摘要:

ABSTRACTVarious concentrations of 2,3,4‐trihydroxyacetophenone (2,3,4‐THAP) and 2,4,5‐trihydroxybutyrophenone (2,4,5‐THBP) have a synergistic effect on the rate of DL‐3,4‐dihydroxyphenylalanine (DL‐DOPA) oxidation by mushroom tyrosinase as measured by absorbance at 475 nm. The synergism results from the ability of dopaquinone to nonenzymatically oxidize 2,3,4‐THAP and 2,4,5‐THBP to the corresponding o‐quinone.Moreover, various concentrations of 2,3,4‐THAP and 2,4,5‐THBP prevent the enzymatic conversion of DL‐DOPA to DOPA‐melanin, probably due to the ability of these trihydroxyphenols to interact nonenz

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1996.tb00555.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe in vitro digestibility of albumin proteins from Phaseolus vulgaris was low (26–32%) and when heated (99C/30 min) it was further reduced to 13–18%, independent of the variety. Phaseolin (the main bean globulin) had, after heating, a digestibility similar to casein, but when heated in mixtures containing as low as 10% of the albumin fraction, it suffered a drastic decrease in its susceptibility to proteolysis. The chemical interactions that occur among the components of the albumin fraction that reduce its digestibility do not occur between phaseolin and albumins. Interactions between phaseolin and albumins depend on pH of heating and are responsible for differences in molecular weight distribution of peptides formed by the action of pepsin, but did not alter overall digestibility of the mixture. The low digestibility indeed was due to heat‐stable trypsin inhibitors found in the acid‐soluble fraction of the albumins. Lectins and α‐amylase inhibitors, glycoproteins of the albumin fraction, showed, in similar experiments, no effect on phaseolin digestibility, in spite of being very poorly digested even aft

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1996.tb00556.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTSix rat monoclonal antibodies (mAbs) to beef myoglobin, which recognize characterized epitopes of the protein, were used as macromolecular probes to detect irreversible conformational alterations occurring in myoglobin heated over the range 55–85C for 60 min. Light scattering measurements indicated the formation of small amounts of aggregated protein between 55–75C and increasing aggregation above 75C. To exclude an increase of immunoreactivity for the polymerized molecules in ELISA tests, all heated samples were filtered. No oligomers were detected in these samples by size exclusion chromatography using an HPLC system. Using competitive and sandwich ELISA the denaturation midpoint was observed around 79C. However, four mAbs that recognize the heme pocket region demonstrated an increased immunoreactivity over the range 55–75C. These results indicate that the heme pocket region undergoes an irreversible conformational change upon heating at temperatures as low as 55–60C, far below the denaturation midpoint. At these same temperatures, no irreversible conformational changes could be detected in the other regions of myoglobin recognized by the correspondi

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1996.tb00557.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe hydrolytic activity of a partially purified chlorophyllase, obtained from an algal source, was investigated in a refined‐bleached‐deodorized (RBD) canola oil model system using various organic solvent media, including water/miscible‐organic, biphasic organic, and micellar ternary systems. Although the use of a ternary micellar system containing Span 85 was found to be the most appropriate medium for the hydrolysis of chlorophyll, the hydrolytic activity of chlorophyllase declined as oil content increased. The effects of various parameters, including surfactant concentration, hexane/buffer proportion, enzyme content, reaction time, incubation temperature, shaker speed, and activator concentration, on chloro‐phyllase activity in the micellar ternary systems containing 20% RBD oil were also investigated. In addition, phytol displayed a noncompetitive inhibition in reaction media containing polysorbate 80 and Span 85. The plot of 1/v versus oil concentrations revealed that the oil had Kivalues of 3.73 and 4.56% in the micellar systems containing polysorbate 80 and Span 85, respectively. Moreover, the presence of 10% oil in the micellar system containing span 85 and polysorbate 80 decreased Vmaxvalues of chlorophyllase activity by 6.2 and 9.6‐fold, res

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1996.tb00558.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTLupin phytase (myo‐inositol hexaphosphate phosphohydrolase) and the degradation of its substrate phytic acid were studied during seed germination. Phytase and acid phosphatase activities were detected in nongerminated seeds and increased from days 1 to 8 of germination, while the concentration of phytic acid decreased during the same period. Phytase was extracted with 2% CaCl2solution and partially purified by ammonium sulfate fractionation and HPLC‐gel permeation chromatography. Substrate specificites were determined using pnitrophenylphosphate or phytic acid. The pH and temperature optima for the fraction obtained by gel permeation were 5.0 and 50C respectively, while the Km and Vmaxvalues were 0.33 mM and 0.13 μmol·mL−1·min−1, respectively. It was not possible to separate phytase from phosphatase by use of gel permeation chromatography due to similarities in apparent molecular mass, however resolution of the two enzymes was achieved by DEAE‐cellulose ch

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1996.tb00559.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Book reviewed in this article:FROZEN AND REFRIGERATED DOUGHS AND BATTERS, Edited by Karel Kulp, Klaus Lorenz and Juergen Brummer.ADVANCES IN SWEETENERS, 1st Edition. T.H. Greenby (ed).FOOD ENZYMES—STRUCTURE AND MECHANISM, Edited by Dominic W.S. Wong.EVALUATION OF SEAFOOD FRESHNESS QUALITY. J.R. Bott

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1996.tb00560.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY