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Effect of fermentation on the nutrient status of locust beans
l')~od Chemistry 5 0980) 303 308
EFFECT OF F E R M E N T A T I O N ON THE NUTRIENT STATUS OF LOCUST BEANS O. U. EKAt
Department of Biochemistry, Abu, Zaria, Nigeria (Received: 11 June, 1979)
ABSTRACT Both jermented and unfermented locust beans were analysed for proximate composition (carbohydrate, moisture, lipid, crude protein and ash) as well as for content of" amino acids and mineral elements. There were changes in the nutrient contents. The amount of protein was increased by fermentation as was the amount of fat. The amount of carbohydrate was greatly decreased by fermentation. The content of essential amino acids was also influenced by Jermentation. The importance of fermented jbod in the traditional diets of people in Africa is discussed.
INTRODUCTION The African locust bean plant (Parkiafilicoidea. Welw.) is widely distributed in the northern parts of Nigeria. It bears fruits in the form of bunches of pods containing yellow powdery pulp with dark brown to black seeds. The sweet pulp is usually made into a traditional carbohydrate food known as dorowa by the Hausas. This food is often supplemented with cereal grains in meat stew or soup. The seeds are usually boiled and fermented and then pounded to give a popular traditional food known by the Hausas as daddawa. Oyenuga (1968) discussed the value of the African locust beans as stock feed. All parts of the fruit, including the pod, the mealy pulpy material and seeds are claimed to constitute valuable cattle food. Several Nigerian foods and also West African foods are fermented at some stage in their preparation. The African locust bean seeds are normally fermented before they are used either as food or as flavouring agents. The main aim of fermentation is to enhance the flavour and the keeping quality. During fermentation, changes both t Present address: Department of Biochemistry, Medical School, University of Calabar, Calabar, Nigeria. 303 Fd. Chem. 0308-8146/80/0005-0303/$02.25 © Applied Science Publishers Ltd, England, 1980 Printed in Great Britain
304 desirable and scanty reports Nigeria (Oke, 1978). The present nutrients as a
o.U. EKA undesirable may occur in the food material. There are only a few on the effect of fermentation on nutritive value of traditional foods in 1965; Akinrele, 1970; Eka & Edijala, 1972; Okoh & Eka, 1978; Eka, series of investigations were carried out to observe the changes in the result of fermentation of African locust beans.
MATERIALS AND METHODS
The locust beans used were purchased from the local markets at Zaria. Fermentation of the beans to produce fermented meal (daddawa) was carried out using the traditional methods described by Simons (1976). In essence, the procedure involves washing the locust bean seeds thrice with water and cooking with added potash until slightly soft. The cooked seeds are then left overnight in a basket. On the following day, ashes are added to the cooked seeds and the mixture pounded until the husks are removed. The edible portion is again emptied into a basket and the yellow portion of the fruit pulp sprinkled over it; leaves are then used to cover the basket. The preparation is left for 48 h at room temperature to ferment. After the fermentation, the fermented bean is dried in the sun for 24 h. The semi-dry material is pounded in a mortar into a pulpy mass and flattened into cakes known as daddawa. The cakes are dried again in the sun since they tend to keep for a long time when dry. The daddawa is usually hawked around and also sold at the local markets.
