Factors Controlling Meat Quality of Pork in Relation to Breed and RN Genotype

Abstract: The Hampshire breed was introduced as the terminal sire in Swedish slaughter pigs in the 1970s, mainly to reduce stress susceptibility and associated problems of meat quality, such as the meat being pale, soft and exudative (PSE). Since then, however, the RN – allele, a mutation which is only found in pure-bred Hampshire and in crosses with it, has been discovered. In Sweden, approximately 65% of all slaughter pigs in which Hampshire has been the sire, carry the RN – allele. Meat from Hampshire as well as from RN –carriers is usually considered to be very tender, but on the other hand, is known for producing meat of low quality in terms of technological yield. The aim of the present work was to gain further knowledge and a better understanding of the mechanisms controlling the eating quality and water-holding capacity in such diversified meat as that produced in Sweden today, and to apply this knowledge in practical conditions in the meat industry. The tenderness, according to the Warner-Bratzler shear force and/or a sensory panel, was found to be greater in M. longissimus dorsi from carriers of the RN – allele than in M. longissimus dorsi from non-carriers, regardless of the breed of the non-carriers. Differences observed in the course of rigor development and ageing in muscle from carriers and non-carriers of the RN – allele suggested that proteolytic action, initiated by a more rapid fall in pH, was the most important factor governing the better tenderness achieved in M. longissimus dorsi of RN – carriers. The myofibrillar length, which is an indirect measure of the proteolytic activity that has occurred in the meat, was shorter for the RN – carriers than for the non-carriers. The rate of pH decline was of major importance for tenderness development, as demonstrated by the high correlation between the pH, measured at 3 to 7 hours post-mortem, and tenderness measured after 3-4 days’ ageing. Lower pH values at these times during rigor contributed to greater tenderness, regardless of whether the decline in pH was due to the presence of the RN – allele or slower chilling. In order to improve the tenderness of M. longissimus dorsi from non-carriers by post-slaughter treatment, either slow chilling or pelvic suspension can be used. However, to reach the same level of tenderness in non-carriers as in RN – carriers, the combination of both forms of post-slaughter treatment was needed. The water-holding capacity and juiciness were related to the presence of the RN – allele, where a higher glycogen content, lower protein content and lower ultimate pH contributed to a lower water-holding capacity, but higher juiciness. In addition to the RN – allele, slower chilling contributed to a somewhat lower water-holding capacity. The implementation of pelvic suspension during rigor development could be attractive for the meat industry in order to optimise the water-holding capacity as well as the tenderness. It was shown possible to separate RN – carriers from non-carriers early post-mortem at the slaughter-line using visual and near-infrared (NIR) spectroscopy.