乳粉中维生素B1和B2含量测定的能力验证分析

目的为加强我国检测机构对乳粉市场的监管,中国食品药品检定研究院(National Institute for Food and Drug Control,NIFDC)组织实施了乳粉中维生素B_1和B_2的含量测定的能力验证。方法制备了分割水平对的样品,采用单因素方差分析和t检验对样品均匀性和稳定性进行分析。对能力验证结果进行稳健统计分析,通过Z比分数评价实验室检测能力。结果样品通过均匀性和稳定性检验要求,满足能力验证计划要求。维生素B_1项目中,参加20个实验室验证,满意结果数为14,满意率为70.0%;维生素B_2项目中,参加22个实验室验证,满意结果数为15,满意率为77.2%;2项检测结果均满意的实验室有12个,满意率为60%。结论绝大多数实验室对乳粉中维生素B_1和B_2的测定处于良好水平,但未达到优良水平,仍需对检测方法进行统一认识,减少系统误差,加强各实验室内部的质量控制。     

The effects of pre-treatment with vitamin B6 on memory retrieval in rats

The effects of pre-treatment with vitamin B₆ on memory retrieval in adult male Wistar rats were evaluated using a step-through passive avoidance task. The rats were divided into three groups of 10 each. All animals were fed standard rodent chow. Vitamin B₆ (50 or 100 mg/kg) was administered intraperitoneally (i.p.) every other day for 1 month before training was initiated. Three retention tests were performed to assess the memory of the rats. Vitamin B₆ (100 mg/kg) significantly increased the step-through latency of the passive avoidance response compared with the control in the first retention test of the passive avoidance paradigm (p < 0.05). In addition, vitamin B₆ at 100 mg/kg significantly increased memory retrieval in the second and third retention tests conducted 2 days and 1 week after training, respectively, compared with the control (p < 0.05). These results indicate that pre-treatment with vitamin B₆ potentially enhances memory retrieval.     

高峰淀粉酶活性对饮料中维生素B2测定结果的影响

目的 调查分析高峰淀粉酶来源和酶解参数对饮料中维生素B₂（核黄素-5''-磷酸钠来源）测定结果的影响。方法 按GB 5009.85—2016对受试样品中维生素B₂（核黄素-5''-磷酸钠来源）的含量进行检测,考察高峰淀粉酶及其工作条件对检测结果的影响。结果 不同来源的高峰淀粉酶对维生素B₂（核黄素-5''-磷酸钠来源）的实测结果有明显的影响,实测值与理论值最大相差10倍以上;前处理过程中建议选择酶解时间12 h,酶解pH值6.0~6.5。结论 国标方法检测饮料中维生素B₂（核黄素-5''-磷酸钠来源）时,预先检测高峰淀粉酶的酶解活性是十分必要的。     

天然燕麦中维生素B12的测定中2种微生物法前处理方式的比较

目的研究使用微生物法对燕麦中维生素B_(12)测定的可行性。方法以国标法为基础,采用标准前处理方式和添加淀粉酶的前处理方式分别对6份燕麦中的维生素B_(12)进行测定,比较2种不同前处理方式对检测结果的影响。结果国标法测定的标准曲线在维生素B_(12)的浓度为0.01~0.1 ng范围内具有良好的线性关系(r2=0.995)。前处理过程中加入20 m L浓度为1%的α-淀粉酶溶液可充分提取出燕麦样品中的维生素B_(12)。标准处理法的最大相对标准偏差(relative standard deviation,RSD)为10.2%,酶解处理法最大RSD为8.83%。结论对于燕麦中维生素B_(12)的测定,酶解处理法有更好的适用性,检测结果更为可靠。     

Influence of methionine supply on the response of lactational performance of dairy cows to supplementary folic acid and vitamin B12

