Effects of Ultrasound Treatment on the Properties of Chymosin

When chymosin was extracted by ultrasound curd tension and syneresis were significantly lower for Berridge substrate coagulated by the ultrasound-treated chymosin than by the control. Experimental chymosin had a shorter induction period and was more heat-sensitive than the control. Activation energy of chymosin obtained by ultrasound treatment was significantly lower than that of the control. Ultrasound treatment did not significantly change the chromatographic patterns of chymosin. Only two distinct enzymatically active proteins were observed with DEAE-cellulose chromatography. Electrophoretic properties were similar for chymosins obtained by ultrasound and control methods.     

Processing Parameters of Chymosin Extraction by Ultrasound

Conventional chymosin (rcnnin) production requires a prolonged extraction. An ultrasound method of chymosin extraction was developed for increased efficiency. Ultrasound extraction was carried out with Tekmar sonic disruptor (TK 1000) and Lauda circulator. Control extraction was carried out by shaking. The use of ultrasound resulted in a significant reduction of extraction time with increases in activity and yield of chymosin. The optimal parameters for ultrasound extraction were: specific intensity, 36 W/cm² at 20 kHz frequency; time of exposure, 80 min; temperature, 25°C; ratio of abomasa to extraction solution, 1:25; and activation time of prochymosin, 13.0-13.5 hr.     

Comparison of Conventional and Ultrasound Assisted Extraction Techniques of Yellow Tea and Bioactive Composition of Obtained Extracts

Yellow tea is the least investigated type of tea (Camellia sinensis), therefore, this study is focused on characterization of bioactive content of yellow tea extracts as well as application of inovative extraction techniques (ultrasound bath and probe) compared to conventional extraction, in water and aqueous ethanol media. Comparison of obtained extracts was based on total flavonoid (TFC) and nonflavonoid (TNC) content, HPLC analysis of individual polyphenols and methylxanthines, and antioxidant capacity. The highest TFC was detected in extracts obtained by ultrasound probe assisted extraction in aqueous ethanol as an extraction medium and the lowest in extracts obtained by ultrasound bath extraction (water and aqueous ethanol) with a trend of increase with prolonged extraction time. Conventional extraction was successful when combined with 75% aqueous ethanol as an extraction medium. Results of HPLC analysis and antioxidant capacity assays were generally in compliance with these results. This study proves that ultrasound probe extraction could succesfully be used for extraction of polyphenols and methylxanthines from yellow tea.     

Effect of Ultrasonic Treatment on the Extraction of Chymosin

Improvement of chymosin (rennin) production is limited by a prolonged extraction process. An ultrasonic method of chymosin extraction was developed to increase efficiency. The application of ultrasonic energy significantly reduced time required for the extraction process as a result of abomasum tissue dispersing, destruction of the cells, intensive blending, separation of particles, and increase of the interphase abomasum-extraction medium. The ultrasonic extraction process significantly increased yield of chymosin.Optimal technological parameters for extraction and properties of extraction medium were established: time of ultrasonic treatment (45 min), intensity of ultrasound (3.34 W/cm²), temperature of extraction medium (15°C), NaCl concentration in solution (5%), ratio of abomasum to extracting solution (1:18), NaCl concentration in solution (5%), ratio of abomasum to extracting solution (1:18), pH of solution (4.2 to 4.3), time of chymosin extract activation (7 h), degree of abomasum shredding (strips 5 to 8 mm wide), and time of abomasum swelling (20 min).     

发酵法生产凝乳酶的概述

凝乳酶是干酪生产过程中的关键性酶,其主要作用是凝聚牛奶中的酪蛋白.本文简要介绍了凝乳酶的起源和它的凝乳机制.并着重阐述了微生物源凝乳酶的特点及研究者们在提高微生物凝乳酶活性降低其蛋白分解活力上所做的研究.     

