RHEOLOGICAL AND PHYSICOCHEMICAL PROPERTIES OF SOME CUSTARD MODEL SYSTEMS

摘要

ab:The custards are semisolid dairy desserts of wide consumption in some countries, including Mexico. This product is composed of milk, starch, hydrocolloids, sugar, colorants and aromas. It is a dairy product with limited information about its characteristics. The objective of this research was to study the properties of some custard model systems, following a factorial design, with 4 variables: starch, gum, sweetener and flavor, in two groups. Formulated systems were analyzed during four weeks of storage at 5 deg C. The obtained results indicated that acidity, color, pH, moisture and density, did not change through the storage. Acidity and pH showed some changes during the storage, but there was not significant difference (p>0.05). Net color difference exhibited a small change, with values 0-5. Adhesive and compressive forces, and serum separation showed significative effect of storage time, with a decreasing trend, as consequence of structural modifications. Syneresis augmented significantly, from 0-16% a the beginning, up to reach 30-60% at the fourth week. All the formulated systems behaved as non-Newtonian fluids and exhibited thixotropy in which the starch influenced the rheological response. Flow properties varied importantly as a functionof the storage time and composition; most of the systems exhibited yield stress and were fitted by the Herschel-Bulkley equation. The flow behavior index did not change significantly with the storage, in contrary to the consistency coefficient and yieldstress, in which a decreasing trend was observed. From the viscoelastic response, a weak gel was identified. Sensorial assessment did not show differences between custard systems with sucrose and fructose.