Indigenous fermented milks from some regions of Cameroon and Chad: production processes, utilizations and challenges. The 1 st International Conference on Local Resource Exploitation

: Nowadays, the demand of traditional fermented foods (Bio character) including traditional fermented milks by consumers, is increased due to their numerous health benefits, important nutritional values and researched organoleptic properties. A great diversity of indigenous fermented milk products is manufactured worldwide and the ingredients involved in their production are also diversified. The aim of the present work is to establish after exploiting some published data, the technological processes of indigenous fermented milks produced in some regions of Cameroon and Chad and, to evocate their utilizations, their potential properties, their limits and some related challenges. In sudano-guinean and sudano-sahelian regions of Cameroon and Chad, the technological processes used to produce indigenous fermented milks remain nearly constant and the final products obtained are only represented by four types: Pendidam and Kindirmou in Cameroon, Rouaba and Rayeb in Chad. They are all produced by fermentation of raw fresh milk from cow origin and used mainly for feeding purposes. The fermented milks produced in these regions cannot act only as sources of nutrients but can also have health benefits like disease preventing or curing properties, as functional or probiotic foods. The challenges of these indigenous fermented milks from sudano-guinean and sudano-sahelian regions of Cameroon and Chad could be their vulgarization which should develop their technological processes, the exploitation of their properties to provide health benefits to consumers such as the fight against COVID-19 pandemic among others, the generation of incomes and employment favorable to economic growth.


INTRODUCTION
Fermentation is a biotechnological process used all over the world since ancient times to produce indigenous fermented foods and alcoholic beverages. The demand of traditional fermented foods by consumers is increased due to their numerous health benefits and important nutritional value (Sharma et al., 2014).
Fermented milks are one of the most popular fermented foods produced and highly appreciated by consumers worldwide. Lactic acid bacteria (LABs) have been reported as the main actors of the fermentation process of indigenous fermented milks (Djoulde et al., 2013;Kaktcham et al., 2012;Shalo et al., 1973). LABs fermentation of foods improves both the nutritional value and digestibility of the end-products (Sharma et al., 2014;Chelule et al., 2010;Nout, 2009) and the bioavailability of minerals, proteins and free sugars (Sharma et al., 2014;Santos et al., 2008;Sripriya et al., 1997). During fermentation, LABs produce metabolites such as organic acids, bacteriocins (Chelule et al., 2010;Joshi et al., 2006;Abee et al., 1995), biosurfactants (Mouafo et al., 2018a, Mouafo et al., 2018bMbawala et al., 2017) that have antimicrobial activity, thus prolong the shelf life of foods. The "researched" properties of each fermented milk depend on the quality of raw materials, ingredients and the technological process used during its production. The skill of fermented milk making such as yogurt, as inherited from the ancestors, have been subjected to industrial standardization process comprising the main obligatory steps that follow: heat treatment (pasteurization) of milk -cooling -homogenizationinoculation -fermentation (during incubation) -packaging -storage (Puniya, 2016). Regardless of the reported benefits interest concerning most of the indigenous fermented milks, their technological processes are still unstandardized and consequently their production remain at the artisanal level. Based on these considerations: what are the technological processes used to produce indigenous fermented milks in sudano-guinean and sudano-sahelian regions of Cameroon and Chad? What could be the health benefits provided to human being after their consumption? And what are some related challenges favoring the vulgarization of their production?
The aim of the present study is to establish the technological processes, the utilizations, the potential properties, the limits and some related challenges of indigenous fermented milks produced in some regions of Cameroon and Chad after exploiting some published data.

PRODUCTION PROCESSES AND DESCRIPTION OF INDIGENOUS FERMENTED MILKS
There are only four types of indigenous fermented milks produced in sudano-guinean and sudano-sahelian regions of Cameroon represented by Pendidam and Kindirmou produced mostly by Fulani people while those of Chad are represented by Rouaba and Rayeb produced by Arab and Peul. They are all produced by fermentation of raw fresh milk from cow origin. Considering the production processes ( Figure 1 to Figure 4), Pendidam is a raw fresh milk, heated, skimmed and fermented (Jiwoua et Millière, 1990) while Kindirmou is a raw fresh full-cream milk, heated and fermented (Essomba et al., 2002); Rouaba is a raw fresh milk, churned and fermented while Rayeb is a full fresh milk, fermented (Koussou and Duteurtre, 2004). Finally, Pendidam is a light curdled milk, very acidic while Kindirmou is a heavy fermented milk, less acidic than Pendidam; Rouaba has a hard acidic taste while Rayeb has a taste nearest to natural yogurt.

LOCAL UTILIZATIONS OF FERMENTED MILKS PRODUCED
According to Essomba et al. (2002), in Cameroon milk and fermented milks play an important role in the Fulani tribe of northern regions since they contribute to income and employment generation to generally female sex producers, transformers and traders. For Fulani people, fermented milks are considered as veritable foods whereas other people with nonbreeding traditions consume it as « dessert ». Fulani people recognize health benefits attributed to fermented milks: its acidity permit children to combat intestinal worms and to consumers they bring power, bravery and toughness. For Fulani people, Pendidam is appointed in priority to children who must consume it regularly while Kindirmou is mostly destined to adults particularly men to whom it gives virility. Koussou and Duteurtre (2004) reported that in Chad, Rouaba and Rayeb are highly consumed by inherent sahelian people as a source of proteinaceous foods. Rouaba is a researched curdled milk because of its acidic taste and also is highly appreciated for its organoleptic properties. Rouaba and Rayeb correspond to a new demand by urban populations concerning refreshing beverages. Their success is also due to "farmer" character of the product since some sellers write in the frontage signboard of their selling points "pure cow milk" to attract customers.

