Produção enzimática de lactulose a partir de soro de leite utilizando a enzima β-galactosidase de Kluyveromyces lactis

Abstract

In the last decades, due to the need to assure higher sustainability in industrial processes, the treatment of the waste deriving from the food industry has received unprecedented attention. An important sector in the business is dairy, which holds a prominent ranking due to the large volume of products processed. Whey, the main by-product of cheese, imposes considerable environmental risks, especially due to its the residual lactose, deeming pretreatment operations indispensable before disposal as an effluent. Among the promising alternatives for whey utilization, it can be highlighted its use as a raw material for the biotechnological production of products with high-added value, which includes the enzymatic hydrolysis of the lactose present for synthesizing oligosaccharides and other molecules with prebiotic function, such as lactulose. The latter has received considerable attention in scientific research due to its numerous uses in the food and pharmaceutical industries, for example, in the treatment of constipation and in the prevention and treatment of hepatic encephalopathy. Given the aforementioned scenario, the objective of the present study was to evaluate the employment of whey in the production of lactulose by an enzymatic route, using β-galactosidase from Kluyveromyces lactis. The results led to the determination of optimal conditions for the production of lactulose using a lactose/fructose-based synthetic medium, which initially were: lactose/fructose ratio of 15/30% (w/v); initial substrate concentration (lactose and fructose) of 200 g/L, temperature of 50 °C, enzymatic load of 7 U/mL, pH 7.0 and with the addition of 0.01% w/v Mg2+. The maximum concentration achieved was 22.59 ± 0.11 g/L of lactulose. Thereafter, the enzymatic lactulose production was investigated (with enzymes soluble and immobilized onto the previouslyselected support chitosan) using whey as raw material. The experiments presented promising results, given the high concentrations of lactulose obtained in the whey. It was concluded that the highest production was achieved when the whey had been treated for protein precipitation and elimination, yielding a total concentration of 17.32 ± 0.88 g/L of lactulose. The reuse cycles were also evaluated using the immobilized enzyme, with a high operational stability, with a synthesis of 63% of lactulose in the third cycle and about 25% at the end of the sixth cycle of reuse. From the hydrolysis of lactose, in addition to the liberated galactose, high amounts of glucose were generated in the reaction medium. As such, in an attempt to take advantage of these, the production of lactulose and ethanol was also evaluated in a single batch using enzymatic (by β -galactosidase from K. lactis) and fermentative (by Saccharomyces cerevisiae) routes, respectively. The results were potentially promising, since it was possible to produce lactulose and ethanol in the same batch at the maximum concentrations of 17.50 ± 0.76 g/L and 8.79 ± 0.65 g/L, respectively. Therefore, it can be concluded that it is possible to use the lactose present in the residual whey from the food industry for the production of lactulose, providing an appropriate destination for this waste, and consequently, reducing the environmental impact it can exert. Furthermore, this practice would result in the production of a substance with higher added value due to its extensive use in the food and pharmaceutical industries.