In the metabolism of triacylglycerol (TG)-rich lipoproteins, 2-monoacylglycerols (2-MG) are produced by lipoprotein lipase (LPL) hydrolysis of TG. The metabolic fate of 2-MG is not known with certainty. 2-MG that accumulate on the chylomicra surface have been proposed to isomerize spontaneously to 1(3)-MG, which are then hydrolyzed by LPL to free fatty acids and glycerol. In this study the rate and the effect of acyl chain saturation on the spontaneous acyl migration of 2-MG in in vitro model chylomicra emulsions were determined. After 1 h of incubation at 37 degrees C, less than 20% of 2-monoolein (2-MO) or 2-monopalmitin (2-MP) spontaneously isomerized to 1(3)-MO or 1(3)-MP, respectively. Accordingly, it was concluded that spontaneous isomerization of 2-MG is not the major mechanism for 2-MG metabolism post-TG hydrolysis in chylomicra. Isomerization rates, expressed as decrease in percentage of 2-MG remaining per hour, were -5.12 and -5.86 in water, and -0.43 and -0.41 in hexane for 2-MO and 2-MP, respectively. There was no significant difference between the isomerization rates of 2-MO and 2-MP. Thus, in the present study, saturation of the MG acyl chain did not influence spontaneous acyl migration in either water or hexane, but isomerization of 2-MG was faster in water than in hexane.

The influences of fluorescent light exposure and packaging atmosphere on the headspace volatiles and color of Cheddar cheese shreds were evaluated using gas chromatography-mass spectrometry and spectrocolorimetry, respectively. Cheddar cheeses were packaged under atmospheres of 100% carbon dioxide or 100% nitrogen and stored at 4 degrees C under fluorescent light for 6 weeks. Cheeses stored under carbon dioxide contained higher concentrations of aldehydes and fatty acids and lower concentrations of alcohols and esters than cheeses stored under nitrogen. Carbon dioxide atmospheres potentiated light-induced oxidation in shredded Cheddar cheeses, as evidenced by aldehyde and fatty acid headspace volatiles measured following storage. Color bleaching occurred only in cheeses packaged under carbon dioxide and exposed to light. The shift in color is proposed to be due to an interaction between carbon dioxide and high-intensity light, leading to the oxidation of the pigment molecule, bixin. The results have significant implications for procedures used to handle and store pigmented cheeses to ensure desirable flavor and consumer acceptability.

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The amount of acyl heterogeneous triacylglycerol (TGHET) solubilized by phosphatidylcholine (PC) vesicles, prepared by co-sonication of egg PC and small amounts (<6% w/w) of TGHET, was determined using 13C nuclear magnetic resonance (NMR). The acyl chains of TGHET were predominantly 16 or 18 carbons in length, 50% saturated, and approximately 21.7% 13C isotopically enriched at the carbonyl carbon. The 13C NMR spectra revealed two carbonyl resonances at chemical shift values between PC carbonyls and oil-phase TG carbonyls, confirming the presence of TGHET solubilized in PC vesicles. Oil-phase TG carbonyl peaks were present only in spectra of vesicles containing >3 wt % TGHET. Integration of TGHET carbonyl resonances determined that PC vesicles solubilized 3.8 wt % of TGHET, compared to 2.8 wt % of acyl homogeneous triolein. The difference between the maximum solubility of TGHET and that of homogeneous TG (TGHOM) with similar acyl chain lengths provides evidence that specific acyl composition, in addition to the acyl chain length of triacylglycerols, affects the solubility of TG in PC vesicles and TG-rich lipoprotein surfaces. Thus, TGHET may innately be a better model substrate than TGHOM for determination of substrate availability of TG at lipoprotein surfaces. Keywords: Solubilization; heterogeneous; triacylglycerol; vesicle; 13C nuclear magnetic resonance