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

How food matrices modulate folate bioaccessibility: A comprehensive overview of recent advances and challenges

The incomplete absorption of dietary folate makes it crucial to understand how food matrices affect folate bioaccessibility. Bioavailability encompasses bioaccessibility, which depicts the proportion that is liberated from the food matrix during digestion and becomes available for absorption. Bioavailability studies are expensive and difficult to control, whereas bioaccessibility studies utilize in vitro digestion models to parameterize the complex digestion, allowing the evaluation of the effect of food matrices on bioaccessibility. This review covers the folate contents in various food matrices, the methods used to determine and the factors affecting folate bioaccessibility, and the advances and challenges in understanding how food matrices affect folate bioaccessibility. The methods for determining bioaccessibility have been improved in the last decade. Current research shows that food matrices modulate folate bioaccessibility by affecting the liberation and stability of folate during digestion but do not provide enough information about folate and food component interactions at the molecular level. In addition, information on folate interconversion and degradation during digestion is scant, hindering our understanding of the impact of food matrices on folate stability. Moreover, the role of conjugase inhibitors should not be neglected when evaluating the nutritional value of food folates. Due to the complexity of food digestion, holistic methods should be applied to investigate bioaccessibility. By synthesizing the current state of knowledge on this topic, this review highlights the lack of in-depth understanding of the mechanisms of how food matrices modulate folate bioaccessibility and provides insights into potential strategies for accurate evaluation of the nutritional value of dietary folate.

Scientific opinion on the tolerable upper intake level for folate

Following a request from the European Commission (EC), the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver a scientific opinion on the revision of the tolerable upper intake level (UL) for folic acid/folate. Systematic reviews of the literature were conducted to assess evidence on priority adverse health effects of excess intake of folate (including folic acid and the other authorised forms, (6S)-5-methyltetrahydrofolic acid glucosamine and l-5-methyltetrahydrofolic acid calcium salts), namely risk of cobalamin-dependent neuropathy, cognitive decline among people with low cobalamin status, and colorectal cancer and prostate cancer. The evidence is insufficient to conclude on a positive and causal relationship between the dietary intake of folate and impaired cognitive function, risk of colorectal and prostate cancer. The risk of progression of neurological symptoms in cobalamin-deficient patients is considered as the critical effect to establish an UL for folic acid. No new evidence has been published that could improve the characterisation of the dose-response between folic acid intake and resolution of megaloblastic anaemia in cobalamin-deficient individuals. The ULs for folic acid previously established by the Scientific Committee on Food are retained for all population groups, i.e. 1000 μg/day for adults, including pregnant and lactating women, 200 μg/day for children aged 1-3 years, 300 μg/day for 4-6 years, 400 μg/day for 7-10 years, 600 μg/day for 11-14 years and 800 μg/day for 15-17 years. A UL of 200 μg/day is established for infants aged 4-11 months. The ULs apply to the combined intake of folic acid, (6S)-5-methyltetrahydrofolic acid glucosamine and l-5-methyltetrahydrofolic acid calcium salts, under their authorised conditions of use. It is unlikely that the ULs for supplemental folate are exceeded in European populations, except for regular users of food supplements containing high doses of folic acid/5-methyl-tetrahydrofolic acid salts.

5-Methyltetrahydrofolate Is a Crucial Factor in Determining the Bioaccessibility of Folate in Bread

This study investigated the bioaccessibility of folate in wheat bread baked with different ingredients and processing methods. Next, different matrices were spiked with 5-methyltetrahydrofolate, gallic acid (GA), or both to investigate the stability of 5-methyltetrahydrofolate during in vitro digestion. The folate bioaccessibility in bread varied from 44 to 96%. The inclusion of whole-grain or faba bean flour significantly improved both folate content and bioaccessibility. Baking with yeast increased the folate content by 145% in bread but decreased folate bioaccessibility compared to the bread without added yeast because of the instability of 5-methyltetrahydrofolate. Spiking experiments confirmed oxidation as a critical reason for 5-methyltetrahydrofolate loss during digestion. However, GA protected this vitamer from degradation. Additionally, 5-methyltetrahydrofolate was less stable in whole-grain wheat matrices than other matrices. This study demonstrated that the stability of 5-methyltetrahydrofolate is crucial for folate bioaccessibility in bread, and methods for stabilizing this vitamer should be further studied.

