Actual Milk Coagulation Time and Inverse of Chymosin Activity

Coagulation of Berridge substrate by several different chymosin concentrations was followed with a spectrophotometer to obtain actual coagulation times. Actual coagulation times plotted as functions of inverse enzyme concentrations produced an intercept within experimental error of zero. Deviations of this intercept from zero are artifacts of methods used to measure coagulation time.     

猪血球胃蛋白酶水解物抗氧化活性的研究

以脂质氧化抑制力(LA)、亚铁离子螯合能力(FICP)、二苯代苦味酰肼(DPPH)自由基清除能力(DRSA)为测定指标,探讨了猪血球胃蛋白酶水解物(PDPH)的抗氧化活性。结果表明,PDPH具有极好的亚油酸脂质氧化抑制力(P<0.01)、一定的FICP(P<0.05)和DRSA(P<0.05)。PDPH的脂质氧化抑制力在10μg/mL时为α-生育酚的4.38倍,100μg/mL时为5.50倍;金属离子螯合能力在100μg/mL样品浓度,50μmol/L FeCl2时的螯合率约为10μmol/L EDTA的1.23倍;在10-100μg/m L样品浓度时基本无DRSA,但在500μg/m L的DR-SA为53.8%。     

牡丹菊粉低脂扣碗酪的研制及其抗氧化活性

以牡丹花、菊粉和米酒为主要研究对象,以感官评分为指标,利用单因素和正交试验优化牡丹菊粉低脂扣碗酪的最佳配方,并分析产品的抗氧化活性。结果表明,牡丹菊粉低脂扣碗酪的最佳配方为:牡丹花浆添加量20 mg/mL,菊粉添加量4%,米酒添加量22%,发酵剂接种量0.35%。抗氧化试验表明,10 g的牡丹菊粉低脂扣碗酪对羟基自由基(·OH)、超氧阴离子自由基(O;)和DPPH自由基的清除率分别为41.65%、26.09%和42.66%,显著高于对照组(P<0.05),可见牡丹菊粉低脂扣碗酪具有良好的抗氧化活性。     

大豆皂苷提取工艺优化及对胃蛋白酶抑制活性

为深入研究大豆功能分子对消化酶的作用,以市售大豆为研究对象,采用超声辅助提取大豆粉中总皂苷,在超声时间、超声温度、料液比、乙醇浓度等单因素实验的基础上,选用响应面法优化超声提取大豆总皂苷的最佳工艺参数,并考察了最佳提取工艺条件下大豆总皂苷的抗氧化活性及对胃蛋白酶的抑制作用,同时深入分析酶的抑制机制。实验结果表明,大豆总皂苷的最佳提取工艺参数为料液比60 mL/g、乙醇浓度64%、超声时间20 min、超声温度41 ℃,实际提取率为(4.26±0.17)%。抗氧化实验表明,大豆总皂苷对ABTS⁺自由基和DPPH自由基均有清除效果,该皂苷具有一定的抗氧化活性。胃蛋白酶抑制实验表明,大豆皂苷对胃蛋白酶具有抑制作用,其IC₅₀为(0.585±0.021)mg/mL。酶动力学研究表明大豆皂苷与胃蛋白酶属于非竞争性抑制。研究结果为大豆总皂苷作为天然抗氧化剂和酶抑制剂的开发提供参考。     

Interactions of Calcium,pH, Temperature,and Chymosin During Milk Coagulation,

Holstein milk samples with good and poor chymosin-coagulation characteristics were coagulated in the Formagraph using different combinations of five levels of chymosin, three pH, and three temperatures in the presence and absence of .02% added calcium chloride.All the main factors significantly altered both coagulation time and curd firmness. Multiple comparisons of mean coagulation times showed that lower concentrations of chymosin (.01, .02, and .03 rennin units/ml milk) were significantly different in altering coagulation time and were different from higher concentrations (.04 and .05 rennin units/ml milk). The three pH produced significantly different mean coagulation times. Addition of more than .02 rennin units/ml milk was not necessary for adequate curd firmness in 30 min after chymosin addition where the pH of the milk was 6.4 or lower. Addition of .02% calcium chloride to milk was not necessary for adequate curd firmness 30 min after chymosin addition if other milk coagulation factors were adequately adjusted (pH ≤ 6.4; chymosin concentration = .02 rennin unit/ml milk; temperature = 37°C).     

