Browning and Aroma Development During Heating of Bovine Muscle Systems as Affected by Lipid Composition of the Muscle

Browning and aroma development were studied in heated lyophilized meat systems of differing lipid composition. To achieve variation in lipid content of the meat systems, bovine muscle was obtained from animals that were fed differently as to both ration and overall plane of nutrition. These included grass-fed, limited grain-fed and full grain-fed animal. Chloroform-methanol extracts of lyophilized meat from grass-fed, limited grain-fed and full grain-fed animals were analyzed for phospholipid content by phosphorus analysis. The extracted lipid was fractionated, and methyl esters of the neutral lipid and phospholipid fractions were analyzed by gas-liquid chromatography.

Four lyophilized meat systems from beef of each dietary treatment were heated for browning and aroma assessment. The four systems were treated before lyophilization as follows: (1) no treatment, (2) added glucose (4% by weight), (3) glucose oxidase treatment and (4) glucose oxidase treatment plus added glucose (4% by weight). Hunter L, a and b color values were obtained for the heated lyophilized systems. Aroma of heated systems was assessed by means of aroma profiling by a trained sensory panel of seven members.

There was a significant effect of animal diet on neutral lipid (P < 0.01) and phospholipid (P < 0.05) content of steaks used for the preparation of lyophilized systems. Beef from grass-fed animals had higher concentrations of polyunsaturated fatty acids than did beef from grain-fed animals.

Dietary treatment of the animals had a significant effect on Hunter L values of heated systems (P < 0.01). The addition of glucose at 4% had a significant effect on both Hunter L (P < 0.001) and b (yellowness) values (P < 0.01). Systems with added glucose were visibly much browner than systems with no added glucose. The removal of intrinsic glucose by enzymatic treatment, however, had little or no effect on browning.

Panel assessments of meat system aroma in terms of 14 standard aromas indicated that both dietary treatment of the beef animal and system modification imposed by the researcher affected panelists' responses to most aroma notes. Grass and ammonia aromas were more often used to characterize heated systems containing grass-finished beef than those containing grain-finished beef. Rancid fat and beef aromas were more characteristic of heated systems containing grain-finished beef. Dominant aroma notes expressed for systems containing added glucose were brown sugar, toast and burnt paper.

Although lipid analysis in this investigation indicated significant dietary influences on proportions and fatty acid composition of neutral lipid and phospholipid, the browning data suggest that the addition of reducing sugar was a more important factor in meat browning than was lipid composition as affected by animal diet. Similarly, although diet affected both lipid composition of the meat and panelists' perception of most aroma notes in the heated systems, a direct relationship between lipid composition and aroma development was not observed. Possibly the added glucose obscured aroma differences that might have been attributed to diet.