What Is the Use of Residue Stevia Leaf in Hindi?

Stevia, also known as stevia, sweet grass, and sweet tea, is native to northeastern Paraguay. It is a perennial shrub in the Asteraceae family, and its leaves can be used to extract a type of natural high-potency low-energy sweetener called steviol glycosides. Its sweetness is 180 to 450 times that of sucrose, making it the world's third-largest source of sweetness [1]. Stevia was introduced to China from Japan in 1977, and China has now become the world's largest commercial grower of stevia and producer of steviol glycosides [2].

The large-scale cultivation of stevia and the extraction of steviol glycosides produce a large amount of stevia waste residue. Stevia waste residue belongs to the category of agricultural and sideline processing waste, and only a small amount is used as agricultural fertilizer [2]. The rest is mostly disposed of by burning or landfill, which is not only a huge waste of resources, but also causes environmental pollution.

Stevia leaves waste residue contains high levels of crude fiber and crude protein, and is also rich in amino acids, vitamins, minerals, oligosaccharides, terpenes, polyphenols and flavonoids. It is a valuable feed ingredient that is widely available, inexpensive and has a long shelf life. Stevia waste residue can be added directly or after fermentation and extraction to livestock and poultry feed, which not only reduces environmental pollution, but also alleviates the shortage of feed raw materials in the stevia producing areas, reduces feed costs and improves economic benefits. This paper mainly reviews the comprehensive application of stevia waste residue in livestock and poultry feed, and discusses the possible effective components, potential functions and mechanisms of stevia waste residue, with a view to providing a reference for the further development and utilization of stevia waste residue in livestock and poultry feed.

1. Nutritional value and biological activity of stevia

Stevia leaves are high in protein, with essential amino acids accounting for up to 7.7% of the total. They are also rich in fibre, with a content of up to 15%–18% [1]. The sweetening components in stevia leaves account for 4%–20% of the dry weight of the leaves, with the main sweetening component being stevioside. Stevioside is resistant to high temperatures and low heat, and is safe and stable. It is widely used as a sweetener in food, medicine, and daily chemicals, and as a sweetener in livestock and poultry feed. In addition to being rich in steviol glycosides, stevia also contains many bioactive substances. María et al. [3] extracted and identified 89 compounds from stevia leaves. These phytochemicals have biological activities such as antioxidant, antitumor, anti-inflammatory, antibacterial, and hypoglycemic effects [4].

It has long been recorded that stevia concentrate and stevia powder can be used as medicine to treat livestock and poultry with reduced appetite, fever, mastitis, respiratory diseases and gastroenteritis [5]. Stevia waste residue is a by-product of stevia after stevioside extraction, and it is rich in nutrients and bioactive substances. Stevia waste residue and fermented waste residue are used as feed ingredients in formulated feeds for livestock and poultry, and do not affect the growth performance of livestock and poultry, while also reducing the feed conversion ratio [6-7]. Stevia waste residue contains bioactive substances such as steviosides, chlorogenic acids, and flavonoids. Stevia waste residue active substance extracts have the effect of regulating the body's immune system and have good antioxidant activity [8-9]. When applied to livestock and poultry, they can be expected to have a good effect of promoting the growth of young animals.

2. Active ingredients and mechanism of action of stevia waste residue

2.1 Steviol glycosides

Stevia waste residue is a by-product of stevioside extraction, and contains a lot of stevioside components that have not been extracted. Steviol glycosides are one of the possible active ingredients in stevia waste residue. They are a type of terpene compound. Stevia is rich in steviol glycosides, represented by stevioside and rebaudioside A, which are all kaurene-type tetracyclic diterpenoid glycosides. Steviol glycosides are highly sweet, stable, heat-resistant, and have good safety properties, with no teratogenic toxicity [10]. Stevioside, in particular, has the properties of lowering blood sugar, blood pressure, anti-oxidation, anti-inflammation, anti-tumor, and immune regulation [8]. Steviol glycosides are added to livestock and poultry feed as a sweetener to improve palatability. Adding 213 mg/kg stevioside to the diet of weaned piglets not only increases feed intake and weight gain, but also reduces diarrhea in piglets [11].

