Abstract
Fats containing the stearoyl-rich triacylglycerols (TAGs) of 1,2-distearoyl-3-oleoylglycerol (SSO) and 1,3-dioleoyl-2-stearoylglycerol (OSO) were synthesized via the lipase-catalyzed acidolysis of tristearin (SSS)-rich fat and oleic acids, followed by solvent fractionation. Their physicochemical properties and in vitro digestibilities were compared. The SSS-, SSO-, and OSO-rich fats comprised 81.6%, 52.9%, and 33.1% stearic acid, respectively, whereas oleic acid comprised 2.9%, 37.5%, and 56.2%, respectively. The SSS-, SSO-, and OSO-rich fats contained the TAGs of SaSaSa (100.00%), SaSaMo (86.98%), and MoSaMo (67.12%), respectively, and the major TAGs were SSS, SSO, and OSO, respectively. Melting and crystallization temperatures were higher and fat crystals were larger and densely packed in the descending order of SSS-, SSO and OSO-rich fats. Both in vitro multi-step digestion and pH-stat digestion were more rapid for OSO- than SSO-rich fat. Oleic acid was digested faster than stearic acid during the initial digestion, then the rate decreased, whereas that of stearic acid increased over prolonged digestion. Fats that were richer in stearoyl at the sn-1,3 position of TAG melted and crystallized at higher temperatures, had a densely packed microstructure of large fat crystals and were poorly digested. Stearic acid imparts the essential physical attributes of melting and crystallization in solid fats, and the low digestible stearoyl-rich fat would be a viable substitute for trans fatty acids in food lipid industry.
Highlights
The type and stereospecificity of fatty acids (FAs) in triacylglycerols (TAGs) determine the physicochemical and digestion properties of dietary fats, oils, and food products
The FAs of SSO-rich and OSO-rich fats consisted of stearic, oleic, palmitic, and linoleic acids, and the stearic acid content was significantly higher in SSO-rich fat (52.89%) than in OSO-rich fat (33.14%) (p < 0.05), whereas the oleic acid content was higher in OSO-rich fat (65.23%) than in SSO-rich fat (37.45%) (p < 0.05) (Table 1)
Lipozyme RMIM catalyzed the acidolysis reaction between substrates of SSS-rich fat and oleic acid rich free FAs (FFAs), where FAs at the sn-1(3) positions of TAGs in SSS-rich fat were hydrolyzed, whereas oleic and stearic acids were simultaneously re-esterified in the TAGs producing SSO- and OSO-rich fats
Summary
The type and stereospecificity of fatty acids (FAs) in triacylglycerols (TAGs) determine the physicochemical and digestion properties of dietary fats, oils, and food products. TAGs have a saturated FA such as palmitic (P) or stearic (S) acid at the sn-1 (or 3) position and an unsaturated FA such as oleic acid (O) or linoleic (L) acid at the sn-2 position. They comprise the major TAGs of POS, SOS, and POP in cocoa butter, POO, POP, and POS in beef tallow, and SPO, OPL, and OPO in lard [1]. The digestion, absorption, and metabolic fate of dietary fats are determined by the stereospecificity (sn-1,3 or sn-2) and FAs with different chain lengths and degrees of saturation/unsaturation in TAG molecules [2]. Long-chain saturated FAs such as stearic acid in the sn-1 (or 3) position are hydrolyzed, bound to calcium or magnesium ions, excreted as an insoluble FA soap [1,2]
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