Effect Of Cassava Modified Starch On The Gelling Properties Of Whey Protein

Modified Starch(like hydroxypropylated starch and cross-linked starch)had been widely used as thickening and stabilize agent in the food containing whey protein gel,such as milk pudding,ice creams and dairy dessert,etc.However,the effect of modified starch on the gelling properties of whey protein has not been clarified.The objective of the present work was to investigate the effect of cassava hydroxypropylated starch(CHS)and cassava cross-linked starch(CCS)on the gelling properties of whey protein,which was achieved by the measurement of rheological,thermal,water holding and microstructural properties of cassava modified starch(CMS)-whey protein isolate(WPI)mixed gels at different p H(5.0,7.0 and 9.0)and different starch proportion(0,0.25,0.5,0.75,1.0).The results could provid the thereotical foundation for the application of CMS in the products containing whey protein gel.The mainly results were shown as follow:The rheological properties of sample gels during heating were characterized by small-amplitude oscillatory rheometry to investigate the effect of CMS on the rheological properties of WPI gel.The results showed that the addition of CHS and CCS was contributed to the increase of the elastic modulus(G?)of WPI gels at pH 5.0,and the WPI-CCS mixed gels had greater elastic modulus(G?)values than those of other mixed gels at same starch proportion.However,the addition of cassava modified starch decreased the elastic modulus of WPI gel at pH 7.0 and 9.0.The thermal properties of samples during heating were characterized by differential scanning calorimetry(DSC)to investigate the effect of CMS on the thermal properties of WPI.Based on DSC curves,it could be found that the increase of starch proportion of CHS and CCS resulted in the increasing starch gelatinization peak obscured the WPI denaturation peak,and the order of WPI denaturation and CMS gelatinization was changed with the increase of pH from 5.0 to 9.0.The water holding capacity and water distribution of the mixed gel was analysized by the centrifuge method and low field-nuclear magnetic resonance(LF-NMR)to investigate the effect of CMS on the water holding properties of WPI gel.The results indicated that the addition of CHS and CCS increased the amount of immobilized water in the mixed gel at pH5.0,and the WPI-CHS mixed gels had greater amount of the bound water than that of other mixed gels at same condition.However,the addition of CHS and CCS decreased the water holding capacity of WPI gel at pH 7.0 and 9.0.The microstructure images of the mixed gels were achieved by light microscopy(LM)and scanning electron microscopy(SEM)to investigate the effect of CMS on the microstructure of WPI gel.The light microscopy and SEM images suggested that the addition of HPS and CCS contributed to the formation of compact microstructure at pH 5.0,but the WPI and CMS formed a loose mixed gel structure.