Cassava Flour Session 4 Bioconversion

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  • 8/10/2019 Cassava Flour Session 4 Bioconversion


    SESSION4 :



  • 8/10/2019 Cassava Flour Session 4 Bioconversion



    Fermenta tion in Cassa va Bioconversion


    Cassava fermentation is traditionallypracticed in the tropics. But bothtechnology and productcharacteristics differ according toregion and sociocultural conditions:gar iin East and West Africa,ch i kw angueor fu fuin Central Africa,and sour starch in Latin America. Butthey have in common the aim toeliminate the poisonous cyanidecomponents and conserve cassava by

    lactic acidification.

    The essential role of lactic acidbacteria in the three products wasdemonstrated by studies carried outby the Institut franais de recherchescientifique pour le dveloppement encoopration (ORSTOM) through the

    CHAPTER2 2



    M. Raimba ul t*, C. Ramrez Toro**, E. Girau d***,

    C. Soccol., andG. Saucedo

    STD2 Program of the European Union(EU), otherwise known as Improvingthe Quality of Traditional FoodsProcessed from Fermented Cassava(Raimbault, 1992; Saucedo et al.,1990).

    When producing gar i, lacticacidification of cassava is rapid anddetoxification is sometimesincomplete. Controlling throughinoculation would improve quality.For fu fuor ch i kwangue, retting isessential for texturing and detoxifyingthe cassava. Lactic acid fermentationis heterolactic, operating inassociation with secondary alcoholicand anaerobic fermentation toproduce alcohol and organic acidssuch as butyrate, acetate, andpropionate that develop specialaromatic and organolepticcharacteristics. As for gar i,fermentation for sour starch

    (especially in Colombia and Brazil) ishomolactic, but takes 3 or 4 weeks.Amylolytic lactic acid bacteria havebeen isolated from ch i kw anguebyORSTOM scientists and from sourstarch by CIRAD scientists.

    A. Brauman isolated a new strain,Lactobaci llus p lantaru m A6, which wasdescribed by Giraud et al. (1991). Itsphysiological and enzymological

    characteristics for cultivation oncassava starch media, amylaseproduction, and biochemical

    * Institut franais de recherche scientifiquepour le dveloppement en coopration(ORSTOM), stationed in Cali, Colombia.

    ** Laboratorio de Bioconversin, Departamentode Procesos Qumicos y Biolgicos, Facultadde Ingeniera, Universidad del Valle, Cali,Colombia.

    *** ORSTOM, Montpellier, France. Laboratrio de Procesos Biotecnologia,

    Departamento de Tecnologia Qumica,Faculdade de Engenharia, UniversidadeFederal de Paran, Brazil.

    Departamento de Biotecnologa, Universidad

    Autnoma Metropolitana (UAM), Iztapalpa,Mexico.

    1. No abstract was provided by the authors.

  • 8/10/2019 Cassava Flour Session 4 Bioconversion



    Cassa va Flour and Starch: Progress in Research and Development

    properties have now been described(Giraud et al., 1992; 1993a; 1993b).

    ORSTOM scientists have beenresearching solid fermentationcultivation of fungi on cassava andamylaceous components for more than10 years. Soccol et al. (1994) showedthat protein enrichment is possible bycultivating various strains of Rhizopus,even on crude, nongelatinized cassavaflours. Saucedo et al. (1992a; 1992b;1992c) studied, at the ORSTOMLaboratory, Montpellier, the growthand alcohol fermentation of cassavastarch in solid-state fermentation,using a highly promising amylolyticyeast.

    Swedish and African researchershave described the beneficial effects oflactic acid fermentation on theprophylactic and keepingcharacteristics of those traditionalfoodstuffs made from fermentedcassava, maize, and mixed cereals,and of baby foods. These foods tendto increase childrens resistance to


    All these studies are beingcontinued in new projects comprisingthe EU-STD3 Program. Other EUstudies are being conducted oncassava quality, environment, physicalprocessing, and transformation at alow industrial scale to take advantageof the economic and commercialopportunities in Latin America.

    Sol id-State Ferme ntat ion of Cassava an d St arch y


    For more than 15 years, an ORSTOM

    group has worked on a solid-statefermentation process for improvingthe protein content of cassava,potatoes, bananas, and other starchycommodities used for animal feed.Fungi, especially from the Aspergi l lusgroup, are used to transform starchand mineral salts into fungal proteins(Oriol et al., 1988a; 1988b; Raimbaultand Alazard, 1980; Raimbault andViniegra, 1991; Raimbault et al.,1985). Table 1 shows the overallchanges in composition between theinitial substrate and final products.Through such techniques acassava-fermented product with an18%-20% protein content (dry matterbasis) was obtained.

    More recently, Soccol et al.(1993a; 1993b), also at the ORSTOMLaboratory, obtained good resultswith the Rhizopusfungi, of special

    interest in traditionally fermentedfoods. In particular, they studied theeffect of cooking before fermentationon the availability of starch, proteincontent, and the rate of starchsbioconversion into protein (Table 2).They found that a selected strain ofRhizopus oryzaecould transformuncooked cassava, which containsonly 1.68% protein, into a fermentedcassava containing 10.89% protein.

