# Physicochemical Properties and Oxidation Status of Pork from Three Rearing Systems
## 1 Introduction  
Global pork consumption accounts for 33% of total meat consumption, with large differences among continents in consumption levels [1]. The European Union (EU countries) accounts for 21% of the world production of pork. Recently, there has been a great increase in pork products that are sold with official quality labels and the number of pigs that are produced under alternative production systems [2]. Quality of pork is based on several quality attributes: nutritional, organoleptic and technology (oxidation status during storage and thus shelf life) properties and societal image (animal welfare and environmental impacts) [3]. The traditional rearing methods of the past allowed pigs to range freely during the day and sleep in a spacious pigsty at night. In recent decades, these old traditional methods have been replaced by intensive rearing (conventional) systems in which the pigs are continuously confined in a restricted, stimulus-poor space [4]. However, not only whole food safety and the sensory quality of pork but also the life quality of pigsin rearing systems are very important to consumers and have become a major point of concern as well [5]. Furthermore, it is a common belief among consumers that the quality of pork from pigs raised under extensive systems is better [6]. This led to increased interest in alternative rearing systems such as outdoor, free range and organic production systems. Organic farming is the most regulated alternative production system, providing environmental sustainability and welfare for breeding animals [7]. The rules of organic production systems, encompassing a comprehensive set of guidelines and regulations, are explicitly outlined and defined within the extensive body of European Union legislation. These regulations address critical factors, such as the optimal housing conditions, comprising both indoor and outdoor areas, the intricacies of feeding practices, the consideration of age as a vital determinant and the specific genotype attributes of animals involved in organic production [8]. The core point of rearing system differences is the availability of outdoor areas for animals. Roles of outdoor areas can be summed up mainly by pigs' physical activity, better animal welfare and feed quality (ingestion of herbage and soil in the pasture) which could be reflected in the quality and quantity of meat [9]. Another factor that can play a role through rearing systems in the production properties and meat quality is genotype. Local breeds of pigs are considered to be most suitable for outdoor production systems. On the other side, these local breeds are characterized by inferior carcass qualities, low feed consumption efficiency and growth efficiency in comparison with specialized breeds raised in conventional systems [10]. Rearing conditions of pigs under alternative systems (free range and organic systems, outdoor access) increase energy expenditure for physical activity and thermoregulation, decreasing the growth rate, but improve some properties of meat quality such as the production of lean meat and higher meat oxidative stability [11]. In contrast, other authors indicated that higher intramuscular fat and unsaturated fatty acid composition in organic pork enhanced lipid oxidation, resulting in inferior technological meat quality [12; 13; 14]. Furthermore, it is worth noting that an abundance of investigations and extensive studies have been conducted to explore the multifaceted impacts of various pig rearing systems on both the quantitative aspects and qualitative attributes of pork, encompassing even the intricate evaluation of pork's oxidation status. Remarkably, the findings stemming from these comprehensive examinations have demonstrated a remarkable divergence, thereby yielding a broad spectrum of outcomes and conclusions that often diverge significantly from one another, thus further accentuating the complex nature of this research domain [9; 11; 15; 16; 17].