# Intrinsic and Extrinsic Factors Affecting the Color of Fresh Beef Meat--Comprehensive Review
## 3 Results and Discussion
### Extrinsic Factors  
#### 3.2.1 Production Systems and Feeding  
Management systems and diet compositions might variably influence the color of fresh beef muscle, mainly due to predominant muscle fiber type, number of calories fed to the animals, fatty acid profile, and inter- and intra-muscular fat deposition. Production systems greatly influence lipid oxidation processes, which are strongly associated with myoglobin oxidation and the generation of off-odors and off-flavors in beef [73; 74]. Higher total fatty acid content was recorded in the meat of fed concentrate-based animals rather than grass- or silage-based cattle [75; 76]. It was also described that higher amounts of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and n-6 polyunsaturated fatty acids(PUFA) portions were likely to be found in concentrate-finished animals than in pasture- and silage-fed animals [75; 77]. In addition, most publications agreed that higher PUFA and n-3 PUFA fractions were obtained from pasture-based diets than from concentrate-based diets [78; 79]. Precisely, meat from pasture-fed animals exhibited higher amounts of PUFAs, which could have resulted in higher oxidative phosphorylation than meat from grain-fed animals because it was more accessible for the action of lipases [43; 73]. Higher thiobarbituric acid reactive substances (TBARS) values were reported in the meat of grain-fed rather than in pasture-fed cattle, mostly due to an antioxidant defensive mechanism against lipid oxidation in the latter [80]. Animal diet might have a large influence on the generation of lipid oxidation products such as HNE, which decreases both electron transport-mediated and NADH-dependent metmyoglobin reduction processes, thus increasing oxymyoglobin oxidation [52; 81]. Moreover, it is generally regarded that intensive-managed (grain, concentrate, feedlot) produced brighter muscles (higher L* values) than extensive-managed animals (silage, pasture, grass) [63; 75]. This effect is associated with a higher amount of calories fed to the animals in intensive systems, promoting a glycolytic metabolism and increasing total and intramuscular fat compared to the extensive counterparts [63; 82]. The quality, the amount, and the duration of concentrate feeding in different management systems might have a variable influence on a* values in meat [82; 83]. At constant slaughter weights, similar a* values were obtained for concentrate and grass-based animals [76; 83]. It was also described that grazing periods up to 98 days during the finishing phase did not produce any significant effects in a* values [84]. Increasing the feeding intensity on bulls during the growing and the finishing phase also did not show any differences in pH or meat color between treatments, probably because all animals received a high-calorie diet, which also led to similar slaughter weights [85]. Another publication reported that grain-based diets resulted in meat with lower pH and higher a* values than grass-based animals [86]. It was also found that when gradually increasing the level of concentrate supplementation in a pasture-based diet, the highest a* values were attained at 0.8% of live-weight concentrate replacement, regardless of marbling or myoglobin concentrations in muscle [82]. It was also observed that the higher pigment concentration in the meat of grass-fed animals resulted in higher a* values when compared to grass-based exemplars [87; 88]. This was probably a consequence of higher physical activity due to more time spent walking, standing, or feeding, which increased the proportion of oxidative muscle fibers [89; 90]. It was shown that the oxidative metabolism of cattle-fed pasture-based diets led to higher pH values and darker muscle appearance than their grain counterparts, even if no differences were found in lactate or glycogen concentration (typical for pre-mortem stress) [86]. Production systems can largely affect the color of fresh beef muscle. L* values were consistently higher in intensive compared to extensive systems.