The present experiment was undertaken to determine if the effects of supplementary folic acid on lactational performance were caused by improved methylneogenesis and if the supply in vitamin B₁₂ could affect this metabolic pathway. In this eventuality, supplementary Met, a major source of preformed methyl groups, should reduce the requirements for these vitamins. Sixty multiparous Holstein cows were assigned to 10 blocks of 6 cows each according to their previous milk production. Within each block, 3 cows were fed a diet estimated to supply Met as 1.83% metabolizable protein and 3 cows were fed the same diet supplemented with 18 g of rumen-protected methionine (RPM) to supply Met as 2.23% of metabolizable protein. Within each level of Met, cows received no vitamin supplement or weekly intramuscular injections of 160 mg of folic acid alone or combined with 10 mg of vitamin B₁₂ from 3 wk before to 16 wk after calving. There was no treatment effect on dry matter intake during pre- and postcalving periods: 13.4 ± 0.4 and 21.8 ± 0.4 kg/d, respectively. Milk production was not affected by RPM supplementation. Folic acid and vitamin B₁₂ given together tended to increase milk production during the 16 wk of lactation. This effect was more pronounced during the first 4 wk of lactation: 37.5, 37.7, and 40.3 ± 0.9 kg/d for cows receiving no vitamin supplement, folic acid alone, or folic acid combined with vitamin B₁₂, respectively. Milk fat yield was not affected by treatments. Lactose, crude protein, and total solid yields were greater, in early lactation, in cows injected with folic acid and vitamin B₁₂ together but this effect diminished as lactation progressed. Intramuscular injections of folic acid alone or combined with vitamin B₁₂ tended to decrease plasma concentrations of homocysteine from 5.51 μM with no vitamin supplement to 4.54 and 4.77 ± 0.37 μM, respectively. Results of the present experiment suggest that the effects of the combined supplement of folic acid and vitamin B₁₂ on lactational performance of dairy cows were not due to an improvement in methyl groups supply, because RPM supplement, a source of preformed methyl groups, did not alter the cow responsiveness to vitamin supplements.     

Analysis of vitamin B<Subscript>2</Subscript> using front-face intrinsic beer fluorescence

The study demonstrates an application of front-face fluorescence spectroscopy to characterization of beers. Partial least squares (PLS) regression was used to develop calibration models between emission and synchronous fluorescence spectra of beers, and riboflavin concentration determined by fluorometric titration. The regression models showed a good ability to predict riboflavin concentration.     

Molecular cloning, identification and characterization of 2-methyl-3-hydroxypyridine-5-carboxylic-acid-dioxygenase-coding gene from the nitrogen-fixing symbiotic bacterium Mesorhizobium loti

The gene (mlr6788) of a nitrogen-fixing symbiotic bacterium Mesorhizobium loti MAFF303099 has been identified as a gene coding for 2-methyl-3-hydroxypyridine-5-carboxylic acid dioxygenase (MHPCO), the seventh enzyme in degradation pathway I for pyridoxine, a free form of vitamin B(6). The gene was cloned and overexpressed in Escherichia coli cells co-transformed with chaperonin genes. The homogeneous recombinant enzyme showed similar enzymatic properties to the enzyme from Pseudomonas sp. MA-1. MHPCO was essential for the assimilation of pyridoxine in M. loti, but not for its growth in a nutrient-rich medium. From the infection experiment of a symbiotic plant Lotus japonicus with an M. loti mlr6788 gene disruptant, MHPCO was demonstrated to be dispensable for at least nodule formation on roots of seedlings in symbiosis.     

Effects of oral vitamin D(3) supplementation and supplement withdrawal on the accumulation of magnesium, calcium, and vitamin D in the serum, liver, and muscle tissue and subsequent carcass and meat quality of Bos indicus influenced cattle

Bos indicus crossbred cattle (n=79) were fed vitamin D(3) (0 or 3 million IU/hd/d) for 5d. Afterwards, half of each group was slaughtered immediately, while half was fed, without supplementation, for 7d before processing. Serum calcium concentration was increased (P<0.05) in cattle after supplement removal, but not immediately following supplementation. This also was observed in the M. longissimus lumborum and M. triceps brachii, but not in the M. semitendinosus. Liver biopsy vitamin D(3) concentrations were higher (P<0.05) in supplemented cattle immediately following supplementation, but were not different from controls after supplement removal. Vitamin D(3) did not affect tenderness at supplement removal day 0, but increased the tenderness of the M. longissimus lumborum and M. semitendinosus at supplement removal day 7. Vitamin D(3) supplementation improves muscle tenderness and may be more effective when supplementation is ceased 7d before slaughter, with minimum food safety concerns.     

Predicting the organoleptic stability of beer from chemical data using multivariate analysis

Delaying flavour staling, to prolong the shelf life of beer, is one of the greatest challenges facing the brewing industry today. In this study, a series of lager beers were brewed using five European barley varieties and four chemical indicators of the degree of beer ageing were correlated with the sensory evaluation: E-2-nonenal, β-damascenone, 2-furaldehyde and 5-hydroxymethyl-2-furaldehyde (5-HMF). A statistical strategy using principal component analysis and multiple linear regression was applied to draw relationships between the sensory and chemical data sets. Additionally, the relative significance of each of the chemical data on the organoleptic stability of beer was evaluated within the method. 5-HMF was the only studied carbonyl compound whose concentration cannot be used for predicting the total taste score of beers. E-2-nonenal, in contrast, was found to be the most discriminant carbonyl compound under consideration for predicting the flavour stability of beer.