Analysis of seven folates in food by LC–MS/MS to improve accuracy of total folate data

An improved folate stable isotope dilution assay of unexploited food sources from Brazil

Brazil has a diverse plant community, including underutilized non-conventional food crops (PANCs), which have the potential to be a rich source of food and contribute to food security. For assessing the folate content in a range of Brazilian PANCs, we extended the validation of an existing stable isotope dilution assay (SIDA) for the stably 13C-labelled 10-formyl-Pte[13C5]Glu (10-CHO-Pte[13C5]Glu). The SIDA method with an enzymatic treatment, purification step, and an LC-MS/MS measurement was validated regarding linearity, precision, LoD/LoQ, and recovery for 10-CHO-PteGlu. After successful validation, the study of some underutilized Brazilian non-conventional fruits and leaves from the São Paulo State University campus revealed them as an important source of folates. It provided the first insights into the folate content of unexploited food sources from Brazil. Pequi had the highest folate content among the fruits studied, with mean values of 333 μg/100 g based on fresh weight (FW). The analysis also shows that different cultivars of fruit or fruits from different growing locations have a high variability in folate content or other nutritional factors. In most fruits, the main vitamer was 5-CH3-H4folate, but jenipapo and taioba showed the highest content of 10-CHO-PteGlu with 28.22 μg/100 g (FW) in jenipapo peel and 75.64 μg/100 g (FW) in the taioba leaves. Thus, this study also provides results on the importance of the folate vitamer 10-CHO-PteGlu contributing to the total folate content.

Insights on the Nutritional Profiling of Cantaloupe (Cucumis melo L.) via 1-Naphthalene Acetic Acid

The nutritional components of cantaloupe, including vitamins, minerals, antioxidants, and dietary fiber, contribute to overall health, improved immunity, hydration, and protection against chronic diseases. This study was conducted to investigate the influence of different concentrations (0 (control), 100, 150, and 200 ppm) of 1-naphthalene acetic acid (1-NAA) on the nutritional components of the cantaloupe (Cucumis melo L. Var. Super White Honey). All the studied treatments were applied twice at the 2nd and 4th leaf stages. The applied concentrations of 1-NAA significantly improved the sex expression and fruit yield attributes. Different nutritional components like proximate contents, minerals, vitamins, selected fatty acids, and amino acids were analyzed. The results showed that the maximum moisture content, proteins, carbohydrates, ash, and energy were recorded with 100 ppm. The higher lipids were recorded during the supplementation of 150 ppm. Significantly greater fibers were recorded using 200 ppm. Regarding minerals, 100 ppm was found to be the best as it increased calcium (Ca), magnesium (Mg), potassium (K), sodium (Na), phosphorous (P), manganese (Mn), copper (Cu), iron (Fe), and zinc (Zn). Vitamins were also found to be the maximum with 100 ppm, including vitamin A, vitamin B, vitamin C, vitamin D, vitamin E, and vitamin K. Total selected fatty acids and amino acids were also found significantly greater in the fruits administered 100 ppm.

Development of rice analogues fortified with iron, folic acid and Vitamin A

Fortified rice analogues were developed utilising the broken-rice fortified with selected micronutrients like iron, folic acid and Vitamin A. The purpose of this study was to investigate the feasibility of fortifying rice analogues with micronutrients and retention after extrusion and cooking. Cold extruder operated at 55 rpm screw speed and 1.5 kg/h feed rate was used for the study. The composite flour prepared using broken-rice flour, sodium alginate (1%), water (30%) and micronutrient mix was extruded through rice shaped die at barrel temperature of 60 °C. The level of fortifying nutrient ready mix (FNRM) was statistically optimised based on retention of nutrients after extrusion and cooking. The retention results for iron was observed to be 73.3 to 91.3 per cent after cooking whereas folic acid and Vitamin A being sensitive to processing and culinary operations were 44.2 to 60.4 and 10.1 to 12.4 per cent, respectively. Statistical optimisation resulted 150 per cent of FNRM could supply nutrient levels nearing the standards with the desirability of 0.835. The production cost was calculated as Rs.53.50 per kg whereas, increase in the cost of raw rice mixed with fortified analogues @ 1:50 ratio was about Rs.1.00 per kg with benefit-cost ratio of 1.22:1.

Development of Stable Isotope Dilution Assays for the Analysis of Natural Forms of Vitamin B12 in Meat

The first multiple stable isotope dilution assay method was developed for the simultaneous determination of four cobalamins, namely, hydroxocobalamin (OHCbl), adenosylcobalamin (AdoCbl), methylcobalamin (MeCbl), and cyanocobalamin (CNCbl), in their native forms. The sample preparation was optimized with enzyme treatment and immunoaffinity purification. The analysis was performed by LC-MS/MS using respective ¹⁵N-labeled cobalamins as internal standards. Method validation resulted in limits of detection ranging from 0.19 to 0.58 ng/g and limits of quantification ranging from 0.68 to 1.73 ng/g. Recoveries at three levels were between 82 and 121%. Intra-day and inter-day precisions were below 6% and 11% RSD, respectively. The analysis of a reference material resulted in a variance of <1% from the certified value. The newly developed method demonstrated excellent sensitivity, recovery, accuracy, and reproducibility and was further applied to quantitate the four cobalamins in various meats.

