叶酸强化食品研究进展

叶酸广泛参与人体内的一碳单位代谢，对促进人体生长发育及维护人体健康有重要意义。天然叶酸主要从食物中获取，但由于叶酸的不稳定性，使叶酸在食品加工过程中损失率较高。为了更好地满足人体营养需求，各类营养素强化食品被逐渐研发，但叶酸强化食品发展缓慢。该文综述食品中叶酸含量与食品加工方式的关系，总结各类叶酸保护剂在提高叶酸稳定性方面的研究，归纳国内外叶酸强化功能性食品的研究进展，以期为高叶酸食品开发提供理论参考和技术支撑。     

叶酸与5-甲基四氢叶酸的生物学特征与应用

叶酸在胚胎期、出生后以及成人期都非常重要,叶酸缺乏会导致多种疾病的发生.近年来,随着国内外相关文献报道,叶酸代谢过程中的关键酶亚甲基四氢叶酸还原酶和甲硫氨酸合成酶还原酶的基因存在多态性,导致个体存在叶酸代谢障碍,由此,对于5-甲基四氢叶酸的开发研究成为关键.本文对叶酸及其代谢过程进行综述,并介绍了活性叶酸及天然化叶酸的...     

乳酸菌发酵代谢合成叶酸的影响因素

对嗜酸乳杆菌以及乳酸乳球菌发酵合成叶酸的影响因素进行了研究。结果表明,乳酸菌代谢合成叶酸的产率为17~100μg/L,菌种、培养时间、pH值、对氨基苯甲酸(PABA)质量浓度会影响乳酸菌合成叶酸的产量。与乳酸乳球菌乳酸亚种相比,嗜酸乳杆菌CH-2生成的叶酸产量要高。不同菌株生成叶酸的能力与pH值有关,嗜酸乳杆菌在pH值为4.2叶酸产率明显下降,乳酸乳球菌乳酸亚种产叶酸的能力则不受pH值影响。添加PABA可以显著提高乳酸菌的叶酸产率。选择适宜的乳酸菌菌株,优化发酵工艺参数可以提高乳及相关食品中叶酸的质量浓度,达到生物方式强化叶酸的效果。     

叶酸饮品加工合理性的研究

研究了pH值、温度、蔗糖浓度、氧化剂浓度、还原剂浓度、光照强度等因素对叶酸稳定性的影响,提出了用啤酒酵母泥提取叶酸,加工成叶酸饮品的适宜工艺条件.     

英研究发现：未被吸收的合成叶酸进入血液会引起健康问题

英国食品研究所研究人员Lj前提醒人们慎用合成叶酸，因为未被吸收的合成叶酸如果进入血液，可能会引起一系列健康问题。 研究人员在最新出版的《英国营养学杂志》（Britisn Journal of Nutrition）上发表论文说，研究发现绿叶蔬菜等含有的天然叶酸在人的肠道中被吸收，而合成叶酸是在肝脏内被吸收的。肝脏吸收合成叶酸的量有限，未被吸收的过量合成叶酸会进入血液，有可能引起白血病、关节炎等疾病。     

食品中叶酸测定方法的研究进展

叶酸作为一类人体必需的B族维生素,在人体代谢循环中起到十分重要的作用。人体不能自身合成叶酸,只能从食品中摄取,叶酸缺乏症是全世界范围公认的保健问题,世界卫生组织明确提出了每日叶酸推荐摄入量。天然食品中叶酸含量普遍较低,一些国家进而在谷物制品、婴幼儿奶粉中添加人工合成叶酸;天然强化叶酸的特殊膳食、保健食品也越来越多。因此食品中叶酸含量的准确测定十分关键。本文综述了食品中叶酸提取关键环节与常见的分析检测方法,比较了微生物法、液相色谱法、液相色谱-质谱联用法、荧光法、电化学法等优劣势,期望为建立快速、准确测定食品中叶酸的方法提供参考。     

植物源食品中叶酸的生物合成与调控及其提取与检测技术研究进展

叶酸作为一碳代谢时的辅因子,是生物体的必需物质,对人体健康至关重要。本文综述了植物源食品中叶酸的类型与结构、叶酸合成途径及相关酶、叶酸代谢调控、发芽富集技术、叶酸提取与检测技术,并对开发快速而准确的叶酸测定方法、研发植物性食品中叶酸的富集与提取技术进行了展望。     