POTENTIAL PROPERTIES, LIMITS AND CHALLENGES OF INDIGENOUS FERMENTED MILKS
In addition to investigated traditional utilizations, each indigenous fermented milk produced in sudano-guinean and sudano-sahelian regions of Cameroon and Chad could: -possess probiotics properties depending probably on the varieties of LABs it contains; -be a source of specific and interesting flavors, aromas and textures due to the nature of end-products resulting to microbial phenomena occurring during fermentation processes; -be a source of biomolecules probably produced by LABs, responsible of anti-constipation effect, antihypertensive properties, lipids metabolisms improvement, anti-obesity effect, and cholesterol-lowering activity, etc.
Below are represented unexhaustive citations of some technological and commercial limits of indigenous milk and fermented milks beverages: -insufficiency of quantity and poor quality of the main raw material (milk) produced which is highly linked to the season; -unstandardized starter culture formulation; -low productivity considering increasing consumers demand; -absence of regulation on raw materials supplying and quality, on production processes, packaging and storage; -non-respect of the chilling chain during transportation, distribution and/or commercialization steps; -poor source of incomes and employment to milk and fermented milks producers, transformers and traders.
A general constat can be remarked: absence or insufficiency of microbiological and biochemical investigations on indigenous fermented milks produced in sudano-guinean and sudano-sahelian regions of Cameroon and Chad until now. Thus, a potential field for future research is opened to researchers in cooperation with industrials in how to vulgarize such authentic products with specific flavors, aromas and textures. Results of such studies could demonstrate that most of the fermented milks produced in these regions cannot act only as sources of nutrients but also can: -have health benefits like disease preventing or curing properties (nutraceutics); -possess properties of probiotic and/or functional foods.
For these reasons, the increase of their consumption by population must be recommended by administrative authorities throughout the concerned countries.
To satisfy the increase in demand, breeders have to ameliorate the quantity and the quality of milk produced independently to the season. Controlled fermentation during production can improve the quality and consequently the shelf life of the indigenous fermented milks produced.
Training of fermented milks producers on Good Hygiene Practices (GHP) and Good Manufacturing Practices (GMP) must be done to solve the potential problems due to their lack of education in food safety, particularly in areas where facilities for the safe preparation of foods are absent.

5.
CHALLENGES ABOUT SOME APPLICATIONS OF LABs METABOLITES:

BIOSURFACTANTS/BIOEMULSIFIERS (BS/BE)
A recent data published on Biosurfactants (Smith et al., 2020) hypothesizing that theses bioactives molecules are a Covid-19 perspective, could be verified when considering the fact that Biosurfactants (BS) are: -amphiphilic molecules with both hydrophobic and hydrophilic moieties; -Bioemulsifiers (BE) since they possess emulsifying properties with additional tensioactive characteristics; -mostly produced by bacteria, yeasts, etc. and those produced by Lactobacillus spp. are GRAS (Generally Recognized As Safe); -can be produced by Lactobacilli isolated from a cameroonian hard acidic fermented milk (Pendidam) very consumed (Mbawala et al., 2013a); -cell wall-linked and/or extracellular metabolites; -commonly extracted and/or precipitated from the cell wall or the cell-free supernatant (CFS) of a culture of Lactobacilli by chemical solvents (acids, ethyl acetate, acetone, methanol, ethanol, etc.).
Independently to the consideration that bioethanol is a bio-solvent that can be used to precipitate the Biosurfactants/Bioemulsifiers (BS/BE) from the CFS of cultured Lactobacilli, some applications and challenges of the BS/BE produced by Lactobacilli isolated from « Pendidam », a cameroonian hard acidic fermented milk were demonstrated such as: In fact, some advantages of the BS/BE present in Pendidam were enumerated: they are produced mainly by Lactobacilli and can be extracted with bio-solvent (bioethanol) => GRAS status; they form stable emulsions (48 hours) at extreme pH and temperature, and at varied salinity (NaCl) (Mbawala et al., 2017); they possess tensioactive, antimicrobial, antioxidant and antiadhesive properties and they stabilize the color (Mouafo et al., 2018a; Mouafo et al., 2018b), etc.
Thus, great challenges about health care can be hypothesized concerning these GRAS bioactives compounds: the utilizations of BS/BE extracted from Pendidam to fight against the Covid-19 pandemic, the HIV pandemic, the Influenza viruses pandemic and the cardio-vascular diseases (CVD) by emulsifying HDL-cholesterol depots in blood vessels, etc.

CONCLUSIONS
Fermented milks are the most fermented foods consumed by people of some regions of Cameroon and Chad regardless to religious, ethnical and social considerations.
Suitable and available studies on traditional processes of milk fermentation may provide to people basic information on good manufacturing practices and good hygiene practices which are helpful to realize safe productions.
The future of indigenous fermented milks in these countries must be their popularization, which could develop their technological processes, provide health benefits to more consumers, generate income and employment, and permit economic growth.

ACKNOWLEDGEMENTS
We are grateful to the "Agence Universitaire de la Francophonie (AUF), Bureau Afrique Centrale et des Grands Lacs (Appel d'offre soutien aux équipes de recherche 2017/2018)" which financially supported this study.

CONFLICTS OF INTEREST
The authors declare no conflicts of interest.