Validated B vitamin quantification from lentils by selected reaction monitoring mass spectrometry

A validated method for B vitamin separation and quantification from lentil seeds using ultra high performance liquid chromatography-selected reaction monitoring mass spectrometry (UHPLC-SRM MS) was reported. The use of three enzymes (acid phosphatase, β-glucosidase, and rat serum) with a 4 h incubation was sufficient to convert bound B vitamins into their free forms. Twenty B vitamers were selected and a 5-min UHPLC-SRM MS method was optimized for rapid analysis. This method was applied to quantify B vitamin concentration during lentil seed germination over a 5-day period. Total B vitamins increased up to 1.5-fold on day 5 (from 39.2 µg/g to 60.6 µg/g of dry weight) comparing with dry seeds. Vitamin B5 (pantothenic acid) was the most abundant B vitamin in both dry seeds (34.2%) and in germinated seeds (17.7%-24.5% of total B vitamins); B8 (biotin) and B12 (cyanocobalamin) were not detected in lentil samples.

Identification of the prepared foods promising for dietary folate intake in Beijing, China

The aim of the present study was to analyze folate content and composition in foods consumed daily by Chinese people. The concentration of seven folate derivatives in sixty-four selected foods was determined by a liquid-chromatography tandem-mass spectrometry method. The total folate levels ranged from 0.28 to 129 µg/100 g fresh weight, with an average of 21.18 μg/100 g. The highest folate content was found in boiled egg yolk and waxy corn (>120 µg/100 g), abundant folate levels in cooked vegetables such as hot pepper, spinach, soybean sprout, stem lettuce, coriander, and broccoli (44-72 µg/100 g), and lowest in Coca Cola (0.28 µg/100 g). 5-Methyl-tetrahydrofolate was the major folate derivative in various foods, accounting for 72% of the total folates on average, with the highest being 90% in egg yolk. These data will enable estimation of the daily folate intake and allow dietary recommendations to improve folate status in humans.

Modelling folates reaction kinetics during cowpea seed germination in comparison with soaking

Folate is a fundamental vitamin for metabolism in plants and humans. A modelling approach has been developed to characterize the reactivity of folates in cowpea seeds during germination at 30 °C, using a water-to-seed ratio of 1:1 (w/w). For this purpose, the concentrations of folic acid, 10-formylfolic acid, 5-methyltetrahydrofolate, 5-formyltetrahydrofolate and tetrahydrofolate were determined in seeds during germination times up to 96 h. Two reaction models were sequentially built and adjusted to experimental data to describe changes in concentration in cowpea seed during two germination phases: before 14 h and after 48 h. Results showed intense enzymatic interconversion of all folate vitamers into 5-methyltetrahydrofolate before 14 h of germination and high enzymatic production of 5-methyltetrahydrofolate, 5-formyltetrahydrofolate and tetrahydrofolate after 48 h of germination. This study suggests that a long germination process could be more beneficial than soaking to increase the production of bioavailable folates within the seed for human consumption.

Microalgae a Superior Source of Folates: Quantification of Folates in Halophile Microalgae by Stable Isotope Dilution Assay

A multitude of human nutritional supplements based on Chlorella vulgaris biomass has recently been introduced to the specialty food market. In this study, an analysis of total folate contents in Chlorella sp. and a series of marine microalgae was conducted to evaluate folate content in alternative algae-based food production strains. For the first time, total folate content and vitamer distribution in microalgae were analyzed by stable isotope dilution assay (SIDA) using LC-MS/MS, which has demonstrated its superiority with respect to folate quantification. Consistently, high folate contents were detected in all examined microalgae samples. High folate concentrations of 3,460 ± 134 μg/100 g dry biomass were detected in freshly cultivated Chlorella vulgaris, notably also in other well-researched microalgae strains. To that end, the highest folate content currently documented for any algae sample was measured in the marine microalgae Picochlorum sp. isolate with values of 6,470 ± 167 μg/100 g dry biomass. This calls for alternative products based on other algae biomass. Our data indicate that freshwater and marine microalgae provide extremely high concentrations of folates, which warrant further studies on the regulation of pteroylpolyglutamates in algae as well as on bioaccessibility, absorption, and retention in humans.

Challenges to Quantify Total Vitamin Activity: How to Combine the Contribution of Diverse Vitamers?