抗坏血酸浸渍后草莓中天然叶酸稳定性的变化

为研究抗坏血酸（Ascorbic Acid,AsA）浸渍后草莓中叶酸稳定性的变化,该研究采用真空（0.09 MPa）和常压两种方式浸渍AsA,对比浸渍速率以及浸渍后中天然叶酸的稳定性及草莓的新鲜度。同时探讨真空浸渍AsA的草莓在8 d冷藏过程中,天然叶酸的含量及质构的变化。结果表明,真空浸渍AsA的传质速率更快（k2=0.01）,浓度更高（1.24 mg/g）。草莓中总叶酸含量为100~128 μg/100 g,主要叶酸种类为5-甲基四氢叶酸、四氢叶酸、5,10-亚甲基四氢叶酸及叶酸降解产物或合成底物对氨基苯甲酸。草莓经8 d冷藏后,真空浸渍组和对照组的四氢叶酸分别下降了7.70%和42.51%,对氨基苯甲酸分别上升了57.13%和77.89%,5,10-亚甲基四氢叶酸均未出现显著性变化（p>0.05）,5-甲基四氢叶酸在第4天分别上升了24.47%和12.67%。质构结果表明,第8天时,真空浸渍组硬度（92.60 N）明显高于对照组（57.20 N）。因此,真空浸渍AsA处理可以抑制四氢叶酸降解（p<0.05）,从而提高叶酸在冷藏中的稳定性,保护草莓的质地。该研究为提高草莓叶酸稳定性提供了理论依据和参考。     

叶酸功能性和叶酸强化食品

<正>从1998年1月1日起,美国食品与医药管理局(FDA)开始实施谷物制品必须强化叶酸规定。这是食品强化历史上一个重要事件。这个决定反映了当今食品工业一个发展趋势:营养素不仅用以满足日常营养需要,更应用以预防疾病。FDA自1993年10月起,开始对膳食中叶酸效果进行了讨论。当时,FDA曾建议将叶酸添加到面粉、面包和其它谷物制品中去,以降低发生胎儿神经管缺陷的危险,并允许将此优点标明在富含叶酸的食品标签上。经三年多深入讨论,FDA终于1996年3月5日发布修正叶酸强化标准的法规。     

外源调控叶酸代谢对谷氨酸棒杆菌SYPS-062积累L-丝氨酸的影响

通过外源添加叶酸合成前体对氨基苯甲酸、叶酸途径抑制剂氨甲喋呤扰动叶酸代谢,考察了叶酸对谷氨酸棒杆菌SYPS-062合成L-丝氨酸的影响。实验结果表明,添加对氨基苯甲酸(0~0.4μg/mL)能够促进菌体的生长(最大值为7.8±0.24 g/L),但可显著降低其产酸能力;而添加氨甲喋呤(0~100μg/mL)抑制了谷氨酸棒杆菌SYPS-062的生长,但可提高其单位菌体产酸的能力;代谢通量分析表明,作为调控点的叶酸代谢在SYPS-062生长及积累L-丝氨酸中占主导地位。     

Folate: A Functional Food Constituent

ABSTRACT:  Folate, a water-soluble vitamin, includes naturally occurring food folate and synthetic folic acid in supplements and fortified foods. Mammalian cells cannot synthesize folate and its deficiency has been implicated in a wide variety of disorders. A number of reviews have dwelt up on the health benefits associated with increased folate intakes and many countries possess mandatory folate enrichment programs. Lately, a number of studies have shown that high intakes of folic acid, the chemically synthesized form, but not natural folates, can cause adverse effects in some individuals such as the masking of the hematological manifestations of vitamin B₁₂ deficiency, leukemia, arthritis, bowel cancer, and ectopic pregnancies. As fermented milk products are reported to contain even higher amounts of folate produced by the food-grade bacteria, primarily lactic acid bacteria (LAB), the focus has primarily shifted toward the natural folate, that is, folate produced by LAB and levels of folate present in foods fermented by/or containing these valuable microorganisms. The proper selection and use of folate-producing microorganisms is an interesting strategy to increase "natural" folate levels in foods. An attempt has been made through this review to share information available in the literature on wide ranging aspects of folate, namely, bioavailability, analysis, deficiency, dietary requirements, and health effects of synthetic and natural folate, dairy and nondairy products as a potential source of folate, microorganisms with special reference to  Streptococcus thermophilus  as prolific folate producer, and recent insight on modulation of folate production levels in LAB by metabolic engineering.     

