The effect of encapsulants on the heat of sorption in vacuum-dried cajá powder

ABSTRACT Equilibrium moisture data from the powdered pulp of Spondias mombin, L., both with and without additives - 58% maltodextrin (MD) or 58% gum arabic (GA) - were determined at 20, 30, 40 and 50 °C, using the static gravimetric method for a water activity range of 0.06 to 0.90. The resulting isotherms were sigmoidal and typical Type III, with the Guggenheim-Anderson-de-Boer model (GAB) adjusted to the experimental data for equilibrium moisture vs water activity. The addition of additives was shown to affect the isotherms in such a way that, for the same water activity, samples of CP+GA and CP+MD showed a lower equilibrium moisture content and were not affected by the variations in temperature. The isosteric heat of sorption for the cajá powder with additives was greater (less negative) than that of the cajá powder with no additives, suggesting that polar sites in the product without the addition of GA or MD are more active. An empirical exponential relationship can describe the dependence of the heat of sorption as a function of the moisture content of the material.

摘要：本研究采用静态重量法（static gravimetric method），在20、30、40与50℃条件下，对未添加添加剂、添加58%麦芽糊精（maltodextrin, MD）或58%阿拉伯胶（gum arabic, GA）的刺黄果（Spondias mombin L.）浆粉的平衡水分数据进行测定，测试覆盖的水分活度（water activity）范围为0.06~0.90。所得吸附等温线（isotherms）呈S形，属于典型的第Ⅲ类等温线；研究采用Guggenheim-Anderson-de-Boer模型（GAB模型）对平衡含水率与水分活度的实验数据进行了拟合。结果表明，添加剂的添加会对吸附等温线产生显著影响：在相同水分活度下，CP+GA与CP+MD样品的平衡含水率更低，且不受温度变化的影响。添加了添加剂的卡雅粉（cajá powder）的等量吸附热（isosteric heat of sorption）高于未添加添加剂的卡雅粉（负值更小），这表明未添加GA或MD的样品中极性位点活性更强。吸附热随物料含水率的变化规律可通过经验指数关系进行描述。