Effects of Feed Aroma Agent on Feed Antioxidant Activity and Growth Performance and Meat Quality in Fattening Pig

Shang Yang, Bian Lianquan*, Liu Xianjun, Chen Jing, Luo Wenyou

College of Animal Husbandry and Veterinary Medicine, Shenyang Agricultural University, Shenyang 110866

Abstract: A feeding trial was conducted on fattening pigs by adding different doses of aroma agent to feed to investigate the effects of aroma agent on feed antioxidant capacity, fattening pigs growth performance and meat quality. The results showed that aroma agent significantly reduced the peroxide value of feed (P＜0.05), increased the feed intake and daily gain of fattening pigs (P＜0.05), and significantly reduced the TBA value of the M. longissimus dorsi (P＜0.01). There was a trend towards increasing fatty acid and creatine content in the M. longissimus dorsi, and no effect on content of amino acids and nucleotides (P＞0.05).

Feed aroma agent, also known as feed flavoring agent or flavor agent, are feed additives that can mask the unpleasant odor in feed, improve feed palatability, increase feed quality, increase animal feed intake, and promote animal digestion and absorption. During storage, the nutrients in feed, such as some unsaturated fatty acids, are prone to be oxidated and deteriorated. Some flavoring ingredients in feed aroma agent have antioxidant functions, so adding them to feed can delay（slow） the degree of oxidation. The metabolic process of the body produces harmful free radicals, and many natural perfumes have strong abilities to remove free radicals, which play an important role in maintaining the health of body. This test was based on the above theory, aiming to provide practical evidence for the above theory, and testing the content of flavor precursors (amino acids, fatty acids and flavor nucleotides) in meat to verify whether aroma agent can affect the flavor of pork.

1.2 Test design and feeding management

This test selected 72 healthy and disease-free Duroc crossbred pigs weighing 65 ± 3.6kg, with similar weight and good growth performance (same number of male and female). The pigs were divided into 4（four） groups using a single factor fully randomized design, with 3（three） replicates per treatment group and 6（six） pigs per replicate. Group A was the control group, fed with basic diet; Group B, C and D was（were） fed diet added 500g/t, 750g/t and 1000g/t of aroma agent, respectively.

The feeding test was conducted on August 10, 2012 at the Changtu Guomei Feeding Farm in Tieling City, Liaoning Province, with a pre-feeding period of 7 days and a formal trial of 35 days, totaling 42 days. During the pre-trial period, the test pigs were subjected to ear tagging, deworming, and vaccination. After the pre-trial period, the pigs entered the trial period and were fed with powder feed three times a day (5:00, 10:00 and 16:00) to ensure that the pigs were able to feed and drink ad libitum. Clean pig manure 2-3 times a day and keep the pen clean and naturally ventilated. After the test, all the pigs were slaughtered after fasting (drinking water ad libitum) for 24 hours. One pig was randomly selected from each replicate in each group, 12 pigs in total. Weigh about 1 kg of M. longissimus dorsi and transport them to the animal production laboratory of Shenyang Agricultural University in foam incubator with ice bag for laboratory index measurement.

roxide value.

1.3 Measurement indicators and methods

1.3.1 Feed indicators

The peroxide value of feed was analyzed according to the method of GB/T 5538-1995 and the method of Wang Jianhui et al. ^[1]. Specific operation method: Crush the feed to particles of 40 meshes with a grinder, use analytical balance to weigh about 2 g (accurate to 0.0001 g) of feed sample to be measured, put 10 mL of chloroform and 15 mL of glacial acetic acid into a stoppered triangular flask, plug the bottle, gently shake it to make the feed sample evenly spread, soak it for 20 minutes, add 2 mL of potassium iodide saturated solution, quickly cover the bottle stopper, gently shake it for 1 min, keep it stand in the dark for 15 minutes, add 20 mL of distilled water and 5 mL of 0.5% starch solution, gently shake well, titrate with sodium thiosulfate solution until the blue brown color completely fades, and shake vigorously during titration. Simultaneously, conduct a blank test.

