Vol 5(1996): 49-55. Relationship of breast fillet deboning time to shear force, pH, cooking loss and color in broilers stunned by high electrical current Petri A. Papinaho Department ofFood Technology, University ofHelsinki, Finland Daniel L. Fletcher Department ofPoultry Science, University ofGeorgia, USA Hannu J. Rita Department ofForest Resource Planning, University ofHelsinki, Finland Experiments were conducted to determine the relationships between deboning time and broiler breast meat quality, as determined by objective meat tenderness, pH, color and cooking loss. All birds were processed in a European commercial processing plant using a high current, constant voltage stunning system and air chilling. According to a modified Mitscherlich response equation, pH values reached their ultimate value by 5.77 h post-mortem, with an asymptotic 95 % confidence interval of 5.72 h- -5.81 h post-mortem. The shear force data, which were analyzed using a logistic model, suggested that broiler breast fillets should be aged intact on the carcass for 10.58 h, 5.94 h or 2.28 h to guarantee that over 95 % of the fillets reach Allo-Kramer shear forces of 8.0, 9.0 or 11.0 kg/g, respectively. Since acceptable meat tenderness values vary with country, geographical area, or consumer groups, acceptable ranges should be determined according to potential market demands. No relationships between deboning time and fresh meat color or cooking loss was found. Key words: breast muscle, tenderness, modeling ntroduction In Europe, a growing proportion of fresh broiler breast meat is marketed to consumers as a boneless product. Often the breast meat is mech- anically deboned immediately after air chilling, within 60-90 minutes post-mortem. There have been numerous published studies, mostly in North America, showing that longer aging timesbetween slaughter and deboning are required to produce tender meat (Pool et al. 1959, Dodge and Stadelman 1959,Stewart et al. 1984, Lyon et al. 1985, Sams and lanky 1986, Daw- © Agricultural and Food Science inFinland Manuscript received November 1995 49 AGRICULTURAL AND FOOD SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=muCf_KJbRfVuwJsi.I41E-1clU0HurVQn03LQAw.8bBHqqpYfTEw5PlM4yP4e-FP1mNM3DxJqVV4aDp9sGHz0SavyioGy67y80NGJ3vCRvWzhocgrT2ScwRV3mpVt8Lk0nOhxlGEmD3oFQ2MtYnE1P602Td1xOKBJx-2oEPqOOxxRQ-i9VHV-AjrffyXK6MFUwiKe28jaAEcmRm3w8-4IvrP-wfocTFa6hafE6drsTdWW9VMkNa8TvRjh3of9gjvXEiAVadfDMwki3qkbR4_ZPHaAzuKB-V85AJH5p6Hc07ZG0Jv79ygxXQrCqrsbEr7VGTF6ULnw9eYNUXDeiAwdUcENi-UVeXDDw Papinaho, PA. et.ai: Broiler breast fillet deboning time and quality sonetal. 1987, Sams et al. 1989). Recommenda- tions have been made to age intact broiler car- casses for at least 4 to 6 hours post-mortem prior to removal of the breast muscles (Goodwin 1984, Shelton 1985, Stadelman et al. 1988). These recommendations are primarily based on research and practical experiences from process- ing lines using non-standardized low voltage (and low current) stunners, and rapid ice and water immersionchilling; methods not common- ly used in the Western European poultry indus- try. Early deboning of poultry meat has been re- ported to have some advantages as well as dis- advantages. Early deboned broiler breast meat can be suitable for formulating into processed rolls (Boyd and Ball 1973). Also, sausages made from hot boned thigh meat have been reported to have a higher emulsion capacity, but a greater cooking loss than samples made from cold deboned, aged meat (Lyon et al. 1983). Little has been published concerning the deboning time as related to broiler meat tender- ness, color, and cooking loss, using European high current stunning and air chilling. Also, ex- periments conducted in commercial processing plants have been rarely published. The objective of this study was to determine the relationship between deboning time and broiler breast meat quality in a European com- mercial processing plant using high current stun- ning and air chilling. Breast meat quality was