咸鸭蛋清胃蛋白酶水解产物的抗菌性及抗氧化性

【目的】提高对咸鸭蛋清的综合利用,制备具有生物活性的蛋白水解产物。【方法】采用超滤对咸鸭蛋清进行脱盐及分级,利用胃蛋白酶对不同分子量范围的咸鸭蛋清蛋白组分进行酶解,并对不同组分的水解产物进行体外抑菌试验,测定其最低抑菌浓度(MIC)、最低杀菌浓度(MBC)、细菌细胞膜完整性及抗氧化活性。【结果】超滤后得到3种不同分子量的组分,组分A (Mw>50 kDa)、组分B (50 kDa>Mw>20 kDa)和组分C (20 kDa>Mw>5 kDa)。其中,组分A和组分B的水解产物对大肠杆菌的生长有抑制作用。2种组分的MIC分别为1 024 μg/mL和2 048 μg/mL,MBC均为2 048 μg/mL。大肠杆菌进入稳定期OD₆₀₀值约为1.15,添加2种水解产物浓度达1×MIC时,OD₆₀₀值降至0.79和0.86,浓度达2×MIC时,OD₆₀₀值降至0.50和0.68。2种水解产物可破坏大肠杆菌细胞膜,达到较好的抑菌效果。而金黄色葡萄球菌对3种水解产物均不敏感,抑菌效果较差。另外,3种水解产物均具有抗氧化活性,它们对DPPH自由基清除能力分别达0.5倍Trolox (水溶性维生素E)、0.67倍Trolox、0.38倍Trolox。【结论】超滤可同时实现咸蛋清脱盐及富集不同目标蛋白的目的。目标蛋白酶解组分具备抗菌活性和抗氧化活性,同时可作为一种营养添加剂,提高了咸鸭蛋清的附加价值和利用率。     

Ethanol production from eucalyptus wood hemicellulose hydrolysate by Pichia stipitis

Ethanol production was evaluated from eucalyptus wood hemicellulose acid hydrolysate using Pichia stipitis NRRL Y-7124. An initial lag phase characterized by flocculation and viability loss of the yeast inoculated was observed. Subsequently, cell regrowth occurred with sequential consumption of sugars and production of ethanol. Polyol formation was detected. Acetic acid present in the hydrolysate was an important inhibitor of the fermentation, reducing the rate and the yield. Its toxic effect was due essentially to its undissociated form. The fermentation was more effective at an oxygen transfer rate between 1.2 and 2.4 mmol/L h and an initial pH of 6.5. The hydrolysate used in the experiences had the following composition (expressed in grams per liter): xylose 30, arabinose 2.8, glucose 1.5, galactose 3.7, mannose 1.0, cellobiose 0.5, acetic acid 10, glucuronic acid 1.5, and galacturonic acid 1.0. The best values obtained were maximum ethanol concentration 12.6 g/L, fermentation time 75 h, fermentable sugar consumption 99% ethanol yield 0.35 g/g sugars consumed, and volumetric ethanol productivity 4 g/L day. (c) 1992 John Wiley & Sons, Inc.     

亚硫酸盐甘蔗渣浆酶解液发酵制备乙醇

以亚硫酸盐甘蔗渣浆酶解液作为原料,利用C. shehatae发酵制取燃料乙醇。结果表明：还原糖最适初始质量浓度为葡萄糖140 g/L、木糖60 g/L、酶解液总糖80 g/L。利用初始葡萄糖55.06 g/L、木糖11.18 g/L、纤维二糖4.51 g/L的亚硫酸盐甘蔗渣浆酶解液发酵,经18 h获得乙醇22.98 g/L。乙醇得率为67.23%,葡萄糖利用率为99.27%,木糖利用率为32.96%,C. shehatae适合作为蔗渣为原料的乙醇发酵菌株。     

Fermentation conditions affecting the bacterial growth and exopolysaccharide production by Streptococcus thermophilus ST 111 in milk-based medium

