Produção de poli-hidroxibutirato por bactéria Cupriavidus necator utilizando melaço de cana-de-açúcar

Abstract

Population growth, combined with unbridled consumption, has led to an increase in the use of petroleum-based plastics, and their improper disposal has caused significant negative impacts on terrestrial and aquatic ecosystems, in addition to worrying repercussions for human health. Plastic poses a serious threat to wildlife; animals often mistake plastic fragments for food, ingesting materials that cause obstructions in the digestive tract, malnutrition, and death. In addition, discarded fishing nets and other plastic waste can trap and harm marine animals. In order to minimize the environmental problems arising from their fragmentation and longevity, there is an increasing search for polymers that are easily biodegradable and have low production costs. The objective of this research was to obtain a polymer of microbial origin from a renewable source. Bacterial polyhydroxybutyrate (PHB-B) was produced by Cupriavidus necator, using commercial sugarcane molasses (MCC) as a carbon source in the substrate. The influence of cultivation temperature (30, 34, and 38 ºC) and initial concentration of CCM as a carbon source (5, 10, 15 g.L-1 of reducing sugars AR) on the production of PHB-B in 72 h of cultivation was evaluated. For this purpose, a complete factorial design 22 with three replicates at the central point was performed. The cultivations were carried out in Erlenmeyer flasks with a capacity of 300 mL, containing 200 mL of culture medium composed of KH2PO4 (3 g.L−1), K2HPO4 (7 g.L−1), (NH4)2SO4 (1 g.L−1), MgSO4.7H2O (0.2 g.L−1) and MCC at the concentrations indicated by the factorial design together with the microorganism. Sugarcane molasses proved to be effective as a carbon source, with a maximum yield of 35.70% of PHB-B occurring at 30 °C with 15 g.L-1 of reducing sugars, obtained at 180 rpm. PHB-B presented the same functional groups as commercial polyhydroxybutyrate (PHB-C), as well as the same crystalline structure for both. The degree of crystallinity of PHB-B and PHB-C was 51.71 and 62.01%, respectively. PHB-B presented a double melting peak at 160.79 and 170.05 °C, while PHB-C presented a crystallization temperature in the second heating of 39.93 °C and only one melting peak at 166.09 °C. The initial and maximum temperatures of thermal manipulation were 233 and 262 °C and 258 and 279 °C for PHB-B and PHB-C, respectively, and the thermal purification process occurred in a single step. The activation energy revealed that PHB-B is more resistant to thermal manipulation than PHB-C. The thermodynamic configurations indicate that the thermal manipulation profile is endothermic and that the thermal manipulation processes occur spontaneously for both trained biopolymers. This study proves that commercial sugarcane molasses can produce biodegradable bacterial PHB that is resistant to thermal manipulation, a property of interest for the processing and storage of this biopolymer, enhancing its applications.