干酪乳杆菌胞壁蛋白酶的分离及水解酪蛋白产物特性

通过DEAE-Sephadex A-25和Sephadex G-100对干酪乳杆菌胞壁蛋白酶粗提物进行分离纯化,分离到酶比活力为12.50U/mg的CEP-1与16.67U/mg的CEP-2两种胞壁蛋白酶。CEP-1提纯倍数达到50,回收率为33.61%;CEP-2提纯倍数为66.68,回收率55.17%。对不同时间和底物浓度下CEP-1与CEP-2的α-酪蛋白和β-酪蛋白水解特性进行研究。结果显示,酪蛋白水解产物有显著的抗ACE与抗氧化活性,产生最高ACE抑制活性的水解条件为：CEP-2水解α-酪蛋白,时间6h,酶与底物质量比1:10,此时ACE抑制活性为84.66%;在酶与底物质量比1:40,水解时间4h条件下,CEP-2水解β-酪蛋白产生最佳的O2－ ·清除能力,其IC50为0.2138mg/mL。     

不同酶水解菜籽蛋白的水解物的抗氧化活性研究

使用alcalase、protamex、flavourzyme、木瓜蛋白酶、中性蛋白酶和胰蛋白酶共6种蛋白酶水解菜籽蛋白,研究水解物清除DPPH自由基能力、还原能力和抑制亚油酸过氧化活性。结果表明,6种蛋白酶水解菜籽蛋白的水解物都具有抗氧化活性,但水解物的抗氧化活性与水解所用酶的种类和水解时间有关,胰蛋白酶和flavourzyme水解物显示了较强的清除DPPH自由基和还原能力,6种蛋白酶水解物抑制亚油酸过氧化活性高于VE,但略低于BHT。alcalase水解菜籽蛋白时,水解10~45 m in的水解物清除DPPH自由基和还原能力较强,延长水解时间并不能提高其抗氧化活性。     

The effects of pretreatments on antioxidative activities of protein hydrolysate from the muscle of brownstripe red snapper (Lutjanus vitta)

Different pretreatments of mince from brownstripe red snapper (Lutjanus vitta) including 1) washing; 2) membrane separation; 3) washing followed by membrane separation and 4) membrane separation followed by washing were conducted prior to hydrolysis. Among the resulting minces, that subjected to membrane separation with subsequent washing (MS/W) contained the lowest remaining myoglobin content, phospholipid content, heme iron and non-heme iron contents (p < 0.05) and showed the lowest TBARS values throughout 9 days of storage at 4 °C in the presence and absence of 0.15 mol L⁻¹ cupric acetate (p < 0.05). When hydrolysates from 1) mince, 2) MS/W and 3) protein isolate from MS/W (PI) with different degree of hydrolysis (DH) (20, 30 and 40%) were prepared using proteases from pyloric caeca of brownstripe red snapper, antioxidative activities determined by DPPH, ABTS radical scavenging activities, ferric reducing antioxidant power and metal chelating activity varied with hydrolysates and DH. Antioxidative activities increased with increasing DH up to 40% (p < 0.05). At all DH tested, hydrolysate prepared from MS/W exhibited the highest antioxidative activities determined by all assays, compared to those from mince and PI (p < 0.05). Hydrolysate from MS/W with 40% DH had the molecular weight lower than 6.5 kDa as determined by SDS-PAGE. In liposome oxidation system, the addition of hydrolysate from MS/W resulted in the lower TBARS, compared with the control throughout the incubation period of 48 h at room temperature (25-28 °C). Therefore, fish mince with membrane separation followed by washing was the most appropriate source for production of hydrolysate possessing antioxidative activity with the lowered amount of lipids and pro-oxidants.     

蒸汽爆破尾叶桉木材纤维素酶水解液发酵单细胞蛋白

用高效液相色谱对蒸汽爆破尾叶桉木材的纤维素酶水解液进行了还原糖和乙酸含量分析,通过酿酒酵母和假丝酵母混合接种,对水解液进行了摇瓶发酵单细胞蛋白的工艺研究,确定了发酵的最佳工艺条件。结果表明,水解液中主要含有葡萄糖和木糖,用双菌种混合发酵单细胞蛋白的最佳发酵条件为:酿酒酵母(Sacchromyces cerevisive):假丝酵母(Candida utilis2.587)为1:3,发酵温度31℃,初始pH4.5,初始还原糖浓度17～18g/L,发酵时间27h。     

鸡蛋清蛋白水解物的物化及功能性质的研究

蛋清蛋白质溶解性欠佳且容易起泡,使其应用受限。本文利用Alcalase酶解鸡蛋蛋清蛋白制取水解度为5~15%的酶解物并对酶解物的理化性质和功能性质进行了表征。测定性质包括乳化性、起泡性及稳定性以及溶解性、表面疏水性。所有酶解产物具有较低的表面疏水性,水解大大提高了溶解度,当水解度15%时最大值为89%,但乳化性有所降低,起泡性及稳定性也大约下降了40%。     

