Sunday, August 11, 2013
Pavilion (Sheraton San Diego)
Joosu Kuivanen, Hugo Dantas, Dominik Mojzita, Merja Penttilä and Peter Richard, VTT Technical Research Centre of Finland, Espoo, Finland
The utilization of agricultural residues as a feedstock in bioprocesses is an interesting alternative. One such cheap and abundantly available residue is citrus peel which is a waste from juice industry. More than 100 million tonnes of citrus fruits are produced annually, with a significant share going to juice manufacturing. As a result, about 1 tonne of dry citrus waste is produced per 1 tonne of juice concentrate. Currently, residual citrus peel is partially refined to pectin and D-limonene or used for animal feed. However, due to the limited markets of these products and high costs of feed manufacturing, most of the citrus waste is simply discarded. Therefore, it is desirable to develop alternative ways for its utilization.
Citrus peel is well known of being rich in pectin. Many microbial decomposers are able to hydrolyse pectin to its monomers, mainly to D-galacturonic acid. One of the most efficient microorganisms in pectin hydrolysis is the filamentous fungus Aspergillus niger. In addition, the pathway for D-galacturonic acid catabolism is well known in A. niger. Due to the preceding features, A. niger is a suitable platform organism for citrus peel utilization.
In the present work engineered A. niger strains were developed for the biotechnological citrus peel conversion. D-galacturonic acid pathway was redirected to value-added chemicals such as L-galactonic acid which is a precursor of L-ascorbic acid. Exploiting the natural pectinolytic ability of A. niger, citrus peel was efficiently converted to the product in a consolidated bioprocess without any pre-treatment steps.
