Experimental Studies On The Microwave-Assisted Foam-Mat Drying Of Corn Soaking Water To Produce Yeast Protein Powder

Corn soaking water is rich in kinds of nutrients, and is considered the best material for producing yeast protein powder. However, there is not the effective technology to process this soaking water in meadium and small scale factories. Thus, a large amount of soaking water is discharged directly to the surroundings, which cause a waste of resources and environmental pollution. This study investigated the use of microwave assisted foam drying of corn soaking water to produce the yeast protein powder, with the purpose of getting a new method of processing the corn soaking water.In the experiments about effects of the ratio of carbon and nitrogen on solid content in the fermentation broth,6%glucose and0.2%urea was selected as the carbon source and the nitrogen source, respectively, to add to the corn soaking water under various volume proportions. The results showed that when the proportion of carbon and nitrogen at10:30(v/v), the solid content can be reached up to1.24%in fermentation broth, the solid content of which was higher than other experimental proportions.In the foaming experiments, the corn soaking water was foamed by the addition of glyceryl monostearate (GMS) and soy protein isolate (SPI) at various concentrations, and the foam was stabilized with the addition of methyl cellulose at0.5%concentration. The study proved that the reasonable foaming properties were obtained by treating the corn soaking water with GMS (6%), SPI (6%) and methyl cellulose (0.5%), as well as whipping6min.Based on the results of microwave drying characteristics of foamed corn soaking water, the microwave power, material mass and thickness had great effects on the final moisture content and drying rate. As the increase of microwave power and the decrease of material amount and material thickness, the final moisture content decreased gradually. As the increase of microwave power, material mass as well as the material thickness, the drying process presented by three stages involving in the preheating, drying at constant rate and drying at decelerating rate.A response surface analysis method with four factors and five levels was applied to optimize the drying parameters by integrated indicator of color, final moisture content (d.b.), and the protein content, and the corresponding regression models were established. The results showed that the microwave power, sample load and the time had significant influences on the color and moisture content, the drying time had significant influenceson protein content, The reasonable technologic conditions of drying method were obtained as follows:the microwave power was560W, sample mass was46.88g, the drying time was8.01min, and the thickness of foamed corn soaking water was6.20mm. The parameters were reasonable according to verification experiment.This experiment studied the variation of temperature and moisture distribution of the fermentation broth of corn soaking water dried with microwave-assisted foam. Microwave absorption capacity as a moment amount is related to the dielectric properties, temperature and the moisture content of the material. Then analysis were done to the temperature and dielectric properties of the fermentation broth, finally the curve of dielectric constant and dielectric loss factor with time were obtained, and the relationship between moisture content, temperature and ε, ε were analyzed. Following, the experimental datas were fitted and the fitting equation were obtained, further more, effect surface charts between thickness and temperature, moisture content were obtained.