The color changes taking place in fresh as well as cured pork as a result of high pressure (HP) treatment were investigated, characterized, and explained.
The effect of HP in the range from 200 through 800 MPa at 5 °C or 20°C on the color of fresh porcine longissimus dorsi (LD) immediately after HP treatment and during a six-day storage period was investigated via surface reflectance. Spectroscopic studies (in the form of surface reflectance, UV-vis, and circular dichroism) on the effect of HP treatment on the soluble protein fraction of porcine LD were conducted attempting to explain the color changes observed in fresh porcine LD.
Investigations on the effect of HP at 600 MPa on the color of minced, cured, restructured ham at different levels of drying (20% or 50% weight loss with Quick-Dry-Slice® (QDS)), pH24 (low, normal, or high), and NaCl (15 or 30 g/kg meat), as well as the effect of residual oxygen level (<0.1%, 0.1%-0.2%, or 0.2%-0.3%) on color stability during a 20-day storage period were conducted.
HP treatment above 300 MPa of raw porcine LD with deoxyMb initially present at the surface resulted in formation of a short-lived ferrohemochrome myoglobin species with a positive peak at 540 nm. This short-lived ferrous myoglobin species is possibly a bis-His coordinated myoglobin form, as also suggested by other authors. The short-lived ferrohemochrome disappeared within a few hours after HP treatment and was transformed into an HP-denatured ferric form of the pigment. This HP-denatured ferric myoglobin species was not similar to the heat-denatured pigment, ferrihemochrome, but instead a closely related species sharing features of denatured gobin, ferric iron, and brown color.
The reversibility of the pressure-induced changes often observed for various myoglobin forms in solution were not observed in intact meat.
Cred meat products appear to be much better suited for HP treatment. Though HP treatment altered the color of cured ham with a high water content (dried to 20% weight loss with QDS), it at the same time improved color stability during storage.
The color changes observed during storage for both non-HP-treated and HP-treated minced, cured, restructured ham were most likely not due to oxidation or dissociation of the heme part nitrosylmyochromogen, but instead suggested to be caused by denaturation of the protein part of nitrosylmyochromogen and/or changes in the myofibrillar and/or sarcoplasmic proteins as seen by the lack of change of the shape of the reflectance curves during storage for both 20% QDS and 50% QDS samples. It was not possible to set a specific critical limit of residual O2 for photooxidation without supplementing with further studies. However, it did appear that the critical limit of O2 is higher for dry-cured meat than for cooked, cured meat, possibly due to the reduced molecular mobility in the drier samples. HP treatment appeared to offer an additional protective effect to surface color stability in dry-cured meat, possibly by introducing intermolecular hydrogen bonds with water, thus stabilizing the nitrosylheme.