Optimization of the production of bacterial cellulose by Komagataeibacter spp. on brewer’s spent grains.

Bacterial cellulose (BC) is synthesized by specific acetic acid bacteria (AAB) and is a valuable biopolymer with noteworthy mechanical and technological characteristics. The primary hindrance to industrial production lies in the production cost of this biomaterial. In this context, Agrifood by-products emerge as cost-effective and naturally abundant nutrient sources suitable for microbial fermentation, facilitating BC production. This study examined the growth kinetics and bacterial cellulose (BC) production of Komagataeibacter hansenii 6DB, K. rhaeticus LM2, LM4, and SM1, and Komagataeibacter xylinus DSM 2004 using brewer's spent grains, and yeast as growth media. In addition, an optimization of the production of BC was carried out by modulating parameters such as the addition of a buffer solution, pH, quantity of spent yeast in the formulation and ratio spent grain/water. The results revealed that BC productivity was affected by the AAB strain and the growth conditions. In the absence of a buffer, BC production for all strains was limited to less than 0.5 g/L and this was accompanied by rapid acidification of the growth medium. The addition of phosphate buffer to the growth medium allowed to stabilize the pH and to increase the production of BC for all AAB strains. The higher BC producers were DSM2004 and LM2 (1.5 g/L). It was also observed that cellulose production gradually increased with the increase of incubation time, but the rate of BC formation remained almost constant after 7 days. The optimization of BC production by DSM2004 and LM2 allowed to increase the production rate up to 3g/L in 7 days of incubation. This study allowed to identify AAB strains of interest for the production of BC from brewer's spent grains as well as to optimize the BC production. These aspects are crucial in order to favour the industrial exploitation of BC as innovative biopolymer.