Palatability of grass-finished and grain-finished beef strip loin steaks of varying intramuscular fat levels and wet aging treatments
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Abstract
The objective of this study was to evaluate palatability, lipid oxidation, fatty acid content and volatile compounds of beef strip loins (n = 200; 20 per USDA quality grade/fed cattle type) representing five USDA quality grades (USDA Prime, Top Choice, Low Choice, Select and Standard) and two fed cattle types (New Zealand grass-finished and U.S. grain-finished). Each strip loin was equally portioned into thirds and randomly assigned to one of three wet aging periods (7 d, 21 d or 42 d). Consumer panelists (n = 600; 120/location: Texas, California, Florida, Kansas, and Pennsylvania) evaluated eight grilled beef steak samples for palatability traits, acceptability, and eating quality. Generally, slice shear force (SSF) increased as quality grades worsened. Grass-finished samples were numerically less for SSF than most grain-finished treatments. All palatability traits were impacted by the interaction of diet x quality grade (P < 0.05). Although similar (P > 0.05) to grass Prime steaks for juiciness, tenderness and overall liking, grain Prime steaks rated greater than all other grass and grain treatments for all palatability attributes (P < 0.05). Grass-finished Top Choice, Low Choice, and Standard steaks rated greater (P < 0.05) than the respective grain-finished quality grades for juiciness and tenderness. Grain-finished Standard rated less (P < 0.05) than all other grass and grain-finished treatments for juiciness, tenderness, and overall liking, but was similar (P > 0.05) to grass Standard for flavor liking. Consumer tenderness increased (P < 0.05) as wet age time increased (7d < 21d < 42d). Prime steaks were most acceptable (P < 0.05) and Standard the least acceptable (P < 0.05) for juiciness, flavor liking and overall liking acceptability. There was no difference (P > 0.05) between grass and grain samples for flavor liking acceptability and overall liking acceptability. Grain-finished strip loins aged 42 d had greater thiobarbituric acid reactive substances (TBARS) values than all other shorter aged product (P < 0.05). All grain-finished strip loins, regardless of age, had greater TBARS values than all grass-finished strip loins (P < 0.05). The overall concentration (mg/g) of neutral lipid (NL) concentration followed the same trend as the assessed intramuscular fat percentages for each treatment. The n-6:n-3 NL concentration ratio was clearly greater in all grain fed treatments than grass fed treatments (P < 0.05). Cumulative NL polyunsaturated fatty acid (PUFA) percentage (g/100 g of total FA) generally increased as quality grade worsened, and the grain-finished treatments were greater than the grass-finished treatments within their respective quality grades (P < 0.05). Polar lipid cumulative PUFA percentage was greatest in grain Standard (P < 0.05) and generally decreased with improving quality grade. Additionally, grain-fed steaks were greater for PL PUFA percentage than the respective grass treatment within quality grade (P < 0.05). Volatile compounds were affected primarily by diet or aging treatment or an interaction of diet x aging. Methional was negatively correlated with flavor liking (r = -0.139; P < 0.05). The only volatile compounds positively correlated to flavor liking were Phenylacetaldehyde (r = 0.119); methyl-pyrazine (r = 0.094); 2,5-dimethylpyrazine (r = 0.110); trimethylpyrazine (r = 0.0.91); and 2-ethyl-3, 5/6-dimethylpyrazine (r = 0.087) (P < 0.05). The principle component analysis (PCA) of volatile compounds, treatments, TBARS and consumer ratings showed consumer flavor liking to be most closely associated with ethanol, TBARS and USDA Prime, 42-d aged steaks, from grass and grain fed cattle.