Plant lipases: Biocatalyst aqueous environment in relation to optimal catalytic activity in lipase‐catalyzed synthesis reactions

Abstract

Adsorption and desorption isotherms of two commercial enzyme preparations of papain and bromelain were determined with a Dynamic Vapor System. The Guggenheim-Anderson-deBoer (GAB) modeling of the obtained sorption isotherms allowed the definition of different levels of hydration of those samples. Afterward, these enzyme preparations were used as biocatalysts in water and solvent-free esterification and alcoholysis reactions. The evolution of the obtained fatty acid ester level as a function of the initial hydration level of the biocatalyst, i.e., thermodynamic water activity (a(w)) and water content, was studied. The results show an important correlation between the initial hydration level of the biocatalyst and its catalytic activity during the lipase-catalyzed synthesis reactions. Thus, the Carica papaya lipase (crude papain preparation) catalytic activity is highly dependent on the biocatalyst hydration state. The optimized synthesis reaction yield is obtained when the a(w) value of the enzyme preparation is stabilized at 0.22, which corresponds to 2% water content. This optimal level of hydration occurs on the linear part of the biocatalyst's sorption isotherm, where the water molecules can form a mono- or multiple layer with the protein network. The synthesis reaction yield decreases when the a(w) of the preparation is higher than 0.22, because the excess water molecules modify the system equilibrium leading to the reverse and competitive reaction, i.e., hydrolysis. These results show also that an optimal storage condition for the highly hydrophilic crude papain preparation is a relative humidity strictly lower than 70% to avoid an irreversible structural transition leading to a useless biocatalyst. Concerning the bromelain preparation, no effect of the hydration level on the catalytic activity during esterification reactions was observed. This biocatalyst has too weak a catalytic activity which makes it difficult to observe any differences. Furthermore, the bromelain preparation is far more hydrophobic as it adsorbs only 18 g of water per 100 g of dry material at a(w) around 0.90. No deliquescence of this enzymatic preparation is observed at this a(w) value.

An improved method to validate the relative humidity generation in sorption balances

“…Such instruments are now widely used at pharmaceutical industries and elsewhere to measure sorption isotherms and to study solid-vapour interaction [1][2][3][4][5]. They can also be used for other related types of studies, for example to measure transport properties of films and materials [6; 7] and to study film formation in latex dispersions [8; 9].…”

Lipophilisation de composés phénoliques par voie enzymatique et propriétés antioxydantes des molécules lipophilisées

“…En effet, ce paramètre détermine la quantité d'eau liée à l'enzyme qui lui est nécessaire pour assurer sa structure active optimale. [21]. La courbe en cloche obtenue montre clairement l'effet de l'a w sur l'activité catalytique des lipases pour la synthèse d'esters.…”

Lipases de látex vegetais: propriedades e aplicações industriais

“…Estudos constataram que a atividade desta lipase em reações de esterificação e transesterificação está diretamente relacionada com o nível de hidratação da enzima, sendo o ponto ótimo de 0,22% de atividade de água. Para valores superiores, observou-se uma diminuição no rendimento e aumento da hidrólise 33,34 .…”

“…Reação de síntese do similar ao Salatrim 16,23 Em estudo com o mesmo meio reacional usado para lipase do látex de C. papaya 23 , contendo ácidos graxos com grupos hidróxi, epóxi e ciclopentil em sua estrutura com o 1-butanol, a lipase de bromelina bruta apresentou um maior nível de esterificação com estes ácidos pouco comuns na natureza quando comparados com os de cadeia linear, como o ácido mirístico (C14:0) 44 . Em reações de interesterificação, a lipase de bromelina bruta não apresentou atividade mesmo com baixos níveis de hidratação 29,34,43 .…”