However, Geuns et al. [12], Atteh et al. [13] and Wu et al. [14] did not find any growth-promoting or egg-production-improving effects when adding stevioside to broiler and layer feeds. This may be due to the fact that chickens lack the T1R2 receptor gene that recognizes sweetness [15]. Therefore, adding high doses of stevioside as a sweetener to chicken feed does not increase the feed intake of chickens, and therefore has no effect on their production performance. The steviol glycosides that are more widely used in animal production are high-purity steviol glycosides or rebaudioside A[16], while other types of steviol glycoside components, such as stevioside, rebaudioside B, rebaudioside C, rebaudioside D, rebaudioside E, rebaudioside F, steviol, isosteviol, etc., have been studied less due to their low content [1]. Further research is needed to isolate and identify other steviol glycosides and to study their physiological functions.

2.2 Green source acids

Food nutrition and human health The Beijing High-Quality Innovation Center has carried out a series of studies on the analysis of the active ingredients and physiological functions of stevia waste residue extracts. Stevia waste residue was extracted with acetone and ethyl acetate, purified by adsorption on macroporous resin, eluted, concentrated and freeze-dried to obtain stevia waste residue extract. It was found that the extract has good anti-inflammatory [17], antioxidant [9], regulation of glycolipid metabolism [18], and uric acid-lowering [19] activities. The main active ingredient was identified as chlorogenic acid [20]. The chlorogenic acid substances are a class of phenolic compounds produced by plants during aerobic respiration via the cinnamic acid pathway. The chlorogenic acid substances in stevia waste residue extracts mainly include chlorogenic acid (3-CQA), cryptochlorogenic acid (4-CQA), neochlorogenic acid (5-CQA), chlorogenic acid A (3,5-diCQA), isochlorogenic acid B (3,4-diCQA), isochlorogenic acid C (4,5-diCQA), and artichoke (1,3-diCQA). Among these, isochlorogenic acid C is the most abundant, followed by chlorogenic acid [20].

At present, most of the chlorogenic acid products on the market come from honeysuckle, coffee, eucommia, honeysuckle, sunflower, etc., and there is less attention on the chlorogenic acid derived from stevia. In chlorogenic acid components derived from other plants (Eucommia ulmoides, honeysuckle, sunflower, coffee), neochlorogenic acid is the main component, while in chlorogenic acid derived from stevia, the proportion of isochlorogenic acids (isochlorogenic acid A, isochlorogenic acid B, isochlorogenic acid C, and silybin) is significantly higher than in other sources [21]. Isochlorogenic acid is a dicaffeoylquinic acid compound. One molecule of isochlorogenic acid has two caffeoyl groups, so it has stronger antioxidant activity.

Studies have found that the total isochlorogenic acid in stevia has strong in vitro antioxidant, antibacterial activity and mildew prevention effects, and has great potential as an antioxidant and mildew inhibitor in animal feed [22]; the main active ingredient in stevia waste residue extract, isochlorogenic acid C, has a very good anti-inflammatory effect, which can significantly reduce the production of nitric oxide (NO) in a lipopolysaccharide (LPS)-induced mouse monocyte-macrophage inflammation model, and can significantly reduce the content of mouse serum NO and prostaglandin (E2) in a carrageenan-induced mouse foot swelling model [17]. At present, most research on isochlorogenic acid focuses on its medicinal value [23], and there has been relatively little research on its application in livestock and poultry feed and farming.

However, there have been many reports on the application of chlorogenic acid in livestock and poultry farming. Chlorogenic acid is a condensed phenolic acid composed of caffeic acid and quinic acid esterification. Its chemical name is 3-O-caffeoylquinic acid, and it has good antibacterial, anti-inflammatory, antioxidant, liver protection, regulation of blood sugar and lipid metabolism, immune regulation, anti-cancer and other activities [24].

The addition of chlorogenic acid to feed can delay the oxidation of oils, fats, vitamins, etc., in the feed, effectively prevent the corruption and deterioration of the feed due to microbial contamination, and improve the palatability and stability of the feed. The application of chlorogenic acid to weaned piglets can increase feed intake, reduce the weight gain per unit of feed consumed and the diarrhea rate, increase the height of intestinal villi and the villus-to-crypt ratio, reduce intestinal permeability [25], improve the intestinal flora, increase the gene expression related to digestion and absorption, increase the apparent protein digestibility, and improve the body's antioxidant capacity [26].

Chen et al. [27-28] found that adding chlorogenic acid to the diet of weaned piglets can reduce serum concentrations of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and interleukin-1β (IL-1β), increase serum immunoglobulin G (IgG) and secretory immunoglobulin A (SIgA) concentrations in the serum; reduces the number of intestinal cells in G0 and G1 phases, increases the number of intestinal cells in S phase, and reduces the percentage of late and total apoptotic cells in intestinal cells as well as the ratio of B-cell lymphoma- 2-related X protein (Bax) and B-cell lymphoma-2 (Bcl-2) ratio, upregulate Bcl-2 expression in intestinal cells, and downregulate the expression of caspase-3, caspase-9, and Fas. In fattening pigs, the addition of 1,000 mg/kg chlorogenic acid can improve the antioxidant activity of the muscle, reduce drip loss, cooking loss, and malondialdehyde (MDA) content of the muscle, and significantly improve muscle quality [29].

