Abstract
Clay/chitosan composite beads were prepared and used as the carrier to support lipase by adsorption, to improve the activity and stability of lipase in the hydrolysis of olive oil. Under conditions of pH 6.0, 25 °C and adsorption for 10 h, immobilized lipases on chitosan bead (CB–lipase) and three clay/chitosan composite beads, at different clay to chitosan proportions of 1:8 (CCB-8-lipase), 1:5 (CCB-5-lipase) and 1:3 (CCB-3-lipase), were prepared. By comparing the activity of these immobilized lipases, CCB-5-lipase showed the highest activity, followed by CCB-8-lipase > CCB-3-lipase > CB-lipase; this improvement was attributed to the synergetic effect of enrichment of olive oil by clay at the reaction surface and better biocompatibility of chitosan with lipase molecules. The optimum pH and temperature in the reaction respectively changed from 7.0 and 30 °C for free lipase to 7.5 and 35 °C for immobilized forms. Furthermore, the thermal stability and repeated usability of these immobilized lipases were sequenced as CCB-3-lipase > CCB-5-lipase > CCB-8-lipase > CB–lipase, due to greater rigidity of immobilized lipase with the addition of clay, which was further confirmed by SEM. The study shows that the incorporation of clay with chitosan creates a good synergetic effect to improve the catalytic performance of immobilized lipase on clay/chitosan composite.
Highlights
Lipase is a versatile and important enzyme which can catalyze various reactions, such as hydrolysis, esterification, alcoholysis and transesterification, producing many kinds of important intermediates and products in pharmaceutical and chemical industries, such as chiral alcohol, ester, carboxylic acids, amines, and so on [1,2,3]
The enrichment of olive oil onto these beads under reaction conditions was compared by carbon content analysis; the results showed that the relative adsorption yield of olive oil on CCB-5 was the highest (100%), followed by CCB-8 (93.6%) > CCB-3 (84.5%) > chitosan bead (CB) (63.7%)
The results indicated that the thermal stability of lipase was notably enhanced by immobilization on clay/chitosan composite beads, and the enhancing range was proportional to the
Summary
Lipase is a versatile and important enzyme which can catalyze various reactions, such as hydrolysis, esterification, alcoholysis and transesterification, producing many kinds of important intermediates and products in pharmaceutical and chemical industries, such as chiral alcohol, ester, carboxylic acids, amines, and so on [1,2,3]. Lipase used in its free form is very sensitive to heat and pH variation, and it is hard to separate free lipase from the reaction medium to be reused for continuous cycles [4,5]. To overcome these problems, lipase has been immobilized onto various natural and synthetic carriers to maintain its activity and stability [6,7,8,9]. Compared with synthetic matrix [10,11], natural materials are more eco-friendly and compatible with lipase molecules, contributing to good catalytic performance of immobilized lipase [12,13].
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