A N A L Y S I S OF THE S A M P L E S
The methods of treatment of samples and analyses were similar to those recommended by the Association of Official Analytical Chemists (AOAC, 1970) and by Joslyn (1970). The cooked edible portion of the locust bean seed and the fermented beans were analysed for proximate composition, mineral elements and amino acids. The chemical analyses, except for moisture determination, were carried out on oven-dried samples. In all cases the material was dried at 60-70 °C to constant weight using a vacuum oven and then ground into powder until it passed through a 40 mesh sieve (AOAC, 1970). The dry material was preserved in the refrigerator for subsequent analysis. The methods of analysis followed were those described by the A OAC (1970). The ash was determined by incineration of known weights of the samples in a muffle furnace at 550 °C until ash was obtained. The lipid composition was determined by exhaustively extracting a known weight of the sample with petroleum ether (boiling point 40-60 °C) using a Soxhlet apparatus. Protein (N × 6.25) was determined by the macro-Kjeidahl method. The carbohydrate content was obtained by the
EFFECT OF FERMENTATION ON THE NUTRIENT STATUS OF LOCUST BEANS
305
difference method, that is, by subtracting the total crude protein and crude lipid from the organic matter. Crude fibre was determined by acid and alkaline digestion methods described by Joslyn (1970) and the AOAC (1970). The elemental composition was also determined using the methods of the AOAC (1970). Sodium and potassium were determined by flame photometric methods: calcium, magnesium, zinc, iron, and copper were determined using absorption spectrophotometer; phosphorus was determined by colorimetric methods using ammonium molybdenate. The amino acid contents of the samples were determined using the automatic amino acid analyser (Beckman 120 C). The vitamins were determined using the methods of the Association of Official Vitamin Chemists (AOVC) (1966). Thiamine was estimated as thiochrome by the fluorimetric method, riboflavine was also estimated fluorimetrically, using a Locarte fluorimeter. Vitamin C (ascorbic acid) was estimated by the N-bromo-succinimide method described by Evered (1960). Oxalate was determined by the method of Dye (1956) and as modified by Oke (1965). Hydrocyanic acid content was determined by the alkaline titration method (AOAC, 1970). Phytic acid was estimated by a photometric method adapted from the methods of McCance & Widdowson (1935), and Briggs (1922).
RESULTS AND DISCUSSION
The results are shown in Tables 1-4. Table I shows the proximate composition of the fermented and unfermented samples of locust bean expressed as an average of six TABLE 1 PROXIMATE COMPOSITION OF FERMENTED AND UNFERMENTED SAMPLESOF LOCUST BEAN IN g/100g (+_SE)
g/lO0 g dr)' weight of material
g/lO0 g wet weight Sample
Moisture
Ash
Crude protein
Petroleum ether exlracl
Total carbohydrate
Crude fibre
Unfermented locust beans
12.66+1.12
5.14+0.75
30.57+1.55
15.20_+1-20
49.09+2.25
7-83+0-86
Fermented locust bean cakes
13.75+1-11
6.75+0-95
38.5_+1-16
31-20+1.35
23.55_+2.13
6.23+0.55
determinations. The moisture contents of both samples were close in value and also low since sun-dried samples were used. There were high values of ash content in both samples and the fermented samples showed slightly higher total ash content. The crude protein was high in both, being comparable to the amount in soya beans. The fermented samples had a higher protein content than the unfermented samples. The
306
o.U. EKA
petroleum ether extract of the fermented samples was double that of the unfermented samples. The total carbohydrate was greatly reduced in the fermented samples and was almost 50 ~ that of the unfermented samples. The crude fibre was slightly higher in the unfermented samples than in the fermented samples. On the whole, the locust bean seed appears to be a good source of nutrients and fermentation seems to improve the nutrient status of the locust bean food. The high fibre content may, however, influence the availability of the nutrients to man and animals. Table 2 shows the mineral element content of the fermented and unfermented samples of locust bean. The samples were rich in all the elements determined and there was a slight increase in element content in fermented samples. The elements were adequate to meet the recommended daily allowance. For example, the recommended daily allowance for iron is 12mg/100g dry matter (Oke, 1972; Lutham, 1969). The actual amount of the mineral elements available to the consumer may depend on various factors such as the limitation of absorption by phytic acid or oxalic acid present in the food. TABLE 2 MINERALELEMENTCONTENT OF FERMENTEDAND UNFERMENTEDSAMPLESOF LOCUSTBEANSIN mR/100 g DRY MATTER ( _+SE)
Sample
K
Na
Zn
Mg
Ca
Cu
Fe
P
Unfermented locust beans
250+5.5
2 4 0 + 3 . 8 15.0+1.2 80.5+3.5 330+4.3
1.54-0.1
22.5+1.4 2 8 0 + 3 . 5
Fermented locust bean cakes
5 50+4.8
250+2.0
2.0_+0-1
28.0_+1.2 320_+2.5
18-04-1.1 83.5+2.7 360+4.1
Table 3 shows the amino acid composition of the fermented and unfermented locust bean samples. The samples were rather low in the sulphur-containing amino acids such as cystine and methionine. They were also low in the essential amino acids leucine, isoleucine, phenylalanine and tryptophan. Tryrosine was low and this was also true of histidine. Fermentation resulted in increased yield of most of the amino acids except arginine, leucine and phenylalanine. The results indicate that even though the locust bean seeds are high in crude protein content, the quality of the protein is not very high. The deficiency in some of the essential amino acids and the sulphur-containing amino acids tends to mitigate against classifying the locust bean, fermented and unfermented, as a source of high quality protein. Table 4 shows the content of vitamins B 1 (thiamine), B 2 (riboflavine) and C (ascorbic acid) in both the fermented and unfermented locust bean samples. The vitamins B 1 and B 2 and C were low in both samples but there were higher amounts of thiamine and riboflavine in the fermented samples. The level of vitamin C (ascorbic acid) was, however, adversely affected by fermentation (Oke, 1967a).
