Determination of moisture sorption isotherms of wheat germ in different temperatures and investigation of oxidation properties

The aim of this study was to determine the moisture sorption isotherms of wheat germ at different temperatures and investigate the oxidation properties. Wheat germ is separated during flour production process and generally recognized as a source for animal feed. Due to the improvements in food technology and healthier food perception of society, many research are conducted in recent years to utilize wheat germ as a food source. The studies basically focus on enriching food products by addition of wheat germ into the formula but rapid rancidity of the germ, which has high oil content, causes a the major problem. In literature review it was seen that, decreasing rancidity degree of wheat germ was generally achieved by limiting enzyme activities by various stabilization methods while there was no study about relations between sorption isotherms and oxidation properties of wheat germ. The study contains two stages which are determining moisture sorption isotherms of wheat germ and investigation of oxidation properties in determined monolayer moisture content. In the first stage, the sorption isotherms of wheat germs at 15, 25 and 35°C were determined and adaption of obtained data to various sorption equations were investigated to determine the monolayer moisture content and the best fitting equations. In the second stage of the study, the samples were stored in 2 different moisture content (monolayer moisture content, 4.25 g water/ 100g dry matter and natural moisture content, 14.39 g water/ 100g dry matter) and in 2 different temperature values (4 °C and 25 °C) for 28 days and analysed in day 0, 7, 14, 21 and 28 for moisture content, water activity, pH value, titration acidity, free fatty acid content, peroxide value, iodine number and specific absorbance value. The sorption isotherms of the wheat germ at 15, 25 and 35 °C were determined as Type II by the evaluation of obtained data. It was revealed that the Halsey equation is the most suited to the wheat germs among the studied sorption equation and the average monolayer moisture content (on g.moisture/100 g dry basis) of the wheat germ was determined as 4.10 and 4.40 by means of the BET and GAB equations and constants, respectively. It was determined that the moisture content and water activity of the samples stored in the monolayer moisture content increased from 4.55 to 6.41 g.moisture/100g dry basis and from 0.24 to 0.36 during the storage, respectively. The moisture content and water activity of the samples stored in the natural moisture content were not affected by the storage process and it was noted as an average of 14.39 g.moisture/100g dry basis and 0.68, respectively.Titration acidity values were determined lower in monolayer moisture content in respect to storage moisture content and in 4 °C in respect to storage temperature while there was no change in pH value depending on storage moisture content and teperature. Titratable acidity of the wheat germs had increased from 0.48 to 0.59 and pH values decreased from 6.55 to 6.47 accordingly during storage. Iodine number of samples stored at 4°C with monolayer mositure content were determined higher than the samples stored at 25°C with natural moisture content and it decreased from 134.65 to 125.98 during storage. Free fatty acid content, peroxide value and specific absorbance (K232) value of wheat germ samples stored at 4°C with monolayer moisture content were determined lower than the samples stored at 25°C with natural moisture content. Free fatty acidity (oleic acid %), peroxide value (O2 mEq/ kg oil) and specific absorbance value of samples increased during storage period from 2.56 to 20.41, 1.87 to 8.63 and 0.37 to 0.84, respectively. As a result, storage of impermeably packaged wheat germ in low temperature and monolayer moisture content (4.10-4.40 g.moisture/100g dry basis) is an applicable method to decrease degree of rancidity and prolong shelf life.