Michael Enser

Dietary manipulation of fatty acid composition in lamb meat and its effect on the volatile aroma compounds of grilled lamb

The effect on lamb muscle of five dietary supplements high in polyunsaturated fatty acids (PUFA) was measured. The supplements were linseed oil, fish oil, protected lipid (high in linoleic acid (C18:2 n-6) and α-linolenic acid (C18:3 n-3)), fish oil/marine algae (1:1), and protected lipid/marine algae (1:1). Eicosapentaenoic acid (C20:5 n-3) and docosahexaenoic acid (C22:6 n-3) were found in the highest amounts in the meat from lambs fed diets containing algae. Meat from lambs fed protected lipid had the highest levels of C18:2 n-6 and C18:3 n-3, due to the effectiveness of the protection system. In grilled meat from these animals, volatile compounds derived from n-3 fatty acids were highest in the meat from the lambs fed the fish oil/algae diet, whereas compounds derived from n-6 fatty acids were highest in the meat from the lambs fed the protected lipid diet.

Effects of dietary linseed on nutritional value and other quality aspects of pig muscle and adipose tissue.

This study reports improvements in the nutritional value of pork by including linseed in the diets of boar and gilt pigs. Two feeding strategies, either short-term or long-term, were employed: (i) 0 g or 114 g linseed per kg of food provided to 16 pigs of 87 kg live weight for 20 or 27 days; (ii) 0 g, 10 g, 20 g or 30 g linseed per kg of food provided to 64 pigs of 46 kg live weight for 54, 62, 68 or 75 days. All diets were supplemented with DL-α-tocopheryl acetate (0•2 g/kg). The 18 : 3n-3 contents (18 : 2n-6 :18 : 3n-3 ratios in parentheses) of the short-term 0 g and 114 g/kg, and long-term 0g, 10 g, 20 g and 30 g/kg linseed diets, were 2•1 g (7•75), 28•1 g (0•70), 1•0 g (8•86), 3•4 g (2•73), 6•0 g (1•66) and 8•1 g/kg food (1•25) respectively. The long-term 30 g/kg diet reduced the n-6 : n-3 ratio of muscle and adipose tissue as successfully as the short-term 114 g/kg diet to accord with guidelines for the overall human diet (5 :1 or less) but required only 0•73 as much linseed and increased the proportion of C20-22 n-3 fatty acids more effectively; compared with their respective control diets, the 114 g/kg and 30 g/kg diets more than halved the n-6 : n-3 ratios in muscle to 3•8 and 3•9, approximately trebled the concentrations of 18 : 3n-3 in muscle to 0•43 mg and 0•28 mg/g tissue, and doubled the concentrations of 20: 5n-3 in muscle to 0•08 mg and 0•10 mg/g tissue. Similar changes occurred in adipose tissue. With both strategies, the majority of the changes had occurred by the time the first groups were slaughtered. There was a strong relationship between the 18 : 2n-6 :18 : 3n-3 ratio of the food and tissues and the accumulation of all C20-22 n-3 fatty acids, except 22 : 6n-3, which was unaffected by dietary linseed. The improvements in nutritional value were obtained without changes in organoleptic characteristics, as measured by a trained taste panel, or significant loss of shelf-life, as measured by TBARS analysis and colour stability.

Modelling the effect of fatty acids in odour development of cooked meat in vitro: part I - sensory perception

We have investigated the contribution of muscle components to the development of cooked meat odour in an aqueous model system using trained taste panels. Reaction mixtures were prepared with oleic, linoleic and linolenic acids with or without cysteine and ribose in a buffer with or without ferrous sulphate. Odour profiles were assessed and triangular tests were used to determine the ability of panellists to discriminate between mixtures. The presence of sugar and amino acid was highly detectable by panellists independently of the fatty acid considered (P<0.001). However, the presence of C18:3 made differences more obvious between mixtures than the presence of C18:1 or C18:2. Meaty notes were only associated with cysteine and ribose. Fishy notes were only apparent in C18:3 mixtures with or without sugar and amino acid, although the presence of cysteine and ribose decreased the perception. The addition of Fe(++), a pro-oxidant present in the muscle, produced a reduction in the score of the attributes although the pattern was the same as when Fe was not used in the mixtures. Only fishy notes that were exclusively perceived in C18:3 mixtures showed a higher score in the presence of iron. Iron also produced a better discrimination in C18:3 mixtures, which were closely related to grassy notes in the presence of cysteine and ribose.

Effects of litter size and subsequent gold-thioglucose-induced obesity on adipose tissue weight, distribution and cellularity in male and female mice: an age study

1. Over- or undernutrition of newborn mice was caused by suckling in litters consisting initially of four or eighteen pups. After weaning mice were fed ad lib. At 13 weeks of age some mice from large litters received gold thioglucose (GTG: 600 mg/kg intraperitoneally) to induce hyperphagia, and mice were killed at 13, 19.5, 26, 39 and 52 weeks. 2. Total carcass lipid and the size and number of adipocytes in the inguinal subcutaneous, genital, perirenal and mesenteric depots were determined. 3. Mice, both male and female, raised in small litters were heavier and had more carcass fat at all ages than mice raised in large litters. After GTG-treatment mice from large litters were heavier and fatter than mice raised in small litters. 4. Fat distribution between the depots was related to carcass lipid content and not to treatment. The order of depot development was subcutaneous, parametrial, perirenal and mesenteric in females and epididymal, subcutaneous, perirenal and mesenteric in males. At 13 weeks the depots in males were more developed than those in females. 5. Litter size had no effect on adipocyte volume in female mice at 13 weeks but by 52 weeks small-litter mice had larger cells in all depots and more cells in the parametrial and perirenal depots. 6. Male mice from small litters had bigger cells at 13 weeks in all depots compared with males from large litters but by 52 weeks no significant differences remained. Greater numbers of cells were present only in the perirenal and mesenteric depots of small-litter males at some ages. 7. Depots of GTG-treated large-litter female mice had larger cells than those of small-litter females, while a similar number of cells was found by 52 weeks in all but the perirenal depot, which had significantly more cells. 8. GTG treatment of male mice from large litters also caused bigger cells than in small-litter mice, and an increased depot cell number at earlier ages in all but the epididymal depot. By 52 weeks cell numbers were similar in depots from small-litter and GTG-treated large-litter mice, except for the epididymal depot from the latter which had fewer cells. 9. Increases in cell numbers with age in different depots occurred independently of existing cell mean volume and even of tissue growth, suggesting the presence of an in-built chronology, at least in older mice.(ABSTRACT TRUNCATED AT 400 WORDS)