碱性蛋白酶Alcalase凝固豆乳的物性特征

在Alcalase凝固豆乳过程中pH下降程度小于0.2,SDS-PAGE电泳表明,大豆蛋白质各亚基在凝固过程中均降解为8～14kDa的肽段,说明大豆蛋白的部分降解是Alcalase凝固豆乳的根本原因。对Alcalase与盐类凝固剂氯化镁和氯化钙凝固豆乳的主要流变学性质比较发现,Alcalase凝固豆乳的硬度比盐类凝固剂大,凝胶强度比盐类凝固剂低,粘附性比盐类凝固剂高10倍以上,使凝胶较粘,乳清不易排出。     

蛋白酶对豆乳的凝固作用研究

以凝固时间和凝固强度为指标,考察了13种蛋白酶的豆乳凝固能力,发现胃蛋白酶、凝乳酶和风味蛋白酶没有豆乳凝固活性,Alcalase、木瓜蛋白酶和菠萝蛋白酶具有较强的豆乳凝固能力。各种蛋白酶的最适豆乳凝固温度范围比最适水解温度范围高20℃左右,豆乳凝固能力随pH的降低而增强。40℃和70℃下用蛋白酶作凝固剂得到的豆乳凝块破断强度最大为105.2Pa和148.2Pa,小于用氯化钙作凝固剂的豆乳凝块的破断强度(40℃,142.4Pa和70℃,198.4Pa),而且用酶凝固的豆乳凝块黏度较大,乳清不易排出。Alcalase具有较强的豆乳凝固能力,而且形成的豆乳凝块质地细腻,无苦味,具有一定的实际应用价值。     

豆腐盐类凝固剂的凝固特性与作用机理的研究

本文研究了盐类凝固剂 (氯化钙、氯化镁和硫酸钙 )对豆腐凝胶强度、保水性的影响 ,分析了盐类凝固剂的作用机理和凝固特性。增加盐类凝固剂浓度 ,可以强化豆腐凝胶强度 ,但对保水性有弱化作用。盐的阴离子对凝固特性的影响比阳离子更重要     

水的硬度对豆乳凝胶特性的影响

水的硬度对豆乳的凝胶特性有很大的影响。水的硬度作为表示水质的一个重要指标,是指水中各种可溶性钙盐和镁盐的含量。用2种硬度的水来制备豆乳凝胶(水硬度以Ca CO3计,分别为0 mg/L和307 mg/L,定义为对照组和实验组),GDL(葡萄糖酸-δ-内酯)为凝固剂,并设置0.2%、0.3%、0.4%3个质量浓度。通过测定豆乳凝胶的保水性、硬度、动态黏弹性等指标,来探究水的硬度对豆乳凝胶特性的影响。结果表明:实验组的豆乳凝胶,其水分含量较高,硬度及弹性更小;在低浓度凝固剂条件下,实验组的豆乳凝胶凝固速率更快,水中的钙镁离子可起到加快凝固速率的作用。     

豆乳凝固特性试验研究

利用自行设计的计算机一超声凝乳凝固时间检测分析系统试验研究了豆乳在两种凝固剂浓度和两个温度下凝固特性。试验结果表明,立乳在凝固超声衰减曲线上有一明显转折点即凝固初始点。凝固初始点显示出豆乳初凝完成并向凝固过程转变的特性在选 温度范围内,凝固时间的长短主要与凝固剂的浓度有关。     

模拟溶液法对豆腐凝固机理的研究

用豆乳模拟溶液与豆乳溶液对比的方法，发现在豆腐凝固过程中豆乳的ｐＨ值随温度升高而下降，证明盐凝固剂中的二价金属离子与植酸盐、柠檬酸盐等发生络合反应是豆乳ｐＨ值下降的原因，阐明了酸和盐凝固豆腐本质上的一致性。     

盐类凝固剂短时间内凝固特性的研究

研究了豆腐盐类凝固剂(氯化镁、硫酸镁、氯化钙)短时间内的凝胶强度、持水性、pH的变化规律。在较短的时间内,增大盐类凝固剂的浓度,凝胶强度增大,持水性降低,pH降低;温度越高,凝胶强度越大,持水性越低;时间越长,凝胶强度越大,持水性越高。氯化钙的凝固速率略大于氯化镁,大于硫酸镁。     

即食豆腐脑中盐类凝固剂包埋的研究

研究了盐类凝固剂的不同包埋比例对即食豆腐脑的凝胶强度、失水率及感官评定得分的影响。试验结果表明,对盐类凝固剂进行包埋,有利于盐类凝固剂分散均匀,可在一定程度上延缓大豆蛋白与盐类凝固剂的作用,有利于形成比较均匀的凝胶。盐类凝固剂∶麦芽糊精为1∶3时,所得的即食豆腐脑产品较好。     