EFFECT OF FERMENTATION ON THE NUTRIENT STATUS OF LOCUST BEANS
307
TABLE 3 AMINOACID
COMPOSITION OF FERMENTED AND UNFERMENTED SAMPLES OF LOCUST BEAN SEEDS IN r a g / 1 0 0 g SAMPLES (_+ S E )
Amino acids
Lysine Histidine (Ammonia) Arginine Tryptophan Aspartic acid Threonine Serine Glutamic acid Proline Glycine Alanine Cystine (half) Methionine lsoleucine Leucine Tyrosine Phenylalanine
Unfermented locust beans
Fermented locust bean cake
4.24 _+0.55 1.60 _+0.02 (3,20 _+0.05) 2,84 _+0-05 0.12 _+0.01 8,40 -+ 1-10 3,80 + 0.65 3.22 + 0.55 16.00 _+2.11 4-24_+ 1-12 6.84 _+0.95 5.60 _+0-85 1.20 + 0-01 0.12 _+0.01 0.88 +0.03 1.44 _+0.04 1.12 + 0.04 0-32 _+0-02
6.72 +0.65 1.68 + 0.02 (4-96 _+0.07) 2.88 + 0.03 0.24 -+0.02 12-00 -+ 1.10 4-48 -+0- 55 5.62 + 0.55 19.60 _+2.24 6-11 _+ 1.15 9.20 _+1.17 7.84 + 1-15 2-10 _+0.45 0.24 _+0.01 0-40 _+0.01 0.80 + 0.03 0-80 _+0.04 0-16 _+0.01
TABLE 4 VITAMINSANDSOMETOXICSUBSTANCESlN FERMENTEDANDUNFERMENTEDSAMPLESOF LOCUSTBEANSEEDSIN mg/100 g DRY SAMPLES( _+SE) Samples
Unfermented locust beans Fermented locust bean cakes
Vitamin Bl
Vitamin B2
Vitamin C
Oxalate as soluble oxalic acid
0.65_+0.05 0.45_+0.03 7.50+__1.1 tl.21 +0.01
HC N
Total phytic acid P
Phytic acid P as %, of total P
2 6 x l 0 4 51.0+_1.85 15.0_+1.22
1,35+0.08 1.30_+0-07 5.20+0.90 0-12_+0.12 12x10 "* 31.0_+2.10
7.5_+0.83
T a b l e 4 also s h o w s the levels o f o x a l i c acid, p h y t i c acid a n d h y d r o c y a n i c acid in the two l o c u s t b e a n s a m p l e s . All t h e s e t o x i c s u b s t a n c e s w e r e f o u n d in r e d u c e d a m o u n t s in the f e r m e n t e d s a m p l e s . T h e h y d r o c y a n i c acid levels w e r e b e l o w the d a n g e r o u s levels ( O k e , 1967b, 1969a). T h e p e r c e n t a g e o f t o t a l p h o s p h o r u s p r e s e n t as p h y t i c acid p h o s p h o r u s was 15.0 in the u n f e r m e n t e d s a m p l e s a n d 7.5 in the f e r m e n t e d samples. T h e p e r c e n t a g e o f s o l u b l e o x a l a t e p r e s e n t w a s 0.21 in the u n f e r m e n t e d s a m p l e s a n d 0.12 in the f e r m e n t e d s a m p l e s . T h e s o l u b l e o x a l a t e is k n o w n to be t h e f r a c t i o n o f o x a l a t e t h a t c a n be t o x i c to a n i m a l s b u t t h e levels in b o t h s a m p l e s w e r e r a t h e r low ( O k e , 1969b). P h y t i c a c i d a n d o x a l i c a c i d a r e also k n o w n to f o r m i n s o l u b l e salts w i t h
308
o.U. EKA
mineral elements and therefore prevent their utilisation. In this aspect the levels of phytic acid and oxalic acid may call for some consideration. It appears from the results that the seed of locust bean is high in nutrients, particularly in protein. The amino acid content of the proteins tends to indicate that there are deficiencies of some essential amino acids. Even though these results agree with those of previous workers in certain respects (Oyenuga, 1968) the method of assay of these amino acids might have influenced the results, for example, in the case of the low content of tryptophan and cystine. There is a need for biological studies involving feeding experiments to be able to confirm or disprove the evidence presented by chemical scores. It is also clear from the results of the experiments that fermentation in most cases resulted in better quality food material both in terms of contents of nutrients and toxic substances. The traditional practice of fermenting the locust beans before consumption should be encouraged and efforts should be made to understand what goes on during the fermentation processes. Studies in all these directions are now in progress.
