The effect of electrical input during beef processing on resultant meat quality

[摘要] ENGLISH ABSTRACT: The two main determinants of post-slaughter processing outcomes are rates of pH and temperature decline.Muscle pH and temperature interact continuously during rigor development to affect both the musclecontracture and proteolytic enzyme activity. The pH, however, can be manipulated independently oftemperature by electrical inputs applied to the carcass. Electrical inputs that should be considered rangefrom electrical stunning to the various forms of electrical immobilisation (EI) and stimulation (ES) that occurduring and after the dressing procedures. EI is used to suppress convulsions that occur after electricalstunning to ensure operator safety to maintain high throughputs speeds while ES is used to induce rapidtenderisation, although having other biochemical and biophysical effects on meat.The objective of the study was to supply information on the effect of different EI and ES treatments,frequencies and pulse widths on the meat quality of beef. There are very little data on the effect of EI when itis combined with ES on meat quality. This study used two different EI frequencies (high – 800 Hz; HFI andlow – 15 Hz; LFI) combined with either high (1040 V; HVS) or medium (300 V; MVS) voltage ES to study theeffect of these treatments on meat quality. In the following experiment the EI waveform and ES wasstandardised using HFI with MVS with the frequency being changed to either 5, 15 or 50 Hz. Then the pulsewidth of the waveform was changed to 0.1, 0.5, 1 and 10 ms to optimise the ES system.Meat quality measurements were made from the Longisimmus dorsi (LD) and Semimembranosus (SM) after1, 5 and 9 days of chilled storage at 0 C. The LD (shear force = 94.3±2.2; cooking loss = 26.85±0.29; retaildrip = 0.996±0.037; storage drip = 2.78±0.155; WBC (water binding capacity) = 45.4±0.36) had significantlylower shear force and higher water binding capacity than the SM (shear force = 103.7±2.5; cooking loss =34.63±0.25; retail drip = 2.12±0.103; storage drip = 3.63±0.245; WBC = 59.3±0.57). Day of assessment (Day1 = 122.7±2.9; Day 5 = 87.7±2.2; Day 9 = 81.0±2.4) had a significant effect on tenderness of the LD as shearforce declined with an increase of day of assessment. The LFI HVS (storage drip = 3.30±0.223; shear force= 102.9±4.5) produced significantly greater drip during storage and shear force values when compared to theHFI followed by either HVS (storage drip = 2.45±0.261; shear force = 85.2±4.0) or MVS (storage drip =2.60±0.178; shear force = 94.2±4.2) in the LD, probably attributable to different rates of pH decline postmortem. LFI HVS (a* = 20.79±0.31; chroma = 22.92) and LFI MVS (a* = 20.24±0.27; chroma = 22.23±0.30)had a redder and more vivid bloomed colour than HFI HVS (a* = 19.71±0.33; chroma = 21.49±0.37) and HFIMVS (a* = 20.00±0.27; chroma = 21.98±0.31), while LFI HVS (a* = 15.27±0.40) and HFI MVS (a* = 14.64±0.29) had a redder colour compared to HFI HVS (13.85±0.35) at day 9 for the LD. The oxygenconsumption rate (MTT assay) correlated inversely linear (r = -0.63 and -0.73) with the a* values 24 hrs postmortem allowing for 3 hrs of bloom.Stimulation with 15 Hz (0.47±0.040) and 5 Hz (0.41±0.045) had a higher pH decline (ΔpH) during stimulationthan 50 Hz (0.29±0.027). Shear force measurements and cooking loss percentage were obtained from theLD after 24 hrs of chilled storage at 0 C. There were no difference between the stimulation treatments forshear force (15 Hz = 121.3±3.3; 5 Hz = 123.8±7.6; 50 Hz =114.8±7.94), while cooking loss was higher in 15Hz (28.8±0.47) than 50 Hz (25.9±0.71) which correlated (r = 0.43; p = 0.01) with ΔpH.There were no differences between 10 ms (0.46±0.020), 1 ms (0.43±0.020) and 0.5 ms (0.44±0.019) pulsewidths on the ΔpH while 0.1 ms (0.33±0.020) had a lower decline. Stimulation with a 1 ms (94.6±5.6) pulsewidth had the lowest shear force that varied from 10 (111.3±3.8) and 0.1 ms (111.3±5.8). While cooking loss(0.1 = 25.3±0.48; 0.5 = 26.9±0.67; 1 = 25.9±0.63; 10 = 25.5±0.66) and water-holding capacity (0.1 = 36.1±1.60; 0.5 = 37.3±1.42; 1 = 37.5±1.15; 10 = 36.9±1.45) was not affected in the LD after 24 hrs of chilledstorage at 0 C. Colour measurements on the SM indicated that a 0.1(a* = 19.38±0.50; chroma =22.70±0.51), 0.5 (a* = 20.89±0.49; chroma = 24.34±0.56) and 10 ms (a* = 19.69±0.46; chroma =22.98±0.58) pulse width had a deeper red and a more vivid colour than 1 ms (a* = 16.66±0.37; chroma =19.99±0.32) at day nine of retail display.In conclusion, HFI improves meat quality when combined with either HVS or MVS and that MVS eitherimproves (colour stability) or has no adverse effects on meat quality (tenderness and WBC) in relation toHVS when combined HFI. In addition, it shows that there are alternative electrical parameters to voltage thatcan be used to change the pH decline and by changing frequency and pulse width, subtle changes can bemade to an ES system. Since every abattoir is different due to layout, chiller space and cooling regime theseelectrical parameters can be modulated to optimise an electrical stimulation system without expensivemodification to the whole system.

[发布机构] Stellenbosch University