Production of Docosahexaenoic Acid from Aurantiochytrium limacinum SR21 using Non-Conventional Carbon Sources

Abstract

ABSTRACT: In recent years, the supply of polyunsaturated fatty acids (PUFAs) has faced two different problems. Firstly, the production from traditional sources, namely capture fish, has remained stagnant while demand continues to increase. Secondly, capture fish has been targeted as a source for heavy metals, hazardous for the human health, due to bioaccumulation of these components as a result of ocean pollution. Consequently, new sources have been studied. In this way, Aurantiochytrium limacinum SR21, a marine chromist, presents itself as an alternative due to its capability to accumulate up to 60% of its weight in lipids. These lipids are rich in Docosahexaenoic Acid (DHA), an essential PUFA. However, producing DHA from A. limacinum SR21 is expensive as it uses glucose as its carbon source. For lowering the costs in the production of DHA from A. limacinum SR21, this work evaluates different non-conventional carbon sources that have the potential to substitute glucose as carbon source. These materials are thought to lower the medium cost, which has shown to be one of the most representative costs in biorefineries. To do so, this work evaluated the potential of amylaceous and lignocellulosic materials. Potato and corn washes were evaluated as waste from the chips and arepa industries. Coffee mucilage, barley spent grain, and empty fruit bunch were used from the coffee, beer, and palm oil industries. All materials were subjected to different pretreatments. Specifically, the materials were pretreated with alkaline pretreatment (2% NaOH) and Liquid Hot Water (LHW) at 121°C and 1.5 atm. The pretreatments were performed aiming to obtain the highest yield of glucose when performing the enzymatic hydrolysis for assessing their usefulness as a replacement for glucose. Finally, the most suitable conditions were tested in a kinetic study to stablish which materials have the best potential to replace glucose as carbon source in the culture of Aurantiochytrium limacinum SR21 to produce DHA. From this study, it was found that all lignocellulosic materials had the potential for producing 50 g/L and above of glucose after the enzymatic hydrolysis. It was also possible to stablish that both barley spent grain and empty fruit bunch mediums were able to produce over 1 g/L of DHA in the culture. The economical estimation showed that the culture medium from empty fruit bunch can be an economical alternative to glucose when producing DHA from A. limacinum SR21.