Physicochemical Properties of Casein-Starch Interaction Obtained by Extrusion Process
| 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_190_198.doc |
| Abstract: | Summaries. Extruded samples of starch-casein blends were processed by using a single-screw extruder. The independent variables in the process were temperature (126-194°C), moisture content (18-29%) and starch-casein blend (5-95%). These independent variables affected significantly the physicochemical and texturai properties of the biopoly-mers. The highest values for expansion (EXP) and water absorption index (WAI) were found when a higher starch proportion was present in the blends, at 126°C barrel temperature and moisture content higher than 25%. By increasing the barrel temperature, from 126°C to 194°C, the water solubility index (WSI) and color parameter were increased. Initial viscosity (IV) and viscosity at 90°C (V90) were mainly affected by the barrel temperature at 194°C. However, the viscosity at 50°C (V50) was affected neither by the different extrusion variables nor by the biopolymer proportion in the blends. Compression force (CF) was strongly dependent on moisture content and casein proportion in the blend. The higher CF values were found at starch concentrations around 50% and 25% moisture content, for higher or lower values than these the obtained extruded products were softer and consequently had lower CF values. Conclusions. Independent variables in the extrusion process such as temperature, moisture content and the starch-casein ratio in the blend significantly affect the physicochemical and textural properties of these biopolymers. Blends with 90 to 95% starch, extruded at barrel temperatures from 126 to 194°C, undergo starch fragmentation and casein de-naturation, which also promote the interaction between both polymers. Thus, at 194°C barrel temperature and lower moisture content, the expansion index increased, but the bulk density and compression force of extrudate decreased. Also, higher casein concentrations in the blend and lower moisture content, at 194°C barrel temperature, increase expansion and decrease compression force. Starch fragmentation as well as protein denatura-tion cause stronger interaction between both polymers and formation of inter- and intramolecular bonds, which changes water absorption and water solubility indexes and viscosity values of extruded products. When casein is denatured under the extrusion conditions, it loses its hydration capacity, which causes a decrease in viscosity values. However, increased starch content in the blend increases these viscosity values, which are directly correlated with water absorption index and color intensity. The darkening of extruded products, caused by Maillard reaction at high temperatures is an indicator of degradation and starch-casein interaction. |
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| ISSN: | ISSN 0038-9056 |
