Fermented cassava products like lafun (edible starch) are important staple foods in many African homes. Natural fermentation time is usually long resulting in slower acidification process and inconsistent nutritional composition of products which could be overcome with the use of starter culture. However, most available starter cultures are used for single food fermentation and are uneconomical. This necessitates the development of a starter culture for multiple related food products to reduce cost. Hence this study was designed to produce a cassava fermentation for the production of lafun.

Cassava varieties TME 30572, TME 4(2)1425 and TME 50395 were obtained from the International Institute of Tropical Agriculture, Ibadan and landraces from Bodija market. Fresh, peeled, chipped and grated cassava tubers were spontaneously fermented in the laboratory. Lactic Acid Bacteria (LAB) were isolated from the fermenting mash and identified phenotypically. Genotypically identified starters were selected based on screening for starch hydrolysis, linamarase and pectinase enzyme production, antimicrobial compound production and rate of acidification using standard methods. The starters were utilised singly and randomly combined to initiate fermentation for production of lafun. Un-inoculated fermentation mash served as control. Rate of production of organic acids, various sugars, metabolic enzyme assays, nutritional and anti-nutritional content of the resulting mashes were monitored using standard procedures. Best starter was applied in the final production of lafun. Shelf-life of the products were evaluated and compared with the control. Data were subjected to descriptive statistics and ANOVA technique at p=0.05.

Ninety-eight LABs were identified as Lactobacillus plantarum (50.0%), L. acidilactici (12.2%), L. brevis (11.3%), L. fermentum (10.3%), L. delbrueckii (8.2%), L. mesenteroides (6.0%), and L. lactis (2.0%). Screened isolates did not hydrolyse starch but produced pectinase, linamarase alongside hydrogen peroxide, diacetyl and lactate with a rapid decrease in medium pH (6.5 - 3.6). Selected potential starters were genotypically identified as L. pentosus F2A (A), L. plantarum subsp. argentolarensis F2B (B), L. plantarum F2C (C), L. plantarum U2A (G) and L. paraplantarum U2C (I). The best starter combination CGI gave significant reduction in fermentation pH (7.1 - 3.7) and lactic acid ranged between 0.04mg/ mL and 6.9mg/mL. Sugars produced include xylose (3.2µg/mL), arabinose (1.4µg/mL), fructose (26.2µg/mL), glucose (30.3µg/mL) and sucrose (99.7g/mL). Enzyme assay revealed peak amylase (10.1U/mL) and pectinase (4.4U/mL) activities at 24 hours as well as linamarase (0.8U/mL) at 48 hours in fufu, whereas, in usi, highest linamarase (0.7U/mL) and pectinase (1.0U/mL) activities were recorded at 72hours with no amylase activity. The CGI-produced lafun had significant reduction in phytate (0.3-0.1mg/g and 0.3-0.27mg/g), tannin (35.4-34.0mg/g and 35.4-32.3mg/g), cyanide (0.1-0.05mg/g and 0.1-0.0mg/g), and moisture (7.3%-5.1% and 7.3%-5.4%) content while total protein content increased (1.0-1.3% and 1.0-1.8%) respectively. Starter fermented lafun had shelf-life of five days while control had three days.

The selected starter was able to ferment both lafun to yield products with improved nutritional content, better shelf-life and reduced anti-nutritional composition. This could be employed in the production of indigenous fermented foods.

Keywords: Lactic acid bacteria, Starter culture, Lafun, Shelf-life, Fermented food

1.1 Background to the study
In Africa, cassava is very important to the people because fermented cassava products are known to constitute a major part of the daily diets in many homes. It is cultivated widely as a food crop, ranked as the world′s sixth most important (Soccol, 1996) and fourth on the list of major food crops in developing countries after rice, wheat and maize (Mingli et al., 1992). De Bruijin and Fresco (1989) reported a progressive increase in demand of fermented cassava products yearly as a result of the high energy content due to the fact that it provides averagely more than 50% of daily energy intake.

However, cyanogenic glucosides inherent in cassava usually restrict its use as a food crop (Koch et al., 1992; Peifan et al., 2004) even though there is an endogenous linamarase (β-glucosidase), an enzyme which can easily hydrolyse linamarin, situated in the cell wall (Mkpong et al., 1990). It was reported that the endogenous linamarase could not completely breakdown the linamarin (Ikediobi and Onyike, 1982; Mkpong et al., 1989) thus, bringing about the addition of an exogenous linamarase during fermentation, which is by far the most important and widely used means of processing cassava (Oyewole, 1992; Nweke et al., 2002) to reduce cyanogenic toxicity (Ikediobi and Onyike, 1982).

