The objective of the present study was to evaluate the oxidative susceptibility of LDL in human volunteers following supplementation with various low doses (<1 g/d) of n–3 polyunsaturated fatty acids (PUFA). Sixty-two healthy volunteers (thirty-seven males and twenty-five females, aged 19–63 years) were recruited to take part in a randomised placebo-controlled trial. Volunteers were required to take 0.9, 0.6 or 0.3 g n–3 PUFA as fish oil or placebo capsules daily for 16 weeks. Susceptibility of LDL to oxidative modification was assessed by measuring the production of conjugated dienes and thiobarbituric acid-reactive substances in LDL oxidised by Cu2+ (15 μM) OR 2,2″-AZOBIS(2-AMIDINOPROPANE) DIHYDROCHLORIDE (1 Mm) for 5 h. Plasma fatty acid and LDL-fatty acid composition, cholesterol levels and antioxidant concentrations were also measured. While post-treatment n–3 PUFA compositions of plasma and LDL reflected the capsule contents, no meaningful differences in antioxidant concentrations or cholesterol levels were observed between the groups. Supplementation with low doses of n–3 PUFA as fish oil did not influence the oxidative susceptibility of LDL. The results of the present study suggest that moderate dietary intakes of n–3 PUFA do not significantly influence the susceptibility of LDL to oxidative modification in vitro.

The effect of 15 amides and related compounds on the heat stability of milk was investigated; of these urea, biuret, triuret, methyl urea and ethyl urea had a similar stabilizing effect. These 5 compounds reacted with lysine to form a ninhydrin-positive compound, possibly homocitrulline, and with lactose produced Maillard-type browning, but some of the other compounds studied were also capable of participating in one or both of these reactions. The only effect which the 5 stabilizing amides had in common and which the other compounds did not share was a significant pH-buffering capacity in synthetic systems and in milk. It is suggested that urea exercises its stabilizing influence in milk principally through its ability to buffer the pH of the system during heating.