Folate contents in insects as promising food components quantified by stable isotope dilution

Concerning the increasing population, edible insects are of growing interest due to several advantages such as sustainable production and as a source of high-quality nutrients. One of the less studied nutrients are folates, in the context of insects is folates, which play an important role in human metabolism. In the article, we describe how six different insect species are reared and extracted for five common folate vitamers by high-performance liquid chromatography interfaced with tandem mass spectrometry (LC-MS/MS). For this purpose, house crickets (Acheta domesticus—adults), Jamaican field crickets (Gryllus assimilis—adults), discoid cockroaches (Blaberus discoidalis—nymphs), migratory locusts (Locusta migratoria—adults), mealworms (Tenebrio molitor), and lesser mealworms (Alphitobius diaperinus) were investigated. The total folate content differs between 59.1 ± 6.50 and 143 ± 11.1 μg/100 g. Also, the feed, which was adapted to the needs of the insects and differed for some species, was extracted for their total folate content. The four different feed compositions (rapeseed, chicken feed, bramble leaves, and a mix of chicken feed, wheat bran, and carrot/apples) showed a folate content of about 100 μg/100 g, except for hay, where the content was 300 μg/100 g. In general, the insect folate content is comparable to other food and seems to be a promising source of folates. However, the amount of consumption needed to meet the requirement must also be considered. Moreover, the effect of different influencing factors is not yet entirely clear and needs further investigation.

The Bioaccessibility of Folate in Breads and the Stability of Folate Vitamers during in vitro Digestion

Both the liberation and stability of endogenous folate are relevant to the bioaccessibility of folate. Since folates are unstable, in addition to studying the natural folate content in foods, bioaccessibility...

Highly sensitive analytical method for the accurate determination of 5-methyltetrahydrofolic acid monoglutamate in various volumes of human plasma using isotope dilution ultra-high performance liquid chromatography-mass spectrometry

One predominant and bioactive folate vitamer circulating in the blood is 5-methyltetrahydrofolate (5-Me-THF). In this study, a method for the accurate determination of 5-Me-THF in human plasma samples of various volumes was established using isotope dilution ultra-high performance liquid chromatography-mass spectrometry (ID-UPLC-MS). For this purpose, 500 μL of homogeneous human plasma was initially employed, and the 5-Me-THF and the ¹³C₅-5-Me-THF standard solutions prepared using 1% ascorbic acid in water gave the calibration solution and spiking sample. The desired amount of ¹³C₅-5-Me-THF standard solution was spiked into the sample followed by sample pretreatment. The method was validated for its repeatability, reproducibility, recovery, and limits of detection and quantification. Subsequently, it was applied to smaller volumes of human plasma samples (i.e., 50 and 10 μL), the results of which corresponded well with those obtained using 500 μL. The feasibility of the method was further confirmed using 10 μL of a standard reference material, SRM 3949, which is a human serum sample containing three different levels of 5-Me-THF. The established ID-UPLC-MS method was successfully applied to various volumes of human plasma or serum ranging from 500 to 10 μL, which exhibited particularly good sensitivity in addition to reliable results for the quantification of 5-Me-THF. Our method therefore expands on the ability to obtain accurate quantitative results for 5-Me-THF using small volumes of blood.

The combined effect of fermentation of lactic acid bacteria and in vitro digestion on metabolomic and oligosaccharide profile of oat beverage

Oat (Avena sativa L.) is widely appreciated for its beneficial properties for human health, which have led to the introduction of more food products on the market, including oat beverages. The fibre components found in the oat are recognized for their beneficial effects, despite other bioactive compounds with healthy properties being present. This work aimed to evaluate the metabolites profile of a commercial oat beverage, either fermented with lactic bacteria or not, following in vitro gastro-intestinal digestion. UHPLC-QTOF untargeted metabolomics allowed investigation of the bioaccessibility of health-related metabolites from the oat beverage at the intestinal level. The results identified flavonoids, phenolic acids (avenanthramides), amino acids and steroids as the major classes of compounds. In particular, after in vitro digestion, amino acids, peptides, and phenolic acids showed the highest increases. The co-fermentation of oat milk by Lactobacillus spp. and Bifidobacterium spp. strains decreased the levels of both lignans and phytic acid, while increased the levels of some polyphenols like avenanthramides. Furthermore, fermentation by microorganisms increased the bioaccessibility of specific amino acids, vitamins, and polyphenols (flavonoids and phenolic acids). Interestingly, despite lacking a significant part of beta-glucans, the HPAEC-PAD profiling of our oat beverage evidenced that the fermentation process did not alter the oligosaccharides profile, thus preserving its prebiotic potential. The phytochemical profile of oat milk was shown to have a functional potential. Nonetheless, the fermentation by bacterial strains changed the profile of metabolites during in vitro digestion, thus offering an interesting option in the future development of cereal-based beverages.

