[Efficiency and mechanism of action of hydrocolloids in preventing serum separation in Doogh]

Doogh is a kind of Iranian fermented dairy-based drink produced by adding water and salt to yoghurt. The major problem of this product is serum separation during storage, because of its low pH and aggregation of caseins. In the present study, the efficiency of some hydrocolloids in preventing serum separation as well as the stabilization mechanism of gum tragacanth-a local gum-were investigated. The effects of high-methoxyl pectin, tragacanth, and locust bean gum at different concentrations, individually and in combined forms, tragacanthin, and soybean soluble polysaccharides type M, on the stability of sour Doogh were investigated. In addition, the influence of gum tragacanth and locust bean gum on the stability of prebiotic Doogh [containing inulin] was also studied. In each case the duration of the study was 30 days. In order to elucidate the stabilization mechanism of gum tragacanth, the rheological properties, zeta potential, and microstructural characteristics of the stabilized Doogh samples were measured. According to our findings, tragacanthin, tragacanth and locust bean gum could inhibit serum separation for 30 days at a concentration of 0.1, 0.2 and 0.3%, respectively, while type M soybean soluble polysaccharides caused the stabilization at a concentration of 0.6% only for 6 days. Furthermore, combinations of gum tragacanth and locust bean gum were also effective in fully stabilizing Doogh [at a concentration of 0.15% and ratios of 80:20 and 50:50]. Inulin was not effective in stabilizing the sour Doogh samples. However, tragacanth and locust bean gums inhibited serum separation in prebiotic Doogh. Based on our findings, the most suitable rheological model for the control samples and the samples containing hydrocolloids were the Newtonian and Power law, respectively. Based on the results of this study, tragacanthin [the water-soluble part of gum tragacanth] seems to have a major role in stabilizing Doogh, probably by being adsorbed onto caseins [via electrostatic and steric repulsion]. On the other hand, bassorin [the water-insoluble part of gum tragacanth] may help stabilization by increasing viscosity. Therefore, gum tragacanth could be strongly recommended to be used as an adsorbing hydrocolloid in sour Doogh to inhibit serum separation

[Optimization of the extraction of soybean soluble polysaccharides from Okara]

Background and objectives: Soybean soluble polysaccharides [SSPS] are a food additive with various applications, including the stabilization of emulsions and dairy-based acid beverages. They are normally extracted from okara, a waste product in the production of soy products. In this study the feasibility of the extraction of SSPS from dried okara with and without demethoxylation and from wet okara [obtained in the process of soy milk extraction] with demethoxylation was investigated. In order to optimize the demethoxylation conditions, the response surface methodology [RSM] was used and demethoxylation was carried out at different temperatures [60, 75 and 90°C] and okara: water ratios [1:6, 1:8and 1:10].Different types of SSPS were extracted at various temperatures [120 and 130°C], pHs [3 and 4.5] and heating times [2 and 3 h]. Then, the extracted juices were purified [using ethanol for precipitation of high-molecular weight SSPS], dehydrated, and analyzed. Each one of the independent variables [demethoxylation temperature and okara: water ratio] was linearly related to the response [total soluble solids extracted], the effects being statistically significant [P<0.01 and P<0.0001, respectively]. In addition, the total soluble solids increased at high extraction temperature and low pH conditions. The findings also showed that pH was an important factor in the extraction of high-molecular weight SSPS [HM-SSPS]. Furthermore, when the demethoxylation process was used, the maximum yield of HM-SSPS [22.4% +/- 1.04%] was achieved at the following conditions: 130°C, 3h, and pH=4.5; on the other hand, without demethoxylation the highest yield [30.8% +/- 1.6%] was obtained at these conditions: 120°C, 2 h, and pH=4.5. The soymilk okara was found to be a feasible natural source for the extraction of various types of SSPS. Our findings also revealed that the dehydration of wet okara could prevent its spoilage and improve the yield of SSPS