International Journal of Research and Development in Pharmacy & Life Sciences
Open Access

Ruminant’s (cattle, buffalo, sheep, and goats) are considered as the largest contributor in the emission of greenhouse gases which results in global warming. Six gases have been identified as constituting the greenhouse gases; mainly carbon dioxide (CO2) and methane (CH4) with trace amounts of other gases are responsible for this climate change. Because animals consume plants that uses CO2, so it has not been considered as a net contributor to this climate change but the role of CH4 and N2O have contribute a lot to this climate change and has 21-times more global warming potential then CO2 (Haque [1]). Methane emission is not only related to this climate change but also associated with the energy loss, reductions in their retention and use of energy. Microbial activity in the rumen plays (Table 1) a vital role in the conversion of gross energy (GE) in feed into CH4. There is a need of sustainable and immediate mitigation strategies from ruminants through dietary manipulation, which is simplistic and pragmatic approach to alter the pathway of fermentation for the reduction of CH4 emission up to 40% depending upon the degree of change and nature of intervention (Haque, 2018 [1]). Several studies have been done for the discovery of alternative natural feed additives and propolis is one of them which has been considered as an alternative feed additive to antibiotics to improve the feed efficiency and body weight gain (Soltan et al. 2016 [2]; Morsy et al. 2015[3]). Propolis is generally known as the “bee glue” collected by honeybees from exudates and buds of various plants species, mixed with wax and pollen, and modified by the enzymatic activity of honeybees (Soltan and Patra, 2020[4]). It is used by honeybees as a defense material for the protection of hive, to fill the cavities of the beehive, for maintenance of internal temperature (350C) during cold days and protection from invasion by predators. For decades it has been the main interest of researchers to investigate its chemical composition and biological properties. Propolis chemical composition depends upon plants species and phyto-geographic conditions which generates problem for the exact standardization and quality control, but many studies have been made to overcome this and give results. It is noteworthy here that every source of propolis has its own significant biological activity.

Table1: Rumen Microbiota.

Biologically it has many antioxidant, antibacterial, antifungal, antiviral, anti-inflammatory, antiparasitic, anti-methanogenic, immune-modulatory, and anticancer properties. Due to higher antimicrobial activity of propolis against gram positive than gram negative bacteria it has been observed that it plays a key role in the modification of ruminal fermentation to reduce the loss of energy as methane (Soltan & Patra, 2020[4]). The objective of this review is to demonstrate the efficiency of propolis for the mitigation of methane emission from ruminants as a natural feed additive.

Method

Search for previous studies on the subject was made by using peer-reviewed journal articles published in English. Databases of Scopus, Science Direct, Google scholar, Academia, Research- Gate and Wiley online were used for the literature search between 2014 and 2021. The initial keywords search was Propolis Phytochemicals, ruminal microorganism, mitigation strategies. For more focused search, we looked at titles and abstracts containing predefined keywords or terms such as phytochemicals, (Table 2)

Table 2: Effects of Phytochemicals on Microbial Ecosystem.

Table 3: Effect of different Plant extracts on Rumen Fermentation process.

Consequently, we sorted articles on phyto-constituents in in vitro and in vivo (ruminants) assays separately. We mapped out the content of the selected literatures by extracting information based on the following questions (i) what was the composition of phytochemicals? (ii) Did the propolis affect ruminal microbiota? (iii) Did it affect ruminal fermentation? We, therefore, ensured that the methodologies used in considered articles met the selected systematic methods for reducing bias, improving the reliability of the review findings, and drawing reasonable conclusions.

Phyto-chemistry of Propolis

The chemical composition of propolis depends upon plant species; phytogeography, climatic factors, collection season and every source have its own significant applications. So, the researchers have a keen interest in the investigation of detailed chemical composition from every source of propolis. To date 300 compounds have been identified in propolis and Alkaloid, Flavonoid, Phenolics, (Figure 1) Terpenoid, Tannin, Glycoside and Anthraquinone, have been identified as the basic groups among these compounds (Soltan et al. 2016[2]).

Figure 1: Schematic representation of classification of phenolic compounds.

