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• 202650-88-2 3-caffeoylquinic acid 

Relevant academic research and scientific papers

Characterization of polyphenol oxidase in coffee

Polyphenol oxidase (PPO) was characterized in partially purified extracts of leaves (PPO-L) and fruit endosperm (PPO-E) of coffee (Coffea arabica L.). PPO activity was higher in early developmental stages of both leaves and endosperm of fruits. Wounding or exposure of coffee leaves to methyl jasmonate increased PPO activity 1.5-4-fold. PPO was not latent and was not activated by protease treatment. PPO activity was stimulated 10-15% with sodium dodecyl sulphate (SDS) at 0.35-1.75 mM, but at higher concentrations activities were similar to the control samples, without detergent. Prolonged incubation of extracts-with trypsin or proteinase K inhibited PPO activity but pepsin had no effect. Inhibition of PPO with proteinase K was increased in the presence of SDS. PPO activity from both tissues was optimal at pH 6-7 and at an assay temperature of 30°C. Activity was highest with chlorogenic acid as substrate with a K(m) of 0.882 mM (PPO-L) and 2.27 mM (PPO-E). Hexadecyl trimethyl-ammonium bromide, polyvinylpyrrolidone 40, cinnamic acid and salicylhydroxamic acid inhibited PPO from both tissues. Both enzymes were inactivated by heat but the activity in endosperm extracts was more heat labile than that from leaves. The apparent M, determined by gel filtration was 46 (PPO-L) and 50 kDa (PPO-E). Activity-stained SDS-polyacrylamide gel electrophoresis (PAGE) gels and WeStern blots probed with PPO antibodies suggested the existence of a 67 kDa PPO which is susceptible to proteolytic cleavage that generates a 45 kDa active form. (C) 2000 Elsevier Science Ltd.

Properties of chlorogenic acid quinone: Relationship between browning and the formation of hydrogen peroxide from a quinone solution

Chlorogenic acid is the major polyphenol in foods derived from plants and is a good substrate for polyphenol oxidase. Chlorogenic acid quinone (CQA-Q), which is an oxidative product of chlorogenic acid by polyphenol oxidase, is an important intermediate compound in enzymatic browning. CQA-Q was prepared, and its properties and the relationship with browning were examined. The quinone solution was yellow or orange, and its molecular absorption coefficient was estimated to be 1.7 × 103 for 325 nm and 9.7 × 10 2 for 400 nm in an acidic aqueous solution. Chlorogenic acid and H2O2 were spontaneously generated in the CQA-Q solution as the yellowish color of the solution gradually faded. A pale colored polymer was the major product in the reaction solution. Amino acids such as lysine and arginine added to CQA-Q solution did not repress the fading of the yellowish color of the solution. We concluded from these results that CQA-Q itself and a mixture of CQA-Q and amino acids did not form intensive brown pigments in the acidic aqueous solution. H2O2 spontaneously formed in the CQA-Q solution, and other polyphenols might have played an important role in the formation of the brown color by enzymatic browning.

ROLES OF o-QUINONES AND THEIR POLYMERS IN THE ENZYMIC BROWNING OF APPLES

Enzymic browning and the bleaching produced by the addition of ascorbic acid have been studied simultaneously in crushed apple tissue and in pure solutions of (+)-catechin and chlorogenic acid.Spectrophotocolorimetry was used to study crushed apple tissue