Fungal Cell Factories - Food and Industrial Bioproducts and Bioprocessing - page 201

In submerged fermentation , the microorganism is grown in nutrient broth in large,
aerated vessels, such as stirred tank reactors or tower fermentors, under rigorously controlled
environmental conditions. Submerged fermentation has several advantages over other
fermentation methods, as it requires less space, is less labor intensive and higher production
rates are obtained. The majority of citric acid is now produced by submerged fermentation
(Sahasrabudhe and Sankpal, 2001; Bentley and Bennett, 2008). However, facilities that use
surface culturing techniques to produce citric acid are still operated today, as they are simple
and economical to maintain.
In addition to optimizing fermentation parameters, fungal strain improvement and
selection, either by classical mutagenesis or more sophisticated targeted molecular genetic
approaches, are important research avenues to increase productivity and yield of industrial
fermentations (Ruijter et al ., 2002 ).
8.2 HISTORICAL PERSPECTIVE
The first known utilization of filamentous fungi for beneficial purposes is the traditional
food and beverage fermentations used in many Asian cultures.
8.2.1 Koji
Fungal fermentation has been employed for thousands of years in China, Japan, Korea,
Indonesia and other parts of Asia to enhance the palatability of rice, soybeans and other
plant-based foods. In a process dating to the Chou dynasty (1121-220 BC), the mold
inoculum was isolated and identified by its characteristic yellow-green hue (Bentley, 2006).
Depending on what is being made, Aspergillus oryzae or other Aspergillus species, including
A. sojae and A. awamori , is cultivated on steamed cereal grains, commonly rice or barley,
with or without soy, to produce koji with distinctive characteristics and flavors. Koji, or
“bloom of the mold”, is the Japanese name for mold-fermented grains or soybeans. The
resulting koji “starters” make a variety of fermented foods and beverages, including miso
(soybean paste), shoyu (soy sauce), sake (rice wine), shochu (spirits) and yonezu (rice
vinegar) (Reddy et al ., 1986 ).
Filamentous fungi secrete enzymes including proteases, amylases, lipases and pectinases
as they invade and degrade their substrate. These enzymes in turn hydrolyze proteins to
peptides and amino acids, and degrade starches to simple sugars. Fermentation enhances
flavor, preservation and nutritional value as well as providing substrates for additional yeast
or lactic bacterial fermentations. These fermentations, now collectively known as koji
processes, are a very early example of solid-state fermentation (Machida et al ., 2008 ;
Murooka and Yamshita, 2008). Solid-state fermentation is the basis for many modern
commercial processes to produce a variety of enzymes, organic acids and secondary
metabolites.
Japanese-born scientist Jokichi Takamine developed the commercial use of mold-
derived enzymes and introduced these fungal products to industry. Takamine, the “Japanese
father of American biotechnology”, brought a modification of the koji process to the
United States in the late nineteenth century (Bennett, 1985; Machida et al ., 2008 ). He
believed koji-derived amylolytic enzymes could revolutionize the American distillery
industry. His method involved growing A. oryzae on steamed bran and using aqueous