Fermentation

As hinted in the earlier part of this dissertation, fermentation leads to changes and subsequent improvement in nutritional qualities, taste, shelf life and aroma (Mugocha et al., 2000; Kohajdova & Karovicova, 2007). It also aids in the preservation of many products by suppressing the survival and growth of unwanted microflora(Ross et al., 2002; Kohajdova & Karovicova, 2007; Saleh et al., 2013). Fermentation has been identified to detoxify, reduce the levels of antinutrients, improve in vitro protein digestibility (IVPD) which further enhances bio-accessibility of proteins among other functions as depicted in Figure 2.8 (Elyas et al., 2002; Bladino et al., 2003; Poutanen et al.,

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2009; Saleh et al., 2013). These effects have been attributed to the limited degradation of complex protein storage to more soluble and simple products (Chavan et al., 1988; Elyas et al., 2002; Hassan et al., 2006). Elyas et al. (2002) noted that natural fermentation of pearl millet also reduces phytic acid, polyphenols and causes no changes in tannin contents. According to Murali & Kapoor, (2003), one of the most effective and economic technique of increasing the extractability of minerals, amino acids, water soluble proteins and vitamins is fermentation. This has been validated by several other authors who reported such increases and have attributed such to proteolysis (by bacterial proteases) and metabolic synthesis during fermentation (Arora et al., 2003; Murali & Kapoor, 2003; Kohajdova & Karovicova, 2007; Saleh et al., 2013; Galati et al., 2014).

Figure 2.8: Potential mechanisms by which fermentation influences nutritional quality (Adapted from Poutanen et al., 2009).

Depending on the type of millet fermentation process, metabolites differ and may consequently result in varying physicochemical properties of the respective products (Galati et al., 2014; Adebiyi et al., 2016a). Changes in the functional properties during millet fermentation have been found to result in an increase in emulsifying capacity and oil-binding capacity, oilabsorption and water absorption capacity (Adebiyi et al., 2016b). These changes were attributed to structural changes in the protein, degradation of starch polymers and lower hydrophilic composition (Akubor & Badifu, 2004; Adebiyi et al., 2016b). Due to starch hydrolysis, release of starch granules and

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modifications in the amylose and amylopectin chains, the crystallinity of fermented millets are generally reduced (Taylor & Emmambux, 2008; Dhamaraj et al., 2014; Adebiyi et al., 2016b). As such the crystalline structure of fermented millet ischanged from the “A-type” (common for most cereals) to a more diffused crystalline nature (Amadou et al., 2014; Dhamaraj et al., 2014; Sun et al., 2014; Adebiyi et al., 2016b). Through these microbial actions happening during this process, inter and intra molecular bonds are formed and broken, while the cellular structure of the millet is further affected (Van Der Weerd et al., 2001; Adebiyi et al., 2016b).

2.8.2 Malting

Malting of millet grains may result in some biochemical alterations resulting in a malt with better nutritional quality which are further utilized in several traditional recipes. Likewise, malting helps to significantly increase the nutritional composition, fibre, vitamins B, C and their availability, minerals, improve sensory qualities and bioavailability and bioaccessibility of nutrients (Sangita & Srivastav, 2000). Such improvements after malting can be attributed to exploitation by increasing sprouts and actions of hydrolytic enzymes (Archana & Kawatra 2001). Fat contents of millets have however been found to reduce after malting and such has been ascribed to oxidation of fatty acids and hydrolysis of lipid (Hooda & Jood 2003; (Desai et al., 2010; Choudhury et al., 2011; Krishnan et al., 2012). Similarly, antinutritional factors such as phytic acid and phytase are reduced (Mamiro et al., 2001; Florence-Suma & Urooj, 2011; Krishnan et al., 2012).

Malting of pearl millet increases protein content, energy value and crude fiber, through dry matter loss during germination (Parameswaran & Sadasivam, 1994; Malleshi & Klopfenstein, 1998; Obilana, 2014; Sarker, 2015). Through proteolysis which occurs during the malting process, the amino acids in malted millet are significantly improved (Saleh et al., 2013; Adebiyi et al., 2016b). The enriched amino acid contents in millet malt thus makes them preferable substrates for the formulation of nutritious and health promoting foods (Saleh et al., 2013). Sequel to this, millet malt is used as a supplementary food and cereal base for low dietary bulk, dense calorie weaning foods and also amylase-enriched foods (Saleh et al., 2013; Jaybhaye et al., 2014). Malting decreases paste viscosity of flour than many other heat treatments (Malleshi & Desikachar, 1981). Similar to fermentation, it also improves functional properties of flour, decreases crystallinity to

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an amorphous nature and affects the cellular structure of millets (Taylor & Emmambux, 2008; Dhamaraj et al., 2014).

2.8.3 Baking

Studies of Desai et al. (2010) have reportedly increased the nutritional quality of cakes with respect to the fibre and mineral content and sensory qualities. Other studies have also reported an improvement in protein, carbohydrate and digestibility (Eneche, 1999; Sehgal & Kawatra 2007; Saha et al., 2011). According to Katina et al. (2005), biochemical changes affecting nutritional quality as well as texture, taste, flavor and color occur during baking. Levels of folate have been shown to increase, whereas levels of antinutrients such as phytate have reportedly decreased after baking (Frolich et al., 1986; Larsson & Sandberg, 1991; Kariluoto et al., 2004). While baking may confer desirable attributes to the final product, extreme heat application may cause undesirable browning and decrease in overall nutritive value (O’Brien & Morrisey, 1989).

2.9 Concluding remarks

An overview of pearl millets and some processing operations (fermentation, malting and baking) for transforming them into millet-based foods have been discussed. It has also been found that pearl millet possesses good nutritional components and health promoting properties. Despite these benefits of pearl millet documented in literature, there is still a limited commercial demand of this cereal crop. Pearl millets have enormous potential to add variety to our diet, address the issue of celiac disease and augment the intake of a health beneficial food.In order to explore the prospects and potential of pearl millet, there is need to investigate possible uses of pearl millet in the preparation of RTE foods, which this study was aimed at. It is hoped that through the adoption of the recommendations in this study by appropriate authorities, there will be improvement in the utilization and productivity of millet. This will subsequently contribute to economic development and alleviate food insecurity in Africa.

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