This state-of-the-art review aims to highlight the challenges in quantifying vitamin activity in foods that contain several vitamers of a group, using as examples the fat-soluble vitamins A and D as well as the water-soluble folate. The absorption, metabolism, and physiology of these examples are described along with the current analytical methodology, with an emphasis on approaches to standardization. Moreover, the major food sources for the vitamins are numerated. The article focuses particularly on outlining the so-called SLAMENGHI factors influencing a vitamer's' ability to act as a vitamin, that is, molecular species, linkage, amount, matrix, effectors of absorption, nutrition status, genetics, host-related factors, and the interaction of these. After summarizing the current approaches to estimating the total content of each vitamin group, the review concludes by outlining the research gaps and future perspectives in vitamin analysis. There are no standardized methods for the quantification of the vitamers of vitamin A, vitamin D, and folate in foods. For folate and β-carotene, a difference in vitamer activity between foods and supplements has been confirmed, whereas no difference has been observed for vitamin D. For differences in vitamer activity between provitamin A carotenoids and retinol, and between 25-hydroxyvitamin D and vitamin D, international consensus is lacking. The challenges facing each of the specific vitamin communities are the gaps in knowledge about bioaccessibility and bioavailability for each of the various vitamers. The differences between the vitamins make it difficult to formulate a common strategy for assessing the quantitative differences between the vitamers. In the future, optimized stationary digestive models and the more advanced dynamic digestive models combined with in vitro models for bioavailability could more closely resemble in vivo results. New knowledge will enable us to transfer nutrient recommendations into improved dietary advice to increase public health throughout the human life cycle.

Recent trends in analytical methods for water-soluble vitamins

In this review, recent advances in the analysis of water-soluble vitamins (WSVs) have been reported considering the advantages and disadvantages of various extraction, separation and detection techniques, commonly used for their quantification. Acid hydrolysis, enzyme treatment, SPE based methods and some other extraction methods have been discussed. Particular attention has been devoted to the analytical techniques based on liquid chromatography and electrophoresis. Furthermore, suitability and selectivity of hydrophilic interaction liquid chromatography (HILIC) for WSVs has been discussed in detail. Problems related to these techniques and their possible solutions have also been considered. Special focus has been given to the applications of liquid chromatography (since 2014-2019) for the simultaneous analysis of WSVs and their homologous in complex food samples.

The use of a plant enzyme for rapid and sensitive analysis of naturally-occurring folates in food by liquid chromatography-tandem mass spectrometry

A rapid, sensitive and reproducible method for analysis of naturally-occurring folates and folic acid in food has been developed and validated. A single-enzyme extraction step, in which a pure recombinant enzyme of plant origin (Arabidopsis thaliana) was used, enabled fast and reproducible deglutamylation during folate extraction within the incubation time of 1 h. Six commonly occurring folate forms (tetrahydrofolate, 5,10-methenyltetrahydrofolate, 10-formylfolic acid, 5-formyltetrahydrofolate, folic acid and 5-methyltetrahydrofolate) were detected and quantified in 9 min using liquid chromatography-tandem mass spectrometry (LC-MS/MS). ¹³C₅-labeled 5-formyltetrahydrofolate, ¹³C₅-labeled folic acid and ¹³C₅-labeled 5-methyltetrahydrofolate were used as internal standards for the quantification. The method is described by a calibration curve (R²>0.99 and trueness 85-115%), a limit of quantification at 0.1 μg/100 g, trueness at 80-120% in spiked samples and certified reference materials, and a precision <10%. However, the precision in quantification of tetrahydrofolate was not within the acceptable limits due to the lack of use of the corresponding internal standard. An interconversion study of unstable formyl forms was performed which showed that 50% of 5,10-methenyltetrahydrofolate is converted to 5-formyltetrahydrofolate during the analysis. The developed LC-MS/MS method is a candidate for a future standard method for folate analysis in food.

Quantification of Cellular Folate Species by LC-MS after Stabilization by Derivatization

Folate cofactors play a key role in one-carbon metabolism. Analysis of individual folate species is hampered by the low chemical stability and high interconvertibility of folates, which can lead to severe experimental bias. Here, we present a complete workflow that employs simultaneous extraction and stabilization of folates by derivatization. We perform reductive methylation employing stable isotope labeled reagents to retain information on the position and redox state of one-carbon units as well as the redox state of the pteridine ring. The derivatives are analyzed by a targeted LC(HILIC)-MS/MS method without the need for deconjugation, thereby also preserving the glutamation state of folates. The presented method does not only improve analyte coverage and sensitivity as compared to other published methods, it also greatly simplifies sample handling and storage. Finally, we report differences in the response of bacterial and mammalian systems to pharmacological inhibition of dihydrofolate reductase.

Buchanania obovata: An Australian Indigenous food for diet diversification

AIM

Buchanania obovata Engl., the Green Plum, is a small green fruit eaten by Australian Indigenous peoples of the Northern Territory and Western Australia that has had limited study and has potential as a source of food for diet diversification. The flesh and seed of the fruit are eaten and the plant is used as bush medicine.

METHODS

Physical characteristics of the fruit were measured. The flesh and seed freeze dried powders were measured separately for proximates, mineral/trace elements and heavy metals, and folate analysis. Vitamin C was analysed in the flesh.