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.     

Application of the Key Events Dose-response Framework to Folate Metabolism

Folate is a vitamin that plays a role as a cofactor and coenzyme in many essential reactions. These reactions are interrelated and any change in folate homeostasis could affect other reactions. With food fortified with folic acid, and use of multivitamin, unmetabolized folic acid (UMFA) has been detected in blood circulation, particularly among older adults. This has raised concern about the potential harmful effect of high folic acid intake and UMFA on health conditions such as cognitive dysfunction and cancer. To examine what is known about folate metabolism and the release of circulating UMFA, the Key Events Dose-Response Framework (KEDRF) was used to review each of the major key events, dose-response characteristics and homeostatic mechanisms of folate metabolism. The intestine, liver and kidneys each play essential roles in regulating body folate homeostasis. But the determining event in folate metabolism leading to the release of UMFA in circulation appears to be the saturation of dihydrofolate reductase in the liver. However, at each of the key events in folate metabolism, limited information is available on threshold, homeostatic regulation and intracellular effects of folic acid. More studies are needed to fill in the knowledge gaps for quantitatively characterizing the dose-effect relationship especially in light of the call for extending folate fortification to other foods.     

Low folate content in gluten-free cereal products and their main ingredients

Folate content in some gluten-free cereal products and their main ingredients was determined using a validated method based on reversed-phase high performance liquid chromatography (HPLC) with fluorescence and diode array detection. The main folate forms found in gluten-free products were 5-methyl-tetrahydrofolate and tetrahydrofolate. Starches and low protein flours commonly used as main components in gluten-free products appeared to be poor folate sources with folate content ?6 μg/100 g fresh weight. Folate content in gluten-free breads was higher (15.1–35.9 μg folate/100 g fresh weight) due to use of bakery yeast which is a rich folate source. Overall, folate content in gluten-free products was lower than in their gluten-containing counterparts. Therefore, fortification of gluten-free products with folic acid or enrichment of these products with nutrient-dense fractions of cereals naturally free from gluten (such as buckwheat, quinoa, amaranth or millet) can be of interest.     

Folate concentrations of fast foods measured by trienzyme extraction method

Folate concentrations in common fast foods containing beef were measured using a new trienzyme folate extraction method and compared to the values using traditional folate conjugase. A total of 56 fast foods were purchased from local restaurants after the 1998 mandate of folic acid fortification in enriched cereal grains. One serving of hamburger, sandwich, pizza (one eighth of a 30-cm pizza) and Mexican foods contained a mean of 314 (±98, S.D.), 401 (±115), 221 (±45) and 282 (±126) μg of folate, respectively. Breakfast items provided the lowest folate amount among the foods (165±89 μg per serving). These values are markedly higher than those in the literature most likely due to the mandate of folic acid fortification in cereal-grain products and the use of the new folate extraction technique. We hope that the information presented here is a useful means to accurately calculate dietary folate intake.     

HPLC Determination of Folate in Liver and Liver Products

Our objective was to produce reliable data on the contents of folate vitamers in pig, beef and chicken liver, beef kidney and some liver products. Folate contents were determined in monoglutamate form, using reversed-phase HPLC. Pig and beef livers contained 730-1470 mg folates in 100g, tetrahydrofolate being the most abundant form detected. Frozen chicken liver also contained about 1000 μg folates in 100g. Processed foods containing liver, except canned baby foods, were also good folate sources. In processed foods, 5-methyltetrahydrofolate was the predominant folate form. The detected folate contents were high, compared with published data.     

