Effects of dietary fat source on physical , chemical and sensorial quality of calves ’ meat

The effects of including rape seed (10%) and fi sh oil (4%) into the diet for 30 calves (7-90 days of life) on the physical, chemical and sensorial quality of meat were investigated. The analyses encompassed nutrient content in the diet, pH, colour and tenderness measurement, and evaluation of sensorial properties such as texture, tenderness, fl avour, tastiness and juiciness. Fat supplementation had no signifi cant effect on the chemical and physical properties of meat. Rape seed did not change the sensorial quality of meat, in contrast to fi sh oil, which deteriorated the texture, fl avour and tastiness of meat.


INTRODUCTION
Meat from ruminants is a major source of essential nutrients for humans (amino acids, iron, zinc and B-group vitamins) but contains excess saturated fat, which can be a major risk for the development of coronary heart disease (Williams, 2000).Feeding calves diets high in unsaturated fatty acids, especially n-3 and n-6 PUFA, can improve the health quality of meat (Zymon et al., 2005;Zymon and Strzetelski, 2006) but not necessarily its sensory value.Ruminant meat is an attractive type of food, especially because of its sensory quality traits: colour, tenderness, fl avour and juiciness.These tissue characteristics depend on many breeding factors including nutrition, physiological state and genetic type of the animal, as well as rearing systems (grass-or grain-fed) of animals (Geay et al., 2002).The aim of this study was to determine the effect of rape seed or fi sh oils as ZYMON M. ET AL. a fat supplement to calf diets on the dietary value of meat, physical and chemical traits and sensory qualities of calf meat.

MATERIAL AND METHODS
Thirty Black-and-White bull calves, aged from 7 to 90 days, were randomly divided into 3 equal groups.Calves were fed ad libitum a concentrate without or with rape seed or fi sh oil (Table 1).For the fi rst 56 days the calves also received a milk replacer.At the end of the experiment the calves were slaughtered and samples of meat from the Musculus thoracis were taken for analysis.The nutrient content of meat was determined by standard procedures (AOAC, 1998).pH was measured 45 min and 24 h after slaughter, meat colour was determined according to the CIE L*a*b* system (Boccard et al., 1981).After 48-h cooling of meat samples, thermal weight loss and tenderness were measured (Joseph, 1979).Meat samples were sliced into 1.5 cm thick steaks and cooked at 165°C to an internal temperature of 70°C.Sensory evaluation was performed according to a 5-point scale (Baryłko-Pikielna, 1975).The results were analysed statistically using the one-way analysis of variance procedure of SAS (Enterprise Guide, 2002).The differences were assumed to be not signifi cant at P>0.05.

RESULTS
No differences were found among groups in dry matter and protein contents, although a tendency towards a higher fat content in the meat of calves fed fi sh oil (1.2% DM) than in those fed rape seed oil (0.9% DM) and the control feed (1.0%DM) (P>0.05) was noted.The studied fat sources did not cause signifi cant differences (P>0.05) in the physicochemical characteristics of meat (Table 2).A trend was noted, however, towards a decrease in thermal weight loss in meat from calves fed rape seed and fi sh oils.At the same time, however, this meat was characterized by a somewhat worse tenderness.Twenty-four h after slaughter the meat of calves fed rape seed showed a tendency towards paler colour and lower yellow saturation, whereas 48 h after slaughter, to lower red saturation.After 48 h of cold storage, the meat from calves in all groups was characterized by a lighter colour and greater yellow saturation than meat in cold storage for 24 h.In all groups the pH was on a uniform level, with a proportional decline notes after 24 h.It was found that the meat of calves fed fi sh oil had the least pleasant smell (P≤0.05),despite its intensity being weaker than in other groups (Table 3).The fi sh-oil group also had the lowest structure and tastiness desirability scores (P≤0.05).Rape seed signifi cantly improved the tastiness desirability of meat in comparison with fi sh oil (P≤0.05).In the group of calves fed rape seed, a tendency was noted towards a worse structure, but also towards greater fl avour intensity and better juiciness of meat.

DISCUSSION
The fi rst trait that a client takes into account when buying meat is its colour.In this experiment, colour parameters were characteristic for veal (Sterrenburg et al., 1991), although in the case of feeding rape seed, the meat was slightly darker.Krełowska-Kułas et al. (1991) using a 30% addition of crushed rape seed in feeds for young bulls showed that the meat was characterized by desirable colour traits.The lightening of colour and lowering of the pH that occurred after 48 h of cold storage was probably related to the post-slaughter acidifi cation of meat, resulting in the formation of lactic acid.The rapid cooling of meat after slaughter lowers the intensity of glycolytic processes, and therefore the rate at which the pH declined in meat (Guignot et al., 1994).In ruminants, variations in diet composition allow some modifi cations in digestive processes, which regulate the nature and proportion of absorber nutrients and thereby affect meat tenderness (Geay et al., 2001).When rape seed and fi sh oil were fed, a tendency towards deterioration of meat tenderness in comparison with controls was found, although this change did not reach statistical signifi cance.In the opinion of Hocquette et al. (1998) the differences in meat tenderness can be explained by the differences in growth rate and fattiness.Meat fl avour can be modifi ed by rearing animals using nutritional conditions which change fat contents and compositions or which change compounds involved in the Maillard reaction (Geay et al., 2001).The reason for the deterioration of the fl avour and smell of the meat when fi sh oil was fed was probably the different fatty acid profi le of the meat fat, which has a signifi cant infl uence on the nature of the compounds arising during thermal processing of meat (Reineccius, 1994).The long-chain fatty acids in fi sh oil can bypass rumen biohydrogenation with minimal change (Scollan et al., 2004).This increase in unsaturation can lead to negative fl avour perception.Juiciness depends on the degree of water binding by protein and on the content of intramuscular fat (Farmer, 1994).It is therefore diffi cult to explain why the least juicy was the meat from calves fed fi sh oil, despite the meat from this group having the highest fat level.According to some authors, the nature of the diet does not infl uence juiciness.Indeed, no signifi cant difference has been observed in the juiciness of meat from young bulls fed either an lucerne silage diet or a concentrate diet (Mandel et al., 1998).Similarly, no signifi cant difference in juiciness has been observed between grass-fed and grain-fed young bulls despite differences in carcass fatness and meat tenderness (Vestergaard et al., 2000).However, meat from muscles of young bulls fattened with hay is juicier than meat from muscle of bulls fed grass silage (Listrat et al., 1999).

Table 2 .
The physical properties of meat

Table 3 .
The sensory quality of meat