Water Activity Adsorption Isothems And Laws In Quality Change Of Four Mouldy Feedstuffs In Common Use

Four feedstuffs in common use (maise, soybean meal, rapeseed meal and fish meal) water activity adsorption isotherms and laws in quality change of mouldy were researched in this paper. Two trials were carried out to study the water activity adsorption isotherms and laws in quality change of four moulding feedstuffs.In the first trial, four feedstuffs water activity adsorption isotherms were studied and the most adaptable equation of five mathematical models to match the isotherms was evaluated at temperature of 25±1℃, 17±1℃and 11±1℃, respectively. The results showed that Chungfost model could be most adaptable for fitting adsorption isotherms of maise at the temperature of 25±1℃and 17±1℃, and at 11±1℃condition is the line model; Halsey model could be most adaptable for fitting adsorption isotherms of soybean meal at the temperature of 25±1℃, Henderson model could be the most adaptable at 17±1℃, and at 11±1℃condition is the Line model; Henderson model could be the most adaptable to match the isotherms at every temperature we studied; Halsey model could be most adaptable for fitting adsorption isotherms of fish meal at temperature of 25±1℃, and at 17±1℃is the Chungpfost model, at 11±1℃is the Henderson model. The water activity adsorption isotherms equation was established with the most adaptable model at temperature of 25±1℃, 17±1℃and 11±1℃respectively, and the relative safety moisture content and absolute safety moisture content was calculated: The relative safety moisture content of maise was 10.94%, 11.18%, and 12.38% at temperature of 25±1℃, 17±1℃and 11±1℃respectively, the absolute safety moisture content was 12.67%, 12.94% and 14.13% at temperature of 25±1℃, 17±1℃and 11±1℃respectively; The relative safety moisture content of soybean meal was 9.36%, 10.00%, and 12.37% at temperature of 25±1℃, 17±1℃and 11±1℃respectively, the absolute safety moisture content was 12.59%, 12.78%, and 14.12% at temperature of 25±1℃, 17±1℃and 11±1℃respectively; The relative safety moisture content of rapeseed meal was 8.70%, 9.52%, and 10.22% at temperature of 25±1℃, 17+±1℃and 11±1℃respectively, the absolute safety moisture content was 11.13%, 11.80%, and 12.33%; The relative safety moisture content of fish meal was 8.39%, 9.64% and 10.83%.In the second trial, distilled water and suspend solution of mold spore were added in the feedstuffs and the samples were stored in constant temperature and humidity box at condition of temperature at 28±1.5℃and humidity at 65% to 85% for a period in order to study the laws of quality change of double-low rapeseed meal molding. The results showed that with increase of storage time the crude protein, zearalenone content and aflatoxin B1 of soybean meal, rapeseed meal and fish meal of the samples have no change; and with increase of storage time, water content and water activity showed tendency to decrease first, then increased; but the molds amount, fatty acid value and volatile basic nitrogen content of maise, soybean meal, double-low rapeseed meal and acid value of fish meal increased first, then decrease subsequently; the concentration of ether extract, true protein and starch always showed tendency to decrease; and TBA value, aflatoxin B1 content of maise showed tendency to increase.