18.1.1 Definition and history of nutraceuticals

‘Nutraceutical’, a word combining ‘nutrition’ and ‘pharmaceutical’, is used to describe a special food or food ingredient with medical or health benefits such as prevention and/or treatment of disease (DeFelice, 1992). Nutraceuticals may refer to dietary supplements, plant extracts, or food designed for specific purposes (DeFelice, 1995). The earliest recognition of nutraceuticals was in the 1980s with calcium, fiber, and fish oil being recognized as health-promoting agents (DeFelice, 1995). With significant research efforts being pursued to explore functional components from plants, marine organisms, and microorganisms (actinomycetes and fungi) (Cocks et al., 1995), nutraceuticals have expanded from basic dietary supplements to a vast range of compounds such as bioactive constituents extracted from plants (polyphenols and lycopene) (Carlos Espin et al., 2007), food ingredients produced by microorganisms (amino acids and omega-3 fatty acids) (Hermann, 2003; Athalye et al., 2009), and microorganisms themselves as an integral part of food (Spirulina and yogurt cultures) (Salminen and Isolauri, 2006; Peiretti and Meineri, 2011).

Nutraceutical development has been in full swing for the past decade. The global market for nutraceuticals was already worth $117.3 billion in 2007 (Ahmad et. al., 2011). With the promotion of the well-being concept and increasing health awareness, the nutraceutical market share is expected to have a steady growth rate in the coming years, and is estimated to attain $176.7 billion in 2013 (Ahmad et al., 2011).

18.1.2 Legislation and regulation of nutraceuticals

With the rapid expansion of the nutraceutical market, more legislation has been implemented to regulate the use and production of this group of products. Beginning in 1994, the United States Congress established the Dietary Supplement Health and Education Act (DSHEA), which provided a clear definition of a dietary supplement in order to distinguish it from medicine and food. It also created the Office of Dietary Supplements within the National Institute of Health (NIH) to institute consumer protections, increase public education, and promote research on the possible health effects of dietary supplements (Office of Legislative Policy and Analysis, n.d.).

The Food and Drug Administration (FDA) has recently established new regulations (termed the ‘Final Rule’) for the nutraceutical industry that are in accordance with the International Conference of Harmonisation (ICH) standards. ICH brings experts from the European Union, Japan, and the United States together to establish guidelines for safe, effective, and high quality medicine (International Conference of Harmonisation, 2012). The Final Rule, established in 2007 and phased in over three years, set standards for dietary supplement production called ‘Good Manufacturing Practices’ (GMPs). Specifically, it established standards for quality control, ingredient labeling, product claims, complaint records, and manufacturing procedures, among others, in an effort to insure that consumers have access to accurately labeled, high quality dietary supplements free from contamination (US Food and Drug Administration, 2009).

GMPs aim to ensure a high quality standard in dietary supplements by holding manufacturers responsible for product identity, purity, composition, and strength. This would prevent the inclusion of pesticides and other contaminants in the saleable product. However, there is no standardization of dietary supplements in the United States (Office of Dietary Supplements, n.d.).

18.1.3 Biorefinery and bio-based nutraceuticals

Bio-based nutraceuticals are defined as nutraceuticals derived from the biomass refinery process. In biomass refinery, where the biomass is completely utilized for sustainable fuels and chemicals production (Amidon et al., 2011), the production of bio-based nutraceuticals, which are regarded as high value co-products, can reduce the cost of the overall production process and thus enhance its economic viability. However, it should be noted that compared with fuels or bulk chemicals, the market size for bio-based nutraceuticals is rather small. If the biomass refinery industry is fully developed, the market for bio-based nutraceuticals will be saturated and thus the prices and the profit margin will inevitably be reduced.