REFERENCES AKINRELE, I. A. (1970). Nutrient enrichment of gari. West African J. Biol. Appl. Chem., 10, 19. AOAC (1970). Methods of analysis 1 lth ed. Association of Official Analytical Chemists, Washington, DC, USA. AOVC (1966). (Association of Official Vitamin Chemists.) Methods of vitamin assay 3rd ed. lnterscience Publishers, New York, London. BRIGGS, A. P. (1922). (Quoted by McCance & Widdowson, 1935.) J. Biol. Chem., 53, 13. DYE, W. B. (1956). Chemical studies on Halogeton glomeratus. Weeds, 4, 5~60. EKA, O. U. (1978). Chemical evaluation of nutritive value of soya paps and porridges; the Nigerian weaning foods. Food Chemistry, 3, 199-206. EKA, O. U. 81, EDIJALA, J. K. (1972). Chemical composition of some traditionally prepared Nigerian foods. Nigerian. J. Sci., 6, 177. EVERED, D. F. (1960). Determination of ascorbic acid in highly coloured solutions with Nbromosuccinimide. Analyst, 85, 515. JOSLYN, M. A. (1970). Methods of Jood analysis 2nd ed. Academic Press, New York, London. LUTHAM, M. C. (1969). Human nutrition in tropical Africa. FAO, Rome, p. 67. McCANcE, R. A. & WIDDOWSON, E. M. (1935). Phytin in human nutrition. Biochem. J., 29, 2694-9. OKE, O. L. (1965). Chemical studies on some Nigerian foodstuffs--Lafun. West AJrican J. Biol. App/. Chem., g, 53. OKE, O. L. (1967a). Ascorbic acid content of some Nigerian vegetables. J. Food Science, 32, 85. OKE, O. L. (1967b). Chemical studies on some Nigerian pulses. West African J. Biol. Appl. Chem., 9, 52-5. OK~, O. L. (1969a). Role of hydrocyanic acid in nutrition. World Review of Nutrition and Dietetics, I l, 170-98. OKE, O. L. (1969b). Oxalic acids in plants and in nutrition. Worm Review of Nutrition and Dietetics, 10, 262-303. OKE, O. L. (1972). A nutrition policy for Nigeria. Worm Review of Nutrition and Dietetics, 14, 1. OKOH, P. N. & E KA, O. U. (1978). Effect of traditional methods of preparation on nutrient status of furanono; a fermented milk-cereal based food of the Hausas and Fulanis in northern Nigeria. Savana, 7, 67-70. OYENUGA, V. A. (1968). NigerianJbods andJeeding stuffs. 3rd ed. lbadan University Press, Nigeria. SIMONS, E. B. (1976). Caloric and protein intakes in three villages of Zaria Province. May 1970-June 1971. Samaru Miscellaneous Paper 55, Ahmadu Bello University, Zaria, Nigeria.
EFFECT OF F E R M E N T A T I O N ON THE NUTRIENT STATUS OF LOCUST BEANS O. U. EKAt
Department of Biochemistry, Abu, Zaria, Nigeria (Received: 11 June, 1979)
ABSTRACT Both jermented and unfermented locust beans were analysed for proximate composition (carbohydrate, moisture, lipid, crude protein and ash) as well as for content of" amino acids and mineral elements. There were changes in the nutrient contents. The amount of protein was increased by fermentation as was the amount of fat. The amount of carbohydrate was greatly decreased by fermentation. The content of essential amino acids was also influenced by Jermentation. The importance of fermented jbod in the traditional diets of people in Africa is discussed.
