hic grap Peer-reviewed article no upplem o s ent M s er ie s Folate: sources , production and bioavailability SHALINI S. ARYA*, K. PAVITRA Shalini S. Arya *Corresponding author Institute of Chemical Technology, Food Engineering and Technology Department NM Parikh Marg, Matunga, Mumbai, 400 019, India KEYWORDS: Folate; production; sources; bioavailability. ABSTRACT: “Folate” is a generic term for forms of Vitamin B9 and their derivatives. Initially detected in brewer’s yeast and isolated from spinach, folates play a vital role in body functions like nucleic acid synthesis and RBC formation. Natural folates are preferable over synthetic forms since they have lesser side effects and are body-own forms; and also the metabolism of synthetic folic acid is very individual specifi c. Some physiological conditions like sickle cell disease and renal dialysis might increase cellular folate requirements. Folate defi ciency must be treated considering its metabolic inter-relationships with vitamin B12 and choline. The present review focuses on natural and synthetic folate sources, microbial production and bioavailability. Monographic supplement series: INTRODUCTION folates are pteroylmonoglutamates. Pteroylpolyglutamates with up to 11 glutamic acid residues exist naturally. Folates is an essential nutrition component (important B Naturally occurring folates can have a variety of production vitamin) in the human diet, involved in many metabolic methods as follows (5). pathways, mainly in carbon transfer reactions such as purine and pyrimidine biosynthesis and amino acid inter-conversions. Folates exist as vitamers (one carbon folate derivatives) that are ployglutamates with varying oxidation states and substituents (1). Folates are important as they synthesize neurotransmitters by depleting excess homocysteine from the DIETARY SUPPLEMENTS: omega-3, proteins, vitamins blood, thereby benefi ting cardio vascular disease patients (2). The major sources of folates are green leafy vegetables, liver, beans and legumes, egg yolk, wheat germ, yeast, and folate fortifi ed breakfast cereal products. CLASSIFICATION OF FOLATES Folates exist in two forms- Naturally occurring folates are found in foods and in metabolically active forms in the human Figure 1. Structure of natural folates (reduced one carbon body (3). The synthetic form of folic acid is the folate found in substituents of polyglutamates) (10). supplements and fortifi ed foods. This is the more stable form and occurs rarely in foods or in the human body. FERMENTED FOODS NATURALLY OCCURRING FOLATES Fermented foods are divided into three categories. - A groFOOD Fresh fruits, leafy green vegetables and legumes are some Dairy products natural sources rich in folate (4). Natural folates differ in the The elaboration of extent of the reduction state of the pteroyl group, nature fermented milks of the substituent on the pteridine ring and the number of containing elevated industry hi-tech glutamyl residues attached to the pteroyl group. They include levels of natural form of 5- methyltetrahydrofolate (5-MTHF), 5-formyltetrahydrofolate folates is a better suited (5-formyl-THF), 10 formyltetrahydrofolate (10-formyl-THF), alternative. According 5,10-methylenetetrahydrofolate (5,10 methylene-THF), to a study (5), fermented - Table 1. Folate concentrations July/August 2012 5,10-methenyltetrahydrofolate (5,10-methenyl-THF), in dairy products (11). milk products contribute 5 formiminotetrahydrofolate (5-formimino-THF), signifi cantly to the 5,6,7,8-tetrahydrofolate (THF) and dihydrofolate (DHF), reference daily intake of folates. It is observed that Ropy as depicted in Figure 1. Most naturally occurring folates milk showed the highest folate concentration (110 + 20 µg/ - are pteroylpolyglutamates, containing two to seven mL) because of the presence of actively growing bacterial vol 23 n 4 glutamates joined in amide linkages to the γ-carboxyl strains, giving the milk its characteristic ropy appearance. of glutamate. The principal intracellular folates are These strains continued to produce folates into the milk matrix, pteroylpentaglutamates, while the principal extracellular causing the natural folate levels to rise (Table 1). XXIII Cereal based fermented products dominant producer, elevating folate levels in skim milk, while It is possible to increase the folate content in Egyptian lactobacilli have been found to deplete the available folate baladi bread using germinated wheat fl our from 30 μg/ 100 in the skim milk. It has been analysed experimentally that the g Dry Matter (DM) to 50 μg/ 100 g DM by parameters like adaptation of L. bulgaricus from a plant-associated habitat germination temperature and drying conditions (6). to the stable protein and lactose-rich milk environment through the loss