Maataloustieteellinen Aikakauskirja Vol. 61: 433—440, 1989 Influence of carcass temperature, glycogenolysis and glycolysis 45 min postmortem on the development of PSE pork MARKKU HONKAVAARA Finnish Meat Research Centre, Box 56, SF-13101 Hämeenlinna, Finland Abstract. This study investigated the effect of slaughter stress, scalding and process time from stunning to chilling on carcass temperature, muscle glycogen and lactate content, and the development of PSE meat (pH,<5.B). Blood creatine kinase (CK) activity was positively (P<0.001) related to carcass tempera- ture at slaughter. During scalding, carcass temperatureraised by 1.2± I.4°C, 13 %of muscle glycogen was broken down and lactate level elevated by 5 %. Furthermore carcass tempera- ture fell by 0.7±0.8°C, 5 % of muscle glycogen was consumed and lactate content increased by 35 % between scalding and chilling. The time elapsed from stunning to splitting and further to chilling had a minor effect on carcass temperature, muscle glycogen or lactate content. Whereas, lactate production was posi- tively correlated with the increase in carcass temperature both during scalding (PcO.Ol) and between stunning and chilling (P<0.01), and with muscle glycogen breakdown (PcO.OOl). Consequently, the enhanced glycogenolysis during scalding, the accelerated glycolysis between scalding and chilling, and the elevated carcass temperature 45 min postmortem (p.m.) resulted in the development of PSE meat. Index words: slaughter, creatine kinase, postmortem glycogenolysis, glycolysis, PSE meat Introduction The efforts to imrove pork quality should include the proper handling and management of pigs all along the line from farm to chilling. At the abattoir, the treatments just before slaughtering are easier to control than the p.m. biochemical reactions triggered by stress- ful handling. Wismer-Pedersen and Briskey (1961a) presented four types of p.m. pH falls: a slow gradual, a gradual, a relatively rapid and a sharp, significant decrease. PSE meat resulted when pH, (45 min p.m.) was decreased to about 5.4 while tissue temperature remained above 25°C. However, the accelerated chill- ing rate had no significant effect on final lac- tic acid content but it did reduce the rate of 433 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=v09OlP-G8bud5G7h.pZKBTrjDwTFVNGubmmKHQg.n7SKXTV7HPk6QO0RksXl5BQ5GFbl_Wyn9VZLegwbejVPaNqX-VE9695N1w0R8Jp030km9enAwGi7IlEn_P35nVFIuUbQjG0n1RWtu0HSNRXPVOUCTiMxK66wrUuatY0SUyFq_2DUE0i_QDTv1U6szcKe3EAU4AT9MrXQv4Z9jg lactate formation (Wismer-Pedersen and Briskey, 1961b). The heat production and loss from muscles were brought to equilibrium 30 min p.m. (Bierning-Sorensen, 1976). Moreover, the rigor and temperature measurements 45 min p.m. gave information about the intensity of treatment before and during slaughtering (Sybesma and van Logtestun, 1966).Finally, the rapid pH fall combined with a high carcass temperature developed PSE meat (Wol- tersdorf and Troeger, 1987 T Earlier papers (Honkavaara, 1988, 1989a and 1989b) considered the effect of porcine stress on blood composition and early p.m. meat quality in pigs of different halothane genotypes; the influence of selection phase, fasting and transport on porcine stress and on the development of PSE; and the influence of lairage on blood composition of pig and on the occurrence of PSE. The purpose of this study was to evaluate the effect of blood CK activity and slaughter line on carcass temperature, muscle lactate and glycogen content, and the development of PSE. Material and methods Test animals 38 Finnish Landrace (L) pigs, 8 Finnish Yorkshire (Y) pigs and 56 LxY crosses were slaughtered at three abattoirs. The Central As- sociation of Artificial Insemination Societies determined the halothane genotype of 52 animals, and the results were combined by the Finnish Animal Breeding Association to get the probability for the genotype, the rest were of unknown genotype. The collection and treatment of animals are described earlier (Honkavaara, 1989a, 1989b). Measurements at the abattoir The temperature and relative humidity were measured with a portable hygrometer (Hu- micap HMI 31, Vaisala, Finland) in the lairage and on the slaughter line at splitting and be- fore carcass chilling. Moreover, it was mea- sured