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1.
Purified red kidney bean (Phaseolus vulgaris) amylase inhibitor forms a 1:1 stoichiometric complex with porcine pancreatic α-amylase leading to complete loss of enzyme activity on starch. Rate of complex formation is pH dependent and is maximal at pH 5. The rate constants for complex formation, as measured by loss of amylase activity, were 2.85 × 104 M-1 sec-1 at pH 6.9 (ionic strength of 0.918) and 2.55 × 105 M-1 sec-1 at pH 5 at 30°C. At pH 6.9, rate of complex formation was 4.8 times faster at 0.918 ionic strength as compared with the rate at 0.138 ionic strength. At 30°C, pH 6.9 and ionic strength of 0.168 the dissociation constant of the enzyme-inhibitor complex was determined to be 3.5 × 10-11 M. The rate constant for dissociation of the complex was calculated to be 8.7 × 10-8 sec-1 under the same conditions. The rate constant for complex formation, at ionic strength of 0.168, was 1.1 × 104 M-1 sec-1 at 370 and 9.77 × 102 M-1 sec-1 at 25.7°C. The calculated activation energy for complex formation is 39.5 kcal/mole suggesting a rate-controlling conformational change. Oxidation of the carbohydrate moiety of the glycoprotein inhibitor caused complete loss of activity. Maltose, a competitive inhibitor of α-amylase, bound as readily to the enzyme-inhibitor complex as to free α-amylase. Trypsinized α-amylase, although still able to bind to Sephadex, did not bind inhibitor. The experiments with maltose and trypsinized amylase suggest the inhibitor may not bind at the active site of α-amylase.  相似文献   

2.
A crude extract of α-galactosidase obtained by fermenting Aspergillus oryzae on wheat bran was purified 35 fold by ethanol precipitation, gel filtration and ion-exchange chromatography. The final preparation was free of protease activity but contained invertase activity. The molecular weight of the enzyme was estimated as 64,000 daltons. The pH and temperature optima were 4.0 and 60°C, respectively. The enzyme was stable over the pH range 3–7.5 and at temperatures up to 55°C (pH 4.0). The Km values for p-nitrophenyl α-Dgalactopyranoside (PNPG) and raffinose were 4.0 × 10−4M and 1 × 10−2M, respectively. Divalent cations were not required for activity. More than 80% of the oligosaccharides in soy milk were hydrolyzed after 3 h at 50°C using 0.113 PNPG units/mL milk.  相似文献   

3.
Glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate: NADP+ oxidoreductase, EC 1.1.1.49; G6PD) was purified from coriander (Coriandrum sativum) leaves; the kinetic behavior and some properties of the enzyme were also investigated. The purification was done at 4C and involved two steps: ammonium sulfate fractionation, and DEAE-Sephadex A50 ion exchange chromatography. The enzyme was obtained with a yield of 26.4% and had a specific activity of 1.826 U/mg protein. Optimum pH, stable pH, optimum temperature, molecular weight, KM and Vmax values for NADP+ and glucose 6-phosphate (G6-P) were also determined.
The overall purification was about 74-fold. SDS-PAGE of the purified enzyme showed a single band. Enzymatic activity was spectrophotometrically measured according to Beutler's method at 340 nm.
The molecular mass was estimated to be 74.4 kDa by SDS-PAGE and 73.2 kDa by Sephadex G-200 gel filtration column chromatography. The enzyme had an optimum pH at 8.5 and was stable at pH 8.0 in 0.1 M Tris-HCl buffer. The optimum temperature was at 30C. The KM values for NADP+ and G6-P were 0.026 mM and 0.116 mM, respectively. The Vmax values for these substrates were 0.035 EU/mL and 0.038 EU/mL, respectively.  相似文献   

4.
Both fresh and frozen chicken meat were evaluated for microbiological status by screening for total bacterial counts and for the presence of pathogens like Enterobacteria , Bacillus cereus, coagulase positive Staphylococci and Salmonella spp. Most of the samples exhibited heavy bacterial contamination (1.2 × 105 - 2.6 × 106/g), mainly with Staphylococcus spp. (1.5 × 104 - 2.8 × 105/g). All the chicken samples also showed the presence of Salmonellae (3 × 101 - 2.1 × 102/g). Among the different serotypes observed in chickens . S. typhimurium was common in fresh as well as frozen chicken. Radicidation at 2 kGy at cryogenic conditions (−40°C) was efficient in eliminating the natural pathogenic contamination of the poultry . Salmonella spp. viz. S. seftenberg and S. typhimurium differed in radiation sensitivity, the D10 values in phosphate buffer (pH 7.2) being 0.25 kGy and 0.12 kGy, respectively. Chicken homogenate (10%) offered approximately 2-fold protection to these cells. Chicken samples artificially inoculated with a heavy inoculum (108 cells/g) of these 2 serotypes required higher gamma radiation doses of 4–5 kGy. The findings suggested that a dose of 2 kGy is adequate for normally contaminated chicken samples, but for the heavily contaminated chicken a dose of 4–5 kGy, depending upon the predominating Salmonella serotype present, is required .  相似文献   

5.
Four Nigerian traditionally fermented foods (wara, nono, ogi and kununzaki) were evaluated for the presence of some microorganisms of public health concern. Among the dairy foods , Staphylococcus aureus and Klebsiella sp. were isolated from wara while Escherichia coli, Salmonella sp. and Klebsiella sp. were isolated from nono. The cereal-based fermented foods (ogi and kunu-zaki) contained Bacillus subtilis, E. coli, S. aureus, Klebsiella sp. and Enterococcus faecalis. The mesophilic aerobic counts were: 5 × 105 for wara; nono, 1.53 × 107; ogi, 3.6 × 106 and kunu-zaki, 2.6 × 106 cfu/mL. The enterobacteriaceae counts on nono, wara, ogi and kunu-zaki were 1.79 × 107, 4.5 × 105, 4.0 × 105 and 1.2 × 106 cfu/mL, respectively. No Vibrio count (detection limit: <10 cfu/mL) was recorded in all the food samples considered. The yeast and mold counts ranged from 1.0 × 105– 3.31 × 107 among the food products. The antimicrobial susceptibility patterns of the organisms isolated from dairy products (nono and wara) revealed that they were resistant to ampicillin (100%) and sensitive to gentamicin (100%) and nalidixic acid (100%). Most isolates from cereal based products (ogi and kunu-zaki) were 100% resistant to penicillin, ampicillin and chloramphenicol. This work highlights the need to maintain hygienic standards in the preparation of our locally fermented cereal and dairy foods.  相似文献   

6.
The properties of tomato polygalacturonases at two ripening stages were investigated. Two isoenzymes, PG I and II, were isolated from underripe fruits with an orange skin color. Fully ripe fruits contained only polygalacturonase II. PG I and II were purified by chromatography on DEAE-Sephadex A-50, Sephacryl S-200 and CM-agarose chromatography. PG I had a Mr of 199,500 as determined by Sephacryl S-300 gel filtration and was 50% inactivated at 66.5°C and pH 4.5 after incubation for 5 min. It had an activation energy (Ea) of 16.8 Kcallmol (70.3 times 103 Jlmol), Vmax of 27.7 units/mg protein and Km value of 7.5 times 10−2 mM polygalacturonic acid. PG II had a Mr of 45,700 and was 50% inactivated at 58°C under the same conditions. Both isozymes had a pH optimum of 4.6. PG II had an Ea value of 14.8 Kcallmol (61.9 times 103 Jlmol), Vmax value of 58.8 units/mg protein and Km value of 3.8 times 10−2 mM polygalacturonic acid. PGI gave rise to only one band during electrophoresis in polyacrylamide gels, whereas PG II showed one major and one minor band both with PG activity. Gel electrophoresis in the presence of sodium dodecyl sulfate resulted in two major bands (Mr= 47,500 and 41,000) for PG I and only one major band (Mr= 47,500) for PG II. PG I is composed of several subunits, all of which are glycoproteins.  相似文献   

7.
Hazard Analysis and Critical Control Point (HACCP) approach was used to assess the safety of a fresh filling pasta (ricotta-filled ravioli) manufacturing plant in La Plata region, Argentina. Household practices like cooking and holding meals before serving were also evaluated. Samples of ricotta, main raw material of the filling, showed colony counts of Enterobacteriaceae total microorganisms, molds and yeasts of (5 × 103-1 × 105), (1x105−1x108) and 1 × 105 CFU/g, respectively. E. coli was also detected in one out of five samples, suggesting a hazardous condition of this raw material. Salmonella spp. was not isolated from any of the dough samples tested. Ricotta filling showed high colony counts of mesophilic microorganisms (6 × 106 CFU/g), Enterobacteriaceae (1 × 105 - 1 × 106 CFU/g), while E. Coli was detected in 20% of the samples. Counts of B. cereus, S. aureus were less than 1 × 102 CFU/g in the analyzed materials. In the finished product (ricotta-filled ravioli), the colony counts of mesophilic microorganisms and Enterobacteriaceae were 3 × 108 and 8 × 105 CFU/g, respectively. Critical Control Points found were cooking and holding time before serving. The implementation of suggested corrections allowed the microbial quality of the final product (ricotta-filled ravioli) to be improved considerably. The growth of total microbial counts during refrigerated storage (0, 4, 8 and 10C) were measured and the shelf-life of ricotta and ricotta-filled ravioli was calculated.  相似文献   

