Fermentation Conditions and Process Optimization of Citric Acid Production by Yeasts

Abstract

The aim of this study was to isolate and screen citric acid producing yeasts using low cost substrates. Thirty three yeast isolates were obtained from pineapple, plantain and sugar cane waste and identified as; Saccharomyces cerevisiae, Schizosaccharomyces pombe, Candida tropicalis, Pichia guilliiermondii, Debaromyces sp., Candida parapsilosis, Candida rugosa, and Candida krusei. Candida tropicalis had zone of clearance of 49±2.1 mm in diameter, Pichia guilliermondii had 40±1.2mm. Saccharomyces cerevisiae produced citric acid with glucose with 105.0 mg/l. C. tropicalis yielded 132.2 mg/l with sodium nitrate. S. cerevisiae and C. tropicalis produced citric acid at pH 6 with 23.70mg/l and 23.80mg/l. P. gulliermondii at pH 4 produced 23.00mg/l. The temperature of 30°C favoured S. cerevisiae and C. tropicalis yielding 40.80mg/l and 39.80 mg/l. After extraction, the yield of the citric acid was 4.231g, 3g of which was recrystallized to yield 2.16g of pure citric acid resulting into 72% recovery. The result indicated that pineapple wastes, plantain wastes and sugarcane cane are potential sources of yeasts that can be used for the production of citric acid. Contribution/Originality: This study contributes in the existing literature by providing basic information for other researchers regarding the isolation and the screening of yeasts for the production of citric acid using low cost substrates, as well as to study the effect of various fermentation parameters on citric acid production. 1. INTRODUCTION Citric acid (2-hydroxy-1, 2, 3-propanetricarboxylic acid) is an intermediate and important commercial product of metabolism and its traces are found in all plants and animals tissues (Kamzolova et al., 2008).Citric acid is a commercially valuable organic acid, widely used in food, pharmaceutical and beverage industries. It has several applications in cosmetic industries as an acidulant flavour enhancer, preservative, antioxidant and emulsifier and chelation agent (Roehr, 1998). Citric acid (C6H8O7) is a natural component and common metabolite of plants and animals. It is the most versatile and widely used organic acid in foods, beverages, detergents and pharmaceuticals. Citric acid is accepted as GRAS (Generally Recognized as Safe) and approved by the Joint FAO/WHO Expert Committee on Food Additives (Dhillon et al., 2011). In its pure form, this citric acid is colourless, soluble in water and solid at room temperature. Due to its functionality and environmental acceptability, it is used in numerous industrial and research applications for chelation, buffering, pH adjustment, and also as a source of energy for controlled bacterial metabolism (Yoo et al., 2004).

Optimization of Citric Acid Production by Immobilized Cells of Novel Yeast Isolates

“…The trees showed that the strain KKU-L42 sequence clustered with the C. tropicalis sequences (Figure 2(A)), while the sequence from strain KKU-L53 clustered with the P. kluyveri sequences (Figure 2(B)), confirming the original identification of the two strains. The citric acid-producing yeast isolates were obtained from pineapple, plantain, and sugar cane waste and molecular identified as Saccharomyces cerevisiae, Schizosaccharomyces pombe, C. tropicalis, Pichia guilliiermondii, Debaromyces sp., Candida parapsilosis, Candida rugosa, and Candida krusei [1].…”

“…Several studies mentioned that the optimum pH for citric acid production was varied even for the same strain at a broad value between pH 3.5 and pH 7.0. The maximum citric acid production by Y. lipolytica was achieved at pH 5.5-6.0 [8,10,25,42], Y. lipolytica 57 and Y. lipolytica NBRC 1658 at pH ranges of 5.2-7.0 [17], S. cerevisiae at pH of 4.5 [6], whereas for S. cerevisiae and C. guilliermondii at pH 3.5 [34], while for S. cerevisiae and C. tropicalis citric acid was produced at pH 6 and pH 4.0 for P. gulliermondii [1].…”

“…Various studies have reported different temperatures for maximum citric acid production, suggesting that the optimal temperature depends on the strain [10]. The citric acid was produced between 24 and 31 C for Candida oleophila [44], 30 C for S. cerevisiae and C. guilliermondii [34,41], 27 C for Y. lipolytica [25,42], and 30 C for S. cerevisiae and C. tropicalis [1].…”

“…Interestingly, Çelik et al [25] reported that optimum citric acid production (66.2 g/L) by Y. lipolytica was achieved using ammonium sulfate as the nitrogen source, while Yalcin [48] showed that ammonium chloride was the optimum nitrogen source for citric acid production by Y. lipolytica (50 g/L). On the other hand, C. tropicalis produced 132.2 mg/L using sodium nitrate as an optimum nitrogen source [1]. The biochemical role of intracellular ammonium ions in the regulation of the production of citric acid was clarified; the increase of intracellular ammonium ions could lead to the prevention of citrate's inhibition of phosphofructokinase activity, which would result in an overproduction of citric acid [46,47].…”

“…Microbe-based systems are important and versatile biotechnological processes for the production of various chemical substrates because of the limited space required for their cultivation, their rapid growth, and diverse physiological and biochemical properties [1]. Citric acid is one of the most common microbial fermentation-based commercial products for which there is a never ending demand.…”