Moisture Loss as Related to Heating Uniformity in Microwave Processing of Solid Foods

Abstract

Moisture loss due to internal evaporation and its relationship to nonuniformity of heating in microwave reheating of high moisture solid foods was studied. A simple heat and mass transfer model was developed that excluded diffusional limitations of moisture movement. Microwave absorption and some dielectric and thermal properties were measured as input parameters to the model. Effect of varying microwave penetration with moisture level and temperature was included. For smaller total moisture loss, typical for a reheating application, predictions of total moisture loss and temperatures matched well with experimental data. Most of the moisture loss occurred from the edges due to higher temperature at these locations. Uniformity of heating to achieve a given average temperature is the key variable controlling total moisture loss. When starting from a frozen material, heating is much more nonuniform, leading to a greater moisture loss. As surface area increases for a given volume, uniformity of heating increases and the total moisture loss reduces. This simple model can be an effective tool in computer‐aided optimization of food products and processes.

Cooking Pattern and Quality Properties of Ground Pork Patties as Affected by Microwave Power Levels

“…This result probably may be caused by the edge overheating effect. Similar results were reported by Ni et al (1999), who found that most of the moisture loss occurred from the edges due to higher temperature at these locations. Fat content of patties cooked at 360 W was higher (p<0.05) at the edges than at the center position.…”

“…A sharp edge or corner will act as an antenna and attract more energy than the surrounding areas (Ohlsson and Bengtsson, 2001;Ohlsson and Risman, 1978). These effects are well documented in many literatures (Chamchong and Datta, 1999;Ni et al, 1999;Ohlsson et al, 1974;Zeng and Faghri, 1994). Zeng and Faghri (1994) studied thawing patterns for cylindrically-shaped tylose samples with different aspect ratios.…”

“…The boiling temperature of water is 100 o C; thus, when this temperature is reached, all additional absorbed microwave energy is expected to contribute to the evaporation of water. Therefore, the temperature is maintained near 100 o C (Chamchong and Datta, 1999;Ni et al, 1999). Differences in mean temperature between the edge position and the center position and their standard deviation resulted in non-uniformity in microwave cooking (Fig.…”

“…When the edge position of the patty reached to near 100 o C, its non-uniformity had the highest, and then gradually decreased with increasing cooking time, regardless of microwave power level. According to Ni et al (1999), since everywhere in the food tends to reach approximately the boiling temperature of water, temperature non-uniformity eventually starts to decrease. As expected, maximum temperature differences and standard deviation of differences in temperature between at the edge position and at the center position were observed in patties cooked at 900 W. Conversely, non-uniformity of temperature was lower at reduced power levels and was the lowest in patties cooked at 360 W. These results are due to the increased diffusion energy transfer, resulting in more uniformity of temperature.…”

Numerical solution of coupled mass and energy balances during osmotic microwave dehydration

“…The behavior of the electromagnetic field inside the microwave oven is very complex; then it can be used an approximation that considers an exponential decay inside the food, the Lambert's law [6,7].…”