Key words: butter, north-eastern region of Poland, fatty acid composition, vaccenic acid, CLAThe study investigated the fatty acid composition (fatty acids, FA) of 19 samples of butter originating from the north-eastern region of Poland throughout the year. The annual variability was observed in the FA composition of butter. A higher content of short and medium chain saturated FA (SCFA) was determined in the samples from the winter season (12.6-13.4%) and lower one in the summer samples (11.2-12.1%). The major FA of the saturated long chain acids (LCFA) of butter were: palmitic C16:0: (25.7-34.6%) and myristic C14:0: (9.7-11.9%), their higher contents were found in the samples from the winter and early-spring production. Butters produced in the summer period were characterised by a higher content of oleic acid C18:1 9c (20.6-23.1%) belonging to monounsaturated FA (MUFA) as compared to the samples produced in the winter and spring (18.3-21.4%). Contents of FA belonging to polyunsaturated fatty acids (PUFA) were: 1.0-1.5% for linoleic C18:2 9c 12c (LA) and linolenic acids C18:3 9c 12c 15c (ALA), which were subjected to seasonal variation in the range of 0.1-1.0%. The content of predominant trans isomer in ruminant fats, i.e. vaccenic acid C18: 1 11t (VA), resulting from "biohydrogentaion" of the PUFA (LA and ALA) in the rumen, has been strictly connected with the season of production: a higher content of VA was determined in butter samples from the summer and autumn (1.9-3.8%) and lower one in the samples produced in the winter and spring (0.8-1.3%). Similarly, seasonal variation was also observed in the content of conjugated linoleic acid C18: 2 9c11t (CLA). Its signifi cant content -580 mg CLA /100g of product on average -was determined in butter samples produced in the summer and autumn season in the north-eastern region of Poland.

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An appropriate composition of milk fatty acids (FA) improves the nutritional value of milk and milk products, and improves milk processing. Polish dairy farms in the mountainous region are rather small, animal nutrition there is based on locally produced forages and this, together with the transitional climate zone brings about seasonal changes in FA composition of milk. The aim of the study was to evaluate the composition of FA in bovine milk fat in relation to fat intake in forages and their FA profiles. The study involved 5 herds reared in low-input mountain farms located at an altitude of 670-780 m above sea level (Beskid Mountains). The cows were fed forages produced locally. FAs in forages and milk samples were subjected to gas chromatography. Highest fat intake observed in grazing season (4·2-4·7%) and high amounts of polyunsaturated FA in forages from that period (51·8-64·1 g/100 g FA) resulted in a markedly high content of valuable FAs: t-11 C18:1 (3·22 g/100 g FA), c-9, t-11 C18:2 (CLA; 1·20 g/100 g FA) in milk. Lower fat intake of forages containing high amount of SFA (32·42-38·83 g/100 g FA) in the indoor period resulted in changes in milk composition. The content of total short-chain saturated FA (SCFA) was highest in winter and early spring samples (14·10 and 13·44 g/100 g FA, respectively), like the amounts of myristic C14:0 and palmitic C16:0 acids (11·80 and 37·92 g/100 g FA). Total odd- and branched-chain fatty acids (OBCFA; 6·58 g/100 g FA) content was highest at the beginning of the grazing period. Fresh grass consumed by cows promoted the activity of Δ(9)-desaturase in mammary gland as evidenced by higher C14:1 : C14:0 (0·054) and C16:1 : C16:0 (0·026) ratios in grazing than in the indoor periods.

The effect of incorporation of different contents of chokeberry polyphenols extract (CPE) into cookie recipe on the oxidative stability of the lipid fraction of cookies was determined in the study. Margarine and butter cookies with different contents of CPE were prepared. Contents of primary (Peroxide value, PV) and secondary (Anisidine value, AV; thiobarbituric acid reactive substances, TBARS) lipid oxidation products and fatty acids profi le were measured during storage. Different course of lipid degradation depending on both polyphenols content and storage time was shown. Cookies were characterised by a low PV (1.45 and 4.90 meq of O/kg of fat in margarine and butter cookies, respectively). The AV increased during storage both in margarine and in butter cookies. Losses of PUFA in margarine cookies (0.34%) apply mainly to α-linolenic acid. It appears safe to incorporate 100 mg and 250 mg of CPE into margarine cookies stored for 9 weeks and 1000 mg of CPE into butter cookies stored for 9 weeks. The incorporation of 1000 mg CPE into cookies resulted in a signifi cant increase in the intensity of astringent taste, acidic taste, off-taste and off-fl avour.

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This review analyzes the current state of knowledge on odd- and branched-chain fatty acids present in milk fat. Special attention is devoted to the characteristic, synthesis in ruminants, factors affecting their content in milk fat and pro-health properties of these compounds. The group of odd- and branched-chain fatty acids includes mainly saturated fatty acids with one or more methyl branches in the iso or anteiso position. These fatty acids are largely derived from ruminal bacteria and they have been transferred to ruminant tissue (milk and meat). For that reason they have been used as biomarkers of rumen fermentation. Odd- and branched-chain fatty acids are exogenous products for humans, and therefore have specific properties. The results of research from recent decades show that odd- and branched-chain fatty acids have anti-cancer activity. Branched-chain fatty acids may reduce the incidence of necrotizing enterocolitis. Additionally, these compounds have a beneficial effect on proper tissue function and on functioning and development of the infant gut, whereas odd-chain fatty acids are considered as biomarkers of milk fat intake by humans. So far, not all the mechanisms of activity of these compounds are known thoroughly. They should be more carefully studied for application of their biological effects in prevention and treatment.

The aim of the study was to assess the effects of partial replacement of soybean meal with a protein-equivalent amount of rapeseed cake in the diet on milking parameters and fatty acid (FA) composition of milk in dairy cows. Two groups of Holstein-Friesian cows, 8 each, consisting of randomised blocks were studied: a control group (C) was given a traditional high-protein supplement (extracted soybean meal) and the experimental group (E), had part of extracted soybean meal replaced with rapeseed cake. Dry matter intake and milk yield in both groups were not affected by the diet but milk fat percentage and yield were decreased in both groups. Rapeseed cake had no effect on milk acidity or on protein (including casein) and lactose contents. A lower concentration of urea in milk in E group indicated a proper ratio of protein to energy in the fodder. Health condition of mammary gland and indicators of metabolic profile were not affected by rapeseed cake supplementation. In E group, the share of atherogenic saturated fatty acids (FA) was reduced after 11 weeks: palmitic, by 26% and myristic, by 22%; moreover, as compared with control cows, the content of monounsaturated FA in milk increased by 44% after 3 weeks and by 68% after 11 weeks, t-18:1 and c-9 t-11 isomer of CLA increased about 2.5-fold after 11 weeks. In E group, the atherogenic index (AI) was significantly (P < 0.001) lower than in C (by 54% on average) and the decrease with time was considerable (by 29%, P < 0.001). Contents of odd- and branched- chain FA in milk were not significantly affected thus reflecting proper rumen function. Partial replacement of soybean meal with rapeseed cake in the diet of cows may improve both milking indices and FA profile of milk.