Duration of exposure to a high-concentrate diet prior to pasture-finishing affects palatability of beef strip loin steaks
Milopoulos, Jillian Taylor
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Most cattle in the United States are finished on high-energy, grain-based diets. However, perceived health benefits have led to an increase in consumer interest in pasture-fed beef. Production of pasture-fed beef depends on seasonal patterns of pasture quality, and pasture-fed beef has been reported to have less favorable palatability traits than grain-fed beef. The current study was designed to determine if early feeding of a grain-based diet when pasture quality is low could produce palatable pasture-finished beef. Angus-cross steers (n = 48 [12 head / treatment]) were provided a high-concentrate diet for 0 d (0D), 40 d (40D), 80 d (80D), or 120 d (120D) prior to pasture-finishing on high-quality forages to a target final BW (487 kg). Strip loins were collected at harvest, and 8 were selected from each treatment based on USDA marbling scores targeting USDA Select quality grade (average marbling score: 370 ± 33.1). Eight additional process-verified grass-fed strip loins were selected from a commercial harvest facility in New Zealand to be included as a baseline (NZ). Strip steaks were used for proximate analysis, objective tenderness measurement, consumer assessment of palatability, determination of fatty acid composition, and quantification of volatile compound. Proximate composition and Warner-Bratzler shear force did not differ (P > 0.05) among treatments. Consumers (n = 220) assigned the greatest scores for tenderness to NZ (P < 0.05), and NZ was most often rated as acceptable for tenderness (P < 0.05). Steaks from NZ and 120D received greater sensory scores for juiciness than 0D and 80D (P < 0.05); 40D was intermediate (P > 0.05). Samples from 120D were more often rated as acceptable than 0D, 40D, and 80D (P < 0.05). Flavor scores were greater for NZ than all other treatments (P < 0.05) except 120D (P > 0.05). Percentage of samples rated as acceptable for flavor did not differ among treatments (P = 0.27). Samples from 120D and NZ received greatest scores for overall liking (P < 0.05), and NZ was more often rated as acceptable for overall liking than all treatments (P < 0.05) except 120D (P > 0.05). Flavor was highly correlated with overall liking (P < 0.01; r = 0.89). Saturated fatty acids were decreased (P < 0.05) and monounsaturated fatty acids increased (P < 0.05) in NZ compared to all other treatments. Odd-chain fatty acids were greater with grain exposure (40D, 80D, 120D; P < 0.05) than in pasture-finished treatments (NZ, 0D). Trans-vaccenic acid was greater (P < 0.05) in treatments exposed to grain than NZ, and conjugated linoleic acid was greater (P < 0.05) in all other treatments than NZ. The ratio of n-6 to n-3 polyunsaturated fatty acids was greater (P < 0.05) in 80D and 120D than all other treatments. Samples from NZ produced the greatest amounts of non-enzymatic browning-derived ketones (2,3-butanedione and 3-hydroxy-2-butanone; P < 0.05). Differences among treatments in lipid-derived volatile compounds were primarily of alcohols and aldehydes. In particular, 1-penten-3-ol was greater in NZ than all other treatments (P > 0.05). Hexanal was greater in NZ than all other treatments (P < 0.05) except 80D (P > 0.05), and octanal was greater in NZ than 80D and 120D (P < 0.05). Additionally, 2-pentylfuran was greater in NZ than all other treatments (P < 0.05). Results indicate that early exposure to grain-based diets for 120 d prior to pasture-finishing may produce beef that is comparable to grass-fed beef from New Zealand in palatability, but beef produced in pasture-finishing systems in the United States, with or without grain exposure, differs chemically from beef produced under New Zealand grass-fed systems.