Effect of equilibrium pH on the structure and properties of bleach-damaged human hair fibers.

Hair proteins are significantly affected by environmental pH. This impact tends to increase with prior hair damage. To understand how pH affects bleached hair properties, we utilized a number of techniques allowing for the determination of hair thermal properties, swelling and water sorption, and dry and wet tensile properties. At pH 5, hair proteins had the best structural integrity, as determined by differential scanning calorimetry and the highest tensile modulus. At pH 10, protein cross-linking density decreased, water content and hair cross-sectional diameter increased. Alkaline treatment, when compared with pH 5, did not reduce intermediate filament conditions (evaluated via enthalpy measurement) nor mechanical property performance in the wet state. In contrast to alkaline-treated hair, bleached hair equilibrated at pH 3 behaved very differently: it contained two different crosslink density zones, was the least stiff in dry and stiffest in wet conditions. Additionally, it absorbed less water and had the lowest diameter because of reduced water binding by protonated carboxyl groups. The pH 3 to 10 did not affect the mechanical strength of bleached hair in dry or wet conditions.

Impact of Interfacial Composition on Emulsion Digestion Using In Vitro and In Vivo Models.

This study explored the influence of different emulsification layers as mono- and bilayers on lipid digestion by using in vitro and in vivo digestion methods. The monolayer emulsion of rapeseed oil contained whey proteins and the bilayer emulsion, whey proteins and carboxymethyl cellulose. The in vitro digestion using human gastrointestinal enzymes showed that the lipid digestion as free fatty acids was slowed down in the bilayer emulsion compared with the monolayer. Droplet size was still low in the gastric phase and pseudoplasticity was well preserved (even though viscosity decreased) during in vitro gastrointestinal digestion. The in vivo studies confirmed a lower fat bioavailability from bilayer emulsions by a reduction in the triglyceride level in the blood of rats, fed by the bilayer emulsion. The results clearly showed that lipid digestion was slower in the bilayer emulsion than in the monolayer. These results provide bio-relevant information about the behavior of emulsions upon digestion. PRACTICAL APPLICATION: The layer-by-layer production approach that was presented here allows the preparation of emulsions with slower fat bioavailability. Such behavior of the bilayer emulsion made it interesting for the formulation of food products with low fat bioavailability.

Effect of human and simulated gastric juices on the digestion of whey proteins and carboxymethylcellulose-stabilised O/W emulsions.

In this study, we analysed the impact of carboxymethylcellulose (CMC) on lipid digestion and physicochemical properties of whey proteins (WP)-stabilised emulsions during in vitro digestion with either artificial or human gastrointestinal juices. The emulsions were made by adsorbing WP on the fat droplets and subsequently adding CMC, which does not interact with the adsorbed proteins. The limited hydrolysis of lipids and their higher physical stability was recorded for WP-stabilised emulsions in the presence of CMC under simulated gastrointestinal conditions. The possible mechanism by which CMC lowers the digestion of WP-stabilised emulsions is related to the limited interaction of fat droplets with gastrointestinal fluids due to the extended thickening network formed by CMC in the continuous phase. The digestion of WP- and CMC-stabilised emulsions in the in vitro model with human gastric fluids led to greater lipid hydrolysis, although the enzymatic activity in both in vitro models was observed at the same level.