Biotechnological production of citric acid

Abstract

This work provides a review about the biotechnological production of citric acid starting from the physicochemical properties and industrial applications, mainly in the food and pharmaceutical sectors. Several factors affecting citric acid fermentation are discussed, including carbon source, nitrogen and phosphate limitations, pH of culture medium, aeration, trace elements and morphology of the fungus. Special attention is paid to the fundamentals of biochemistry and accumulation of citric acid. Technologies employed at industrial scale such as surface or submerged cultures, mainly employing Aspergillus niger, and processes carried out with Yarrowia lipolytica, as well as the technology for recovering the product are also described. Finally, this review summarizes the use of orange peels and other by-products as feedstocks for the bioproduction of citric acid.

Overview of citric acid production from Aspergillus niger

“…Yeasts, penicillia, lactic bacteria and species of Aspergillus are the most common sources of contamination (Soccol et al 2006). After completion of the second phase, the citric acid is recovered by washing the mycelial mats and the impregnated citric acid is extracted (Max et al 2010). Other research on surface culture includes Sakurai and colleagues' kinetics study of A. niger citric acid production by surface culture and their research on surface liquid fermentation of banana waste (Sakurai et al 1991).…”

“…It requires more sophisticated installation, higher energy cost and rigorous control, and there is formation of foam (which can be resolved using antifoaming agents), but it provides higher productivity and yields, has reduced capital, maintenance and labour costs, and carries lower contamination risks. In addition, it is less sensitive to change in the medium composition, providing a wider range of substrates and better control of substrates; this advantage makes molasses usable as a medium for citric acid production (Max et al 2010). Submerged fermentation is mostly operated as a batch system (Kishore et al 2008); however, continuous systems are possible and are used in practice.…”

“…There is also a limited pool of viable microorganisms, and strains with large nitrogen and phosphorus requirements cannot be used. Agro-industrial wastes that have been utilized include banana peel (Max et al 2010), cotton waste (Kiel et al 1981), kiwi fruit peel (Hang et al 1987), date pulp (Assadi & Nikkhah 2002), apple pomace ultrafiltration sludge and solid waste (Kareem et al 2010), orange peel waste (Torrado et al 2011), pineapple waste (Kareem et al 2010), wheat bran and soya bean meal (Sauer et al 2008), fresh kumara (Ipomoea batatas), potato (Solanum tuberosum) and taro (Colacasia esculenta) (Arshad et al 2014). …”

“…In the germination stage, the germinating spores absorb ammonia and release protons, thereby increasing the acidity of the medium and favouring the production of citric acid. At low pH of about less than 2, the formation of unwanted products such as oxalic and gluconic acid is inhibited, and the possibility of contamination by other microorganisms is also reduced, making recovery of citric acid easier (Max et al 2010). The initial pH of a medium must be optimized and defined to suit the microorganism, substrate and production technique.…”

“…Some of the nutrients, such as trace metals like manganese, phosphate and nitrogen, must be below defined limits to have a positive effect on the fermentation process. However, other elements, such as oxygen and sugar, are required in excess (Soccol et al 2006;Max et al 2010).…”