    Table 1. Effects of Aspergil lus nigeron protein and sugar contents of different starches (percentage of drymatter) after 30 h of fermentation in solid-state culture.

    Substrate Initial composition Final composition

    Proteins Sugar Proteins Sugar

    Cassava 2.5 90 18 30

    Banana 6.4 80 20 25

    Banana waste 6.5 72 17 33Potato 5.1 90 20 35

    Potato waste 5.1 65 18 28

  • 8/10/2019 Cassava Flour Session 4 Bioconversion



    Fermenta tion in Cassa va Bioconversion

    Table 2. Growth of Rhizopus oryzaein solid-state cultivation on cassava granules after various cookingtreatments.

    Treatmenta Dry matterb Total sugarc Proteinsc

    Initial Final Initial Final Initial Final

    I 60.90 46.48 80.01 46.78 1.20 11.69 II 59.18 45.35 84.11 60.72 1.61 12.40

    III 57.95 42.12 82.44 52.57 1.56 13.93

    IV 55.63 43.88 82.49 56.62 1.47 11.89

    V 45.57 37.88 82.04 56.62 1.68 10.89

    a. Treatment:

    I = Cassava autoclaved for 30 min at 120 C, frozen, dried, and ground

    II = Cassava flour (40% water) autoclaved for 30 min at 120 C

    III = Cassava flour (30% water) autoclaved for 30 min at 120 C

    IV = Cassava flour (30% water) vapor cooked for 30 min at 100 C

    V = Untreated crude cassava flour

    b. g/100 g total weight.

    c. g/100 g dry matter.

    SOURCE: Soccol et al., 1994.

    Table 3 shows results of amylasebiosynthesis in solid or liquidculture, using raw or cookedcassava. The amount ofglucoamylase was 10 to 15 times

    higher in solid than in liquid culture,and higher in raw starch mediumthan in cooked cassava.

    This work is being continued inthe EU-STD3 Program at theBioconversion Laboratory of theUniversidad del Valle, Cali,Colombia. It focuses on simplifyingcassava processing by learning moreabout the specificity of Rhizopus

    strains in degrading the raw starchgranule. But clean flours of rawcassava are needed. The commonflours of cassava contain too muchnatural microflora to allow microbialstudies with fungi; they must first besterilized and (unfortunately)gelatinized. Ramrez et al. (1994)developed raw cassava flour with avery low content of bacteria andfungi, and little gelatinization.

    To measure gelatinization, thesimple method of Wotton et al.

    (1971) was adopted and a goodcorrelation coefficient for thecalibration curve was obtained.Table 4 shows the effect of thermictreatment and microwaves on starch

    gelatinization in cassava flour (watercontent typically lower than 10%).Where water content was very low,gelatinization was also low.

    The same thermic treatment ofdry cassava flour eliminated thenatural microflora contained in rawflour, from 109bacteria/g of dry flourto fewer than 103bacteria/g afterheating the flour for 30 min at

    90 C. With gelatinization limited toless than 5% under such conditions,obtaining clean, raw cassava flour ispossible in the laboratory.

    Figures 1 and 2 show the effectsof various physical and thermictreatments on the bacteria content ofcassava flour. Cassava flour will beused as a solid substrate forcultivating Rhizopusstrains, and to

    compare the capacity of selectedstrains to grow on raw or gelatinizedcassava starch.

  • 8/10/2019 Cassava Flour Session 4 Bioconversion



    Table 3. Effect of cooking and type of culture on the growth and amylases of various strains of Rhizopus oryza ecultivated on

    Strain of Liquid-state culturea SolidRhizopus

    Raw cassava Cooked cassava Raw cassava

    Gluco- Protein Gluco- Protein Gluco- Protein

    amylase amylase (g/100 g amylase amylase (g/100 g amylase amylase (g/100(U/g DM) (U/g DM) DM) (U/g DM) (U/g DM) DM) (U/g DM) (U/g DM) DM)

    28168 42.20 9.60 3.90 157.20 3.10 10.00 39.30 55.30 10.60

    34612 40.40 7.30 4.60 168.50 5.70 9.30 55.00 70.00 12.60

    28627 76.00 7.80 4.00 145.40 3.30 9.60 98.00 108.00 11.40

    a. DM = dry matter; U = enzyme units.

    SOURCE: Soccol et al., 1994.

  • 8/10/2019 Cassava Flour Session 4 Bioconversion



    Fermenta tion in Cassa va Bioconversion

    Table 4. Effect of temperature and microwaves on starch gelatinization of cassava flour.

    Temperature Time Gelatinization rate (%)a

    (min)Exp. 1 Exp. 2 Exp. 3 Mean

    Test 1 75.439 84.063 88.911 82.80

    (80% gel.)

    Test 2 25.411 26.184 29.702 27.10

    (20% gel.)

    80 C 60 3.529 3.444 2.714 3.23

    85 C 30 3.529