Produção de β-galactosidase a partir do permeado de soro de leite utilizando a levedura Kluyveromyces marxianus ATCC 36097

Abstract

The use of substrates from industrial processes is a viable alternative to obtain products with high added value. The dairy industry, for example, is responsible for the generation of high COD and BOD residues such as whey permeate, a byproduct of cheese whey concentration. The permeate is basically lactose, a fermentable disaccharide by the yeast Kluyveromyces marxianus, which converts lactose to galactose and glucose due to the enzymatic activity of β-galactosidase. However, it does not have all the nutrients needed for cell growth, so it needs supplementation. Thus, a central rotational composite design with temperature, agitation and salt composition (ammonium sulfate, dibasic potassium phosphate and magnesium heptahydrate) was designed to evaluate the production of β-galactosidase from the fermentation of whey permeate by Kluyveromyces marxianus yeast ATCC 36907. Assays were performed with 2 gcél L-1, 10 g L-1 yeast extract, under conditions of 30 to 50 ºC, 120 to 180 RPM, 0 to 20 g L-1 ammonium sulfate, 1 to 9 g L-1 dibasic potassium phosphate, 0.2 to 1 g L-1 magnesium sulfate heptahydrate and enzymatic activity were determined by the ONPG method. After determining the condition that provided the highest enzymatic activity, the bioreactor assay with 3.5 L medium was performed. The results obtained in the experiments proposed by the planning presented a constant in relation to the enzymatic activity during the follow up for 8 hours and the best answers were obtained for the central points - at 40 ºC, 150 RPM and 10 g L-1 1 of yeast extract. 10 g L-1 ammonium sulfate, 5 g L-1 dibasic potassium phosphate and 0.6 g L-1 magnesium sulfate heptahydrate, with activities of 20,726, 20,890 and 20,879 UONPG gcél-1 and at 40 ºC, 180 RPM and 10 g L-1 yeast extract, 10 g L-1 ammonium sulfate, 5 g L-1 dibasic potassium phosphate and 0.6 g L-1 magnesium sulfate heptahydrate, which showed 20,771 UONPG gcél-1, but with a low cell yield. Statistical treatment showed that the tested variables were significant but had a negative effect for the response variable. The bioreactor assay was performed with the central condition of the design and the enzymatic activity ranged from 20.409 to 19.256 UONPG gcél-1 within 5 hours of cultivation. The COD and BOD evaluation showed that bioreactor fermentation allowed the reduction to 41.105 and 63.95% of the organic load, respectively. Thus, the results show that whey permeate has potential for use as substrate for β-galactosidase production but requires studies on supplementation sources and fermentation can be a method used to reduce the pollutant level of the material.