scalding temperature and time, the time elapsed from stunning to splitting, and from splitting to chilling. Evaluation of meat quality Methods used for the evaluation of meat quality are described earlier (Honkavaara, 1988). Furthermore, the increase in carcass temperature during scalding and that from stunning to chilling were calculated by sub- tracting the temperature of 0 min p.m. from that of 10 min p.m. and from that of 45 min p.m., respectively. In addition, the rate of muscle glycogen breakdown and lactate for- mation were calculated from the samples of M. longissimus dorsi (LD) by the formulas: micromoles (pmol) of glycogen (MG) broken down per 100 g of wet tissue in one minute = MG 0 min p.m. (pmol/100 g)-MG 45 min p.m. (pmol/lOO) time elapsed from exsanguination to chilling (min). pmol of lactate (ML) formed per 100 g of wet tissue in one minute = ML 45 min p.m. (pmol/100 g) — ML 0 min p.m. (pmol/100 g) (ime elapsed from exsanguination to chilling (min) Variables The following 34 variables were used in statistical analyses: loading timeof day, trans- port temperature and duration (TD), lairage time, temperature of lairage (TL), humidity of lairage, stunning time of day (ST), fasting duration (FD), scalding temperature (STE) and time (STI), temperature on line at split- ting and that before chilling (TEC), humidity on line at splitting and that before chilling, time elapsed from stunning to splitting (TS) and that elapsed from splitting to chilling (TC); blood creatine kinase (CK) activity on farm, during unloading and at exsanguination (CKE); serum glucose (SG), glycerol, lactate and pH; carcass temperature 0 (CT O), 10 (CT, O) and 45 min p.m. (CT4S); muscle glyco- 434 gen 0 (MG O), 10 (MG I0) and 45 min p.m. (MG 4S); muscle lactate 0 (MLO), 10 (ML 10) and 45 min p.m. (ML 4S); muscle pH 45 min p.m. (pH,) and carcass hot weight (CW). The CK values were log,0 transformed. Statistical analyses Conventional statistical methods were used to calculate means, standard deviations and standard error of the means (SEM). The re- lations between the measured variables and meat quality traits were analysed by simple regression. The difference among the means were evaluated by analysis of variance. More- over, stepwise regression analyses were used to examine the relative predictive valueof the measured variables for carcass temperature, muscle glycogen, lactate and pH value 45 min p.m. (statistical program PATO for micro- computers, Mikrovuo, Finland). The regression model (1) included the de- pendent variable Y, (i= 1 —8) and the 33 in- dependent variables X s (j = 1 33, j =£ 1) and the standardized regression coefficients Bj (j = 1 33, j*i). Yi = B I X, + B 2X 2 + B 3X 3 + ... +B„X„ (1) Prediction equations (2) were developed us- ing stepwise regression analysis (Honkavaa- ra, 1989a). (2)Y, =BO + B,X, + B 2X2 + ... + BnXn (i=l—B, n = 3—6) Results Prediction of the development of PSE meat Table 1 shows the combined effects of studied variables on muscle pH, value and on the changes in carcass temperature, mus- cle glycogen and lactate content 45 min p.m. Thus, the coefficient of determination (R 2 100) of the prediction equations were for the rate of lactate formation and glycogen break- down, increase in carcass temperature from Table 1. The best stepwise regression models11 for predicting biochemical changes in the M. tongissimus dorsi 45 min postmortem. Carcass temperature 45 min p.m.= 6.152 + 0.247TD +0.209FD + 0.601CT,,, +0.217ML45 +0.227CW Increase in carcass temperature during scalding = 31.892 -0.603CT,, + 0.2065G + O.2IBSGL -0.213MG„ Increase in carcass temperature from stunning to chilling= 11.523 +0.247FD + O.37TEC —0.965 CTo +0.569CTIO +0.241ML45 + 0.196CW Muscle glycogen 45 min p.m. = 515.25 —O.I67FD+ O.5O4MG||, +O.I7BML,|—0.471ML 45 Muscle lactate 45 min p.m.