A vast amount of research work and experimentation has been done on the problem of fat spoilage, the reactions involved, and the various tests bearing on rancidity.It is impossible, in a paper of this kind, to give a comprehensive bibliography or to mention more than a small portion of the work done. However, some of the more pertinent references are given.In recent articles, Vibrans 2~ and Wheeler 22, list a large number of references and discuss the work of various investigators briefly.The work covered by this paper grew out of a demand for a quick method for comparing the stability or keeping qualities of lard samples. At present several methods for determining the stability of fats are in use in the baking and packing industries, all of which are open to one or more objections.The methods in common use are:1. Incubation Tests--such as Schaal's and similar tests :In these tests the fats are exposed to the air in a heated incubator and examined organoleptically at regular intervals until they become rancid. Such tests are objectionable because of the time involved, and because the results are dependent entirely on personal judgment. Oxygen Absorption Tests 1 to 12 lnolu~ivo:In these tests either the amount of time required by the fat to absorb a certain amount of oxygen, or the amount of oxygen absorbed in a fixed time is taken as indicative of the keeping qualities of a fat. These methods require complicated and expensive apparatus and produce results which are influenced by changes in absorption rate due to changing pressure and the presence of volatile oxidation products.3. Color Reaction Tests--such as the Kreis ~, modifications of it 14-~5 and the Schiff tests 16-17.These are tests which produce a color reaction in the presence of the aldehyde products of fat decomposition and have been shown to give no indication of the keeping qualities of a fresh fat. Tests

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Steers (n = 868) were raised, feedlot-finished with ad libitum access to a high-energy diet and harvested to determine if there is genomic control of fatty acid profile traits in beef breeds common to the United States. Cattle included purebred and crossbred progeny of Angus, Red Angus, Hereford, Shorthorn, Simmental, Charolais, Limousin, Gelbvieh, Maine Anjou, Chiangus, Braunvieh, Salers, Brahman, Brangus, Santa Gertrudis, and Beefmaster as well as three composite lines. Either directly or through imputation, genotypes were determined for > 133,000 functional single nucleotide polymorphisms (SNP). At approximately 38 h postmortem, a 2.54-cm-thick longissimus steak was obtained from the 13th rib region of the left side of each carcass. At 14 d postmortem, steaks were cooked and subsequently longissimus was pulverized in liquid nitrogen. Fatty acid profile was determined by gas chromatography and mass spectrometry. A genome-wide association study was conducted for fatty acid profile traits expressed as a deviation from the contemporary group mean using the Mixed Linear Model Analysis of SNP & Variation Suite 8.8.3 (Golden Helix) and Pre-computed Kinship Matrix using the GBLUP Genomic Relationship Matrix. A SNP in coiled coil domain containing 57 (CCDC57; Chromosome 19 at 51,349,695) affected the percentage of C14:0 (P < 10–46), short-chain fatty acids (P < 10–36), and saturated fatty acids (P < 10–17). Also, a SNP in thyroid hormone responsive (THRSP; Chromosome 29 at 18,090,403) affected the percentage of C14:0 (P < 10–16) and short-chain fatty acids (P < 10-10). The percentage of polyunsaturated fatty acids was affected by SNP in myostatin (Chromosome 2 at 6,213,980; P < 10–15). These results show that fatty acid profile of beef can be changed through genetic selection but, it is not clear if the level of change will be great enough to impact human health.

Understanding the biological factors regulating animal variation in meat quality traits continues to challenge meat scientists. Meat scientists have studied the impacts of numerous intrinsic and extrinsic variables on meat quality traits. Often, component traits, known to directly contribute to the trait of interest, have been utilized to determine the mechanisms by which these impacts are made. However, only a limited amount of the variation in these traits is explained by component traits, indicating that a significant knowledge gap exists. The rise of genotyping assays for functional alleles provides an opportunity to further understanding of the biological basis of meat quality traits. For example, lean color is the primary factor utilized by consumers in making purchasing decisions. Cuts from some carcasses discolor rapidly and must be discounted or discarded. Component traits (reducing ability and oxygen consumption) generally explains a total 30 to 40% of the variation in lean color stability. A genome-wide association study (GWAS) was conducted using GGP-F250 genotypes from 2,476 steers representing crosses of 18 beef breeds that had been phenotyped for lean color change during simulated retail display. The GWAS identified 417 single nucleotide polymorphisms (SNP) explaining the heritable variation (0.45). Identified genes included genes coding for reductases and cytochromes as well as mitochondrial genes, which are consistent with conventional wisdom regarding lean color stability. However, other genes identified are related to muscle contraction, action potential mediation, calcium binding, actin binding, stress response, and apotosis. In addition, gene ontology analysis indicates 128 genes contributing to metabolic processes, with 74 being associated with nucleobase containing compound metabolic processes. Thus, these results suggest novel mechanisms, which have not been previously studied in detail in relation to lean color stability. This approach provides a means to increase understanding of the biological regulation of meat quality traits.

The Halo condition is a meat quality defect characterized by very pale lean tissue on the superficial portion of fresh ham muscles. This tissue does not allow proper cured color development and has been the subject of customer complaints for ham processors. Surveys of raw materials revealed an issue affecting many suppliers and genetic lines. Further investigation indicated that the condition was most prominent in the distal portion of the biceps femoris muscle and was present in pigs of all ages and stages of production. Halo-affected tissue had much higher proportion of white muscle fibers. Consequently, Halo-affected tissue exhibited much lower myoglobin concentration, as well as much greater lightness, and much lower redness values, compared to normal tissue in the deeper portion of the muscle. These differences are consistent with increased expression of genes coding for white muscle fiber specific proteins in the Halo-affected tissue relative to tissue from the Inside portion of the biceps femoris muscle. Virtually all muscles evaluated have exhibited some degree of the Halo condition, but significant variation exists in the size of the affected portion of the muscle as well as the severity of the condition. Sire has a substantial impact on variation in Halo condition severity. Thus, genetic selection should help mitigate the condition. We will provide an overview of efforts to characterize the Halo condition and discuss genetic selection as a means to mitigate the condition.