DDGS中水溶性成分比例与吸湿平衡的关系及其模型拟合

Modeling Effects of Water Soluble Part in DDGS on Moisture Sorption Isotherms

可再生的燃料酒精产量剧增导致其主要副产品（干酒糟/DDG和含可溶物的干酒糟/DDGS）产量迅速增加。但对其吸湿解吸平衡的研究报道非常少。吸湿解吸平衡与其持水力和加工与贮存性能密切相关。采用静态平衡重量法,利用饱和盐溶液制备了11个相对湿度环境（11.3%~97.3%,对应的水活度（wateractivity,Aw）为0.113~0.973）,研究比较了市场上4种不同DDGS在常压下25℃时的吸湿平衡,比较了9个模型的拟合效果,并将水溶性成份比例（water soluble part,WSP）作为变量纳入模型。平衡含水率随WSP含量的增加而上升,随湿度的增加其平衡含水率的差异迅速扩大。BY、GDW、GAB、Oswin和Lewicki模型较好地模拟了单一DDGS的吸湿平衡结果,而引入WSP变量后改进BY模型（mBY）具有最好的拟合精度（R2=0.9983,平均相对偏差P=4.29%）。其次为改进的Peleg、GDW、GAB、Oswin和Lewicki。Henderson、Halsey和Chung-Pfost模型及其改进型拟合程度不佳。WSP含量与中性洗涤纤维含量线性负相关。由GAB估计的单层水随WSP线性增加。

Dramatic increasing production of ethanol as a renewable fuel resource consequently boosts the output of the key coproduct,dried distiller grains with solubles（DDGS）.Extensive work has been carried out on its application to animal feeds,but study on its moisture sorption behavior is far limited.Moisture sorption equilibrium is closely related to water binding capacity,processing performance and storage.This study compared the sorption isotherms at 25℃ of four different DDGS,using the gravimetric methods with 11 relative humidity points（11.3%~97.3%,or water activity,Aw,0.113~0.973） created by saturated salt solutions.Nine regression equations and relevant modified forms with water soluble part（WSP,%） incorporated were evaluated.Results：Equilibrium moisture content（EMC,%,dry basis） increases with higher WSP.The difference in EMC expands in higher water activity range.BY,GDW,GAB,Oswin and Lewicki equation fit well the sorption of individual DDGS.The fitness（R2 is 0.9983,mean relative deviation P is 4.29%） by modified BY（mBY） ranks the first among all the modified forms,followed by mPeleg,mGDW,mGAB,mOswin and mLewicki.Both the original and the modified form of Henderson,Halsey and Chung-Pfost model give much less fitting goodness.WSP linearly decreases with increasing neutral detergent fiber（NDF）.The monolayer moisture content estimated by GAB model increases linearly with increasing WSP.