Influence of oat components on lipid digestion using an in vitro model: Impact of viscosity and depletion flocculation mechanism

Abstract

Depletion flocculation is a well-known instability mechanism that can occur in oil-in-water emulsions when the concentration of non-adsorbed polysaccharide exceeds a certain level. This critical flocculation concentration depends on the molecular characteristics of the polysaccharide molecules, such as their molecular weight and hydrodynamic radius. In this study, a range of analytical methods (dynamic shear rheology, optical microscopy, and static light-scattering) were used to investigate the interaction between lipid droplets and polysaccharides (guar gum and β-glucans) of varying weight-average molecular weight and hydrodynamic radius, and concentration. The aim of this work was to see if the health benefits of soluble fibers like β-glucans could be explained by their influence on the structure and digestibility of lipid emulsions. The apparent viscosity of the emulsions increased with increasing polysaccharide concentration, molecular weight, and hydrodynamic radius. Droplet flocculation was observed in the emulsions only at certain polysaccharide concentrations, which was attributed to a depletion effect. In addition, the water-soluble components in oat flakes, flour, and bran were extracted using aqueous solutions, to examine their impact on emulsion stability and properties. Then, the rate and extent of lipolysis of a sunflower oil-in-water emulsion in the presence of these oat extracts were monitored using the pH-stat method. However, the inhibition of lipolysis was not linearly related to the viscosity of the oat solutions. The water-soluble extracts of β-glucan collected from oat flakes had a significant inhibitory effect on lipolysis. The results of this study increase our understanding of the possible mechanisms influencing the impact of oat constituents on lipid digestion. This work also highlights the importance of considering the molecular properties of polysaccharides, and not just their impact on solution viscosity.

Oat and lipolysis: Food matrix effect

“…On the contrary, in the present study the oil bodies did not appear to coalesce in the oat endosperm ( Figures 2A1 and A2), but they tended to flocculate once extracted from the oat matrix ( Figures 2B1 and B2). This phenomenon was recorded in our recent work where depletion flocculation of sunflower oil droplets was induced by the β-glucan released from the oat matrix following incubation of oat flakes and flour (Grundy, McClements, Ballance, & Wilde, 2018). However, no β-glucan was detected in the oil body preparation when stained with a dye specific to the polysaccharide, i.e., calcofluor white (data not shown).…”

“…Almond oil bodies have been shown to form similar structures during gastric digestion than to the ones observed in Figure 3C, some of the almond proteins being resistant to pepsin activity (Gallier & Singh, 2012). Hence, the network formed by a combination of compounds (possibly proteins, phytosterols, galactolipids, saponins, and phospholipids) around, or at the vicinity, of the droplets is likely to have hindered the access of the lipase to its substrate (Chu et al, 2009;Grundy, McClements, Ballance, & Wilde, 2018). Flocculated oil bodies could be clearly seen in Figures 3C3 and C4 confirming that these newly formed structures were difficult to degrade.…”

“…However, it is likely that the observed benefits on health are also due to other structural features unique to the oat grain that would dictate the way it behaves during digestion. For instance, our recent in vitro data suggests that oat compounds, other than β-glucan, may have an impact on lipid digestibility (Grundy et al, 2017;Grundy, McClements, Ballance, & Wilde, 2018). Oat is rich in macronutrients and bioactives phytochemicals, including arabinoxylans, antioxidants (e.g.…”

Bioavailability of nutraceuticals: Role of the food matrix, processing conditions, the gastrointestinal tract, and nanodelivery systems

“…Also, it should be mentioned that carbohydrates provide the necessary energy for the body and influence the nutraceutical release by enhancing the viscosity of the food matrix. Certain authors showed that the use of diet fibers (chitosan, sodium alginate, and locust bean gum) influences the size and electrical properties of oil droplets, the viscosity of nanoemulsions, and the formation of FFAs by the nanoemulsion digestion (Grundy, McClements, Ballance, & Peter, 2018; Qin et al., 2017).…”

A review of the rheological properties of dilute and concentrated food emulsions

“…The magnitude of the osmotic attraction increases with increasing hydrocolloid concentration and eventually it can become large enough to overcome any repulsive forces and promote flocculation. Both theoretical and experimental studies have shown that there can be a substantial increase in emulsion viscosity due to depletion flocculation, as well as the generation of a yield stress (Berli, ; Berli et al, ; Grundy, McClements, Ballance, & Wilde, ; Preziosi et al, ). This phenomenon may therefore be utilized to create novel textural characteristics in food emulsions. Bridging flocculation : This kind of droplet aggregation occurs when a hydrocolloid links two or more oil droplets together (Dickinson, ).…”