积累5-甲基四氢叶酸双抗突变株的选育及条件优化

目的 选育积累5-甲基四氢叶酸(5-MTHF)的双重药物抗性高产突变株,探讨发酵时间和温度对叶酸积累形式的影响.方法 紫外线和EMS联合诱变;磺胺、甲氨蝶呤药物培养基筛选菌株;单因素实验检测发酵条件对叶酸积累形式的影响;HPLC检测叶酸含量和存在形式.结果 获得稳定性良好的抗性突变株,其叶酸产量是原始菌株的2.2倍.适合5-MTHF积累的发酵时间为16 h,积累量为68.94 μg/g干菌.结论 抗性突变株能提高菌株产叶酸能力,5-MTHF含量受发酵时间影响大,而发酵温度对产物形式和产量影响不显著.     

9个柑橘品种不同组织中5-甲基四氢叶酸含量的比较

以9个不同种和品种柑橘为试验原料,采用反相高效液相荧光检测法(RP-HPLC-FLD)测定不同柑橘品种中各组织5-甲基四氢叶酸的含量。结果表明:甜橙类果实果肉中含5-甲基四氢叶酸最高,尤以哈姆林甜橙最高,为29.28μg/100 g;其次为柚类,沙田柚果肉中5-甲基四氢叶酸的含量为23.45μg/100 g,梁平柚15.01μg/100 g;柑类品种果实果肉5-甲基四氢叶酸的含量较低,早津温州蜜柑果肉中的5-甲基四氢叶酸含量为15.58μg/100 g,台湾椪柑8.92μg/100 g;柠檬中的含量最低,只有4.1μg/100 g。大多数品种中,不同组织5-甲基四氢叶酸含量的基本排序为种子>果肉>囊衣>果皮。从整体上看,甜橙类果实中5-甲基四氢叶酸的含量最高。     

积累5-甲基四氢叶酸双抗突变株的选育及条件优化

目的选育积累5-甲基四氢叶酸（5-MTHF）的双重药物抗性高产突变株,探讨发酵时间和温度对叶酸积累形式的影响。方法紫外线和EMS联合诱变;磺胺、甲氨蝶呤药物培养基筛选菌株;单因素实验检测发酵条件对叶酸积累形式的影响;HPLC检测叶酸含量和存在形式。结果获得稳定性良好的抗性突变株,其叶酸产量是原始菌株的2.2倍。适合5-MTHF积累的发酵时间为16 h,积累量为68.94μg/g干菌。结论抗性突变株能提高菌株产叶酸能力,5-MTHF含量受发酵时间影响大,而发酵温度对产物形式和产量影响不显著。     

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。     

高效液相荧光检测法测定柑橘中5-甲基四氢叶酸的含量

利用5-甲基四氢叶酸自身产生荧光的特性,建立高效液相荧光检测法来测定柑橘中5-甲基四氢叶酸的含量。使用ODS-C18反相色谱分离柱,流动相为6%乙腈,94%0.05mol/L磷酸二氢钾溶液(pH3.0)作为流动相,流速1.0mL/min,柱温23℃,进样量为20μL,激发波长为290nm,发射波长为360nm。结果表明,5-甲基四氢叶酸在0.003μg/mL-0.1μg/mL有良好的线性关系,相关系数为0.9999,检出限为0.01ng/mL,样品测定的精密度为0.99%,样品加标平均回收率为96.6%。建立的高效液相荧光检测法具有良好的精密度和回收率,适合用于柑橘中5-甲基四氢叶酸的测定。     

叶酸与食管癌关系的研究进展

叶酸在DNA合成、修复和甲基化过程中有重要作用,可能与肿瘤的发生发展相关。目前国内外有关叶酸与食管癌关系的研究越来越多,研究的角度和方法有所不同,但有关叶酸与食管癌发生的内在机理研究较少,大部分研究集中在叶酸代谢关键酶亚甲基四氢叶酸还原酶(MTHFR)基因多态性与食管癌的关联性,目前研究结果存在不确定性,需要进一步的探讨。本文综述近年来国内外有关食管癌与叶酸关系的研究进展。     

L-5-甲基四氢叶酸钙液相分析方法验证

依据2015版中华人民共和国药典第四部通则中《9101药品质量标准分析方法验证指导原则》的要求,对L-5-甲基四氢叶酸钙液相分析方法进行了验证,结论：检出限为0.015μg/mL,定量限为0.05,μg/mL,RSD为0.31%,加标回收率范围97.3%-114%,方法适用。     

