We evaluated whether the adipose tissue content of 2 fatty acids of exogenous origin specific for ruminant fat, 15:0 and 17:0, reflect average long-term dairy fat consumption in free-living subjects. In 81 healthy women aged 30-77 y, we compared the relative content of these 2 fatty acids in subcutaneous adipose tissue with relative intake (% of total fat) based on four 1-wk weighed diet records made 3-4 mo apart and on a food-frequency questionnaire reflecting average past year consumption. The mean (+/-SD) daily milk fat intake was 20.0 +/- 9.1 g and fat from ruminant meat was 3.0 +/- 1.5 g according to food records, representing 29.2 +/- 8.9% and 4.6 +/- 2.2% of total fat, respectively. The intake of 15:0 and 17:0, which are 1.05% and 0.61% of milk fat and 0.43% and 0.83% of ruminant meat fat, was 0.22 +/- 0.10 and 0.15 +/- 0.06 g, respectively. Content of 15:0 and 17:0 in adipose tissue was 0.35% and 0.24% and relative dietary intake was 0.33% and 0.22% according to the food records and 0.32% and 0.21%, respectively, according to the food-frequency questionnaire. Correlation coefficients between 15:0 content in adipose tissue and intake from dairy foods only, according to food records, were 0.63 (Pearson) and 0.59 (Spearman); corresponding values for 17:0 were 0.42 and 0.45, respectively. Content of 15:0 and 17:0 in subcutaneous adipose tissue might be a valid biological marker of long-term milk fat intake in free-living individuals in populations with high consumption of dairy products.

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Milk samples from five commercial dairy herds having severe problems with spontaneous oxidised flavour (SOF) and milk samples from five herds without such problems were analysed for parameters connected with SOF in milk. The study was directed towards analysing parameters which primarily are influenced by feeding. The fatty acid compositions of both neutral lipids and phospholipids were determined as well as the concentrations of α‐tocopherol, β‐carotene and copper in the milk. The samples were also analysed by dynamic headspace GC to determine volatile oxidation products. The results showed that the reasons for the occurrence of SOF in a specific herd are still obscure, since the only consistent result found for the five control herds, when compared with the corresponding experimental herd, was a higher proportion of the 18:1 trans fatty acid. However, within the affected herds, the difference between cows giving milk with off‐flavour and cows giving milk without off‐flavour was quite clear. In four out of five herds the ratio between antioxidants and fatty acid unsaturation was lower in milk with off‐flavour, and in the fifth herd an extremely high proportion of 18: 2 in the phospholipids seemed to have been the reason for the off‐flavour that developed. One of the herds also had a higher copper content in milk showing SOF. The data showed differences in importance of α‐tocopherol and β‐carotene, in different herds. Also the unsaturation in fatty acids of both neutral lipids and phospholipids had different importance for the flavour stability in different herds. © 1998 SCI.

The incidence of spontaneous oxidized flavor (SOF) is commonly assumed to be dependent on the combination of substrate supply and contents of pro-and anti-oxidants in milk. A total of 142 cows in the experimental herd at the Swedish University of Agricultural Sciences were included, 87 of the Swedish Red breed and 55 of the Swedish Holstein breed. Altogether 893 milk samples were analyzed for milk composition, copper content, and milk flavor. Milk copper concentration was highest in early lactation and during the spring period. Oxidative off-flavor was most common during the first 3 weeks of lactation. However, when adjusting for copper concentration the odds ratio for incidence of SOF was instead highest in lactation weeks 14Á39. The higher incidence of SOF during the first 3 weeks of lactation is proposed to be a consequence of the high copper concentration in milk during this period.