Result calculation: POV (meq/kg) = C (V₁-V₀) × 1000/m

Where: V₁- Volume of sodium thiosulfate solution used for determination, mL;

V₀- Volume of sodium thiosulfate solution used for blank test, mL;

C- Concentration of sodium thiosulfate solution, mol/L;

m- Feed weight, g.

1.3.3 Meat quality indicators:

1.3.3.1 TBA value of the M. longissimus dorsi ^[2]: Weigh 10 g of pork sample and cut it into small pieces. Add 50 mL of 7.5% trichloroacetic acid (containing 0.1% EDTA), thoroughly homogenize with a homogenizer, shake for 30 minutes, and filter with double-layer filter paper. Measure 5 mL of filtrate and add 0.02 mol/L TBA solution. Take a water bath in 90℃ water bath for 40 minutes, remove and cool it to room temperature. Centrifuge for 5 minutes (1600 r/min). Add 5 mL of chloroform to the supernatant and shake well. Let it stand for layering. Take the supernatant, conduct colorimetric detection at a wave length of 532 and 600 nm, record the extinction value, and calculate the TBA value using the following formula:

3 Discussion

3.1 Effect of aroma agent on feed peroxide value

The results of this test indicated that the aroma agent had antioxidant function. With the increasing of feed storage time, adding aroma agent can effectively alleviate the oxidation of feed, and the best effect was achieved when the addition amount was 1000 g/t.

Under the influence or catalysis of high temperature, ultraviolet ray, enzyme or other oxidation factors, unsaturated fatty acids in fats (such as rice bran, fish meal, cake or meal and added oil, etc.) of feeds will react with oxygen in the air to form peroxides, which continue to decompose to produce low-grade aldehydes and carboxylic acids. Feed oxidation seriously affects feed quality. Some active substances in aroma agent can bound free radicals, while others can slow down the oxidation rate by forming mixed free radical complexes or metal chelates.

The antioxidant mechanisms of active ingredients in perfumes can be summarized as follows:

3.1.5 Synergistic antioxidant mechanism of various components in spices

when present alone, phenolic hydroxyl groups, unsaturated double bonds, and reducing heteroatoms, etc., have antioxidant effects, and when combined, they also have antioxidant effects, and most of them have synergistic effects, enhancing reducibility. Alkaloids containing reducing heteroatoms are combined with phenols. After the nitrogen atom of alkaloid is protonated by the hydrogen of phenols, the chemical bond combining with the nitrogen atom will become loose and easy to be broken, and its electrode potential will drop, making it easy to be oxidized; After the hydrogen of phenols is lost, the electron cloud of phenols ring will be weakened, and its electrode potential will drop, leading to phenols being more easily oxidized to quinones. Therefore, their antioxidant capacity will be greatly enhanced after combination. The chemical components in perfumes that have weak reducing ability when present alone undergo a series of biochemical reactions during storage, processing, or use, resulting in substances with strong reducing ability. In other words, there are also potential antioxidant components in natural perfumes.

3.2 Effect of aroma agent on growth performance of fattening pigs

The results of this test indicated that adding aroma agent to feed had an attractant effect on fattening pigs, increasing feed intake and daily gain. The best effect was achieved when(with) the(an) addition amount was 1000 g/t.

Aroma agent can stimulate the olfaction and gustation of pigs, increase appetite and induce eating, thereby increasing feed intake. Under the joint action of olfaction and gustation, feeding signals are transmitted to the digestive system through conditioned reflexes, leading to increase the secretion of saliva, gastric juice, intestinal juice, pancreatic juice, and bile in the digestive tract and increase the content of proteases, amylases and lipases increases, strengthen intestinal peristalsis, enhance mechanical digestion movements and nutrients in the feed are fully digested and absorbed, thereby promoting its growth and development and improving daily gain ^[4].

