Starch Phosphates Produced by Extrusion: Physical Properties and Influence on Yogurt Stability
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0038-9056 |
| Online Access: | http://www.viks.sk/chk/star_5_04_199_207.doc |
| Abstract: | Summaries. Starch phosphorylation with sodium tripolyphosphate (STP) was performed using a single-screw extrusion process. The extrusion variables studied were temperature (from 99.5°C to 200.4°C), water content (16.3% to 19.7%, w/w), and STP content (0.82% to 4.18%, w/w). The resulting phosphorylated starch was evaluated with respect to expansion, water solubility index (WSI), water absorption index (WAI), degree of substitution (DS), and viscosity. The phosphorylated starch was tested as a stabilizing additive in yogurt formulations, with respect to the syneresis index (SI) and the syneresis susceptibility coefficient (SSC). The results show that the expansion increases with increasing STP content, and decreases with increasing temperature and water content employed in the process. Increasing extrusion temperatures and decreasing water content resulted in increasing WSI and decreasing WAI. The DS was dependent on STP content, increasing as STP content increased, but appeared to be insensitive to changes in water content (between 16% and 20%, w/w). The highest level of yogurt stability, as measured by the syneresis index (SI) and the syneresis susceptibility coefficient (SSC), were obtained when the yogurt was formulated with the starch of the highest DS (0.018), which had been obtained at 150°C, 18% water content, and 4.12% (w/w) of STP. Conclusions. The variables with the greatest effect are temperature and STP content in the phosphorylation of wheat starch. The effects of water content are minor, with no significant effects seen for this parameter on DS, SI, and SSC, though the water content does have some effect on other properties. Thus, expansion increases with increasing STP content, and decreases with rising temperature. The values of WSI and of WAI show that at the higher temperatures (200°C) and low water content (16%), a greater extent of fragmentation takes place in the starch, resulting in higher WSI values, but an increase in water content to 20% reduces dextrinization, thus improving the WAI; this holds for 4.18% STP. The highest DS by STP for starch (0.018) was obtained under extrusion conditions of 150°C, 4.18% STP, and a water content of 18%. The best yogurt stability, judging by SI (6.74%) and SSC (0.27) was obtained when the yogurt was formulated with the starch of the highest DS. These results show that the more numerous the phosphate groups in the starch molecules, the better will be the retention capacity and texture stability of the gel formed by the milk proteins and the phosphorylated starch. |
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| ISSN: | ISSN 0038-9056 |