of superfl uous functions and proto-co- Fermented vegetables operation with Streptococcus thermophilus makes it a It is possible to select lactic acid-producing starter cultures potent folate producer (13). that produce signifi cant amounts of 5-MTHF (almost doubling its concentration) during fermentation of vegetables (7). Optimization of the whole process of enhancing folate BIOAVAILABILITY OF NATURAL FOLATES concentrations in fermented vegetables is needed. On comparison of synthetic folic acid with natural dietary folates, synthetic folic acid has a substantially higher MICROBIAL PRODUCTION OF FOLATES bioavailability than natural folates, being rapidly absorbed across the intestine (16). The ability of de novo folate production is found in bacteria, Mammals are unable to synthesize a pteridine ring, one green plants, fungi and certain protozoa. The limitations of of the three groups of tetrahydrofolates; the other two use include the requirement of strict anaerobic conditions for groups are p-aminobenzoate and glutamate. They obtain folate production and possibilities of folate utilization by co- tetrahydrofolates from their diets or from microorganisms cultures. Folate produced in situ by the colonic microbiota in their intestinal tract. The intestinal absorption of folates is absorbed across the large intestine and incorporated into occurs at the monoglutamyl level. Many labile folates may the liver and kidney of piglets (8). be lost during residence in the acid peptic milieu of the stomach. For folate absorption, luminal digestion to the Native strains monoglutamyl form by an intestinal enzyme known as folate Some authors have isolated and identifi ed two new conjugase found in the brush border is the rate limiting step. vol 23 n 4 This enzyme is an exopeptidase and is activated by zinc - Lactobacillus strains from dairy products with an ability of high folate production and also potential to act as probiotics (17). A second enzyme, intracellular hydrolase, is found in (9). the lysosomes of intestinal cells, has a pH optimum of 4.5 In humans, folates produced by the microbiota in the small and is an endopeptidase (18). The function of the former is intestine are assimilated by the host (3). Folates produced believed to be primarily in the digestion of dietary folates July/August 2012 - in situ by the colonic microbiota are utilized by cells in the and that of the latter is still unknown. Monoglutamates are colonic epithelium. Research is required to determine if present in portal circulation, which is taken by the liver and these bacteria produce folates in the intestinal environment, converted into polyglutamate derivatives and stored or the form in which this folate occurs, the availability of this released into the blood. folate for transport and utilization by colonocytes from the In their reduced form cellular folates function conjugated industry hi-tech lumen; and the contribution of the intestinal microbiota to to a polyglutamate chain. The reduced forms are the total folate requirement of colonic epithelial cells. unstable chemically. They are easily split between the C-9 and N-10 bond to yield a substituted pteridine groFOOD and p-aminobenzoylglutamate, which have no biologic A Metabolic engineering of production strains - The genes for folate biosynthesis have been identifi ed as activity (19). Substituting a carbon group at N-5 or N-10 Lactococcus (Lc) lactis and Lactobacillus (L) plantarum, decreases the tendency of the molecule to split, however, and it has been shown that L. bulgaricus also possesses the the substituted forms are also susceptible to oxidative folate biosynthesis genes. Metabolic engineering can be chemical rearrangements and, consequently, loss of activity used to increase folate levels in Lc. lactis, L. gasseri and L. (19). The folates found in food consist of a mixture of reduced reuteri (12). It has been shown that L. bulgaricus possesses all folate polyglutamates. the folate biosynthesis genes (13). Synthetic folates (Folic Acid) Production by co culture method Folic acid is itself not biologically active; its biological The concurrent production of folate and Vitamin B12 with importance is due to tetrahydrofolate and other derivatives Lactic and Propionic Acid Bacteria was studied (14). L. after its conversion to dihydrofolic acid in the liver (20). plantarum SM39 (397 ng/mL extracellular folate) and P. freudenreichii DF 13 (1.6 µg/mL intracellular vitamin B12) were Folic Acid fortifi ed foods selected for the development of a batch co-culture process According to the Guidelines provided by the UNO and FAO in Yeast supplemented Whey Permeate Medium for high for fortifi cation (2006), grain fl our and enriched cereal grain and concurrent production of both vitamins. L. plantarum