determinedusing objective meat tenderness, pH, color and cooking loss. Material and methods Three trials, with 56 birds in each, were con- ducted using mixed sex, 37-day-old Ross 208 broilers. Feed was removed from the birds at 8- 10h before slaughter, but birds were allowed free access to water. The birds were caught and cooped about 4—5 h prior to slaughter. The broilers were slaughtered in a commercial processing plant. Stunning was done using a constant volt- age in-line stunner with voltage of 100 V and frequency of 50 Hz. Six birds were in the stun- ner circuit at the same time, the measured aver- age amperage per bird was 120 mA. The birds were exsanguinated unilaterally, bled for 180 s and scalded at 54 °C for 180 s and picked. After evisceration, the broilers were air chilled for 45 min at 0 °C in circulating air. The end point tem- perature of breast fillets was 4-6 °C. Eight different deboning times post mortem were used: 10 min, 65 min, 2 h, 4 h, 6 h, 8 h, 12 h, and 24 h. For the 10 min group, the breast muscles were excised from carcasses which were takenfrom the processing line immediately after defeathering (hot-boned). The 65 min samples were removed from carcasses which were taken from the processing line immediately after chill- ing. The carcasses for the later groups were re- moved from the processing line after air chill- ing, and held packed in crushed ice until the time of sampling. The excised breast muscles were placed in plastic bags, transported in ice to the laboratory and were then stored at 4°C until the meat quality measurements could be performed on the following day. One breast muscle from each bird was used for pH measurement, while the muscle from the opposite side of the same bird was used to de- termine color, cooking loss and shear force. For pH determination, duplicate samples were re- moved from the inner cranial area of the muscle immediately after deboning, and were analyzed according to the iodoacetate method described by Jeacocke (1977). The color, cooking loss and shear force measurements were done at 30-36 h post-mortem. Meat color was determined from the inside surface of the uncooked muscle with a Minolta CR-200 colorimeter using illuminant D6J . Muscle samples were then weighed and cooked for 20 min in 90°C steam. The samples were allowed to equilibrate to room temperature and were reweighed. Cooking loss was calcu- lated as a percentage of weight loss from the un- cooked muscle weight. Shear force was deter- mined using an Allo-Kramer shear cell in an Instron Universal Testing Machine (Instron, High Wycombe, England). A square shaped sample. 50 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Vol. 5 (1996): 49-55. 20 X 20 mm, was cut from the thickest part of the cranial area of the muscle, such that two sides of square were parallel to the surface muscle fibers. Full scale load was set at 10kg and cross head speed was set at 80 mm/min. Statistical analysis The GLM procedure of SAS®/STAT program (SAS Institute 1990) was used to determinetime by trial interactions for pH and shear force data. Since no significant time by trial interactions were found the three trials were combined for further analyses. The pH data was analyzed with NLIN proced- ure ofSAS®/STAT program (SAS Institute 1990). A modified Mitscherlich response equation was used to characterize pH levels of broiler breast muscle as a function ofpost-mortem time (Ware et al. 1982). The model presented is _y = (3(1 +pe - a( *~e) ) where y = pH level of broiler breast at x hours post- mortem (3 = the asymptotic minimum value of pH a = rate of decrease in pH-level 0 = time (x) when the pH value is IOOp % above asymptotic minimum Shear force gives a objective, quantitative measurement to the tendernessof meat. The vari- ance of shear force changes considerably with time. Therefore ordinary regression or analysis of variance applications may not be suitable for comparing the significance of differences in shear force over