Pork meat quality after exposure to low (0.5 Gy) dose of gamma radiation

Abstract

Farm animals in the immediate vicinity of damaged nuclear facilities (Chernobyl, Fukushima), may be affected by an external radiation dose and a radiation dose from internal contamination. In the experiment, pigs weighing 30 kg were exposed to a full body irradiation (60Co) at a dose of 0.5 Gy. Samples from longissimus dorsi muscles at the last rib and semimembranosus muscles were collected. No significant differences of monitored meat colour indicators L*, a*, b*, C*, ΔE*, pH value, (45 min and 24 h post mortem) lactic acid concentration, water content and fat content (24 h post mortem) and drip loss indicators (24 and 48 h post mortem) between the experimental and control group (10 and 10 pigs, respectively) were observed. If there is no internal contamination, and external radiation dose does not exceed 0.5 Gy, pigs from the affected area may be used for slaughter purposes. The results show that oxidative stress resulting from exposure to this dose of ionizing radiation does not affect the meat quality. Ionizing radiation, pig, meat colour, food safety Nowadays, more and more emphasis is given on studying the effects of low doses of ionizing radiation on living organisms. In the case of a whole body exposure, the imaginary borderline between stochastic and deterministic effects of ionizing radiation on humans and pigs represents a dose of 0.5 Gy. Consequences of farm animals being exposed to ionizing radiation (Chernobyl, Fukushima) affecting food safety are still present (Kostiainen 2007; Beňová et al. 2016). Mainly farm animals in the immediate vicinity of the damaged nuclear facilities may be affected by an external radiation dose and a radiation dose from internal contamination (Ohmori et al. 2014). Animals in the ex-evacuation zone might have experienced some changes owing to radioactive materials, including contaminated soil, small animals, and insects. It has been demonstrated that some changes in gene expression occurred in the small intestine of wild boar in the ex-evacuation zone after irradiation (Morimoto et al. 2017). It is difficult to conclude that these alterations are caused by only artificial radionuclides from the Fukushima Daiichi Nuclear Power Plant. External exposure to ionizing radiation causes oxidative stress that accelerates lipid peroxidation of polyunsaturated fatty acids liberating alkanes and alkane metabolites (Phillips et al. 2015). Meat represents muscle tissue in a state of degradation. Degradation reactions generate free radicals, especially from unsaturated fatty acids, which are highly reactive. In the muscle, or rather, in meat as such, membranes maintaining mitochondrial integrity (and indeed the entire muscle cell) are more susceptible to the action of radicals, and subsequently to the degradation of cellular components. These processes accelerate metmyoglobin formation and change the levels of myoglobin, haemoglobin and cytochromes, affecting the meat colour (Young and West 2001; Bekhit and Faustman 2005). ACTA VET. BRNO 2019, 88: 481–486; https://doi.org/10.2754/avb201988040481 Address for correspondence: Jana Doležalová Palackého tř. 1946/1 612 42 Brno, +420 541 562 623 Czech Republic E-mail: [email protected] http://actavet.vfu.cz/ Meat quality is, however, affected by many other intravital factors such as stress during the transport and pre-slaughter treatment (Warris et al. 1994; D’Souza et al. 1998), structure of muscle fibres (Ryu and Kim 2005), and nutrition (Lindahl et al. 2006). As demonstrated in previous experiments where 10,000-fold higher doses of ionizing radiation (5 kGy) were used, the cell membrane’s integrity is directly associated with the drip loss (Dvořák et al. 2004); however, no significant reduction in the tissue enzyme activity was noted (Dvořák et al. 2006). Because ionizing radiation causes oxidative stress, a higher incidence of meat with an atypical maturation pattern such as PSE (Pale Soft Exudative) or others cannot be ruled out. On the other hand, the actual whole-body dose is important, with relatively lower doses not necessarily causing this negative effect. The aim of this study was to determine whether a whole-body irradiation exposure to a doseof 0.5 Gy will have a negative impact on selected pig meat quality indicators. Materials and Methods The experiment was approved by the Ethics Committee in Slovakia in 2007 (7/2007/EK). A total of 20 pigs of the Slovak Large White breed (Sus scrofa domestica) were included in the experiment. Pigs were divided randomly into two groups of 10 animals (an experimental and a control group). Both groups consisted of gilts and barrows at a ratio of 50:50. At the beginning of the experiment, the pigs were at 2 months of age, weighing 30 kg. They were housed in holding pens (separate for experimental and control groups) with access to daylight, and were reared under standard conditions. During the experiment, a standard pig feed mixture OS 03 for the corresponding age category was administered. Water and food were available ad libitum at nipple drinkers and food dispensers. Pig handling and transport in both the control and the experimental group were identical, except for irradiation. In order to reduce the effects of other stress factors, two weeks prior to irradiation pigs of both the control and the experimental group were repeatedly placed in irradiation cages and to the transport lorry for adaptation. No animal died during the experiment. The experiment was performed in August. The pigs were mounted in cages appropriate to their size. Anaesthetics were not used during the experiment. The distance was determined by the Chisostat irradiation machine so that the gamma dose was homogeneous throughout the body. Ten pigs from the experimental group were irradiated by a single whole-body dose of 0.5 Gy gamma radiation 60Co, at a dose rate of 0.98 Gy·h-1. The other 10 pigs represented the control group. Irradiation was performed at the Faculty of Science, of the Pavol Jozef Safarik University in Kosice, Slovakia, located 35 km away from the farm by a device CHISOSTAT (Chirana, Czech Republic). Three days after irradiation, the pigs were transported to the slaughterhouse in Zemplínska Teplica (UVMP in Kosice) located just one km from the farm. After a rest period of 3 h at the slaughterhouse they were slaughtered. Electric prods were not used either during the pig housing, or during the loading and unloading. In case of a real accident, the evacuation of pigs is carried out within three days, therefore the same experiment time was determined. Pigs were slaughtered and samples of the longissimus dorsi (LD) muscle at the last rib and of the semimembranosus (SM) muscle were collected. Muscle (meat) pH value and colour were measured at 45 min and 24 h post mortem. The pH value was measured using the Orion 250 A+ digital pH meter equipped with an Orion puncture electrode. Calibration was performed on three buffers of pH 4.01; 7.00 and 9.00. The pH value was recorded after the automatically measured value got stabilized. Meat colour was determined in the CIELAB system using the portable Colour-guide sphere spex spectrophotometer (BYK Gardner, Germany), excluding gloss, using a spherical geometry d/8°, D65 as a source of light, the standard observer’s angle set to 10°, and the diameter of the opening being 8 mm. The instrument was calibrated to the food foil prior to measurement. Meat colour at the cut perpendicular to the muscle fibres was determined by using the mean of the values collected from three separate measurements (CIE 1986). For comparative studies it is essential to maintain a precise instrumentation (Brewer et al. 2001); similarly, in determining the pH value (Henckel et al. 2000). In order to compare the results, further indicators of the CIELAB system were calculated from the mean values of L* (Lightness), a* (Redness), b* (Yellowness) coordinates (Honikel 1998). The distance between the two points, ΔE* (CIE total colour difference) was calculated according to the formula: ΔE* = [(ΔL*)2 +(Δa*)2 +(Δb*)2]1/2. The total colour difference (DE*) aggregate values of all the three above mentioned indicators L*, a* and b*. The chroma C*ab is a value that indicates the difference between the respective value of colour and the grey colour, according to the formula: C*ab = (a*2 +b*2)1/2. Determination of drip loss was carried out by a standard method within the time period from 24 to 48 h post mortem, and also by a modified method using a container (Dvořák and Mikulík 1990; Honikel 1998) within 482