Theoretical reasons for rapid heating of vegetable oils by microwaves.

Water and high-moisture foods are readily heated in microwaves due to their relatively high dielectric loss factors. Vegetable oil, on the other hand, has a much smaller loss factor (about 1/100th that of water), and is generally believed to be unsuitable for microwave heating. In this study, we conducted experiments to compare heating rates between vegetable oil and pure water in a 2450 MHz microwave oven. We found that the vegetable oil samples were heated rapidly in microwaves, and even faster (1.4-2.0 times) than the water samples. To provide a theoretical explanation, we developed a 3-D computer simulation model. The simulation revealed an approximately 10-fold stronger electric field in oil compared to water, resulting in a similar amount of microwave power being absorbed by the oil and water samples. As the absorbed microwave power was converted into thermal energy, the oil samples were heated faster due to their smaller specific heat (1/2 that of water). But we also found that when the dimensions of oil are smaller than half the microwave wavelength, oil is heated slower than water due to the absence of hot spot areas. This study provides a theoretical explanation for microwave heating of vegetable oils and demonstrates opportunities for utilizing microwave energy to electrify industrial heating of vegetable oils.

Optimization of Shea (Vitellaria paradoxa) butter quality using screw expeller extraction.

The quality of Shea butter is highly affected by processing factors. Hence, the aim of this work was to evaluate the effects of conditioning duration (CD), moisture content (MC), and die temperature (DT) of screw expeller on Shea butter quality. A combination of 33 full factorial design and response surface methodology was used for this investigation. Response variables were refractive index, acid value, and peroxide value. The model enabled to identify the optimum operating settings (CD = 28-30 min, MC = 3-5 g/100 g, and DT = 65-70°C) for maximize refractive index and minimum acid value. For minimum peroxide value 0 min CD, 10 g/100 g MC, and 30°C were discovered. In all-over optimization, optimal values of 30 min CD, 9.7 g/100 g MC, and 70°C DT were found. Hence, the processing factors must be at their optimal values to achieve high butter quality and consistence.