Phytogeography

To understand the chemical composition of propolis of one region in connection with the other, researchers give a detailed description of propolis production. Generally, honeybees collect lipophilic plant substance from buds, leaves, lattices, mucilage, branches, and barks, usually within a radius of 1-2 km from the hive. Mainly in the temperate zone, honeybees collect lipophilic materials from May to November, but most frequently in the late summer (Ristivojevića et al. 2015 [5]). When propolis extracts were obtained by supercritical extraction (SCO2) and ethanolic extraction (EtOH), in eight samples of different types of propolis (red, green, and brown) from different regions in Brazil, the concentration of Artepillin C and pcoumaric acid was very high in the extracts from SCO2 (Machado et al. 2016 [6]). African propolis (Congo and Cameroon) showed twenty-one secondary metabolites belonging to four different chemical groups, three triterpenes and two diprenyl-flavonoids were identified from Congo propolis, while thirteen triterpenes, three diprenyl-flavonoids, two monoterpenic alcohols and one fatty acid ester have been identified from Cameroon propolis samples. (Papachroni et al. 2015 [7]). High-field nuclear magnetic resonance spectral profiling of propolis samples from Kangaroo Island, South Australia of sedge plant Lepidosperma sp. Montebello (Cyperaceae) showed have high proportion of prenylated hydroxystilbene and C- and O-prenylated tetrahydroxystilbenes (pTHOS) while prenylated p-coumarate concentrations were in very small amount. The isolation of five pTHOS which was not previously reported showed: (E)-4-(3- methyl-2-buten-1-yl)-3,40,5trihydroxy-30 -methoxystilbene, (E)-2,4- bis(3-methyl-2- buten-1-yl)-3,30,40,5tetrahydroxystilbene, (E)-2- (3-methyl-2-buten-1-yl)-3-(3- methyl-2-butenyloxy)- 30,40,5trihydroxystilbene, (E)-2,6-bis(3-methyl-2-buten-1-yl)-3,30,5,50 - tetrahydroxystilbene and (E)2,6- bis(3-methyl-2-buten-1-yl)-3,40,5-trihydroxy- 30 –methoxystilbene. A chemical study of propolis from the Baha region of Saudi Arabia identified 61 chemical compounds with distinct chemical structures from the following classes: 19 phenol/alcohol/ aldehydes, 10 aromatic acids, 8 esters, 6 aliphatic acids, 4 flavonoids, 4 ketones, 4 fatty acid esters, 3 terpenes 2 sugars, and 1 steroid. Turkish propolis has high total phenolic (314.36 ± 3.65 mg GAE/g propolis) and total flavonoid contents (522.71 ± 11.45 mg QE/g propolis) (Ozdal et al. 2018 [8]). The chemical composition of propolis samples collected from different geographical regions showed that flavonoid and phenolic (Figure 2) compounds are frequent in all propolis samples and determine its characteristic properties.

Figure 2: Nomenclature of Simple Phenols.

Seasonal effect

A limited number of studies have been conducted to evaluate the seasonal effect of propolis, however when polish propolis collected throughout three seasons of the year. The number of flavonoids and phenolic acids were highest, when harvested during the spring (125.14 mg/g) and the lowest amount in the fall (110.09 mg/g) (Wozniak et al. 2019 [9]). Artepillin C was found high in the propolis samples of southern Brazil collected during summer and autumn (Tomazzoli et al. 2020 [10]). The bioactivity of Caborca propolis (CP) collected from an arid zone of the Sonoran Desert showed that spring and autumn collection have higher amounts of bioactive compounds in comparison to the rainy seasons of summer and winter (Mendez- Pfeiffer et al. 2020 [11]). According to a comparative study conducted between March and June of 2013 and March of 2015 for the chemical composition of Africanized bees’ propolis and the author concluded that similarity of chemical profiles of collected samples were same. The main difference was in the content of phenolic acids, propolis extract produced in 2015 showed a higher content of phenolic acids caffeic, ferulic and p-coumaric and ferulic acid and this change in phenolic acid concentration was due to the difference in temperature because temperature can influence the production of secondary metabolites in plants. These environmental variabilities affect the resins, flower buds and resinous exudates which are sources of material to produce propolis and a variation in the chemical composition of these materials means changes in the composition of propolis (Calegari et al. 2017[11]). Additionally, previous reports have shown that seasonality does not significant change the chemical composition of propolis, but it can influence the quantitative chemical profile of propolis (Valencia et al. 2012 [12])

Plant Origin

In the recent year researchers focused on the chemical composition of plant origin. Phenolic profile of propolis exudates from plant Zuccagnia punctata showed eleven compounds. Among them, two uncommon dihydrochalcones, i.e., 40 -hydroxy-20 -methoxydihydrochalcone and 20 ,40 -dihydroxydihy drochalcone, were described for the first time as major constituents of Z. punctata,(Solorzano et al. 2017 [13]). A phytochemical screening of the propolis of plant Dalbergia ecastophyllum showed that it has variety of phenolic compounds including flavonoids (catechins, chalcones, aurones, flavones and flavanols), phlobaphene tannins, xanthones and pentacyclic triterpenoids (de Mendonça et al. 2015 [14]). Profiling of Trigona Apicalis propolis extract has higher concentration of flavonoid compounds as compared to phenolic (Rosli et al. 2016 [15]).

Propolis on Ruminal Microbial Fermentation and Digestion

Rumen microbiota

Rumen has a diversity of microbial ecosystem including bacteria, ciliate protozoa, anaerobic fungi, and archaea, which are involved in the degradation of feedstuffs and the production of volatile fatty acids (VFAs), lactate, amino acids, lipids, and hydrogen, which are crucial to the maintenance, growth, and production performance of ruminants (Kruger Ben Shabat et al. 2016 [16]). The host also uses microbial (Table 4) biomass and some unfermented feed components once these exit the rumen to the remainder of the digestive tract (Henderson et al. 2015 [17]).

Table 4: Effect of Propolis on Rumen Microbial Population, Rumen Fermentation, and methane Emission.

