Small Scale Literature Review
Running Head: Factors Affecting Citric Acid Production by Aspergillus niger
Factors Affecting Citric Acid Production by Aspergillus niger
Ong Chia Swing, Student.
Citric acid is a natural preservative or conservative that is used to add an acidic, sour taste to foods and beverages. In the context of biochemistry, the conjugate base of citric acid which is the citrate plays an important role as an intermediate in the citric acid cycle which occurs in the metabolism of all aerobic organisms. Due to its importance to most organisms, more than a million tonnes are produced every year via fermentation. It is used mainly as an acidifier, flavouring and as a chelating agent. B. Kristiansen et al. (1999) and A.E Bodie et al. (1994) stated that most citric acid used in foods is derived from carbohydrate fermentation by Aspergillus niger. Aspergillus niger fermentation is considered as the world’s leading source of commercial citric acid. However, in this literature review, it is hypothesised that many factors have been affecting the citric acid production by Aspergillus niger. Hence, many research studies that have been done to understand in details of which of the best factors studied being applied in producing citric acid more effectively by Aspergillus niger. The following five research articles that have been studied attempt to demonstrate and support the hypothesis:-
2.1Citric Acid Production from Whey with Sugars and Additives by A. niger
In a research paper by Murad and Khalaf (2003), a question was raised and discussed for guiding the study. The question was that, would the production rate of citric acid (CA) by Aspergillus niger ATCC9642 from whey can be affected by different specific concentration of sucrose, glucose, fructose, galactose riboflavin, tricalcium phosphate and methanol in surface culture process? The focus of the investigation was to produce citric acid by Aspergillus niger from cheese whey fortified with different concentrations of sucrose, glucose, fructose, galactose, tricalcium phosphates, methanol and riboflavin in a liquid surface culture process. It is believed that the CA production from whey alone is significantly low despite added with other different concentration of sugars due to the presence of galactose moiety of lactose in the whey (Hossain et al., 1984). It was hypothesised that Aspergillus niger can readily utilise galactose its presence or that of its metabolic products which causes the inhibition of citric acid production as well as reducing the rate of glucose utilisation. According to Moddax et al. (1986), galactose was found interfering with the glucose repression of the key enzyme, 2-oxoglutarate dehydrogenase. There is a strong relationship between citric acid production and the activities of this enzyme and pyrovate dehydrogenase in cell free extracts. On top of that, Hossain et al. (1985) explained that the nature of sugar source has a marked effect on citric acid production by Aspergillus niger. Then, Moddax et al. (1986) and Hossain et al. (1985) stated that the presence of methanol in the fermentation media may increase citric acid production by Aspergillus niger. This is due to the inductive effect of methanol for citric acid production may be due to reduction of the inhibitory effect of metal ions (Kiel et al., 1981). In addition of tricalcium phosphate and riboflavin together with methanol to whey may cause similar adverse effects by chelating certain metal ions like Cu2+ which is reported to be significant component in the structure of the productive fungal pellets (Benuzzi and Segoria, 1997). In short, the research has shown that using whey alone as a natural fermentation medium for citric acid production was inferior to whey fortified with sugars and the production rate of citric acid (CA) by Aspergillus niger ATCC9642 from whey can be affected by different specific...