Lower ultimate meat pH (as observed in LL) decreases mitochondria respiration, thereby increasing the availability of oxygen to bind to Mb, and consequently increases surface oxymyoglobin
levels and R630/580 .
The preference for meat is decreased when oxymyoglobin
(acceptable cherry red color) is converted into metmyoglobin (unacceptable brown color).
When exposed to oxygen, deoxymyoglobin is transformed into oxymyoglobin
, changing the colour from purple to the bright red colour associated with freshness.
Depending on the particular type of meat and its processing, the deoxymyoglobin oxygenates into oxymyoglobin
at a higher concentration of oxygen.
Primary products of lipid oxidation generate changes in myoglobin such as the oxidation of oxymyoglobin
(OMB) to metmyoglobin (MMB) inducing color changes [1, 7]; these changes result in a decrease in heme redox stability, rather than the oxidation of specific amino acid residues.
The differences around 432 nm were probably due to the absorption by met Hb and/or met Mb, the peak at 550 nm may be mainly caused by deoxymyoglobin, the differences around 574 nm are caused by the content of oxymyoglobin
changing during different storage times , and the peak around 621 nm may be caused by hemin chloride .
However, vacuum-packaged fresh meat is unsuitable for the retail market because the lack of oxygen in the package causes a change of meat color from red to purple due to the conversion of oxymyoglobin
to deoxymyoglobin .
This could be explained by the increase of brown pigments as a result of oxidation of oxymyoglobin
to metmyoglobin (Mancini & Hunt, 2005).
NIRS technique is based on two fundamental characteristics [23,24]: relative transparency of human tissue to light in the near-infrared region (700-1000 nm) and the oxygenation-dependent absorption of oxyhemoglobin and oxymyoglobin
(HbO2, MbO2) and deoxyhemoglobin and deoxymyoglobin (Hb, Mb).
Masuda, "Effective conversion of metmyoglobin to oxymyoglobin
by cysteine-substituted polyphenols," Journal of Agricultural and Food Chemistry, vol.
structure reveals its role as a muscular store of [O.sub.2] (3); additionally, this protein functions as a scavenger of reactive species of [O.sub.2] and nitric oxide (4).
[alpha] -Tocopherol slows the conversion of oxymyoglobin
to metmyoglobin in beef thereby slowing the development of an undesirable brown color in displayed beef (LANARI et al., 1994).