Depending on the biorefinery processe used, production of bio-based nutraceuticals is usually achieved through two routes: physical separation/extraction from biomass materials or biological production by various microorganisms. Some biomass materials contain active compounds that can be extracted to make nutraceutical products while they are mainly used as feedstock for fuels and chemicals. For example, acetylic acids, β-carotene, vitamin B, astaxanthin, polyunsaturated fatty acids, and lutein are some valuable products found in microalgae, which can be integrated into algal-based biofuel production and potentially enhance the economic feasibility of the process (Christaki et al., 2011). Current breakthroughs in bioseparation methods such as chromatography techniques, supercritical fluid extraction (SFE), and nanotechnology separation (Walker et al., 2006) have brought in great opportunities for the economic production of bio-based nutraceuticals from biomass feedstock. For example, recent studies have shown that supercritical fluid extraction can be an economic and scalable tool in extracting functional ingredients from different natural resources, including plants, food by-products, algae, and microalgae (Herrero et al., 2006).

Many nutraceutical-based compounds can be co-produced by microorganisms during microbial fermentation for fuels and chemicals. For example, carotenoids, astaxanthins, and polyunsaturated fatty acids can be synthesized by microalgae while the algal cells are mainly used as feedstocks for fuel and energy production (Christaki et al., 2011). Currently, microbial production of nutraceuticals in general is limited by several factors such as the high cost of substrate and low production yield. Inexpensive feedstocks from biomass refineries can provide a cheap substrate for microorganisms, but may still be limited by other factors such as the lack of a robust strain with high product yield. Metabolic engineering has become an effective tool to enhance the cells’ capability of synthesizing certain desired compounds for nutraceuticals (Hugenholtz and Smid, 2002). For example, fermentative production of mannitol from lactic acid bacteria has been successfully implemented by modification of the genomic information and redirection of the metabolic flux (Ferain et al., 1996; Neves et al., 2000).

In general, nutraceuticals from bio-based materials can be classified as lipid-based, protein and peptide-based, and carbohydrate-based, depending on the nature of the functional constituents. Some small molecular bioactive compounds such as secondary metabolites are also considered to be bio-based nutraceuticals. This chapter discusses the recent research progress of bio-based nutraceuticals, the advantages and limitations of bio-based nutraceutical production, and its potential opportunities and challenges.

18.2.1 Types, properties, and functions of lipid-based nutraceuticals

Lipids refer to a group of naturally occurring compounds that are readily soluble in organic solvents. They are classified as neutral or polar type depending on the nature of their chemical structures. Triglyceride and its derivatives (mono-, di-glyceride, and free fatty acid), waxes, sterols, fat-soluble vitamins (A, D, E, and K), phospholipids, and sphingolipids are the major lipid types present in nature. They exist in different parts of living organisms and have various biological functions. Triglyceride and its derivatives are abundant in microorganisms as well as the fatty tissues in human bodies where they serve as energy storage molecules. Phospholipids are the major components of the cell membrane while sphingolipids work as signaling molecules in cell metabolism. Sterols are the precursors of steroid hormones and vitamins play important roles in biological systems, such as regulating cell and tissue growth and differentiation (vitamin A), promoting calcium absorption (vitamin D), and performing antioxidant function (vitamin E) (http://lipidlibrary.aocs.org/).

Lipid-based nutraceuticals encompass various products including omega-3 polyunsaturated fatty acids (PUFAs), phytosterols, lipophilic vitamins and their analogues as well as polar lipids with specific functions. The main focus of this chapter will be on PUFAs, phytosterols, and polar lipids.

Polar lipids

Polar lipids with amphiphilic nature are often associated with membrane structure, and play a variety of biological functions. A majority of polar lipids (Fig. 18.1) found in cell membranes are glycerophospholipids (GPLs), which have a glycerol backbone with fatty acids attached. Some examples of GPLs include phosphatidyl choline, phosphatidyl ethanolamine, and phosphatidyl serine. When the polar lipids are derived from sphingosin, the corresponding polar lipids are classified as sphingophospholipids (SPLs). Sphingomyelin, consisting of a ceramide unit and a phosphorylcholine moiety, is the most representative SPL found in the neural system (Oshida et al., 2003). By interacting with cellular membranes, dietary polar lipids can alter the membrane compositions, and thus affect a series of signaling process and enzymatic functions (Küllenberg et al., 2012). Some beneficial effects exerted by polar lipids consist of anti-inflammatory, anti-cancer, cholesterol lowering, and brain development (Küllenberg et al., 2012).

