Physicochemical properties and food bolus properties in black-rice formula prepared with different powder size

Abstract

Black rice (Oryza sativa L.) is popular in Asian countries where it is often mixed with white rice prior to cooking to enhance the flavor, color, and nutritional value. It is intensely colored because of anthocyanins (e.g., cyanidin 3-glucoside and peonidin 3-glucoside) found in the surface cells of the grain. It has a number of nutritional advantages over common rice, such as higher protein, total essential amino acids, vitamin B1, and minerals (Fe, Zn, Mn, and P), the latter of which varies with cultivar and production location. The main goal of food oral processing is to prepare a food bolus suitable for deglutition. The bolus preparation consists in food breakdown and processing during which oral sensations are generated. Before swallowing, the food is reduced into small particles that form a cohesive mixture with saliva and the liquid released from the food itself. The resulting bolus can flow smoothly and safely down along the pharyngeal walls during deglutition. The objective of this study was to investigate the physico-chemical, thermal and rheological properties of black rice fractions, and to analyze food bolus properties in black rice formula prepared with different powder size. In the first chapter of this study prepared the black rice powder milled with different powder sizes at the range of 11.20 to 177.06 μm, and studied the physico-chemical properties made with the black rice flour and the dispersion properties made with the black rice flour using by Turbiscan Lab. As a results were indicated that decreased particle size was increased amylose contents. The decreased particle size was indicated decreased water binding capacity and fat binding capacity. Damaged starch granules resulted from mechanical grinding of jet mill during milling. The amount of damaged starch, which resulted from jet milling, increased in smaller black rice fractions and affected to dispersion stability. In the second chapter of this study, the black-rice flour was fractionated into seven parts: 11.20, 12.66, 16.97, 33.80, 35.41, 97.80 and 177.07μm. The thermal properties of formula made with different sizes of the black rice flour were measured by using differential scanning calorimetry and the visco-elastic properties of each formula were measured using by Turbiscan rheoLaser Lab. In addition, the flavor-releasing pattern of black rice formula was measured by using electronic nose. The thermal transitions were occurred between 65.75℃ to 71.11℃ as determined by DSC. The rheological properties of black rice formula made with fine particle fraction had a high viscoelastic characteristic compare to the coarse fraction. The pattern recognition analysis based on discriminant function analysis showed that the 35.41 and 97.80 μm sample has a difference flavor (electronic nose) pattern. In the third chapter of this study was performed to examine the different particle size in the bolus formed by semi-solid food as black-rice formula. Six young subjects with normal oral cavity were asked to chew the food and to expectorate the bolus just before swallowing, while oral processing parameters were observed. The collected saliva (un-stimulated or stimulated) sample was studied by pH value, saliva secretion and flow rate between the subjects. And then, the each black-rice formula bolus of different particle size was evaluated by pH value, saliva amylase activity and visco-elasticity property. As a result, both of saliva parameters for stimulated saliva and for un-stimulated saliva, does not significantly resulted in values between genders. However, significant subject and stimulation effects (p <0.05) were observed for pH, saliva secretion and Flow rate. In addition, the decreased particle size of black-rice formula samples affected pH value and viscosity property of food boli.