INTRODUCTION The African locust bean plant (Parkiafilicoidea. Welw.) is widely distributed in the northern parts of Nigeria. It bears fruits in the form of bunches of pods containing yellow powdery pulp with dark brown to black seeds. The sweet pulp is usually made into a traditional carbohydrate food known as dorowa by the Hausas. This food is often supplemented with cereal grains in meat stew or soup. The seeds are usually boiled and fermented and then pounded to give a popular traditional food known by the Hausas as daddawa. Oyenuga (1968) discussed the value of the African locust beans as stock feed. All parts of the fruit, including the pod, the mealy pulpy material and seeds are claimed to constitute valuable cattle food. Several Nigerian foods and also West African foods are fermented at some stage in their preparation. The African locust bean seeds are normally fermented before they are used either as food or as flavouring agents. The main aim of fermentation is to enhance the flavour and the keeping quality. During fermentation, changes both t Present address: Department of Biochemistry, Medical School, University of Calabar, Calabar, Nigeria. 303 Fd. Chem. 0308-8146/80/0005-0303/$02.25 © Applied Science Publishers Ltd, England, 1980 Printed in Great Britain
304 desirable and scanty reports Nigeria (Oke, 1978). The present nutrients as a
o.U. EKA undesirable may occur in the food material. There are only a few on the effect of fermentation on nutritive value of traditional foods in 1965; Akinrele, 1970; Eka & Edijala, 1972; Okoh & Eka, 1978; Eka, series of investigations were carried out to observe the changes in the result of fermentation of African locust beans.
MATERIALS AND METHODS
The locust beans used were purchased from the local markets at Zaria. Fermentation of the beans to produce fermented meal (daddawa) was carried out using the traditional methods described by Simons (1976). In essence, the procedure involves washing the locust bean seeds thrice with water and cooking with added potash until slightly soft. The cooked seeds are then left overnight in a basket. On the following day, ashes are added to the cooked seeds and the mixture pounded until the husks are removed. The edible portion is again emptied into a basket and the yellow portion of the fruit pulp sprinkled over it; leaves are then used to cover the basket. The preparation is left for 48 h at room temperature to ferment. After the fermentation, the fermented bean is dried in the sun for 24 h. The semi-dry material is pounded in a mortar into a pulpy mass and flattened into cakes known as daddawa. The cakes are dried again in the sun since they tend to keep for a long time when dry. The daddawa is usually hawked around and also sold at the local markets.
A N A L Y S I S OF THE S A M P L E S
The methods of treatment of samples and analyses were similar to those recommended by the Association of Official Analytical Chemists (AOAC, 1970) and by Joslyn (1970). The cooked edible portion of the locust bean seed and the fermented beans were analysed for proximate composition, mineral elements and amino acids. The chemical analyses, except for moisture determination, were carried out on oven-dried samples. In all cases the material was dried at 60-70 °C to constant weight using a vacuum oven and then ground into powder until it passed through a 40 mesh sieve (AOAC, 1970). The dry material was preserved in the refrigerator for subsequent analysis. The methods of analysis followed were those described by the A OAC (1970). The ash was determined by incineration of known weights of the samples in a muffle furnace at 550 °C until ash was obtained. The lipid composition was determined by exhaustively extracting a known weight of the sample with petroleum ether (boiling point 40-60 °C) using a Soxhlet apparatus. Protein (N × 6.25) was determined by the macro-Kjeidahl method. The carbohydrate content was obtained by the
EFFECT OF FERMENTATION ON THE NUTRIENT STATUS OF LOCUST BEANS
305
difference method, that is, by subtracting the total crude protein and crude lipid from the organic matter. Crude fibre was determined by acid and alkaline digestion methods described by Joslyn (1970) and the AOAC (1970). The elemental composition was also determined using the methods of the AOAC (1970). Sodium and potassium were determined by flame photometric methods: calcium, magnesium, zinc, iron, and copper were determined using absorption spectrophotometer; phosphorus was determined by colorimetric methods using ammonium molybdenate. The amino acid contents of the samples were determined using the automatic amino acid analyser (Beckman 120 C). The vitamins were determined using the methods of the Association of Official Vitamin Chemists (AOVC) (1966). Thiamine was estimated as thiochrome by the fluorimetric method, riboflavine was also estimated fluorimetrically, using a Locarte fluorimeter. Vitamin C (ascorbic acid) was estimated by the N-bromo-succinimide method described by Evered (1960). Oxalate was determined by the method of Dye (1956) and as modified by Oke (1965). Hydrocyanic acid content was determined by the alkaline titration method (AOAC, 1970). Phytic acid was estimated by a photometric method adapted from the methods of McCance & Widdowson (1935), and Briggs (1922).