Polyphosphatidyl choline (PPC), extracted from soybean, with themain active ingredient of 1,2-dilinoleoylphosphatidyl choline (DLPC) has been proven to possess beneficial effects in various liver diseases. DLPC is found to have a high content of polyunsaturated fatty acids, particularly linoleic acid. Oral administration of PPC can induce a series of changes, including restoring membrane structure, increasing membrane fluidity, enhancing membrane-associated metabolic functions, reducing peroxidative reactions, improving immune properties, and stabilizing bile compositions (Gundermann et al., 2011). These positive effects revealed from a pharmacological standpoint have also been confirmed in clinical trials. Test subjects with different types of liver disease responded positively to the consumption of PPC with rare and weak side effects. Therefore, soybean-derived PPC is a good nutraceutical supplement in preventing liver disease and promoting the restoration of physical health for patients (Gundermann et al., 2011).

Sulfoquinovosylacylglycerol (SQAG) (Fig. 18.2) is an anionicglycerolipid, associated with monogalactosyldiacylglycerol and digalactosyldiacylglycerol, and present as a structural component in the photosynthetic membranes of plants, algae, and various bacteria (Berge et al., 2002). It is one of the few lipids derived from natural sources with sulfonic acid linkages discovered to date (Sanda et al., 2001). Due to the uniqueness of the chemical nature of SQAG, studies have been conducted to extract and characterize SQAG from various marine red and blue-green algae, and a series of biological functions related to SQAG have been reported. SQAGs derived from algae have shown an inhibitory effect on both eukaryotic DNA α- and β-polymerases and HIV-reverse transcriptase. Hence, they can potentially be used as antiviral and antitumor supplements (Gustafson et al., 1989; Loya et al., 1998; Ohta et al., 1998).

18.3.1 Algae proteins

Unlike milk and egg which have been considered as good protein sources for a long time, algae-derived proteins did not receive much attention until algal biofuel research became a popular topic in recent years. Algal proteins have great potential to mitigate the high production cost of algal-based biofuel, particularly when the proteins have certain biological functions and can be sold as high value products. In general, the protein content of algae varies with species. Green and red algae have relatively high protein content (around 40%) while protein content in brown algae can be lower than 15% (Murata and Nakazoe, 2001). Most algae proteins contain all the essential amino acids with a high content of aspartic acid and glutamic acid and a low level of sulfur-containing amino acids (Fleurence, 1999).

Lectins are sugar-binding proteins naturally occurring in algae. Some bioactive lectins identified in macroalgal species such as Ulva sp., Eucheuma spp. and Gracilaria sp. have exhibited various biological functions including antibiotic, mitogenic, cytotoxic, anti-nociceptive, anti-inflammatory, anti-adhesion and anti-HIV activities (Bird et al., 1993; Smit, 2004; Mori et al., 2005). These bioactive functions are achieved mainly by binding a soluble carbohydrate or a carbohydrate moiety of glycoprotein or glycolipid, and subsequently precipitating the glycoconjugates. Lectins as agglutinins have found applications in biology, cytology, biochemistry, medicine, food science, and technology (Smit, 2004).