RESULTS

The flesh is high in protein (12.8 g/100 g dry weight (DW)) and both flesh and seed are high in dietary fibre (55.1 and 87.7 g/100 g DW, respectively). The flesh is high in potassium (2274.7 mg/100 g DW), and is a good source of magnesium (570.5 mg/100 g DW), calcium (426.0 mg/100 g DW) and phosphorous (216.8 mg/100 g DW), whereas the seed is high in iron (8.15 mg/100 g DW). The flesh contains folate at 752.4 μg/100 g DW and the seed contains 109.5 μg/100 g DW as pteroylmonoglutamic acid equivalents.

CONCLUSIONS

The flesh and seed have good nutritional properties and the results support the use of the Green Plum for diet diversification and nutrition in Indigenous and non-Indigenous populations in Australia.

Simultaneous quantitation of folates, flavins and B6 metabolites in human plasma by LC-MS/MS assay: Applications in colorectal cancer

An analytical method using electrospray ionization and high- performance liquid chromatography/tandem mass spectrometry (LC/ESI-MS/MS) was developed to quantify the vitamin B metabolites found in the folate one-carbon metabolism, using 50 μL of human plasma. Analytes in plasma were extracted using protein precipitation after being stabilized in 1% ascorbic acid. The analytes were separated using a Kinetex 2.6 μm Pentafluorophenyl (2.1 × 30 mm) column utilizing a gradient mobile phase system of 0.1% formic acid in water and 100% acetonitrile in a 13.2 min run. The MS detector run using a positive multiple reaction monitoring with parameters optimized for each analyte's ion pair. The assay was selective and linear for all analytes at defined dynamic ranges. The recoveries were generally above 80% except for the folate metabolites whose recoveries dipped possibly due to the drying process. The inter-day precision (%coefficient of variation) and accuracy (%calculated concentration of the nominal concentrations) for six replicates of all quality control samples were ≤14% and within 12.2%, respectively. The lower limit of quantification ranged from 0.2 to 3.9 nM. No significant instability was observed after repeated freezing and thawing or in processed samples. The LC-MS/MS assay was found applicable for sensitive, accurate and precise quantitation of vitamin B metabolites in plasma of healthy volunteers and colorectal cancer patients.

Improved Stable Isotope Dilution Assay for Dietary Folates Using LC-MS/MS and Its Application to Strawberries

Folates play an important role in the human body and a deficiency of this vitamin can cause several diseases. Therefore, a reliable analytical method is crucial for the determination of folate vitamers in strawberries and other dietary folate sources. A stable isotope dilution LC-MS/MS method for analyzing folates in food was developed and validated. The folate vitamers Pteroylmonoglutamic acid, tetrahydrofolate, 5-methyltetrahydrofolate, and 5-formyltetrahydrofolate were quantified using ¹³C-labeled internal standards. Validation of the assay was accomplished by determining linearity, precision, recovery, limit of detection, and limit of quantification and revealed to be a precise, sensitive, and accurate method to determine folate vitamers. Strawberries are worldwide consumed and known to be a good dietary source of nutritive compounds. Using this method, folate concentrations in selected commercial strawberry cultivars and experimental breeding lines grown in Germany and Australia were investigated. Total folates varied from 59 to 153 μg/100 g on fresh weight basis. Furthermore, folate content after lyophilizing or freezing did not show any significant differences compared to fresh strawberries. However, significant losses of total folates in pureed strawberries could be observed after 5 days of storage with only 16% of the original concentration retained. In summary, some of the investigated strawberry cultivars/breeding lines can be considered as rich dietary sources of natural folates.

Lactic acid fermentation as a tool for increasing the folate content of foods

Folate is an essential micronutrient involved in numerous vital biological reactions. The dietary consumption of naturally occurring vitamin B9 is often inadequate in many countries, and supplementation or fortification programs (using synthetic folic acid) are implemented to alleviate folate deficiency. Other food-based alternatives are possible, such as the use of lactic acid bacteria (LAB) to synthesize folate during fermentation. Many studies have been conducted on this topic, and promising results were reported for some fermented dairy products. However, in other studies, folate consumption by LAB or rather low folate production were observed, resulting in fermented foods that may not significantly contribute to the recommended B9 intake. In addition, the optimum conditions for folate biosynthesis by LAB are still not clear. The aim of this review was thus to (i) clarify the ability of LAB to produce folate in food products, (ii) check if the production of folate by LAB in various fermented foods is sufficient to meet human vitamin B9 requirements and (iii) suggest ways to optimize folate production by LAB in fermented food products.

