YEASTS BIOTECHNOLOGIES APPLICATION AND THEIR INVOLVING IN AFRICAN TRADITIONAL FERMENTED FOODS AND BEVERAGES.

Fermentation is an oldest method of food preservation and food nutritional value improving. It involves the concomitant action of one or more microorganisms, and yeasts are the one which play a significant role in African traditional fermented foods and beverages production. Traditional utilization of yeasts includes alcoholic beverages and fermented food production, but nowadays, with scientific methods developing, yeasts are implicated in medical, pharmaceutical, agriculture and other fields. Saccharomyces cerevisiae has been described as mankind‘s most domesticated organism; it is always exploited in several fields to

Fermentation is an oldest method of food preservation and food nutritional value improving. It involves the concomitant action of one or more microorganisms, and yeasts are the one which play a significant role in African traditional fermented foods and beverages production. Traditional utilization of yeasts includes alcoholic beverages and fermented food production, but nowadays, with scientific methods developing, yeasts are implicated in medical, pharmaceutical, agriculture and other fields. Saccharomyces cerevisiae has been described as mankind's most domesticated organism; it is always exploited in several fields to produce value-added products by raw matter biotransformation and also in industry. Several studies which have been realized on Candida utilis demonstrated it potential utilization for human consumption and as animal fobbed. Modern applications of yeasts have been greatly expanded beyond classical applications. Saccharomyces cerevisiae and other non -Saccharomyces yeast today are increasingly used for the heterologous production of enzymes and pharmaceutical proteins, biofuel, medical drugs... Yeasts have important roles in environmental applications such as bioremediation, organic wastes biotransformation and removal of heavy metals from wastewaters. Yeasts are also used in agriculture as biocontrol agents. Several chemical compounds can be produced using yeast as a biocatalyst. New developments in engineering yeast such as genetic modification have introduced novel capabilities to extend substrate range and produce new products so far yeast cannot produce. Yeast cell constituents at the nanoscale are the new fields of yeast nanobiotechnology thatnanotechniques are used for manipulation.

ISSN: 2320-5407
Int. J. Adv. Res. 7(2), 44-62 46 et al., 2010; Somda et al., 2017). Saccharomyces cerevisiae is the most frequently involved yeast species in the production of yeast foods and food ingredients (Bhalla, 2017). Using yeasts for value added products production is related to the fact that yeasts are able to ferment a broad range of carbon substrate and generate secondary metabolites which can be used in several fields such as food, cosmetic, and pharmaceutical industries…

Yeasts as Food
Yeasts are the predominate microorganisms in most of the traditional fermented foods and beverages such as burukutu, merissa, bhatooru, seera, chhang, fufu, tape, ogi, puto, dosa, idli, papdam, kecap, laochao, warri, etc (Bhalla, 2017). In these traditional foods, yeast either alone or in association with bacteria and mould has substantial influence on taste, aroma, texture and nutritional value of the fermented products. Yeasts have been cultivated also as rich sources of protein, minerals, vitamins (particularly B vitamins), and other nutrients for humans and animals (Wijeyaratne and Jayathilakf, 2000;Ouedraogo et al., 2017). Several yeast species have been used for biomass production, including Candida utilis, other non-methylotrophic Candida spp., Saccharomycopsis fibuligera, Kluyveromyces spp., and Saccharomyces cerevisiae (Dimova et al., 2010;Ouedraogo et al., 2017;Somda et al., 2017). Methylotrophic, ethanol-utilizing, and fat and hydrocarbon-utilizing yeasts including species of Candida, Ogataea, Pichia, and Trichosporon have also been used for biomass production (Türker, 2014). Thus, yeasts play very important role in improving the nutrition and socio-cultural life of people living in rural and tribal areas of various countries across the world.

