The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform

Louise Wicker - One of the best experts on this subject based on the ideXlab platform.

  • total and thermostable Pectinesterases in citrus juices
    Journal of Food Science, 1996
    Co-Authors: R Snir, P E Koehler, Kevin A Sims, Louise Wicker
    Abstract:

    Grapefruits, tangerines and several orange cultivars were evaluated for total and thermostable Pectinesterase (TS-PE) activity. Juices were extracted with a Fresh'n SqueezeTM Multi Fruit Juicer. Variation in total Pectinesterase (PE) and TS-PE was not significantly different between cultivars. No significant contribution by traditional quality control parameters (%pulp, °Brix, % acid, pH), to total PE or TS-PE was observed. Positive correlations were observed between TS-PE and total PE, when expressed on a pulp (0.669) or soluble solids (0.624) basis.

  • pH Affects Marsh Grapefruit Pectinesterase Stability and Conformation
    Journal of Agricultural and Food Chemistry, 1996
    Co-Authors: Daqing Sun, Louise Wicker
    Abstract:

    Thermolabile Pectinesterase (TL-PE) and thermostable Pectinesterase (TS-PE) of Marsh grapefruit were purified by ion-exchange and affinity chromatography. The effect of pH on stability and solvent ...

  • Selective Extraction of Thermostable Pectinesterase
    Journal of Food Science, 1992
    Co-Authors: Louise Wicker
    Abstract:

    Thermostable Pectinesterase was estimated to represent 98% of total activity extracted from Marsh grapefruit pulp by 1M NaCl without pH adjustment or 17% when extracted with 1M NaCl, 0.25M Tris-Cl- pH 8.0. Total units of Pectinesterase solubilized were less in 1M NaCl at endogenous pH values than at pH 8.0, but total thermostable Pectinesterase units remained constant. No conversion of thermostable to heat sensitive isozymes was observed. Preparative isoelectric focusing indicated that most activity focused at alkaline pH values. The constant specific activity suggested co-migration of basic proteins.

  • Stability of Pectinesterases of Marsh white grapefruit pulp
    Journal of Agricultural and Food Chemistry, 1991
    Co-Authors: Thomas A. Seymour, Louise Wicker, James F. Preston, James A. Lindsay, Cheng I. Wei, Maurice R. Marshall
    Abstract:

    Comparaison des 2 formes de Pectinesterases du pomelo : forme thermostable (TS) et thermolabile (TL). La TS est aussi plus resistante au pH acide et a la proteolyse, a une plus longue duree de vie dans le jus de fruit, et est plus stable a la congelation-decongel ation. La TS contient 7 fois plus d'hydrates de carbone que la TL : ceux-ci joueraient un role dans la stabilite et la resistance a la proteolyse. Ces resultats confirment que la TS Pectinesterase est la forme importante en technologie et transformation des agrumes

W H Chang - One of the best experts on this subject based on the ideXlab platform.

  • influence of precooking on the firmness and pectic substances of three stem vegetables
    International Journal of Food Science and Technology, 2007
    Co-Authors: A Wu, W H Chang
    Abstract:

    Summary Edible portions of the stems of sprouting broccoli, asparagus lettuce, and large-stem mustard were compared for total pectin contents, amounts of different pectin fractions, Pectinesterase activities and changes during cooking to investigate effects on the textural changes during cooking. Slices precooked for 30min at temperatures below 60°C (broccoli) or 70°C (lettuce, mustard) were firmer after 15 min recooking in boiling water than those directly cooked without precooking. Optimum temperatures for this firming effect of precooking were 50, 60 and 60°C, respectively, and coincided with the optimum temperatures of activity of Pectinesterases extracted from the fresh tissues. Analysis of pectin fractions revealed that the firming effect of precooking is related to the shift from the cold water-soluble fraction to sodium hexametaphosphate-soluble and hot water-soluble fractions of pectins.

  • influence of precooking on the firmness and pectic substances of three stem vegetables
    International Journal of Food Science and Technology, 2007
    Co-Authors: A Wu, W H Chang
    Abstract:

    Summary Edible portions of the stems of sprouting broccoli, asparagus lettuce, and large-stem mustard were compared for total pectin contents, amounts of different pectin fractions, Pectinesterase activities and changes during cooking to investigate effects on the textural changes during cooking. Slices precooked for 30min at temperatures below 60°C (broccoli) or 70°C (lettuce, mustard) were firmer after 15 min recooking in boiling water than those directly cooked without precooking. Optimum temperatures for this firming effect of precooking were 50, 60 and 60°C, respectively, and coincided with the optimum temperatures of activity of Pectinesterases extracted from the fresh tissues. Analysis of pectin fractions revealed that the firming effect of precooking is related to the shift from the cold water-soluble fraction to sodium hexametaphosphate-soluble and hot water-soluble fractions of pectins.

  • change in particle size of pectin reacted with Pectinesterase isozymes from pea pisum sativum l sprout
    Journal of Agricultural and Food Chemistry, 2001
    Co-Authors: Chiiming Jiang, W H Chang, Hungmin Chang
    Abstract:

    Four Pectinesterase (PE) isozymes were isolated by CM-Sepharose CL-6B chromatography from etiolated pea (Pisum sativum L.) sprouts and then reacted with citrus pectin (degree of esterification = 68%, 30−100 kDa) to observe the change in pectin particle size using a laser particle size analyzer. After incubation of a pectin−PE mixture (pH 6.5) at 30 °C for 4 h, PE 1 was observed to catalyze the transacylation reaction most remarkably, increasing the particle size from ∼50−70 to ∼250−350 nm, followed by PE 3, PE 2, and PE 4. Keywords: Pectinesterase isozyme; pea (Pisum sativum L.) sprout; transacylation reaction; de-esterification reaction; laser particle size analysis

B Jamilah - One of the best experts on this subject based on the ideXlab platform.

