Phenolic composition and susceptibility to browning were determined for nine apricot (Prunus armeniaca L.) cultivars. Chlorogenic and neochlorogenic acids, (+)-catechin and (-)-epicatechin, and rutin (or quercetin-3-rutinoside) were the major phenolic compounds in apricots. In addition to these compounds, other quercetin-3-glycosides and procyanidins have been detected. Chlorogenic acid content decreased rapidly during enzymatic browning, but the susceptibility to browning seemed to be more strongly correlated with the initial amount of flavan-3-ols (defined as catechin monomers and procyanidins). As chlorogenic acid is certainly the best substrate for polyphenol oxidase, the development of brown pigments depended mainly on the flavan-3-ol content.
Using ammonium sulfate precipitation followed by hydrophobic and ion exchange chromatography, two lipoxygenase isoenzymes, LOX 1 and LOX 2, were l&3-and 445fold purified from germinated barley, with 18 and 24% recovery of activity respectively. LOX 1 and LOX 2 were characterized by isoelectric points 4.9 and 6.4, and molecular weights of 90 kd and 110 kd, respectively. Apparent Km values for linoleic acid were 0.06 mM for LOX 1 and 0.18 mM for LOX 2. LOX 1 converted linoleic acid to 9 and 13 hydroperoxides at about 4:1, whereas the 13 hydroperoxide was the major product formed by LOX 2 (ratio 3:7). For both isoforms, thermal inactivation data indicated first order kinetics with activation energies influenced by ionic strength and pH. Isoenzymes composition was analyzed for three kilning schemes: the 1:3 ratio between LOX 1 and LOX 2 observed in germinated barley increased during the course of kilning.
Phenolic compounds have been repeatedly implicated as potent antioxidants. Efficiency has been frequently estimated by radical scavenging activity and few reports have considered lipoxygenase (LOX) inhibition. Horse bean LOX was inhibited by a range of phenolic acids, gallates and flavonoids. All compounds tested were uncompetitive inhibitors with the exception of flavonol aglycons which were non competitive type. In each class of compounds, inhibition constants were strongly affected by structures. Inhibition patterns of (-)-epicatechin on germinated barley LOXs were detailed: (-)-epicatechin acted as an uncompetitive inhibitor while (-)-epicatechin reduced hydroperoxide formation by its radical scavenging activity and thus limited enzyme activation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.