Nutritional quality of yeasts
Yeasts are a great nutritional value and can contain more than 60% of proteins and 15% of lipids (Dimova et al., 2010;Ouedraogo et al., 2017;Somda et al., 2017). Ouedraogo et al. (2017) obtained 54.8% of protein with Candida utilis in Single Cell Protein (SCP) production using tubercules wastes as a substrate. The high rate of protein in yeasts show that yeasts can be used like food complement to increase nutritional value of certain food par example cereal food. Amino acids analysis from yeasts SCP shows that yeasts contain high rates of essential amino acid (Table 1). Tableau 1:-Amino acids contain in yeasts used for SCP production compared with some standard source of protein g/100g of proteins      There is ten (10) essential amino acids which must be present in food to give it a good nutritional value. Unfortunately, vegetable foods are poor for those amino acids comparing to animal foods. However, microorganisms present an interesting profile in amino acids. Indeed, SCP produce from yeasts contain an interesting rates of essential amino acids (tryptophan, lysine, methionine, phenylalanine, threonine, valine, leucine, isoleucine, arginine and histidine) (Dimova et al., 2010;Anvari et al., 2011;Watanabe et al., 2013). The comparison of amino acids profile of yeasts used for SCP production with soy flour and fish flour shows that yeasts present a good amino acids balance (Table 1). Because they have an interesting rate of lysine, yeasts can be used to supplement cereal foods that are poor of proteins and lysine. Added, yeasts contained a high rate of vitamin like thiamin, Riboflavin, Niacin… (Table 2). Indeed, vitamin B is the most type of vitamin found in yeast strains used for SCP production. Wijeyaratne et Jayathilak, (2000) obtained 0,231 mg/g of riboflavin and 0,178 mg/g of thiamine with Candida tropicalis used for SCP production. Nangul and Bhatia, (2013)showed that vitamin B12 is mostly found from yeasts and bacteria, and vitamin A is mostly found in algae. Added to all those vitamins, amino acids and proteins, yeasts contain also a high rate of mineral salts. All of those compounds make yeasts a good source of nutriments for food and feed production. . The demonstration of the absence of toxic and carcinogenic compounds originated from the substrates, biosynthesized by the microorganisms or formed during processing are important factors which will be considered before SCP using. Production of yeast SCP has certain advantages compared to plant, animal, and other microbial sources of SCP including rapid growth and accumulation of biomass, high protein content (up to 60%), high contents of vitamins and minerals, and ability to grow on a wide variety of substrates, including various industrial complex wastes (El-Nawwi and El-Kader, 1996; Somda et al., 2017). The production of value-added SCP from inexpensive substrates could help to alleviate world shortages in the food supply, particularly in developing countries. Substrates utilized have included molasses, starch, cassava, Helianthus tuberosus, whey products, sulfite waste liquor, potato wastes, brewery wastes and other waste streams from agricultural processes, food processing, and industrial processes abilities of yeasts, they can be more easily harvested than bacteria from the fermentation liquor. Compared to bacteria, many types of yeast contain low quantities of nucleic acids, which can have detrimental nutritional effects.