8.
The microbiological quality of six varieties of retail market traditionally cured fish in Morogoro, Tanzania was investigated over a five-month period. The fish were contaminated with bacteria and molds at levels of: total aerobes, 106 - 1.7 × 107 c.f.u/g; faecal coliforms, 1.1 × 101 - 2.5 × 103 MPN/g; faecal streptococci, 1.4 × 101 - 1.3 × 103 MPN/g; Staphylococcus aureus, 1.3 × 103 - 8.6 × 103 c.f.u/g; Aspergillus flavus group, 2.1 × 101 - 2 × 102 c.f.u/g of fish. Of faecal coliform, 45% of the isolates were Escherichia coli. Twenty-five percent of the S. aureus isolates were coagulase positive. Sixteen percent of A. flavus isolates were aflatoxigenic. Aflatoxin contamination ranged from O to 18.5 μg/kg of fish. Insect infestation by Dermestes spp. and mites was observed. The results of this preliminary study emphasize the importance of proper processing and handling offish in the tropics in order to safeguard public health .  相似文献   

9.
The catalytic properties of chitin deacetylase from Mucor rouxii were studied with the aim of using the results for control of the properties of chitosan prepared by enzymatic deacetylation. A crude deacetylase extract from the mycelium of Mucor rouxii exhibited maximal activity at pH 5.8 with both water-soluble and acid-soluble chitosan. The extracellular enzyme of the culture medium exhibited maximal activity at pH 4.8. The deacetylase in the crude extract was stable over the pH range of 4.1–8.9 at 25C, retaining 85–100% of maximal activity at 40C. The extract was most active towards acid-soluble chitosan at 50C and pH 5.8. Chitin deacetylase was stable to 40C when incubated without substrate, with 85% of the activity retained at 50C. Ca2+, Mn2+, and Zn2+ had no effect on activity, while EDTA, Fe2+, and Fe3+ caused partial inhibition in extracts incubated without substrate for 1 h at 25C and pH 5.8. The deacetylase in the mycelial extract and in the culture medium was slightly activated by Co2+. The differences in temperature optima and thermal stability of deacetylase and hydrolytic enzymes can be used for controlling the degree of hydrolysis of chitosan, while the difference in pH stability has been used for prepurification, resulting in 3-fold increase in specific activity of deacetylase .  相似文献   

10.
ABSTRACT: An enzyme with α-L-rhamnosidase activity was purified to homogeneity from a culture filtrate of Aspergillus terreus after growth in a medium containing L-rhamnose as the sole carbon source. The biosynthesis of this enzyme was repressed by glucose. The enzyme had a molecular mass of 96 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and an isoelectric point of 4.6 as determined by analytical isoelectric focusing. The pH and temperature optima for the enzyme were found to be 4.0 and 44 °C, respectively. Using p-nitrophenyl-α-L-rhamnopyranoside as a substrate, the enzyme exhibited Michaelis-Menten kinetics with KM and Vmax values of 0.17 mM and 84 U/mg, respectively. The enzyme was inhibited competitively by L-rhamnose (K1 2.5 mM). Divalent cations such as Ca2+ Mg2+ Zn2+ and Co2+ stimulated the a-L-rhamnosidase activity, whereas this was inhibited by Hg2+ and Cd2+. Ethanol (12% v/v) and glucose (21% w/v) decreased enzyme activity by approximately 20%, while this was not affected by SO2.  相似文献   

11.
12.
SUMMARY: A 5'-nucleotidase, widely distributed in teleost fish muscles, was purified about 20-fold from Pacific cod (Gadus macrocephalus) by chromatography of a dialyzed aqueous extract of the muscle on DEAE-cellulose. The enzyme was unstable and lost 85% of its activity in 1 hr at 37°C 53% in 10 min at 42°C and 40% in 1 hr at 30°C. It was stable for 6 days at 0°C, could be dialyzed for up to 3 days at 0°C against 1 mM tris buffer pH 7.5 and quickly frozen and thawed without loss of activity. However, it was inactivated rapidly when held at −30°C. Brief exposure to pH 4.0 or 5.0 effected marked destruction. Attempts at further purification by means of chromatography on hydroxylapatite, adsorption using alumina Cγ and starch gel electrophoresis failed due to instability.
The enzyme was strongly inhibited by EDTA, pyrophosphate, KF and ZnCl2 (1-10 mM); less markedly inhibited by GSH, 2-mercaptoethanol, carbonate and CaCl2 (10 to 100 mM). It was strongly activated by Mn++ and weakly activated by Mg++. The optimum pH was 7.6, and the Km was 5 × 10−4M with UMP and 8 −4M with IMP. It hydrolyzed, in order of effectiveness, LJMP, IMP, CMP, d-AMP, GMP, d-IMP, d-GMP, d-UMP and AMP, but not p-nitro phenylphosphate, sugar phosphates or a number of other compounds including 2',3'-nucleotides.  相似文献   

