Effects of Freeze-Thaw Cycles on the Structures and Functional Properties of Protein Isolates.

Changes in the functional properties and structures of protein isolate (CSPI) in the process of freeze-thaw (F-T) cycles were explored. Remarkable alterations and the reduced content of protein ordered structure were revealed through structural analysis of CSPI after F-T treatments. The surface hydrophobicity and free sulfhydryl content of CSPI first increased and then decreased. However, after the F-T treatments, the carbonyl content of CSPI continued to increase. Similarly, the water holding capacity (WHC), oil holding capacity (OHC), and solubility of CSPI all declined as the number of F-T cycles increased. The foaming properties and emulsifying properties of CSPI were significantly improved and reached maximum values after three F-T cycles. CSPI undergoing two F-T cycles showed the highest digestibility, maximum polypeptide content, and highest DPPH and ·OH-radical-scavenging activities. The ·OH-radical-scavenging activities and reducing power of the gastrointestinally digested CSPI had the highest value after one F-T cycle. Therefore, it has been demonstrated that F-T treatments could be a residue-free and cost-effective tool for improving mushroom protein functional properties.