RESULTS AND DISCUSSION
The results are shown in Tables 1-4. Table I shows the proximate composition of the fermented and unfermented samples of locust bean expressed as an average of six TABLE 1 PROXIMATE COMPOSITION OF FERMENTED AND UNFERMENTED SAMPLESOF LOCUST BEAN IN g/100g (+_SE)
g/lO0 g dr)' weight of material
g/lO0 g wet weight Sample
Moisture
Ash
Crude protein
Petroleum ether exlracl
Total carbohydrate
Crude fibre
Unfermented locust beans
12.66+1.12
5.14+0.75
30.57+1.55
15.20_+1-20
49.09+2.25
7-83+0-86
Fermented locust bean cakes
13.75+1-11
6.75+0-95
38.5_+1-16
31-20+1.35
23.55_+2.13
6.23+0.55
determinations. The moisture contents of both samples were close in value and also low since sun-dried samples were used. There were high values of ash content in both samples and the fermented samples showed slightly higher total ash content. The crude protein was high in both, being comparable to the amount in soya beans. The fermented samples had a higher protein content than the unfermented samples. The
306
o.U. EKA
petroleum ether extract of the fermented samples was double that of the unfermented samples. The total carbohydrate was greatly reduced in the fermented samples and was almost 50 ~ that of the unfermented samples. The crude fibre was slightly higher in the unfermented samples than in the fermented samples. On the whole, the locust bean seed appears to be a good source of nutrients and fermentation seems to improve the nutrient status of the locust bean food. The high fibre content may, however, influence the availability of the nutrients to man and animals. Table 2 shows the mineral element content of the fermented and unfermented samples of locust bean. The samples were rich in all the elements determined and there was a slight increase in element content in fermented samples. The elements were adequate to meet the recommended daily allowance. For example, the recommended daily allowance for iron is 12mg/100g dry matter (Oke, 1972; Lutham, 1969). The actual amount of the mineral elements available to the consumer may depend on various factors such as the limitation of absorption by phytic acid or oxalic acid present in the food. TABLE 2 MINERALELEMENTCONTENT OF FERMENTEDAND UNFERMENTEDSAMPLESOF LOCUSTBEANSIN mR/100 g DRY MATTER ( _+SE)
Sample
K
Na
Zn
Mg
Ca
Cu
Fe
P
Unfermented locust beans
250+5.5
2 4 0 + 3 . 8 15.0+1.2 80.5+3.5 330+4.3
1.54-0.1
22.5+1.4 2 8 0 + 3 . 5
Fermented locust bean cakes
5 50+4.8
250+2.0
2.0_+0-1
28.0_+1.2 320_+2.5
18-04-1.1 83.5+2.7 360+4.1
Table 3 shows the amino acid composition of the fermented and unfermented locust bean samples. The samples were rather low in the sulphur-containing amino acids such as cystine and methionine. They were also low in the essential amino acids leucine, isoleucine, phenylalanine and tryptophan. Tryrosine was low and this was also true of histidine. Fermentation resulted in increased yield of most of the amino acids except arginine, leucine and phenylalanine. The results indicate that even though the locust bean seeds are high in crude protein content, the quality of the protein is not very high. The deficiency in some of the essential amino acids and the sulphur-containing amino acids tends to mitigate against classifying the locust bean, fermented and unfermented, as a source of high quality protein. Table 4 shows the content of vitamins B 1 (thiamine), B 2 (riboflavine) and C (ascorbic acid) in both the fermented and unfermented locust bean samples. The vitamins B 1 and B 2 and C were low in both samples but there were higher amounts of thiamine and riboflavine in the fermented samples. The level of vitamin C (ascorbic acid) was, however, adversely affected by fermentation (Oke, 1967a).