Yeast in African fermented foods
African fermented foods are fermented foods produced with locally available ingredients, instruments and techniques. Although the production of fermented foods in Africa has deceased globally in recent years due to the spread of mass-produced of industrial food, fermented foods are still popular in sub-Saharan Africa (Kubo and Kilasara, 2016). In this regions, fermented food take place on socially, economically, and nutritionally important roles. Popular fermented food products in Africa include fermented milks, fermented cereals, fermented leaves, sour porridges, and alcoholic and non-alcoholic beverages and the fermentation improves the organoleptic properties of foods, their acceptability, and their nutritional value. Microorganisms responsible for those fermentation can be indigenous microorganisms present on substrates, or they can be added as starter cultures after cooking or preparing the food or beverage ( (Table 3). Fermented cereal foods play an important socio-economic role in developing countries as well as making a major contribution to the protein requirements of natural populations (Achi and Ukwuru, 2015). Mostly, maize (Zea mays), Sorghum (Sorghum bicolor), millet (Peninsetum americanum) are used as raw materials in the production of fermented foods Africa ( Table 3). Cereal grains constitute a major source of dietary nutrients all over Africa. Maize, millet, rice and sorghum are popular substrates used for the production of many fermented foods (Table 3). Although cereals are deficient in some basic components like essential amino acids, proteins, fermentation may be the most simple and economical way of improving their nutritional value, sensory properties, and functional qualities. The fermentation of cereals enhances the availability of nutritional elements in cereal grains (Laurent-Babot and Guyot, 2017).
The most yeast involved in Africa fermented food is Saccharomyces cerevisiae. Indeed, Saccharomyces cerevisiae is always isolated in fermented food and it is also the most representative yeast in fermented foods. The role of yeast in fermented foods production is very important and various. Indeed, the nutritional quality of cereals and the sensorial properties of their products are sometimes inferior or poor in comparison with milk and milk products. With the large method that are used to improve the nutritional qualities of cereals, natural fermentation of cereals leads to a decrease in the level of carbohydrates as well as some non-digestible poly and oligosaccharides. Certain amino acids may be synthesised and the availability of B group vitamins may be improved (Achi and Ukwuru, 2015; Olanbiwoninu et al., 2017). Fermentation also provides optimum pH conditions for enzymatic degradation of antinutritional factor such as phytate which is present in cereals in the form of complexes with polivalent cations such as iron, zinc, calcium, magnesium and proteins. Added to Saccharomyces cerevisiae, Issatchenkia orientalis, Candida pelliculosa, Candida utilis, Candida tropicalis and Rhodotorula muciloginosa… were also isolated from African fermented food.

Fermented milk product
Fermented milk is an important part of traditional diet in African countries. Many traditional fermented milk products were made in Africa including Nunu in Ghana, Amasi in South Africa and Zimbabwe, Laban rayeb in Egypt, Leben/Lben in North, East and Central Africa, Mursik in Kenya, Gappal in Burkina Faso presented in (Table  4). Milk in Africa has a strong connection to pastoralists, who have a long tradition in dairy production (Jans et al., 2017). Milk products are usually consumed and traded either as raw milk or traditional fermented dairy products. For pastoralists, milk is an important source of micronutrients, vitamins and energy-containing fat. Milk contributes 10% of the energy and more than 50% of the micronutrients, including vitamins A, B12 and C, to their diets (Iannotti and Lesorogol, 2014) In Africa countries, milk is also mixed with cereals or other plant materials before fermentation to yield products such as Gappal in Burkina Faso (Tankoano et al., 2017). However, cow milk, camel milk and goat milk are mostly used for fermented dairy products production in Africa such as Nunu (cow; Ghana), Sethemi (South Africa), Suusac (camel; Kenya), Leben/Lben (cow or goat; North, East and Center Africa), Gappal (cow; Burkina Faso), Mabisi (cow; Zimbabwe) ( Table 4). During this process of fermentation, several types of microorganisms are involved including yeasts.
The role of yeasts is often underestimated in fermented dairy products. But, they contribute significantly to product development during fermentation processes through lactose and galactose metabolism, proteolysis, lipolysis and enzymatic degradation, which contributes to flavor development (Quigley et al., 2013). Several types of yeasts such as Candida spp., Cryptococcus spp., Debaryomyces spp., Geotrichum spp., Issatchenkia spp., Kluyveromyces spp. and Saccharomyces cerevisiae were isolated from fermented dairy products in Africa ( Table 4). The presence of yeasts in fermented dairy products suggests that they contribute to product development. However, several studies on yeasts involving in fermented dairy products in Africa are mostly an enumeration of total yeasts in these products (Savadogo et al., 2004;Tankoano et al., 2017), but few reports have made a detailed study of the species present.

