Date of Award

12-2017

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Animal Science

Committee Chair

Brad Kim

Committee Member 1

Paul Ebner

Committee Member 2

Stacy Zuelly

Committee Member 3

Jerrad Legako

Abstract

The United States has the greatest number of cattle on feed and is the largest producer of beef in the world (Jones, 2017). As a major contributor to the American economy, it is vital for the beef industry to provide consumers with high quality products that meet their expectations in order to ensure continued meat purchase (Schroeder and Mark, 2000). To accomplish these objectives, an understanding of beef eating quality attributes and ongoing research to identify how and what factors contribute to these attributes is essential. Beef palatability is assessed by the evaluation of tenderness, juiciness, and flavor (Reicks et al., 2011; Garmyn and Miller, 2014). Multiple factors influence overall eating satisfaction. Live production factors, such as animal age, nutrition, breeding and genetics, sex/castration and handling influence beef palatability, as well as, postmortem factors including carcass chilling rate, freezing and thawing, aging time/method, processing, and cooking. Of particular importance is cattle diet which is known to play a pivotal role in influencing the carcass characteristics and eating quality attributes of beef products (French et al., 2001; Calkins & Hodgen, 2007). Feeding grain to beef cattle prior to slaughter improves beef flavor in comparison with forage-finished beef, mainly due to an increase in deposition of intramuscular fat, also known as marbling (Schroeder et al., 1980; Hedrick et al., 1983). Increased marbling content and subsequent quality grade are proven indicators of eating satisfaction (Platter et al., 2003; Emerson et al., 2013; Corbin et al., 2015). Conversely, grass-finished beef does not present the marbling achieved through conventional grain-finishing. Although carcasses from grassfinished cattle can grade the USDA Choice when provided proper forages with extended feeding periods, in general, grass-fed beef exhibits smaller carcasses with yellow fat and most often grade USDA Select or lower (Mathews and Johnson, 2013). Furthermore, a recent study from Chail et al. (2016) reported that grass-finished beef had lower eating quality characteristics, specifically relative tenderness, juiciness, flavor liking, overall liking, and perceived quality when compared to grain-finished beef. While emerging consumer demand for locally raised grass-finished beef presents a potentially new market for small beef producers (Martinez et al., 2010), inferior eating quality is a major hurdle for this segment of the industry when promoting their products to consumers (Martin et al., 2004). Consequently, there is an imminent need to develop an effective postharvest intervention strategy to mitigate the inconsistent and/or inferior quality issues associated with grass-fed beef. The objective of this research was to evaluate the effect of dry-aging on eating quality, physicochemical, and microbiological attributes of grass-fed beef loins with a low degree of marbling. At 7 d postmortem, eighteen bone-in strip loins (M. longissimus lumborum) from 9 beef carcasses (USDA Select grade; grass-fed) were obtained. Each loin was cut in half yielding a total of 36 sections, which were assigned to three aging methods; wet-aging in vacuum packages (WA), dry-aging (DA) and dry-aging in a water permeable bag (DW; UMAi Dry® Short Loin, Wayzata, MN), according to a pre-allocated balanced incomplete block design (n=12/treatment). All treatments were aged in the same condition at 78% RH, 2°C and air speed of 0.2 m/s for 28 days. Different aging methods had no impact on pH and fat content of grass-fed beef loins (P>0.05). However, WA samples had a significantly higher moisture content, but relatively lower protein and ash contents compared to DA and DW samples (P<0.05). Similar shear force and carbonyl content of grass-fed beef loins were observed regardless of aging methods (P>0.05). The TBARS values of DA and DW samples were slightly higher than those of WA samples, but not enough to influence acceptability (<0.1 mg MDA/kg difference; P<0.05). Fatty acid (FA) analysis revealed no major differences in FA profiles among the treatments. DA samples had the lowest APC and LAB levels (P<0.05). Significant differences in eating quality attributes were found, where DA steaks had higher flavor and tenderness preferences compared to the WA steaks (P<0.05). DW aging resulted in a significantly higher juiciness of steaks compared to DA or WA samples (P<0.05). Our findings indicate that dry-aging could improve eating quality attributes of low marbled grass-fed beef without any adverse impacts on oxidation stability and microbial shelf-life. Hence, dry-aging could be a natural and value-adding post-harvest process to improve eating quality attributes of grass-fed beef. Further studies identifying chemical compounds associated dry-aged flavor of low marbled beef are highly warranted.

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