The bioactivity of chlorogenic acid is mainly dependent on its absorption and metabolism in the intestine. Studies have found that about 33% of chlorogenic acid is absorbed intact in the stomach and/or upper gastrointestinal tract, enters the bloodstream without hydrolysis, and about 7% is absorbed in the small intestine and hydrolyzed to caffeic acid and quinic acid [24]. Microbiota mediate the absorption of chlorogenic acid and metabolites in the colon, and intact chlorogenic acid and its metabolites (mainly 3-hydroxyphenylpropionic acid and benzoic acid) are absorbed and/or metabolized in the liver after entering the bloodstream. The colon is the main site of chlorogenic acid metabolism, and the degree of bioavailability of chlorogenic acid largely depends on the intestinal flora [30]. Chlorogenic acid and the intestinal flora interact to increase the diversity of the intestinal flora, promote the growth of beneficial bacteria, and reduce the abundance of harmful bacteria [31].

The main type of active substance in stevia waste residue is chlorogenic acid, which mainly includes isochlorogenic acid and chlorogenic acid, with isochlorogenic acid accounting for a greater proportion [21]. Existing studies on the antioxidant activity and health benefits of stevia waste residue extracts are based on in vitro cell and mouse models. Studies on large animals are lacking, and the application of stevia waste residue extracts in livestock and poultry feed requires further research and verification.

2.3 Flavonoids

The antioxidant active substances in the stevia waste residue after extraction were analyzed. In addition to chlorogenic acids, another major category is flavonoids, accounting for about 4.6%. The main flavonoids are quercetin and quercitrin [20]. Luo X. Y. et al. [32] used a method combining chitosan flocculation and polyamide adsorption to purify the flavonoids in the ethanol extract of stevia waste residue, which can achieve a final flavonoid purity of 53.42%. Tavarini et al. [33]  identified the flavonoids rutin, myricetin, apigenin-7-O-glucoside, quercitrin, kaempferol and luteolin-7-O-glucoside in stevia.

Tong Hongmei et al. [34] used HPLC with a mobile phase gradient of citric acid-methanol to determine the flavonoid components in the stems and leaves of stevia. It was found that the main flavonoids in the stems and leaves of stevia were rutin, quercetin, hesperidin, kaempferol, etc., and that the flavonoid content was significantly correlated with antioxidant activity. Flavonoids have good anti-inflammatory, antioxidant, anti-tumor, anti-aging and other effects [35]. There have been relatively few studies on the flavonoids in stevia, and most of the existing studies have focused on the extraction, isolation, identification, and in vitro antioxidant activity evaluation of flavonoids.

3 Application of stevia waste residue in livestock and poultry farming

3.1 Stevia waste residue

Stevia waste residue contains about 30% fibre [6]. Due to its high crude fibre content, stevia waste residue has good performance in rumen anaerobic fermentation and can be used as a base material to develop better ruminant feed. Zhang Hui et al. [36] used an in vitro method to evaluate the nutritional value of stevia waste residue for goats and found that stevia waste residue has a good nutrient digestibility in goats.

The degradation rate of dry matter after fermentation in goat intestinal fluid for 18 h was 19.21%, the degradation rate of neutral detergent fiber was 32.28%, and the degradation rate of crude protein was 21.70%. For coarse-fed livestock, high-fiber stevia waste residue can also be a good source of feed ingredients. For example, the apparent digestibility of crude fiber in stevia waste residue by meat geese can reach 56.99%, and the addition of stevia waste residue at a level of 5% to 10% can significantly reduce the feed conversion ratio of meat geese [6].

Sun Yanbin et al. [7] used stevia waste residue to replace peanut straw powder in equal amounts to feed meat rabbits. They found that adding 25% stevia waste residue to the rabbit feed did not affect the growth rate, slaughter rate or feed utilization rate, but it did improve the immune function, making it a good source of feed ingredients. Stevia waste residue is also a good feed ingredient for pregnant sows. Adding 30% stevia waste residue to the feed ration of pregnant sows on a restricted diet can increase the crude fiber content of the feed to 9.15% without increasing the caloric value of the feed, significantly improving the sow's constipation during pregnancy caused by restricted feeding and reduced feed costs by 13.33%; in addition, adding stevia waste residue can significantly increase the abundance of beneficial intestinal bacteria and reduce the abundance of harmful bacteria, which can improve the balance and balance of the intestinal flora of pregnant sows [37].

