婴幼儿配方奶粉中核黄素磷酸钠的测定

针对婴幼儿奶粉国家标准核黄素检测中无法检出核黄素-5-磷酸钠的情况,在样品处理过程中添加磷酸酶.使核黄素-5-磷酸钠转化为核黄素达到检出的目的.对磷酸酶的酶解转化度进行了研究,解决了从核黄素-5-磷酸钠到核黄素之间换算的问题.     

核黄素操纵子在B.subtilis 24R7染色体上整合对核黄素合成的影响

构建含有 B.subtilis 24 核黄素操纵子的整合型核黄素质粒 pRB40、pRB61 和 pRB63,研究了核黄素操纵子分别在B.subtilis 24R7染色体的 rib、amyE和thrC 位点整合对核黄素合成的影响.结果表明,核黄素操纵子通过单交换重组方式整合在上述位点可使核黄素合成量增加14%~19%,而通过双交换重组方式整合在 amyE 或 thrC 位点可使核黄素合成量增加 40% ~44%.增强核黄素操纵子在B.subtilis 24R7染色体上的稳定性可以提高核黄素的合成量.     

从发酵液中分离提取核黄素

核黄素的溶解度受溶液的ｐＨ值影响较大，在碱性条件下核黄素的溶解度较大，而在偏酸性溶液中溶解度较小。实验中分析了温度、ｐＨ值、作用时间和避光条件等因素对核黄素分解损失的影响，在此基础上设计了碱溶法提取核黄素的新工艺，并用核黄素的发酵液进行了试验，获得了较好的效果。与传统的酸溶法提取工艺相比，不仅提高了收得率，能耗也大大降低。     

三聚氰胺与核黄素水凝胶形成机理研究

本文研究了核黄素与三聚氰胺双组分小分子水凝胶的形成,凝胶的持水性质以及不同pH对凝胶性质的影响。利用三维荧光方法光谱详细研究了凝胶形成的机理。结果表明,核黄素能使三聚氰胺荧光猝灭,二者通过形成基态络合物产生静态猝灭,而三聚氰胺则能使核黄素产生荧光增强的作用。核黄素与三聚氰胺之间的多重氢键作用是凝胶形成的根本原因。改变溶液的酸碱度,由于三聚氰胺与核黄素分子结构的改变破坏了核黄素和三聚氰胺之间的氢键作用,所以凝胶的形成只能发生在特定的pH范围内。     

核黄素的开发与应用进展

介绍了核黄素的性能、主要的生产技术路线与最佳的操作条件。对目前核黄素工业化生产采用的主要工艺的技术特点进行了具体的分析和总结,并介绍了核黄素的应用拓展情况。     

核黄素生产技术进展

综述了核黄素生产中发酵、分离提取以及发酵废液处理的工艺进展，展望了核黄素关键生产工艺的发展前景。     

代谢调节理论指导下的核黄素发酵条件

发表了从葡萄糖到核黄素的整条生物合成途径。根据这条代谢途径和Ｔ３０突变株的发酵条件试验结果，对阿舒假囊酵母合成核黄素的过程中碳基质流量在ＥＭＰ和ＨＭＰ途径中的分配，油和骨胶在核黄素合成中的不同作用，以及丙酮酸的氧化能力等与核黄素过量合成的关系进行了初步的讨论。     

利用核黄素粗品制备核黄素5'-磷酸钠

探索利用核黄素粗品制备核黄素5'-磷酸钠的可行性.在吡啶和乙腈的混合溶剂中,使核黄素粗品与其4倍摩尔量的三氯氧磷35℃左右下反应2h,然后水解反应混合物,再用NaOH溶液中和,能够以68.5％以上的收率得到核黄素磷酸钠,产品质量符合美国FCC (7)要求.通过单因素试验,初步优化了核黄素5'-磷酸钠粗品磷酸化反应的条件,即:n (POCl3)/n(VB2)=4.6,n(POCl3)/n(H2O)＝1.65,反应时间2h,反应温度35±1℃.在优化的磷酸化反应条件下,利用核黄素粗品制备核黄素5'-磷酸钠的收率平均可达73.5％以上,能够有效降低核黄素5'-磷酸钠的生产成本.研究结果表明,利用核黄素粗品制备核黄素5'-磷酸钠无论在经济上还是在技术上均是可行的.     

