Animal Science, Department of


First Advisor

Chris R. Calkins

Date of this Version


Document Type



A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Animal Science, Under the Supervision of Professor Chris R. Calkins. Lincoln, Nebraska: May, 2020

Copyright 2020 Nicolas A. Bland


Marbling and tenderness in meat are some of the most impactful factors for the consumer eating experience. The cause of the relationship between marbling and tenderness is still unresolved. This study was conducted to evaluate the effects of feeding different types of processed corn, with or without distiller grains on oxidative stress, and how that relates to tenderness and shelf life of beef steaks of differing quality grades. Steers (n= 240) were finished on dry rolled corn (DRC), DRC + 30% dried distillers grains (DDGS), steam flaked corn (SFC), or SFC + 30% DDGS. Cattle were fed 10 per pen. Only pens with both upper 2/3 Choice and Select-grade carcasses were sampled, with a goal of two (and a minimum of one) of each grade per pen. Three pens per treatment met the selection criterion and 36 carcasses were chosen (21 upper 2/3 Choice and 15 Select). Both strip loins were collected from each carcass, halved, and aged for 2, 9, 16, or 23 d. After aging, steaks were placed under retail display for 7 d. Subjective discoloration and instrumental color (L*, a*, and b*) were determined daily, and Warner- Bratzler shear force (WBSF), slice shear force (SSF), and lipid oxidation (thiobarbituric acid reactive substances; TBARS), were measured after 0 and 7 d of retail display. Fatty acid profile, proximate composition, sarcomere length, sarcoplasmic calcium, pH, proteomic analysis, isoprostane content, and troponin-T (Tn-T) degradation of the lean were obtained. No impacts on sarcomere length, pH, sarcoplasmic calcium, and isoprostane content were found (P> 0.05). The difference in proximate composition was due to fat content between quality grades (P< 0.05). As aging continued, increases in tenderness, degradation of Tn-T, percent discoloration, and lipid oxidation were found, along with a decrease of redness values (P< 0.05). Increases in objective tenderness, discoloration, and decreases in color stability of retail display occurred from 5 to 7 d (P< 0.05). Steaks from cattle fed DRC (compared to SFC) and without DDGS (compared to with DDGS) were statistically lower for discoloration, and C18:2 (linoleic acid) and higher in redness and TBARS values (P< 0.05). Proteomic data revealed greater oxidation of proteins related to tenderness in Upper 2/3 Choice-grade steaks than Select-grade steaks and in steaks from cattle fed DRC+DDGS than steaks from cattle fed DRC. Steaks from cattle fed DRC were more tender than steaks from cattle fed SFC and Upper 2/3 Choice-grade steaks were more tender and have greater oxidative damage in the proteins than Select-grade steaks.

Advisor: Chris R. Calkins