The use of ultrasound and infrared radiation to reduce microbiological contamination of raw materials in the production of citric acid

The microflora of the main raw materials for producing citric acid (beet molasses and grain) is capable of greatly reducing the yield of target metabolite or changing the focus of biosynthesis. Rye, oats and barley grain with humidity of 16% and its grinds (a particle size 1 mm) was treated ultrasound having a capacity of 1.5 kW, frequency 15 and 22 kHz. Infrared radiation treatment was carried out at t 120 to 180 degrees C for 2-30 min and the exposure power W/sq. cm. In molasses there were found spore-forming heat-resistant bacteria with Bacillus subtilis and B. mesentericus being predominated, gaseous, nitrite-forming, acid-forming bacteria, yeast of gen. Candida, Leuconostoc mesenteroides that consume sugar, nitric and mineral substances reducing the biosynthetic activity of Aspergillus niger producer. For molasses treated with ultrasound 1.5 kW and frequency 22 kHz, the total viable count reduces by the order compared to the control. Increasing the exposure time up to 30 min results in slightly reducing the achieved level. Under influence of ultrasound the contamination with bacteria and mold fungi of rye, oats and barley grain grinds reduces by 2-3 orders compared to the control and much more at frequency 22 kHz. The great increase in the parameter of the total viable count is achieved by IR-treatment of grain and grinds. The microflora practically entirely dies by increasing the temperature up to 160-180 degrees C even in case of 2 minute exposure. IR treatment providing t 120 degrees C for 2-6 min resulted in reducing the number of cells of microorganisms by 3-4 orders compared to the untreated control