3.3 Effect of aroma agent on meat quality of M. longissimus dorsi in fattening pigs

3.3.1 Effect of aromatherapy on the TBA value of M. longissimus dorsi in fattening pigs

The results of this test indicated that adding aroma agent to the feed can significantly reduce the TBA value of pork, increase its antioxidant ability, alleviate its oxidative rancidity and deterioration, and extend the time for pork to maintain its flavor and quality. The best effect was achieved when the addition amount was 1000 g/t.

Peroxides generated during the oxidation process of meat can damage protein, fat and DNA in cells, disrupting the integrity of cell membranes. The active substances in aroma agent are digested, absorbed, metabolized and deposited into meat by animals, exerting their antioxidant functions. The mechanism is shown in section 3.1.

3.3.2 Effect of aroma agent on amino acid composition of M. longissimus dorsi in fattening pigs

The results of this test indicated that adding aroma agent to feed can not affect the composition and content of amino acids in pork.

3.3.3 Effect of aroma agent on fatty acid composition of M. longissimus dorsi in fattening pigs

The results of this test indicated that aroma agent can（could） alter the fatty acid composition of pork. Aroma agent contain esters formed by low-grade fatty acids and fatty alcohols, which have the aroma of various fruits. Esters are digested into low-level fatty acids, which are absorbed by the small intestine and participate in the synthesis of body fat. So theoretically, adding aroma agent to feed can increase the content of low-grade fatty acids in pork. But this test did not give this result. In the results of this test, the content of some saturated fatty acids in the treatment groups was significantly higher than that in control group, and the other saturated fatty acids in test group also showed a trend of being higher than that in control group, which may（might） be related to the presence of citric acid in the aroma agent, which can participate in the synthesis of fatty acids in the body ^[5]. In this test, the content of some unsaturated fat acids in the test group was significantly higher than that in control group, and other unsaturated fat acids in treatment groups also tended to be higher than that in control group, which may be related to the antioxidant function of aroma agent. Unsaturated fat is easy to be oxidized and deteriorated during storage, and aroma agent can reduce the oxidation of unsaturated fat, so that the content of unsaturated fat in treatment groups is higher than that in control group. The degradation product of eicosatetraenoic acid in pork, 1-octen-3-ol, and various aldehydes generated by oleic acid degradation, along with the unique product of linoleic acid degradation, 2-pentylfuran, reflect the flavor of pork ^[6]. The results of this test indicated that the content of these three unsaturated fat acids in treatment groups tended to be higher than those of control group, indicating that adding aroma agent could increase the aroma precursors of pork, making the meat flavor of pork more intense during cooking.

3.3.4 Effect of aroma agent on flavor nucleotide content in the M. longissimus dorsi of fattening pigs

Inosinic acid and guanylic acid are the umami flavoring substances in pork ^[6]. In the results of this test, the inosine（inosinic acid） content in the treatment groups showed a higher trend than that in control group, with the 1000 g/t group having the highest inosine（inosinic acid） content; Only the content of guanylic acid in the 1000 g/t group was higher than that in control group. The synthesis of some important methylation products in animals requires methylation, such as the synthesis of carnitine, methionine and creatine, as well as mRNA methylation, but the animal body itself cannot synthesize methyl groups. There are many methyl donors in aroma agent, such as 3-methyl-1-butanol, 3,7-dimethyl-1,3,6-octatriene, etc. Aroma agent may promote methyl metabolism in pig liver, increase the synthesis of carnitine in the liver, enhance the transport of carnitine to muscles, and form acid insoluble carnitine with long-chain fatty acids from body fat breakdown and food sources, which enters muscle mitochondria and promotes the synthesis of fatty acids β-oxidation, promoting the production of ATP in muscles, which is broken down to provide energy and generates AMP, while the IMP in muscles is derived from the deamination and decomposition of AMP ^[7].

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