Environmental Engineering Reference
In-Depth Information
and are considered secondary metabolites of the plants with different chemical
structures and activities, including more than 8,000 different compounds oligo or
polymerized. The polyphenolic concept is used to define substances that have one
or more hydroxyl groups together with an aromatic ring, these compounds are called
polyphenols. Nevertheless, not all the hydroxyl groups are phenols, because they do
not have phenol's properties [2]. An important property of phenolic hydroxyls is
their acidic reactivity [3].
The use of natural antioxidant compounds, especially extracted from plants, as
food preservatives is nowadays widely used. Synthetic antioxidants, such as buty-
lated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and tertiary butyl
hydroquinone (TBHQ), are used in food industry to depress rancidity of fats and
oils. However, the toxicity of synthetic antioxidants as well as increasing consumer
demand for natural products has reinforced the need for effective antioxidants from
natural sources [4]. Several efforts are being carried out by the group of Food
Bioprocesses of Universidad Autónoma de Coahuila to optimize the fungal produc-
tion of certain phenolic antioxidants through solid state fermentation. Main target
molecules are nordihydroguaiaretic acid (NDGA), gallic acid (GA) and ellagic
acid (EA).
Diverse microbial bioprocesses were well developed during the first 60 years
of last century; however, a bioprocess bad attended in that time was the solid
state fermentation (SSF), an alternative method for cultivation of microbes, mainly,
fungi. From the 1970s, western industries started to focus on the production of
microbial metabolites and specific secondary metabolites by cultivation of fungi,
yeasts and bacteria in SSF, in which microbes are grown on a moist solid sub-
strate in the absence of free flowing water [5]. For specific applications, SSF offers
improved yields and product spectra compared to the rest of fermentation systems.
Currently, the main reason for the limited industrial application of SSF is the lack
of engineering data and knowledge about the design and scale-up of solid state
fermenters.
We have applied the SSF process to give an added value to agroindustrial
residues, especially pomegranate husk, creosote bush, tar bush and pecan nut
shells, tannin-rich materials and excellent sources of antioxidants derivated form
biodegradation of lignans or tannins.
2 Background Research
2.1 Nordihydroguaiaretic Acid (NDGA)
Lignans are one of the most important groups of plant bioactive compounds
structurally characterized by possession of a diphenolic ring, which contains a
2,3-dibenzylbutane structure formed from the oxidative dimerization of two cin-
namic acid residues (Fig. 1). These compounds are widely distributed in numerous
plant species and have been found at different levels of abundance in woody portions
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