Bioaccessibility of folate in faba bean, oat, rye and wheat matrices

Cereals and legumes are rich in folate. However, due to the instability of folate, processing and digestion can induce significant folate loss. In this paper, folate bioaccessibility of faba bean, oat, rye and wheat flours and pastes was studied using a static in vitro digestion model. Folate bioaccessibility depended on food matrices, varying from 42% to 67% in flours and from 40% to 123% in pastes. Digestion was associated with the interconversion of formyl folates, as well as the increase of oxidised vitamers and decrease of reduced vitamers. Especially in faba bean, 5-methyltetrahydrofolate showed surprisingly good stability both in digestion and heat treatment, resulting in high bioaccessibility. The physiological concentration of ascorbic acid did not stabilise folate in digestion; however, a higher level helped to maintain reduced vitamers. Heat treatment (10-min paste making) could improve folate bioaccessibility by liberating folate from the food matrices and by altering folate vitamer distribution.

In-vitro bioaccessibility and bioavailability of heavy metals in mineral clay complex used in natural health products

Commercial mineral clays that claim to have healing properties are also known to contain trace amounts of heavy metals, albeit the risk of consuming many of them is not entirely known. The primary objective of this study was to evaluate the in vitro bioaccessibility and bioavailability of Arsenic (As), Cadmium (Cd) and Lead (Pb) in mineral clay samples collected from the Sierra Mountains (USA) using the Unified Bioaccessibility Research Group of Europe (UBM) method and the Caco-2 permeability assay, respectively. After UMB-gastric (UBM-G) digestion, As and Pb bioaccessibility were lower compared to Cd and decreased further in the UMB-gastrointestinal (UBM-GI) assay. Bioavailability estimates using the Caco-2 cell showed very low to non-detectable permeability for all 3 heavy metals. Thus, while initial heavy metal ranged from 3.8–17 ppm, 0.024–0.061ppm, and 5.8–20 ppm for As, Cd, and Pb, respectively, the bioavailability for these metals was reduced to very low levels that followed: non-detectable values of As, <0.007ppm of Cd, and <0.1ppm of Pb. Using UBM-digestion to mimic bioaccessibility, followed by Caco-2 cell bioavailability enabled us to conclude that in vitro assessment of heavy metal exposure associated with mineral clay-based natural health products does not pose a potential hazard to consumers.

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.

Promising Tropical Fruits High in Folates

As the popularity of tropical fruits has been increasing consistently during the last few decades, nutritional and health-related data about these fruits have been gaining more and more interest. Therefore, we analyzed 35 samples of tropical fruits and vegetables with respect to folate content and vitamer distribution in this study. The fruits and vegetables were selected by their availability in German supermarkets and were grouped according to their plant family. All fruits and vegetables were lyophilized and analyzed by stable isotope dilution assay (SIDA) and liquid chromatography mass spectrometry (LC-MS/MS). The results vary from 7.82 ± 0.17 µg/100 g in the horned melon to 271 ± 3.64 µg/100 g in the yellow passion fruit. The yellow passion fruit is a good source for meeting the recommended requirements, as just 110 g are needed to cover the recommended daily intake of 300 µg folate for adults; however, longan fruits, okras, pete beans, papayas, mangos, jack fruits, and feijoas are also good sources of folates. In conclusion, the study gives a good overview of the total folate content in a broad range of tropical fruits and vegetables and shows that some of these fruits definitely have the potential to improve the supply of this critical vitamin.

