Fermentation of cassava
Mô tả tài liệu
The fermentation of cassava which normally takes 3-4 days during village processing can be shortened to 24h by seeding a fresh pulp with cassava juice 4 days old. In the work described here, a further attempt has been made to elucidate the nature of biochemical reactions taking place during fermentation, and to establish the optimum conditions which could be utilised in a modern industry based on this process.
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OF CASSAVA By I. A. AKINRELE Cassava (Manzhot Pohl) is usually fermented during when it This was found to be and and to Lactic and formic acids becomes and develops a flavour. proceed in two stages a t an optimum of about 35". are produced with a trace of gallic acid. The process could be made The of cassava (Manihot uti l issima) is a very important step during the of ' gari ', a popular food among the low income group in the southern regions of Nigeria which is also eaten along the coast of West Africa. Its has already been reported1 that it brings about the of cassava by the of acid at low pH, through the combined of manilaot and Geotricum candida, and the of the flavour of gari. This which normally takes 3-4 days during village can be shortened to 24 h. by seeding a fresh pulp with cassava juice 4 days old. In the work described here, a further attempt has been made to elucidate the nature of reactions taking place during and to establish the optimum which could be utilised in a modern industry based on this process. (I) Effects of on Weighed of grated cassava pulp were put into labelled vacuum flasks and the progress of followed by the of the with mercury Also, samples of about 5 lb. of the grated pulp were placed in beakers, half of which were ' seeded ' by treatment with I pint of cassava juice added to I cwt. of mash. The beakers in pairs, each of ' seeded ' and untreated mash, were covered and incubated at room (about 26"), 35", 40°, 45" and 50" in and the progress of followed by measuring the pH of the expressed juice with a Cambridge direct reading pH meter. (2) of batch and and the effects of sunlight, aeration and Two 3-ft. columns were used-one of glass and the other of The columns were marked into three portions and filled with grated pulp. the portions were marked by rings of dyed cotton wool which slid along with the mash. After each 24 h., the mash at the bottom third portion of the column was pushed out and fresh pulp added at the top. The pH of the juice expressed from each portion of pulp was measured as before. At the same time, control were set up with fresh pulp in open shallow plastic buckets. Their pH were similarly measured after each 24 h. (these were done with unseeded pulp). Three other samples of grated cassava pulp were put into labelled beakers and treated as follows : Sample S was and mixed, Sample A was also but not mixed, while Sample C was neither seeded nor mixed and served as a control The progress of in these samples was again followed by measuring the pH of their juices. (3) by paper of the organic acids produced during of sample Cassava juice was expressed from a mash and kept in a beaker labelled A. A sample of gari was also treated with cold water and the extract put in another beaker labelled B. Both samples were treated with ethanol to starch and the mixtures mixing of the mash J. Sci. Fd Agric., 1964, Vol. 15, September 0 0 590 OF CASSAVA were filtered. Each filtrate was then passed through Amberlite resin IRA-400 in the carbonate form in order to absorb the organic acids,2 and eluted with The excess of ammonium carbonate was by heat during acids3 from these samples were spotted with on to Whatman No. I papers with other spots of the following reference acids : lactic, succinic, oxalic and tartaric. Duplicate papers were prepared, one paper was developed with mesityl formic (75 25 : I) and the other with acid (75 : 25 : I) using The were dried, sprayed with green indicator (0.04 g. in 15 ml. of ethanol + 5 ml. of water, pH adjusted to 5.5) and the R, values measured. acids Sample solutions prepared as above were spotted on two Whatman No. I papers and with (4 : I : 5) by Reference were chosen from the following phenolic viz., vanillin, acid, gallic acid, salicylic acid and One was sprayed with ferric chloride and the other with silver nitrate and the RF values measured. acids4 Another portion of the juice expressed from a cassava mash, which should contain all the volatile acids, was treated with alcohol to starch and then filtered. The filtrate was with hydroxide and centri- fuged. The solution was decanted and almost to dryness. Excess of saturated ammonium oxalate solution (about 5 ml.) was