烹饪及贮藏对八种常见叶菜中叶酸含量的影响

叶菜是居民膳食叶酸的主要来源,我国叶菜种类丰富。为探明常见叶菜中叶酸含量及日常烹饪、贮藏对其影响,以期最大程度保留叶菜中叶酸,以八种常见叶菜为对象,液相色谱检测分析叶菜中5-甲基四氢叶酸和叶酸含量,并研究水煮、清炒、蒸制及冷藏过程中5-甲基四氢叶酸及叶酸含量变化。结果表明:菠菜中5-甲基四氢叶酸含量最高,为75.32μg/100 g,其它依次为小白菜、大白菜、生菜、紫甘蓝、青菜、甘蓝、油麦菜;叶菜中叶酸含量远低于5-甲基四氢叶酸,甘蓝中甚至无检出;烹饪方法对叶菜中5-甲基四氢叶酸和叶酸含量均有不同程度的影响,蒸制可以较好保持叶菜中叶酸含量,水煮次之,清炒效果最差;从叶酸保持角度考虑,叶菜4℃贮藏不宜超过2 d。选择合理烹饪方式及贮藏时间可有效降低叶菜中叶酸损失,进而有望改善居民叶酸缺乏现状。     

叶酸形式、稳定性及天然化叶酸的研究进展

叶酸作为甲基供体参与了许多重要的生物化学反应过程。叶酸缺乏会引发新生儿神经管畸形、癌症、心血管疾病等。天然叶酸存在于各类食品中，但稳定性差，在加工过程中会大量损失，生物利用度低。合成叶酸常用于膳食补充剂及强化食品中，相比天然叶酸稳定性较好，生物利用度较高，但存在代谢风险。天然化叶酸是天然叶酸的稳定形式，无代谢障碍，可直接被人体吸收利用。目前，天然叶酸和合成叶酸的稳定性研究通常只聚焦在pH、温度、光照、氧气等其中一个因素。本文对比了天然叶酸和合成叶酸的代谢途径，总结了光照、温度、pH和氧气对天然叶酸和合成叶酸稳定性的影响。另外，介绍了天然化叶酸的研究进展，为其在食品领域中的开发应用提供理论依据。     

叶酸代谢抑制剂对小鼠骨髓基质细胞增殖和分化的影响

采用四甲基偶氮唑蓝（methyl thiazolyl tetrazolium,MTT）法、细胞形态分析法及诱导分化法结合油红O染色法研究叶酸代谢中二氢叶酸还原酶抑制剂甲氨喋呤（methotrexate,MTX）、甲氨苄啶（trimethoprim,TMP）和乙胺嘧啶（pyrimethamine,PTM）对OP9小鼠骨髓基质细胞增殖和分化的影响,探讨叶酸代谢与脂质合成的关系。MTT实验结果显示,在一定浓度范围内,3 种叶酸抑制剂均能抑制OP9细胞增殖,并呈现一定的剂量-效应依赖关系。且3 种叶酸抑制剂在高浓度时对OP9细胞有毒性作用。倒置显微镜观察和油红O染色检测结果显示,TMP在500～1 000 μmol/L浓度范围内对OP9细胞分化为脂肪细胞具有抑制作用。荧光定量聚合酶链式反应分析表明,TMP会使叶酸代谢途径中二氢叶酸还原酶和亚甲基四氢叶酸脱氢酶的转录水平发生下调,这可能是TMP抑制脂肪细胞诱导分化的原因。     

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.     

Folic acid fortification of parboiled rice: Multifactorial analysis and kinetic investigation

Folic acid fortification of parboiled rice has been systematically studied to obtain quantitative insights into the role of key process variables. Parboiling was conducted with brown rice soaked at 70 °C for 1, 2 and 3 h with four different fortificant concentrations added and dried parboiled rice was milled for three durations (i.e. 0, 60 and 120 s). Both residual folate concentration in treated parboiled rice and pH of the soaking water after soaking stages were measured. Multifactorial model was developed to describe the residual folate retention behaviour and suggested that both soaking and milling were significant factors in folic acid fortification. The optimum soaking time was deduced to be 1.97 h. Folate retention rate followed a 1st order kinetics while the rates of natural rice hydrolysis and folate uptake were both time-dependent.     

The Beneficial Effect of Folate‐Enriched Egg on the Folate and Homocysteine Levels in Rats Fed a Folate‐ and Choline‐Deficient Diet

Abstract: We investigated the effects of folate‐enriched egg yolk powder on folate and homocysteine levels in plasma and liver of rats fed the folate‐ and choline‐deficient diet to determine bioavailability in vivo. Three‐wk‐old Wistar rats were fed (1) the pteroylglutamate (PteGlu), (2) the choline, (3) the PteGlu and choline, (4) the folate‐enriched egg yolk powder diet for 4 wk after having been fed the folate‐ and choline‐deficient diet. The hepatic folate level in the folate‐enriched egg yolk powder group was significantly higher than that in the folate‐ and choline‐deficient or the control groups. The homocysteine concentration in plasma and liver of the folate‐enriched egg yolk powder group was significantly lower than that of the folate‐ and choline‐deficient or the PteGlu groups. The S‐adenosyl‐methionine (SAM)/S‐adenosyl‐homocysteine (SAH) ratio in the folate‐enriched egg yolk powder group was significantly higher than that in the folate‐ and choline‐deficient group. These effects were similar in the PteGlu and choline, but not the PteGlu or the choline groups. These data suggest that the intake of folate‐enriched eggs, as well as of both folate and choline, induced the beneficial effects on folate and homocysteine metabolism. Thus, folate‐enriched eggs could be used as beneficial source of folate with a high bioavailability.     

