The study investigating the role of salt in the digestion of lipid emulsions suggests that the addition of sodium chloride in emulsified fats leads to a reduction in electrostatic repulsion between lipid particles, thus increasing to the formation of ‘bridged’ lipid clusters. However this process was seen to be stopped by digestion.
The researchers, led by Sun Jin Hur from Gyeongsang National University, Korea said an improved understanding of the factors that impact the bioavailability of dietary lipids may enable the food industry to design foods to increase, decrease or control lipid digestion and absorption within the human gastrointestinal tract.
“Knowledge of the role of sodium chloride on lipid digestion may be useful for designing functional foods that are healthier, e.g., reduced fat and salt contents,” they added.
Lipid digestion
Lipids play an important role in the human diet, providing energy, essential nutrients and bioactive components. But when a lipid is ingested can undergo changes in its chemistry and structural organization as it passes through the gastrointestinal tract.
Hur and co workers noted that changes in the amount of salts consumed during a meal may influence the behaviour of other food components, including lipids, within the gastrointestinal tract. They added that the type and amounts of salts present in the gastrointestinal tract determine the magnitude and range of any electrostatic interactions – which affect can the solubility, interactions, and aggregation behaviour of the ingested food components as well as the digestive components secreted by the body.
“However, few studies have previously examined the role of salts in the digestion of major food components. The purpose of the present study was therefore to examine the influence of salt on the in vitro digestibility of emulsified lipids,” said the researchers.
Study details
The researchers prepared oil-in-water emulsions using three per cent either soybean oil, corn oil, olive oil and lard. The emulsified lipids were then passed through a digestion model in the presence or absence of one per cent sodium chloride.
Prior to digestion, the authors observed that emulsified lipid droplets appeared to be bridging together, leading to flocculation (an adhesion process where dispersed or suspended particles form larger sized clusters) in the presence of one per cent sodium chloride.
Moreover, Hur and colleagues reported that lipid droplets in the presence of one per cent sodium chloride were “more disrupted than emulsified lipids with no sodium chloride added.”
However, they reported that sodium chloride induced bridging of lipid droplets was not seen post digestion, in any of the prepared lipid emulsions.
Free fatty acid contents were found to increase after digestion for all emulsified lipids, but were especially high in emulsified lipid made from lard and olive oil.
Reducing repulsion
Hur and co workers said it is often assumed that lipid droplets coated by surfactants have no net charge, but in reality often have “an appreciable negative charge”, due to the presence of surface impurities in the oil phase, such as free fatty acids.
Consequently, they said it is possible that one per cent sodium chloride reduced any electrostatic repulsion between the lipid droplets, and thereby led to increased flocculation.
They suggested that digestion may have changed the interfacial composition lipid droplets, freeing surface fatty acid ‘impurities’, and leading to more stable droplets that do not bridge.
The authors said that future work is needed to understand the effect of sodium chloride additions that occur during digestion, and how sodium chloride relates to changes in lipid digestion or micro structural changes.
Source: Food Chemistry
Published online ahead of print, doi: 10.1016/j.foodchem.2010.12.003
"Impact of Salt and Lipid Type on In Vitro Digestion of Emulsified Lipids
Authors: S.J. Hur, S.T Joo, B.O Lim, E.A Decker,J.D McClements