Bacterial folate biosynthesis and colorectal cancer risk: more than just a gut feeling

Abstract

Folate is a B-vitamin with an important role in health and disease. The optimal folate status with regard to human health remains controversial. A low intake of natural folate as well as excessive intake of synthetic folic acid, were previously linked to an increased risk of colorectal cancer or with aberrant molecular pathways related to carcinogenesis in some studies. Importantly, most studies conducted so far, solely focused on dietary intake or circulating levels of folate in relation to cancer risk. Notably, diet or dietary supplements are not the only sources of folate. Several bacteria in the gastrointestinal tract can synthesize B-vitamins, including folate, in quantities that resemble dietary intake. The impact of bacterial folate biosynthesis concerning human health and disease remains unexplored. This review highlights current insights into folate biosynthesis by intestinal bacteria and its implications for processes relevant to cancer development, such as epigenetic DNA modifications and DNA synthesis. Moreover, we will reflect on the emerging question whether food-grade or intestinal bacteria can be considered a potential target to ensure sufficient levels of folate in the gastrointestinal tract and, hence the relevance of bacterial folate biosynthesis for disease prevention or treatment.     

Critical evaluation of folate data in European and international databases: recommendations for standardization in international nutritional studies

Scope: The objective was to perform an inventory and critical evaluation of folate data in selected European and international databases. The ultimate aim was to establish guidelines for compiling standardized folate databases for international nutritional studies. Methods and results: An ad hoc questionnaire was prepared to critically compare and evaluate folate data completeness, quantification, terminologies, and documentation of 18 European and international databases, and national fortification regulations. Selected countries participated in the European Prospective Investigation into Nutrition and Cancer project and European Food Information Resource Network (EuroFIR). Folate completeness was generally high. “Total folate” was the most common terminology and microbiological assay was the most frequently reported quantification method. There is a lack of comparability within and between databases due to a lack of value documentation, the use of generic or non‐appropriate terminologies, folate value conversions, and/or lack of identification of synthetic folic acid. Conclusion: Full value documentation and the use of EuroFIR component identifiers and/or INFOODS tagnames for total folate (“FOL”) and synthetic folic acid (“FOLAC”), with the additional use of individual folates, will increase comparability between databases. For now, the standardized microbiological assay for total folate and HPLC for synthetic folic acid are the recommended quantification methods.     

Blood as a surrogate marker for tissue-specific DNA methylation and changes due to folate depletion in post-partum female mice

Scope : DNA methylation patterns are tissue specific and may influence tissue‐specific gene regulation. Human studies investigating DNA methylation in relation to environmental factors primarily use blood‐derived DNA as a surrogate for DNA from target tissues. It is therefore important to know if DNA methylation changes in blood in response to environmental changes reflect those in target tissues. Folate intake can influence DNA methylation, via altered methyl donor supply. Previously, manipulations of maternal folate intake during pregnancy altered the patterns of DNA methylation in offspring but, to our knowledge, the consequences for maternal DNA methylation are unknown. Given the increased requirement for folate during pregnancy, mothers may be susceptible to aberrant DNA methylation due to folate depletion. Methods and results : Female mice were fed folate‐adequate (2 mg folic acid/kg diet) or folate‐deplete (0.4 mg folic acid/kg diet) diets prior to mating and during pregnancy and lactation. Following weaning, dams were killed and DNA methylation was assessed by pyrosequencing^® in blood, liver, and kidney at the Esr1, Igf2 differentially methylated region (DMR)1, Igf2 DMR2, Slc39a4CGI1, and Slc39a4CGI2 loci. We observed tissue‐specific differences in methylation at all loci. Folate depletion reduced Igf2 DMR1 and Slc39a4CGI1 methylation across all tissues and altered Igf2 DMR2 methylation in a tissue‐specific manner (p<0.05). Conclusion : Blood‐derived DNA methylation measurements may not always reflect methylation within other tissues. Further measurements of blood‐derived and tissue‐specific methylation patterns are warranted to understand the complexity of tissue‐specific responses to altered nutritional exposure.     

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‐H₄folate, 5‐CH₃‐H₄folate, and, finally, H₄folate. Further studies are required, especially on the diffusion of the vitamers in real foods and on the determination of folate degradation products.