In Vitro Gastrointestinal Digestion of Palm Olein and Palm Stearin-in-Water Emulsions with Different Physical States and Fat Contents

Abstract

The impacts of lipid physical state and content on lipid digestion behavior were investigated using 4 and 20% palm olein-in-water emulsions (4% PO and 20% PO) and 4 and 20% palm stearin-in-water emulsions (4% PS and 20% PS). The changes of lipid physical state, particle size, and microstructure during gastrointestinal digestion; the free fatty acid (FFA) released in the intestinal phase; and the fatty acid composition of micellar phases were investigated. After gastric digestion, all emulsions underwent flocculation and coalescence, with 20% PS showing the most extensive aggregation. During intestinal digestion, the FFA release rate and level decreased as the lipid content increased from 4 to 20%, with 4% PO presenting the highest digestion rate and extent. Besides, the solid fat in 4% PS and 20% PS decreased and increased the maximum lipid digestibility, respectively. These results highlighted the combined roles of lipid physical state and content in modulating dietary lipid digestion.

Structural Mechanism and Hydrolysis Kinetics of In Vitro Digestion Are Affected by a High-Melting-Temperature Solid Triacylglycerol Fraction in Bovine Milk Fat

“…The D [3,2] of 20S was significantly larger than that of 30S, but both of them were significantly smaller than 20L ( P < 0.05, Figure e). Wan et al observed a similar phenomenon: the particle size of 4% solid palm stearin was smaller than that of 4% liquid palm olein after gastric digestion . They inferred that solid fat had a low effect on the stability of the emulsion, which might not be accurate.…”

“…Milk fat is mainly composed of saturated FA (approximately 65%) and long-chain FA (approximately 82%), which contributes to its melting temperature being slightly lower than the human body temperature (37 °C). , Nevertheless, temperature fluctuations during dairy processing can change the polytypism and polymorphism of milk fat. , The polymorphic evolution (subcell structures: unstable α-polymorph → stable β-polymorph) and molecular rearrangement (stacking geometries: unstable 3L arrangement → stable 2L arrangement) caused by crystallization and recrystallization lead to the formation of high-melting-temperature fractions. − The melting temperature of these fat fractions is higher than the human body temperature and exists as a solid in the gastrointestinal tract (GIT). Generally, high-melting-temperature lipids containing solid fat at body temperature tend to have a lower digestibility and bioavailability compared with liquid oils, which was verified by in vitro , , animal, and human , studies. On the one hand, these solid TAG fractions, which are mainly composed of long-chain saturated FAs, have the problem of being indigestible and the risk of inducing cardiovascular diseases .…”

“…Whereas, the dominant peak of the 20L fraction shifted to a larger size (25.2 μm) compared to that of whole butterfat (12.6 μm). This might be because the 20L fraction ( T endset = 22.0 °C, Table S1) existed in the form of liquid oil in the system, and the mobility of exposed liquid-state lipid droplets was greater than that of solid-state lipid crystals, thus weakening steric hindrance and increasing the contact frequency between droplets, which helped to form large-sized aggregates . Interestingly, the physical state of butterfat fractions (liquid oil: 20L vs solid fat: 20S, T endset = 38.9 °C and 30S, T endset = 42.1 °C) did not have a consistent influence on the droplet size.…”

“…Indeed, visual observation of digestive products did not contain any visibly large aggregates or sediments after the small intestinal phase (Figure f). After being hydrolyzed and released, the liquid-state 20L fraction was well dispersed in the digestive juice due to its good mobility, which was accessible to bind with bile salts and/or digestive enzymes at the oil–water interface . Therefore, the 20L-reconstituted MFG emulsion underwent the most extensive dissociation, thereby resulting in smaller particle size than other emulsions during intestinal digestion.…”

“…For the analysis of in vitro digestion products, titration (pH stat) and gas chromatography (GC) are the most commonly used methods, which provide information about the release of total fatty acids and individual fatty acids during digestion, respectively. However, pH-stat titration is not absolutely accurate for the released free fatty acids (FFAs) because some long-chain FFAs in a micellar solution are not ionized at pH 7 and therefore cannot be titrated. , Recently, a fast GC method was used to separate triacylglycerols, diacylglycerols (DAGs), monoacylglycerols (MAGs), and free fatty acids and then simultaneously measured all lipolytic products released during in vitro digestion using a combined analysis of the GC and pH-stat titration . The GC method accurately monitored individual FFA for lipolysis research, but it could not accurately identify individual DAG and MAG with larger molecular weights and higher boiling points.…”