Influence of passion fruit by-product and fructooligosaccharides on the viability of Streptococcus thermophilus TH-4 and Lactobacillus rhamnosus LGG in folate bio-enriched fermented soy products and their effect on probiotic survival and folate bio-accessibility under in vitro simulated gastrointestinal conditions

This study aimed to evaluate the influence of passion fruit by-product (PFBP) and fructooligosaccharides (FOS) on the viability of Streptococcus thermophilus TH-4 and Lactobacillus rhamnosus LGG in folate bio-enriched fermented soy products and their effect on probiotic survival and folate bio-accessibility under in vitro simulated gastrointestinal conditions during storage of the products at 4 °C for up to 28 days (at days 1, 14, and 28). Kinetic parameters and folate contents before and after fermentation were also evaluated. Four different bio-enriched soy products in which the two microorganisms were used in co-cultures were studied and PFBP and/or FOS were added at 1 g/100 g, except for the control product. No differences (p < 0.05) between the fermented soy products (FSP) were observed for the maximum acidification rate (Vmax) and the time to reach the Vmax (Tmax) or pH 5.5 (Tf), indicating that the use of PFBP and/or FOS did not affect the fermentation kinetic parameters. Only Lb. rhamnosus LGG retained the desired viability (>8 log CFU/mL) during storage, whereas St. thermophilus TH-4 populations decreased by day 14 reaching counts between 6.4 and 5.5 log CFU/mL by day 28. The folate content of all FSP increased after fermentation and the simultaneous presence of PFBP and FOS stimulated the co-culture to increase folate production. Folate content in all FSP decreased during storage. Lb. rhamnosus LGG was recovered at the end of the simulated digestion, but PFBP and/or FOS did not affect recovery. The folate content increased during the gastrointestinal assay for all FSP, especially for FSP without supplementation, suggesting an in vitro increase of folate bio-accessibility. Therefore, the bio-enriched probiotic FSP presented a great potential as an innovative functional food by delivering probiotic microorganisms and providing 14% of the recommended daily folate intake. The folate content of the FSP might be increased during gastrointestinal stress conditions, which could contribute to increase the folate bio-accessibility in the gut.

Durian Fruits Discovered as Superior Folate Sources

Durian (Durio zibethinus) is a tropical fruit grown in Southeast Asia and highly appreciated by consumers throughout Asia. Folates are a group of vitamins and are essential nutrients for humans. Here we present the folate analysis of different durian cultivars as well as diverse durian products. An LC-MS/MS method and the application of a stable isotope dilution assay (SIDA) was used for quantitation of the folate vitamers 5-methyltetrahydrofolate, 5-formyltetrahydrofolate, 10-formylfolate, tetrahydrofolate, and pteroylmonoglutamic acid by using [¹³C₅]-labeled internal standards. Total folates varied from 175 to 440 μg/100 g for durian arils and from 15.0 to 417 μg/100 g for durian products. These contents are extraordinarily high compared to other fruits and may be correlated to the upregulated methionine biosynthesis pathway reported recently. In summary, the tropical fruit durian can be considered as a very rich dietary source of natural folates.

Experimental folate deficiency in human subjects: what is the influence of vitamin C status on time taken to develop megaloblastic anaemia?

BACKGROUND

In 1962 Victor Herbert developed megaloblastic anaemia four months after commencing a severely folate-deficient diet whereas, in his self-experiment 50 years later, this author took 19 months to fully deplete his liver folate store. This author proposed that his own larger initial liver folate store, due to his vegetarian diet and consumption of fortified foods, was the cause of the time difference.

MAIN TEXT

This author now proposes that Herbert was also likely to have been deficient in vitamin C, thus shortening the time taken to develop folate deficiency. Several human experiments have confirmed the role of vitamin C in protecting reduced forms of folate from oxidation. Although there has historically been no consensus on the required intake of vitamin C, and official recommendations set a level below that required to ensure plasma saturation, recent research supports an intake that would ensure saturation. There have been no longitudinal experiments on human subjects since the introduction of voluntary or mandatory folic acid fortification of food, and the few published models differ significantly in their estimates of human liver folate storage capacity.

CONCLUSION

Because of the importance of folate in one-carbon metabolism, the potential influence of vitamin C intake on the time taken to deplete the liver folate store should be experimentally investigated.

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.

Emerging opportunities in exploring the nutritional/functional value of amaranth

Amaranthusspp. is a highly nutritive pseudocereal, rich in macronutrients and micronutrients, including vitamins and minerals.