Monitoring the structural alterations induced in β-lactoglobulin during ultrafiltration: learning from chemical and thermal denaturation phenomena

The effect of ion environment changes on retention protein behavior during whey ultrafiltration process

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The ions environment changes were investigated during whey ultrafiltration process.

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Whey protein surface structure changes were contributed to the changing ions’ concentration.

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The relationship between ions around whey protein and membrane fouling was analyzed.

The factors affecting membrane fouling are very complex. In this study, the membrane fouling process was revealed from the perspective of ion environment changes, which affected the whey protein structure during ultrafiltration. It was found that the concentrations of Ca²⁺ and Na⁺ were overall increased and the concentrations of K⁺, Mg²⁺ and Zn²⁺ were decreased at an ultrafiltration time of 11 min, which made more hydrophilic groups buried inside and increased the content of α-helix, leading to more protein aggregation. The relatively higher K⁺ ratio in retention could lead to an antiparallel β-sheet configuration, aspartic acid, glutamic acid and tryptophan increased, which resulted in more protein aggregation and deposition on the membrane surface at 17 min. When the ion concentration and ratio restored the balance and were close to the initial state in retention, the protein surface tension decreased, and the hydrophilic ability increased at 21–24 min.

The effect of ultrafiltration on the acid gelation properties of protein-standardised skim milk systems

In this study, we investigated the impact of ultrafiltration (UF) on the acid gelation of milk using two protein-standardised milk systems, consisting of either skim milk and retentate (SR) or permeate and retentate (PR), over different seasons in New Zealand. The composition and the physicochemical properties of the two systems before heating were comparable, whereas the levels of heat-induced α-lactalbumin denaturation and the association of the casein micelles with α-lactalbumin were significantly lower in PR than in SR. PR displayed superior acid gelation properties compared with SR, which was most pronounced in the late season. The structural modifications of the whey proteins and casein micelles that were induced by UF and the re-equilibration of calcium in the milk mixtures may have affected the acid gelation properties of the milk by influencing the denaturation and micelle association of the whey proteins. The results suggest that UF has the potential as a tool for tuning the acid gelation properties of milk.