摘要:

ABSTRACTThe effect of different concentrations of myoglobin on the enzyme systems involved in lipid degradation were determined. Lipases, including both acid and neutral lipases and acid phospholipase, were inhibited by myoglobin. The neutral lipase was more susceptible to the inhibitory effect of myoglobin (35% of its initial activity at 1 mg/mL of myoglobin), followed closely by acid phospholipase; acid lipase activity was affected to a lesser extent (less than 20% inhibition). This inhibition was also observed on the esterase activities, being greater on the neutral esterase activity (38% of its initial activity at 1 mg/mL of myoglobin) than on the acid one. In view of these results, myoglobin could be considered as an endogenous inhibitor which would determine the lipolytic activity in different type of muscles and therefore, the rate of generation of the free fatty acids.

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1996.tb00574.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACT2,4,5‐trihydroxybutyrophenone (2,4,5‐THBP), in the presence of hydrogen peroxide (H2O2), is a substrate for horseradish peroxidase (HRP) with a Km value of 2.5 mM. An intermediate red product(s), probably 2,4,5‐THBP quinone, characterized by a peak at 490–500 nm, was detected and the time course of its conversion to the final red product(s) was studied. The relationships between the rate of 2,4,5‐THBP oxidation to pigmented product(s) as a function of various concentrations of H2O2, 2,4,5‐THBP and HPR ar

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1996.tb00575.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTPolyphenol oxidase (PPO) was extracted and purified from Stanley plums(Prunus domesticaL.)Crude PPO showed pH optima of 5.8 to 6.4 with different substrates. Heating for 5 min at 75C completely inactivated this enzyme. Plum PPO was stable at ‐20C for 16 weeks. Kmof this enzyme ranged from 17.5 mM with 4‐methylcatechol to 31.2 mM with chlorogenic acid. The enzyme was purified 36‐fold through (NH4)2SO4fractionation and chromatography on DEAE‐cellulose and Sephadex G‐100. PAGE of crude and purified plum PPO showed 7 and 3 bands, respectively, when stained for activity with catechol. The molecular weight of 3 subunits of purified PPO was estimated in the range of

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1996.tb00576.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTTurmeric curcuminoids are important natural pigments but their instability limits their use in many foods. This study was conducted to examine light‐induced degradation of turmeric curcumin as affected by solvent system and oxygen. The rate constants and half‐lives were determined for purified curcumin, demethoxycurcumin and bis‐demethoxycurcumin exposed to 1450 lux using reversed‐phase HPLC. Rates of degradation of each pigment followed first‐order kinetics. Differences in rate constants and half‐lives between the individual pigments were minor in an acetic acid‐NaCl solution; however, in methanol, large differences in stability to light of the individual pigment were observed. Stability of all the pigments to light was several fold greater in methanol than in acid brine. In methanol sparged with air, stability to photooxidation was curcumin>demethoxycurcumin>bis‐demethoxycurcumin. In methanol, curcumin was more stable than the other curcuminoids when sparged with air than when sparged with nitrogen. In methanol sparged with nitrogen, demethoxycurcumin was the most stable pigment. All of the pigments were sta

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1996.tb00577.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe changes in strawberry native proteins and polypeptides during ripening were studied. Analysis of protein extracts by nondenaturing electrophoresis showed the presence of a protein species only in the ‘25% Red’ and later ripening stage. This 40 kD polypeptide was hardly detected in ‘Large green’ and ‘White’ fruit extracts. The polypeptide profile, obtained with SDS‐PAGE, also changed during ripening. While most polypeptides were found in all ripening stages, the distribution of some of them varied during ripening.Protein synthesis (measured by35S‐methionine labelling) in strawberry was mainly directed towards the regeneration of previously existing proteins. As ripening proceeded, the synthesis of 67 and 63 kD polypeptides increased, while those of 82, 56 and 25 kD decreased. Three very‐abundant polypeptides (36, 24 and 23 kD) were located in the achenes and were not labelled in a

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1996.tb00578.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTSerine proteinase inhibitor(s) and small amounts of cysteine proteinase inhibitor were detected in both leaf and stem tissue 48 h after mechanical injury to the lower leaf of 21–25 day old tomato cultivars (cv). Leaves accumulated about 2–15 times more trypsin inhibitor than stem tissue. Approximately 10 times more trypsin inhibitor (TIU) accumulated in plants held at 30C in continuous light compared to plants held under ambient greenhouse conditions after injury. Uninjured plants held at 30C under continuous light accumulated less proteinase inhibitor(s) than injured plants. Holding Bonnie Best in the dark at 30C for 48 h resulted in less inhibitor(s) accumulation in response to mechanical wounding than holding plants at 30C in continuous light. TIU/g tissue recovered from injured plants held at 30C under continuous light varied with cultivar, i.e., for leaves: Bonnie Best (33.61), Alta (21.00; 25.43), Castlemart (16.00; 13.17) and Halley (1.96); and for stems: Castlemart (8.29), Alta (4.47) and Bonnie Best (2.59). SDS‐PAGE assayed for inhibitor activity revealed the main trypsin and chymotrypsin inhibitor(s) in injured leaves both had a molecular mass (Mr) of 19.1 KD on SDS‐PAGE substrate gels. Treatment of the inhibitors with 2.0% SDS at 100C prior to electrophoresis revealed a second major trypsin inhibitor (Mr = 16.4 KD) and two additional major α‐chymotrypsin inhibitors (Mr = 16.

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1996.tb00579.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0145-8884    

DOI:10.1111/j.1745-4514.1996.tb00573.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY