3.2.1 Ostriches and muscle samples
A summary of the experimental procedure for the collection of ostrich muscle samples are presented in Fig. 3.1.
56 Figure 3.1 Summary of the experimental procedure for the collection of ostrich muscle
52 Fifteen rested (approximately 24 h of lairage) ostriches (Struthio camelus), 10 months of age from the same farm (Oudtshoorn Research Farm of the Western Cape Department of Agriculture) were slaughtered as described by Hoffman (2012). The slaughter took place on the same day at the same EU approved abattoir in Oudtshoorn, South Africa, during August of 2017. The 15 ostriches were made up of three genotypes, namely six South African Black ostriches (SAB), three Zimbabwean Blue ostriches (ZB) and six Kenyan Red ostriches (KR). The dead weight of each ostrich was recorded prior to slaughter (“dirty” area of the abattoir), where- after the carcass weights (kg) were recorded subsequent to skinning and carcass dressing as soon as the carcasses entered the deboning area (“clean” area of the abattoir). After the death of the birds, the plucking of feathers, skinning as well as evisceration were completed between 60 and 90 min post-mortem before carcasses arrived at the deboning hall. Hot-deboning of the left leg from the carcasses were subsequently performed at approximately 90 min post-mortem, but definitely completed within 2 h post-mortem. Thereafter the removal of membranes and vacuum packaging of muscles followed, and were completed within 3 h post-mortem.
Each of the left legs were thus excised at approximately 90 min post-mortem (hot- deboning) where-after the leg weights (18.58 kg ± 2.04) were recorded, prior to the excision of the 16 individual muscles. After each of the 16 individual muscles (Table 3.1) were excised, each muscle was weighed individually before membranes (connective tissue surrounding the outer layer of a muscle defined as epimysium), were removed (Davies, 2004). The 16 individual de-membraned muscles were weighed again and the “clean muscle” yield calculated. The combined weight of goulash meat (weight of cubes/portions of meat trimmings suitable to be sold as goulash stew meat of all 16 individual muscles), meat trimmings and membrane trimmings (of all 16 individual muscles) were recorded per animal, respectively. Of the 16 individual muscles, the fan fillet (1.78 kg ± 0.18); rump steak (1.38 kg ± 0.27); big drum (1.07 kg ± 0.18); moon steak (0.88 kg ± 0.12) and triangle steak (0.46 kg ± 0.06) were used for further analyses and vacuum packed accordingly. The five vacuum packed muscles were refrigerated at < 4°C for 24 h post-mortem at the abattoir. The carcasses with the remaining right legs were refrigerated in the same refrigerator for 24 h post-mortem.
After 24 h post-mortem refrigeration at < 4°C, each of the 15 carcasses’ right legs (17.35 kg ± 2.01) were excised (cold-deboning). Before excision of the 16 individual muscles, each of the right legs were weighed and the chiller weight loss calculated. After each of the 16 individual muscles were excised, each muscle was weighed individually before and after the epimysium was removed. Similarly, the combined weight of goulash meat; meat trimmings and membrane trimmings (of all 16 individual muscles) were recorded per animal respectively. Of the 16 individual muscles, the same five muscles: the fan fillet (1.70 kg ± 0.16); rump steak (1.29 kg ± 0.17); big drum (0.98 kg ± 0.28); moon steak (0.90 kg ± 0.13) and triangle steak (0.39 kg ± 0.06) were used for further analyses and vacuum packed accordingly. The five hot- and cold-deboned vacuum packed muscles (of all 15 ostriches) were transported from Oudtshoorn
53 to the laboratories at Stellenbosch University (395 km) in a refrigerated vehicle/ cool truck (< 4°C). The following day each of the hot- and cold-deboned five muscles were cut perpendicular to the longitudinal axis into 1.5 – 2.0 cm steaks for different ageing time periods according to the varying sizes of each muscle. Before the conduction of physical analysis on day 3 steaks, a representative 25 g sample of each muscle was cut, vacuum packaged and stored at -20°C for microbiological analysis. The remaining steaks at day 3 post-mortem were used to perform physical analyses after it was randomly assigned to each ageing time point.
Table 3.1 Description of 16 ostrich muscles’ commercial names with scientific names
Commercial name Scientific name
Tenderloin M. iliotibialis cranialis
Oyster fillet M. iliofemoralis externus
Small drum M. gastrocnemius, pars intermedia
Tournedos M. ambiens
Rump steak M. iliotbialis lateralis
Fan fillet M. iliofibularis
Triangle steak M. flexor cruris lateralis
Eye fillet M. iliofemoralis
Small steak M. flexor cruris medialis
Tender steak M. pubo-ischio-femoralis
Minute steak M. femorotibialis externus
Long fillet M. obturatorius medialis
Moon steak M. femorotibialis medius
Flat drum M. gastrocnemius, pars externa
Big drum M. gastocnemius, pars interna
Drum steak M. fibularis longus
3.2.2 Physical analysis
Muscle temperature (°C) and pH were recorded in the centre of each muscle steak with the use of a portable calibrated (standard buffers of pH 4.0 and 7.0) Crison pH25 pH meter (Alella, Barcelona, Spain) equipped with a pH and temperature probe. Readings were recorded at room temperature and the probe was rinsed with distilled water between every measurement.
The surface colour of the raw muscle steaks were determined using a Colour-guide 45°/0° colorimeter (BYK-Gardner, GmbH, Gerestried, Germany) and recorded according to the method described by Leygonie (2011). Prior to colour measurements, the 1.5 – 2.0 cm thick muscle steaks were allowed to bloom for 60 min at room temperature. Colour measurements were expressed by L* (lightness), a* (green-red) and b* (blue-yellow) coordinates of the CIELab colorimetric space (Boakye & Mittal, 1996; Konica Minolta, 2007)
54 and were recorded for each sample through five measurements at randomly selected positions. Hue angle (hab) for colour definition and Chroma (C*) for colour intensity were
calculated using the CIE a * and b* values as follows:
Hue angle (hab) = 𝑡𝑎𝑛−1(
𝑏∗ 𝑎∗)
Chroma (C*) = √(𝑎∗)2+ (𝑏∗)2
Moisture loss was measured through drip loss and cooking loss percentages. The drip loss percentage in muscle samples were determined by cutting a sample from day 3 steaks and weighing it to establish the initial (reference) weight. Subsequently, samples were placed in inflated plastic bags (without the meat touching the sides of the bag) at ~2°C for 24 h. Thereafter, samples were blotted dry with an absorbent paper towel before the “after” weight was recorded. The drip loss was consequently expressed as a percentage of the initial sample weight:
Drip loss % = weightweightbefore - weightafter
before X 100
The cooking loss percentage of each muscle sample was determined by using a preheated water bath (80°C) for 60 min (Honikel, 1998). After 60 min of cooking, cooked meat samples were removed from the water bath, where-after excess liquid which accumulated during the cooking process was drained after opening the seal from the vacuum bag. The samples were subsequently allowed to cool overnight and placed in a commercial refrigerator (~2°C). The mass of the cooled muscle samples were recorded the following day after each sample was blotted dry with absorbent paper towel. Accordingly, cooking loss was expressed as a percentage of the initial sample weight:
Cooking loss % = weightweightbefore - weightafter
before X 100
The Warner-Bratzler shear force (WBSF) test was used to establish meat tenderness after the mass of the cooking loss samples was recorded (Honikel, 1998; Wheeler et al., 2005). An Instron Universal Testing Machine (Instron UTM, Model 2519-107) fitted with a Warner- Bratzler blade was used to measure the force in Newton (N) necessary to shear a block of meat perpendicular to its longitudinal axis. With the muscle fibres parallel to the longitudinal axis, a minimum of six blocks were cut from the cooking loss steaks to a size of 1 x 1 x 2 cm each. The 1 mm Warner-Bratzler blade had a cutting edge with a semi-circular shape (0.508 mm radius), whilst the opening of the blade was triangular. The Instron operated with a crosshead speed of 200 mm/min and had a load cell of 2 kN. The WBSF value of each sample was calculated as the mean of six Warner-Bratzler readings (North & Hoffman, 2015).
55
3.2.3 Statistical analyses
Statistica 64 version 13’s (2015) VEPAC module was used to perform the statistical analyses (STATISTICA, 2011). Hot- vs. cold-deboning and with/without membranes were used as fixed effects in a mixed model repeated measures of analysis of variance (ANOVA) for the muscle yield results. For the physical meat quality characteristics, however, hot- vs. cold-deboning and muscle type were used as fixed effects in a mixed model repeated measures of ANOVA. The Fisher LSD (least significant differences) test was used for the multiple comparison test. It can be noted that animal was included as random effect while possible outliers were identified using normal probability plots. Significant influences were described as Means and Standard Deviation (SD). A significance level of 5% (p ≤ 0.05) was used as guideline for detecting possible significant effects.