[Immobilization of microbial lactase].

A Illanes, M E Zúñiga, A Ruiz
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Abstract

Lactase (beta-D galactoside-galactohydrolase, E.C.3.2.1.23) is a relevant enzyme to the dairy industry as it modifies undesirable functional and nutritional properties derived from the lactose content in milk and dairies, and as a way of recovering or upgrading cheese whey. This latter aspect has been considered to develop an enzyme catalyst suitable for the continuous hydrolysis of whey permeate. The selection of enzyme and support and the immobilization procedure has been reported previously. Results obtained in the immobilization of fungal lactase on activated chitin have prompted us to scale-up the procedure, a system being developed in which the enzyme is immobilized within the reactor (in situ). Results are presented for the in situ immobilization of lactase with and without recirculation of the reagents. Previous procedure was reproduced, although moderate profiles of activity were generated through the catalyst bed which were not eliminated by recirculation. Packed bed reactors with immobilized lactase were operated at varying flowrates and lactose concentrations, results being compared, in terms of substrate conversion and reactor productivity, with a theoretical model based on the corresponding kinetic expression and ideal flow regime. Deviations are significant at high flowrates which is attributed to backmixing and channeling through the catalyst bed. The model fits reasonably well at low flowrates and high feed substrate concentration. Productivity was 58 g of glucose/l.h at 40 ml/h of 120 g/l of lactose. Stability of the immobilized lactase was assessed in long-term reactor operation with whey permeate (35 g/l of lactose) at 40 degrees C and pH 4.0. Operational half-life was 120 days.

[微生物乳糖酶的固定化]。
乳糖酶(β - d半乳糖水解酶,E.C.3.2.1.23)是一种与乳制品工业相关的酶,因为它可以改变牛奶和乳制品中乳糖含量产生的不良功能和营养特性,并作为一种回收或升级奶酪乳清的方法。后一个方面被认为是开发一种适合于乳清渗透物连续水解的酶催化剂。酶和载体的选择以及固定化的方法已有报道。在活化几丁质上固定化真菌乳糖酶的结果促使我们扩大了这一过程,一种正在开发的系统,其中酶在反应器内(原位)固定化。结果提出了原位固定化乳糖酶有和没有再循环的试剂。之前的程序被复制,尽管通过催化剂床产生了适度的活性分布,这并没有通过再循环消除。将固定化乳糖酶填充床反应器在不同的流速和乳糖浓度下运行,并将结果与基于相应动力学表达式和理想流动状态的理论模型在底物转化率和反应器生产率方面进行比较。在高流速下,偏差是显著的,这归因于反混合和通过催化剂床的通道。该模型在低流速和高进料底物浓度条件下拟合得相当好。产率为58 g葡萄糖/l.h, 40 ml/h, 120 g/l乳糖。在40℃、pH 4.0条件下,用乳清渗透液(35 g/l乳糖)长期反应器操作,评估固定化乳糖酶的稳定性。工作半衰期为120天。
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