production of citric acid from cane molasses

Abou-Zeid et al. (1984) studied corn steep liquor, urea and ammonium salts as nitrogen sources. These sources have been used in citric acid production by yeast.

Nawaz (1986) reported that optimal production of citric acid through cane molasses fermentation by Aspergillus niger was 4.2% at pH 5 with 15% sugar concentration. The optimum temperature observed was 30oC. The minimal yield 0.8 percent was observed at pH 2 with 25 percent sugar concentration at 35oC.

Pervez (1986) reported that production of citric acid from cane molasses by Aspergillus niger. Optimum pH was and optimal concentration of MgSO4, 7H2O KCl and KH2PO4 were 0.025, 0.01 and 0.008% respectively. The optimal fermentation period was 9 days. The yield of citric acid was 4.33% in cleared molasses and 4.09% in crude molasses.

Roukas and Harvey (1988) described that the effect of pH on the production of citric and gluconic acid from beet molasses by Aspergillus niger was studied using continuous culture. At pH values >2.5 gluconic acid was the major product, citric acid being the predominant product at low pH values. The optimum specific activities of citrate synthase, aconitase, NAD-linked isocitrate dehydrogenase, and NADP-linked isocitrate dehydrogenase occurred at pH 4 and of glucose oxidase at pH 5.

Hang and Woodams (1989) reported that a multiple contact countercurrent process was developed for leaching citric acid from apple fermented with Aspergillus niger in solid state culture. Acetone proved the most efficient among the different solvents examined as it yielded that greatest among of citric acid in the leachate and gave an extraction efficiency of 90%.

Begum et al. (1990) stated that the wild type strain CA16 and the mutants 133/40 and 277/30 were grown for 9 days in molasses media containing 12, 14 or 16% sugar, initially at pH 4, the medium was supplemented with Prescott salts (NH4NO3, KH2PO4 and MgSO4.7H2O), either at full strength (respectively concentration 2.23, 1.0 and 0.23 g/litre), half or quarter strength. Citric acid yield was always highest with 16% sugar, being 34 mg/ml for strain CA16 regardless of Prescott salt strength. With mutant 136/40, the highest yield was 63 mg/ml at full strength; with mutant 277/30, it was 88 mg/ml (55% on sugar) at quarter strength.

Roukas (1991) reported that spores of Aspergillus niger were immobilized in alginate gel beads and grown for 4 days at 30oC on molasses medium at pH 6.5 containing 20 g sucrose’s and 0.6 g nitrogenous compounds/liter, in flasks shaken at 250 rpm. The beads washed and incubated at 30oC, in the medium containing 14% total sugars, in shake-flasks aerated at0.5, 1.5 and 2.5 litres/min. pH was adjusted to 3.0 with HCl. Maximum yield of citric acid was observed after 28 days, being 35 g/litre in shake flasks and <28 g/litre (lower with less aeration) in the bioreactor. When the beads were reused in shake flasks, the citric acid concentration in successive batches reached 40, 37.5 and 30 g/litre.

Roukas and Alichanidis (1991) investigated the production of citric acid from beet molasses at a varying pH profile using cell cycle of Aspergillus niger. Best results in terms of citric acid concentration yield, productivity were obtained with a substrate pH of 3.0.

Yigitoglu (1992) worked on the citric acid production through submerged fermentation processes and described wide variation in conditions recommended for successful fermentation. The importance of the nature and quantity of trace metals, carbon and nitrogen sources and correct environmental conditions were found to be very important for citric acid fermentation.

Casida (1993) reported that beet or sugarcane molasses medium containing sugars in the range of 10-20% often was employed in citric acid fermentation and ammonium nitrate, magnesium sulphate and KH2PO4 were usually added into the medium. Hydrochloric acid then, was used to adjust the medium to low pH value and the fermentation were conducted at approximately 28oC to 30oC with proper oration. He also suggested that citric acid fermentation medium should slightly be deficient in phosphate, in one or more of the metals like manganese, iron, zinc and probably copper. Of these, manganese appeared to be particularly important. The molasses, however, contained high quantities of trace metals. Excess of these metals were reduced during pretreatment of the molasses by complexing the metals with ferrocyanide or ferricyanide.