Cassava Fermentation and Associated Changes in Physicochemical and Functional Properties

Prev Page | Next Page

II. Popular Fermented Cassava Products

As mentioned earlier, a number of fermented products are prepared in different parts of the world. Different microorganisms under varying conditions are used to produce a large number of food products with different organoleptic and functional properties. The steps employed in their production and the microorganisms involved are outlined.

1. Gari

Gari is a fermented cassava product widely consumed in many West African countries. The cassava tuber is harvested, peeled and washed, grated, and packed into coarsely knit bags. A weight is put on the bag to express some of the juice. It is then left to undergo natural fermentation for several days. The grated cassava, after sieving to remove any coarse lumps and impurities, is heated by means of constant turning over a heated steel pan.²⁴ On garifying, the grated cassava is dried to about 10% moisture content and the starch is probably partially dextrinized. At this stage a little palm oil may be added to give it color; the final dry granular product is gari.

Cassava fermentation to gari is associated with a community of microorganisms, including yeasts and bacteria. The population densities of the organisms involved fluctuate over the period with the bacteria demonstrating rapid growth initially and yeasts predominating at the later period the fermentation. The microbiology of gari production was originally considered a two-stage process in which Corynebacterium sp. And Geotrichum candidum were reported to be responsible for acid and flavor production. Later studies revealed that among the microorganisms isolated from gari, Lactobacillus plantarum produced the most typical gari flavor. However, the involvement of five genera was revealed in gari fermentation : Leuconostoc, Alcaligenes, Corynebacterium, Lactobacillus, and Candida, and it was concluded that Leuconostoc was the most frequently occurring organism. It was also reported that Corynebacterium sp. Was the most abundant of a total of eight isolates, although its population declined toward the end of the fermentation period. The population densities of Leuconostoc sp. And Lactobacillus sp. Became almost stable after the fourth day, while those of Corynebacterium sp. And Alcaligens sp. Dropped significantly after third day. The contributions of microorganism to the organoleptic properties of gari were also studied.

It was concluded that Lactobacillus plantarum and Leuconostoc mesenteroids were present in large numbers throughout the 96 h duration of cassava mash fermentation, while Corynebacterium Manihot and Geotrichum candidum were isolated only within the first 48 h and in small amounts. Of the wide array of reports on the microbes involved in gari fermentations, perhaps it may be concluded that lactic acid bacterial (LAB) have been found to be the predominant microorganism during the course of fermentation.

2. Fufu

Fufu is the meal of soaked fermented cassava and is popular in African countries. The tubers are peeled, washed, cut into thick chunks (20 cm long) and soaked in water contained in earthen-ware pots or in a slow flowing stream for 5 to 5 d. during this period, the cassava tuber ferments and softens, releasing HCL into the soak water. A characteristic flavor of retted cassava meal is also produced. The retted tubers are disintegrated in clean water, sieved, and the starchy particles that go through the sieve are allowed to settle for about 3 to 4 h. the water is decanted while the sediment is packed into a cloth bag, tied, squeezed, and subjected to heavy pressure to expel excess water. The resulting mean is rolled into balls, and cooked in boiling water for about 30 to 40 min. the cooked mass is poundedin a mortar with a pestle to produce a paste, fufu, which can be eaten with sauce, soups or stew.

The involvement of more than one species of LAB has been repoted in the production of fufu. A total of 134 LAB strains isolated during fufu production was studied in detail to show that the species of Lactobacillus and Leuconostoc dominated the spectrum. The succession among the LAB isolates revealed the dominance fo Lactobacillus plantarum. It was also shown that Saccharomyces cerevisiae, Lactobacilus fermentum, L. Brevis, streptococcus faeecalis, and Escherichia coli appeared to be important in the fermentation for fufu. The significance of Leuconostock and Lactobacillus was also emphasized.

A total of 14 microorganisms was isolated in fufu collected from different areas in Nigeria. The distribution of LAB in cassava fermentations for fufu was examined in detail including characterization of the properties, strain categorization, perentage distribution, and succession of species. However, we are also in agreement of the ever, we are also in agreement of the observation of Adegoka and Babalola that the characteristics of microorganisms associated with the fermentation for fufu preparation have still not been fully elaborated, particularly when it is realized that the methods of preparation vary according to locality.

3. Lafun

Lafun is a fine powdery cassava product that is prepared by fermentation and is commonly consumed in the western states of Nigerai. The whole or peeled roots are immersed in a stream, in stationary water (near a stream), or in an earthen – ware veself or 3 to 4 d and fermented until they become soft. The fermented roots are then taken out, the peel and central fibers of the fermented roots normally removed, and the pump broken into small crumbs and sundried on mats, racks, flat rocks, cement floors, roofs of houses, etc., Drying takes 1 to 3d, depending on the weather. T he dried crumbs are milled into flour. The flour is added into boiling water with constant stirring until a smooth thick paste is formed. The paste is cooled to about 350C and is then served with soups. The fermented and dried cassava pulp, lafun, is similar to ‘Cossettes’ in Zaire and Rwanda, ‘Kanyanga’ and ‘Mapanga’ in Malawi, and ‘Makopa’ in Tanzania.