Phycobiliproteins are water-soluble proteins that are a part of light-harvesting protein-pigment complexes in cyanobacteria and certain microalgae. Spirulina has been found to be a rich source of phycobiliproteins. C-phycocyanin, a major phycobiliprotein, has been reported to possess a variety of biologically beneficial effects, including antioxidant, anti-inflammatory, and neuroprotective benefits. Spirulina-derived phycocyanin has been used in the food and beverage industry as a natural pigment. Phycocyanin has been commercially produced in open ponds and raceway systems at tropical and subtropical Pacific Ocean regions (Lee, 1997; Pulz, 2001; Spolaore et al., 2006). In open raceway systems, the productivities of dry biomass and phycocyanin were around 14 and 0.85 g/m² a day, respectively (Jiménez et al., 2003). The extraction of phycocyanin from algal biomass mainly consists of two steps: disintegration of cells and extraction of the water-soluble phycobiliproteins into aqueous media. Further purification of phycocyanin can be achieved by ammonium sulfate precipitation, chromatographic methods (Boussiba and Richmond, 1979; Zhang and Chen, 1999; Minkova et al., 2003; Niu et al., 2007; Abalde et al., 1998; Soni et al., 2006), and ultrafiltration (Herrera et al., 1989). Recently, a method based on two-phase aqueous extraction followed by chromatography was successfully developed to prepare ultra-pure C-phycocyanin (Patil et al., 2006).

18.3.2 Algae-derived bioactive peptides

Bioactive peptides from algae can be divided into two categories: endogenous peptides and enzymatically hydrolyzed peptides (Harnedy and Fitzgerald, 2011). Endogenous peptides, including linear peptides, cyclic peptides, depsipeptides, and different peptide derivatives, possess various biological activities (Harnedy and Fitzgerald, 2011). Carnosine, an antioxidant peptide due to its capability of chelating transitional metals (Brown, 1981; Fleurence 2004), has been found in macroalgae (Fleurence, 2004; Shiu and Lee, 2005). Glutathione, another antioxidant peptide found in the green macroalga Ulvafasciata, is produced under high oxidative conditions, in which an inherent enzymatic antioxidant system (ascorbate-glutathione) is stimulated and glutathione is produced to scavenge and detoxify oxidative free-radical molecules (Shiu and Lee, 2005). Kahalalide F, a cyclic depsipeptide, produced by the green alga Bryopsin sp., has been proposed as a new natural anti-cancer drug candidate (Hamann and Scheuer, 1993). It has a strong cytotoxic activity in vitro against different cell lines including prostate, breast, and colon carcinomas as well as neuroblastoma, chondrosarcoma, and osteosarcoma (Hamann and Scheuer, 1993; Suárez et al., 2003). In vivo tests and some clinical trials have also been carried out, showing a great prospect for the drug application of Kahalalide F (Luber-Narod et al., 2000; Provencio et al., 2006; Pardo et al., 2008).

Bioactive peptides from algal protein hydrolysates have shown various functionalities such as ACE-inhibitory, anti-hypertensive, antioxidant, antitumor, antityrosinase, anticoagulant, calcium-precipitation-inhibitory, antimutagenic, plasma- and hepatic-cholesterol reducing, blood-sugar-lowering, and superoxide dismutase (SOD)-like activities (Harnedy and Fitzgerald, 2011). These protein hydrolysates were mainly prepared by using food grade enzymes including protamex, trypsin, pepsin, alcalase, flavourzyme, and neutrase (Harnedy and Fitzgerald, 2011). Purification of the bioactive peptides has been achieved by ultrafiltration and nanofiltration, which render a great potential for the application of peptides as functional food ingredients (Korhonen, 2009).

