Effect of divalent minerals on the bioaccessibility of pure carotenoids and on physical properties of gastro-intestinal fluids

Highlights

• Divalent minerals reduced solubility of carotenoids following simulated digestion.

• Bioaccessibility reduction was stronger for calcium than zinc or magnesium.

• Sodium slightly enhanced the bioaccessibility of carotenoids during digestion.

• Bioaccessibility correlated with digesta viscosity, inversely with surface tension.

• Observed effects were generally more pronounced for xanthophylls than for carotenes.

Abstract

During digestion, high concentrations of divalent minerals (DMs) can lead to insoluble lipid–soap complex formation, hampering carotenoid bioaccessibility. The effect of varying concentrations (0–1000 mg/L) of calcium, magnesium, zinc and sodium (control) on the bioaccessibility of lutein, neoxanthin, lycopene and β-carotene, following in vitro gastro-intestinal digestion (GI), was investigated systematically and coupled with physical measurements of the digesta. Addition of DMs significantly decreased (p < 0.001) carotenoid bioaccessibility, up to 100% in the case of calcium. Mean half maximal inhibitory concentrations (EC50) for calcium, magnesium and zinc were 270 ± 18, 253 ± 75 and 420 ± 322 mg/L respectively. Increased DM concentrations correlated with decreased viscosity (r > 0.9) and decreased carotenoid bioaccessibility. Surface tension of digesta correlated inversely (p < 0.05) with the bioaccessibility of carotenoids. This correlation was mineral and carotenoid dependent. Although based on in vitro findings, it is plausible that similar interactions occur in vivo, with DMs affecting the bioaccessibility and bioavailability of carotenoids and other lipophilic micronutrients and phytochemicals.

Introduction

Regular consumption of fruits and vegetables has been commonly associated with the prevention of several chronic diseases (Tapiero, Townsend, & Tew, 2004). Carotenoids are phytochemicals present in a large variety of vegetables and fruits, exerting important biological effects in humans including anti-oxidant, anti-inflammatory and pro-vitamin A activity (Kaulmann and Bohn, 2014, Stahl and Sies, 2005). The association between dietary carotenoid intake and the prevention of chronic diseases such as age-related macular degeneration (Bone et al., 2001), coronary disease (Arab & Steck, 2000), diabetes (Brazionis, Rowley, Itsiopoulos, & O’Dea, 2009) and cancer (Vainio & Rautalahti, 1998) has been the topic of several epidemiological studies. Although results from these studies are not always consistent, evidence for the protective role of carotenoids in the prevention of chronic diseases is increasing (Krinsky & Johnson, 2005).

As humans are not able to synthesize these compounds, they have to be acquired through the diet. However, due to their lipophilic character, bioavailability of carotenoids is low, which has mostly been attributed to their limited bioaccessibility (i.e., the percentage of carotenoids effectively released from the food matrix and available for absorption), varying from 3% to 34% (van Het Hof & West, 2000). In recent years much attention has been given to dietary and host factors influencing carotenoid bioaccessibility (Biehler and Bohn, 2010, Bohn, 2008, Castenmiller and West, 1998, van het Hof and West, 2000). Some of the factors investigated include the presence of dietary fiber and physical properties such as viscosity (O’Connell et al., 2008, Riedl and Linseisen, 1999, Verrijssen et al., 2014), type and amount of lipids present in meals (Gleize et al., 2013, Goltz et al., 2012, Huo et al., 2007), concentration of bile acids, as well as gastro-intestinal pH and enzyme variations (Biehler, Kaulmann, et al., 2011, Tyssandier et al., 2001).

One dietary factor that so far has received little attention is the presence and concentration of divalent minerals (DMs), including trace elements, such as calcium, zinc and magnesium. Previously, we have shown that high concentrations of the DMs calcium, magnesium, iron and zinc impaired the transfer of carotenoids to mixed-micelles to different degrees, thereby reducing micellarization by up to 90% (Biehler, Hoffmann, Krause, & Bohn, 2011), presumably via soap formation with fatty acids. Earlier findings have already shown an association between triglyceride digestion and dietary minerals. While Cheng, Morehouse, and Deuel (1949) found that these minerals reduce the digestibility of triglycerides, Tadayyon and Lutwak (1969) conversely reported that a diet rich in poorly absorbable fats considerably decreases the absorption of calcium and magnesium. As carotenoids require the presence of a certain amount of fat (ca. 5–10 g) to be present in a meal (Biehler and Bohn, 2010, Failla et al., 2008) in order to be effectively solubilized and emulsified, DMs could compromise carotenoid bioaccessibility by limiting the presence of available triglycerides and free fatty acids (FFA). DMs may also have the tendency to bind and precipitate bile acids (Baruch et al., 1991, Hofmann and Mysels, 1992), also reducing the bioaccessibility of carotenoids. In turn, the presence of salts may influence surface tension, viscosity and electrostatic properties of the digesta, potentially modifying the bioaccessibility of lipophilic constituents.

Here, we aimed to investigate the effect of several DMs (calcium, magnesium and zinc) at different concentrations, from physiological to dietary supplement range, on the bioaccessibility of the pure carotenes and xanthophylls, including β-carotene, lycopene, lutein and neoxanthin. For this purpose, we employed a previously established in vitro gastro-intestinal model (Corte-Real, Richling, Hoffmann, & Bohn, 2014), coupled to bioaccessibility determination and rheological analyses such as viscosity and surface tension of the digesta, to gain insight into the mechanisms of action that can alter carotenoid bioaccessibility.