Fermentation processes have become a popular alternative to obtain natural food ingredients such as natural colorants. Filamentous fungi seem to be an attractive source of bio-pigments due to the wide range of colors that are able to produce at high yields. Production of pigments by filamentous fungi in submerged fermentation is affected by a large number of operating variables like pH, temperature, agitation and aeration rate that may interact strongly between themselves and with the specific characteristics and properties of growth medium and microorganisms, creating a unique environment resulting in a particular final yield of the process. Industrial application of fungal pigments will depend on the successful scaling up of the process. In aerobic fermentation, oxygen transfer rate (OTR) is a key parameter utilized on the design and scale up of microbial processes aiming for the highest productivity.
The presented study aimed to characterize the oxygen transfer conditions in shake flask culture and to analyze its effect on growth and pigment production by Penicillium purpurogenum GH2.
Fermentation experiments were carried out in Erlenmeyer flasks (125 mL) for 8 days at 30 oC. Oxygen transfer was controlled by varying agitation speed (200 to 250 rpm) and the medium volume in flask (25, 50 and 75 mL). Oxygen transfer coefficient (kLa) was determined without biological consumption of oxygen using the dynamic method. OTR at the evaluated agitation speeds and liquid volumes was estimated by OTR = kLa (C*-CL) using the obtained kLa values, where (C*-CL) varied approximately from 7.0-7.5 mg/L at the range of conditions studied.
Pigment production and growth were affected by the conditions tested. Pigment production increased as liquid volume decreased from 75 to 25 mL at both agitation speeds (200-250). The highest pigment production obtained at 250 rpm with 25 mL of liquid volume was 14.42 OD500nm which was 23% higher than the obtained with 25 mL at 200 rpm. Meanwhile the maximum biomass growth was obtained at 50 mL (3.36 g/L) at 200 and at 75 mL (3.37 g/L) at 250 rpm. The oxygen transfer coefficient kLa decreased with the liquid volume and increased with the agitation speed (11.02-17.60 h-1). Pigment production showed a linear correlation with kLa (Pigment = 2.17kLa-23.73, R2=0.98) and with OTR (Pigment = 0.32OTR-26.67, R2=0.90). Biomass growth increased by decreasing kLa from 17.60-11.59 h-1 reached a maximum biomass 3.37 gL-1 and decreased at a kLa value of 11.02 h-1.
The above results indicated that oxygen transfer rate in shake flasks depends on agitation speed and working volume used in submerged fermentation. The production of pigments by Penicillium purpurogenum GH2 is strongly affected by the oxygen supply in the medium. A direct correlation was found between pigment production and kLa and OTR which represent a major finding as reference for future scale up of the process from shake flask to bioreactor.
See more of this Group/Topical: Topical Conference: Sustainable Food Production