13.
SUMMARY– A degradation system was developed based on the incorporation of radioactive chlorophyll into a ripening bell pepper carpel.
Pure chlorophyll a in aqueous triton X-100 injected into green bell peppers ( Capsicum frutescens ) variety 035 was degraded up to 50% by the end of ripening, versus a control in buffer pH 5.4 not exceeding 7% loss in 2 weeks. Variety and stage of ripeness affected the amount of degradation.
Labeled chlorophyll a with a specific activity of 7 to 8 × 105 dpm/mg was then prepared from young wheat plants, fed 14Cob and injected in amounts of 0.2 to 0.3 mg. The distribution of activity in pepper extracts after pigment degradation was evaluated. The acetone water extract remaining after transfer of lipid material to petroleum ether acquired activity within 2 days of injection, but the amount remains fairly constant for 12 days. The activity of the extraction residue, and of an 80% ethanol extract thereof, increased throughout the experiment. The residue containing increasing amounts of protein had the largest amount of radioactivity of the three fractions at the conclusion of the experiment.
Preliminary chromatography did not yield isolated radioactive products.
Extracts of pepper show no activity when substituted for soybean extract in a system containing chlorophyll and linoleic acid.
The degradation of chlorophyll by ripening bell peppers provides a tool for further studies for degradation in a physiological system.
Labeling facilitates isolation, identification, and establishment of origin of small amounts of breakdown products.  相似文献   

14.
Lycoperdon perlatum Pers. (Lycoperdaceae, Agaricales, Agaricomycetidae, Agaricomycetes, Basidiomycota, Fungi) was evaluated for its esterolytic potential. Native electrophoresis of the crude extracts showed four bands having Rf values of 0.34, 0.39, 0.52 and 0.59. The esterase showed the highest activity toward a short-chain substrate, p -nitrophenyl acetate. Optimum reaction conditions for L. perlatum crude extract were attained at pH 8.0 and 40C. Esterolytic activity of enzyme extract was stimulated in the presence of Mn2 + , Fe2 + , Ca2 + and Zn2 + in the reaction mixture. The enzyme activity was stimulated by incubation at pH 6.0 but retained 77% of its original activity at its optimum pH after 24 h. Thermal inactivation was displayed after incubation for 20 min at various temperatures above 30C. At 1 mM final concentration, 2-mercaptoethanol, dithiothreitol, ethylenediamine tetraacetic acid and p -methylphenyl sulfonylfluoride inhibited the esterolytic reaction. These results support that the crude L. perlatum extract possesses an esterolytic activity having properties similar to other esterases.

PRACTICAL APPLICATIONS


Esterases catalyzing the cleavage and formation of ester bonds are known α/β-hydrolases (EC 3.1.1.X). Esterases are used for the synthesis of flavor esters for the food industry, modification of triglycerides for fat and oil industry and resolution of racemic mixtures used for the synthesis of fine chemicals for the pharmaceutical industry. Therefore, the search for new enzyme sources is important for the development of new enzymes and applications.  相似文献   

15.
Sixty frozen samples (30 hamburger patties and 30 minced meat) purchased from different retail markets in Ismailia, Egypt were examined for incidence of proteolytic and lipolytic bacteria. Mean values of proteolytic psychrophiles in the examined samples of hamburger and minced meat were 2×105 and 6×104, respectively. Lipolytic psychrophiles in hamburger were 8×105 and 3×105 in minced meat. Proteolytic mesophiles in hamburger and minced meat were 6×105 and 5×104, respectively. Mean values of lipolytic mesophiles were 5×104 for hamburger and 5×103 for minced meat. Proteolytic thermophiles in hamburger and minced meat were 3×103 and 103, respectively. Both proteolytic and lipolytic activities were exhibited by various bacteria that were identified.  相似文献   

