Parakari is a fermented cassava beverage popular among the Amerindians of Guyana. Parakari is unique among New World beverages, because it involves the use of an amylolytic mould (Rhizopus sp., Mucoraceae, Zygomycota) followed by a solid substratum ethanol fermentation (Henkel, 2005). An alcoholic beverage called Tapai is also popular among the Kadazan-Dusun-Murut (KDM) ethnic group of Sabah, East Malaysia. which is used during festive occasions and gatherings. It has an alcoholic aroma with a combination of sweet-sour-bitter taste and sometimes a sparkling feel (Chiang et al., 2006).
5.2.5 Biochemistry of Cassava Cyanogens Detoxification during Fermentation
Fermentation is the major route for detoxification of cyanogens (CG) in cassava (Fau-quet and Taylor, 2001; Westby and Choo, 1994). Cassava fermentation for food processing is either induced by natural microflora consisting mainly of LAB and yeasts (in case of gari, fufu, lapun, etc.) or by use of starter cultures (Kimaryo et al., 2000). Two types of fermentation are generally distinguished: submerged (fufu, lafun) and mash (solid state) fermentation (gari). Heap fermentation of cassava roots followed by sun-drying is capable of reducing the cyanogen levels by up to 95 % (Tivana, 2012). Nearly all fermentation relies on the fortuitous presence of microbes on the roots and/or in the water, and on the prevailing favourable conditions for production of the desired product.
The effect of endogenous linamarase and LAB on cyanide detoxification during gari making was studied by several authors (Lei et al., 1999; Westby and Choo, 1994). Fermentation allowed the elimination of more than 90 % of endogenous cyanide compounds in the roots. The elimination mostly occurred after 48 h, when the endogenous cassava linamarase reached its optimum pH of 5.5 (Ampe and Brauman, 1995). LAB linamarase may participate in the cyanogens degradation (Brauman et al., 1996) and the bacterial pectinases have also been shown to help the process (Ampe and Brauman, 1995). Strains of Lb. plantarum and Lc. mesenteroides isolated from cassava produced simultaneously an intracellular linamarase and extracellular amylase (Gueguen et al., 1997; Lei et al., 1999; Okafor and Ejiofor, 1990). The use of such strains as a cassava fermentation starter for gari production had the following influences: a change from a hetero-fermentive pattern observed in natural fermentation to a homo-fermentation, a lower final pH and a greater production of LA (50 g/ kg dry matter). There are also a few reports that the starter did not play a significant role in cassava detoxification (Mkpong et al., 1990; Vasconcelos et al., 1990). But the majority of reports show that linamarase addition or the inoculation with a strain of Lb. plantarum or Lc. mesenteroides having linamarase activity improved detoxification (Gueguen et al., 1997; Lei et al., 1999).
SmF is the most efficient process for reducing the levels of cyanogens in cassava, where reduction rates of 95-100 % are often reported (Bokanga, 1995). The removal of cyanogens from cassava during SmF is probably the result of several factors, including;
• textural changes in the plant tissues that make it possible for vacuole-bound CGs to diffuse and come into contact with membrane-bound linamarase and for hydrolyzed and intact compounds to leach out;
• increase in β-glucosidase activity in cassava tissue; and
• utilization of CGs and their breakdown products by fermentation microorganisms (Onabolu et al., 1999).
The detoxification of cassava in mash (solid state) fermentation follows a different mechanism. The grating of cassava roots to obtain the mash disrupts the structural integrity of plant cells, allowing the CGs from storage vacuoles to come into contact with linamarase on the cell wall. The subsequent fermentation contributes very little to the breakdown of the glucosides (Vasconcelos et al., 1990). In fact, the low pH (~4.0) rapidly achieved during fermentation is inhibitory to linamarase activity and stabilizes cyanohydrins, thus slowing down linamarin hydrolysis and cyanohydrin breakdown.
5.2.6 Fermented Foods and Beverages from Sweet Potato
Starch is the prime component of interest for food and industrial uses of sweet potatoes (Ray and Ravi, 2005). The efficiency of starch extraction from sweet potato roots was improved by LA fermentation using a mixed culture (Lactobacillus cellobiosus, Streptococcus lactis and Corynebacterium sp.) inoculum (Jyothi et al., 2005). Study of the properties of the starchy flour showed that there was a significant reduction in the starch content and consequently the soluble and apparent amylase contents of fermented samples from all six varieties of sweet potato used.
Alcoholic beverages are prepared successfully from sweet potato biomass in various countries. Sweet potato being a potential substrate for alcohol production, because of its high starch and sugar content, is used to manufacture alcohol for human consumption, chemical and pharmaceutical industries in countries like China, Japan and Korea. A light alcoholic beverage named masato indigenously made from sweet potato is prepared by certain Indian tribes of the Peruvian Amazon region (Austin, 1985). Sometimes it is prepared from orange fleshed sweet potato (p-carotene rich) to give the drink a better colour. In China, a large amount of alcohol is produced by sacchari-fication and subsequent fermentation of the sweet potato chips. The alcohol produced from the sweet potato chips with higher purity is used in the beverage industries. Nowadays, 95 % of the sweet potato alcohol produced by the modern alcohol plants is used for preparation of alcoholic beverages in China. Another alcoholic beverage named shochu, a traditional Japanese alcoholic distilled beverage is prepared from raw materials like barley, buck wheat, crude sugar or sweet potato. Sweet potato contributes 36 % of the total shochu production.
Shochu originated from China in the early 1700s. The sweet potato mash is saccharified by using amylase used from A. niger. Then fermentation is allowed by using S. cerevisiae. After the final alcohol concentration is achieved to 13–15 %, the mash is distilled off. The alcohol is blended uniformly to 20–40 % (v/v) before bottling. Attempts are taken to add anthocyanin pigments from purple fleshed sweet potato to shochu, which can improve the quality of the beverage (Woolfe, 1992). Today, automated plants are established for shochu production.
Lacto-pickles LAB influences the flavour of fermented foods in a variety of ways. In many cases, the most obvious change in LA fermentation is the production of acid and lowering of pH, which increase sourness (Ray and Panda, 2007). It not only produces LA, which imparts taste and flavour to lacto-pickles, but also preserves ascorbic acid, phenols and coloured pigments (p-carotene and anthocyanin), which are potentially considered as anti-oxidants (Shivashankara et al., 2004).