Alcoholic fermented beverages
Yeasts are involved in the production of Africa traditional fermented alcoholic beverages. In several types of alcoholic beverages, yeasts were main microorganisms isolated and Saccharomyces cerevisiae was the main species Yeasts species belong to ascomycetous (Saccharomyces cerevisiae, Schizosaccharomyces pombe, Kluyveromyces lactis, Kluyveromyces marxianus, Schwanniomyces occidentalis, Debaryomyces hansenii, Komagataella pastoris…) and to basidiomycetous (Rhodotorula spp., Rhodosporidium spp., Trichosporon spp., Xanthophyllomyces dendrorhous, Cryptococcus spp., Phaffia rhodozyma…) were used in biotechnologies processes for interesting compounds production.  (Table 5). Industrial recombinant enzymes and those close to commercialization produced by yeasts are presented in (Table 5).
Yeasts are desirable hosts of enzymes for food uses because of their lack of production of toxic secondary metabolites (Olempska-Beer et al., 2006).

Medical application
The yeasts constitute a large group of microorganisms characterized by the ability to grow and survive in different and stressful conditions and then to colonize a wide range of environmental and human ecosystems. The medical applications of yeasts include their using as probiotics and the production of antibodies and viral antigens production. Several studies showed that yeasts can be used against other microorganisms (Mcfarland, 2010

Agricultural Applications
Microorganisms utilization to prevent postharvest losses of stored fruits, vegetables and grains due to decay by fungal pathogens has been done, and in fact, addressing this problem is receiving increasing importance as worldwide demand for food increases. Chemical fungicides utilization to avoid injury postharvest decay of fruits modified has damages on fruits quality and on the consumer health. Postharvest losses of stored fruits can be attribute by several fungal species belonging to Alternaria, Aspergillus, Botrytis, Fusarium, Geotrichum The utilization of microbial antagonists like yeasts, fungi and bacteria like alternative approaches of to prevent fruits postharvest loses has been demonstrated to be quite promising and gained increased attention. Yeasts are the majority of microorganisms studied for their potential use as postharvest biocontrol agents (Table 6). Mainly, the fact that many of these microorganisms are considered as able to prevent fruits postharvest loses should include a rapid growth rate in fruit wounds, the effective utilization of the nutrients present in the wound, and the capability to survive and develop at the infection site better than the pathogen. Also, this should occur at a low temperature, acidic pH, and condition of osmotic stress, resistance to desiccation and tolerance to chemicals. The yeast in postharvest biocontrol formulations apparently presents advantages over other organisms: easy to cultivate, fast growing and readily found in a variety of substrates and conditions (Konlani et al., 1996;Somda et al., 2011;Ouédraogo et al., 2012). They can be used as biocontrol agents (Johnson, 2013). This research has mainly focused on their use for managing postharvest diseases, mainly of fruit; however, this application represents only a small portion of the complete spectrum of plant disease management (Schisler et al., 2011;Türker, 2014).  (Fonseca et al., 2008;Johnson 2013). They were unable to grow on cellulose, chitin, arabinogalactan, and xanthan gum. Also, they grow on phenolic compounds. These results indicate that basidiomycetous yeasts are involved in the natural biodegradation of biomass and may have potential for remediation of various industrial waste streams (Johnson 2013).
Yeast systems have also been developed for the sensing and accumulation of various ecotoxicants such as heavy metals. Xanthophyllomyces dendrorhous,Trichosporon spp., Saccharomyces cerevisiae and Phaffia rhodozyma have been reported to degrade ochratoxin, patulin, a potent mycotoxin (Hatoum et al., 2012). The ability of yeasts to degrade mycotoxins has important health implications (Schisler et al., 2011). Industrial wastes biotransformation is not only to produce value-added products, but it is also the amount to protect environment against pollution and prevent climate change.