time. However, acceptable ten- derness is a binary phenomenon from the point of view of the customer: the tenderness ofmuscle is either acceptable or not. Logit models (Col- lett 1991) are suitable for analyzing data in the form of proportions. For the purposes of logistic modeling of tenderness, three levels of shear force were tested as high delimiters of accept- able tenderness: 8.0, 9.0 and 11.0 kg/g. Let T denote the time post-mortem until deboning (measured in this case on the logarithmic scale) and n(T) the probability that a muscle deboned at timeT post-mortem will turn out to be tender. The logit model used for the dependence of the time T and the probability 7t(T) is k(T) In( )=Y + 6 T 1 - n(T) The transformation of the probability 7t(T) on the left side of the equation is called logistic transformation. The probabilities of being ten- der were thus compared on the logistic scale. Let T 95 be the time T that is needed post- mortem to assure that 95 % of the muscles are tender in the sense of the definition given above. Hence, in terms of the logit model T95 is the time T at which 7t(T) equals 0.95. By substituting this value into the logit model above, T 9J can be solved, as soon as y and 8 are known. As these parameters are estimated from experimental data, the timeT95 is also subject to experimental error. Based on the standard errors and covariances of the parameter estimates, confidence interval for the time T95 was determined by the method of Collett (1991). The data from the color and cooking loss measurements were analyzed by ANOVA using the GLM procedure of SAS®/STAT program (SAS Institute 1990). The main effects ofdebon- ing time, trial, and deboning time by trial inter- action were tested using residual error. Results and discussion Post-mortem breast muscle pH over time is pre- sented in Figure 1. A modified Mitscherlich re- sponse equation was applied to estimate when the values reach their ultimatepH level (level at 24 h post-mortem). According to the model, pH did not change after 5.77 h post-mortem, with an asymptotic 95 % confidence interval of 5.72-5.81 h post-mortem. The result of this study is different from that ofKijowski et al. (1982), 51 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Papinaho, P.A. et.ai: Broiler breastfillet deboning time and quality who reported that pH did not decrease after 2 h post-mortem. The first timepoint for measuring the pH in their experiment was 15 min post-mor- tem, at which time the pH value was 6.14. In this study, the pH was 6.72 at 10 min post-mor- tem. However, at 24 h post-mortem, the pH val- ues were almost the same: 5.75 for Kijowski et al. (1982) and 5.79 in this study. Smith et al. (1992a) also reported a low early pH level: 6.41 at 15 min post-mortem. In contrast to Kijowski et al. (1982), but supported by this study, Smith et al. (1992a) found that the pH at 4 h was still significantly higher than a value at 24 h post- mortem. These differences may be due to differ- ent electrical stunning procedures, as suggested by a previous study (Papinaho and Fletcher 1995), different bird strains, different physiolo- gical state of the birds at time of stunning, or different cooling rates of the breast muscles. Shear force for breast muscles deboned at different timespost-mortem is presented in Fig- ure 2. The logistic model was applied to the shear force data three times, using three different levels of shear force as a highest acceptable values: 8.0, 9.0 and 11.0 kg/g. At each of these levels, the time T post-mortem before deboning was statistically significant in the logit model (p < 0.0001). The estimate for the time T 95 was 5.70 hours with 95 % confidence interval from 3.07 to 10.58 h, when 8.0 kg/g was used as a delimiter of acceptable shear force. The results for highest acceptable shear forces of 9.0 and 11.0 kg/g were 3.50 and 1.59 respectively. The 95 % confidence intervals for these values were from 2.06 to 5.94 and from 1.10 to 2.28, respect- ively. These results indicate thatbreast muscles should be held intact on broiler carcass up to 10.58 h post-mortem to guarantee acceptable tenderness, based on a delimiter value of 8.0 kg/g as suggested by Simpson and Goodwin (1974). However, if a processor can use a higher de- limiter and still meet customer tenderness Fig. I. Breast muscle pH means with 10 % and 90 % fractiles at different times post-mortem. 