Comparison of Citric acid Production through Milk Whey and Glucose fermentation by Aspergillus niger
Chacón Yessica1, Cardona Carlos A1**.
1 Universidad Nacional de Colombia sede Manizales, Instituto de Biotecnología y Agroindustria, (+57) (6) 8879400 ext 55354.
** Corresponding author: email@example.com
The milk whey is one of the most important residues in the dairy industry. This residue is generated during the cheese production. It represents between 85% and 90% of total milk used . Furthermore, around 55% of initials milk compounds are retained in milk whey . This residue is composed by lactose (4,5-5% w/v), soluble proteins (0,6-0,8% w/v), lipids (0,4-0,5% w/v) and mineral salts (8-10% of dried extract) . Nowadays, a special interest has been increased for milk whey due to its high nutritional value and functional properties  . Despite that a portion of this residue is used in beverage, pharmaceutical and food industries, the remaining portion is discharged in soils, drainages and hydric sources. This fact becomes in an environmental problem due to the high organic load .
According to one of the most representative producers of milk in Colombia (Federación Colombiana de Ganaderos (Fedegan)), the total milk whey production in 2006 was 921,672 million liters. Based on the inappropriate disposal of milk whey as well as the Colombian environmental framework, milk whey can be used for obtaining value added products such as organic acids, enzymes, among others.
Citric acid is an organic acid that has high demand for different industries as pharmaceutical, cosmetics, plastics, detergents and food industries . This acid is produced at industrial scale through submerged fermentation by Aspergillus niger using sucrose, cane or beet molasses as feedstock. Alternative feedstocks have been used in the past obtaining great production yields working with brewery waste, spent grain liquor, whey permeate, date syrup, wood hemicellulose, hydrolyzate bagasse, ram horn hydrolyzate, banana extract and milk whey as carbon source        .
This work presents the citric acid production using the strain A. niger. The submerged fermentation process was carried out in a fermenter Liflus GX (BIOTRON, INC-HANIL). The substrates used was milk whey (supplied by local Dairy Company Normandy, obtained from Holstein cow) and glucose. Different pretreatments methods were applied to milk whey aimed to increase citric acid yields. The effect of aeration and pH over citric acid yield was evaluated. The biomass concentration, citric acid and total reducing sugars were tested using the dry weight, HPLC and the Saffran-Densted Methods, DNS (3,5-dinitrosalicylic acid) Method to 540 nm, respectively. Techno-economic and environmental assessments were developed for a citric acid production. Aspen Plus V8.2 was used as computational tool for obtaining mass and energy balances of the process.
Two scenarios for citric acid production were evaluated. The first scenario, (named base case) was simulated using glucose as substrate. The second scenario was simulated using milk whey as substrates. The total production cost per kg of product was calculated with Aspen Process Economic Analyzer . Techno-economic assessment was made in the Colombian context using a tax rate of 25% and an interest rate of 17% and electricity and water costs reported in the literature . The life of the project was fixed at 10 years and the straight-line method for depreciation of capital was used. The environmental assessment was performed through the Waste Algorithm Reduction (WAR), developed by the Environmental Protection Agency (EPA).
The Potential Environmental Impact (PEI) of the process was calculated as well as the impact over eight environmental categories .
The results revealed that milk whey can be used as substrate being an attractive alternative for citric acid production. The results of techno-economic assessment allowed to identifying the optimal yields to formulate a competitive production scheme.
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