Avaliação da extração de celulose bacteriana a partir do resíduo de Kombucha (SCOBY): caracterização microbiológica, físico-química e aplicação como carga em composições de borracha

Abstract

Kombucha is a slightly carbonated fermented beverage produced from sweetened Camellia sinensis tea and a Symbiotic Culture of Bacteria and Yeasts (SCOBY, from the English, Symbiotic Culture of Bacteria and Yeast). At the end of production, this SCOBY is discarded as production waste or partially reused to generate new fermentations. The SCOBY is composed of bacterial cellulose, which in kombucha is known as Kombucha Cellulose (KC). KC has attracted growing interest in biotechnological applications. As a result, several studies have focused on its use in different industrial segments. Considering its high potential as a reinforcing filler, the present work aimed to evaluate the KC extraction process from SCOBY, perform its physicochemical characterization, and investigate its feasibility in natural rubber (NR) compositions. Additionally, microorganisms (bacteria and yeasts) were isolated and the microbial diversity of the SCOBY was characterized through metagenomic analysis. In the microbiological characterization, six bacteria were isolated, two of which had characteristics of Acetic Acid Bacteria (AAB), belonging to the genus Komagataeibacter sp., and two yeasts. The metagenomic analysis resulted in 24 bacteria and 6 fungi, with the most abundant bacterium being Komagataeibacter sucrofermentans and the yeast being Zygosaccharomyces bailii. Kombucha production yielded 3.83 g/L of SCOBY, with a sugar conversion rate of 0.078 g/g and an average productivity of 0.26 g/L·day. To evaluate cellulose extractions, the SCOBYs were treated by three methods: alkaline treatment with 1M NaOH (TA), autoclaving (AU), and a combination of both methods (AUTA). The compositional analysis assessed the three extraction methods and it was observed that the TA and AUTA methods promoted a greater reduction of 86% and 70% in lipids, respectively. In both cases, protein removal averaged 84%. Scanning electron microscopy (SEM) micrographs revealed that, in the TA extraction, the fibers were more dispersed and predominantly nanometric in diameter (<100 nm). On the other hand, the combination of both methods (AUTA) resulted in a more compact structure. Of all the extraction methods, TA was chosen as the treatment for using SCOBY in latex application. Freeze-dried and milled KC-TA samples were subjected to FTIR and XRD analyses, where KC showed characteristics of type I cellulose, with a crystallinity index of 58.4% and a maximum degradation peak of 315°C in TGA-DTG. KC was then added to latex in fractions of 0, 2.5, 5, 10, and 15 phr (parts per hundred). The addition of KC influenced the mechanical and structural properties of the rubber, resulting in a reduction in vulcanization time and an increase in torque, crosslink density, hardness, and tear resistance. However, it reduced elongation and tensile strength.