| Summary: | 碩士 === 輔仁大學 === 食品科學系碩士班 === 104 === Rapid growth of aging population has become a worldwide issue in recent years. Elders with dysphagia usually face problems such as choking, dehydration, malnutrition and aspiration pneumonia. Thus, precise control of the rheological properties of liquid food with thickener is crucial for the safe consumption. Rheometer is a fundamental-based instrument for measuring the rheological properties of materials. However, it is unaffordable for many demanders and the empirical-based viscometer is an alternative instrument. Therefore, the objectives of this study were to investigate the rheological properties of xanthan gum and guar gum thickened water, commercial milk, soymilk and nutritional supplements; to evaluate the effects of standing time and temperature on the viscosity of both gums thickened drinks using rheometer and viscometer; and to measure the diffusivity parameters of thickened liquid diets using the line spread test (LST) and evaluate their correlation with viscosity values. Results showed that the flow behaviour of drinks thickened with both gums were shear-thinning fluid with yield stress. The liquid diets thickened with both gums showed an increase in the consistency index, yield stress and viscosity with increasing the gum concentration. However, great changes in the shear stress of guar gum thickened drinks at low shear rate were observed. The flow behavior of both gums thickened nutritional supplements were completely different. The viscosity of drinks thickened with xanthan gum did not vary a lot during long term standing, and had higher storage stability, but that of drinks thickened with guar gum increased with time. The viscosity of drinks thickened with both gums was higher at a lower standing temperature and that was lower at a higher standing temperature. However, the viscosity of xanthan gum thickened water solution was stable at different temperature. The viscosity values of thickened drinks measured by viscometer was overestimated as compared with that measured by rheometer. The viscosity values measured by viscometer could be effectively calibrated through the linear equations. The spread diameter of different drinks tested on glass plate was higher than that tested on plastic plate. The yield stress of drinks thickened with both gums had better correlation with LST parameters. The degree of thickness of xanthan gum thickened drinks could better evaluated by LST. This research observed that the solid contents of liquid diets would have different interaction with xanthan gum and guar gum, consequently affecting the rheological properties of different thickened drinks. The viscosity values measured by viscometer could be effectively calibrated through the linear equations. The yield stress of drinks thickened with both gums had better correlation with LST parameters, it could be the standard for viscosity of drinks.
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