Performance of Fungal Growth Through Integrated Gompertz Model and Respiratory Quotient by Solid State Fermentation in Multi-Layer Squared Tray Solid State Bioreactor with Aeration Strategies

Abstract

A newly designed, laboratory-scaled and multi-layer squared tray solid state bioreactor (SSB), was developed and successfully operated in solid state fermentation (SSF) conditions. The bioreactor was divided into eight layers of squared perforated trays. Wheat bran was used as a solid substrate for the growth of Aspergillus awamori and Aspergillus oryzae. The SSB was equipped with an oxygen (O2)/carbon dioxide (CO2) gas analyser and a thermocouple. Continuous on-line monitoring of fungal growth could be performed by indirect methods that measure O2 consumed, production of CO2 and metabolic heat. The advantage of using this method is that there are no tedious and time-consuming sampling processes. The evolution of CO2, which represents an accumulation term, was integrated with time and fitted to the Gompertz model in a log-like equation. The Gompertz model generated values that may be used to stimulate and verify the experimental data. Results strongly suggest that the evolved and accumulated CO2, excellently described fungal growth. Simulated results agreed with experimental results. The respiratory quotient (RQ), which is the ratio of CO2 evolution rate (CER) to O2 uptake rate (OUR), was determined by the gas balance method. CER and OUR confirmed that measurements correlated to fungal activity. Each RQ values can explain the differences of each SFF process carried out. Yet, heat evolved by fungal activity also described fungal growth. The current findings is an excellent pre-liminary experimental work, evidencing that multi-layer squared tray SSB with forced moistened aeration present a promising alternative of instrumented bioreactors for SSF processes.

Fungal Cell Factories for Efficient and Sustainable Production of Proteins and Peptides

“…There are four bioreactor main types available for SSF: trays, packed beds, rotating (or stirred) drums, and forcefully aerated agitated bioreactors [41,160,161]. The selection of an appropriate bioreactor depends on the specific growth rate of the fungal strain and its tolerance to agitation, as e.g., trays do not facilitate agitation.…”

“…Among the challenges in SSF is the control of process parameters, such as temperature, pH, moisture, and oxygen, which is more difficult than with SmF. This is due to the uneven distribution of fungal biomass, nutrients, moisture, temperature, and pH [10,41,160,161]. SSF has a much higher risk of bacterial contamination and problems with heat build-up, slower microbial growth, and product recovery.…”

“…According to Lee [155] and Manan and Webb [160], on the other hand, SSF has several advantages over SmF, as SSF exhibits higher volumetric productivity, uses less water and energy (especially if no agitation is required), generates less waste and is less timeconsuming. In addition, it is a relatively inexpensive technology with the potential to use solid agro-industrial by-products or waste as substrates.…”

“…SSF is also difficult to scale-up due to possible contamination, low substrate utilization rate, and the lack of commercial SSF reactor designs [41,155,160]. Among the tools to facilitate the up-scaling of SSF bioreactors are to use mathematic models to integrate growth kinetics with process parameters such as energy, moisture, and oxygen consumption and to integrate monitoring devices into the bioreactors [160,161,164,165]. Among the main difficulties are the heterogeneity of the substrates and the fungal growth, which gives huge complexity on the micro-scale.…”

“…As the fungi secrete efficient lignocellulolytic enzymes, they are probably the best suitable microbes to utilize these side-and waste-streams. Traditionally, fermented mycoprotein-rich food is produced on foods [78,79,89], but there is an untapped potential in upgrading non-food substrates, e.g., spent grains, into novel mycoprotein-rich feed-or food ingredients [91,160].…”