3.2 Stevia waste residue fermentate

The direct and large-scale addition of stevia waste residue to livestock feed is often not ideal. For non-herbivorous animals, too high a fibre content is not conducive to digestion and absorption, which limits the application of stevia waste residue in non-herbivorous animal feed. Microbial fermentation can effectively decompose fiber and reduce its anti-nutritional substance content. Fermentation of stevia waste residue with Aspergillus niger, Lentinula edodes and Saccharomyces cerevisiae in a ratio of 8%, 4% and 3% can effectively reduce the crude fiber content and increase the protein, amino acids and soluble reducing sugar content [38].

The addition of stevia waste residue fermentation material at a rate of about 40% can significantly increase the slaughter rate, lean meat rate and reduce the back fat thickness of the local pig [39], and can also reduce the content of monounsaturated fatty acids in the muscle [40]. However, some studies have also pointed out that stevia waste residue fermentation products have no significant difference in the muscle protein and muscle fatty acid composition of the Muscovy duck [41].

Recently, Liu Zhenyi et al. [42] found that although the addition of stevia waste residue fermented by lactic acid bacteria and yeast had no significant effect on the growth performance, slaughter performance, and immune performance of Muscovy ducks, 10% stevia waste residue fermented product could significantly reduce the total nitrogen level in Muscovy duck feces and reduce sewage discharge. Stevia waste residue can be used as a good source of feed raw materials after fermentation. However, due to differences in raw material species, raw material sources, fermentation strains and fermentation methods, the composition of stevia fermentation products varies greatly, and the amount added to the feed also varies greatly depending on the animal species, so the final application results on livestock and poultry may not be consistent.

3.3 Stevia waste residue extract

In addition to being rich in crude protein and crude fiber, stevia waste residue also contains many bioactive substances. After stevia waste residue is extracted and purified with water and organic solvents, a mixture of active substances can be obtained, which is rich in antioxidant active substances such as chlorogenic acids and flavonoids. Stevia waste residue extract can be used as a good antioxidant and anti-mildew agent in livestock and poultry feed [22]. At present, research on stevia waste residue extract mainly focuses on its health-promoting functions, and its functional activity research also focuses on in vitro cells and mouse models. Its application in animal feed still needs to be further verified and developed.

4 Summary and outlook

Stevia is widely cultivated in China, and China is also a major stevia glycoside producer, so a large amount of stevia waste residue is generated every year. The comprehensive application of stevia waste residue in livestock and poultry feed has the advantages of a wide range of raw material sources and low prices. It can alleviate the shortage of feed raw materials, reduce feed prices, improve economic efficiency, and reduce environmental pollution. The effective components of stevia waste residue (such as stevioside, chlorogenic acid, and flavonoids) have good biological activities such as immunomodulation, anti-oxidation, and improving intestinal flora.

Therefore, stevia waste residue has great potential for use in livestock and poultry feed. However, there are still many problems with the use of stevia waste residue in livestock and poultry feed: ① Due to differences in stevia varieties, places of origin, harvest seasons, and stevioside extraction processes, the content of bioactive substances in stevia waste residue varies greatly; ② due to differences in fermentation bacteria, raw material compatibility, fermentation methods, etc., the composition of stevia waste residue fermentation product composition varies greatly; ③ stevia waste residue extract due to the source of raw materials, extraction methods, etc., the composition and content of the effective ingredients vary greatly; ④ at present, stevia waste residue is used in livestock and poultry farming in a variety of ways, as a feed ingredient added directly, or added after fermentation, but the addition rate of stevia waste residue in the feed is still still in the exploratory stage. ⑤Stevia waste residue is rich in steviosides, chlorogenic acids, and flavonoids, but also contains other functional substances such as amino acids, vitamins, minerals, trace elements, and oligosaccharides. It is mostly added to livestock and poultry feed as a mixture, which can easily lead to unclear effective ingredients and mechanisms of action.

In summary, stevia waste residue and fermentation products have been widely explored as feed ingredients for livestock and poultry farming. Compared to stevia waste residue extract, stevia waste residue and fermentation products are simpler and more convenient in terms of production cost and process, and are therefore more easily promoted in livestock and poultry farming.

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