Preparation and physicochemical properties of calcium-fortified soymilk powder

Soymilk products can be limited for the relatively low calcium content of soymilk and its unpleasant beany odor in the food industry. In this study, a systematic investigation was made to explore the effects of calcium addition and homogenization pressure on the physicochemical properties, sensory evaluation, and composition of volatile flavor compounds of soymilk powder. Hydroxyapatite (HA) was also taken as a calcium-fortifying agent. The results showed that the addition of calcium decreased the fluidity of soymilk powder, whereas, the wetting and dispersion time increased significantly (P<0.05). The shear viscosity and, the oral friction coefficient increased significantly. The texture was thicker after the soymilk powder was brewed. Homogenization treatment with the 1.5% calcium addition was used to further improve the quality of soymilk powder. Low-pressure homogenization (≤60 MPa) improved the fluidity, wetting, and dispersibility of soymilk powder. The surface of soymilk powder particles was much smoother and slumped less with the increase of homogenization pressure, indicating the spheric-like morphology. Meanwhile, the morphology of powder particles was slightly broken, when the homogenization pressure increased to 80 MPa. Homogenization treatment significantly reduced the viscosity of soymilk after brewing, and the coefficient of oral friction. The smoother taste improved the deterioration of soymilk powder properties and brewing properties caused by calcium fortification. A total of 41 volatile flavor compounds were detected by headspace-solid phase microextraction-gas chromatography-mass spectrometry, including 13 aldehydes, 11 alcohols, 7 ketones, 3 hydrocarbons, 4 esters, and 3 others. The total number of volatile flavor compounds decreased within 26 in the uncalcified soymilk after homogenization. Among them, the relative content of aldehydes significantly (P<0.05) decreased, whereas, the relative contents of alcohols, ketones, and esters significantly (P<0.05) increased. The number of total volatile flavor compounds increased up to 35 with the addition of HA after homogenization. Compared with the unhomogenized calcium-fortified soymilk powder, 20 MPa homogenization treatment significantly (P<0.05) reduced the amount of critical beany flavor compounds (n-Hexanal, etc). The critical non-beany flavor compounds (n-Nonenal, (E)-2-Octenal, and (E)-2-Nonenal) were better retained, where the color, flavor, smoothness, and taste of soymilk powder were significantly (P<0.05) improved with the highest sensory scores. However, the excessive pressure treatment (80 MPa) caused a slight increase in the n-Hexanal content and a significant (P<0.05) decrease in the n-Nonenal and (E)-2-Nonenal, which were deteriorated the sensory quality of the soymilk powder with the decrease in the sensory scores. The finding can provide a scientific basis for the processing and sensory quality improvement of calcium-fortified soymilk powder.