Submitted to: Georgia Fruit Newsletter
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 17, 2001
Publication Date: September 18, 2002
Interpretive Summary: Industrially processed corn generates enormous quantities of low-cost coproducts, which offer great potential for replacing petroleum-based polymers in single-use consumer products. However, successful utilization would require knowledge and understanding of their biodegradation properties, particularly under variable moisture, temperature, and pH conditions in a compost. Compost maintained at 40 degrees C, pH 7.0, and 50%-60% moisture content, was most suitable for the degradation of protein-rich coproducts. Whereas, alkaline pH (11.0) and acidic pH (4.0), low temperatures (25 degrees C), and low moisture (30%) conditions slowed the rate and the extent of biodegradation of coproducts rich in carbohydrate, fiber and protein. Addition of 1% urea as a nitrogen source decreased biodegradation, but metabolically active microbial cells were required for polymer degradation. Beside value-addition, research will help predict functional lives and environmental residence times of corn coproducts, and encourage their use in environmentally biodegradable consumer products.
Technical Abstract: The rate and extent of biodegradation of corn fiber (CF), corn zein (CZ), cornstarch (CS), distillers grain (DG) and corn gluten meal (CGM) were evaluated in compost environments under variable temperature, pH, and moisture conditions. Generally, composts with higher temperature (40 degree C), neutral pH (7.0) and 50%-60% moisture content appeared to be ideal experimental conditions for corn coproduct biodegradation, particularly for CGM and CZ. Low moisture conditions slowed biodegradation considerably, but degradation rates improved with increased moisture content up to 60%. Thereafter, increased moisture content particularly slowed the degradation of CGM and CZ, whereas CS degradation remained unaffected. At low pH (4.0) and high pH (11.0) the rate of degradation of most coproducts was slowed somewhat. CS degradation was slower at pH (7.0), but degradation improved with increased temperatures. Increase in compost temperature from 25 degree C to 40 degree C (in 5 degree C increments) also improved biodegradation of CF and DG. Addition of 1% urea to compost as a nitrogen source decreased the extent of biodegradation nearly 40% for CGM, CZ and 20% for CS samples. Treatment of compost with 0.02% azide inhibited biodegradation of all coproducts, suggesting that the presence of metabolically active microbial cells is required for effective degradation of biobased materials in a compost environment.