Production of citric acid from pineapple waste via fermentation
1996
Samorn Muttamara (Asian Institute of Technology, Pathum Thani (Thailand). Environmental Engineering Div.)
Raw liquid obtained from juice of pineapple soild waste which was discarded by the cannery was used as a fermentation medium for the production of citric acid. The chemical analysis showed that the raw liquid contained about 5-7 percent sugar which increased to 7-8 percent after autoclaving. The study proved the suitability of raw liguid for fermentation. Inoculum identified under the microscope was named Aspergillus niger MAT-1 which is a wild strain from tropical countries. Shake flask studies at 30 deg C on a rotary shaker of 150 rpm indicated that the optimum conditions for fermentation are as follows: inoculum size, 10 percent (v/v); spore suspension of 50 percent transmittance: fermentation duration, 144 h; pH, 3.0-4.0; added phosphate (KH2PO4), 0.5-1.0 g/l. The yields of the citric acid varied from 5.0-13.6 g/l of the liquid, depending on the sugar content in the samples. Addition of nitrogen compounds not only markedly reduced the amount of citric acid formed but also reduced fungus growth. The addition of methanol at a concentration of 2-4 percent proportionally increased the formation of citric acid from the raw liquid of the waste. However, the yield of citric acid was suddenly dropped at methanol concentration of 5 percent. On the other hand, the mycelial growth was markedly increased with addition of methanol at first, then slowly reduced. Pilot plant studies in a ferment indicated that yield of citric acid was 5.65 g/l of fermentation liquid, and 36.8 percent on basis of the sugar consumed. Yield of mylecial dry weight was 14.6 g/l and 65.5 percent based on the sugar consumed. It contains 27.3 percent protein and is a good source of single-cell protein.
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