微生物源凝乳酶的研究进展

本文简要介绍了凝乳酶的一般特性和凝乳机理 ,综述了微生物源凝乳酶的研究进展和利用基因工程生产凝乳酶的发展状况 ,最后对凝乳酶的生产与开发进行了展望     

Characterization of Actin and Myosin Extracts Obtained Using Two Improved Laboratory Methods

Actin and myosin are the most important contractile proteins in the muscle. Numerous authors developed different methods for isolation and purification of myofibrillar proteins. The aim of this study was to obtain suitable actin and myosin extracts from post-rigor porcine muscle to be used in further studies, such as testing the proteolytic activity of microbial cultures. Actin and myosin were quantified in the extracts using spectrophotometric methods, yielding 0.17 and 0.22 mg/mL, respectively. The isolation methods proposed in this study provided low contaminated extracts, showing purity percentages of 74.36 % in the case of actin and 65.43 % for myosin, as determined by sodium dodecyl sulfate–polyacrylamide gel electrophoresis. Subsequently, these extracts were sterilized through a 0.22-μm polyvinylidene difluoride filter with no significant retention observed. In conclusion, the procedures described in this work for actin and myosin isolation can be recommended for microbiological studies requiring sterilized pure muscle proteins extracts.     

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。     

Changes in Quality Characteristics of Fresh-cut Cucumbers as Affected by Pressurized Argon Treatment

This study evaluated efficacy of pressurized argon (Ar) treatments in preserving quality of fresh-cut cucumbers. Cucumber cubs were, respectively, treated with 0.5 MPa Ar, 1.0 MPa Ar, 1.5 MPa Ar and 1.5 MPa air for 1 h at 20 °C and without pressurized treatment (control) and then stored at 4 °C and 90 % relative humidity (RH) for 12 days. Physiological, textural, chemical, and microbial attributes were measured at 1–2-day intervals. Results indicated that pressurized Ar treatments inhibited respiration, water loss, softening, chlorophyll degradation, and color change. The treatments also reduced loss of ascorbic acid and soluble solids. Treated cucumbers carried significantly less microbial population as indicated by total plate counts of yeasts and molds. Therefore, it was concluded that pressurized Ar treatment was beneficial to preserve quality of fresh-cut cucumbers.     

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.     

Comparative Physico-chemical and Functional Properties of Cassava Starches Obtained by Conventional and Enzyme-Integrated Conventional Techniques

Comparative studies on the physico-chemical and functional properties of the cassava starches, obtained by conventional and enzyme-integrated conventional techniques, indicated no adverse chemical modifications and nearly equal X-ray diffraction patterns as well as granular structure. The starch obtained by enzyme-integrated technique has 50% lower ash content and nearly double water solubility at room temperature. The swelling power, the swelling volume and the viscosity indices were slightly lower. Better cooking properties of the starch isolated by enzyme-integrated technique is indicated by its lower set-back viscosity. The data thus indicate a number of improved properties of cassava starch manufactured by enzyme-integrated conventional technique.     

几种植物提取物的生理特性及其应用

辣椒、大蒜是人们经常食用的蔬菜品种,研究发现,辣椒和大蒜中含有的功效成分对人体生理功能具有特殊的作用,同时在食品工业中具有广泛的应用前景。本文主要介绍了这两类植物提取物的结构特点、生物学特性以及应用。     

Structural Characteristics of Protein Gels as Determined by an Ultrasound Imaging Technique

Structural density features of gels formed with gelatin, egg albumen, and poultry thigh natural actomyosin were determined with an ultrasound system equipped with a real time monitor, imager and photographic unit. Echo recordings of the acoustic impedance showed that all protein gels were similar in respect to structural density differential patterns. Increases in protein concentration increased the net area occupied by protein junctions and interlinks. The ultrasound imaging technique confirmed the aggregated junction, interlink and interstitial regions that are common features of protein gels.     

