Penicillium and Aspergillus

As previously mentioned, these molds are among the most common and widespread in foods. In the older literature, they were often referred to as "Fungi Imperfecti," due to the absence of a sexual stage in their life cycle. Penicillium and Aspergillus are mainly of concern due to their role in food spoilage and as potential producers of mycotoxins; however, some species of Penicillium and Aspergillus are also used to produce fermented foods. In fact, one of the most famous of all organisms used in fermented foods is Penicillium roqueforti. This mold gives Roquefort and other blue-veined cheeses their characteristic color. It is also largely responsible for the flavor and aroma properties of these cheeses. A related white mold species, Penicillium camemberti, is equally important (and no less famous), due to its involvement in the manufacture of Camembert and Brie cheeses.

Although the role of Aspergillus in fermented foods manufacture is somewhat less prominent (at least in foods popular in Western cultures), species of Aspergillus are involved in some of the world's most widely-consumed fermented foods. Specifically, two species, Aspergillus oryzae and Aspergillus sojae, are used in the manufacture of soy sauces and soy pastes and sake and other rice wines, so-called Oriental or

Asian fermented foods that are consumed literally by billions of people (Chapter 12).

There are many different species of Penicillium and Aspergillus. As with the yeasts, speci-ation is based on morphology, structure, and spore type. Biochemical and physiological properties of the fungi, however, are generally less diagnostic. These fungi are heterotrophic and saprophytic, and are usually very good at breaking down complex macromolecules (e.g., protein, polysaccharides, lipids) via secretion of proteinases, amylases, and lipases.The hydrolysis products can then be used as substrates for growth.

Despite their readily observed structural differences, Penicillium and Aspergillus do share some common features. Both are filamentous and produce conidiospores, and are probably related. Typical spore-bearing structures of Penicillium and Aspergillus are shown in Figure 2-9. Finally, Rhizopus oligosporus species are used to produce a fermented soybean product known as tempeh that is popular in Indonesia and other Southeast Asian countries (Chapter 12).Typical morphological structures of Rhizopus are shown in Figure 2-9.

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