Abstract
Previous research reported the role of nonenzymatic metmyoglobin (MetMb) and methemoglobin (MetHb) reduction in meat color; however, limited studies have characterized the cofactors involved in nonenzymatic reduction. The objective of this study was to characterize electron donors and carriers in nonenzymatic MetMb and MetHb reduction at various temperatures and postmortem muscle pHs in vitro. Methylene blue and cytochrome c (cyt-c) were evaluated as electron carriers and nicotinamide adenine dinucleotide, reduced form (NADH) and ascorbate were considered as electron donors. All combinations of electron donors and carriers were evaluated in the following order: NADH plus methylene blue, ascorbate plus methylene blue, NADH plus cyt-c, and ascorbate plus cyt-c. Spectrophotometry was utilized to monitor the rates of reduction. The results indicated that methylene blue was an effective electron carrier than cyt-c in the presence of NADH. Temperature and pH had cofactor-specific effects on nonenzymatic MetMb and MetHb reduction. Lower temperature resulted in an increased nonenzymatic MetMb reduction for methylene blue regardless of electron donor (ascorbate, P = 0.03, NADH, P = 0.04). As pH increased, MetHb reduction was enhanced in the presence of ascorbate plus cyt-c. Nonenzymatic MetHb reduction was numerically lower than nonenzymatic MetMb reduction in the presence of NADH plus methylene blue. In summary, in addition to NADH, the current in vitro research demonstrated that ascorbate plus cyt-c could contribute to nonenzymatic MetMb and MetHb reduction at meat-pH and storage temperature.
Highlights
Myoglobin and hemoglobin are the primary proteins responsible for meat color
Addition of methylene blue to NADH increased (P < 0.0001) nonenzymatic MetMb reduction compared with NADH alone, but the addition of ethylenediaminetetraacetic acid (EDTA) to methylene blue and NADH did not impact (P = 0.91) nonenzymatic MetMb reduction
The presence or absence of EDTA showed no changes (P = 0.38) in nonenzymatic MetHb reduction when combined with NADH and methylene blue
Summary
Myoglobin and hemoglobin are the primary proteins responsible for meat color. Autoxidation of hemoglobin and myoglobin results in the formation of met–heme forms (Richards et al, 2002; Grunwald and Richards, 2006; Yin et al, 2017) and brown appearance on the lean surface (Carpenter et al, 2001; AMSA, 2012). Nicotinamide adenine dinucleotide, reduced form (NADH) is an important electron donor involved in MetHb or MetMb reduction (Faustman and Cassens, 1990; Tang et al, 2005; Ramanathan and Mancini, 2018). Limited knowledge is currently available on the roles of other electron carriers and electron donors involved in MetHb and MetMb reduction at postmortem muscle conditions
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
