Effect of Animal Age at Slaughter on the Muscle Fibres of Longissimus thoracis and Meat Quality of Fresh Loin from Iberian × Duroc Crossbred Pig under Two Production Systems

SIMPLE SUMMARY: This paper is in attempt to assess the impact of the production system Montanera and intensive, and the age at slaughter in each of them, on the muscle fibres of Longissimus thoracis (LT) and meat quality of fresh loins from Iberian pigs. The age at slaughter affected the fibre size of Montanera LT muscles, while the production system influenced the fibre type I population and type IIB fibre size. The age at slaughter affected the fresh loin quality trait depending on the production system; Montanera and intensive fresh loins from older animals yielded higher myoglobin and redness values. Additionally, intensive fresh loins derived from older animals yielded the lowest intramuscular fat and the highest cook loss and shear force in the Warner-Braztler shear force test. These above-mentioned parameters differed due to production systems, Montanera fresh loins less fat-infiltrated and tough but with higher redness values. The results of the present study contribute to shedding light regarding how the production-related factor animal slaughter age may influence the muscle fibre population, size and quality traits of fresh meat. ABSTRACT: Two production systems and several ages at slaughter were used: 12, 14 and 16 months for outdoor rearing (with the final finishing phase in the Montanera system, in which fed was based on natural resources, mainly acorns and grass) and 8, 10 and 12 months for animals reared indoors (intensive system: with feed based on commercial fodder) to evaluate their effect on the muscle fibre population and size of the Longissimus thoracis, (LT) muscle, as well as fresh loin quality traits. Animals that were older at slaughter revealed increased fibre sizes of the LT muscles in the pigs reared in the Montanera system. The LT muscles of the animals reared in intensive systems had a lower percentage of type I fibres and higher size of type IIB than those reared in the Montanera system. The approximate composition and instrumental colour of Montanera fresh loins were affected by the animal slaughter age. In the case of the intensive system, the effect of animal slaughter age had an impact on the approximate composition, instrumental colour, water loss and textural properties. Therefore, different ages at slaughter of Iberian pigs showed variations in some quality parameters in the fresh loins in both the Montanera and Intensive systems, thus proving to be a factor of variability and homogeneity of the Iberian products. The meat from Iberian pigs reared in an intensive system and slaughtered at a younger age proved to be more tender. The production system affected all the above quality traits, with the exception of water loss.