摘要:

ABSTRACTMaltol (3‐hydroxy‐2‐methyl‐4H‐pyran‐4‐one) inhibits the rate of oxidation of different o‐dihydroxyphenols by tyrosinase when assayed spectrophotometrically, but not when assayed polarographically. The spectral changes occurring during the oxidation of different o‐dihydroxyphenols by tyrosinase (or by sodium periodate) in the absence or presence of maltol were different, suggesting that maltol conjugates with the o‐quinones formed. Maltol does not inhibit tyrosinase activity per se but only gives an apparent inhibition probably due to its ability to conjug

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00469.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTIt has been suggested by some workers that decomposition of trimethyl N‐oxide (TMAO) to dimethylamine (DMA) and formaldehyde in gadoid fishes occurs via enzymic processes while others have suggested a nonenzymic pathway. DMA production in frozen red hake muscle is shown in this study to be enzymic by the necessity of the high molecular weight soluble or insoluble fraction from red hake to convert the low molecular weight components of flounder muscle to DMA. In red hake muscle the TMAO demethylase activity is approximately evenly divided between the high molecular weight soluble and the insoluble fractions: the amount of potential activity in either fraction is 60–100 times that required for the production of DMA that normally occurs during frozen storage of the muscle tissue. The Kmfor TMAO of the soluble enzyme was approximately 3 mM; the concentrations of TMAO in red hake muscle range from 60 to 140 mM (calculation based on water content of 80%). Thus, it seems unlikely that TMAO or TMAO demethylase limit the rate of the reaction. On the other hand, the Kmvalues for flavin mononucleotide and NADH are higher than the concentrations of these components found in the tissue suggesting that the cofactors limit the rate of TMAO breakdown to DMA and formaldehyde in the stored muscle. This supports other studies (Landolt and Hultin 1982; Banda and Hultin 1983) in which the same conclusion is reached based on other considerati

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00470.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTThe pH optimum for demethylation of TMAO in minced red hake muscle at –5C was approximately 7.0. This value was higher than the pH optimum for the crude soluble enzyme in an anaerobic system utilizing flavin and NADH and for an aerobic system with ferric iron and ascorbate but was similar to the pH optimum observed with the flavin‐NADH system in the presence of air. Both the anaerobic and aerobic flavin‐NADH systems had sufficient activity in the presence of optimal concentrations of cofactors to account for all of the demethylation of TMAO observed in minced muscle. Comparison of concentrations of flavins and NADH and their rate of change during storage at temperatures both below and above freezing with previously determined kinetic constants suggest that this cofactor system may be critical in determining the rate of TMAO demethylation in post mortem red hake muscle. The extent of TMAO breakdown at –5C caused by the iron‐ascorbate system was barely sufficient to account for the amount of DMA produced in the minced muscle. With the relatively low concentrations of iron and ascorbate present in the tissue, this system seems unlikely to be a major factor in TMAO degradatio

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00471.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTWheat gliadins, that are glutamine rich and lysine poor proteins, are good substrates for transglutaminases reactions. This study was conducted to determine the efficiency with which guinea pig liver transglutaminase catalyzes transfer and hydrolysis reactions of native and acylated gliadins. In all reactions, 35% of the total glutaminyl residues were modified. Neutral pH simultaneously enhanced glutaminyl residue hydrolysis and protein cross‐linking, while acidic pH reduced the cross‐linking reaction. Functional properties of two enzymatically modified gliadins and a chemically deamidated one were tested at neutral pH. A deamidation level of 25–27% appeared to be an optimum for the emulsification properties. Enzymatically modified gliadin showed better resistance to coalescence than the chemically deamidated one; a result that probably is related to the presence of high molecular weight pol

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00472.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

ABSTRACTA chemically prepared conjugate of avidin and E. coli β‐galactosidase was adsorbed to biotinylated controlled‐pore glass beads and used in a fluidized‐bed bioreactor to assess the feasibility of bioselective adsorption immobilization technology. Biotinylated 200 nm pore diameter porous glass beads were prepared by reaction of 3‐aminopropyl‐glass beads with sulfosuccinimidyl‐6‐(biotinamido) hexanoate. Avidin and biotinylated β‐galactosidase were sequentially adsorbed to the matrix. The fluidized‐bed bioreactor was characterized with respect to β‐galactosidase activity using both a lactose solution and o‐nitrophenyl β‐D‐galactopyranoside (ONPG) as substrates. A lactose solution (4.5%, pH 7) was assayed for lactose hydrolysis at various flow rates. The bioreactor was operated for three months at 65–75% lactose hydrolysis with no loss in enzyme activity. The biocatalyst was characterized by amino acid analysis to determine the amount of each of the two proteins adsorbed. Results indicated 162 μ protein/mg beads of which 36% was avidin and 64% was β‐galactosidase corresponding to 1 mole of avidin per mole of β‐galactosidase monomer. Biocatalyst activity using ONPG as the substrate was 430 μmoles/min/mg protein, yielding a specific activity of 672 μmoles/min/mg β‐galactosidase. These results lead to the conclusion that biospecific adsorption of the β‐galactosidase conjugate onto biotinylated glass beads via avidin results in a biocatalyst that

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00473.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Book reviewed in this article:Enzymes in Food Processing, Edited by T. Nagodawithana and G. Reed.

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1993.tb00474.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY