Department of Agricultural, Food and Nutritional Science, University of Alberta, Ag/For Centre 4-10, Edmonton, Alberta Canada T6G 2P5.
Centro de Desarrollo Tecnológico para la Industria Láctea A.C., Camino Ojo de la Yegua, Campo 70, Municipio de Riva Palacio, Chihuahua Mexico.
J Food Sci Technol. 2014 Oct;51(10):2393-403. doi: 10.1007/s13197-012-0765-1. Epub 2012 Jun 26.
Moisture adsorption isotherms of fresh and ripened Mexican Mennonite-style cheese were investigated using the static gravimetric method at 4, 8, and 12 °C in a water activity range (aw) of 0.08-0.96. These isotherms were modeled using GAB, BET, Oswin and Halsey equations through weighed non-linear regression. All isotherms were sigmoid in shape, showing a type II BET isotherm, and the data were best described by GAB model. GAB model coefficients revealed that water adsorption by cheese matrix is a multilayer process characterized by molecules that are strongly bound in the monolayer and molecules that are slightly structured in a multilayer. Using the GAB model, it was possible to estimate thermodynamic functions (net isosteric heat, differential entropy, integral enthalpy and entropy, and enthalpy-entropy compensation) as function of moisture content. For both samples, the isosteric heat and differential entropy decreased with moisture content in exponential fashion. The integral enthalpy gradually decreased with increasing moisture content after reached a maximum value, while the integral entropy decreased with increasing moisture content after reached a minimum value. A linear compensation was found between integral enthalpy and entropy suggesting enthalpy controlled adsorption. Determination of moisture content and aw relationship yields to important information of controlling the ripening, drying and storage operations as well as understanding of the water state within a cheese matrix.
采用静态重量法，在 4、8 和 12°C 下，研究了新鲜和成熟的墨西哥门诺派奶酪的水分吸附等温线，水分活度（aw）范围为 0.08-0.96。通过加权非线性回归，使用 GAB、BET、Oswin 和 Halsey 方程对这些等温线进行了建模。所有等温线均呈 S 形，表现出 II 型 BET 等温线，数据最适合 GAB 模型描述。GAB 模型系数表明，奶酪基质的水分吸附是一个多层过程，其特点是单层中结合紧密的分子和多层中略微结构化的分子。使用 GAB 模型，可以估计热力学函数（净等焓、微分熵、积分焓和熵以及焓熵补偿）作为水分含量的函数。对于两种样品，等焓和微分熵随水分含量呈指数下降。积分焓在达到最大值后逐渐随水分含量的增加而降低，而积分熵在达到最小值后随水分含量的增加而降低。在积分焓和熵之间发现了线性补偿，表明焓控制吸附。确定水分含量和 aw 关系可以为控制成熟、干燥和储存操作以及了解奶酪基质内水分状态提供重要信息。
