Filamentous ascomycetes fungi as a source of natural pigments

Abstract

Filamentous fungi, including the ascomycetes Monascus, Fusarium, Penicillium and Neurospora, are being explored as novel sources of natural pigments with biological functionality for food, feed and cosmetic applications. Such edible fungi can be used in biorefineries for the production of ethanol, animal feed and pigments from waste sources. The present review gathers insights on fungal pigment production covering biosynthetic pathways and stimulatory factors (oxidative stress, light, pH, nitrogen and carbon sources, temperature, co-factors, surfactants, oxygen, tricarboxylic acid intermediates and morphology) in addition to pigment extraction, analysis and identification methods. Pigmentation is commonly regarded as the output of secondary protective mechanisms against oxidative stress and light. Although several studies have examined pigmentation in Monascus spp., research gaps exist in the investigation of interactions among factors as well as process development on larger scales under submerged and solid-state fermentation. Currently, research on pigmentation in Neurospora spp. is at its infancy, but the increasing interest for biorefineries shows potential for booming research in this area.

Keywords: Ascomycetes; Carotenoids; Edible filamentous fungi; Neurospora; Pigments.

Fig. 1

Overview of some sources that can be used for extraction of synthetic or natural-origin pigments [–14]

Fig. 2

a Structure of polyketide pigments followed by two examples of some classes of fungal polyketide pigments. Acetyl-CoA serves as a building block, condensation of acetyl unit with malonyl units and simultaneously decarboxylation result in polycarbonyl compounds that serve as substrates for various cyclases that produce aromatic compounds. b General carotenoid structure followed by two examples of a carotene and a xanthophyll carotenoid [5, 44, 45]

Fig. 3

Chemical structures of some common carotenoids found in microorganisms that are also of economic value [8] as well as the structure of the carotenoid acid neurosporaxanthin [22]

Fig. 4

The possible carotenoid biosynthetic pathway of Neurospora crassa. The gene products/enzymes responsible for each enzymatic reaction are indicated. Site of chemical changes from precursor molecules are shaded. Molecular groups that distinguish xanthophylls from carotenes are marked with red circles. The pigments found in N. intermedia N-1 are presented in boxes

Fig. 5

The possible carotenoid biosynthetic pathway of Neurospora crassa. The gene products/enzymes responsible for each enzymatic reaction are indicated. Site of chemical changes from precursor molecules are shaded. Molecular groups that distinguish xanthophylls from carotenes are marked with red circles. The pigments found in N. intermedia N-1 are presented in boxes

Fig. 6

The possible carotenoid biosynthetic pathway of Neurospora crassa. The gene products/enzymes responsible for each enzymatic reaction are indicated. Site of chemical changes from precursor molecules are shaded. Molecular groups that distinguish xanthophylls from carotenes are marked with red circles. The pigments found in N. intermedia N-1 are presented in boxes

Fig. 7

Schematic process scheme of the main starch-based bioethanol process stages leading to the production of ethanol, DDGS and CO₂. Adapted from Ferreira et al. [120], and suggested production of pigments represented in dashed lines using filamentous fungi