16.
The effects of raw materials and process variables on the heat penetration times into diced tomatoes (Halley Bos 3155 cv) were evaluated. Variables included dice size (1.27 and 2.54 cm), maturity at harvest (red and red+2 weeks), and processing temperature (88 and 92C). Heat penetration times between dice sizes were significantly different, but not between maturities or processing temperatures. Tomatoes were also evaluated for firmness, pectin-methylesterase (PME) and polygalacturonase (PG) activities. Half-inch size diced tomatoes were processed at 88 and 92C, and evaluated for firmness using the shear-compression method. Firmness decreased to 60% of the initial raw firmness from 8.8 × 105 to 5.3 × 105 g-mm after 15 s at 88C, and to 50% from 8.8 × 105 to 4.4 × 105 g-mm after 15 s at 92C. Diced tomato firmness showed a slight firming trend after 150 s at both temperatures. PME was inactivated after 45 s, while 5% residual PG activity remained after 3 min.  相似文献   

17.
RHEOLOGICAL AND CHEMICAL PROPERTIES OF MOZZARELLA CHEESE   总被引:1,自引:0,他引:1  
Dynamic viscoelastic parameters and chemical properties of Mozzarella cheese produced using a "no-brine" cheese making method with 3 different cooking temperatures (38, 41, and 44C) were determined. Samples were stored for 3 weeks at 4C before dynamic mechanical analysis at 22C. G', G" and tan δ were 5.8 – 6.4 × 105 dyne/cm2, 1.9 – 2.1 × 105 dyne/cm2, and 0.33 – 0.35, respectively, at 1% strain and 10 rad/s. The percentage of intact αs-casein and β-casein were 38–40% and 33–35% of total protein in the cheese, respectively. The range of cooking temperatures used in this experiment had little effect on dynamic viscoelastic properties or the amount of intact protein for the cheese.  相似文献   

18.
This study was designed to determine the ability of esculetin to inhibit lipoxygenase activity in soybean. Lipoxygenase was extracted from ground soybean using 0.1 M Tris-HCl buffer (pH 8.6) and centrifuged at 3000 g for 15 min at 4C. The extract was mixed with different volumes of 0.05M esculetin solutions to provide 1.8 × 10−4M, 3.3 × 10−4M, 4.6 × 10−4M and 5.7 × 10−4M to final assay systems, respectively. Lipoxygenase activity decreased as the concentration of esculetin solution mixed in soybean extract increased. Mixing of 1.8 × 10−4M esculetin solution to soybean extract showed the least inhibition effect and was significantly different from that of 3.3 × 10−4M, 4.6 × 10−4M and 5.7 × 10−4M which inhibited LOX (lipoxygenase)'s activity of soybean extracts. In the study comparing the inhibition abilities for lipoxygenase activity among selected antioxidants, esculetin was significantly better than BHA (butylated hydroxyanisole) and α-tocopherol.  相似文献   

19.
The effect of aerobic mesophilic microfloral concentration on the isolation of Listeria monocytogenes LM82 was studied in 31 (18 cheeses and 7 noncheese) retail foods having standard plate counts of 101 to 108 colony forming units (CFU)/g. Foods were spiked with L. monocytogenes and enriched at 30°C for 24 h in a selective enrichment broth used in a U.S. Food and Drug Administration method. Inoculum levels for isolation on modified McBride agar ranged from 0.1 to > 5 × 103 with a geometric mean value of 5 inoculated CFU/g or 1.4 CFU/g. Pure Enterococcus (Streptococcus) faecalis ( 0 to 6 × 106 inoculated CFU/mL ) in the absence of food matrix had no effect on the enrichment of L. monocytogenes. Ease of isolation of LM82 was independent of the food microflora concentration both generally and in the specific food type of 9 Brie cheeses. Competition, when it occurs, therefore, may be due to specific bacterial competitors rather than bacterial numbers .  相似文献   

20.
The microbiological quality of 125 samples of the most popular Egyptian meat products (75 Egyptian fresh sausage "EPS" and 50 basterma) was determined. The aerobic plate count (APC) and Lactobacillaceae count of basterma ranged from 1 × 104 to 9 × 106 CFU/g, respectively . Enterobacteriaceae, mold and yeast counts for basterma were similar (<1 × 102 CFU/g). Artificially contaminated slices of meat and garlic paste of basterma showed that the paste inhibited growth of Salmonella typhimurium. APC and Enterobacteriaceae counts of EFS ranged from 1.1 × 104 to 1 × 108 and from 1 × 102 to 1 × 107 CFU/g, respectively. Nearly 26% and 29% of EFS were positive for Clostridium perfringens and coagulase-positive Staphylococcus aureus, respectively . Salmonella could not be detected in any examined samples. Bacteriologically, EFS might pose a potential health hazard, making it imperative to institute sanitary measures during its production and sale .; Accepted for Publication July 2, 1997  相似文献   

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