Influence of lactose on the formation of whey protein microparticles obtained by dry heating at alkaline pH

Maturation of demineralized arabinogalactan-proteins from Acacia seyal gum in dry state: Aggregation kinetics and structural properties of aggregates

The aggregation in dry state of mineral-loaded arabinogalactan-proteins (AGPs) from Acacia seyal gum (GA) generally occurs above 70 °C. This study focuses on the aggregation sensitivity of AGPs after their demineralization. The dry incubation in mild temperature (25 °C to 70 °C) of demineralized AGPs induced the formation of aggregates, not observed with GA. AGPs aggregated following a self-assembly mechanism for which temperature only modulated the aggregation rate. The activation energy was around 90-100 kJ·mol^-1 that could correspond to chemical condensation reactions induced by the AGPs surface dehydration. The aggregation kinetics were characterized by the formation of soluble aggregates during the first times of incubation, whose molar mass increased from 1 · 10⁶ g·mol^-1 to 6.7 · 10⁶ g·mol^-1 (SEC MALS) or 12 · 10⁶ g·mol^-1 (AF4 MALS) after 1.66 days of dry heating at 40 °C. These soluble aggregates revealed they adopted a similar conformation to that of not aggregated AGPs with a ν_h value around 0.45. Above 1.66 days at 40 °C, the soluble aggregates grew up to form microparticles with sizes ranging from 10 to around 200 μm. This study highlighted the protective role of cations from AGPs whose demineralization increased their sensibility to dry heating and their chemical reactivity for aggregation.

Analysis of the glycosylation products of peanut protein and lactose by cold plasma treatment: Solubility and structural characteristics

Cold plasma (CP) treatment was used to prepare the glycosylation conjugates of high-temperature peanut protein isolate (HPPI) and lactose to improve the solubility of HPPI. We observed that by increasing the CP treatment time to 3 min, the solubility of the conjugates increased to 1.34 mg/mL. An increase in the degree of glycosylation and a decrease in the degree of browning indicated that although CP treatment accelerated the glycosylation of HPPI and lactose, it interfered with the formation of melanoidin. The analysis of protein tertiary structure showed that tryptophan and tyrosine residues in proteins undergoing CP treatment were the primary sites for the Maillard reaction. The relative decrease in surface hydrophobicity and FT-IR analysis indicated that the increase in the -OH stretching vibration intensity on the protein surface represented the formation of the covalent bonds between HPPI and lactose during the CP treatment. An increase in the denaturation temperature of proteins was observed after grafting with lactose. Changes in the secondary structure and surface structure of proteins showed that lactose covalently bonded to the surface of HPPI during CP treatment, forming a more stable ordered structure.

Influence of casein on the formation of whey protein microparticles obtained by dry heating at an alkaline pH

Dry heating (DH) at 100 °C for 36 h of a whey protein isolate powder conditioned at pH 9.5 leads to the formation of stable, large and porous whey protein microparticles (PMs), resulting from the crosslinking of proteins inside the powder. These PMs could be used as high-viscosity food ingredients. Casein, present as a contaminant in whey protein powders, has been shown to become incorporated into the PMs. In this study, we investigated the effect of adding increasing amounts of sodium caseinate to whey protein powders on the formation of PMs during DH at 100 °C for 36 h. In addition, we studied PM formation during DH of a micellar casein-enriched milk protein powder (Casmic). The browning index of the dry-heated powders, and the size and water content of the microparticles were also characterized. We confirmed that sodium caseinate was incorporated into the PMs. The highest PM D[4,3] values (270 μm) were observed for powders with around 40% caseinate. Powders without added caseinate displayed D[4,3] values of 150 μm. The yield of conversion of proteins into PMs increased from 0.6 to 0.8 g/g with caseinate addition, whereas the amount of water entrapped in the PMs decreased from around 30 to 20 g/g. PMs were also formed by DH of the Casmic powder, but these particles were smaller, with sizes of around 80 μm. In conclusion, our study shows that the process of DH at pH 9.5 could be applied to all milk proteins to obtain PMs with functional properties that could be used in the food industry.