The effect of adding xanthan-curdlan hydrogel complex (XCHC) at 2 concentrations (0.25 and 0.5% w/w) on the freeze-thaw stability of heat-induced whey protein isolate (WPI) gel was investigated. Samples were stored at 4 °C for 24 h before subjected to 5 freeze-thaw cycles alternating between -16 °C (18 h) and 25 °C (6 h). Adding XCHC to the WPI solution resulted in the reduction of a significant amount of syneresis up to 5 repeated freeze-thaw cycles. Addition of XCHC decreased the amount of syneresis from 45% in the control sample (pure WPI gel) to 31.82% and 5.44% in the samples containing 0.25% and 0.5% gum, respectively, after the 5th freeze-thaw cycle. XCHC increased the storage modulus (G') of the gels and minimized the changes of the G' values over the 5 freeze-thaw cycles, indicating improvement of the stability of the system. Furthermore, the minimum protein concentration for gel formation decreased in the presence of the XCHC. Scanning electron microscopy (SEM) images showed that addition of XCHC resulted in the formation of a well-structured gel with numerous small pores in the network, which consequently improved the water retention ability during the temperature abuses up to 5 freeze-thaw cycles. These results have important implications for using XCHC in the formulation of the frozen WPI-based products with improved freeze-thaw stability and rheological properties.
Practical application: Application of XCHC in the formulation of frozen dairy-based food products has the potential to enhance freeze-thaw stability and minimize moisture migration caused by temperature abuses of the products during distribution and consumer application.
Keywords: SEM; freeze-thaw cycle; rheological properties; whey protein isolate; xanthan curdlan hydrogel.
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