18.4.1 Bioactive polysaccharides

The first bioactive polysaccharide reported to have specific functionality is lentinan, a polysaccharide found in the mushroom L. edodes Sing., with strong antitumor activity(Chichara et al.,1969). Lentinan has a1,3-β-glucopyranosidic structure with two1,6-β-D-glucopyranosidic branches every five glucose units in the main chain (Fig. 18.3). The strong antitumor activity of lentinan was attributed to its highly ordered structure; which can induce interleukin-12 (IL-12), a secreted protein/signaling molecule responsible for stimulating natural killer cells and T lymphocytes production (Wiederschain, 2007). Another anti-cancer polysaccharide, schizophyllan, was also isolated from the mushroom S. commune in the earlier days (Komatsu et al., 1969). These antitumor polysaccharides possess a similar structural characteristic, i.e., the skeletion of 1,3-β-glucan with some 1,6-β-glucose branches (Yagita, 1997). Biologically active compounds can be obtained by the enzymatic hydrolysis of the hemicellulose skeleton in the cell wall of fungal mycelia, which explains the presence of a wide variety of anti-cancer polysaccharides in different fungi species.

A sulfated polysaccharide extracted from marine red alga, Schizymenia pacifica, was found to have anti-HIV functions. This polysaccharide was proven to be a member of λ-carrageenan with 20% sulfonate content. The molecular weight of the bioactive polysaccharide is around two million; the major sugar units are galactose and 3,6-anhydrogalactose (Nakashima et al., 1987a, 1987b). This sulfated polysaccharide can selectively inhibit HIV reverse transcriptase (RT) and replication in vitro.

Sulfated polysaccharides are the most studied bioactive polysaccharides. In addition to their antivirus capabilities, numerous sulfated polysaccharides isolated from algae have also been reported to show antioxidant, proliferative, immuno-inflammatory, antimicrobial and antilipidemic behavior (Jiao et al., 2011; Wijesinghe and Jeon, 2012). For example, a sulfated fucoidan, from commercially cultured Cladosiphon okamuranus TOKIDA, has demonstrated its anti-proliferative activity in human leukemia U937 cells by inducing apoptosis associated with degradation of PARP, caspase-3 and -7 activation in U937 cells (Teruya et al., 2007). The producer of sulfated fucoidan, C. okamuranus TOKIDA has been cultivated commercially. A fucidan from C. okamuranus TOKIDA has been used as an additive in health foods, drinks, and cosmetics in Japan (Teruya et al., 2007).

Dietary fibers, primarily composed of polysaccharides, have also attracted tremendous research and public attention. Consumption of dietary fiber has been related to a multitude of health-promoting benefits, including lowering total and LDL cholesterol, regulating blood pressure, alleviating constipation, and stimulating the proliferation of gut microflora (Dhingra et al., 2012). Pectins are one type of dietary fibers with D-galacturonic acid as a principal constituent. They are structural components of fruit and vegetable cell walls (Maxwell et al., 2012), and have been produced from dried citrus peel or apple pomace, both by-products of juice production (Sato et al., 2011; Guo et al., 2012). β-Glucans are another type of valuable dietary fibers with D-glucose monomers linked by β-glycosidic bonds. They are predominantly non-starch polysaccharides present in cereal crops, particularly in barley and oat (Ahmad et al., 2012). Both pectins and β-glucans have special physical properties such as thickening, stabilizing, emulsification, and gelation, which make them suitable to be incorporated in soups, sauces, beverages, and other food products (Burkus and Temelli, 2000; Maxwell et al., 2012).

18.4.2 Extraction and purification of polysaccharides

Extraction of polysaccharides from biomass sources is commonly conducted using the following procedures:

The purification of polysaccharides can be achieved by using different chromatographic techniques, including ion exchange, gel permeation, and affinity chromatography (Srivastava and Kulshreshtha, 1989). However, these techniques are limited by their loading capacities and can only be used on a small scale. The simulated moving bed (SMB) technique has recently received more attention due to its high separation efficiency and applicability for sugar purification. It is a scalable method and suitable for industrial processing of functional carbohydrates (Walker et al., 2006).

