L-阿拉伯糖对正常及高糖高脂喂养大鼠生长及糖脂代谢的影响

目的观察L-阿拉伯糖对正常大鼠和高糖高脂喂养大鼠生长及糖脂代谢的影响。方法雄性Wistar大鼠60只,按体重和空腹血糖随机分为6组(n=10):空白对照组、高剂量对照组、模型对照组以及L-阿拉伯糖低、中、高剂量实验组,分别以普通饲料和高糖高脂饲料喂养6周,观察大鼠的体重、食物利用率,测定大鼠的糖脂代谢指标。结果L-阿拉伯糖对正常大鼠的体重、体脂、食物利用率、空腹血糖均无影响;能显著提高正常大鼠的糖耐量(P<0.01);降低正常大鼠的血清甘油三酯(P<0.05)并增高血清高密度脂蛋白胆固醇(P<0.01)。模型对照组和各实验组大鼠的体重、体脂、糖耐量、血清总胆固醇均显著高于空白对照组(P<0.05)。以87.5、175、525mg/kgBW剂量的L-阿拉伯糖灌胃高糖高脂饲料喂养的肥胖模型大鼠6周,各剂量L-阿拉伯糖均能显著改善肥胖模型大鼠的糖耐量(P<0.01),高剂量组大鼠的体脂含量明显下降(P<0.05)。结论L-阿拉伯糖能显著增强正常和高糖高脂喂养大鼠的糖耐量,降低大鼠血清甘油三酯,增高血清高密度脂蛋白胆固醇,并有降低大鼠体脂含量和减缓体重增加的趋势。     

Effect of phenolic acids on glucose and organic acid metabolism by lactic acid bacteria from wine

The influence of phenolic (p-coumaric, caffeic, ferulic, gallic and protocatechuic) acids on glucose and organic acid metabolism by two strains of wine lactic acid bacteria (Oenococcus oeni VF and Lactobacillus hilgardii 5) was investigated. Cultures were grown in modified MRS medium supplemented with different phenolic acids. Cellular growth was monitored and metabolite concentrations were determined by HPLC-RI. Despite the strong inhibitory effect of most tested phenolic acids on the growth of O. oeni VF, the malolactic activity of this strain was not considerably affected by these compounds. While less affected in its growth, the capacity of L. hilgardii 5 to degrade malic acid was clearly diminished. Except for gallic acid, the addition of phenolic acids delayed the metabolism of glucose and citric acid in both strains tested. It was also found that the presence of hydroxycinnamic acids (p-coumaric, caffeic and ferulic) increased the yield of lactic and acetic acid production from glucose by O. oeni VF and not by L. hilgardii 5. The results show that important oenological characteristics of wine lactic acid bacteria, such as the malolactic activity and the production of volatile organic acids, may be differently affected by the presence of phenolic acids, depending on the bacterial species or strain.     

Effects of buffer and temperature on formation of furan, acetic acid and formic acid from carbohydrate model systems

Effects of temperature, pH and phosphate buffer on volatiles formed by heating model solutions of fructose, glucose, sucrose, lactose or starch were investigated by selected ion flow tube-mass spectrometry (SIFT-MS). Among the carbohydrates studied, the monosaccharide reducing sugars fructose and glucose were more reactive than macro molecular starch, lactose and sucrose, which are not reducing sugars. Furan was formed from fructose heated at 120, 100 and 80 °C at pH 5-7 in phosphate buffer and at 100 °C in unbuffered solution. Glucose did not yield furan in unbuffered solution at 100 °C but glucose did yield furan in phosphate buffer solution at a similar pH. Furan formation increased as temperature and pH increased. As temperature, pH value, and buffer components changed, furan formation may occur by different reactive pathways. Both of the buffer components, NaH₂PO₄ and citric acid, enhanced the formation of thermal degradation products from fructose. The enhancing effect of NaH₂PO₄ was stronger than citric acid. Formic and acetic acids were concomitantly formed with furan. More formic acid was produced from fructose than glucose, and more acetic acid was produced from glucose than fructose.     

Thermomechanical study of the phase behaviour of agarose/gelatin mixtures in the presence of glucose syrup as co-solute

In an effort to draw attention to the subject of structure/function relationships in high-solid biopolymer mixtures, this investigation produces binary composites of agarose with gelatin and systematically increases the amount of glucose syrup, which is the co-solute in this system. Experimental work was carried out using small-deformation dynamic oscillation on shear and modulated differential scanning calorimetry. Agarose/gelatin mixtures in an aqueous low-solid environment form non-interactive bicontinuous networks. Addition of glucose syrup to the polymeric blend prevents the formation of stable double helices in the environment. Gelatin, on the other hand, better withstands the co-solute-induced change in solvent quality. At subzero temperatures, materials go through the rubber-to-glass transition whose DSC glass transition temperature (T_g) is governed by the total level of solids in the system. Estimation of the mechanical T_g acquires physical significance by utilising the theory of free volume, as modelled by the Williams, Landel and Ferry (WLF) equation. The single value of T_g estimated by this approach argues in accordance with experimental observations for the predominance of the gelatin network in the high-solid mixture.     

