Konjac glucomannan retards the deterioration of whey protein isolate gel quality after freeze-thaw cycles and their application in frozen skimmed yogurt

The mechanism of konjac glucomannan (KGM) retards the deterioration of whey protein isolate (WPI) gel quality after freeze-thaw cycles (FTC), and the application of KGM-crosslinked WPI in frozen skimmed yogurt was investigated. Compared with natural WPI, the WPI composite gel with 0.2 % KGM exhibited excellent gel strength, rheological properties, thermal stability and a dense gel network structure after two FTC. During FTC, KGM interacted with WPI causing changes in protein conformation, with β-turn shifting to β-sheet, an increase in disulfide bonds, and an unchanged amount of immobilized water, which made the system more stable. Meanwhile, KGM was filled in the WPI gel networks to absorb water, reducing the formation of ice crystals, and this gel network structure could also restrict the movement of water molecules, inhibiting the growth of ice crystals, thereby reducing the losses caused by FTC. Overall, KGM significantly alleviated the deterioration of WPI gel quality after FTC through inducing protein structure changes to facilitate the formation of a dense gel network, inhibiting ice crystal formation, and regulating moisture. In addition, after freeze-thaw treatment, the water-holding capacity, rheological properties, and mouthfeel of skimmed yogurt with KGM cross-linked WPI were far superior to those of pure skimmed yogurt and skimmed yogurt with only WPI added. These findings demonstrated the potential of KGM as a cryoprotectant, offering the possibility of achieving high-quality frozen dairy products.