18.4.3 Prebiotics

Prebiotics are defined as ‘selectively fermented ingredients that allow specific changes, both in the composition and/or activity of the gastrointestinal microbiota that confers benefits upon host well-being and health’ (Gibson et al., 2004). Most prebiotics are oligosaccharides, which resist digestion by pancreatic and brush border enzymes. They can be produced by extraction from plant materials, enzymatic hydrolysis of polysaccharides, and microbial/enzymatic synthesis (Figueroa-Gonzalez et al., 2011).

Inulin is one of the most established prebiotics with the structure of β(2-1)-fructans (Gibson et al., 2004; Figueroa-Gonzalez et al., 2011). It can be extracted from chicory root and Agave tequilana with the degree of polymerization (DP) varying from 2 to 65. Partial enzymatic hydrolysis of inulin using an endo-inulinase (EC 3.2.1.7) can lead to the production of oligofructose (DP 2-7). The food industry has developed specific products known as Synergy® (Orafti NV, Tienen, Belgium) by mixing oligofructose and long-chain inulin. Different industrial products have different DP distribution and, therefore, varying technological properties (Franck, 2002).

Galacto-oligosaccharides (GOS), which are mixtures of oligosaccharides derived from the enzymatic transglycosylation of lactose, are another type of prebiotic. β-Galactosidases are the primary enzymes responsible for the conversion of lactose to GOS. As β-galactosidases have the capability of conducting both transgalactosylation and hydrolysis reactions, the yield of GOS is low due to the presence of the hydrolysis process (Ganzle, 2011). Methods to improve the yield of GOS have been investigated including enzyme selection, protein engineering, and optimizing reaction conditions. GOS yields have been achieved from 40 to 60% in the final product (Park and Oh, 2010).

Prebiotics have also been produced through a biorefinery process as valuable products. For example, oligofructose was enzymatically synthesized when the aqueous extracts from dairy by-products were used as substrate (Smaali et al., 2012). Xylooligosaccharides with prebiotic activities have been manufactured from solid waste in malting industries by double hydrothermal processing (Gullon et al., 2011). Prebiotics, as carbohydrate-based functional compounds, have been receiving tremendous research efforts within the context of biorefinery production.

18.5.1 Phenolic compounds

Phenolic compounds are the most abundant and widely represented class of plant natural products. With a growing body of evidence that bioactive phenolics exert strong health-promoting effects, phenolic compounds have a great potential to be used as nutraceutical supplements and pharmacological agents (Wildman, 2007).

Phenolic compounds are a group of structurally diversified chemicals derived from phenylalanine and tyrosine. Plant phenolic compounds comprise simple phenols, phenolic acids (both benzoic and cinnamic acid derivatives), coumarins, flavonoids, stilbenes, hydrolysable and condensed tannins, lignans, and lignins (Naczk and Shahidi, 2004). Some of those phenolic compounds have bioactive functions while others have no noticeable bioactivity, depending on their biosynthesis pathway. In general, the bioactive group of phenolic compounds are derived from shikimic acid and/or polyacetate biosynthesis pathways (Bernal et al., 2011).

Fruits and vegetables are a rich source of simple phenolics such as hydroxycinnamic acid conjugates and flavonoids. These compounds are considered to have protective effects against cancer and cardiovascular diseases due to their antioxidant activities (Boudet, 2007). Epidemiological studies have confirmed the health-promoting effects of phenolics by revealing that a high consumption of antioxidant-rich fruits and vegetables is inversely correlated with the incidence of cancer (Knekt et al., 2002). The possible mechanisms of the antioxidant activities are:

Polyphenolic compounds are receiving increasing attention due to their positive roles in the treatment of neurodegenerative diseases, prevention of cardiovascular, cerebrovascular and peripheral vascular diseases, and function as phytoestrogen (Boudet, 2007). As neuroprotective agents, polyphenolics are capable of reducing or blocking neuron death induced by oxidative stress, and exert benefits through different metabolic pathways including signaling cascades, anti-apoptotic processes or the synthesis/degradation of the amyloid β peptide (Ramassamy, 2006). Polyphenolics contained in red wine have been found to have cardioprotective function by interfering with the molecular processes related with initiation, progression, and rupture of atherosclerotic plaques (Szmitko and Verma, 2005).

