The influence of fiber size distribution of type IIB on carcass traits and meat quality in pigs Gap-Don Kim, Jin-Yeon Jeong, Eun-Young Jung, Han-Sul Yang, Hyun-Tae Lim, Seon-Tea Joo ⁎ Division of Applied Life Science (BK21 Program), Institute of Agriculture and Life Science, Gyeongsang National University, Jinju, Gyeongnam 660-701, Republic of Korea abstract article info Article history: Received 27 September 2011 Received in revised form 23 September 2012 Accepted 3 February 2013 Keywords: Muscle fiber Fiber size Meat quality Pork The effects of detailed characteristics such as the size and proportion of type IIB fibers in longissimus thoracis muscle on carcass traits and pork quality were investigated. A total of 96 pigs were classified into four groups by the proportion of different IIB fiber sizes. Group NS (high proportion of both small- and normal-sized IIB fibers) had a higher total number (136.4) and density (231.31) of type IIB fibers, backfat thickness (37.20 mm) and intramuscular fat content (4.77%) than the other groups (P b 0.05), whereas Group NS had the lowest values of cross-sectional area (3413.85 μm 2 ) and diameter (60.15 μm) of type IIB fiber among the groups (P b 0.05). Pig muscles with higher percentage of large IIB fibers exhibit tougher, lighter and more exudative meat than pig mus- cles with a higher proportion of small- or normal-sized IIB fibers. Therefore, an increase in the proportion of large IIB fibers causes poor quality of pork. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction Skeletal muscle is composed of several types of fiber, each having different morphological and biochemical characteristics. Muscle fibers are commonly classified as type I (slow-twitch, oxidative), IIA (fast- twitch, oxidative glycolytic), and IIB (fast-twitch, glycolytic), based on stains for enzymes involved in oxidative metabolism (Peter, Barnard, Edgerton, Gillespie, & Stempel, 1972) and myosin ATPase activity (Brooke & Kaiser, 1970). Individual fibers differ in oxidative capacity and myosin ATPase activity as well as size, lipid and myoglobin content (Cassens & Cooper, 1971; Essén-Gustavsson, Karlstrom, & Lundstrom, 1992; Rosser, Norris, & Nemeth, 1992). These varying characteristics of different fiber types are related to meat quality and carcass traits in various species, such as cattle (Hwang, Kim, Jeong, Hur, & Joo, 2010; Ozawa et al., 2000; Picard, Juire, Duris, & Renand, 2006), pigs (Fiedler, Rehfeldt, Dietl, & Ender, 1997; Ryu & Kim, 2006) and poultry (Dransfield & Sosnicke, 1999; Kim et al., 2008). For example, increasing the proportion of type I fiber is associated with lightness decreasing and water-holding capacity improving in pigs (Choi, Ryu, & Kim, 2006; Gil et al., 2003; Ryu & Kim, 2005) and with tenderness and juiciness improving in cattle (Maltin et al., 1998). Also, type IIB fibers are closely related to toughness, paleness, protein denaturation and low water- holding capacity in porcine longissimus muscle (Choi et al., 2006; Karlsson et al., 1993; Kauffman et al., 1998; Larzul et al., 1997; Renand, Picard, Touraille, Berge, & Lepetit, 2001; Ryu et al., 2008). In general, the longissimus muscle of pigs has a greater size and higher percentage of type IIB fiber than of type I or IIA fibers. There is also a large variation in size among type IIB fibers within the same species and the same muscle. It has been reported that the proportions of type IIB fibers were 69.7–90.3% of area and 70.92–94.73% of number in porcine longissimus muscles from various breeds, such as Berkshire, Yorkshire, Landrace, Duroc and their crossbred pigs (Lee et al., 2012; Ruusunen & Puolanne, 2004; Ryu et al., 2008). The size distribution of type IIB fiber has been reported to range from 2771 μm 2 to 8522 μm 2 in cross-sectional area and from 61.32 μm to 71.51 μm of diameter (Larzul et al., 1997; Lee et al., 2012; Miller, Garwood, & Judge, 1975; Ryu, Rhee, & Kim, 2004). In our previous study, it was observed that the proportion and size distribution of type IIB fiber in longissimus muscle from crossbred (Korean native black×Landrace) pigs were 75.72–82.62% of area and 70.78–82.17% of number, and 76.07– 83.93 μm in diameter, respectively (Kim et al., 2013). However, most researchers studied the characteristics of muscle fiber types by comparing their mean values of size. Up to now, specific studies on the large variations in size and proportion among individual fibers of type IIB have not been conducted. Therefore, in the present study, we investigated the size distribution and proportion of type IIB fiber, and the influence of these factors on meat quality and carcass characteristics in porcine longissimus muscle. 2. Materials and methods 2.1. Samples and carcass traits A total of 96 crossbred (Korean native × Landrace) F 2 pigs (56 gilts and 40 castrated males) were fed the same commercial diet. Pigs of 202±5 days old (112±6 kg of live weight) were slaughtered at a commercial slaughtering house according to the standard commercial Meat Science 94 (2013) 267–273 ⁎ Corresponding author. Tel.: +82 55 772 1943; fax: +82 55 772 1949. E-mail address: stjoo@gnu.ac.kr (S.-T. Joo). 0309-1740/$ – see front matter © 2013 Elsevier Ltd. 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