Produção biotecnológica de ácido lático a partir de bagaço de caju e sua utilização para síntese enzimática de ácido polilático

Abstract

Sociocultural and, in particular, environmental issues have led to the search for new methods of synthesizing materials alternatively to those originating from fossil fuels. In this sense, the production of polylactic acid (PLA), a biodegradable substitute for plastic, can become viable from a clean biotechnological route using agro-industrial waste. Therefore, a strategy is proposed for the use of cashew apple bagasse (CAB) as a raw material for the production of lactic acid (LA) by the bacteria Lactobacillus plantarum LAB07, isolated from cheese, and L. plantarum LAB14, isolated from pepper sauce. After the production of AL, it is used for the synthesis of PLA. The use of CAB represents a relevant factor in the development of sustainable processes, due to the amount of waste that is rejected by the agroindustry and its potential use in biorefinery processes, due to the fact that cellulose, hemicellulose and lignin, the main fractions that compose it, to be used for the synthesis of a wide range of bioproducts. Initially, a treatment with diluted sulfuric acid was carried out to obtain the cashew apple bagasse hydrolyzate (CABH) with fermentable carbohydrates. Afterwards, several conditions were evaluated during the LA production bioprocesses, such as the growth phase of the microorganisms to be inoculated, being evaluated by the inoculum time (16, 20 and 24 hours), temperature (25, 30, 37 and 45 °C), rotation (100, 150 and 200 rpm) and CABH supplementation with nitrogen source (yeast extract, ammonium sulfate and urea). The CABH presented 39.9 g/L of glucose and 28.0 g/L of xylose and was used to determine the best fermentation parameters for LA production in an orbital shaker, after being evaluated in a bioreactor, with controlled pH. The results showed that the most favorable condition for LA production occurred using a culture at the beginning of the stationary phase obtained with an inoculum time of 24 h (LAB07) and 20 h (LAB14) and the process conducted at 30 °C and 100 rpm, adding urea as a source of nitrogen and controlling the pH with the addition of NaOH 5 mol/L, producing 31.6 g/L and 29.58 g/L of levorotatory LA (L) with strains LAB07 and LAB14, respectively. The use of CAB as a carbon source and urea as a nitrogen source in the production of AL caused a reduction of 90% compared to the MRS medium (commonly used medium). After that, different solvents for LA extraction (1-butanol, chloroform, hexane, octanol and toluene) were evaluated and it was observed that the best result was obtained when using 1-butanol, resulting in a recovery of 72.1%. Then, the polymerization of the LA was carried out using the enzyme lipase B of Candida antarctica (CALB) as catalyst and by analysis of Nuclear Magnetic Resonance (NMR), the synthesis of the biopolymer PLA was confirmed. It was concluded that it was possible to produce LA using CABH, an agroindustrial by-product, and to produce PLA from an enzymatic route, being a viable and sustainable alternative for obtaining a biodegradable polymer with several industrial applications.