核黄素结晶热力学研究

本研究采用平衡法测定了核黄素在纯水和在283、288、293、298及303K的HCl-水体系(HCl的摩尔分率w分别为0．14、0．16、0．17、0．20、0．24)中的溶解度,建立了溶解度模型,并应用实验得到的溶解度数据估算了核黄素的溶解热和溶剂化焓变;测定核黄素在283、288和293K的HCl-水体系中溶解与超溶解特性,得到核黄素的结晶介稳区,这些热力学研究为核黄素的工业化生产奠定基础。     

代谢工程改造嘌呤合成途径以提高核黄素产量

核黄素又名维生素B₂,是人体必不可少的营养物质之一，而鸟苷三磷酸则是核黄素合成的重要前体。为在高产菌株的基础上进一步提高核黄素产量，该研究以高产核黄素的枯草芽孢杆菌S1为出发菌株，利用CRISPER/Cas9介导的基因组碱基编辑技术对嘌呤合成途径阻遏蛋白基因以及鸟嘌呤核苷酸（guanylate, GMP）还原酶基因进行失活，并利用质粒过表达的方法进行了一系列的代谢工程改造。结果显示，guaC基因的失活阻断了GMP到肌苷酸的回补途径，使GMP得到积累，使核黄素产量达到3.04 g/L,而purR基因的失活没有效果；使用PvegI启动子过表达希瓦氏菌来源的ribA后，核黄素产量提高到3.33 g/L。将失活guaC基因与PvegI启动子过表达希瓦氏菌ribA结合，最终使核黄素产量达到3.43 g/L,较出发菌株核黄素产量提升22%,转化率提升25.8%。     

Nutrient Content of Special Fed Veal Ribeyes

The nutrient content of special fed veal (SFV) was analyzed and compared to previously reported values for veal and beef. Ribeyes of SFV from 8 different U.S. producers were analyzed for moisture, total fat, protein, cholesterol, folacin, thiamin, riboflavin, niacin, B₆, B₁₂, vitamin A, pantothenic acid, 16 amino acids and 8 minerals. Special fed veal was found to be similar in nutrient content to reported values for beef and veal with one exception; the Fe content of SFV was 14–25% of reported values for beef.     

Determining riboflavin level in urine (comparative analysis of the methods)

Four methods of riboflavin content estimation in urine were studied: they are based on specific titration of vitamin B by riboflavin-binding protein (1), riboflavin decomposition by boiling in alkali (2), riboflavin fluorescence suppression by dithionate (3), and high-performance liquid chromatography. A conclusion has been made on the necessity of a home standard for riboflavin estimation by methods 1-3. The results obtained with the above methods correlated well, regression equations were derived describing correlation of these results. Methods 1 and 3 are most simple and highly specific and sensitive, therefore they could be recommended for wide use in large-scale clinical investigations.     

Kinetics for Singlet Oxygen Formation by Riboflavin Photosensitization and the Reaction between Riboflavin and Singlet Oxygen

ABSTRACT: The formation of singlet oxygen by riboflavin and the kinetics and mechanisms of riboflavin degradation in aqueous solution under light were determined. The singlet oxygen formation rate by riboflavin was 2.31 μmole oxygen/mL headspace/h of serum bottle. The degradations of riboflavin were 66% in D₂O and 40% in H₂O, respectively, under light after 24 h. The results indicate that singlet oxygen is involved in riboflavin destruction under light. The riboflavin destructions were 94.0% and 15.7% with 0 mM or 160 mM ascorbic acid, respectively, under light after 96 h. The reaction rate between riboflavin and singlet oxygen was 1.01 × 10¹⁰/M/s, which is a diffusion-controlled reaction rate. This explains the extremely fast degradation of riboflavin in foods under light. Ascorbic acid and sodium azide reduce the degradation of riboflavin under light with different quenching mechanisms. Ascorbic acid quenched both singlet oxygen and excited triplet riboflavin. Sodium azide quenched only the singlet oxygen in riboflavin solution with a quenching rate of 1.547 × 10⁷/M/s. With the involvement of both the Type-I and Type-II mechanisms in the riboflavin degradation under light, singlet oxygen quencher alone could not protect the riboflavin from degradation completely. Addition of ascorbic acid can protect riboflavin oxidation in foods exposed to light.     