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.     

In vitro bioaccessibility of added folic acid in commercially available baby foods formulated with milk and milk products

Food Science and Biotechnology - Milk contains a certain amount of folate binding proteins. The binding capacity varies in acidic conditions and affects the bioavailability of folic acid. Folic...     

Folate, Cognition, and Depression in the Era of Folic Acid Fortification

ABSTRACT: It has long been recognized that folate deficiency is associated with impaired cognitive function, particularly in older adults. Moreover, folate deficiency contributes to the symptoms of clinical depression and negatively influences the efficacy of antidepressant medications. The pathophysiological mechanisms by which folate deficiency influences cognition and depressive mood are not clearly understood, but may be mediated by decreased intracellular concentration of the methyl donor S-adenosylmethionine in the brain and increased concentration of the putative vascular toxin homocysteine in the blood (hyperhomocysteinemia). Folic acid fortification of flour in the United States, intended to reduce the risk of neural tube defects, has been in effect since January 1, 1998. The program has proven to be highly successful having lowered the prevalence of folate deficiency and hyperhomocysteinemia, as well as the incidence of neural tube defects. An important question is whether associations between folate status, cognition, and depression remain significant. In this presentation, the evidence supporting the relationships between folate status, cognition, and depression will be summarized. In addition, epidemiological data will be presented from the Sacramento Area Latino Study on Aging (SALSA), a community-based cohort study of physical and cognitive function in Latino Americans age 60 years and older, that indicate folate status remains a significant determinant of cognitive function and depressive mood despite the success of folic acid fortification.     

Effects of dietary supplements of folic acid and rumen-protected methionine on lactational performance and folate metabolism of dairy cows

The present experiment was undertaken to determine the interactions between dietary supplements of folic acid and rumen-protected methionine on lactational performance and on indicators of folate metabolism during one lactation. Fifty-four multiparous Holstein cows were assigned to 9 blocks of 6 cows each according to their previous milk production. Within each block, 3 cows were fed a diet calculated to supply methionine as 1.75% metabolizable protein, equivalent to 70% of methionine requirement, whereas the 3 other cows were fed the same diet supplemented with 18 g of a rumen-protected methionine supplement. Within each diet, the cows received 0, 3, or 6 mg/d of folic acid per kg of body weight. Rumen-protected methionine increased milk total solid concentration but not yield. Supplementary folic acid increased crude protein and casein concentrations in milk of cows fed no supplementary methionine and the effect increased as lactation progressed; it also decreased milk lactose concentration. Folic acid supplements had the opposite effects on milk crude protein, casein, and lactose concentrations in cows fed rumen-protected methionine. Milk and milk component yields and dry matter intake were unchanged. Folic acid supplementation increased serum folates and this response was greater at 8 wk of lactation. It decreased serum cysteine in cows fed rumen-protected methionine, whereas it had no effect in cows fed no supplementary methionine. The highest serum concentrations of cysteine but the lowest of vitamin B(12) were observed at 8 wk of lactation. Serum clearance of folic acid following an i.v. injection of folic acid was slower at 8 wk of lactation. During this period, the high concentrations of serum folates and cysteine, the low serum concentrations of vitamin B(12) and methionine, and the slow serum clearance of folates strongly suggest that the vitamin B(12) supply was inadequate and interfered with folate use. It could explain the limited lactational response to supplementary folic acid observed in the present experiment.     

Analysis of Folate Form Distribution in Spanish Beers Using Combined Affinity and Ion‐Pair Chromatography

Folates and derivatives usually occur as polyglutamates, in different oxidized forms and substitutions in nature. The multiplicity of forms and the generally low content in food makes quantitative analysis of folate a difficult task. A method that uses affinity chromatography followed by ion‐pair high performance liquid chromatography was adapted to the analysis of folate distribution in Spanish beers, with simultaneous information on the pteridine ring structure and the glutamate residues. On average, total folate concentration (as sum of individual vitamers expressed in folic acid) in the analyzed beers was 2.0 μg/100 mL. For all the beers, folates were present as monoglutamates and the analysis showed a total absence of polyglutamyl folates. The distribution of the monoglutamyl folate derivatives analyzed in Spanish beers was: 10‐formyltetrahydrofolate (41.7% of total folate), tetrahydrofolate (26.5%), 5‐methyltetrahydrofolate (17.2%) and folic acid (14.6%). This study provides new information regarding the distribution of naturally occurring folates in beer and contributes to the assessment of folate bioavailability in this beverage.