice recrystallization inhibition (IRI) of the LpIBP from total concentrated extracellular protein extracts was demonstrated in a sucrose solution used as a simplified ice cream model. IRI lasted up to 7 days, demonstrating the potential of secreted products from microalgae for use as food additives.

Effects Of Spray Drying On Physical Properties, Total Phenolic Content And Antioxidant Activity Of Carob Molasses

Abstract In the present study carob molasses (pekmez) was spray dried to obtain a powder with desired improved handling properties. Maltodextrin with dextrose equivalent (DE) values of 8.6, 15.3 and 18.6 was used as a drying agent. Different molasses to maltodextrin ratios (25:75, 50:50), and dryer air inlet temperatures (160 °C, 210 °C) were additional parameters. The spray dried powders were analyzed for glass transition temperature, moisture content, water activity, wetting behavior, particle size, color, total phenolic content and antioxidant activity. The expected increasing effect of decreasing DE value on the glass transition temperature was obscured by different moisture contents. The glass transition temperature was mainly lowered by increasing the pekmez to maltodextrin ratio but also by increasing the air inlet temperature resulting in increasing moisture content. Wetting behavior was strongly influenced by the DE value. Total phenolic content was reduced in general by about 10 % and antioxidant activity changed by about 20 % independent from the investigated parameters. It can be concluded that spray drying of pekmez with addition of maltodextrin is a suitable method to improve and adjust handling properties of pekmez without loss of its nutritional value.

How to Meet the Freeze Drying Standard in Combined Drying Processes: Pre and Finish Drying of Carrot Dice

Freeze-drying (FD) processes are well known to produce high-quality consumer products. Major problems are long drying times, high investment costs, and resulting maintenance and operating costs that make FD a very costly process. In this study, the potential of air drying (AD) and microwave vacuum drying (MVD) is tested to reduce freeze-drying times and make better utilization of the investment by combining FD with alternative lower cost drying processes using a pre or finish drying step while preserving the qualwity of the final product. Using carrot dice as a sample product, predrying did not lead to the desired qualities and reduction in drying time, whereas finish drying produced promising results. FD/MVD was 40% faster than pure FD and achieved freeze-drying standards regarding volume retention, shape, color, and rehydration. The good performance of microwave vacuum finish drying can directly be traced back to a time effect that is possibly linked to a characteristic collapse time of the cellular matrix. In order to use this effect, a stable skeleton must have developed at the point of process changeover, changeover has to be immediate, and finish drying has to be quick.

APPARENT SPECIFIC HEAT CAPACITY OF CHILLED AND FROZEN MEAT PRODUCTS

In this article, apparent specific heat capacities of meat and meat products, minced beef, hamburger patties, soudjouk, minced turkey meat, turkey sausage, and turkey soudjouk, were measured at temperatures ranging from −60°C to +40°C, using a differential scanning calorimeter. Experimental data were compared with values calculated from different predictive models given in the literature. Measured apparent specific heat capacities were also mathematically interpreted as a function of temperature, moisture and fat content by application of nonlinear regression analysis for frozen and unfrozen samples. The developed models were found to be in good agreement with the experimental data.

Food Freezing: Crystal Structure and Size

The quality of frozen food products is strongly dependent on the ice crystal size and shape. In ice cream, for example, the size distribution of ice crystals has a significant impact on smoothness, meltdown, and cooling properties. Therefore, controlling the size and shape of ice crystals in frozen foods is a primary concern to the food industry. This article gives a short review on ice crystal morphology and the factors influencing ice crystal shape and size. In addition some brief fundamentals about crystallization are given.

Serial combination drying processes: A measure to improve quality of dried carrot disks and to reduce drying time

ABSTRACT Conventional drying processes like hot air-drying (HAD), freeze-drying (FD) and microwave vacuum drying (MVD) have specific advantages and disadvantages concerning product quality and drying time. Recent studies have shown that serial combinations of these processes can lead to better product quality (water content, color, hardness, rehydration, volume, and ingredient retention) and favorable process parameters (shorter time, less energy consumption). However, little is known about the timing of the changeover point between the different processes. In this study, we investigated the development of quality parameters (volume retention, rehydration properties) during FD, HAD, and MVD either as a single or as a serial combination process with varying changeover point. Therefore, carrot disks were processed in a modular drying processor to different final relative moisture contents. On this basis, recommendations were derived for certain combinations of drying processes to achieve desired product quality parameters, partially with shorter drying times.

Investigation on the Usage of Effervescent Atomization for Spraying and Spray Drying of Rheological Complex Food Liquids and on the Resulting Particle and Product Properties

The effervescent atomizer is an internal mixing pneumatic atomizer in which a two-phase flow prior to the nozzle orifice is created by adding gas in a mixing chamber. The resulting flow pattern is responsible for atomization of the liquid feed. In this study, two different single-phase and two multiphase model feeds were employed. Research was focused on the influence of the flow pattern inside the atomizer and the air-to-liquid ratio by mass (ALR) on the spray performance. The flow pattern inside the mixing chamber of the atomizer was recorded by high-speed cameras, while the one inside the nozzle orifice was determined by an optical sensor. Plug and annular flow was found in the mixing chamber, while a bubbly flow—reported for low viscous liquid feeds in literature—could not be formed due to the feed viscosity investigated in this study. The spray morphology investigations (shadowgraphy imaging and time-resolved spray drop size measurement) showed a clear connection of flow pattern and spray fluctuations. The latter are found for plug flow and have to be avoided for spray drying applications. Annular flow was found to be suitable for fine and stable spray characteristics and consequently atomizer geometry and ALR conditions for annular flow were determined. Moreover, the models of Lund and Geckler [J Fluids Eng 130:61303, 2008, Atomization Sprays, 3:77–89, 1993] were used to predict spray drop sizes. The comparison of these values to measured data gave additional insight in the spray mechanism. To investigate the influence of the atomization process on an inner phase of a multiphase feed, oil-in-water-emulsions were atomized and changes in the oil drop size were determined. Oil drop breakup and coalescence was found and could be described by classical emulsification theory. Finally, the investigated effervescent atomizers were used for spray drying experiments with single-phase feeds. The particle characteristics of the dried products were determined and showed a good agreement with the literature.

Influence of Working Parameters and Primary Breakup Conditions on the Quality of Twin-Fluid Atomizers Spray Quality

In this study we investigated four twin-fluid atomizers with different internal mixing mechanisms: Y-jet, outside in gas (OIG), outside in liquid (OIL) and CFT atomizers. The main goal was to relate the measured droplet sizes, characterized by the Sauter mean diameter (ID32), to the corresponding working regimes of atomizers and primary breakup conditions characterized by the criterion Dmax, estimated from critical Weber number of the primary breakup. For the OIL, OIG and CFT atomizers, the common relation of the primary breakup characteristics and normalized droplet sizes (ID32/Dmax) was found. As the Y-jet atomizer showed a different trend, which was related to the considerably lower Weber numbers of the near-nozzle flow, a change in the normalization criterion was necessary to obtain similar results as for other tested atomizers. The main benefit of presented results is the potential to predict spray droplet sizes entirely from primary breakup characteristics regardless of the atomizer’s design or the atomized liquid.