= 9.054 -0.237TD + 0.3495 T -0.392MG45+0.377ML„-0.31 pH, Rate of glycogen breakdown from stunning to chilling= - 6.393 + 0, 1 335T1 + 0.948MG,, - 1.021MG4, Rate of lactate formation from stunning to chilling= 4.493 -0.112TS-0.198TC -0.715ML0+ 1,063ML 4S pH| = 11.148+ 3.14TL—0.325CT|„—0.217ML 10—0.382ML 4S Prediction equations'1 J Regression models have significant F-values (P<0.002). b Abbreviations given in text. I Coefficient of determination x 100 II Degrees of freedom. R 2 100 Dfd % 74.2 5/56 60.4 4/50 84.9 6/48 63.9 4/94 70.6 5/59 96.1 3/96 96.9 4/86 60.2 4/50 435 436 stunning to chilling and during scalding, and muscle pH, 96.9, 96.1, 84.9, 60.4 and 60.2 %, respectively. In addition, the R 2 100 values of prediction equations for carcass tem- perature, muscle lactate and glycogen 45 min p.m. were respectively 74.2, 70.6 and 63.9 %. The combined effects of the independent vari- ables of the prediction equations are discussed below. Carcass temperature during scalding The average increase in carcass temperature during scalding was 1.2+ I.4°C. Carcass tem- perature 0 min p.m. was highly significantly positively correlated with log CK at exsangui- nation (r= 0.47, PcO.OOl). Moreover, this CK activity contributed 12.9 % of the varia- tion in carcass temperature 0 min p.m. (Hon- kavaara, 1989a). Figure 1 shows the differ- ence in carcass temperature before and after scalding between the pigs with a low and elevated CK activity. Thus carcass tempera- tures of 38.5 and 39.6°C at slaughter, X, led to the respective temperature increases of 1.3 and O.4°C during scalding, Y (Y = 35.985 — 0.902X, R : 100=45 %, PcO.OOl). On the other hand, the higher the blood CK activity at exsanguination, X the smaller was the in- crease in carcass temperature during scalding, Y (Y = 3.757 -0.72810gX, R 2 100 =8 %, Pen 05). The most contributing components of the increase in carcass temperature during scald- ing were carcass temperature 0 min p.m., se- rum glucose and glycerol, and muscle glyco- gen 0 min p.m. (partial R 2 100 = 45.3, 5.9, 4.9 and 4.3 °7o, respectively, Table 1). In the present study, neither stunning order nor car- cass hot weight had no significant influence on the increase in carcass temperature during scalding. The lactate content of the LD muscle of the carcasses with the highest CK values were 45.6 pmol/g before scalding and 62.2 pmol/g af- ter scalding. The former value was in the mean range of 45.5 + 12.2 pmol/g, whereas the lat- ter was significantly (Pc0.05) higher than the respective average value of 47.8 pmol/g in this study. So it was suggested that the great oc- currence of reactors (20 °7o) led to a high heat generation due to accelerated glycolysis dur- ing scalding in carcasses with the highest CK values (Fig. 1). Furthermore, the effect of halothane genotype on carcass temperature is discussed more accurately earlier (Honkavaa- ra, 1988). Carcass temperature from stunning to chilling The average carcass temperature 0 and 45 min p.m. was 38.6+1.0 and 39.0±1.1°C, respectively. Moreover, the mean increase in carcass temperature during scalding and that from stunning to chilling was respectively 1.2± 1.4 and 0.5 ± I.3°C. Consequently, car- cass temperature fell by 0.7 ±O.B°C between scalding and chilling. In order to present the influence of carcass temperature on meat quality, the collected datawere classified into three groups of nearly the same number of pigs according to the car- cass temperature rise between stunning and chilling. Consequently, Table 2 shows the variation in those variables that differed sig- nificantly between the groups. On the slaughter line, the increase in car- cass temperature was negatively correlated with the temperature (r = —0.49, P< 0.001) and humidity (r = —0.49, P<0.001) at split- ting, temperature (r = —0.47, PcO.OOl) and Fig. I. Effect of CK activity (logarithmic transformation) at exsanguination on carcass temperature. Table 2. Effect of carcass temperature on studied variables. Variable Change in carcass temperature from stunning to chilling, °C SEM Temperature on line at splitting ,°C Humidity » , % 0.33 1.56 Temperature on line before chilling, °C Humidity » , % 0.34 1.65 Time elapsed from stunning to splitting, min Time elapsed from splitting to chilling, min Carcass temperature 0 min p.m., °C Increase in carcass temperature during scalding, °C Rate of glycogen breakdown from stunning to chilling. 0.46 0.54 0.13 0.20 pmol/(100 g X 1 min) 2.5“ 1.211.lb 17.8“ 23.3“ 51.l b 76.977.8 76.3 30.050.0 27.8 0 11.138.9 45.050.0 55.5 55.038.9 5.6 0 0 27.8 0.44 Rate of lactate formation from stunning to chilling, pmol/(IOO gxmin) 0.34 Carcass hot weight, kg 0.79 Prime grading class, E+, % pH,<5.B, % 5.8