Fermentation, the oldest method of food processing, started over 6000 years ago (Holzapfel, 2002) in which the traditional methods and outdated techniques of producing fermented foods were based on spontaneous fermentation due to naturally occurring microorganisms in the environment and on the raw materials. However, fermentation durations were long due to the lag phase of the organisms, thus, yielding a longer acidification process and making it difficult to produce an end product of consistent quality. Developing countries cannot continue to be dependent on the historic methods for food processing because of factors such as increasing populations, drought and other natural disasters, inadequate food production as well as other associated problems such as long fermentation time, inconsistencies in final products and the presence of pathogenic organisms, all because it depended on chance inoculation from the environment.

Common research approaches have included isolation and characterization of microorganisms that could be used as starter culture with modifications to fermentation regimes. To date, little of this research has been put to use. Part of technology considerations suggested by Baseline Consultancy Report for Cassava in 2010 included the use of isolated starter cultures in maintaining product quality. Therefore, an improved fermentation method that will not compromise the quality and safety of the product would be through the use of starter cultures which are preparations or materials containing large number of viable microorganisms which may be added to facilitate improved and controlled fermentation process (Holzapfel, 1997, 2002).

Lafun (edible starch) are among the products of cassava fermentation in Africa (Etejere and Bhat, 1985). Fufu is an important basic commodity, ranked next to gari as a native food of most Nigerians (Sanni et al., 1998) and widely eaten in many parts of West Africa and the Tropics (Sanni, 1989). It is a sticky cassava mash which is cooked in boiling water and consumed with soup. It is eaten mostly in the Eastern and Western parts of Southern Nigeria as well as some other areas of West and Central Africa; and unlike other fermented cassava products, it has very intense odour (Lancaster et al., 1982). Usi is an indigenous food of the Itsekiri and Urhobo in Southern Nigeria, who also refer to it as edible starch. It is a very pasty, light yellow food eaten with any oil or pepper soup. The starch is precipitated out of the solution pressed out of the grated cassava during the preparation of gari and sometimes, obtained from grated cassava, soaked directly in water (Etejere and Bhat, 1985). Both cassava products undergo lactic acid fermentation by several microorganisms, thus yielding various metabolites which confer positive effects such as preservation, flavour development, cyanide reduction and changes in functional properties on the final product (Akindahunsi et al., 1999).

The use of starters will provide a means of standardising the production process resulting in products of uniform quality and contributes to reduction in processing time. Furthermore, such starter will have the ability to detoxify, while retaining the desirable organoleptic qualities of the product, grow rapidly to significantly shorten fermentation time, rapidly drop the pH and increase the acidity, as acidic conditions inhibit the growth of and toxin production by pathogens (Mugula et al., 2002).

1.2 Statement of Problem
Constantly, there is an increase in demand for fermented cassava products because they are high energy yielding foods but indigenous spontaneous fermentation have been characterized with longer acidification time, inconsistencies in the nutritional composition and quality of the final products. Use of starter culture has brought some improvement on fermented cassava products, but most available starter cultures are used for single food fermentation and are uneconomical.

1.3 Justification
The ability to isolate strains of microorganisms with desirable physiological and metabolic characteristics for use as starter culture will result in a high degree of control over the fermentation process, thus, maintaining consistency. Furthermore, the possibility of developing a cassava fermentation for multiple related food products will reduce cost and be of economic importance.

1.4 Scope of the research
In order to establish the selection process, this study was approached in four phases, namely; isolation, characterization, identification and screening for potential starters; utilization of potential starters both singly and in combination for controlled fermentation; physiological studies and optimisation of growth conditions of selected starter(s); utilisation of the starter(s) in lafun fermentation and final product assessment.

1.5 Aim and objectives
The overall aim of this study is to select a cassava fermentation for the production of lafun. Specifically, this study was designed to:

· Isolate, characterize and identify lactic acid bacteria involved in the fermentation of cassava to produce lafun.

· Screen for, and genotypically identify potential starters.

· Utilise selected isolates solely and in combination to ferment cassava in lafun production, monitoring microbiological, nutritional and technological properties as well as derived metabolites during the fermentation processes, thus, select isolate(s) of best fit.

· Carry out optimization of growth studies on the potential starter(s) selected

· Apply the selected starter(s) in the production of the two products and analyse the end products.

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Item Type: Project Material  |  Size: 100 pages  |  Chapters: 1-5
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