CHARACTERIZATION OF INTERACTION BETWEEN WHEY PROTEIN ISOLATE AND XANTHAN/CURDLAN HYDROGEL TO IMPROVE FREEZE-THAW STABILITY

Abstract

Syneresis, the liquid separation from a food product, is one of the major challenges in the frozen food industry. It is often accelerated by unintentional temperature fluctuations, i.e. repeated freezing and thawing during distribution, transportation, storage, and consumption. It has been demonstrated that the combination of xanthan and curdlan is capable of reducing syneresis up to five freeze-thaw cycles (FTCs) with relatively stable rheological and textural properties. The present study aimed at developing an effective mixture of whey protein isolate (WPI) and xanthan-curdlan hydrogel complex (XCHC) to minimize moisture migration over multiple FTCs. The addition of XCHC to WPI solution significantly reduced the syneresis of heat-induced gels, increased the storage modulus (G') of the gels, reduced the minimum concentration of whey protein isolate required to form a gel, and minimized the discrepancies of G' in frequency sweep tests over 5 FTCs. By comparing the microstructure of mixed WPI-XCHC and pure WPI gels, it was found that XCHC served as a pore-forming agent, namely increasing the porosity, reducing the pore size, and consequently improving the gel's water retention over multiple FTCs. Results from dynamic rheological measurements showed that both G' and the gelation temperature of mixed WPI-XCHC complex were strongly pH-dependent. Moreover, the interactions between WPI and XCHC in aqueous solution were characterized. An edible coating solution containing the mixture of WPI, xanthan, and curdlan was tested on mushroom and green bell pepper. Fresh mushroom and green bell pepper samples treated with WPI-XCHC significantly prevented moisture migration after 10 days of frozen storage. The coating also decreased the changes of whiteness and greenness in mushroom and bell pepper, respectively, while significantly improved the firmness of bell peppers. Such information could provide useful guidelines when designing novel food products utilizing the unique properties provided by WPI-XCHC.