The contributions of lean muscle, intramuscular fat, and subcutaneous fat to lipids within the beef matrix

Incidence of obesity and associated metabolic diseases is increasing at a rapid rate, with one in three Americans diagnosed as obese. This creates an urgent need for an understanding of the nutritional value of foods and the roles they play in the development of obesity and metabolic diseases. When evaluating the role of beef in the diet, all of beef's nutritive and non-nutritive components should be considered as part of a whole food beef matrix. A serving of beef may contain multiple tissue types including lean muscle (LM), intramuscular fat (IMF), and subcutaneous fat (SF). As these are metabolically unique tissues, we hypothesize that these tissues contribute unique lipids to the beef matrix. To test the hypothesis, LM, IMF, and SF were dissected from five strip loins from cattle finished using a standard feedlot diet. The lipidome of the tissues was then determined using shotgun lipidomics. Each tissue type had a distinct lipid signature and contained different proportions of storage lipids, membrane lipids, and lysolipids (P < 0.01). Notably, LM contained fewer storage lipids and higher proportions of membrane lipids and lysolipids compared to IMF and SF, whereas IMF and SF did not differ significantly from each other. While most triacylglycerol (TAG) classes were similar across all tissues, SF contained greater proportions of TAG with 53, 55, and 56 carbons than LM and IMF (P ≤ 0.03). Across all tissues, TAG with 52 carbons and 2 double bonds was the most abundant. Membrane lipid composition of SF contained higher proportions of phosphatidylcholine, phosphatidylglycerol, phosphatidylserine, and ceramide than LM and IMF (P ≤ 0.03). Proportion of diacylglycerol in IMF and SF membrane lipids was higher compared to LM (P < 0.01). Lean muscle contained higher proportions of ether-linked phospholipids than IMF and SF (P < 0.01). Lysolipids make up ≤ 1% of total lipids in LM, IMF, and SF; LM contains a higher proportion of lysolipids than IMF or SF (P < 0.01). Of the lysolipids. Of the lysolipids, lysophosphatidylcholine (LPC) is the most abundant across all tissue types; IMF contains higher proportions of LPC compared to LM and SF (P < 0.01). These data provide insight into the lipid composition of the whole food beef matrix of beef strip steaks and suggest that the whole food beef matrix may be influenced by fat trim level (amount of SF) and IMF content.