Original article Classification of wooden breast myopathy in chicken pectoralis major by a standardised method and association with conventional quality assessments Line B. Dalgaard, 1,2 Martin Krøyer Rasmussen, 1 Hanne C. Bertram, 3 Jens A. Jensen, 1 Hanne S. Møller, 1 Margit D. Aaslyng, 4 Eva K. Hejbøl, 5 Jacob R. Pedersen, 6 Dieter Elsser-Gravesen 7 & Jette F. Young 1 * 1 Department of Food Science, Aarhus University, Blichers All e 20, 8830 Tjele, Denmark 2 Section for Sports Science, Aarhus University, Dalgas Avenue 4, 8000 Aarhus C., Denmark 3 Department of Food Science, Aarhus University, Kirstinebjergvej 10, 5792  Arslev, Denmark 4 Danish Meat Research Institute, Technological Institute, Gregersensvej 9, 2630 Taastrup, Denmark 5 Institute of Clinical Research, University of Southern Denmark, Odense, Denmark 6 Danpo A/S, Vestre Skovvej 3, 9600 Aars, Denmark 7 ISI Food Protection, Agro Food Park 13, 8200 Aarhus N, Denmark (Received 1 November 2017; Accepted in revised form 13 February 2018) Summary Wooden breast (WB) abnormalities of broilers compromise the quality of fresh and processed meat. Yet, no standardised classification method for evaluating WB currently exists. We here provide a novel classifi- cation method to determine the severity of WB by palpation. Data were evaluated by one-way ANOVA. The classification method proved robust and reliable to classify broiler filets into three distinct categories (no, moderate and severe WB). This was supported by histological findings, demonstrating less muscle tis- sue in WB-affected samples. Moreover, moisture content, resistance to compression, mobile water frac- tion, drip loss and cooking loss, as well as intramuscular and surface pH also increased with WB. Using the classification method, we demonstrated that severe WB increased the diversity of the endogenous microflora and promoted growth of Enterobacteriaceae. In conclusion, the presented classification method correlates with known meat quality traits and will be a valuable tool for future studies on WB. Keywords Histology, microbiology, muscle tissue, poultry, scoring method, severity grading, texture. Introduction Intensive genetic selection and feeding optimisation in broiler production over the past decades have resulted in a faster growth rate and increasing breast yields. For example, as described for the fast-growing broiler line Ross 308, over a 10-year period, the age to reach a body weight of 2.2 kg was dramatically decreased from 43 to 35 days, while at the same time, Musculus pectoralis major (PM) increased from 15.8% to 21.1% of the total body weight (Petracci et al., 2015). This may be ascribed to genetic selection, but environmen- tal factors such as feeding regimes were also optimised in the same period (Havenstein et al., 2003). The long- term production performance optimisation has caused some adverse side effects to emerge at the tissue level. Phenomena such as ‘white striping’ (superficial white striations) and ‘wooden breast’ have previously been described for the PM of fast-growing broiler strains, reviewed by Petracci et al. (2015). Wooden breast (WB) is characterised by pale and bul- ging hard areas (Sihvo et al., 2014) and has several impli- cations for the quality of the fresh and processed products. This muscle tissue abnormality can be pheno- typically detected by palpation of the breast area, and further characterisation of the WB myopathy at the mor- phological level has suggested that muscle fibre necrosis, fibrosis and muscle fibre regeneration (Sihvo et al., 2014; Velleman & Clark, 2015), as well as substitution of adi- pose tissue, can occur (Radaelli et al., 2017). These tissue alterations affect meat quality such as texture, pH and water-holding capacity (Dransfield & Sosnicki, 1999) and may also influence microbiological growth and therefore food safety and shelf life. Partic- ularly for microbial growth potential, pH is of utmost importance, and an increased pH in breast muscle *Correspondent: E-mail: jettef.young@food.au.dk Line B. Dalgaard and Martin Krøyer Rasmussen Contributed equally to this work. International Journal of Food Science and Technology 2018 doi:10.1111/ijfs.13759 © 2018 Institute of Food Science and Technology 1