A kinetic expression for hydrolysis of soluble starch by glucoamylase

As the hydrolysis of starch by glucoamylase proceeds with stepwise removal of glucose units from the nonreducing ends of the starch chain, the number of available substrate molecules is essentially unchanged in the course of the degradation. In view of this aspect, a simple practical kinetic expression, which consists of a modified Michaelis-Menten form with product inhibition, is presented for the hydrolysis of soluble starch. It is assumed that the values of kinetic parameters V(m) and K(m) vary linearly from the values for starch toward those for maltose. The applicability of this kinetic expression is verified through the simulation with the experimental results for the hydrolysis of two soluble starches with different average molecular weights of 3 x 10(4) and 3 x 10(6).     

Rapid method for detection of urea hydrolysis by yeasts.

A method is described for the rapid detection of urea hydrolysis by yeasts, using the Berthelot color reaction. The results could be determined within 30 to 50 min with this method, compared with 8 to 72 h usually required with Christensen urea agar.     

Rapid method for detection of urea hydrolysis by yeasts.

A method is described for the rapid detection of urea hydrolysis by yeasts, using the Berthelot color reaction. The results could be determined within 30 to 50 min with this method, compared with 8 to 72 h usually required with Christensen urea agar.     

A rapid colony screening method for the detection of arsenate-reducing bacteria

A rapid and simple method has been developed for the detection of arsenate reducing bacteria based on the presence of arsenite [As (III)], the end product of anaerobic arsenate [As (V)] respiration. Confirmation of As (III) product is made by the reduction of starch-iodine complex. The method can be used over a large pH range (5.5–9.0) and can easily be determined at arsenite concentration as low as 0.025 mM. Major advantages of this technique are that a large number of samples can be analyzed easily at a time.     

A rapid method for the detection of tryptophanase in anaerobic bacteria

A total of 633 anaerobic bacteria were examined for tryptophanase production using a rapid method which distinguishes within 5 to 180 minutes between anaerobes that contain tryptophanase and those that do not. Of the 196 tryptophanase-positive isolates tested, 99% showed tryptophanase activity within 2 hours as compared with 94.4% in 24 hours by a conventional method. A total of 299 tryptophanase-negative organisms were tested. Ninety three percent of these remained negative after 24 hours as compared with 95.3% when tested with a 24-h conventional method. Additional information was obtained on the sensitivity of this test and the time-dependent production of indole by tryptophanase.     

利用色谱法快速检测分析啤酒腐败菌的新方法

啤酒在生产过程中很容易染菌,而传统的用于啤酒腐败菌检测的方法耗时长,不能满足实际需求.由于腐败菌污染的啤酒通过色谱检测,相应组分(生物胺、有机酸和风味物质)都会有特征峰的产生,所以本研究通过建立无腐败菌污染的啤酒中各组分的标准色谱图,再使啤酒强制染菌,对其组分进行色谱分析,并与标准色谱图进行比较,从而找出各组分对应的特征峰.未来,此方法可用于实际生产线上快速检测啤酒是否发生微生物污染.     

A method for the specific detection of resident bacteria in brine shrimp larvae

In this study, we describe an easy but efficient method to specifically target the intestinal resident microbiota in brine shrimp larvae during DGGE analysis, hereby excluding the interference of both transient (luminal) bacteria and body surface bacteria. This effective technique has several advantages over alternative methods, with respect of ease of use and rapidity.     

Rapid tests for esculin hydrolysis by anaerobic bacteria

Esculin hydrolysis is one of the biochemical tests used in the identification of anaerobic microorganisms. The conventional method by use of growing microbial cells requires 24–48 hours of incubation. On the other hand, growth independent methods like the buffered esculin test, the spot test, and the PathoTec strip test utilize the presence of constitutive enzymes and, therefore, yield results in 1–4 hours. A total of 817 anaerobic organisms were used in this study to determine the sensitivity and specificity of the three rapid methods. All three rapid methods gave excellent correlation with the standard conventional method. Over 99% of the organisms gave comparable results with the spot test and the buffered esculin test within one hour; the PathoTec strip test required up to 4 hours. The former two were not only more rapid but also more economical than the PathoTec strip test.     

A new pullulanase from a hyperthermophilic archaeon for starch hydrolysis

A crude preparation of thermostable pullulanase from Thermococcus hydrothermalis produced glucose and maltose syrups from starches. The use of pullulanase reduced the saccharification reaction time up to 37.5%. In the case of maltose syrup production, the addition of pullulanase to - amylase led to an almost total hydrolysis of the substrate (dextrins) which is translated into a rise in the yield of the whole sugars from 6.5 to 14%.     

