Abstract
Polyphenol oxidase (PPO) was extracted from whole peaches and its catecholase activity was studied spectrophotometrically against three substrates: catechol (Cat), 4-methyl catechol (4MC), and chlorogenic acid (CA). Peach PPO specificity was: CA > 4MC ā Cat. 4-hexylresorcinol (4HR, 0.5 mM) inhibited oxidation of Cat and CA by 50% or more, at all substrate concentrations, but had no effect on the oxidation of 4MC, suggesting that laccase-like activity was present in the extract. Ī²-cyclodextrin (Ī²-CD, 10 mM) inhibited only CA oxidation and this effect was not abolished when free substrate concentrations were calculated suggesting a mechanism, additional to substrate complexation, in Ī²-CD action. Combination of 4HR and Ī²-CD had only a weak inhibitory effect on CA oxidation. In conclusion, Ī²-CD and specially 4HR could be used as browning inhibitors in peach products and also as tools for studying different phenol oxidases. Combination of both compounds is not recommended for peaches.
Se extrajo la enzima polifenoloxidasa (PPO) a partir de duraznos completos y se estudiĆ³ su actividad catecolasa, espectrofotomĆ©tricamente, frente a tres diferentes sustratos:catecol (Cat), 4-metilcatecol (4MC) y Ć”cido clorogĆ©nico (CA). La especificidad de la PPO fue: CA > 4MC ā Cat. El 4-hexilresorcinol (4HR, 0,5 mM) inhibiĆ³, en un 50% o mĆ”s, la oxidaciĆ³n de Cat y CA, pero no tuvo ningĆŗn efecto sobre la oxidaciĆ³n del 4MC, lo cual sugiere que el extracto posee actividad lacasa. La Ī²-ciclodextrina (Ī²-CD, 10 mM) inhibiĆ³ Ćŗnicamente la oxidaciĆ³n del CA, aĆŗn si se consideran las concentraciones libres del sustrato, lo cual sugiere que la acciĆ³n de la Ī²-CD depende de un mecanismo adicional a la complejaciĆ³n de sustrato. La combinaciĆ³n de ambos inhibidores tuvo un efecto dĆ©bil sobre la oxidaciĆ³n del CA. Se concluye que la Ī²-CD y especialmente el 4HR pueden ser usados como inhibidores del oscurecimiento enzimĆ”tico en productos de durazno, asĆ como para estudiar los diferentes tipos de fenoloxidasas. La combinaciĆ³n de ambos agentes no es recomendable en duraznos.
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Acknowledgements
This study was supported financially from UACJ (Internal projects) and CONACyT-Gobierno del Estado de Chihuahua, MĆ©xico (CHIH-2005-C01-22028) is gratefully acknowledged. G. Mercado-Mercado is a recipient of an undergraduate scholarship from SAGARPA-CONACyT (SAGARPA 2002-C01-0787).