基于图像处理的印品质量在线检测

一、引言随着科学技术的发展,人们对印刷品的要求越来越高,印刷品也越来越精细,这样也导致了印刷品的生产难度不断增加。当前印刷生产已经达到了自动化和数字化,印刷速度也越来越高,而图案复杂且细节丰富繁多的印刷品往往会由于印刷过程中印刷机械和印刷材料的不完善以及一些不易避免的随机因素而出现各种弊病。这就要求我们在印刷的过程中能对印刷品出现的各种缺陷进行准确的识别和判断,并把得到的信息及时地反馈给印刷机,并对印刷机进行适当的调整,以实现对印刷过程的实时控制和印刷品质量的在线检测。为了保证与印刷生产和质量检测的自动…     

Effect of Heat-Stable Proteases on the Kinetic Parameters of Milk Clotting by Chymosin

The milk clotting per unit casein hydrolytic activities of proteases from 14 psychrotrophic pseudomonad isolates of raw milk ranged from 0.77 to 9.97 at 30°C. The milk clotting activities of chymodn and T16 protease were not completely additive, especially at high chymosin concentration when clotting time was relatively fast. The T16 protease was not effective in catalyzing the enzymic step of milk clbtting at O°C in the time expected on the basis of its milk clotting at 30°C. Milk incubated with the T25 motease for 8 days at 4°C and then clotted with chymosin at 30°C exhibited weak curd consistency.     

Effects of Humic Substances Obtained from Shives on Flax Yield Characteristics

The effects of humic substances (HS) extracted from flax shives on the fiber and seed yield of fiber flax were examined during 3 years field experiment. HS from shives consists of humic acids—5.3 gL^?1 and fulvic acids—0.7 gL^?1 were applied (6·10^–2 gL^?1 concentration, with 300 Lha^?1 of spraying liquid) in “herring-bone” stage (BBCH 13 growth stage). The HS action was evaluated in different climatic conditions and in three varieties. Application of HS on early stage of vegetation of flax plants increased fiber yield (exceeding control on 16.0–28.1%) and quality (5% of cellulose content), protein and oil content in seeds (up to 1.9–4.2% and 1.6–3.5%, respectively). Positive reply of flax plants on HS from flax shives in tested cultivars allows saying about prospects of this type of humic substances.     

不同熟度牛肉与高水分组织蛋白品质特性的比较研究

使用低场核磁共振、TPA(Texture Profile Analysis)等分析方法对不同熟度牛肉与高水分组织蛋白(High Moisture Texturized Vegetable Protein,HMTVP)的弛豫时间、质构特性进行比较,并结合感官评价实验,寻找HMTVP的目标参照指标,选择最佳HMTVP配方,...     

Jaboticaba Pomace Powder Obtained as a Co-product of Juice Extraction: A Comparative Study of Powder Obtained from Peel and Whole Fruit

This study presents the evaluation of an emergent co-product generated during the production of jaboticaba juice by steam drag: the jaboticaba pomace. A comparison of physicochemical, technological and morphological properties of the jaboticaba powders obtained from the pomace, from the whole fruit and from the peel was performed. All the powder samples underwent the same processing: freeze-drying, milling and sieving. The powders appeared reddish, with an average diameter of approximately 64.83–103.51 μm and pH values of 3.45–3.74, water activity of 0.3133–0.3270, water holding capacity of 2.63–4.28 g H₂O/g and oil holding capacity of 2.79–2.98 g oil/g. Differential scanning calorimetry analysis showed that the endothermic peak temperature was 158.9–164.4 °C. Proximate composition analysis showed a large amount of total dietary fibre and insoluble dietary fibre in jaboticaba pomace (20.54 and 16.42 g/100 g, respectively), while jaboticaba peel had a good amount of soluble dietary fibre (10.72 g/100 g). Jaboticaba pomace had a large quantity of phenolic compounds (43.39 mg GAE/g d.w.), especially monomeric anthocyanin (3.92 mg cyanidin-3-glucoside/g d.w.), compared to the whole fruit. Jaboticaba pomace is valuable due to its high phenolic content (2.5 times higher than the whole fruit) and total dietary fibre content (2.2 times higher than the whole fruit). The results obtained in this study reinforce the idea that this co-product could be re-used in the development of functional ingredients and show that the industrialisation of these materials is one possible alternative for food diversification. Pomace powder could be added to many types of foods, such as cereals, snacks, drink mixes, and breads, or could be used for pharmaceuticals, such as slow-release antioxidants in packaging films.