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

Abstract

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.

Influence of Proteins on the Absorption of Lipophilic Vitamins, Carotenoids and Curcumin – A Review

“…Similarly, significant differences on the postprandial plasma AUC of TRL-carotenoid concentrations (nmol h L −1 ) between WPI and SPI for individual carotenoids, that is, phytoene (160 ± 3.3 versus 82 ± 3.3), phytofluene (55 ± 0.9 versus 31 ± 0.9), and 𝛼-carotene (14 ± 0.6 versus 3 ± 0.6) were observed. [14] This was the first study reporting an effect of added proteins on carotenoid absorption in humans, confirming the previously reported in vitro results, pointing out that a well digestible protein such as WPI could be beneficial for carotenoid bioavailability, whereas the less digestible SPI resulted in hampered bioavailability of carotenoids. The lower digestibility of SPI versus WPI has been earlier emphasized, for instance in studies focusing on sport supplements, with SPI showing significantly slower breakdown into amino acids.…”

“…[12] It has recently been shown that well digested proteins, such as those present in whey protein isolate (WPI), are able to modify the bioavailability of liposoluble microconstituents, such as carotenoids from a juice, both in vitro [13] and in vivo. [14] Similarly, for vitamin D3, a positive effect on postprandial absorption in mice was found following the simultaneous intake of WPI. [15] The positive effects of proteins on the absorption of liposoluble microconstituents are thought to be related to the following features: (a) Emulsifying properties, that is, produced peptides during digestion could foster the solubility and stability of lipid droplets while interacting with their surface, promoting their processing into mixed micelles [16] ;…”

“…In our recent human study, we reported the effect of WPI and SPI at a concentration of 50% of the RDA (about 30 g), on postprandial absorption of carotenoids from a carrot–tomato juice mixture, as determined by their plasma triacylglycerol‐rich lipoprotein (TRL) levels. [ 14 ] The absorption kinetics (i.e.AUC) of carotenoids and triacylglycerols (TAGs) were measured in 24 adults at timed intervals up to 10 h after test meal intake, and WPI‐supplemented meal increased carotenoid/TAGs AUC significantly by 45% compared to control, and by 57% compared to SPI‐supplemented meal, while the latter did not differ significantly compared to control meal. AUC for total carotenoids (nmol h L −1 ±SEM) was significantly higher for the WPI‐supplemented meal (249 ± 7.0) versus the SPI meal (124 ± 7.0).…”

“…[196] The findings suggest that absorption of both carotenoids and TAGs can be significantly impacted by the presence of proteins. [14] However, care should be taken to extend results from long-term trials on TAGs to short, that is, postprandial bioavailability results of carotenoids. Nevertheless, such long-term protein intakes may influence also circulating carotenoid concentrations, as well as other lipophilic concentrations such as those of vitamins, also associated with circulating lipoproteins.…”

“…[ 12 ] It has recently been shown that well digested proteins, such as those present in whey protein isolate (WPI), are able to modify the bioavailability of liposoluble microconstituents, such as carotenoids from a juice, both in vitro [ 13 ] and in vivo. [ 14 ] Similarly, for vitamin D3, a positive effect on postprandial absorption in mice was found following the simultaneous intake of WPI. [ 15 ] The positive effects of proteins on the absorption of liposoluble microconstituents are thought to be related to the following features: Emulsifying properties, that is, produced peptides during digestion could foster the solubility and stability of lipid droplets while interacting with their surface, promoting their processing into mixed micelles [ 16 ] ; Improving the enzymatic access to the surface of lipid droplets by altering surface tension and viscosity [ 17 ] ; Stabilizing the mixed micelles in the small intestinal phase (i.e., the chyme), by interacting with their surfaces, which prevents their aggregation [ 9 ] ; Improving solubility and perhaps preventing the oxidation of lipophilic constituents following their interaction with proteins, via hydrophobic pockets within peptides.…”