Naturally occurring folates in selected traditionally prepared foods in Southern India

A wide range of Indian foods (cereals, pulses, vegetables and milk based preparations) were analysed for five folate vitamers naturally present in the foods (n = 44). A liquid chromatography-mass spectrometry (LC-MS/MS) method using reversed phase chromatography and tandem mass spectrometry, coupled via positive mode electrospray ionization was used for the detection and quantification of the vitamers. The optimized LC-MS/MS method was capable of analysing the five most commonly-occurring folates (folic acid, 5-methyl tetrahydrofolic acid, tetrahydrofolic acid, 10-formyl folic acid and 5-formyl tetrahydrofolic acid) in 20 min. Quantification of folates was performed using ¹³C labelled internal standards. 5-methyl tetrahydrofolate was predominant in cereals, pulses and vegetable preparations. Fermented cereal preparations, beverages (coffee and tea) and green leafy vegetables were the main sources contributing to 5-formyl THF. Folic acid was identified in home-made yoghurt. All the values obtained in the present study using LC-MS/MS were compared to the total folate analysed using the microbiological assay in 2010 to generate data on the same foods. Findings suggest that the data obtained using both techniques showed agreement in the values (total folate calculated by adding the individual vitamers in the case of the LC-MS/MS values) particularly when foods were predominant in 5 methyl tetrahydrofolate.

Metabolite damage and repair in metabolic engineering design

The necessarily sharp focus of metabolic engineering and metabolic synthetic biology on pathways and their fluxes has tended to divert attention from the damaging enzymatic and chemical side-reactions that pathway metabolites can undergo. Although historically overlooked and underappreciated, such metabolite damage reactions are now known to occur throughout metabolism and to generate (formerly enigmatic) peaks detected in metabolomics datasets. It is also now known that metabolite damage is often countered by dedicated repair enzymes that undo or prevent it. Metabolite damage and repair are highly relevant to engineered pathway design: metabolite damage reactions can reduce flux rates and product yields, and repair enzymes can provide robust, host-independent solutions. Herein, after introducing the core principles of metabolite damage and repair, we use case histories to document how damage and repair processes affect efficient operation of engineered pathways - particularly those that are heterologous, non-natural, or cell-free. We then review how metabolite damage reactions can be predicted, how repair reactions can be prospected, and how metabolite damage and repair can be built into genome-scale metabolic models. Lastly, we propose a versatile 'plug and play' set of well-characterized metabolite repair enzymes to solve metabolite damage problems known or likely to occur in metabolic engineering and synthetic biology projects.

Simulation of Food Folate Digestion and Bioavailability of an Oxidation Product of 5-Methyltetrahydrofolate

Generating bioavailability data from in vivo studies is time-consuming and expensive. In vitro simulation can help to investigate factors influencing bioavailability or facilitate quantifying the impact of such factors. For folates, an efficient deconjugation of polyglutamates to the corresponding monoglutamates is crucial for bioavailability and highly dependent on the food matrix. Therefore, the bioaccessibility of folates of different foodstuffs was examined using a simulated digestion model with respect to folate stability and the efficiency of deconjugation. For realistic simulated deconjugation, porcine brush border membrane was used during the phase of the simulated digestion in the small intestine. For a better understanding of folate behaviour during digestion, single folate monoglutamates were also investigated with this in vitro digestion model. The results for bioaccessibility were compared with data from a human bioavailability study. They support the idea that both stability and deconjugation have an influence on bioaccessibility and thus on bioavailability. Tetrahydrofolate is probably lost completely or at least to a high extent and the stability of 5-methyltetrahydrofolate depends on the food matrix. Additionally, 5-methyltetrahydrofolate can be oxidised to a pyrazino-s-triazine (MeFox), whose absorption in the human intestinal tract was shown tentatively.

Folates in Plants: Research Advances and Progress in Crop Biofortification

Folates, also known as B9 vitamins, serve as donors and acceptors in one-carbon (C1) transfer reactions. The latter are involved in synthesis of many important biomolecules, such as amino acids, nucleic acids and vitamin B5. Folates also play a central role in the methyl cycle that provides one-carbon groups for methylation reactions. The important functions fulfilled by folates make them essential in all living organisms. Plants, being able to synthesize folates de novo, serve as an excellent dietary source of folates for animals that lack the respective biosynthetic pathway. Unfortunately, the most important staple crops such as rice, potato and maize are rather poor sources of folates. Insufficient folate consumption is known to cause severe developmental disorders in humans. Two approaches are employed to fight folate deficiency: pharmacological supplementation in the form of folate pills and biofortification of staple crops. As the former approach is considered rather costly for the major part of the world population, biofortification of staple crops is viewed as a decent alternative in the struggle against folate deficiency. Therefore, strategies, challenges and recent progress of folate enhancement in plants will be addressed in this review. Apart from the ever-growing need for the enhancement of nutritional quality of crops, the world population faces climate change catastrophes or environmental stresses, such as elevated temperatures, drought, salinity that severely affect growth and productivity of crops. Due to immense diversity of their biochemical functions, folates take part in virtually every aspect of plant physiology. Any disturbance to the plant folate metabolism leads to severe growth inhibition and, as a consequence, to a lower productivity. Whereas today's knowledge of folate biochemistry can be considered very profound, evidence on the physiological roles of folates in plants only starts to emerge. In the current review we will discuss the implication of folates in various aspects of plant physiology and development.

