The effects of exogenous factors and post mortem interventions to improve beef quality of Sudanese Baggara cattle

Thesis (PhD (Animal Science))--University of Pretoria, 2020.

This study investigated the effects of electrical stimulation (ES), age and weight at slaughter, breed type, post-freezing ageing, and the proteolytic extract of Solanum dubium (Gubbain) seeds on the carcass and meat quality of Sudanese Baggara cattle in Sudan. The study also assessed the microstructural and biochemical properties of Afrikaner x Bonsmara crossbred steer muscles treated with the Gubbain protease in South Africa. In order to achieve these goals, three trials were conducted. In the first trial, eighty Baggara cattle were selected according to breed type and age. The cattle (expermintal animals) were divided into two equal groups that were representative of the typical white Nyalawi breed type (n = 40) and typical red Mesairi breed type (n = 40). Each breed type was divided into two age groups: 20 bulls of about 5 to 5.5 years old, weighing between 280 and 310 kg; and 20 bulls of about 4 to 4.5 years old, weighing between 240 and 260 kg. The bulls were slaughtered and dressed according to the standard Halal method. Electrical stimulation (110 V for 30 seconds) was randomly applied to 50% of the carcasses in each group at 20 minutes post mortem (pm). The carcasses were stored in a chiller (2-4°C) within 45 minutes post mortem. Carcass pH and temperature were recorded at 0.17, 1, 3, 6, 9, 12, and 24 hours pm. Samples of m. longissimus dorsi (LD) were collected for meat analyses. Meat colour (L*, a*, b*, chroma, hue) was measured at 24 hours pm, and then each sample was labelled and put in a plastic bag and frozen at -20°C until processing. The frozen samples were thawed and cut into two equal steaks. Half of the steaks were immediately analysed, while the rest were aged at 4°C for seven days and then analysed. The samples were analysed for instrumental colour, water-holding capacity (WHC), cooking loss (CL), Warner-Bratzler shear force (WBSF) values, and sensory quality. The second trial was for exploratory purposes, while the third trial was for detailed analyses. In the second trial, thirty LD were sampled at 24 hours pm from two age groups of Sudanese Baggara bulls. The ultimate pH and instrumental colour were determined at 24 hours pm. The beef LD samples were each cut into two steaks and randomised into two treatments injected with the Gubbain protease extract (10 per cent muscle weight) and left as a control. The steaks were incubated at 4oC for 24 hours, after which they were analysed for pH, colour, CL, WBSF and sensory quality. The third trial was conducted on muscles from Afrikaner x Bonsmara crossbred steers to study the efficacy of the Gubbain protease extract injection in muscle tenderisation. Twelve m. longissimus thoracis et lumborum (LTL) steaks were sampled from both sides of several carcasses at 24 hours pm. Each steak was cut into two equal samples and then randomised for treatments (injection with Gubbain protease extract vs no injection). The steaks were incubated at 4oC for 24 hours. They were then analysed for colour, sarcomere length (SL), myofibril fragment lengths (MFLs), WBSF, collagen solubility, muscle fibre types, quantification meat degradation, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The results suggest that ES, animal age and weight affected meat quality attributes, while breed type had no significant effect. ES hastened the rate of pH decline significantly up to 24 hours pm. The ES of the Sudanese Baggara beef carcasses and the use of lighter and younger bulls showed higher L* values, lower a* values, higher hue values, and lower values for WBSF. The carcasses of the Mesairi breed type responded better to ES in terms of tenderness than those of the Nyalawi breed type. The meat from electrically stimulated carcasses resulted in lower WHC with no effect on CL, compared with non-electrical stimulation (NES) carcasses. The WHC of the meat improved as age and weight at slaughter increased. No risk of cold shortening was observed in any of the treatment groups. Although post-freezing ageing showed a negative influence on meat colour stability, it resulted in lower shear force values, which suggest more tender beef. Panellists did not recognise any variations in meat sensory quality between the two age groups. In contrast, the differences in sensory tenderness and overall acceptability due to post mortem interventions (ES and enzymatic protease) were detected. The meat injected with the Gubbain protease extract reduced the WBSF values by 62 to 65% compared with the non-injected samples. The Gubbain protease treatments increased b* values, cooking losses, and the sensory juiciness, tenderness, and overall acceptability of the beef. The injection with the protease extract showed better L* values compared with the control samples. Muscle samples treated with Gubbain protease had shorter MFLs (23.65 ± 3.22 vs 33.09 ± 2.33), probably due to the increased proteolytic activity, and also showed lower WBSF values (1.95 ± 0.70 vs 5.13 ± 1.01) than those samples from the control group. The muscles treated with the protease extract had a higher percentage of collagen solubility (36.30%) than the control muscles (18.40%). The muscle fibres from the treated samples with the Gubbain protease had more breaks and fractures than those from non-injected samples. The SDS-PAGE pattern of the LTL samples showed losses in the higher molecular weight fractions, accompanied by the appearance of many new lower molecular weight bands after treating the muscle with the Gubbain protease extract. The study has shown that there is potential to improve the quality of beef of Sudanese Baggara cattle types if certain interventions (ES, slaughtering younger and lighter bulls, post-freezing ageing, and injection with Gubbain protease) are used. The study also paved the way for a novel and promising meat tenderiser for the beef industry.

University of Pretoria (UP) Postgraduate Research Support Bursary Prof. Webb’s meat science research fund at the University of Pretoria

Animal and Wildlife Sciences

PhD (Animal Science)

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