Author: Matylda Kupka, Technical University of Lodz
Topic: The influence of feed containing herbs mixtures on pork quality.
Date of submission: 24.02.2021
The expectations towards the quality of meat have changed over the years. Nowadays, it became more difficult to surprise the customers and meet their needs. Meat-eaters are on the hunt for new flavors, textures and even smells of the product they purchase. For those reasons, pig breeders are constantly working on new methods to improve the quality of pork. One of the most commonly used practices is adding herbs mixtures to the feed. Such technique is supposed to change the smell of the meat and make it more pleasant to the consumer. This article gives some clarity on this topic and shed some light on it.
- What makes a pork smell in a certain way?
The scientific name of pork odor is ‘boar taint’. This term is used to describe an offensive odor or taste which can be evident during the cooking or eating of pork products derived from non-castrated male pigs. Such odor is found in approximately 20% of entire male finishing pigs. It is caused by two compounds- skatole and androstenone, which accumulate in fat tissue1. Studies show that around 75% of consumers are sensitive to boar taint. Therefore, it is crucial for pork producers to control the odor and constantly work on changing it so it would appear as more pleasant to the customers.
Androstenone is a steroidal pheromone produced in pigs’ testes. The compound is predominantly found in the saliva of male pigs, and, when inhaled by female pigs, may be perceived as the mating stance. Androstenone is synthesized from androstadienone by 5α-reductase, and can be converted into 3α-androstenol or 3β-androstenol by 3-ketosteroid reductase2. According to the studies conducted by researchers from the Montreal Neurological Institute3, approximately 40% of humans cannot smell any odor when presented with androstenone. When not perceived, the compound is considered as neutral, neither pleasant nor unpleasant. What is interesting is that it is possible to acquire the ability to perceive androstenone after repeated exposure. The secretion of androstenone can be controlled by castrating the male pigs before they reach puberty. It is a common practice in North America and Europe, hence the meat produced in those regions has less perceptible smell. Recently, experts have been working on some less invasive and more ethically correct method of controlling the boar’s taint. One of the techniques is the genetic selection against the genes responsible for the production of androstenone and skatole4.
It is not likely to find high concentrations of androstenone in breeding pigs, but rather in wild boars5.
Figure 1. The molecular structure of androstenone6
The second compound contributing to boar’s taint is skatole. Skatole (3-methylindole) is a compound most commonly found in the mammalian feces. The compound is produced by the decomposition of tryptophan in the digestive tract. Tryptophan is converted to indoleacetic acid, which decarboxylates to give the methylindole. Both tryptophan from the diet and from cell debris from degradation of intestinal mucosa can be metabolised to skatole. The compound does not appear to have any physiological role in the pigs’ organisms. Skatole is toxic for many ruminant species and may even be responsible for pulmonary edema and emphysema, however it is not toxic or dangerous to pigs7.
At low concentrations, it has a floral aroma, which is responsible for the pleasant smell of flowers8. Moreover, skatole contributes to bad breath and together with androstenone, it causes the boar taint. Unlike the smell of androstenone, the majority of people have the capacity to detect the smell of skatole. When combined, the two compounds form an offensive smell, which is often described as fecal-like or urine-like.
Figure 2. The molecular structure of skatole9
Even though both skatole and androstenone can be found in most of the non-castrated pigs, the smell is not felt by everyone or has different variations for different people. According to the study conducted by a group of researchers from Duke University Medical Centre10, the smell of pork perceived by humans is genetically determined. In their study, the researchers gave samples of pork containing androstenone and asked the subjects to smell them. A total of 23 subjects were recruited: 13 consumers and 10 professional sensory assessors. Then, the subjects were separated into two groups- those who experienced the offensive smell and those who did not. After observing such results, the researchers conducted a genetic analysis of the subjects. The examination revealed that the gene responsible for smelling the boar taint is a form of gene known as OR7D4. Subjects who did not enjoy the smell of pig’s meat had two copies of this gene. The others had only one copy. What is even more interesting, the study found that most people did not notice the smell of androstenone at all. 11 The idea behind the experiment was to see how important androstenone is for the pork’s smell, as there are some concerns on the topic of pigs’ castration. Some European countries are considering the ban of castration.
3. The effect of herbal additives in pigs’ feed on the pork’s smell
One of the methods of improving the pork’s smell and getting rid of the boar taint is to use the herbal additives in pigs’ feed. The vegetal substances with antimicrobial and antioxidant properties increase the shelf life of meat products. The diets containing antioxidants contribute to the prevention of lipid oxidation and color deterioration. Since those compounds can be easily found in herbs, it seems like a promising technology and an opportunity to replace the synthetic antioxidants with natural ones12. Most common replacements for synthetic antioxidants are phenolic-rich plants and their extracts, such as rosemary, thyme, olives or tea. They inhibit protein and lipid oxidation in meat, giving it a nice color, texture and, of course, smell. The prevention of lipids oxidation is crucial in controlling the smell of meat, as this process is responsible for the presence of offensive, strong odor. Especially important here are fatty acids, which after undergoing the process of oxidation, are responsible for the unpleasant aromatic sensations. Controlling the lipids oxidation helps to control the meat’s smell and preserve its quality.
3.1 The use of rosemary as an additive to pigs’ feed
In the year 2000, a group of researchers from University College Cork-National University of Ireland conducted a study concerning the influence of rosemary on the quality of pork13. Distilled rosemary leaves were added to the pregnant ewes diet. Such inclusion proved to increase the concentration of carbonic acid, carnosol and rosmarinic acid in the meat. Fresh meat from the subjects presented lower DPPH values and higher total ferric reducing antioxidant power. The results indicated that rosemary reduced lipid oxidation giving the meat a better taste and smell. Its extract contains antioxidant compounds, the most active being phenolic diterpenes such as carnosic acid, carnosol, rosmanol, epirosmanol, isorosmanol, methylcarnosate and rosmarinic acid. These compounds have been shown to help prevent oxidationAnother study conducted on lamb’s reported similar results14. In addition, another study conducted in the USA showed that feeding vitamin E to pigs increased pork stability during storage and essentially improved shelf-life performance15. However, the study conducted by another group of researchers found that diet supplemented with rosemary had no effect on the lipid stability in the fresh meat16.
