Abstract:
Malic acid is a specialty chemical that is currently mainly used in the food and beverage industry (market value
of $182 million) but has a potential market value of $3.5 billion if used to produce maleic anhydride. The results
from the study indicated that the production of malic acid by A. oryzae requires the presence of the alkaline
earth metals calcium or magnesium in significant quantities. It was observed that replacing an amount of CaCO3
(240 g.l-1 CaCO3), significantly over that required for pH buffering (21 g.l-1 CaCO3), with an equivalent amount
of MgCO3 (192 g.l-1 MgCO3 based on CO32+) results in similar malic acid yields and final malic acid titers. In
contrast, a marked reduction in glucose consumption and malic acid production rates were observed. These
observations are likely due to an evolutionary response to calcareous soils. These soils tend to immobilize
minerals in solid precipitates resulting in nutrient depletion, while the production of malic acid solubilizes these
minerals making them bioavailable. The higher rates observed for the calcium vs magnesium runs were likely a
result of the stimulatory effect of Ca2+ on the ATP generating pathways as well as several regulatory responses
within the fungal physiology. In addition, it was found that A. oryzae was capable of assimilating malic acid from
the environment, therefore, minimizing the loss of valuable carbon due to malic acid excretion. This study
provides invaluable information required for economically viable malic acid production by A. oryzae which could
markedly reduce reliance on the petrochemical industry.
