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Abstract v- SUMMARY Citric acid is used in food industries such as soft drinks, candies, flavouring extracts; in pharmacy and smallar sm o un t s as ingredients in ink, in dyeing, printing and silvering agent. This work was carried out for citric acid production by local strains of ~. niger and study various factors affecting the citric acid production. The study revealed the following results: 1- Screen Lng of the local citric acid producers. The isola t,~s of ~ niger stra in s were sc re ened for cit ric acid production. Most active strains were selected for the study. A strains of ~ niger (AS) gave the best c.Lt r I n acid production among the other investigated ~trains. 2- The USI~ of diluted molasses (to give 15% sugar) as a medium gave weight. On low citric acid yield and low mycelial dry addition of the maj or inorganic nutrients of BerJlhauer’s medium (NH4N03, 2 giL; KH Z P0 4 , 1 giL; MgSO4.7120, 0.25 giL), to the molasses medi urn inc reased ci~ric acid production. 3..~..The. chemical analysis showed that molasses was very poor in nutrient elements but contained high ash, iron and. zinc wt:ich exerted deleterious effect on citric acid --- .- - - - ._ .. -- - - - ---. -- - - 73 - fermentation. The addition of the beet molasses ash to Bernhauer’s medium decreased citric acid yield. Tr ea t m enr; of molasses to reduce the deleterious effect of ash elements on citric acid production as the following: A- Dilut:.on of molasses: The best dilution of molasses to give the highest yield of citric acid was to 15% sugar. B- Different types of alcohols such as methanol, ethanol and isopropanol were added to molasses medium to increase citric acid yield. Addition of ethanol stimulated citric acid I roduction. It was found that 2% ethanol was the optimun concentration which gave the best yield of citric acid. The proper time for addition of ethanol was from commen :ement of fermentation up to 72 hr and the most sui tab le time for its addition was after 24 hr from inoculation (yield, 49.2%, conversion coefficient, 53.2%), c- The u~e of potassium ferrocyanide at a concentration of 1 giL for precipitating excess heavy metals gave yield :4%, conversion coefficient 58%). D- The 6-8 adj ustment wa s found of to the pH 0 f the molasses med iurn from be the best range for citric acid production. .- -.- --_ ... _- - --- _. ---- -----._---~~-- - 74 - The study showed that beet molasses which is a byproduct Jf Sugar industry can be Used economically j n the citric a c i d production by strains of ~ niger when the beet mol::tsses medium was treated by the following two methods: 1- The beEt molasses Was diluted to 15% sugar and Bernhauer’s inorganic nutrients were added and pH was adj Usted to pH 7, :’% ethanol was added to molasses med ium from the commencpment of fermentation up to 72 hr s , The most SUitablE addition time was after 2/, h r s (Yield, 63.1%. conversion coefficient, 69.08%). 2- The bee’ molasses was dil u t e d to 15% Sugar and the Bernhaue. ’s inorganic nutrients were added and pH was adj Usted to 7, I giL potassium fcrrocyanide was added to molasses medium. The Yield (69.9%), Coefficielt (75.5%) were scored. conversion |