Five major microbial groups, similar to the spectrum of those implicated in other fermented cassava foods, were consistently isolated during lafun preparation. These include Bacillus sp., Klebsiella sp., Leuconostoc sp., Corynebacterium sp., Candida sp., and Lactobacillus sp. The microbial succession culminating in the domination of years and LAB after 48 h of fermentation was also elucidated. Nwachukwu and Edwards have associated five years, two molds, and three bacteria with the fermentation for lafun production, essentially stressing the role of LAB. However, the method of preparation adopted by them for lafun is not conforming to the earlier reports and has been questioned subsequently.

4. Chickwangue

Chickwangue is the most popular processed food form of cassava in Zaire. ‘Myondo’ and ‘Bobolo’ in Cameroon, ‘Mboung’ in Gabon, ‘Mangbele’ in Central African Republic belong to this group. Similar products are consumed in Congo, sudan and Angola.

Cassava roots are peeled, steeped in water, and left for 3 to 5 d to ferment until they become soft. Fibers are removed from the pump, which is heaped on a rack for further fermentation or covered with leaves and pressed using heavy objects to drain off excess liquid. The pulp is then ground on a stone or pounded in a mortar. The fine pulp is wrapped in leaves of plantain or species belonging to family Zingiberaceae, tied firmly with fibers from banana and steamed in pots. Chickwangue is a very stiff paste, much stiffer than fufu. The size, shape, and texture of the chickwangue food group vary among countries. Theya re produced under more hygienic conditions and contain the least cyanide compared with most other fermented cassava products.

5. Polvilho Azedo

Sour cassava starch, known as ‘polvilho azedo’, is a typical Brazilian product obtained by fermentation of raw cassava starch for a period of about 30d. The end point of fermentation is not easily identified. The fermented starch, which has a strong and characteristic flavour, has many applications in local cookery and in the manufacture of biscuits and cheese breads. The sour starch process consists basically of root washing, peeling, grating, pressing and sieving under running water, fermentation, and drying in the sun.

During the starch fermentation, the pH decreases as organic acids are released. The microorganisms involved in the process were analyzed, and it was concluded that no specific group prevails. However, Bacillus subtilis and Leuconostoc citrovorum were observed in almost all batches and are considered to be responsible for flavour development. Similar fermented starch is an important product in Colombia and used for the production of pan de yucca and pan de bono. However, the period of fermentation is usually shorter in Colombia. The shorter time required for the starch fermentation in Colombia is attributed to the higher ambient temperature prevalent there compred with that in Brazil.

6. Attieke

It is fermented product popular in the Ivory Coast. T he roots are peepled, steeped in water for initial fermentation, and then ground to paste like for fufu and the paste is again left to ferment for 2 d in jute sacks and pressed. Finally, the paste is removed from the sacks crumbled or granulated, and then steamed. Attieke has a slightly sour taste and is eaten with milk or meat and vegetables. The difference from fufu preparation is the steaming step in the final stages.

7. Peujeum

It is a traditional food prepared from cassava in Java. The roots are peeled and steamed until tender, allowed to cool, and dusted with finely powdered ‘ragi’ (a mixture of flour and spices in which fungi and yeasts have been active). The cassava mash mixed with ragi is wrapped in banana leaves and left for 1 to 2 d ferment in earthenware. The peujeum has a refreshing acidic and slightly alcoholic flavour and is eaten either as is or after baking.

8. Fermented Sour Flour and Fermented Sweet Flour

It has been found that cassava tuber when subjected to fermentation with a select group of microorganisms comprising Lactobacilus cellobiosus, Streptococcus lactis, Corynebacterium sp., and Pichia membranaefaciens softened the tubes and improved extraction of starchy flour without liberating foul smell.

Freshly harvested cassava a tubers are peeled and cut to form 10-cm cylindrical pieces. The tuber pieces are stacked in a large plastic bucket of 100 1 capacity. Tap water is added to provide a 10 to 15 cm column of water over the stacked pieces. One hundred kilograms of tuber pieces require about 100 1 of water to have such a surface column. Mother liquor from an earlier batch of fermentation is added to give a concentration of 2% by volume of the steep water as the source of mixed culture inoculum. The tuber pieces in steep water are stirred well to mix the inoculum uniformly. The container is covered with a muslin cloth and kept undisturbed for 48 h. The steep liquor is then decanted and the softened tuber pieces taken out and placed on an inclined wire net for faster sun drying. The dried pieces are powdered and passed through 30 mesh sieve to get fermented sour flour (SRF). The softened pieces are mashed, sieved, and allowed to settle in excess of water (1:5) and the sediment dried to yield fermented sweet flour (SWF) (Figure 1).

Raw cassava flour possesses a cohesive texture on heating in the presence of water, and this imparts a rubbery consistency to the processed food products. The cohesive texture is due to the rapid breakdown of starch granules in raw cassava flour and adversely affects the substitution of cassava flour in place of cereal flour for preparation of food items. Fermented cassava flour offers additional stability to starch granules, thereby reducing the cohesive texture. The improvement in cooking quality of the fermented flour may be attributed to the enhanced quantity of fibrous residue and higher elasticity imparted to the starch granules,, which prevents easy break down.