Application of mesoporous silica materials for the immobilization of polyphenol oxidase

Abstract

Enzymatic browning is one of the most important reactions that occur in fruits and vegetables, resulting in negative effects on color, taste, flavour and nutritional value. The main agent responsible for this reaction is polyphenol oxidase (PPO), also called tyrosinase, because it oxidises phenolic compounds and generates dark pigments. Mesoporous materials have been popular for a variety of applications in the last two decades, such as catalysis and gas separation, and they are an interesting option to immobilize the PPO as an alternative to the established industry process based on heat treatments. The objective of the present work is to study the possibility to remove this enzyme or even inhibit its activity from apple juice, since this beverage is rich in polyphenols and it is susceptible to suffering enzymatic browning. Different mesoporous silica materials were tested with different structures, morphologies and porosities in order to see their influence on the immobilization rate. Besides, the pH value of the solution and time were fully analysed and they provide results to obtain a good immobilization capacity. Pore volume, is the textural characteristic which affects the most the immobilization assay. Aeroperl® and SBA-15 are the materials which can adsorb larger quantity of PPO at pH 4.00, because electrostatic interactions can exist between the enzyme and the silica walls. Fitting power law and Higuchi models, we can assume that the PPO loading into mesoporous materials is diffusion controlled. The commercial mesoporous material reveals highest inhibition rates in real apple extracts.KEYWORDS: mesoporous material, silica, tyrosinase, polyphenol oxidase, PPO, juice treatment, enzymatic browning. 2 RESUMENLa principal reacción que afecta tanto a frutas como a verduras y que causa un detrimento en su color, sabor, olor y valor nutricional es el pardeamiento enzimático. La polifenol oxidasa (PPO), también llamada tirosinasa, es la principal responsable de esta reacción, ya que oxida los compuestos fenólicos generando pigmentos parduzcos. Los materiales mesoporosos han tenido una gran variedad de aplicaciones en las últimas dos décadas, como por ejemplo catálisis y separación de gases, y estos materiales son una interesante opción para inmovilizar la PPO como alternativa a los tratamientos térmicos implementados en la industria. El objetivo de este trabajo es estudiar la posibilidad de retener este enzima o incluso inhibir su actividad aplicándolo sobre zumo de manzana, puesto que, como esta bebida es rica en compuestos fenólicos, es más susceptible de sufrir esta reacción de pardeamiento. Para ello, se han estudiado diferentes materiales mesoporosos de sílice con diferentes estructuras, morfologías y porosidades para poder dilucidar su influencia en la tasa de inmovilización. Además, otros factores que han sido ampliamente estudiados han sido la influencia del pH de la solución de inmovilización y el tiempo de contacto entre el material y el enzima. La característica textural que parece ser decisi...

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“…f) SEM cross section of porous Al 2 O 3 structured using cyclic anodization. Reproduced with permission: a) [ 33 ] Copyright 2010, American Chemical Society; b) [ 34 ] Copyright 2016, Elsevier Ltd.; c) [ 35 ] Copyright 2012, American Chemical Society; d) [ 36 ] Copyright 2012, American Chemical Society; e) [ 37 ] Copyright 2005, American Chemical Society; f) [ 38 ] Copyright 2009, Wiley‐VCH.…”