Dr. Gul Mohammad Rahat Ullah, Dr. Partha Das & Dr. Venkat Shelke,Kemin Industries South Asia Pvt. Ltd
INTRODUCTION
Phytic acid (phytate) is a mixture of calcium–magnesium salts of myo-inositol hexaphosphate and is considered an anti-nutritional factor in poultry because it binds with phosphorus and other important nutrients and thereby decreases their bioavailability. About 2/3rd of the total phosphorus present in plant feed ingredients is in phytate form. Typically, poultry diets contain from 2.5 to 4.0 g/kg of phytate phosphorus, depending on the inclusion level and type of plant-based ingredients used. Poultry has limited capability to utilize Phytate phosphorus & it ranges from 0-50%. Dietary Phytate is an anti-nutritive factor that hinders energy utilization & Protein digestibility & may negatively impact the quality of chicken meat production. However, the ill effects of dietary Phytate are counteracted by exogenous Phytase enzyme. Phytase (EC 3.1.3.8, myoinositol hexaphosphate phosphohydrolase) is an enzyme that catalyses the stepwise removal of inorganic orthophosphate from phytic acid.
Supplementation of phytase improves the performance of phosphate, calcium, magnesium, and zinc, thereby enhancing animal performance. The enhancement in growth performance observed in broiler chickens supplemented with phytase has been attributed to multiple physiological mechanisms. Phytase supplementation increases feed intake and feed efficiency primarily through the liberation and improved utilization of phosphorus (P) from the phytate–mineral complex, thereby enhancing mineral availability. In addition, the hydrolysis of phytic acid releases myo-inositol, which serves as an essential metabolic intermediate that contributes to improved energy metabolism and intestinal health. Phytase may also enhance starch digestibility by reducing the formation of phytate–starch complexes in the gut and improving the utilization of protein and amino acids by minimizing phytate–protein binding and increasing the activity of digestive enzymes. Collectively, these effects lead to an overall improvement in nutrient availability and utilization, resulting in superior growth performance and feed efficiency in broiler chickens. However, the impact of phytase is not limited to reductions in P excreted by broilers, as phytase may also enhance growth performance and nutrient retention. Next to energy and protein, P is considered the next most expensive nutrient in the diet of nonruminant animals, including poultry.
Phytate
Phytate is the salt form of Phytic acid, which is composed of an inositol ring with six phosphate groups. It can bind to mineral cations like copper, calcium, zinc, and iron.
Phytic acid makes phytate phosphorus poorly available to animals because it binds to amino acids and proteins. It also inhibits digestive enzymes, which lowers nutrient digestibility and animal performance. Therefore, phytic acid is considered an antinutritive factor in plant-based feeds, emphasizing the need for its enzymatic hydrolysis.
The most abundant organic phosphate in the world is Inositol hexakisphosphate (InsP6), also known as phytic acid. In nature, phytic acid(C6H18O24P6), Fig. 1, can exist as free acid, phytate, or phytin, depending on the physiological pH and metal salts.
Phytase, known as Myo-inositol hexakisphosphate phosphohydrolase, is an enzyme capable of decomposing nutrient-binding phytate into inositol penta-, tetra, tri, di-, and monophosphate (IP6 through IP1). This enzymatic process releases one phosphate molecule at a time in a sequential manner. Because IP6-3 has the anti-nutritional effect of reducing nutrient absorption in monogastric animals, it is important to reduce the presence of IP6-3 by using phytase.
Figure 1. Structure of phytic acid - myo-inositol, 1,2,3,4,5,6-hexakisphosphate IP6,( IUPAC-IUB-1989).
Phytase
Phytases are myoinositol hexakisphosphate phosphohydrolases that catalyze the hydrolysis of phytic acid to inorganic phosphate and myoinositol phosphate derivatives. They catalyze the cleavage of phosphate from phytate in a stepwise hydrolysis reaction and release available forms of inorganic phosphorus (Fig. 2). Phytase is the most widely used feed enzyme, and farmers increasingly rely on phytase supplementation to release phosphate from the feed phytate. As a result, the supplemented phytase activity covers more than 50% of the animals’ requirement for phosphate.
Figure 2. Schematic diagram showing (A) phytase mechanism of action; (B) hydrolysis of phytate complexes.
The prohibition of protein meals of animal origin, which also provide P, has accelerated the acceptance of phytase feed enzymes in certain countries. Also, in recognition of the so-called ‘extra-phosphoric effects’ of phytase, some nutritionists elect to place matrix values on phytase feed enzymes for protein/amino acids and energy, in addition to calcium (Ca)and P.
The Nomenclature Committee of the International Union of Biochemistry (1979) lists two phytases.
(1) 3-phytase (Enzyme Classification 3.1.3.8.)