3.2 The use of thyme essential oil as an additive to pigs’ feed
Thyme essential oil is known for its beneficial effects, as it contains more than 60 ingredients. For instance, some of the beneficial properties of thyme EO are antiseptic, antimicrobial, and carminative. The most important compounds of thyme EO are the phenols thymol (68.1%) and carvacrol (3.5%), which constitute the major and most active constituents, as well as the monoterpene hydrocarbons p-cymene (11.2%) and γ-terpinene (4.8%), which are known to have antioxidant properties and slow antimicrobial activity. Due to their lipophilic nature, they are accumulated in the membranes and take part in membrane-associated events, such as energy depletion. Moreover, the phenolic compounds found in thyme essential oils are known for their redox properties, which allow them to act as reducing agents, hydrogen donors, singlet oxygen quenchers and metal chelators17. Using thyme as an additive to pigs’ feed presented good results in terms of oxidative deterioration18.
3.3 The use of cilantro as an additive to pigs’ feed
Yasuyoshi Hayata and colleagues note that chitlins — hog large intestines — are infamous for their foul smell, which is reminiscent of the waste material that once filled the intestine. Chitlins are popular in the United States during winter holidays, and despite the odor, many people enjoy this delicacy. Hayata’s group knew that fresh cilantro can help to mask an unpleasant smell of chitlins. They have previously proved that cilantro could help to remove the fecal or sewage-like odor from the dish. In their most recent study, they set out to discover the identity of the deodorizing chemical compounds in cilantro. The researchers treated the samples of hog large intestines with cilantro extracts of different concentrations. A group of human sniffers identified the concentrations that were most effective in reducing the odor. Using high-tech instruments, the scientists then isolated the main deodorizing ingredients in the most effective extracts. The scientists found that (E,E)-2,4-Undecadienal had a flowery fragrance that seemed to completely erase the odor. That substance worked at concentrations as low as 10 parts per billion — an equivalent to about 10 drops of substance in an Olympic-size swimming pool19. Such results were obtained on already slaughtered animals, however they suggest that cilantro indeed improves the smell of pork. The research indicates that introducing cilantro to pigs’ diet may have beneficial properties in terms of the meat’s odor. No further data on the use of cilantro as an additive to hogs’ feed was found.
3.4 The addition of plant’s extracts to pigs’ feed
In 2020, a group of researchers from Mexico conducted an extensive study concerning the addition of plant extracts to pigs’ diet. In the experiment, the products containing the extracts from following plants were used: artichoke (Cynara sculymus), celery (Apium graveolens), beet (Beta vulgaris), onion (Allium cepa), garlic (Allium sativum), spinach (Spinacea olerace), avocado (Persea americana), oats (Avena sativa), and parsley (Petroselinum crispun). Pigs received one of the three diets:
- control diet: designed to satisfy the nutrients for high lean potential, high productivity and used as a commercial ration in Mexico
- 1% PE, which was the control diet +0.1% (as fed) of plant extracts, PROTORGAN®
- 15% PE, which was the control diet +0.15% (as fed) of plant extracts, PROTORGAN®
Diets were formulated to be isonitrogenous and isocaloric20.
Table 1. Composition of experimental diets for pigs in growing-finishing stages.21
Sensory assessment was performed by a trained panel of 10 members. One day before performing the sensory analysis, the meat cuts were removed from the freezer and cooked. The panel assessed the cooked samples in terms of odor intensity, taste intensity, fatty sensation, tenderness, juiciness, and amount of connective tissue. The meat cuts from animals supplemented with 0.15% PE had a better taste than those from control animals, and those supplemented with 0.1% of PE (p > 0.05). No differences were detected in the odor of meat supplemented with PE. The rest of the observations are presented in Table 2.
Table 2. Sensory quality of meat from pigs supplemented with plant extracts (PE) during the growing-finishing stage22
4. Conclusions and discussion
The studies discussed in this article indicate that only some of the herbal additives may have an influence on the odor of pork. According to the research, rosemary and thyme possess antioxidative properties, which help to prevent the lipids oxidation. Lipids oxidation is a process which is often responsible for the foul smell of pig’s meat. Therefore, preventing lipids oxidation is crucial in controlling the smell of pigs’ meat. Among the studied plants, Chinese cilantro shows promising results, as its components have flowery smell and help to reduce the offensive odor of pork. However, no studies discussing the effect of introducing cilantro to animals’ diets were found. The most recent study, conducted by a group of researchers from Mexico, concluded that the addition of plant extracts from artichoke , celery, beet, onion, garlic, spinach, avocado, oats, and parsley have no effect on the meat’s odor. All of the discussed studies were conducted on slaughtered animals. However, it is commonly known that the diet has an influence on the body odor and sweat composition. Changing the diet to a healthier, more balanced one may have beneficial effects on the smell of living pigs. Nevertheless, no studies concerning the smell of meat in living pigs have been found.
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20 José Luis Dávila-Ramírez et al. (2020) ‘Addition of a Mixture of Plant Extracts to Diets for
Growing-Finishing Pigs on Growth Performance, Blood Metabolites, Carcass Traits, Organ Weight as a Percentage of Live Weight, Quality and Sensorial Analysis of Meat’, published by Animals