Origins of the difference between food folate analysis results obtained by LC-MS/MS and microbiological assays

To investigate the often reported disagreement in food folate quantitation between the microbiological assay and high-performance liquid chromatography methods, different foods were analyzed both by a microbiological assay and by a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. For the LC-MS/MS analysis we emphasize the need for complete deconjugation of polyglutamic folate forms. Moreover, our results revealed no need for an additional enzyme treatment except in the deconjugation step. To check the efficiency of deconjugation without additional sample preparations, the amount of diglutamates was quantified and samples were screened for additional polyglutamates. A thorough investigation of a substance with a polyglutamate chain deconjugated like the folates revealed that it was an oxidation product of 5-methyltetrahydrofolate, a pyrazino-s-triazine called MeFox in previous reports. The latter is not microbiologically active and, therefore, does not contribute to the amount of total folates. But we found it is commonly present in foods, especially in those low in ascorbic acid. The microbiological assay showed different responses to the single vitamers. Therefore, it was necessary to perform calibration with the folate that had the highest portion in the folate distribution. The investigations showed that both methods can provide similar results when they both include a deconjugation step. This is particularly important for LC-MS/MS but probably also for the microbiological assay. Additionally, consideration of the folate distribution was found to be crucial for the accurate calibration of the microbiological assay.

A rapid method for sensitive profiling of folates from plant leaf by ultra-performance liquid chromatography coupled to tandem quadrupole mass spectrometer

Previous published methods for the analysis of folates are time consuming because of lengthy sample extraction, clean-up and total running time. This study details the development and validation of a rapid, sensitive and robust method that combines a simple extraction step with ultra-performance liquid chromatography coupled to tandem quadrupole mass spectrometry. Here, we reported application of a tandem quadrupole mass spectrometer to analyze maximum seven vitamers of folate from plant origin. The analytical performance was evaluated by linearity, sensitivity, precision, recovery test and analysis of certified reference materials. The limit of detection and limit of quantification ranged between 0.003 and 0.021μg/100g FW and between 0.011 and 0.041μg/100g FW, respectively; the recovery and precession ranged from 71.27 to 99. 01% and from 1.7 to 7.8% RSD, respectively, depending upon folate vitamers. This newly developed and validated method is rapid (a chromatographic run time of 5min), easy to be performed (no laborious and time consuming clean-up) and can be used to simultaneously analyze seven vitamers of folate from plant sources.

Folates: Chemistry, analysis, occurrence, biofortification and bioavailability

Folates (Vitamin B₉) include both naturally occurring folates and synthetic folic acid used in fortified foods and dietary supplements. Folate deficiency causes severe abnormalities in one-carbon metabolism can result chronic diseases and developmental disorders, including neural tube defects. Mammalian cells cannot synthesize folates de novo; therefore, diet and dietary supplements are the only way to attain daily folate requirements. In the last decade, significant advancements have been made to enhance the folate content of rice, tomato, common bean and lettuce by using genetic engineering approaches. Strategies have been developed to improve the stability of folate pool in plants. Folate deglutamylation through food processing and thermal treatment has the potential to enhance the bioavailability of folate. This review highlights the recent developments in biosynthesis, composition, bioavailability, enhanced production by elicitation and metabolic engineering, and methods of analysis of folate in food. Additionally, future perspectives in this context are identified. Detailed knowledge of folate biosynthesis, degradation and salvage are the prime requirements to efficiently engineer the plants for the enhancement of overall folate content. Similarly, consumption of a folate-rich diet with enhanced bioavailability is the best way to maintain optimum folate levels in the body.

Stable Isotope Dilution Assays for Clinical Analyses of Folates and Other One-Carbon Metabolites: Application to Folate-Deficiency Studies

Folate deficiency is generally accepted as a potential direct or indirect risk factor for diseases including spina bifida, coronary heart diseases, malfunctions of the central nervous system, and cancer. The direct inclusion of folates in the methylation cycle, including the remethylation of homocysteine and regeneration of S-adenosylmethionine, underlines the importance of these vitamins and other components of one-carbon metabolism. Therefore, the aim of the present study was to develop a multiple stable isotope dilution assay (SIDA) for the respective analytes in plasma and tissue samples to allow for a closer look at the interaction between a severe folate deficiency and local folate status, as well as further interactions with circulating S-adenosylmethionine, S-adenosylhomocysteine, and homocysteine. The analytical methods were based on SIDAs coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis using the deuterated folates [2H4]-5-methyltetrahydrofolic acid, [2H4]-5-formyltetrahydrofolic acid, [2H4]-tetrahydrofolic acid, [2H4]-10-formylfolic acid, and [2H4]-folic acid and the deuterated one-carbon metabolites [2H4]-homocysteine, [2H4]-S-adenosylhomocysteine, and [2H3]-S-adenosylmethionine as internal standards. Three analytical methods have been developed for the analysis of homocysteine, S-adenosylmethionine, S-adenosylhomocysteine, and six folate vitamers. Validation data for the analysis of C1-metabolites in plasma and tissue samples or folate analysis in tissue samples revealed excellent sensitivity, precision, and recovery for all analytes studied. The miniaturized methods using sample volumes as low as 50 μL and weighed portions of 5-25 mg will allow the assessment of the status of folates and additional biomarkers of impaired one-carbon metabolism during folate deficiency.