added and the whole mixed and The filtrate which contained the ammonium salts of the volatile acids was used for the This solution was next spotted on two Whatman No. I papers and developed with ammonia (50 : 50). Reference spots were made with formic, acetic, butyric and lactic acids which had been made alkaline with ammonia. The were dried and one was sprayed with green and the other with silver nitrate to between acetic and formic acids. The R p values of the developed spots were then measured. Results The increases in in the vacuum flasks are typified by curves shown in Fig. I for two series of results. The pH readings taken to compare batch and and also the effects of sunlight and exposure to air are recorded in Table I. The effect of the frequent mixing of the mash on the progress of measured by the fall of pH with time, is shown 0 20 40 60 80 TIME, h. 0 FIG. rise during of cassava pulp (two sets of results) J. Sci. Fd Agric., 1964, Vol. 15, September OF CASSAVA 591 Table I p H readtngs durzng batch and of cassava mash Batch in open buckets in tubes Control (exposed to light) Glass Porcelain Sample 24 h. 48 h. 72 h. 96 h. 24 h. 48 h. 72 h. 96 h. 24 h. 48 h. 72 h. 96h. -_ 4.20 3.85 3.85 - 4.1 4.05 4.0 4.0 4.0j 4.1 - A H 4.25 4.3 4.3 - - 4.2 4.0 4.1 c 4'35 4'3 4'3 4.2 4.1 4.05 -- 4.2 4.1 4.1 - E 4. j 4.3 4.1 - 4.r.j 4.1 4.0 - 4.1 4.2 4.15 - - 4'25 3'9 3'9 - D 4.2 4.2 4.25 -- 4-25 4.2 4.1 - 4'2 4.15 4'15 - 1; 4'3 4.15 - 4.15 4.2 4.0 - 4'1 4.2 4.0 - 4'0 G 4.25 - 4.1 3.8 4.15 - 4'0 3'7 4'1 4'1 3'7 4'2 3-9 3'9 Average 4 . 3 ~ 4.26 4.12 3.97 4.19 4.11 3.98 3.86 4-13 4.11 4-08 3.9 in Table I1 ; whilst Fig. z shows the between the rate of fall of pH and time a t 45". The effect of the mash a t various is shown in Fig. 3. The RB. values obtained during the of the organic acids of cassava mash and gari are recorded in Tables 111-V. Passage of the gas evolved during fer- through lime water produced a but the remaining gas was not absorbed by 40% sodium hydroxide solution. It is inferred that the formic acid present is to carbon dioxide and probably hydrogen. - 4.15 3.8 3.8 - 4'3 3'9 4'05 - H Table I1 PH of cassava mash at various times at 4j0 __ Time, Incubated .- .. a t 35' h. S A C S A c 0 2 4 7 I1 12 I4 16 I8 20 22 2 5 28 30 5'90 5.60 5'51 5'05 4'25 4.05 3'94 3'83 3'70 3.67 3'67 3.62 3'45 3'44 5'90 5'58 5.50 5.06 4.46 4'24 4.02 3.88 345 3'72 3.69 3.66 3'51 3'49 5.90 5'74 5.50 5.38 4'63 4'30 4'22 4.12 4'0 4'0 4'0 3'94 3.78 3.78 5.93 5'75 5'50 5'35 4% 4'55 4'25 4'2 4'0 3.85 3'7 3'7 3'65 - 5'93 5'93 5'70 5'75 5'46 5-65 5'05 5'55 4'95 4'95 4 4 5 4'95 4.65 4'75 4'65 4'6 4'37 4'45 4-25 4'40 4.05 4.2 3'97 4'1 4.20 4'25 - - S = acid mixed ,, but not mixed C = control - - 0.1251 I I TIME, h FIG. 2.-Rate of fa l l of PH during of cassava pul9 at 45" x unmixed 0 mixed 0 unmixed (control) J. Sci. Fd Agric., 1964, Vol. 15, September 592 OF CASSAVA w 3 A > I a a -0 10 20 30 TIME, h. FIG. 3.-pH values after diflerent times f o r of cassawa pulp at different 0 50' 0 45' A 40' A 35' X 26" 0 - - - 0 Table 111 RF Values of acids in cassava mash solvent Mesityl ~ acid 0.24 Lactic acid 0.67* Succinic acid 0.71 Gari acid 0.62 Pulp acid 0.61 Tartaric acid - Oxalic acid 0'52 acid 0.17 0.13 0.72 0.71 0.70 0.69 0.41 0.38 0.71 0.71 0.72 0.70 0.29 0.25 * Three spots were obtained at RF 0.67, 0 8 1 and 0.88 Table IV RF Values of aromatic acids in cassawa mash solvent 4 : I : 5) Phenols and aromatic acids acid Gallic acid acid Gari acids Pulp acids 0.87, 0.83 0.80, 0.82 0.70, 0.71 0.84, 0.85 0.60, 0.64 0.81, 0.82 0.09, 0.66 ; 0.11, 0.66 0.09, 0.65 ; 0.13, 0.67 _ _ - _ values 0'92 0.85 0'77 0.90 0.69 0'95 0.88 0.76 - - ,4 very striking feature of the of cassava is the good results in various in which crude culture were used. It would appear that the medium is against by micro- and that studies could be carried out on it. The of gari is to a large extent by its sourness and this in turn is directly related to the degree of In Table VI is seen the direct of the pH of cassava mash to the flavour quality of gari prepared The J. Sci. Fd Agric., 1964, Vol. 15, September OF CASSAVA 593 least flavour is found with material of pH 3.95 which is the average value obtained in for 4 days under normal (see Table I). This value can sometimes be attained more quickly, in locations where cassava is a regular practice. Table V R p Values of volatile acids in fe iwent ing cassaua mash solvent 50 : 50) Acids silver green spray nitrate spray Formic 0'10 + Dark brown Acetic 0'12 - - Propionic 0'2 I Butyric 0.31 - Lactic 0.08, 0.15 + Yellow Pulp 0.08 + Dark brown Table VI Effect of PH and acidity on $avow quality of gari pH of cassava mash 3'70 3.60 3.80 3.87 3.90 3'93 Total acidity (yo as