Functional Properties And Applications Of Whey Protein Isolate Fibers

Whey protein isolate（WPI）,a kind of mixed protein obtained from milk,is widely used in processing of foods.WPI can change to whey protein fibers（WPF）at low p H,low ionic strength and by thermal processes.Previous researches were focused on studying the functional properties of WPF under specific preparing conditions.A few studies were reported about the functional properties of WPF during fibril formation and the interaction between WPF and other food components.Therefore,in this project,WPI was used to prepare WPF,and the effects of heating time on the functional properties of WPF as well as the interaction between WPF and gum Arabic（GA）were studied.WPF-GA wes employed to prepare mayonnaise analogues.The main results are as follows:（1）WPF was prepared to explore the effects of heating time on its physicochemical properties and antioxidant activities.The results showed that the fluorescence intensity and conversion rate of WPF increased with increasing heating time.After 16 hours heating（WPF16）,the fluorescence intensity of WPF16 increased by 42 times,and the conversion rate was 32%.The heat treatment could improve the ABTS·radical scavenging ability and iron ion reducing ability of WPF.Compared with WPI,the ABTS·radical scavenging rate of WPF16 increased by three times and the iron ion reducing ability increased by two times.（2）The effects of heating time,fiber length and p H on the rheological behavior were investigated.The shear viscosity of WPF increased with heating time.When the shear rate was 1 s^-1,the shear viscosity of WPF16increased from 0.002 Pa·s to 0.2 Pa·s.The extensional viscosity of WPF first increased and then decreased with heating time and reached to a maximum value after 8 hours of heating.With the decrease of the fiber length,the extensional break-up time decreased while the shear viscosity and extensional viscosity did not change significantly.The extensional rheological behavior of WPF was affected by the p H.The maximum extensional break-up time and relaxation time at p H 3.5 were 43 ms and 17ms,respectively.（3）The effect of heating time on the interaction between WPF and GA was investigated.The results showed that the insoluble complex（WPF-GA）could be formed at p H 2.0～6.0 that was a bundle structure with multiple fibers.The p H_φ1 and the yield of the coacervates increased with the heating time of WPF,and the maximum yield was obtained for WPF16-GA（67%）.When WPF-GA were used as emulsifiers,the viscosity of emulsions increased with the heating time of WPF.The maximum shear viscosity was observed for the emulsion stabilized by WPF16-GA,which was 22 Pa·s at0.1 s^-1.Compared with WPI-GA,the emulsion stabilized by WPF-GA showed a better storage stability and less oxidative stability.（4）Mayonnaise analogues were prepared by using WPF16-GA as emulsifier.Compared to two commercial mayonnaises and a home-made mayonnaise,the particle size of mayonnaise analogue was bigger（19.7μm）.At 0.1 s^-1,the home-made mayonnaise showed lowest viscosity（2.3 Pa·s）,followed by mayonnaise analogues（59 Pa·s）and two commercial mayonnaises（82 Pa·s）.The amount of gel strength was similar for mayonnaise analogs and commercial mayonnaises,which was much higher than that for the homemade mayonnaise.Mayonnaise analogues showed good storage stability.The sensory score for home-made mayonnaise and mayonnaise analogues were similar（25 points）,lower than that for commercial mayonnaise（34 points）.