Pilot Study on Folate Bioavailability from a Camembert Cheese Reveals Contradictory Findings to Recent Results from a Human Short-term Study

Different dietary sources of folate have differing bioavailabilities, which may affect their nutritional “value.” In order to examine if these differences also occur within the same food products, a short-term human pilot study was undertaken as a follow-up study to a previously published human trial to evaluate the relative native folate bioavailabilities from low-fat Camembert cheese compared to pteroylmonoglutamic acid as the reference dose. Two healthy human subjects received the test foods in a randomized cross-over design separated by a 14-day equilibrium phase. Folate body pools were saturated with a pteroylmonoglutamic acid supplement before the first testing and between the testings. Folates in test foods and blood plasma were analyzed by stable isotope dilution assays. The biokinetic parameters C_max, t_max, and area under the curve (AUC) were determined in plasma within the interval of 0–12 h. When comparing the ratio estimates of AUC and C_max for the different Camembert cheeses, a higher bioavailability was found for the low-fat Camembert assessed in the present study (≥64%) compared to a different brand in our previous investigation (8.8%). It is suggested that these differences may arise from the different folate distribution in the soft dough and firm rind as well as differing individual folate vitamer proportions. The results clearly underline the importance of the food matrix, even within the same type of food product, in terms of folate bioavailability. Moreover, our findings add to the increasing number of studies questioning the general assumption of 50% bioavailability as the rationale behind the definition of folate equivalents. However, more research is needed to better understand the interactions between individual folate vitamers and other food components and the potential impact on folate bioavailability and metabolism.

Folates in Fruits and Vegetables: Contents, Processing, and Stability

Folates play a key role in human one-carbon metabolism and are provided by food. It is well established that folates are beneficial in the prevention of neural tube defects and cardiovascular and neurodegenerative diseases. Fruits and vegetables, and especially green vegetables, are the main sources of folates. In parallel, fruits and vegetables, with high contents of folates, are mostly consumed after processing, such as, canning, freezing, or home-cooking, which involve folate losses during their preparation. Hence, it is important to know the percentage of folate losses during processing and, moreover, the mechanisms underlying those losses. The current knowledge on folate losses from fruit and vegetables are presented in this review. They depend on the nature of the respective fruit or vegetable and the respective treatment. For example, steaming involves almost no folate losses in contrast to boiling. Two main mechanisms are involved in folate losses: (i) leaching into the surrounding liquid and (ii) oxidation during heat treatment, the latter of which depending on the nature of the vitamer considered. In this respect, a vitamer stability decreases in the order starting from folic acid followed by 5-HCO-H₄ folate, 5-CH₃ -H₄ folate, and, finally, H₄ folate. Further studies are required, especially on the diffusion of the vitamers in real foods and on the determination of folate degradation products.

A new approach to the determination of folic acid at trace levels: using a Fe(iii)-folic acid complex to amplify analytical signal

A fast, efficient, and cost-effective, and environmental friendly analytical methodology was developed for preconcentration and determination of trace folic acid in food samples prior to HPLC-DAD.

Quantitation of 5-Methyltetrahydrofolic Acid in Dried Blood Spots and Dried Plasma Spots by Stable Isotope Dilution Assays

Because of minimal data available on folate analysis in dried matrix spots (DMSs), we combined the advantages of stable isotope dilution assays followed by LC-MS/MS analysis with DMS sampling to develop a reliable method for the quantitation of plasma 5-methyltetrahydrofolic acid in dried blood spots (DBSs) and dried plasma spots (DPSs) as well as for the quantitation of whole blood 5-methyltetrahydrofolic acid in DBSs. We focused on two diagnostically conclusive parameters exhibited by the plasma and whole blood 5-methyltetrahydrofolic acid levels that reflect both temporary and long-term folate status. The method is performed using the [²H₄]-labeled isotopologue of the vitamin as the internal standard, and three steps are required for the extraction procedure. Elution of the punched out matrix spots was performed using stabilization buffer including Triton X-100 in a standardized ultrasonication treatment followed by enzymatic digestion (whole blood only) and solid-phase extraction with SAX cartridges. This method is sensitive enough to quantify 27 nmol/L whole blood 5-methyltetrahydrofolic acid in DBSs and 6.3 and 4.4 nmol/L plasma 5-methyltetrahydrofolic acid in DBSs and DPSs, respectively. The unprecedented accurate quantification of plasma 5-methyltetrahydrofolic acid in DBSs was achieved by thermal treatment prior to ultrasonication, inhibiting plasma conjugase activity. Mass screenings are more feasible and easier to facilitate for this method in terms of sample collection and storage compared with conventional clinical sampling for the assessment of folate status.