Effect of milk fermentation on riboflavin content and stability

The effects of Lben and yogurt fermentation on riboflavin content and the riboflavin photolysis in milk and Lben were examined. Samples of Lben and milk were exposed to fluorescent light, and the calculated rates of riboflavin photolysis were compared. The rate constant for riboflavin photolysis in milk was about four times as high as the rate constant in Lben. The difference in pH between milk and Lben did not explain the difference found in riboflavin photostability. To determine the effect of Lben and yogurt fermentation on riboflavin content, samples were taken before incubation and at the end of the process. Standard yogurt and Lben fermentations did not affect the riboflavin content significantly. However, yogurt fermentation carried out in the laboratory for 5 h reduced the riboflavin content.     

Antioxidant Effects of Protein-Bound Riboflavin and Free Riboflavin

We studied the antioxidant effects of protein-bound riboflavin and free riboflavin using methyl linoleate in a water system in the dark. The protein-bound riboflavin inhibited the formation of hydroperoxides. After exposure to light, the protein lost its antioxidant effect, which suggested that it was not the protein-bound riboflavin but the riboflavin itself that had the antioxidant effect. These results showed that riboflavin inhibited the formation of hydroperoxides, which suggested that it did have an antioxidant effect.     

Influence of Initial Riboflavin Content on Retention in Pasta During Photodegradation and Cooking

Samples of enriched pasta were stored under controlled lighting conditions and the loss of riboflavin was determined. After an initial rapid degradation, the riboflavin level continued to decrease slowly. After 12 wk, more than 80% the riboflavin had degraded. When pasta samples- with varied levels of riboflavin enrichment were exposed to light for 2 days, riboflavin losses ranged from 57.8–64.3%. Riboflavin leaching from pasta during cooking was also shown to be concentration independent with 34.5–37.6% of the riboflavin solubilized in the cooking water. Riboflavin in pasta which had been exposed to light for 2 days prior to cooking had a similar percentage of the undegraded riboflavin leached into the cooking water.     

Vitamins in brewing: the impact of wort production on the thiamine and riboflavin vitamer content of boiled sweet wort

Wort production contains a number of processing steps that are aimed at the optimal extraction of nutrients from malt, including vitamins. This research revealed that the different wort production processing steps imposed different influences on the thiamine and riboflavin vitamer content of the final sweet wort. These vitamins play vital roles within yeast metabolism, where they act as enzyme cofactors. As such thiamine vitamers play a crucial role in many decarboxylating enzymes, while riboflavin vitamers play an integral role in energy production and redox maintenance. While mashing releases valuable starch into the liquor, both thiamine and riboflavin are also extracted. The extraction of these vitamins is the greatest at 65°C and is indirectly linked to the amylase activity. When the starches are broken down during mashing, the thiamine and riboflavin vitamers are gradually released into the mash liquor. The boiling and trub removal (whirlpool) processes impose losses in both vitamins owing to the high temperatures exhibited during these stages. While hop pellets were shown to contribute a small proportion of the vitamers studied, the use of kettle finings caused a significant reduction in both thiamine and riboflavin vitamers. Copyright © 2014 The Institute of Brewing & Distilling     

Riboflavin content in lupine seeds and blood plasma riboflavin status in broilers fed diets containing high levels of lupine seeds

BACKGROUND: The potential of lupine as a source of protein and other nutrients in poultry has attracted considerable attention in countries dependent on imports of soybean meal (SBM), as well as in organic farming. Nutritional aspects of riboflavin in lupines are poorly understood. This work evaluated riboflavin content in whole and dehulled seeds of three lupines (L. albus, L. angustifolius, L. luteus) and riboflavin status in broiler fed diets containing high levels of lupine seeds in comparison to SBM. RESULTS: Riboflavin is concentrated mainly in lupine cotyledons, predominantly as flavin mononucleotide. Its content in whole seeds ranged from 2.07 to 2.70 mg kg^?1, and was comparable to content in SBM (2.35 mg kg^?1). In comparison to the SBM‐fed group, broilers fed lupine diets showed higher plasma riboflavin (P < 0.05), but their growth rate and feed intake parameters were significantly lower (P < 0.05). CONCLUSION: Lupine seeds contain moderate to high levels of riboflavin. Feeding diets containing high levels of lupine seeds did not have adverse effects on plasma riboflavin status in broilers. Poor performance of broilers fed lupine diets is not associated with inadequacy of riboflavin. Copyright © 2008 Society of Chemical Industry