AIMS: To study the effect of different fermentation conditions and to model the effect of temperature and pH on different biokinetic parameters of bacterial growth and exopolysaccharides (EPS) production of Streptococcus thermophilus ST 111 in milk-based medium. METHODS AND RESULTS: The influence of temperature and pH was studied through fermentation and modelling. Fermentations under non-pH controlled conditions with S. thermophilus ST 111 indicated that the EPS production was low in milk medium, even if additional nitrogen sources were supplemented. Under pH-controlled conditions, addition of whey protein hydrolysate to the milk medium resulted in a fivefold increase of the EPS production. This medium did not contain polysaccharides interfering with EPS isolation. Primary and secondary modelling of different fermentations revealed an optimum temperature and pH of 40 degrees C and constant pH 6.2, respectively, for growth in milk medium supplemented with whey protein hydrolysate. Maximum EPS production was observed in the range of 32-42 degrees C and constant pH 5.5-6.6. Whereas growth and maximum EPS production were clearly influenced by temperature and pH, the specific EPS production was only affected by stress conditions (T = 49 degrees C). CONCLUSIONS: Addition of whey protein hydrolysate to milk medium resulted in an increased growth and EPS production of S. thermophilus ST 111 under pH-controlled conditions. A modelling approach allowed studying the influence of temperature and pH on the kinetics of both growth and EPS production. SIGNIFICANCE AND IMPACT OF THE STUDY: The use of an appropriate milk-based medium and a combined model of temperature and pH can be of practical importance for the production of yoghurt or other fermented milks as well as for process optimization of the large-scale production of starter strains to be used for their EPS production.     

Racemization of Individual Aspartate Residues in Human Myelin Basic Protein

Human myelin basic protein (MBP), a long-lived brain protein, undergoes gradual racemization of its amino acids, primarily aspartic acid and serine. Purified protein was treated at neutral pH with trypsin to yield peptides that were separated by HPLC using a C18 column. Twenty-nine peptides were isolated and analyzed for amino acid composition and aspartate racemization. Each aspartate and asparagine in the protein was racemized to a different extent, ranging from 2.2 to 17.1% D isomer. When the racemization was examined in terms of the beta-structure model of MBP, a correlation was observed in which six aspartate/asparagine residues assumed to be associated with myelin membrane lipids showed little racemization (2.2-4.9% D isomer), whereas five other aspartate residues were more highly racemized (9.9-17.1% D isomer). Although the observed aspartate racemization may be related to steric hindrance by neighboring residues and/or the protein secondary structure, interaction of aspartates with membrane lipids may also be a major factor. The data are compatible with a model in which each MBP molecule interacts with adjacent cytoplasmic layers of myelin membrane through a beta-sheet on one surface and loops and helices on the other surface, thereby stabilizing the myelin multilamellar structure.     

Kinetics of ethanol production by recombinant Escherichia coli KO11

The fermentation kinetics for separate as well as simultaneous glucose and xylose fermentation with recombinant ethanologenic Escherichia coli KO11 are presented. Glucose and xylose were consumed simultaneously and exhibited mutual inhibition. The glucose exhibited 15 times stronger inhibition in xyclose fermentation than vice versa. The fermentation of condensate from steampretreated willow (Salix) was investigated. The kinetics were studied in detoxified as well as in nondetoxified condensate. The fermentation of the condensate followed two phases: First the glucose and some of the pentoses (xylose in addition to small amounts of arabinose) were fermented simultaneously, and then the remaining part of the pentoses were fermented. The rate of the first phase was independent of the detoxification method used, whereas the rate of the second phase was found to be strongly dependent. When the condensate was detoxified with overliming in combination with sulfite, which was the best detoxification method investigated, the sugars in the condensate, 9 g/L, were fermented in 11 h. The same fermentation took 150 h in nondetoxified condensate. The experimental data were used to develop an empirical model, describing the batch fermentation of recombinant E. coli KO11 in the condensate. The model is based on Monod kinetics including substrate and product inhibition and the sum of the inhibition exerted by the rest of the inhibitors, lumped together. (c) 1995 John Wiley & Sons, Inc.     

Optimization of dose of collagen hydrolysate to prevent UVB-irradiated skin damage

Collagen hydrolysate (CH) was orally administered to UVB-irradiated hairless mice at doses of 20, 200–2000 mg/kg BW/day. The low dose of CH increased the skin hydration and reduced the transepidermal water loss on damaged skin. These results suggested the optimal dose of collagen to improve the UV-damaged skin condition.