lactic) of gari made therefrom 0.92 I '04 0.66 0.58 0'43 0.40 Taste and flavour Good Good Just Rather Swelling index 4'75 4'40 4.20 4.60 5.10 4'30 poor That this is by the evolution of heat is well in Fig. I. The two peaks shown in each appear to be and coincide with the periods of dominant growth of the isolated and in the cassava mash. This would, seem to confirm the two-stage put forward by Collard & Levi.l The results in Table I indicate that is possible and that it is more than the batch type. The process could therefore be probably by the use of a tunnel without a great risk of serious The effect of sunlight the results for porcelain and glass tubes in Table I) also becomes only after 48 h. of normal when a lowering of the pH of the mashes is It is that this period should again coincide with the onset of the second stage of during which the fungus, Geotricmn calzdida, is re- ported to and to produce a variety of aldehydes and esters. This could mean that light may have a effect on the growth of the fungus whose optimum pH for growth is known5 to be about 3. Cassava pulp when exposed to air soon acquires a brownish from the oxidation of its viz., and cyanidin. The deeper layers, however, which are rendered anaerobic by the evolution of carbon dioxide and acid during fer- do not undergo this change. When cassava was fermented in open shallow vessels with a wire mesh bottom so as to increase the surface area exposed to air, a slowing down of the rate of was noticed. This therefore raises a strong that aeration during could be From Fig. 3 it could be inferred, in general, that 35" is the optimum for the This is confirmed by the extremely rapid fall of pH in the seeded mash incubated at this While it may be said that will take place at 45" quite satis- a marked is a t 50" which results in the of the second stage. From the results in Table 11, it would appear that it is to mix the mash during but it can be observed from Fig. 2 that this advantage is only after 7 h. of Two organic acids have been as products of the of cassava (Tables 111-V), viz., lactic and formic acids, but only lactic acid was found in gari. During the J. Sci. Fd Agric., 1964, Vol. 15, September 594 DATA OF COMMON FRUITS of the and aromatic acids, two spots with equal RF values derived from the fermented pulp and gari were located close to the value obtained for gallic acid, but they were much paler in colour than the standard, probably due to their low It is quite likely that the gallic acid may have been produced from the tannins of the inner cortex of the cassava root by an enzyme ' tannase ' which is known5 to occur in some fungi. It is confirmed that the of cassava proceeds in two stages during which the mash is gradually against microbial growth. During the first phase, cassava bacteria ' manihot ' attack the starch with the of lactic and formic acids, a reaction by the evolution of heat. When the pH of the medium has fallen to about 4-25, a mould Geokicum candida, begins to rapidly bringing about further and the of the aroma of gari. Hydrogen cyanide is liberated during through the of the of cassava at low pH. It is also believed that some of the formic acid breaks down by a system to form carbon dioxide and probably hydrogen. All these gases tend to render the medium seems to proceed best at a of about 35', and with pulp with fermented cassava juice a product has been produced under 15 h. Frequent mixing of the mash and exposure to light appear to during the second stage. A system is possible and, in fact, gives a better than does the batch process. Exposure to air or oxygen and contact with iron should be reduced to a minimum to avoid Federal Institute of Research Private Mail Bag 1023 Ikeja Airport Nigeria TO December, 1963 ; amended 28 January, 1964 Gawler, J. H., J . Sci. F d Agric., 1962, 13, 57 a Bryant, F., & Overell, B. T., Nature, Lond., 1951, Cochrane, V. W., ' of Fungi' (New I. A., Cook, A. S., & Holgate, R. A., Fed. Inst. industr. Res. Rep., 1962, No. 12 (Lagos) P., &Levi, S., Nature, Lond., E., & Lederer, M., ' 167, 361 York: Wiley) (London : Elsevier) DATA OF SOME COMMON FRUITS AND CONTENTS By R. W. MONEY data of some common fruits were published in 1950' and 1958 ;2 these have been extended by of the potassium and contents of further samples taken over a period of about 3 years. Some has been given to the use of these values to calculate the fruit content of products such as jam, but as will be shown below, care must be exercised when such are applied to samples of unknown origin. The content was with an E.E.L. flame and without ashing ; the results are given as mg. of K/IOO g. The was after dry ashing J. Sci. Fd Agric., 1964, Vol. 15, September