New developments in efficient biofuel and organic acids production by yeasts
Energy crisis is a growing global concern nowadays because of the dependence on petroleum-based fossil fuel which is exhausted very fast to meet the continuously increasing demands. Biofuels could be an alternative solution to energy security, rising prices of petroleum based fuels and for reduction in greenhouse gas emissions (Hull et al., 2014;Singhania et al., 2014). Biofuel includes solid, liquid and gas and the major biofuels encompass bio-ethanol, biodiesel, biogas, bio-methanol, bio-syngas (CO + H 2 ), bio-oil, bio-char, bio-hydrogen, Fischer-Tropsch liquids petroleum and vegetable oil… (Gupta and Prakash, 2015).
Lignocellulosic biomass like sugar cane wastes provides a promising and renewable resource for sustainable biofuel production. But several types of agro-residues have been used to produce bio-ethanol such as rice-straw, wheat straw, sugarcane bagasse, sugarcane molasses, mangoes residues, soft bamboo, bamboo processing wastes and all are considered as abundantly available feed stocks ( showed that yeasts can be used to produce amino acids including essential amino acids (lysine, methionine, phenylalanine and proline). Currently, yeast nanobiotechnology is a recent field which interest nanobiotechnologists, who are used nanotechniques to manipulate and analyse yeast cells and cell constituents at the nanoscale (Willaert et al., 2016;Willaert, 2017).

Impact of optimal Yeast use for developing countries
Historically, traditional fermented foods have benefit effects on human health. The traditional fermented foods and beverages in Africa have social, religious, cultural and nutritional importance. Yeasts utilization as sources of food ingredients and additives, such as flavors, colours, antioxidants and vitamins could allow in malnutrition fighting in developing countries (Kayodé et al., 2012;Douradinha et al., 2014;Hull et al., 2014;Bhalla, 2017). Also, S. cerevisiae var. boulardii, has been successfully used over the last 20 years as an oral, biotherapeutic agent to treat diarrhea and other gastrointestinal diseases at humans (Czerucka et al., 2007).The last decade has recorded few reports showing probiotic properties of yeast strains isolated from African traditional fermented foods (Kayodé et al., 2012;Bhalla, 2017). Large-scale utilization of yeasts in biotechnology processes could contribute greatly to the development of developing countries especially for African countries. She could allow African countries to improve their medical, environmental, economical, agricultural and social sectors. Economically, biotechnology processes used in industrial wastes biotransformation is a great advantage in environment protection and value-added products production. In African countries, most of industrial residues are thrown in a nature and constitute pollution source of environment. Several studies on bioconversion processes using yeasts like Saccharomyces cerevisiae, Candida utilis, Candida tropicalis, Rhodotorula muciloginosa… to produce value-added products from industry residues have been 57 realized. The utilization of yeasts for pharmaceutics products expression, enzymes production and virus-like particles (VLP) production for medical sector application could allow African countries to improve their medicine.

Conclusion:-
Yeasts are interesting microorganisms and more of them are used in traditional food fermentation. Although considerable progress has been made in isolation, identification and characterization of yeast from African traditional fermented foods and beverages, continued research in these fields will lead to develop novel fermented products based on the exploitation of new and genetically modified strains of yeasts of fermented food origin. Nowadays, the number of yeast species identified and their biotechnological potential are accelerating. Their involvement and importance in biotechnological products production is increasing and others potentialities of yeasts remain to discover. New developments in engineering pathways in yeast using system biology and rDNA technologies have introduced novel capabilities to extend substrate range, to improve cellular properties and to produce new products yeast cannot produce. Yeasts nanobiotechnological application is a new field and other complex products can be produced through yeasts. With their medical utilization, yeasts are the most important industrial microorganisms. Also, many yeasts species have strong oxidative metabolism that enables the bioremediation and degradation of chemicals, pollutants such as aromatic compounds, plastics, and other recalcitrant compounds and polymers. These advances provide important strategies and tools for enhancing the biotechnological importance of yeasts. But, there is not enough information on yeasts nanobiotechnological application and a reviewed article on this topic will allow more information about yeasts and will increase their application for human interest and environment protection.