鮟鱇鱼皮酶溶性胶原蛋白对自由基的清除作用

采用胃蛋白酶从鮟鱇鱼皮中提取胶原蛋白,分析胃蛋白酶酶溶性胶原蛋白的氨基酸组成和超微结构,并研究体内外清除自由基机理。结果表明:胃蛋白酶酶溶性胶原蛋白的超微结构呈均匀网状分布,是良好的药物载体,体外清除自由基效果呈质量浓度依赖性,当质量浓度为10 mg/L时,清除超氧阴离子自由基(O2-·)和羟自由基(·OH)能力最强。体内实验显示其能显著抑制小鼠皮肤中丙二醛生成,提高超氧化物歧化酶、过氧化氢酶、谷胱甘肽过氧化物酶和羟脯氨酸含量,当剂量为100 mg/(kg·d)时最好。提示该胶原蛋白具有体内外清除自由基作用,其氨基酸组成、超微结构与清除自由基能力有关,提取的鮟鱇鱼皮酶溶性胶原蛋白清除自由基活力接近于提取的胶原蛋白肽。     

Pepsin Digestibility and Antioxidant Activity of Egg White Protein in Model Systems with Green Coffee Extract

Model systems of egg white protein and green coffee extract were dry heated at 110 or 180^oC for up to 1 h to investigate the extent of interactions between coffee polyphenols and a protein of high nutritional significance. Saccharose, starch, sunflower oil, and ferrous ions were also applied to the model mixtures. In heated and control systems amino acid profiles, in vitro pepsin digestibility, color, and antioxidant properties were analyzed. Among heated samples, high protein nutritional value was obtained in the system containing 3% of green coffee extract, while the least favorable conditions for maintaining protein high nutritional value were observed in system of protein, saccharose, starch, and sunflower oil without addition of coffee polyphenols. The samples of high protein nutritional value were also characterized by high antioxidant activity.     

牛凝乳酶全长cDNA的克隆及其原核表达载体的构建

从小牛皱胃中提取凝乳酶(Chymosin)总RNA,经过RT-PCR获得凝乳酶cDNA,纯化后与pMD-18T载体连接,转化大肠杆菌JM109,通过双酶切和序列测定,获得了凝乳酶全长基因序列。序列测定表明,凝乳酶全长核苷酸长度为1 143 bp,编码381个氨基酸。与GenBank上已发表序列NM_180994进行比较,核苷酸同源性为99.56%。将该基因片段克隆到原核表达载体pET-22b中,构建重组质粒pET-22b/Chymosin,所获重组质粒经过酶切、测序鉴定,证实含有目的片段,且连接、构建正确,为凝乳酶的进一步表达奠定了基础。     

干酪加工专用凝乳酶及其基因工程酶的研究

凝乳酶是干酪加工中必须用到的酶制剂,本文详细的介绍了凝乳酶的结构,凝乳酶的不同来源,凝乳机理以及影响凝乳酶活性的因素等内容,并阐述了基因工程凝乳酶的研究现状及凝乳酶的发展前景,为解决我国凝乳酶的短缺问题提供思路.     

果蔬粒豆腐与传统豆腐比较研究

对果蔬粒豆腐和传统豆腐进行了比较研究。其结果表明:由于果蔬中含有大量的维生素和纤维素,弥补了单纯黄豆豆腐的不足,其营养价值有很大提高。     

Use of Recombinant Chymosin in the Manufacture of Cheddar and Colby Cheese

Recombinant chymosin purified from E. coli K12 (Genencor Inc.) was examined for its suitability to manufacture Cheddar cheese. Commercial calf rennet or recombinant chymosin with and without Bacillus subtilis cellular homogenate was used to determine if enzyme sources affected Cheddar cheese quality or yield. Cheese was evaluated at 3 and 6 mo of age. Purified enzyme was mixed with cellular extracts from B. subtilis at approximately one and four times the protein concentration in the initial homogenates. Cellular materials did not affect clot times, cheese quality, or inhibit cheese acid development. No differences were noted between the yields of Colby cheese manufactured with calf rennet and recombinant chymosin. Initial Cheddar cheese manufactured with recombinant chymosin were excessively bitter, typical of cheese retaining excessive amounts of proteases. Dilution of purified prochymosin preparations increased total enzymic activity 2.7 times. Evidently, the purified recombinant preparations contained some oligomers that became active after being incorporated into the cheese mass, causing bitter flavors to develop during aging. Diluted enzyme preparations were used successfully in the manufacture of Cheddar cheese.     

不同泌乳期羊乳的理化特性及其酶凝固特性

以不同泌乳期羊乳为原料,研究其基本理化特性(色泽、膻味、p H值、酸度、密度、乳化学成分)及酶凝固特性(硬度、内聚性、弹性)和持水力,以便为羊乳制品的开发提供更适宜的生产原料。结果表明,不同泌乳期羊乳的各理化特性和酶凝固特性差异较大。随着泌乳期的延长,羊乳由乳黄色逐渐变为乳白色,其膻味逐渐变淡,p H值缓慢上升,而酸度、密度、乳化学成分含量及酶凝固特性、持水力均呈下降趋势。经综合分析,建议将泌乳第120~150天的羊乳作为稀奶油生产的较优质原料;泌乳第4~150天的羊乳更适合用于凝固型酸奶和奶酪的加工;而泌乳第7~240天的羊乳均可用于生产液态羊乳或羊乳粉,但需要对其主要化学成分进行标准化处理。     

