**Abstract**

Pork is one of the most popular foods in Chile. Consumers are concerned about their nutritional quality and about the characteristics of the production systems. Outdoor production systems are the most valued by consumers due to animal welfare conditions related to the nutritional quality of the product. On the other hand, intensive or traditional confined pig production systems represent an environment that alters the nutrients in meat products. For this reason, outdoor production systems become more important, especially when nuts (Quercus spp.) are included in pig feeding. Acorn nuts have a high level of fatty acids transferred to the meat, increasing flavor and juiciness. This proposal is a bibliographic review that will also include the advantage of controlling an invasive species, such as wild boar for a small producer in southern Chile, who could obtain a meat product with healthy fatty acids, favoring the sustainability of the ecosystem**.**

**Keywords:** feed, nuts, meat quality, pig production system, wild boar

### **1. Introduction**

Pork meat is one of the most popular food products in Chile. Its consumption reaches a value close to 23% of the total meat consumed. Consumers of meat products are increasingly interested in the nutritional quality of meat, and pork has particular attention given the implications for people's health [1]. Feed quality influences the fat intramuscular fat content of the pig, with some aspects of quality decreasing as the composition of fatty acid in intramuscular lean carcass content [2]. Compared to extensive and natural systems, the inferior quality of pork from intensive systems presents quality defects such as exudates from meat juices and a decrease in the amount of intramuscular fat [3].

### **2. Meat composition**

The composition of meat comprises moisture, protein, fat, minerals, and a small proportion of carbohydrates. Chemically, a piece of lean meat contains approximately


*Zn: Zinc h L: Longissimus*

**Table 1.**

*Nutritional composition of different food products [6].*

72% water, 21% protein, 5% fat, and 1% ash. The macronutrient protein is the most valuable component in nutrition and processing [4]. In addition, it is a source of essential amino acids, vitamin B12, iron, and zinc [5]. It is low in carbohydrates and does not contain dietary fiber (**Table 1**).

#### **2.1 Acorn characteristics**

*Quercus robur* L., the common oak, is a plant in the family Fagaceae [7] composed of 300 species around the world, including deciduous and evergreen trees [8]. The Quercus genus can be located in America, temperate Europe, Asia, and subtropical Africa [9]. This tree, whose fruit is known as "bellota" has different shapes and varies in size [10]. Because of their content and nutritional importance, they have been called "secondary human food," being part of the human diet for centuries, as raw material in bread making [8, 11].

In Europe, the Quercus tree is considered the main tree species in floodplain forests of central Europe [8]. In the Czech Republic, the clear-cut silvicultural system represents a predominant method of regeneration of oak stands in a flooded forest [11].

The consumption of acorns in human food has a long history. The population of Italy and Spain consumes this fruit.

Using acorns in human nutrition has a long history. In Italy and Spain, it has been part of the local diet for some time, contributing up to 25% of consumed food by the poorest classes as a substitute for coffee [12]. Algeria, Morocco, and the US used acorn oil as a cooking oil and medicine for burns and injuries [13].

Acorn oils have similar properties to olive oil, such as color, iodine value, UV extinction coefficient, fatty acid composition, and refractive index [14, 15]. In South America, the *Q. robur* tree is part of the forests of Southern Chile, including Chilean Patagonia and Argentina. The fruits of this tree are part of the diet of wild boars and domestic pigs, and it is used as an ornamental tree species in squares in different cities (**Figure 1**).

Acorn's nutritional composition is rich in unsaturated fatty acids (75–90%), especially oleic acid (65%) and linoleic acid. These unsaturated fatty acids are essential for synthesizing eicosanoids, favoring the reduction of blood triglycerides and the increase of HDL cholesterol [16]. Compared to commercial foods, acorns have a higher content of crude fat, net energy, and metabolizable energy [17] (**Table 2**).

In Europe, acorns are used as a feed source for free-range animals, especially Iberian pigs, during the montanera season [18]. Montanera is the fattening period of Iberian pigs that weigh more than 40 kg in two or three months. In the Iberian Peninsula, the Iberian pig is an autochthonous breed. The Iberian pig system is linked to the dehesa lands of *Quercus* spp., in the Iberian Peninsula [19]. The abundant food provided by acorns is used to fatten the pigs from early November to late February [20].

In the dehesa, the pig diet is based upon acorns and grass, the most abundant resources in the area during this period [21]. Grazing is a repeated ingestion of small quantities of food [20]. Grass bites can be very light, but pigs need a lot of them as a source of protein to compensate for the low concentration of this nutrient in the acorn.

#### **Figure 1.** *Oak tree (Quercus robur) in the square of Coyhaique city, Chilean Patagonia.*

Pigs have a good sense of smell and taste [22]. They select their food depending on crude protein content and essential amino acids such as lysine, methionine, and tryptophan [23]. This sensory ability allows pigs to differentiate between acorn fruits from different oak trees [24].

The feeding systems for pigs, whose feeding base is the acorn fruit, contribute to delivering characteristics to the carcass and the meat, especially in the composition of fatty acids of the adipose tissues [20].
