Does feeding high oleic soybeans to finishing pigs affect lipid profile?
Or consumer taste preference of pork?
By Natalie Acosta Castellanos, Robert Thaler and Eric P. Berg
Pork is recognized as one of the best sources of high-quality protein in the human diet, which, in addition to its characteristic flavor and high carcass yield, makes this meat one of the most consumed around the world. However, consumers’ perception associating red meat, such as pork, with a higher risk of heart disease, obesity and some types of cancer lead them to limit their red meat intake as part of a “healthier diet.” Therefore, altering the fatty acid composition in meat may alter consumers’ impression of the nutritional value of pork.
This demand for greater nutritional quality has led the pork industry to develop different strategies that aim to modify the fatty acid profile of swine adipose tissue by increasing the deposition of unsaturated fatty acids (UFAs) at the expense of their saturated counterparts (SFAs). UFAs, especially polyunsaturated fatty acids (PUFAs) from the Omega-3 family, are widely recognized for their beneficial roles in reducing/preventing cardiovascular diseases and supporting neural function, while the Omega-6 family (i.e. high amounts of C18:2, n-6, linoleic acid) and subsequent high n-6: n-3 PUFA ratio may have pro-inflammatory effects in humans. In contrast, consumption of oleic acid (C18:1, Omega-9), the major monounsaturated fatty acid (MUFA) in pork fat, has been associated with cardioprotective benefits and enhanced physiological utilization of free fatty acids by the body. Therefore, producing pork with a lower n-6: n-3 ratio and increased concentration in MUFA is desirable.
Dietary fatty acids are the major source of pre-formed fatty acids deposited in muscle and lipid tissues of swine. Therefore, modifications in the fatty acid composition of finishing diets are considered as one of the most effective ways to influence the fatty acid profile of pork and pork products. Theoretically, feeding a swine diet high in UFAs, with a balanced n-6: n-3 PUFA ratio and/or increased content of MUFA will improve the content of these fatty acids in pork fat, generating an enriched pork product.
However, several authors have reported that a high concentration of PUFAs in pork fat may negatively impact processing properties such as bacon firmness and yield, palatability, and oxidative stability of the final product. The addition of MUFAs to swine finishing rations has shown contrasting results.
Advances in soybean genetics have resulted in the development of a non-GMO high oleic soybean (Trusoya) that contains 70% oleic acid, 30% less saturated fatty acids, and has an ideal n-6: n-3 PUFA ratio, making it very appealing as an ingredient for swine rations. There is, however, limited data evaluating the impact of soybeans with enhanced fatty acid composition on fresh pork quality and palatability. Therefore, this study aimed to determine if soybeans with a high concentration of oleic acid included in a swine finishing ration had an impact on lipid oxidation and palatability of fresh pork.
For this study, 72 crossbred pigs (Landrace × Yorkshire, Duroc × Landrace × Yorkshire) were sorted by weight (initial body weight = 78 ± 9 kg) and sex, then distributed within 18 pens (4 pigs/pen). Each pen was randomly assigned to one of three experimental diets containing traditional control soybean meal (CTRL), extruded conventional soybeans (CONV), or extruded, high oleic acid soybeans (TRU). These rations were offered to the animals during the finishing period in a two-phase feeding program.
Phase one was fed until the pigs reached 109 kg and phase two was fed from 109 to a market weight of 118 (± 5) kg. Upon reaching market weight, pigs were transported to the NDSU Meat laboratory for humane harvest under USDA-FSIS inspection. Six different harvest groups (n = 12 pigs / group) were created across treatments to ensure uniformity of final body weight. Thus, animals were retained on test for 34, 37, 41, 42, 48 or 50 days.
Boneless loin chops (2.5 cm thick) were fabricated from the 11th rib of each right-side carcass, vacuum sealed, aged for seven days at 2 ºC and then frozen at -18 ºC for later sensory analysis. On the day of the evaluation, pork chops were thawed, cooked and portioned following the procedures of AMSA sensory guidelines (2016), until offered to panelists. The consumer panel, consisting of 115 participants, was asked to rate the acceptability of each sample using hedonic scales (Figure 1). A nine-point scale was used to rate overall like, pork flavor acceptability, tenderness acceptability, and juiciness acceptability, while a five-point scale was used to determine level of tenderness, level of juiciness, level of pork flavor, and presence of off flavors.
An additional 50g chop was collected from the loin muscle adjacent to the 12th rib of each right carcass, vacuum packaged, aged for 14 days at 2 ºC and frozen at -80ºC for evaluation of malondialdehyde (MDA) as indicator of shelf-life lipid oxidation. In addition, subcutaneous fat samples were obtained adjacent to the first thoracic vertebra, packed in Whirl-Pak® Bags, and frozen at -18 ºC for determination of total lipid and fatty acid profile; including saturated (SFA), monounsaturated (MUFA), and polyunsaturated fatty acids (PUFA) as a percentage of total fat.
Fat content and fatty acid composition in lean and adipose tissues have a direct effect on the palatability perception of pork due to the release of compounds that act as flavor and aroma precursors during thermal oxidation. Our results presented in Table 1 indicate that consumers did not perceive differences in overall like, tenderness acceptability, pork flavor intensity and acceptability, or presence of off-flavors in pork chops across experimental diets.
However, panelists were able to identify differences in juiciness acceptability, level of juiciness and level of tenderness. We found a high positive correlation between the perception of juiciness and perception of tenderness by consumers, and a weak but positive correlation between the PUFAs content in fat and the perception of juiciness. This could explain why pork chops from the CONV treatment were perceived as juicier and more tender than samples from CTRL and TRU diets.
Results presented in Figure 2 reveal that the inclusion of TRU soybeans during the finishing period successfully changed the fatty acid profile in subcutaneous fat towards a higher deposition of MUFA. The fatty acid shift was predominantly represented by oleic acid, at the expense of SFAs (palmitic and stearic) and linoleic acid. In addition, linoleic acid, known for negatively impacting bacon firmness, was higher in the CONV treatment. This condition was also reflected in an increased iodine value (IV), a measure of the degree of unsaturation, in the CONV diet. IV values between 70-75g/100g are preferred for acceptable pork fat quality and firmness, which were achieved in all our dietary treatments.
Lipid oxidation is considered as one of the main causes of deterioration in quality in fresh meat and is directly related to the amount and composition of fat. Over time in retail display, UFAs are more prone to oxidation than SFAs, and PUFAs are extremely susceptible to oxidation and rapid propagation of rancid notes and colors. We did not find significant differences among diets, but tendencies are presented in Figure 3. The MDA concentration expressed per kilogram of meat was slightly higher in the TRU treatment compared to CONV and CTRL.
ConclusionThe high oleic acid soybeans can be used to modify the composition of fatty acids in swine tissues to meet consumers’ interest in purchasing food items containing less saturated fat, while maintaining the eating characteristics when compared to pork obtained from a traditional corn-soybean meal diet. Therefore, TRU soybeans represent a dietary alternative to improve the perceived nutritional value of pork without increasing lipid oxidation during retail display or affecting pork chop palatability and fat firmness.
AcknowledgementsMinnesota Soybean Research and Promotion Council, North Dakota State University Meat Science, Northern Crops Institute and South Dakota State University Extension.
Castellanos is a product development scientist with PTC ingredients, Nestle Purina; Thaler is Farm Credit Services of America Endowed Chair in Swine Production, Distinguished Professor and Extension swine specialist at South Dakota State University; and Berg is a professor in animal sciences at North Dakota State University.
