Whey- and Soy Protein Isolates Added to a Carrot-Tomato Juice Alter Carotenoid Bioavailability in Healthy Adults

Recent findings suggested that proteins can differentially affect carotenoid bioaccessibility during gastro-intestinal digestion. In this crossover, randomized human trial, we aimed to confirm that proteins, specifically whey- and soy-protein isolates (WPI/SPI) impact postprandial carotenoid bioavailability. Healthy adults (n = 12 males, n = 12 females) were recruited. After 2-week washout periods, 350 g of a tomato-carrot juice mixture was served in the absence/presence of WPI or SPI (50% of the recommended dietary allowance, RDA ≈ 60 g/d). Absorption kinetics of carotenoids and triacylglycerols (TAGs) were evaluated via the triacylglycerol-rich lipoprotein (TRL) fraction response, at timed intervals up to 10 h after test meal intake, on three occasions separated by 1 week. Maximum TRL-carotenoid concentration (Cmax) and corresponding time (Tmax) were also determined. Considering both genders and carotenoids/TAGs combined, the estimated area under the curve (AUC) for WPI increased by 45% vs. the control (p = 0.018), to 92.0 ± 1.7 nmol × h/L and by 57% vs. SPI (p = 0.006). Test meal effect was significant in males (p = 0.036), but not in females (p = 0.189). In males, significant differences were found for phytoene (p = 0.026), phytofluene (p = 0.004), α-carotene (p = 0.034), and β-carotene (p = 0.031). Cmax for total carotenoids (nmol/L ± SD) was positively influenced by WPI (135.4 ± 38.0), while significantly lowered by SPI (89.6 ± 17.3 nmol/L) vs. the control (119.6 ± 30.9, p < 0.001). Tmax did not change. The results suggest that a well-digestible protein could enhance carotenoid bioavailability, whereas the less digestible SPI results in negative effects. This is, to our knowledge, the first study finding effects of proteins on carotenoid absorption in humans.

Structural and foaming properties of whey and soy protein isolates in mixed systems before and after heat treatment

The partial replacement of proteins from animal sources by plant proteins in formulated food products has been proposed as useful to improve sustainability aspects of the products without dramatically changing their techno-functional properties. Although several research groups have published on the gelling properties of mixed systems containing whey and soy protein isolates (WPI and SPI), their foaming properties are much less described. In this context, the main objective of this paper was to evaluate the structural and foaming properties of samples containing different mass ratios of WPI:SPI (100:0, 75:25, 50:50, 25:75 and 0:100) before and after heat treatment. The samples were evaluated according to their solubility, foaming capacity (FC), foam microstructure and foam stability (FS). Before heat treatment, mixing SPI to WPI did not affect the solubility of whey proteins, but, after heat treatment, insoluble co-aggregates were formed. Similar FC was measured for all samples despite their WPI:SPI ratio and the applied heat treatment. The partial replacement of WPI by SPI changed the microstructure of the foams and had an antagonistic effect on the FS of the samples, due to the negative effect of insoluble soy protein aggregates and/or insoluble co-aggregates on the reinforcement of the air-water interfacial film.