EFFECT OF FERMENTATION ON THE NUTRIENT STATUS OF LOCUST BEANS
307
TABLE 3 AMINOACID
COMPOSITION OF FERMENTED AND UNFERMENTED SAMPLES OF LOCUST BEAN SEEDS IN r a g / 1 0 0 g SAMPLES (_+ S E )
Amino acids
Lysine Histidine (Ammonia) Arginine Tryptophan Aspartic acid Threonine Serine Glutamic acid Proline Glycine Alanine Cystine (half) Methionine lsoleucine Leucine Tyrosine Phenylalanine
Unfermented locust beans
Fermented locust bean cake
4.24 _+0.55 1.60 _+0.02 (3,20 _+0.05) 2,84 _+0-05 0.12 _+0.01 8,40 -+ 1-10 3,80 + 0.65 3.22 + 0.55 16.00 _+2.11 4-24_+ 1-12 6.84 _+0.95 5.60 _+0-85 1.20 + 0-01 0.12 _+0.01 0.88 +0.03 1.44 _+0.04 1.12 + 0.04 0-32 _+0-02
6.72 +0.65 1.68 + 0.02 (4-96 _+0.07) 2.88 + 0.03 0.24 -+0.02 12-00 -+ 1.10 4-48 -+0- 55 5.62 + 0.55 19.60 _+2.24 6-11 _+ 1.15 9.20 _+1.17 7.84 + 1-15 2-10 _+0.45 0.24 _+0.01 0-40 _+0.01 0.80 + 0.03 0-80 _+0.04 0-16 _+0.01
TABLE 4 VITAMINSANDSOMETOXICSUBSTANCESlN FERMENTEDANDUNFERMENTEDSAMPLESOF LOCUSTBEANSEEDSIN mg/100 g DRY SAMPLES( _+SE) Samples
Unfermented locust beans Fermented locust bean cakes
Vitamin Bl
Vitamin B2
Vitamin C
Oxalate as soluble oxalic acid
0.65_+0.05 0.45_+0.03 7.50+__1.1 tl.21 +0.01
HC N
Total phytic acid P
Phytic acid P as %, of total P
2 6 x l 0 4 51.0+_1.85 15.0_+1.22
1,35+0.08 1.30_+0-07 5.20+0.90 0-12_+0.12 12x10 "* 31.0_+2.10
7.5_+0.83
T a b l e 4 also s h o w s the levels o f o x a l i c acid, p h y t i c acid a n d h y d r o c y a n i c acid in the two l o c u s t b e a n s a m p l e s . All t h e s e t o x i c s u b s t a n c e s w e r e f o u n d in r e d u c e d a m o u n t s in the f e r m e n t e d s a m p l e s . T h e h y d r o c y a n i c acid levels w e r e b e l o w the d a n g e r o u s levels ( O k e , 1967b, 1969a). T h e p e r c e n t a g e o f t o t a l p h o s p h o r u s p r e s e n t as p h y t i c acid p h o s p h o r u s was 15.0 in the u n f e r m e n t e d s a m p l e s a n d 7.5 in the f e r m e n t e d samples. T h e p e r c e n t a g e o f s o l u b l e o x a l a t e p r e s e n t w a s 0.21 in the u n f e r m e n t e d s a m p l e s a n d 0.12 in the f e r m e n t e d s a m p l e s . T h e s o l u b l e o x a l a t e is k n o w n to be t h e f r a c t i o n o f o x a l a t e t h a t c a n be t o x i c to a n i m a l s b u t t h e levels in b o t h s a m p l e s w e r e r a t h e r low ( O k e , 1969b). P h y t i c a c i d a n d o x a l i c a c i d a r e also k n o w n to f o r m i n s o l u b l e salts w i t h
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mineral elements and therefore prevent their utilisation. In this aspect the levels of phytic acid and oxalic acid may call for some consideration. It appears from the results that the seed of locust bean is high in nutrients, particularly in protein. The amino acid content of the proteins tends to indicate that there are deficiencies of some essential amino acids. Even though these results agree with those of previous workers in certain respects (Oyenuga, 1968) the method of assay of these amino acids might have influenced the results, for example, in the case of the low content of tryptophan and cystine. There is a need for biological studies involving feeding experiments to be able to confirm or disprove the evidence presented by chemical scores. It is also clear from the results of the experiments that fermentation in most cases resulted in better quality food material both in terms of contents of nutrients and toxic substances. The traditional practice of fermenting the locust beans before consumption should be encouraged and efforts should be made to understand what goes on during the fermentation processes. Studies in all these directions are now in progress.
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