Consumer acceptability and purchase intent of probiotic yoghurt with added glucose oxidase using sensometrics,artificial neural networks and logistic regression

This research aimed to identify the drivers of acceptance and purchase intent of a probiotic (Bifidobacterium longum BL05) nonflavoured yoghurt supplemented with glucose oxidase, and to model the consumers’ acceptability using sensometrics and artificial neural networks (ANN). Consumers (n = 100) evaluated the degree of liking of yoghurt assays in respect of appearance, aroma, taste, texture and overall linking. Sensometric techniques – multiple linear regression (MLR), partial least squares regression (PLS), principal component regression (PCR) – and ANN were used to model the overall liking. Sensory drivers of global acceptance and purchase intent were also determined using logistic regression (LR). Hierarchical cluster analysis (HCA) identified three consumer segments that presented differences in all sensory attributes evaluated (P < 0.05). The ANN model showed the best performance to predict overall liking, followed by the MLR, PLS and PCR, indicating that taste and texture were the most significant attributes impacting the yoghurts overall liking. In accordance with the logistic models, overall acceptance and purchase intent could be predicted with 81.94 and 85.49% accuracy, respectively. The logistic regression indicated that taste was the attribute that contributed significantly (P < 0.0001) to higher scores for purchase intent and was considered the driver of acceptance.     

葡萄糖异构酶的研究——酶的分离提纯

葡萄糖异构酶细胞经丙酮处理,缓冲液抽提。DEAE—纤维素离子交挟柱层析和Sephadex G—200凝胶柱层析等方法得到分离井纯化。该法与超声破碎法相比,比活提高3.3倍,活力收率为74%,得到了高纯度异构酶,经Sephadex G—200凝胶柱层析获得较高收率的电泳纯制品。     

Extracellular polysaccharides production by Arthrobacter viscosus

In this study the production of extracellular polysaccharides by the non-pathogenic soil bacteria Arthrobacter viscosus has been investigated. Different variables affecting extracellular polysaccharide production such as the carbon source (glucose or xylose), the agitation speed and the pH have been analysed.

In a first stage, experiments in shaken conical flasks (250 ml), containing 50 ml of culture medium, were carried out. Using xylose (25 g/l) as the carbon source at an initial pH 8 improved the extracellular polysaccharides levels obtained.

In a second stage, the experiments were scaling in bioreactors. Cultivation was carried out in discontinuous mode and with/without pH control. Polysaccharide production reached a maximum of 10 g of crude product per litre of growth medium after 14 days and the relationship between product formation and cell growth of A. viscosus is 2.7 g polysaccharide per gram biomass. This production was obtained at the optimal conditions determined with pH control at pH 7, xylose as carbon source (25 g/l) and an agitation rate of 800 rpm.     

GLUCOSE OXIDASE REACTION FOR ESTIMATION OF GLUCOSE WITHOUT HORSERADISH PEROXIDASE. SOME MICROBIOLOGICAL AND FERMENTATION APPLICATIONS

An enzymic method has been developed for analysis of glucose. Glucose oxidase acts on glucose to produce hydrogen peroxide which acts to directly reduce the green Cu(II) 2–2′-bicinchoninate complex to a violet complex without horseradish peroxidase. A concentration range of 20–200 μM glucose was used but the reaction shows a linear range of 20–800 μM glucose. Interference is controlled by using a blank determination which has not been treated with glucose oxidase. The reaction has been used to estimate glucose levels in Saccharomyces cerevisiae fermentation and α-amylase, invertase and β-galactosidase reactions and coloured corn-steep fermentation media.     

Isolation and sequence of the MIG1 homologue from the yeast Candida utilis

The Mig1p repressor from the food yeast Candida utilis has been isolated using a homologous PCR hybridization probe. This probe was amplified with two sets of degenerate primers designed on the basis of highly conserved motifs in the DNA-binding region (zinc-finger domain) from yeast Mig1p and fungi CreA repressors. The cloned gene was sequenced and found to encode a polypeptide of 345 amino acids which shows significant identity with other yeast and fungus repressors in the DNA-binding domain and also with the yeast Mig1 proteins in the C-terminal region (effector domain). The MIG1 repressor gene from C. utilis was able to complement functionally the mig1 mutation of S. cerevisiae. The sequence presented here has been deposited in the EMBL data library under Accession No. AJ277830.