*While the full article for this executive summary is currently under peer review, these initial findings are being made available on BeefResearch.org to enable the industry to act on the research, inform the scientific community of ongoing work, and help prevent duplication of research efforts. Once peer review is complete, a link to the published article will be added to this summary.
KEY TAKEAWAYS
- Preharvest events may induce oxidative stress, which has an appreciable metabolic disturbance resulting in tissue damage.
- Physical stress may be a contributor to substantial increases in the production of reactive oxygen species. A failure to manage stress and maintain balance in antioxidant systems has been shown to increase reactive oxygen species.
BACKGROUND
Beef quality is dictated by appearance at point of sale and final palatability during consumption. Loss of beef appearance, or color, costs the industry over $3.73 billion each year. Food waste caused by discoloration is estimated to represent 2.55% of U.S. beef or 194.7 million kg annually, the equivalent of 780,000 finished cattle and all inputs involved in their production. Without question, discoloration of beef has significant implications towards the sustainability of U.S. agriculture and food systems. It is estimated that a 1% decrease in beef discoloration may significantly mitigate environmental losses associated with food waste, which equate to 23.95 billion liters of water, 0.40 million tons of carbon dioxide equivalent emissions, and 96.88 billion megajoules of energy. When palatability attributes such as tenderness, juiciness, and flavor are not acceptable, consumers have little chance of a positive eating experience. When eating experience is poor, consumers’ willingness to pay for beef decreases. Therefore, improving beef palatability is a critical need. Beef quality, including palatability, has major economic implications for the U.S. beef industry.
Beef color, odor, aroma, and flavor may each be influenced by oxidation. In general oxidation of lipids and proteins can lead to a decline in beef quality through losses in appearance and palatability. Therefore, any processes that predispose beef to oxidation are disadvantageous to quality. Prior to harvest oxidative stress results when the antioxidant capacity of tissues is reduced relative to reactive oxygen species creating predisposition to oxidative damage of tissues. Resulting beef color and palatability decline because of oxidative damage to myoglobin, lipids, and other proteins. Therefore, the objective of this work was to evaluate the available literature regarding oxidative stress mechanism and potential meat quality impact.
The aerobic processes that occur continuously in living tissues may also contribute to oxidation of cells, lipids, and proteins via reactive species. However, in a healthy host, there is an appropriate balance between reactive species and antioxidants. A perfect balance would prevent natural events from occurring, such as regulation of gene expression or aging. Furthermore, the balance is rather a matter of “control” than complete elimination of reactive species due to energy costs, as it is more efficient to repair damage rather than to completely intercept the damaging species. It is when a severe imbalance between the two occurs that oxidative stress becomes more prevalent.
Oxidative stress, in excess, can ultimately lead to a cascade of events, including cell death and damage, but may also contribute to increased cell proliferation. Thus, for oxidative stress to occur, two things must happen: diminished antioxidants and increased production of reactive species. Physical stress may be a contributor to substantial increases in the production of reactive oxygen species due to the mitochondrial electron transport chain and generation of hydrogen peroxides. A failure to manage stress and maintain balance in antioxidant systems has been shown in numerous live animal studies where factors such as heat stress, transportation, and extensive illness contributed to increased reactive oxygen species in vivo. Given the influence of oxidation on post-mortem meat quality, it seems reasonable to hypothesize that oxidative stress prior to harvest will have lasting impacts on meat quality. Multiple literature reviews of oxidative stress in livestock have pointed to the potential influence of oxidative stress on meat quality, however, no one has yet addressed the topic through a comprehensive study.
Implications
Stress prior to harvest is known to be relevant for meat quality under conditions that lead to muted pH decline and dark firm and dry (DFD) beef carcasses. However, among normal pH beef carcasses there may still be additional influences from stress. In review of the literature oxidative stress is a phenomenon that may lead to lipid oxidation and protein oxidation. Therefore, it is plausible that a meaningful level of oxidative stress may exist that ultimately leads to product quality decline through oxidation postmortem. Relatively few papers have worked to address this hypothesis in beef. Therefore, future efforts should address oxidative stress as it relates to beef quality.