Honey inhibits lipid oxidation in ready-to-eat ground beef patties.

Our objective was to evaluate the antioxidant capabilities of clover (CH) and wildflower honeys (WH) in delaying lipid oxidation in cooked and reheated ground beef patties stored in refrigerated and frozen states. CH and WH (5%, 10%, or 15% w/w) were each mixed separately into ground beef chuck (18% fat) and formed into 30g patties mixed with 1% salt (w/w). A control (CON) with no honey and a control with sodium tripolyphosphate (STP; 0.25% w/w) were used for comparison. Patties were cooked to 71°C, overwrapped with oxygen-permeable PVC film and either stored refrigerated (4°C) for 12 days or frozen (-18°C) for 45 days. Cook yield, pH and water activity were measured on day 0. On designated sampling days, patties were reheated to 71°C. Thiobarbituric acid-reactive substances (TBARS) and lipid hydroperoxides (LOOH) were measured spectrophotometrically to assess lipid oxidation. TBARS and LOOH of ready-to-eat (RTE) ground beef patties containing either CH or WH were lower (P<0.01) than CON patties following storage; however, STP patties had lower TBARS values than honey-containing patties (P<0.01). WH and CH at 15% were equally effective in suppressing LOOH compared to STP in refrigerated and frozen patties. All honey concentrations improved cook yield, with 10% WH being more effective than STP. Both CH and WH delayed lipid oxidation in RTE ground beef patties stored at 4°C and -18°C, with WH decreasing LOOH formation in refrigerated patties as effectively as STP. Honey may be a natural alternative to phosphates to delay lipid oxidation.

Bovine metalloprotease characterization and in vitro connective tissue degradation.

Metalloproteases that selectively hydrolyze connective tissue proteins may tenderize meat without creating texture problems associated with myofibrillar protein degradation. Our objective was to characterize the activity of bovine placental proteases to determine whether they can improve meat tenderness through disruption of the connective tissue matrix. Enzymes were extracted, crudely purified, and proteolytic activity was assessed against gelatin and collagen under varying pH and temperature conditions using both SDS-PAGE and zymography. Gelatin zymography revealed proteolysis between 57 and 63 kDa, with decreased activity as buffer pH decreased from pH 7.4 to 5.4 (37 degrees C). Proteolytic activity was pronounced at 37 degrees C, moderate at 25 degrees C, and absent at 4 degrees C following 48-h incubation (pH 7.4). Placental enzymes were metalloproteases inhibited by excess EDTA. Maximum proteolysis was achieved in the presence of Ca2+, with or without Mg2+ and Zn2+. Absence of Ca2+ decreased proteolytic activity. Complete degradation of both the 125- and 120-kDa proteins of the alpha-chains of gelatin was achieved following enzyme incubation for 6 h at 37 degrees C or 24 h at 25 degrees C. No degradation was observed following enzyme incubation with native Type I collagen. Given the marked decrease in enzyme activity at pH 5.4 and 4 degrees C (standard industry conditions), bovine placental metalloproteases would not be expected to contribute to connective tissue degradation or improve meat tenderness.

Induction of redox instability of bovine myoglobin by adduction with 4-hydroxy-2-nonenal.

The redox stability of myoglobin (Mb) is compromised by many factors, including lipid oxidation and its products. 4-Hydroxy-2-nonenal (HNE) is an alpha,beta-unsaturated aldehyde derived from the oxidation of omega-6 polyunsaturated fatty acids and is highly reactive and cytotoxic. Our objective was to study potential binding of HNE to Mb and determine how it affects redox stability. OxyMb (0.15 mM) was incubated with HNE (1 mM) at 4, 25, and 37 degrees C at pH 7.4 or 5.6. Samples were analyzed for MetMb formation and by Western blot analyses, LC-MS, LC-MS-MS, circular dichroism (CD), and differential scanning calorimetry (DSC). MetMb formation increased with increasing temperature and was greater at pH 5.6 than at pH 7.4 (P < 0.05). At 37 degrees C, HNE accelerated oxidation at pH 7.4 but not at pH 5.6 (P < 0.05). At both 25 and 4 degrees C, HNE accelerated oxidation at pH 7.4 and 5.6 (P < 0.05). LC-MS revealed the covalent binding of HNE to Mb at both pH values via Michael addition, while Western blot analysis indicated that HNE was bound to histidine (HIS) residues. LC-MS-MS identified six histidine residues of Mb that were readily adducted by HNE, including the proximal (HIS 93) and distal (HIS 64) histidine associated with the heme group. Secondary structure differences between control Mb and Mb incubated with HNE were not detected by CD. However, DSC revealed a decreased T(m) for Mb reacted with HNE at pH 7.4, indicating Mb tertiary structure was altered in a manner consistent with destabilization. These results suggest that HNE accelerates bovine skeletal muscle OxyMb oxidation in vitro by covalent modification at histidine residues.