Effects of phytochemicals on ruminal microbiota

Changes in dietary supplementation strongly affects the composition, efficiency, and the fermentation of the diet-dependent ruminal microbiota (Yoshimura et al. 2018 [18]). Different bioactive compounds have different antimicrobial effect, propolis causes modulation of the ruminal fermentation (Soltan & Patra, 2020 [4]). Propolis has bacteriostatic activity against Gram-positive and some Gram-negative bacteria (S. Ehtesham et al. 2018 [19]). Cell wall of gram-negative bacteria are less rigid as compared to gram positive bacteria, so they have higher resistance to propolis due to higher complexity of these structures, with liposaccharides and high lipid content. The flavonoid (Figure 3) compounds in the propolis extract act against microorganisms through inhibition of cell membrane function, bacterial activity, or synthesis of nucleic acid, which explains the higher degradability and cumulative gas production of diets when added with propolis extract in relation to the negative control, which had complete bactericidal action and suggests that presence of flavonoids in the extract is probably capable of affecting fermentation in rumen fluid, acting through bacteria selection. It was recommended that 100% propolis extract supplementation may improve the degradation and fermentation of ruminant diet (Gomes et al. 2017 [20]). Presence of phenolic compounds in the propolis increases the microbial protein synthesis and total VFA concentration in the rumen so it has been studied that improvement in the ruminal fermentation depends upon the phenolic compounds present in propolis extract especially when high forage and low N diets are fed (de Paula et al. 2016 [21]). Three Brazilian propolis extracts (containing naringenin, caffeic acid, p-coumaric acid chrysin and artepillin C) was studied against different ruminal bacteria in vitro. It was observed that propolis extracts inhibited the growth of Ruminococcus flavefaciens, Ruminococcus albus 7, Fibro-bacter succinogenes, Butyrivibrio fibrisolvens, Prevotella albensis and Streptococcus bovis, but R. albus 20, Prevotella bryantii and Ruminobacter amylophilus were resistant to all the extracts. Propolis was effective against the hyper ammonia producing bacteria Clostridium aminophilum and Peptostreptococcus sp. (Soltan & Patra, 2020 [4]). It was assumed that phenolic compounds in the Brazilian propolis have a great antimicrobial activity (Machado et al. 2016 [6]).

Figure 3: Flavonoid nomenclature.

Effect of Propolis on Rumen Fermentation and methane Emission

Rumen Fermentation

Anaerobic fermentation in the rumen depends upon the supply of substrate (i.e., quantity and frequency), preservation of a favorable condition for microbial growth (e.g., temperature, pH, substrate mixing), and constant removal of undesirable substances (e.g., bacterial toxins, hydrogen), so that the profile and amount of volatile fatty acids (VFA) produced and microbial protein leaving the rumen meets the ruminant's daily requirements for energy and protein without having deleterious impacts in the rumen health and functionality (Tedeschi et al. 2021 [22]). For decades different types of antibiotics are used to meet this criterion of rumen fermentation, but now the consumers denied the use of antibiotics due to some deleterious effects on ruminant health and researchers trying to implement the use of ecologically relevant ionophores because these ionophores modulates the rumen fermentation process and provides health benefits for ruminants. It has been described in the Table-3 how different plant extracts effects on rumen fermentation.

Methane mitigation

Methane emission can be done by changing rumen fermentation pattern by desirable dietary products. Increased dietary level of concentrate reduces CH4 production (Haque, 2018 [1]). However,a comprehensive exploration for a sustainable methane mitigation approach is still lacking. In the recent years it was reported that ciliates are the main source of hydrogen supply to the endosymbiotic and episymbiotic methanogens and inhibition of protozoa reduces the methane emission from ruminants (Soltan et al. 2016 [2]). Based on phyto-chemistry results, the propolis could be used as a natural alternatives product to obtain the desired rumen fermentation. Red propolis extract (RPE) supplementation in late pregnant ewes enhanced the apparent digestibility and microbial protein syntheses, and decreased CH4 emission (Morsy et al. 2021 [23]). When the propolis was examined at different doses studies showed that it did not improve the production rate and the profile of ruminal short-chain fatty acid (SCFA), while it is able to inhibit ruminal NH3-N concentration (Ozturk et al. 2010 [24]).

Conclusion

Propolis stimulates the rumen microorganism for the consumption of hydrogen by changing in total VFA and it was suggested that there is a need to study the effect of propolis for the mitigation of methane based on phytogeography, botanical origin, climatic condition, and collection methods for the further effective applications of propolis in the mitigation of methane in vitro/in vivo (Morsy [23-57]). A little work has been done on the effects of propolis from 2015 to 2021 for the mitigation of methane and rumen fermentation process as indicated in the Table-4. Further studies on the basis phytochemical constituent’s reaction to rumen microbiota can be performed to understand the effects of these propolis flavonoid and phenolic reaction with on the cell of bacteria and by using different phytochemical additives we can explore the chemical effects of these ionophores on bacterial cell wall for the investigation of methane emission process from ruminants.

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