Both summer and winter butterfats were fractionated using a laboratory procedure which was designed to simulate a commercial fractionation process. The process is based on a slow, controlled cooling of the melted fat, a short stabilization time at the fractionation temperature, and separation of the crystals from the liquid oil by vacuum filtration using a stainless steel perforated disc. Fractionation temperatures of 29, 26, 23 and 19 C for winter butterfat and 29 and 19 C for summer butterfat were used to obtain solid and liquid fractions at each temperature. Three replications at each temperature showed good reproducibility of results. The fractions were characterized by their fatty acid and triglyceride compositions, melting and crystallization behavior, iodine value, peroxide value and melting point.

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To evaluate the thermal oxidative behavior of butterfat in comparison to selected vegetable oils, samples of winter and summer butterfat, liquid and solid butterfat fractions, and selected vegetable oils were heated at 185 C in the presence of air (30 ml/min) for 8 and 16 hr. The resultant heated fats and oils, as well as the methyl esters of their fatty acids, were examined by gel permeation chromatography. The results indicated that butterfat is much more stable to thermal oxidation than canola, sunflower and soybean oils. This was evidenced by a substantially higher content of both dimeric and higher oligomeric triglycerides in the vegetable oils than in any of the butterfat samples after both 8 and 16 hr of heating. The corn oil also exhibited a high degree of stability to thermal oxidation after 8 hr of heating. The 16 hr corn oil data, however, was less certain due to the presence of a very viscous and dark colored material which could not be removed from the oxidation flask; this was believed to contain highly polymerized oil and was not observed with any of the other samples. There were some differences in the inter‐ and intramolecular polymerization of the butterfat fractions compared with each other and with whole butterfat. With the winter butterfat samples, after 8 hr of thermal oxidation, both the solid and liquid butterfat fractions exhibited more stability toward intermolecular polymerization than did the whole butterfat. After 16 hr of heating the ratio of trimeric and higher oligomeric triglycerides to dimeric triglycerides increased with increasing degree of unsaturation of the butterfat and with increased time of heating. Similar trends were observed with regard to the degree of intramolecular polymerization.

It is well known that inadequate insulin therapy stimulates body protein loss in insulin-dependent diabetes mellitus (IDDM). It is less well known, however, that accelerated body protein loss (as indicated by increased leucine oxidation) occurs in IDDM even during conventional glycemic control. It is not known whether intensified insulin therapy fully normalizes protein oxidation or, more importantly, whether such therapy is sufficient to allow the adaptive decrease of protein oxidation that normally occurs when protein intake is restricted below the customary surfeit level. We used two measures of protein oxidation [daily urinary nitrogen (N) excretion over several days of intensive insulin therapy and plasma [1-13C]leucine oxidation during short-term strict euglycemia] to assess the response of 7 men with IDDM and 12 normal men after adaptation first to a control diet providing maintenance energy and conventional (surfeit) protein then to an isoenergetic protein-free diet. After adaptation to the protein-free diet and during short-term strict euglycemia achieved using intravenous insulin, leucine turnover and oxidation decreased equivalently in normal and diabetic subjects. However, daily urinary obligatory N excretion, which indicated the effect of the low-protein diet and intensive subcutaneous insulin therapy over several days, was increased by 18% in the diabetic group (P less than 0.05). Even mildly elevated average blood glucose values well within the guidelines for intensive therapy were strongly correlated with high rates of urinary N excretion (r = 0.97, P = 0.0002). Thus insulin therapy of IDDM that imposes strict euglycemia is compatible with a normal ability to diminish body protein oxidation in response to protein restriction.(ABSTRACT TRUNCATED AT 250 WORDS)

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