52 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Vol. 5 (1996): 49-55. expectations, deboning times from 2.28 to 5.93 hours may be used. Lyon et al. (1985) reported that shear force did not significantly (P < .05) decrease after 4 h post chilling (5 h post-mortem) and Stewart et al. (1984) found that shear values from broiler breast muscles deboned at 3 h post-mortem were not significantly different from intact muscles aged for 24 h. Dawson et al. (1987) found sig- nificant differences in shear force of broiler breast muscle even for muscles deboned at 8.33 and 24 h post-mortem. However, he suggested that aging for 3.33 h would be sufficient for ten- derization with no advantage in tenderness gained by deboning at later times up to, and in- cluding, 8.33 h. Smith et al. (1992b) reported that shear force values for muscles deboned at 6 h post-mortem were still significantly higher than 24 h values. However, all these results were gen- erated in North America using differentstunning and chilling methods which may have resulted in faster post-mortem muscle reactions (Papin- aho and Fletcher 1995). Selecting the correct shear force level to cor- respond to acceptable sensory tenderness values has been the point of interest in some previous research. Simpson and Goodwin (1974) report- ed that Allo-Kramer shear force values greater than 8.0 kg/g corresponded to sensory scores of “slightly tough” to “tough”, and values below 8.0 kg/g corresponded to “tender” to “very ten- der”. Using more recent techniques to simulate commercial processing conditions for test birds, Lyon and Lyon (1990) reported that shear force values below 6.0kg/g corresponded to “very ten- der”, when values from 6.0 to 8.8 kg/g were in the “slightly tender” to “moderately tender” range. No differences were found in color and cook- ing loss values within the different deboning times. The average color values were 54.1 ± .2 for lightness (L*), 2.0 ± .1 for redness (a*) and Fig. 2. Allo-Kramer shear force for broiler breast muscles. Lines show means with 10 % and 90 % fractiles for muscles deboned at different times post-mortem. 53 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Papinaho, P.A. et.al.: Broiler breast fillet deboning time and quality 4.7 ± .2 for yellowness (b*). The average cook- ing loss formuscles was 19.8 ±.2% of uncooked weight. On the basis of this study, similarrecommenda- tions to those ofGoodwin (1984), Shelton (1985) and Stadelman et al. (1988) can be given for broiler breast muscle deboning times, when high voltage stunning and air chilling are used. The shear force data, which were analyzed by the logistic model, suggest that broiler breast fil- lets should be aged intact on carcasses for 10.58, 5.94 or 2.28 h to guarantee that over 95 % of the fillets to reach shear forces of 8.0, 9.0 or 11.0 kg/g respectively. Since acceptability of certain meat tenderness may be different in different countries or areas, as well as in different cus- tomer groups, the shear force range that is con- sidered as an objective measurement for an ac- ceptable tenderness should be individually de- termined for each case. Acknowledgments. This study was supported in part by Ministry of Forestry and Agriculture of Finland and Finn- ish Food Research Foundation. The authors also wish to thankDr. Glen Ware forhis advice on the statistical model- ing of pH, and Ms. Satu Haapala for her technical assist- ance in processing the samples. References Boyd, L.C. & Ball, H.R.Jr. 1973. Performance of fresh and aged hot cut broiler meat in chicken rolls. Poultry Science 52: 2000-2001. Collett, D. 1991. Modelling Binary Data. Chapman and Hall, London. 