Dietary inclusion of tomato pomace improves meat oxidative stability of young pigs

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Besides being considered an excellent source of protein, minerals and vitamins B6, B12 and D, pork provides significant amounts of n‐3 polyunsaturated fatty acids (n‐3 PUFA). However, it is known that pork contains a low polyunsaturated/saturated fatty acid (PUFA/SFA) ratio that raises cholesterol level and has impacts negatively on human health (Ferguson, 2010; McAfee et al., 2010). In addition, cholesterol oxidation is directly related to meat cholesterol content (Engeseth and Gray, 1994) and inversely related to meat antioxidant content (Engeseth et al., 1993). Crucially, cholesterol oxidation products exhibit mutagenic, carcinogenic and cytotoxic properties (Guardiola et al., 1996).
An important factor that determines the amount and composition of fatty acids in pig adipose tissue is animal's diet (Tikk et al., 2007); thus, considerable effort has been made over several decades to meet human dietary recommendations by manipulating animal fat composition through diet modifications (Wood et al., 2004; Teye et al., 2006). By altering the source of fat in pig feed, a positive effect on human health can be obtained; for example, animal fat rich in saturated fatty acids (SFA) can be replaced by vegetable fat with higher proportion of unsaturated fatty acids (Corino et al., 2002; Alonso et al., 2010, 2012). However, increasing PUFA concentration of pig feed leads to oxidative instability in pig meat and fat, which compromises preservation under refrigeration (Apple et al., 2009) and reduces palatability after processing (Rosenvold and Andersen, 2003).
Like pig meat and fat, liver is one of the most nutritious animal products, representing an excellent source of vitamins B12 and A. Liver is also rich in protein and cholesterol, but poor in lipids (Domínguez et al., 2015). Although pig liver is consumed in many traditional dishes, such as iscas and almôndegas in Portugal and meatballs in the United Kingdom (Nollet and Toldrá, 2011), its nutritional value under different dietary treatments remains to be elucidated.
Several studies have shown that some pig feed additives (e.g. vitamins, minerals and antioxidants) can control lipid oxidation in pork and significantly improve its overall quality. Thus, the demand for feed additives derived from natural sources, such as plants, fruits, spices, oil and seeds, has increased in recent years (Rossi et al., 2013). Tomato pomace is a by‐product from the tomato processing industry that is rich in fibre and bioactive compounds, such as antioxidants, like lycopene and β‐carotene. Lycopene is the pigment responsible for the red colour of some fruits (Markovic et al., 2006) and is able to protect lipids, proteins and DNA from oxidative damage (Riso et al., 2010). Due to its acyclic structure and the presence of a large number of double bonds, lycopene is recognized as the carotenoid with the greatest reactivity and antioxidant effect (Ivanov et al., 2007). In animal feeding, tomato pomace represents a considerable source of protein, vitamins and minerals; however, its energy value is limited by a high fibre content. On a dry matter basis, its crude protein level varies between 15% and 25% and the neutral detergent fibre (NDF) level is more than 50% (Del Valle et al., 2006). Portugal produces around 55 thousand tons of tomato pomace per year and its incorporation in animal feed is widely accepted to promote meat nutritional quality, antioxidant effect, preservation extension and organoleptic characteristics (Cadoni et al., 2000; Del Valle et al., 2006). In addition, young pigs are consumed as a gourmet food product in some countries, including Portugal. Therefore, the aim of this study was to assess the nutritional effect of tomato pomace, in combination with two distinct fat sources (lard or soya bean oil), on young pig meat, subcutaneous fat and liver.
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