玉米蛋白抗氧化肽的制备及其在熟肉糜中的应用

采用碱性蛋白酶(Alcalase)水解玉米蛋白制备出具有抗氧化活性的玉米蛋白肽。通过测定玉米蛋白水解物对卵磷脂脂质氧化体系的抑制作用和还原能力研究其抗氧化活性,结果表明,当水解条件为底物浓度10%,加酶量(E/S)为1:100,水解时间5h时,所得水解产物抗氧化活性最强;采用凝胶层析法对5h水解物进行分离纯化,得出抗氧化最强部分的分子量范围为147～1745。将玉米蛋白肽加入到熟肉糜中,当添加量为2%时,与对照组相比可以保持肉糜鲜红的颜色,且延缓肉糜氧化。     

鱼糜副产物蛋白水解物的抗冻活性及对嗜热链球菌的抗冻效果及机制

研究鱼糜加工副产物蛋白水解物（surimi by-product protein hydrolysate,SBPH）的结构与抗冻活性,并通过测定嗜热链球菌（Streptococcus thermophilus）在冷冻处理后的生长性能、丙二醛（malondialdehyde,MDA）含量、相关蛋白酶活力、代谢活性与膜电势等指标探究SBPH对嗜热链球菌的抗冻作用机制。结果表明,SBPH的分子质量范围为260～2 550 Da,共鉴定出78 个氨基酸长度为8～18的肽段,部分肽段具有三肽重复序列的特征结构,赋予SBPH较高的抗冻活性（热滞活性为1.76 ℃）。与其他抗冻剂（蔗糖、脱脂牛乳、甘油）相比,SBPH（质量浓度2 mg/mL）可提升冷冻处理后嗜热链球菌的细胞存活率、生长活性和细胞酸化活性,并且SBPH可减轻低温对细胞造成的氧化应激损伤,显著抑制相关蛋白酶活力的下降（P＜0.05）,并提升细胞代谢活性,减轻细胞膜的超极化,利于保持细胞膜的完整性和流动性。SBPH可在一定程度上维持磷脂双分子层间的作用力,保护细胞膜的结构。综上所述,SBPH可保护细胞的功能和完整性,在一定程度上降低了细胞的低温损伤。     

Incorporation of dairy ingredients into wheat bread: effects on dough rheology and bread quality

 Dairy ingredients are used in breadmaking for their nutritional benefits and functional properties. The effects of the traditionally-used whole and skimmed milk powder, sodium caseinate, casein hydrolysate and three whey protein concentrates on dough rheology and bread quality were studied. Whole and skimmed milk powders improved sensory characteristics. Sodium caseinate and hydrolysed casein displayed beneficial functional properties in breadmaking including low proof time, high volume and low firmness. Both ingredients increased dough height measured with the rheofermentometer. Bread with 2% or 4% sodium caseinate added was rated highly in sensory evaluation. Incorporation of whey protein concentrates generally increased proof time, decreased loaf volume and decreased dough height measured with the rheofermentometer. Received: 6 April 1999 / Revised version: 13 July 1999     

Emulsifying and Bactericidal Properties of a Protamine-Galactomannan Conjugate Prepared by Dry Heating

Protamine was conjugated with galactomannan (GM) in a controlled dry state at 60° and 79% relative humidity. The covalent attachment of GM to protamine was confirmed by SDS-PAGE and gel chromatography. The resulting protamine-GM conjugate had excellent emulsifying properties without significant loss in bactericidal activity. The emulsifying activity was six times and the emulsion stability of the conjugate more than 10 times higher than those of protamine. In acidic (pH 3) and salt (0.2M NaCl) systems the conjugate showed much more effective emulsifying properties than commercial emuJsifiers. In addition, the emulsifying properties of the conjugate were retained after preheating at 90°. Protamine-GM conjugate could be used for processed foods as a bifunctional food additive, emulsifier and antibacterial reagent.     

The photosynthetic hydrogen production performance of a newly isolated Rhodobacter capsulatus JL1 with various carbon sources

Rhodobacter capsulatus is a photosynthetic bacterium with the ability to produce H₂ under photosynthetic condition. In this study, a new strain JL1 isolated from lake water was identified as Rhodobacter capsulatus by phylogenetic analysis of 16S ribosomal DNA (rDNA) sequence. Initial medium pH and l-glutamate (nitrogen source) concentration were optimized. At optimum pH 7.0 and 7 mmol/L l-glutamate, R. capsulatus JL1 could grow and produce hydrogen on the carbon sources of acetate, butyrate, glucose, xylose and fructose with the maximum substrate to H₂ conversion efficiencies of 67.5%, 26.6%, 46.1%, 46.2% and 46.6%, respectively. The maximum H₂ production rate, 124 ± 0.6 mL/(L·h), was obtained using 20 mmol-glucose/L as the carbon source. The addition of appropriate acetic acid to the tests with low concentration of glucose was able to improve the H₂ yield. Under the optimum operation parameters, the maximum H₂ yield and H₂ production rate of R. capsulatus JL1 from 16.4 g-corn straw/L-culture were 2966.5 ± 43.2 mL/L and 71.1 ± 4.5 mL/(L·h), while the chemical oxygen demand (COD) removal rate was up to 49.6%. This study indicates that R. capsulatus JL1 can serve as good candidate strain for H₂ production with organic waste water as well as effluent of dark-fermentation.