腐乳的研究概况与发展前景

腐乳是我国传统的发酵豆制品,以其独特的风味、丰富的营养等特点受到很多国家的推崇。文中简要介绍了腐乳的研究概况及发展前景,并分析了其存在的问题。     

Effect of Plant Originated Coagulants and Chymosin on Ovine Milk Coagulation

The coagulation of ewe's milk was studied by using plant source coagulants namely the artichoke, Cynara scolymus L. cv. Blanca, and latex from the fig tree (Ficus carica L.). A turbidimetric method was used to evaluate and compare the coagulation properties of the novel coagulants with chymosin treated samples. Syneresis capacity and sensory evaluation of resultant cheese samples were studied and it was found that both cynara and chymosin produced sigmoidal increase in turbidity to the milk with three distinct phases. The coagulation kinetics was affected substantially by both coagulants. Plant coagulant induced shorter gelation time compared to chymosin however required longer time for restructuration (end of coagulation). The coagulum obtained with the latex of Ficus carica had a higher yield, owing to its high water retention capacity. With the exception of color, the overall sensory attributes did not show significant differences among coagulants.     

HACCP在鸡蛋干生产中的应用

结合鸡蛋干企业生产实际,以ISO22000:2005《食品安全管理体系食品链中各类组织的要求》为理论指导,对鸡蛋干生产工艺过程进行危害分析,探讨确定了4个关键控制点,并确定关键控制点的保障措施和出错纠正措施。     

Residual Avid in Activity in Cooked Egg White Assayed with Improved Sensitivity

An assay, based on binding of the dye 2–(4'hydroxyazobenzene)-benzoic acid (HABA) and widely used in studies of avidin in liquid systems, was combined with an aqueous extraction method and used to assay avidin in cooked egg white. The method was validated for linearity of response to increasing avidin concentrations, precision, accuracy, recovery and sensitivity. Mean residual avidin activity in fried, poached and boiled (2 min) egg white was 33, 71 and 40% of the activity in raw egg white.     

Inhibition of Chymosin and the Coagulation of Para-Casein Micelles by Anions

The effect of monovalent anions on the coagulation of para-casein micelles was determined by monitoring light transmission after adding different Ca salts (40 mM) to partially hydrolyzed casein micelles. The release of macro-peptide by chymosin was quantified using fluorescamine. The average rate of the chymosin-initiated coagulation of casein micelles, approximated by the reciprocal of clotting time, was determined as a function of anion type and concentration to determine the simultaneous effects of anions on chymosin velocity and para-casein micelle aggregability.Chymosin velocity and the coagulation of para-casein micelles were progressively inhibited by anions; the larger the anion, the greater the inhibition (SCN⁻ > NO₃⁻ > Br⁻ > Cl⁻). This is attributed to the binding of anions to cationic binding sites on kappa-casein and para-kappa-casein. The relative effect of the larger anions compared with that of Cl⁻ on the average rate of the chymosin-initiated coagulation of casein micelles increased with anion concentration (6 to 120 mM) but became limited at 120 mM. In the presence of 120 mM SCN⁻, NO₃⁻ and Br⁻, the average rate of coagulation was 26, 59, and 78% of that obtained with 120 mM Cl⁻.The marked sensitivity of the interactions between chymosin and kappa-casein and between para-casein micelles to anion type support conclusions that cationic sites on kappa-casein are important in the mechanism of the chymosin-initiated coagulation of casein micelles. Thus, monovalent anions may be useful to elucidate the mechanism of protein-protein interactions in food systems.     

根霉凝乳酶的分离纯化及其酶学特性研究

采用70%乙醇对凝乳酶进行粗提,回收率为52.65%.采用DE-52和Sephadex G-75柱进行纯化,经冷冻干燥成酶粉,其活力1813.74 U/mg,回收率为11.25%.该酶的最适反应pH为5.7,在pH 5～7.5范围酶活力保持稳定;最适反应温度45℃,60℃保持20min,酶完全失活.Ca2+、Fe2+、Mg2+、Cu2+、Zn2+、Al3+对该酶的活力有不同程度的促进作用,其中以Al3+和Ca2+的促进作用最显著,Na+和K+对该酶的活力有抑制作用.通过SDS-PAGE测定,该酶的分子质量约35kDa.     

Effects of Processing on Curd Yield and Nutrient Composition of Rapid Hydration Hydrothermal Cooking and Traditionally Processed Soymilk and Soybean Curd

Soymilk processed by the Rapid Hydration Hydrothermal Cooking (RHHTC) method had higher thiamin and protein when compared to traditionally extracted soymilk (P<0.0001). Traditionally processed soybean curd had higher protein (P < 0.0001) and fat (P < 0.001) while carbohydrate and ash were lower (P<0.0001) when compared to RHHTC produced soybean curd. Variation in amino acid compositions occurred in soymilks and soybean curds. RHHTC-produced soybean curd had greater curd yields than traditionally produced soybean curd.