S. D. Senter

APC values and volatile compounds formed in commercially processed, raw chicken parts during storage at 4 and 13 °C and under simulated temperature abuse conditions

Skinless chicken breast fillets, thighs, wings and boneless breast with skin were selected from the production line of a commercial processor. Samples were evaluated over time in storage at 4 and 13 °C and under temperature abuse conditions for microbial proliferation and production of volatile compounds (VCs). Aerobic plate counts (APCs) were enumerated and VCs quantitated at 24 h storage intervals; however, APC increases were not reflected by significant correlations with headspace VCs. Compounds isolated from sample headspaces by solid phase microextraction (SPME) and direct headspace sampling and then analysed by gas chromatography (GC), gas chromatography/mass spectrometry (GC/MS) and gas chromatography/chemiluminescence detection (GC/SCD) were hydrogen sulphide, methanethiol, ethanol, acetone, C5, C6 and C7 hydrocarbons, dimethyl sulphide, methyl ethyl ketone, carbon disulphide, 1-propanol, ethyl acetate, 1-butanol, S-methyl thioacetate, 3-methyl-1-butanol, dimethyl disulphide and dimethyl trisulphide. Compounds appearing in the samples with any degree of consistency and therefore considered pertinent for these analyses were ethanol, acetone, methyl ethyl ketone, ethyl acetate, hydrogen sulfide, dimethyl sulphide and carbon disulphide. Elevated APCs and VC diversity occurred more prevalently in those samples from higher-temperature storage. Published in 2000 for SCI by John Wiley & Sons, Ltd.

Variability in Residual Myoglobin Content and Glutamic Oxaloacetic Transaminase (GOT) Activity in Cooked Bovine Semimembranosus Tissue as Related to Temperature of Cooking Media above End-point Temperature and Sample Size

The variables, sample size and temperature of cooking media, were tested to determine their influence on myoglobin content and glutamic oxaloacetic transaminase (GOT) activities in bovine semimembranosus tissue thermally processed in a model heat treatment system. Data were obtained from 2.9 and 5.5 × 8.0 cm samples that were thermally processed to end-point temperatures (EPTs) of 62.8, 71.1 and 79.4°C in a water bath that exceeded EPTs by 2 and 20°C. Myoglobin denaturation differed (P < 0.05) by EPTs within samples, by sample size at the specified EPTs and by temperature of the heating media used to attain the EPTs within sample sizes. Similar variations at this probability level were observed in the analyses for residual GOT activities of the samples. Data indicate the inadequacies of analysis of these parameters in model systems that do not duplicate the actual process being evaluated.

Colour values of cooked top-round beef juices as affected by endpoint temperatures, frozen storage of cooked samples and storage of expressed juices

Juices from beef semimembranosus/adductor tissue, cooked to endpoint temperatures (EPTs) of 76, 78, 80, 82 and 84°C in a model heat-treating system, were evaluated for changes in CIELAB L*a*b*, chroma (C) and hue angle (H) values before and after storage of the cooked meat at -20°C for 3 weeks and after storage of the expressed juices under N 2 at 3°C for 72 h. Increases in EPTs altered all colour values of the juices. Lightness (L*) increased while yellowness (b*) decreased; redness (a*) and C decreased progressively while H increased toward the vertical axis. Storage of the expressed juices at 3°C under N 2 did not inhibit changes in a*, b*, C and H values. Regression coefficients of changes in relation to EPTs and time of storage of the expressed juices under N 2 were established. Storage of the cooked meats for 3 weeks at -20°C did not change any of the colour values of the juices. These data indicate that evaluations of cooked beef for doneness by colour of expressed juices must be performed immediately after expression of the juices before oxidation of the myoglobin pigments occurs. Storage of cooked meat at -20°C does not alter the colour of the juices, therefore, valid assays for doneness of meat in relation to juice colour can be made after frozen storage.

Glutamic-Oxaloacetic Transaminase Activity: A Potential End-Point-Temperature Indicator for Imported Cooked Beef†

Glutamic-oxaloacetic transaminase (GOT) activities in thermally processed beef samples were determined with a diagnostic test kit (no. 505P, Transaminases ALT/GPT and AST/GOT, Sigma Chemical Co.) procedure for possible use as indicators of cooking end-point temperatures (EPTs) between 71.1 and 82.2°C. GOT activity in the beef samples decreased curvilinearly with increasing EPTs. Activity was 3,450, 120, and 6 Sigma-Frankel units/ml (SFUs/ml) at 71.1, 75.6, and 82.2°C, respectively; a reduction of 99.8%. GOT values at 78.9,79.4, and 80.0°C, the critical range of EPTs in evaluating beef logs imported from South America, were 31, 17, and 14 SFUs/ml, respectively. Values within this range of temperatures differed significantly (P < 0.05); we suggest that residual GOT activity may be used as an EPT indicator for imported cooked beef products.