  • purification and properties of Pectinesterase from soursop anona muricata pulp
    Food Chemistry, 1997
    Co-Authors: S M Arbaisah, B A Asbi, A H Junainah, B Jamilah
    Abstract:

    Two forms of Pectinesterase were purified using the techniques of ammonium sulphate fractionation, ion-exchange chromatography and gel filtration. PE I had a specific activity of approximately 4 units mg−1 (43-fold), that of PE II was 6.4 units mg−1 (229-fold). These Pectinesterases (PE I and PE II) had approximate molecular weights of 29 100 and 24 100, respectively, as estimated by gel filtration, and 31 000 and 28 000, respectively, as estimated by sodium dodecyl sulphate polyacrylamide electrophoresis. The optimum temperature for enzyme activity was shown to be 60 °C for both PE I and PE II. The activation energies of PE I and PE II were calculated as 36 kJ mol−1 and 42 kJ mol−1, respectively. The optimum pH values for both Pectinesterases lie within the range 7.0–8.0. The Km value for PE I was 0.52 mg ml−1 and 0.0843 mg ml−1 for PE II. PE I had a maximum velocity (Vmax) of 154 μmol mg−1 min−1, and PE II a Vmax of 726 μmol mg−1 min−1.

  • determination of optimum conditions for Pectinesterase extraction from soursop fruit anona muricata using response surface methodology
    Food Chemistry, 1996
    Co-Authors: S M Arbaisah, B A Asbi, A H Junainah, B Jamilah
    Abstract:

    Optimum conditions for the extraction of Pectinesterase from soursop (Anona muricata) have been established. A fractional factorial design and response surface methodology was applied in this study, as a means of improving the method for developing an enzyme extraction procedure. Among the variables tested, NaCl and pH showed greater significant effects, while PVP, EDTA and incubation time seemed to have a lowering effect on the efficiency of Pectinesterase extraction from soursop. The maximum enzyme extraction was obtained by using 1.92 M NaCl solution at pH 8.4.

Maurice R. Marshall - One of the best experts on this subject based on the ideXlab platform.

  • Stability of Pectinesterases of Marsh white grapefruit pulp
    Journal of Agricultural and Food Chemistry, 1991
    Co-Authors: Thomas A. Seymour, Louise Wicker, James F. Preston, James A. Lindsay, Cheng I. Wei, Maurice R. Marshall
    Abstract:

    Comparaison des 2 formes de Pectinesterases du pomelo : forme thermostable (TS) et thermolabile (TL). La TS est aussi plus resistante au pH acide et a la proteolyse, a une plus longue duree de vie dans le jus de fruit, et est plus stable a la congelation-decongel ation. La TS contient 7 fois plus d'hydrates de carbone que la TL : ceux-ci joueraient un role dans la stabilite et la resistance a la proteolyse. Ces resultats confirment que la TS Pectinesterase est la forme importante en technologie et transformation des agrumes

S M Arbaisah - One of the best experts on this subject based on the ideXlab platform.

  • purification and properties of Pectinesterase from soursop anona muricata pulp
    Food Chemistry, 1997
    Co-Authors: S M Arbaisah, B A Asbi, A H Junainah, B Jamilah
    Abstract:

    Two forms of Pectinesterase were purified using the techniques of ammonium sulphate fractionation, ion-exchange chromatography and gel filtration. PE I had a specific activity of approximately 4 units mg−1 (43-fold), that of PE II was 6.4 units mg−1 (229-fold). These Pectinesterases (PE I and PE II) had approximate molecular weights of 29 100 and 24 100, respectively, as estimated by gel filtration, and 31 000 and 28 000, respectively, as estimated by sodium dodecyl sulphate polyacrylamide electrophoresis. The optimum temperature for enzyme activity was shown to be 60 °C for both PE I and PE II. The activation energies of PE I and PE II were calculated as 36 kJ mol−1 and 42 kJ mol−1, respectively. The optimum pH values for both Pectinesterases lie within the range 7.0–8.0. The Km value for PE I was 0.52 mg ml−1 and 0.0843 mg ml−1 for PE II. PE I had a maximum velocity (Vmax) of 154 μmol mg−1 min−1, and PE II a Vmax of 726 μmol mg−1 min−1.

  • determination of optimum conditions for Pectinesterase extraction from soursop fruit anona muricata using response surface methodology
    Food Chemistry, 1996
    Co-Authors: S M Arbaisah, B A Asbi, A H Junainah, B Jamilah
    Abstract:

    Optimum conditions for the extraction of Pectinesterase from soursop (Anona muricata) have been established. A fractional factorial design and response surface methodology was applied in this study, as a means of improving the method for developing an enzyme extraction procedure. Among the variables tested, NaCl and pH showed greater significant effects, while PVP, EDTA and incubation time seemed to have a lowering effect on the efficiency of Pectinesterase extraction from soursop. The maximum enzyme extraction was obtained by using 1.92 M NaCl solution at pH 8.4.