Preparation of phenolic compounds from raw plant materials has been extensively studied. As plant phenolics exist in both simple and highly polymerized forms, and may also complex with carbohydrates, proteins and other plant components, the solubility of phenolics varies significantly (Naczk and Shahidi, 2004). Therefore, different solvent systems have been applied to extract specific groups of phenolic compounds. Water, ethanol, methanol, acetone, ethyl acetate, propanol, and dimethylformamide are commonly used. The combinations of those solvents have also been adopted to increase the extraction range of substances (Antolovich et al., 2000). The phenolic extracts are always a mixture of various types of phenolics and non-phenolic compounds. Therefore, additional steps are required to remove the undesired compounds. Petroleum ether, ethyl acetate, or diethyl ether extractions are usually added to concentrated phenolic extracts in order to remove lipids and unwanted polyphenols (Naczk and Shahidi, 2004). In terms of the fractionation and purification of phenolic compounds, solid phase extraction and different chromatography methods have been proven to be effective. Mateos et al. (2001) used diol-bonded phase cartridge to extract phenolics from olive oil. The oil sample was washed through the column with different solvent systems including hexane, a mixture of hexane/ethyl acetate (90:10, v/v), and methanol. The phenolics were found in the methanol eluted fraction. Mateus et al. (2001) employed a Fractogel (Toyopearl) HW-40(s) column to fractionate anthocyanin-derived pigments in red wines. The eluent was water–ethanol pigments.

In the biorefinery scenario, phenolic compounds, as valuable co-products, can be produced through either direct extraction of food or agricultural byproducts or fermentation of those byproducts as substrates. For example, olive mill wastewater has been subjected to different extraction and purification techniques to recover the polyphenols. Methods used include solid phase extraction (Bertin et al., 2011), integrated member system (Garcia-Castello et al., 2010), Azolla (aquatic fern) matrix, and active carbon adsorption (Ena et al., 2012). The major component of the total phenolics in olive mill wastewater is flavonoids with subgroups of flavanols and proanthocyanidins, which exhibited considerable antioxidant activity (El-Abbassi et al., 2012). Phenolic compounds have also been extracted from other food wastes, including potato peels (Oreopoulou and Russ, 2007), apple skins (Schieber et al., 2001), grape skins (Pinelo et al., 2006), carrot peels (Chantaro et al., 2008), raspberry waste (Laroze et al., 2010), and coffee byproducts (Murthy and Naidu, 2012).

Solid state fermentation (SSF) has been employed to increase the phenolic content in some food products as well as to produce phenolics from agro-industrial residue. Starzyńska-Janiszewska et al. (2008) have applied Rhizopus oligosporus to cooked seeds of grass peas, and found that the phenolic compound content had a great increase after fermentation. Wheat grain and soybean products have also been fermented by different fungal species. The resultant products exhibited higher content of phenolics and stronger antioxidant behavior (Bhanja et al., 2009; Singh et al., 2010). Agricultural and forestry wastes including straw, bagasse, stover, cobs, and husks are lignocellulosic biomass with lignin as one of the major chemical components. Filamentous fungi like white-rot fungi Phanerochaete chrysosporium, Trametes versicolor, Trametes hisuta, and Bjerkandera adusta have the capability of breaking down lignin to produce phenolic compounds, which can potentially increase the nutritional value of the materials as animal feed or soil fertilizer (Nigam and Pandey, 2009).

18.5.2 Alkaloids

Alkaloids are low molecular weight nitrogen-containing compounds found in about 20% of plant species (Facchini, 2001). They are mostly derived from the amino acids, phenylalanine, tyrosine, tryptophan, lysine, and ornithine. Alkaloids are commonly produced in response to stressed situations as secondary metabolites with characteristic toxicity and pharmacological activity. These properties were used by human beings for hunting, execution, and warfare in old times, but now are mostly used for the treatment of disease (Mann, 1992).