A kinetic model of starch hydrolysis by alpha- and beta-amylase during mashing

Kinetics of malt starch hydrolysis by endogeneous alpha- and beta-amylases has been experimentally investigated in laboratory-, pilot- and industrial-scale reactors. The production rates of glucose, maltose, maltotriose and total extract, and the separate alpha- and beta-amylases deactivation rates are measured at varying mashing temperature and different initial starch concentrations and qualities. Based on the experimental results, a model is proposed that takes into account the initial carbohydrates and enzymes dissolution, the starch gelatinization, the separate hydrolytic action of alpha-and beta-amylases on insoluble and soluble starch and dextrins, and the influence of temperature both on enzyme activities and thermal denaturation rate. The model can predict, at the three scales, the final sugars concentrations in the wort for given initial malt concentrations and enzymatic contents, and for a fixed temperature profile during the mashing process.     

Iteration model of starch hydrolysis by amylolytic enzymes.

An elaborate computer program to simulate the process of starch hydrolysis by amylolytic enzymes was been developed. It is based on the Monte Carlo method and iteration kinetic model, which predict productive and non-productive amylase complexes with substrates. It describes both multienzymatic and multisubstrate reactions simulating the "real" concentrations of all components versus the time of the depolymerization reaction the number of substrates, intermediate products, and final products are limited only by computer memory. In this work, it is assumed that the "proper" substrate for amylases is the glucoside linkages in starch molecules. Dynamic changes of substrate during the simulation adequately influence the increase or decrease of reaction velocity, as well as the kinetics of depolymerization. The presented kinetic model, can be adapted to describe most enzymatic degradations of a polymer. This computer program has been tested on experimental data obtained for alpha- and beta-amylases.     

A stochastic model for predicting dextrose equivalent and saccharide composition during hydrolysis of starch by alpha-amylase

A stochastic model was developed that was used to describe the formation and breakdown of all saccharides involved during alpha-amylolytic starch hydrolysis in time. This model is based on the subsite maps found in literature for Bacillus amyloliquefaciens alpha-amylase (BAA) and Bacillus licheniformis alpha-amylase (BLA). Carbohydrate substrates were modeled in a relatively simple two-dimensional matrix. The predicted weight fractions of carbohydrates ranging from glucose to heptasaccharides and the predicted dextrose equivalent showed the same trend and order of magnitude as the corresponding experimental values. However, the absolute values were not the same. In case a well-defined substrate such as maltohexaose was used, comparable differences between the experimental and simulated data were observed indicating that the substrate model for starch does not cause these deviations. After changing the subsite map of BLA and the ratio between the time required for a productive and a non-productive attack for BAA, a better agreement between the model data and the experimental data was observed. Although the model input should be improved for more accurate predictions, the model can already be used to gain knowledge about the concentrations of all carbohydrates during hydrolysis with an alpha-amylase. In addition, this model also seems to be applicable to other depolymerase-based systems.     

A flow cytometry method for rapid detection and enumeration of total bacteria in milk

Application of flow cytometry (FCM) to microbial analysis of milk is hampered by the presence of milk proteins and lipid particles. Here we report on the development of a rapid (/= 0.98) between the FCM assay and the more conventional methods of plating and direct microscopic counting was achieved. Raw milk data showed a significant correlation (P < 0.01) and a good agreement (r = 0.91) between FCM and standard plate count methods. The detection limit of the FCM assay was 相似文献   

Co-immobilization of amyloglucosidase and pullulanase for enhanced starch hydrolysis

Summary Amyloglucosidase and pullulanase were co-immobilized using a hydrophilic polyurethane foam (Hypol^® 2002). The combined amyloglucosidase and pullulanase activity of the immobilized enzyme was 32.2% ± 1.7% relative to the non-immobilized enzyme. The co-immobilized enzymes were capable of using a variety of glycogen and starch substrates. Co-immobilization of amyloglucosidase and pullulanase increased the glucose yield 1.6-fold over immobilized amyloglucosidase alone. No decrease in activity was observed after 4 months storage for the co-immobilized enzymes. The results suggest that co-immobilization of amyloglucosidase and pullulanase in polyurethane foams is a potentially useful approach for commercial starch hydrolysis. Offprint requests to: K. B. Storey