豆乳凝固酶来源、凝乳机理及其应用研究进展

豆乳凝固酶是制备大豆食品的优质凝固剂,具有广阔的开发前景。对近年来国内外关于豆乳凝固酶的研究进展进行了综述,主要包括豆乳凝固酶的来源、凝乳机理、应用研究等内容,以期为今后豆乳凝固酶的研究和应用提供理论参考。     

豆腐家族展新姿

1　蔬菜豆腐一般豆腐用天然卤水作凝固剂。天然卤水是从海水浓缩而成的粗盐中提取的 ,很难取得。为了提高豆乳的凝固效率 ,人们普遍使用海水高度精制分离而成的氯化镁和工业生产的硫酸钙、氯化钙。也就是说 ,目前制成的豆腐大多数都不能说是 1 0 0 %的天然食品。日本一家公司研制成功用无头甘蓝及洋白蔬菜汁作凝固剂的色拉豆腐 ,完全不用添加剂。钙能使豆乳凝固 ,而植物所含的水溶性钙盐 ,也具有凝固作用。作为豆乳凝固剂使用的食物有 :无头甘蓝、元白菜、芥菜、小松菜、辣椒叶、苏紫叶等。其中辣椒叶的水溶性钙盐含量最高 ,每 1 0 0ｇ豆乳…     

Effect of Alkaline Treatment on the Dispersibility of Soy Protein Isolates and Properties of Milk Clots formed from Nonfat Milk and Treated Soy Protein Mixtures

Dispersibility of soy protein isolates was improved by adjusting pH to 12 and acidifying to pH 6.5. Alkaline treated isolates added to reconstituted nonfat milk reduced rennet induced coagulum firmness and syneresis more than did untreated soy protein isolates. Treated soy protein added to reconstituted nonfat dry milk reduced coagulum firmness and syneresis more than untreated soy protein. Soy protein interference with coagulum firmness and syneresis increased with an increase in pH becoming most severe at pH values above 11. Adjusting the pH of reconstituted NFDM in the absence of soy protein to pH 8 and holding for 30 min before adjusting it back to pH 6.5 had no effect on coagulum firmness or syneresis. However, higher pH treatments (pH 10 and above) caused reduction in coagulum firmness and in syneresis.     

Effects of Enzyme Modified Soy Protein on Rennet-Induced Reconstituted Nonfat Dry Milk Coagulum Properties

Soy protein was hydrolyzed by trypsin, pepsin and α-chymotrypsin. Effects of adding hydrolyzed soy protein on rennet-induced nonfat milk coagulum texture and syneresis were studied. Pepsin-modified soy protein increased coagulum firmness and syneresis greater than untreated soy protein. Soy protein hydrolyzed with trypsin for 150 min and added to nonfat milk increased coagulum firmness greater than nonfat milk with no soy protein added. Chymotrypsin-modified soy protein acted similarly to the trypsin modified soy protein except the coagulum firmness was less than nonfat milk alone. Soy protein hydrolyzed by trypsin followed by pepsin increased coagulum firmness more than hydrolysis by a single enzyme and was close to nonfat milk without soy protein.     

TEXTURAL AND MICROSTRUCTURAL PROPERTIES OF RENNET-INDUCED MILK COAGULUM AS AFFECTED BY THE ADDITION OF SOY PROTEIN ISOLATE

The effect of the addition of soy protein on the textural properties and microstructure of reconstituted nonfat dry milk coagulum with time after rennet addition was studied using an Instron Universal testing machine with a newly developed test cell, and by scanning electron microscopy. Soy protein added to reconstituted nonfat dry milk at 5% of the total solids resulted in a reduction in firmness, a decrease in syneresis and a looser microstructure of the coagulum at any given time up to two hours after rennet addition as compared to the control without added soy protein. An increase in the level of soy protein to 10 and 20% of the total solids resulted in a further reduction in coagulum firmness and in syneresis. Syneresis was also followed during changes in coagulum firmness. Analysis of the textural as well as microstructural data suggests that changes in coagulum firmness and syneresis of rennet-induced milk coagulums (with or without added soy protein) with time after rennet addition were associated with the extent to which casein micelles coalesced during coagulum formation. The Instron test and the syneresis test developed in this study were simple and practical.     

Effects of pH, CaCl2 and Soy Protein on [Ca2+] in Reconstituted Nonfat Dry Milk and on Rennet-Induced Coagulum Properties

Increasing CaCl₂ and lowering pH caused a significant increase in [Ca²⁺] in reconstituted nonfat dry milk (RNDM), while the addition of soy protein caused a significant reduction in [Ca²⁺]. Lowering pH greatly increased rennet-induced coagulum firmness in RNDM and slightly increased it in RNDM-soy protein mixtures. Added CaCl₂ increased coagulum textural parameters and syneresis in both systems. The extent to which these properties were increased was higher in RNDM than in the coagulum containing soy protein depending on the time after rennet addition and the amount of CaCl₂ added. The first increment of CaCl₂ added had the highest effect in improving textural properties and increasing syneresis.     

The evaluation of proteases as coagulants for soy protein dispersions

The ability of different proteases to induce the gelation of soy protein isolate dispersions (5.33% w/w) was studied. The coagulation time and gel firmness were determined using dynamic viscoelastic measurements. Among the six protease tested, papain was the most effective coagulant in terms of gel strength and coagulation speed; the second was alcalase. Degree of hydrolysis (DH), pH and viscosity profiles of soy proteins were tested during the coagulation with different proteases. The result suggested that strong interactions, other than electrostatic interaction, existed between peptides in papain and alcalase induced coagulation. Thermal and pH stability tests indicated that papain was more stable than alcalase in the temperature (60–90 °C) and pH (5.8–7.0) ranges studied. Higher papain dosages within the range of 5–13.3 U/ml resulted in firmer soy protein gels, but concentrations higher than 13.3 U/ml produced weaker gels. With the addition of 0.625 mM cysteine, the soy protein coagulation ability of papain was improved. A soy protein gel formed with 0.025% papain in the presence of 0.625 mM cysteine had about the same strength as that induced by 0.133% papain without cysteine.     

Investigation of an in-line prototype fluorescence and infrared backscatter sensor to monitor rennet-induced coagulation of skim milk at different protein concentrations

Coagulation of milk is one of the most important steps in cheese manufacture. Cutting the coagulum at optimum firmness is important to optimise the yield and quality of the cheese produced. The aim of this study was to investigate a prototype sensor to monitor rennet-induced coagulation of skim milk at different protein concentrations (3.3%, 4.0% and 4.7%) and to develop a model to predict the coagulum cutting time at a desired storage modulus (G′). Fluorescence and infrared backscatter profiles were recorded at wavelengths of 350 and 880 nm, respectively. Rheological measurements were used as a reference method to determine the times required for the coagulum to reach G′ values of 0.5, 5 and 20 Pa. Time parameters extracted from the optical profiles generated during the coagulation process were used to develop a model to predict the cutting time at which the coagulum reaches selected G′ values. This study demonstrated that the investigated prototype sensor, combined with the developed prediction model, can be used as an in-line PAT tool for real-time monitoring of milk coagulation and prediction of cutting time in cheese manufacturing.     

毛霉蛋白酶在腐乳成熟中的作用

采用SDS—PAGE与ESI—MS相结合的方法研究了毛霉蛋白酶和Alcalase蛋白酶对SPI的酶促降解作用，研究结果表明，Alcalase是一种典型的内切型蛋白酶，它能在1h内催化大豆蛋白降解为分子量10000D以下的肽段，但降解产物容易相互聚合而沉淀，毛霉蛋白酶则具有较强的肽酶活性，能够以大豆蛋白或多肽为底物酶促降解生成多量的水溶性肽，为后期嗜盐菌的生长提供了可供利用的速效氮素营养，毛霉蛋白酶还具有消除苦味、形成鲜味物质的作用，与腐乳风味形成有关。     

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.     

Enzymic modification of extruded soy protein concentrates as a method of obtaining new functional food components

Response surface methodology was used to determine optimal conditions for limited hydrolysis of the extruded soy protein concentrate with Alcalase and Esperase, which would allow one to obtain new products with desirable functional properties. The best results can be obtained by conducting the process at 60°C with water addition 13 g/g protein, enzyme addition 8 × 10⁻³ Anson Units/g protein, as well as pH 8.3 and 8.6 and time 120 and 60 min using Alcalase and Esperase, respectively. It was shown that hydrolysates obtained from extruded soy protein concentrate differ from those from non texturized raw material in the content of sulfhydryl groups, disulphide bonds and surface hydrophobicity. Also, as was shown by SDS-PAGE, protein breakdown in them was less selective.     

水酶法提取大豆油工艺中乳状液的酶法破乳研究

为降低水酶法提取大豆油过程所产乳状液的稳定性,得到较高的游离油回收率,研究了α-淀粉酶、纤维素酶、Alcalase碱性蛋白酶、7L中性蛋白酶的破乳效果;通过破乳率、Zeta电位、粘度、粒径分布和平均粒径指标,分别考察了Alcalase碱性蛋白酶和7L中性蛋白酶对乳状液稳定性的影响。结果显示,在所选酶中Alcalase碱性蛋白酶、7L中性蛋白酶破乳效果最好,相同水解条件下,Alcalase碱性蛋白酶的破乳率高于7L中性蛋白酶。2%的7L中性蛋白酶酶解60 min时破乳率达100%,而在相同酶解时间内,1% Alcalase碱性蛋白酶即可实现100%破乳。经Alcalase碱性蛋白酶和7L中性蛋白酶水解后,乳状液的粘度变低,电位电势减弱,油滴发生聚集,导致乳状液稳定性下降。随Alcalase和7L蛋白酶浓度和酶解时间的增加,相应地,乳状液的粘度进一步降低,破乳率上升。