BIOTECHNOLOGY - V. H. Herasymenko - 2006

Part II. Special Biotechnologies

Chapter 21. BIOTECHNOLOGY OF PROTEIN PRODUCTION

21.9. PRODUCTION OF HIGH-PROTEIN FEED SUPPLEMENTS FROM RENEWABLE RAW MATERIALS

21.9.1. Submerged Fermentation, or Deep Cultivation of Microorganisms

Typically, these fermentations utilize both starch-bearing and Cellulose-bearing plant raw Materials.

The Fermentation of starch-based raw materials employs producer microorganisms equipped with starch-hydrolyzing Enzymes (amylases). These include Yeasts of the genus Candida and certain Molds (genera Fusarium, Chrysosporium, Aspergillus, Myrothecium, etc.). The producer microorganisms are cultivated in standard fermenters on synthetic media supplemented with starch or starchy raw materials (potatoes and potato-Processing products, crushed corn grain, etc.) serving as carbon and Energy Sources.

The product of such fermentation is a preparation containing residues of the initial raw material enriched with 17–20% protein derived from Yeast and mold biomass.

To obtain microbial protein-enriched feed supplements from plant raw materials that are difficult for microorganisms to degrade—such as straw, wood, sawdust, and other industrial and agricultural wastes (consisting primarily of cellulose and Lignin)—microorganisms possessing cellulolytic enzymes are employed. These are predominantly mycelial Fungi and, less frequently, Bacteria.

The complex supramolecular Structure OF THE lignocellulose plant substrate is highly resistant to enzymatic attack. To facilitate the access of microbial enzymes to the Polysaccharides of the plant material, preliminary pretreatment is carried out using various Methods. The most common approach combines chemical and thermal Treatment, exposing the substrates to weak alkalis at elevated temperatures. Other methods for disrupting lignocellulose supramolecular structures are also applied, including mechanical and physical treatments (e.g., straw crushing/flattening).

Protein enrichment of lignocellulosic raw materials via submerged fermentation reaches 10–12%. Canadian researchers have developed the "Waterloo Process" technology, based on cultivating the fungal strain Chaetomium cellulolyticum on substrates (sawdust, straw, the solid fraction of ruminant manure) pre-treated with alkali at elevated temperatures. The resulting product contains 20 to 45% crude protein (12–14% true protein, 35% CARBOHYDRATES, and 10% Lipids). The protein contains 6.8% Lysine, 2.6% Methionine + Cysteine, and 6.1% Threonine, rendering it nutritionally complete. It is used as a protein Supplement in animal diets.