(2) 6-phytase (Enzyme Classification 3.1.3.26):
Initial hydrolysis is the phosphate group at the C6 position, which is known as 6-phytases, whereas those whose initial site of hydrolysis is the phosphate group at the C3 position are known as 3-phytases. It is said that 6-phytase is better than 3-phytase because 6-phytase will dephosphorylate a phytic acid molecule completely, whereas 3-phytase may leave the job unfinished, leaving at least one unit of phosphorus unreleased. (ABTL Enzymes. 2023). Recent trials demonstrate that modern bacterial 6-phytases can provide greater phosphorus release and improved tibia mineralization and growth performance in broilers compared with standard P-deficient diets, supporting their practical superiority in many commercial feeding situations.
Nutritional Benefits of Phytase
Many studies have evaluated the effects of dietary phytase on the digestibility and utilization of phosphorus in farm animals. Phytase increases the bioavailability of P, Ca, and amino acids. Supplementation of microbial phytase increases body weight gain, feed intake, feed efficiency, and overall growth performance in broilers. The improvement in growth performance in chickens fed with phytase may be due to increased bioavailability of phosphorus by phytase, an increase in feed intake and feed efficiency, and an increase in utilization of inositol.
Phytase supplementation improves protein utilization in poultry by countering the anti-nutritive effects of phytic acid and thereby enhancing the utilization of methionine, lysine, valine, isoleucine, and total amino acids in broiler diets.
A study by Yu Myunghwan et al. (2024) showed that Phygest HT, an Escherichia coli-derived 6-phytase supplementation in broiler diets, effectively reduces IP₆ to IP₃ & further lowers esters of Phytic acid & Inositol throughout the gastrointestinal tract and enhances nutrient digestibility, including calcium, phosphorus, energy, ash, and crude protein. Continuous phytase (Phygest HT) use from 1 to 35 days of age of broiler birds promoted phytate degradation into lower inositol phosphates, resulting in improved growth performance, Fig.3, FCR, Fig.4, and tibia bone mineralization in broilers, Fig. 5. In the study Seven dietary treatments were used (1) Positive control (PC): 0.45% AP (starter) and 0.42% AP (grower); (2) NC-1: PC minus 0.10% AP; (3) NC-2: PC minus 0.15% AP; (4) NC-3: PC minus 0.20% AP; (5) NC-3 + 500 FTU/kg Phygest HT; (6) NC-3 + 1000 FTU/kg Phygest HT; (7) NC-3 + 1500 FTU/kg Phygest HT,(8) NC-3 + 1500 FTU/kg “A” Phytase.
By day 35, the NC-3 group showed significantly reduced tibia weight, confirming the detrimental impact of severe AP deficiency. In contrast, birds fed NC-3 + 1500 FTU/kg phytase (Phygest HT) exhibited higher tibia calcium and phosphorus content than all other groups, indicating improved bone mineralization & birds' performance.
Figure 3: Effect of Phytase (Phygest HT) inclusion in diets on growth performance of broiler chickens.
Exogenous microbial phytase
Exogenous microbial phytases are isolated from numerous bacteria, yeast, and fungi. Improvement in fermentation led to commercial phytase use in pig/poultry diets. While the original phytase feed enzymes were produced mainly by fungi, recent developments in the production of enzymes by other forms of micro-organisms, such as bacteria and yeast, have resulted in new exogenous phytases. Such bacterial phytases seem to be more efficacious compared with phytases of fungal origin in broilers. E. coli phytases are more active at a lower pH range (e.g., pH 2.5–4.5) than fungal phytases. When compared with fungal phytase, E. coli phytase remains active up to the jejunal region because it is more resistant to the proteolysis that occurs in the small intestine.
Figure 4 Effect of Phytase (Phygest HT) inclusion in diets on FCR of broiler chicken
Phytate and Mineral Bioavailability
One molecule of phytic acid binds with 3 to 6 molecules of Ca to form an insoluble complex at the pH of the small intestine. Excess Ca in the diet leads to the formation of calcium phytate complexes, which are highly insoluble and poorly digested. Zinc forms the most insoluble salt with phytic acid; therefore, zinc is a limiting mineral in high phytate diets as it forms a highly insoluble complex at pH 6.4, which is the pH of the upper intestine where most mineral absorption occurs. Phytic acid can bind di- and trivalent minerals and form very stable complexes, decreasing their availability as well as the availability of phytate P to animals. As phytic acid (and phytate)dissociates and is soluble at acidic pH (e.g., stomach), the formation of minerals and phytic acid complexes occurs mainly at the upper small intestinal pH. Phytate forms complexes with cations in the following descending order: Cu2+>Zn2+>Co2+>Mn2+>Fe3+ >Ca2+ . Phytic acid and phytate have a strong binding affinity to the dietary minerals calcium, iron, and zinc, inhibiting their absorption in the small intestine. The addition of vitamin D3, along with phytase, increases the utilization of phytate. Supplementation of microbial phytase increases the availability of Ca in broiler chicks. Retention of Ca increases as the level of phytase increases in the diet and decreases as the ratio of Ca: P becomes wider in the diet.
Phytase improves Zn utilization by reducing Zn excretion in broilers and thereby reduces the requirement of Zn in the broiler diet. In addition, phytic acid can increase endogenous losses of minerals such as sodium in poultry. Sodium deficiency can have an impact on the activity of Na⁺/K⁺-ATPase in the gastrointestinal (GI) tract, which is involved in the absorption of nutrients. It has been reported that ingestion of phytic acid reduced the activity of Na⁺/K⁺-ATPase (sodium–potassium ATPase )in the GI tract in broilers.
Figure 5 Effect of Phytase (Phygest HT) inclusion in diets on Tibia wt (g) of broiler chickens.
Phytate and protein bioavailability
Phytate also non-selectively binds to proteins and has been shown to inhibit enzymes, including trypsin and 𝛼-amylase, thus reducing protein digestibility in animals. In addition, phytic acid can increase endogenous amino acid losses due to increased secretion of digestive enzymes and mucins and reduced reabsorption of the endogenously secreted amino acids in the small intestine. It is therefore likely that when phytase hydrolyses the ester bonds to release P from the phytic acid molecule, it will also release the phytate-bound protein and remove the negative effects of phytic acid on proteolytic enzymes, thus increasing the digestion and absorption of protein and amino acids. Poultry fed phytase had higher digestibility for Val, Ile, nonessential amino acids, and total amino acids.
Phytate Interaction with Digestive Enzymes
Phytate inhibits digestive enzymes such as pepsin, alpha- amylase and trypsin. Phytate inhibits proteolysis by altering the protein configuration of digestive enzymes. Phytate binds with trypsin via Ca, forming a tertiary complex and thereby inhibiting the trypsin activity. Inhibition also results from the chelation of Ca ions, which are essential for the activity of trypsin and alpha-amylase. Phytase is a phosphatase enzyme that hydrolyses phytic acid to inositol and inorganic phosphorus, leading to improved phosphorus utilization.
Phytic acid ____Phytase_> Inositol + Inorganic Phosphorus
Energy Utilization
It is well documented that the ingestion of phytate can have substantial adverse effects on endogenous secretion and energy utilization in poultry. Phytate can form phytate–mineral complexes that may contribute to the formation of insoluble metallic soaps with starch & fatty acids in the GIT, which limits lipid utilization. Ca phytate forms metallic soaps with starch & fatty acids in the GIT, which limits the digestibility & utilization of carbohydrates & lipids, reference added in. Phytase supplementation can reduce the degree of soap formation and enhance the utilization of energy-derived lipids. In addition, phytate can increase the endogenous losses of Na in poultry. Sodium deficiency can have a direct impact on the activity of Na+ K+-ATPase (sodium–potassium ATPase)in the GIT that may compromise the Na-dependent transport. Phytase reduces the negative impact of phytate on Na⁺/K⁺-ATPase by hydrolyzing phytate, releasing Mg²⁺ and Ca²⁺, and thereby restoring optimal enzyme activity crucial for nutrient absorption and energy metabolism.
It has been suggested that phytate may directly or indirectly bind with starch, and even more can inhibit α-amylase activity. Phytate may also reduce the solubility of starch by binding it, reducing its absorption, and hence lowering glucose utilization. Therefore, supplemental phytase had positive effects on dry matter digestibility by releasing bound organic nutrients.
Improve gut health & immunity
A combination of carbohydrates with phytase and acidifier decreases E. coli count and increases villus length in broiler chicken. Phytase breaks down phytate (IP₆) into lower inositol phosphates, phosphate, and free minerals, thereby releasing bound Zn, Ca, and Mg. Zinc availability enhances immune organ development (bursa, spleen) and supports T- and B-cell functions, and it has also been reported to improve immunity in chickens against infectious diseases like Newcastle Disease.
Conclusion
Phytase plays a strong role in mitigating the anti–nutritional effects of phytate by hydrolyzing the phytic acid to inositol and inorganic phosphorus. Phytase improves the growth performance and retention of Zn, Ca, Cu, Mg & Na as well as other trace minerals when included in poultry diets. It also helps to increase the available metabolizable energy(AME)and ileal digestibility of protein and amino acids in poultry to increase the growth performance, digestibility of nutrients, and reduce the feed cost. Bacterial sources like E.coli phytases are stronger than fungal phytases to hydrolyze the phytate phosphorus properly. On the other hand, 6-phytase is better than 3-phytase, because 6-phytase will dephosphorylate a phytic acid molecule completely. Phygest HT, a novel state-of-the-art E. coli derived 6-phytase from Kemin, has been shown to enhance nutrient digestibility, including calcium, phosphorus, energy, ash, and crude protein, resulting in improved growth performance and tibia bone mineralization in chickens.
References are available upon request.