Plant-derived alkaloids currently used in clinical applications consist of the analgesics morphine and codeine, the anti-cancer agents vinblastine and taxol, the gout suppressant colchicine, the muscle relaxant (C)-tubocurarine, the antiarrythmic ajmaline, the antibiotic sanguinarine, and the sedative scopolamine (Facchini, 2001).

Glucosinolates, present in cruciferous vegetables (e.g., broccoli and brussel sprouts), are a class of alkaloids with a core sulfated thiocyanate group conjugating to thioglucose, and a side chain (Clarke, 2010). They are toxic at high doses, but under subtoxic level, glucosinolates serve as activators for liver detoxification enzymes and show protective effects against carcinogenesis, mutagenesis, and other forms of toxicity (Dillard and German, 2000). Most of the beneficial effects possessed by glucosinolates are attributable to the hydrolysis product isothiocyanates produced by the plant enzyme myrosinase or intestinal microflora. One example of isothiocyanate is sulforaphane (R-1-isothiocyanato-4-methylsulfinyl butane, SF), a hydrolysis product of glucosinolate in broccoli. It has been reported that SF has the potential to reduce the risk of various types of cancers, diabetes, atherosclerosis, respiratory diseases, neurodegenerative disorders, ocular disorders, and cardiovascular diseases (Elbarbry and Elrody, 2011). Indole-3-carbinol is another degradation product of glucosinolate that shows multiple anti-carcinogenic properties. These properties are delivered by changes in cell cycle progression, apoptosis, carcinogen bioactivation, and DNA repair (Weng et al., 2008). Both SF and indole-3-carbinol are widely available as dietary supplements.

18.5.3 Carotenoids

Carotenoids are terpene-derived pigments found in chloroplasts and chromoplasts of plants and photosynthetic organisms. They play a vital role in mediating the electron transfer process or protecting organisms from oxidation-induced damage. In humans, carotenoids have been linked with antioxidant activities and a series of disease prevention effects (Edge et al., 1997; Hughes, 2001). Therefore, carotenoids have received great commercial interest; as a result, various related products have appeared in the nutraceutical market.

Based on different chemical characteristics, carotenoids can be classified as xanthophylls and carotenes. Xanthophylls are carotenoids with oxygen present in the molecules, such as lutein, astaxanthin, and zeaxanthin. Carotenes are unoxygenated carotenoids which contain only carbon and hydrogen. Examples of carotenes include α-carotene, β-carotene, and lycopene (Cuttriss et al., 2011).

Carotenes are firstly known as vitamin A precursors and play an essential nutritional role. Recent studies have shown that β-carotene and lycopene also exhibit immune stimulatory and cancer preventive effects (Hughes, 2001). Xanthophyll typically cannot be converted to vitamin A in the human digestive tract; however, they can still offer protection for the biological system against free radicals.

Marketed carotenoids consist of β-carotene, astaxanthins, and more recently, lutein and lycopene (Walker et al., 2006). The production of carotenoids can be from both natural and synthetic sources. Astaxanthin, for instance, can be produced from the microalgae Haematococcus pluvialis. However, nearly all commercial astaxanthin for aquaculture applications is produced synthetically due to the low cost of synthetic production as compared to natural extraction. Recent advances for the understanding and manipulation of carotenoid metabolism have shown promise for producing carotenoids from natural sources. Examples of natural carotenoid producers include the fungus Blakeslea trispora, microalga Dunaliella salina, and yeast Phaffia rhodozyma (Enes and Saraiva, 1996; Hejazi et al., 2002; León et al., 2003; Denery et al., 2004). Utilization of substrates from agricultural byproducts, such as molasses and whey, also shows great potential in reducing the production cost from these microorganisms (Aksu and Eren, 2005).