Challenges in the determination of unsubstituted food folates: impact of stabilities and conversions on analytical results

Tetrahydrofolate is the parent molecule of the folate coenzymes required for one carbon metabolism. Together with other unsubstituted folates such as dihydrofolate and folic acid, tetrahydrofolate represents the third pool of dietary folates following 5-methyltetrahydrofolate and formyl folates. Low intake of dietary folates and poor folate status are common problems in many countries. There is a critical need for reliable methods to determine folate in foods to accurately estimate folate intakes in populations. However, current values for folates in foods in databanks are often underestimated due to the high instability of several folate forms, especially tetrahydrofolate. The present review highlights the occurrence of unsubstituted folates in foods and their oxidation mechanisms and chemical behavior as well as interconversion reaction between tetrahydrofolate and 5,10-methylenetetrahydrofolate. The review shows also the important role of antioxidants in protecting folates during analysis and describes strategies to stabilize unsubstituted folates throughout all steps of the analytical procedure.

Folate content in faba beans (Vicia faba L.)-effects of cultivar, maturity stage, industrial processing, and bioprocessing

Faba beans are an important source of folate and commonly consumed in Egypt. This study examined the effects of Egyptian industrial food processing (e.g., canning and freezing), germination, cultivar, and maturity stages on folate content, with the aim to develop a candidate functional canned faba bean food with increased folate content. The folate content in four cultivars of green faba beans ranged from 110 to 130 μg 100 g⁻¹ fresh weight (535–620 μg 100 g⁻¹ dry matter [DM]), which was four- to sixfold higher than in dried seeds. Industrial canning of dried seeds resulted in significant folate losses of ∼20% (P = 0.004), while industrial freezing had no effect. Germination of faba beans increased the folate content by >40% (P < 0.0001). A novel industrial canning process involving pregermination of dried faba beans resulted in a net folate content of 194 μg 100 g⁻¹ DM, which is 52% more than in conventional canned beans. The consumption of green faba beans should be recommended, providing ∼120 μg dietary folate equivalents per 100 g/portion.

Mechanisms of folate losses during processing: diffusion vs. heat degradation

Though folates are sensitive to heat treatments, leaching appears to be a major mechanism involved in folate losses in vegetables during processing. The aim of our study was to study folate diffusivity and degradation from spinach and green beans, in order to determine the proportion of each mechanism involved in folate losses. Folate diffusivity constant, calculated according to Fick's second law (Crank, 1975), was 7.4×10(-12) m(2)/s for spinach and 5.8×10(-10) m(2)/s for green beans, which is the same order of magnitude as for sugars and acids for each vegetable considered. Folate thermal degradation kinetics was not monotonous in spinach and green beans especially at 45 °C and did not follow a first order reaction. The proportion of vitamers changed markedly after thermal treatment, with a better retention of formyl derivatives. For spinach, folate losses were mainly due to diffusion while for green beans thermal degradation seemed to be preponderant.

HPLC Analysis of Water-Soluble Vitamins (B2, B3, B6, B12, and C) and Fat-Soluble Vitamins (E, K, D, A, andβ-Carotene) of Okra (Abelmoschus esculentus)

Okra is consumed as a vegetable by populations in Africa and Asia and particularly in Egypt. In this study, we investigated some nutritional components of okra grown in four different geographical locations of Egypt. A comparative analysis of water-soluble vitamins (B2, B3, B6, B12, and C) and fat-soluble vitamins (E, K, D, A, andβ-carotene) in okra pods was carried out. Results of principal component analysis (PCA) showed three clusters of varieties. The first cluster included the Dakahlia (D) and Kafr El-Sheikh (K) varieties. The second and the third clusters separated out the Suez (S) and Mansoura (M) varieties independently. The S pod showed the highest contents of vitamins B6 (49.81 μg/100 g) and E (1.47 mg/100 g) but contained the lowest contents of vitamins B3 (1.42 μg/100 g) and B12 (undetected). The K pod showed the lowest vitamin C content (11.60 mg/100 g). The M pod showed the highest contents of vitamins B3 (22.70 μg/100 g), B12 (91.20 μg/100 g), C (27.14 mg/100 g), and K (0.21 mg/100 g). The D pod showed the lowest contents of vitamins E (0.15 mg/100 g), K (0.05 mg/100 g), and B6 (11.50 μg/100 g). These findings could help develop meal planning at the community level by incorporating okra varieties with high vitamin content.

Occurrence, stability, and determination of formyl folates in foods

The B-vitamin folate has specific tasks as a one-carbon (C1) group supplier in the building and repair of DNA and RNA as well as in the methylation of homocysteine to methionine. Folate occurs in all living cells as a dynamic pool of several interconvertible forms carrying different C1 groups. Along the food chain, this dynamic pool of folates constantly changes due to either enzymatic or chemical interconversions during food processing and storage. These interconversions make it difficult to determine individual folate forms in foods. The formyl folates, the second most predominant forms of food folates, after 5-methyltetrahydrofolate, are particularly prone to interconvert at low pH. Today, this knowledge is often neglected, leading to risks for analytical underestimation of formyl folates. The purpose of the review is to explore the stability and interconversions of formyl folates in foods as well as to analyze the pitfalls in the determination of formyl folates.