21
2.3 Production
Mushrooms or fungi are underutilized compared to other sources of dietary fiber
such as cereals, fruits, legumes, and vegetables (O’Shea et al. 2012; Elleuch
et al. 2010).
Fungi that have distinctive and visible fruiting bodies are defined as mushrooms
(Chang and Miles 1992) and they include edible and medicinal ones. The flesh or
dried form fruiting bodies of edible mushrooms (e.g., Lentinus edodes) are mainly
consumed, while medicinal mushrooms (e.g., Ganoderma lucidum) are non-edible
fungi that are used for biopharmaceutical purposes because they contain bioactive
components such as polysaccharides and triterpenoids.
Mushroom cell walls enclose a mixture of fibrillar and matrix components which
include chitin (a straight-chain (1 → 4)-β-linked polymer of N-acetyl-glucosamine)
and the polysaccharides such as (1 → 3)-β-d-glucans and mannans, respectively
(Bartnicki-Garcia 1970).
2.3.1 Preparation of Fungus (Mushroom) as Dietary Fiber
Dietary fiber preparation involves the removal of non-dietary fiber materials by
either enzymatic or chemical methods. Soluble dietary fiber is extracted by water or
other aqueous solution with pH control, while insoluble dietary fiber is improved as
insoluble filtrate. The most widely accepted method for total dietary fiber determination is the AOAC enzymatic-gravimetric method 985.29 (AOAC International
2000) involving the use of three analytical enzymes: heat-stable α-amylase (EC
3.2.1.1), protease (EC 3.4.21.14), as well as amyloglucosidase (EC 3.2.1.3) to
remove all non-fiber materials including starch and protein. Chemical methods for
dietary fiber preparation are usually simple but non-specific.
Compared to mycelium, mushroom sclerotium has the highest level of nondigestible carbohydrates and an ideal source of commercial dietary fiber. Recently, an
enzymatic procedure modified from the AOAC method 985.29 for preparing some
novel dietary fibers from three mushroom sclerotia including Pleurotus tuberregium (PTR), Polyporus rhinocerus (PR), and Wolfiporia cocos (WC) using analytical and industrial food-grade enzymes was developed in laboratories (Wong and
Cheung 2005, 2009). The effects of these enzymes on both the yield and nondigestible carbohydrate composition of sclerotial dietary fiber were compared. Use of
industrial grade enzymes in the preparation the total dietary fiber gives a very high
yield of sclerotial dietary fibers [PTR, 81.2%; PR, 86.5%; WC, 96.2% dry weight
(DW)] with purity that was comparable to that of analytical enzymes (Wong and
Cheung 2009; McCleary 2000). Additionally, in the application of food products,
sclerotial dietary fiber has functional properties such as water- and oil holding,
emulsifying, and mineral binding (Wong and Cheung 2005). In the food industry,
2 Fungal Production of Dietary Fibers
2.3 Production
Mushrooms or fungi are underutilized compared to other sources of dietary fiber
such as cereals, fruits, legumes, and vegetables (O’Shea et al. 2012; Elleuch
et al. 2010).
Fungi that have distinctive and visible fruiting bodies are defined as mushrooms
(Chang and Miles 1992) and they include edible and medicinal ones. The flesh or
dried form fruiting bodies of edible mushrooms (e.g., Lentinus edodes) are mainly
consumed, while medicinal mushrooms (e.g., Ganoderma lucidum) are non-edible
fungi that are used for biopharmaceutical purposes because they contain bioactive
components such as polysaccharides and triterpenoids.
Mushroom cell walls enclose a mixture of fibrillar and matrix components which
include chitin (a straight-chain (1 → 4)-β-linked polymer of N-acetyl-glucosamine)
and the polysaccharides such as (1 → 3)-β-d-glucans and mannans, respectively
(Bartnicki-Garcia 1970).
2.3.1 Preparation of Fungus (Mushroom) as Dietary Fiber
Dietary fiber preparation involves the removal of non-dietary fiber materials by
either enzymatic or chemical methods. Soluble dietary fiber is extracted by water or
other aqueous solution with pH control, while insoluble dietary fiber is improved as
insoluble filtrate. The most widely accepted method for total dietary fiber determination is the AOAC enzymatic-gravimetric method 985.29 (AOAC International
2000) involving the use of three analytical enzymes: heat-stable α-amylase (EC
3.2.1.1), protease (EC 3.4.21.14), as well as amyloglucosidase (EC 3.2.1.3) to
remove all non-fiber materials including starch and protein. Chemical methods for
dietary fiber preparation are usually simple but non-specific.
Compared to mycelium, mushroom sclerotium has the highest level of nondigestible carbohydrates and an ideal source of commercial dietary fiber. Recently, an
enzymatic procedure modified from the AOAC method 985.29 for preparing some
novel dietary fibers from three mushroom sclerotia including Pleurotus tuberregium (PTR), Polyporus rhinocerus (PR), and Wolfiporia cocos (WC) using analytical and industrial food-grade enzymes was developed in laboratories (Wong and
Cheung 2005, 2009). The effects of these enzymes on both the yield and nondigestible carbohydrate composition of sclerotial dietary fiber were compared. Use of
industrial grade enzymes in the preparation the total dietary fiber gives a very high
yield of sclerotial dietary fibers [PTR, 81.2%; PR, 86.5%; WC, 96.2% dry weight
(DW)] with purity that was comparable to that of analytical enzymes (Wong and
Cheung 2009; McCleary 2000). Additionally, in the application of food products,
sclerotial dietary fiber has functional properties such as water- and oil holding,
emulsifying, and mineral binding (Wong and Cheung 2005). In the food industry,
2 Fungal Production of Dietary Fibers