369 p. Dawson, P.L., Janky, D.M., Dukes, M.G., Thompson, L.D. & Woodward, S.A. 1987. Effect of post mortem boning time during simulated commercial processing on the tenderness of the broiler breast meat. Poultry Sci- ence 66: 1331-1333. Dodge, J.W. & Stadelman, W.J. 1959. Postmortem ag- ing of poultry meat and its effect on the tenderness of breast muscles. Food Technology 13: 81-84. Goodwin, T.L. 1984. It takes tough discipline to make tender chicken! Broiler Industry 47: 43-44. Jeacocke, R. E. 1977. Continuous measurement of the pH of beef muscle in intact beef carcasses. Journal of Food Technology 12: 375-386. Kijowski, J., Niewiarowiz, A. & Kujawska-Biernat B. 1982. Biochemical and technological characteristics of hot chicken meat. Journal of Food Technology 17: 553- 560. Lyon, C.E., Hamm, D., Thomson, J.E., Hudspeth, J.P., Ayres, J.L. & Marion J.E. 1983. Effects of hot or cold deboning on functional properties of broiler dark meat and quality of sausage. Poultry Science 62: 965-970. - & Lyon, B.G. 1990. The relationship of objective shear values and sensory tests to changes in tenderness of broiler breast meat. Poultry Science 69: 1420-1427. - , Hamm, D. & Thomson, J.E. 1985. pH and tender- ness of broiler breast meat deboned various times after chilling. Poultry Science 64:1103-1111. Papinaho, P.A. & Fletcher, D.L. 1995. Effect of stun- ning amperage on broiler breast muscle rigor develop- ment and meat quality. Poultry Science 74: 1527-1532. Pool, M.F., de Fremery, D., Campbell A.A. & Klose, A.A. 1959. Poultry tenderness. 11. Influence of process- ing on tenderness of chickens. Food Technology 13: 25- 29. SAS Institute. 1990. SAS/STAT User’s Guide, Version 6, Fourth Edition. SAS Institute Inc., Cary, N.C. Sams, A.R. & Janky, D.M. 1986. The influence of brine chillingon tenderness of hot-boned, chill-boned, and age- boned broiler breast fillets. Poultry Science 65: 1316- 1321. - , Janky, D.M. & Woodward, S.A. 1989. 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The influence of hot boning broiler breast muscle on pH decline and toughening. Poultry Science 63: 1935-1939. Ware, G.0., Ohki K. & Moon, L.C. 1982. The mitscher- lich plant growth model for determining critical nutrient deficiency levels. Agronomy Journal 74: 88-91. 54 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Vol. 5 (1996): 49-55. SELOSTUS Korkealla virranvoimakkuudella tainnutettujen broilereiden rintafileen irroitushetken vaikutus lihaksen leikkausvoiman vastukseen, pH;hon, keittohävikkiin ja väriin Petri Papinaho, Hannu Rita ja Daniel L. Fletcher Helsinginyliopistoja University ofGeorgia, USA Koesarjan avulla määritettiin broilerin rintafileen (M. pectoralis) irroitushetken suhdetta lihan laatuun. Laa- dun mittareina käytettiin leikkausvoimaa (objektiivi- nen mureusmääritys), pH:ta, tuoreen lihan väriä ja keittohävikkiä. Kaikki koelinnut prosessoitiin suoma- laisessa siipikarjateurastamossa, jossa käytettiin kor- keaa tainnutusjännitettä ja -virtaa sekä ilmajäähdy- tystä. Nämä ovat nykyaikaisen eurooppalaisen siipi- karjan prosessointilinjan tyypillisiä piirteitä, japoik- keavat vastaavasta pohjoisamerikkalaisesta käytän- nöstä. Muunnetun Mitscherlichin vastemallin avul- la analysoiduista pH-tuloksista nähtiin, että pH-arvot saavuttivat lopullisen arvonsa 5,77 h postmortem, kun 95% asymptoottinen luotettavuusväli oli 5,72-5,81 h postmortem. Leikkausvoimatulokset analysoitiin lo- gistisella mallilla. Niistä voitiin todeta, että broile- rin ruhot tulee varastoida kokonaisina vähintään 10,58 h ennen fileiden irroitusta, jotta voidaan var- mistaa, että yli 95% fileistä alittaa leikkausvoiman 8,0 kg/g. Koska hyväksyttävä mureustaso vaihtelee maantieteellisestä alueesta ja kuluttajaryhmästä riip- puen, sen raja tulee määrittää tapauskohtaisesti vas- taamaan markkinoiden vaatimuksia. Rintafileen ir- roitushetki ei vaikuttanut tuoreen fileen väriin eikä keittohävikkiin. 55 AGRICULTURAL AND FOOD SCIENCE IN FINLAND