Exploring sugarcane vinasse for sustainable lipid production applied to biodiesel generation by Rhodotorula glutinis r4

Abstract

Oleaginous yeasts such as Rhodotorula spp. efficiently accumulate ~50-70% (w/w) of neutral lipid storage, mainly in the form of triglycerides, under specific growth conditions. These microbial oils offer a viable alternative to vegetable oils for biodiesel production. Vinasse is a highly polluting by-product generated from the bioethanol production process from sugarcane. For each liter of alcohol produced, between 13 and 15 L of vinasse are generated and pose a significant environmental challenge. It is crucial to explore alternatives to generate value-added products. The main objective of this study was to obtain lipids suitable for biodiesel production by the oleaginous yeast R. glutinis R4, using vinasse sourced from the sugarcane-alcohol industry in Tucumán as a substrate. Vinasse, obtained from a Tucumán distillery, was utilized to formulate the culture media. The growth and lipid production of R. glutinis R4 were evaluated in diluted vinasse (10% and 25%, v/v), supplemented with glucose (40 g/L) as the sole carbon source. Additionally, growth was assessed in 10% vinasse with added glucose (40 g/L) and yeast extract (3 g/L), and in 10% vinasse with crude glycerol (40 g/L)- a biodiesel industry by-product- as the sole carbon source. GMY culture medium with glucose (40 g/L) was utilized as a control. Cultures were incubated at 25°C, 250 rpm for 168 h. Growth, cellular biomass and lipid production were monitored at different culture times. Fatty acid profiles of lipids produced by R4 were analyzed using GC-MS, and biodiesel quality parameters were estimated. The results revealed the capacity of R. glutinis R4 for growth and intracellular lipids synthesis using 10% and 25% diluted vinasse as substrate, with glucose as the sole carbon source. No significant differences were observed in cell biomass between the two evaluated conditions. However, in the case of 10% diluted vinasse, lipid accumulation was higher, with lipids constituting 88% of the cell biomass after 96 h. Additionally, 10% diluted vinasse supplemented with glucose and yeast extract, or crude glycerol were also evaluated. In both conditions, the growth, lipid production (5.1-5.9 g/L), and lipid accumulation (40%) exhibited by R4 was comparable to those achieved in the GMY control medium (7 g/L of lipids; 48.6%). The fatty acid profile of the microbial oils obtained from R4 revealed the presence of long-chain fatty acids similar to those found in vegetable oils, with a high content (~80%) of palmitic (C16:0) and oleic (C18:1) acids, which are suitable for biodiesel synthesis. Biodiesel quality parameters complied with the established by international biodiesel standards. Vinasse and crude glycerol could be considered for formulating culture media in the design of processes for sustainable microbial oil production by R. glutinis R4, enabling the valorization of these wastes. R4 emerges as a promising strain for alternative oil sources for various biotechnological applications.