Cassava Fermentation and Associated Changes in Physicochemical and Functional Properties

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F. Protein

Changes in protein quality and quantity during different fermentation techniques have also been studied. Crude protein was enhanced to 2.56% during fufu production and 3.68% in Pukuru, but was reduced to 1.43% in gari and 1.14% in Kpokpo gari compared with 2.04% in cassava chips.39 Although there was reduction in protein content in the latter products, there was general improvement in feed intake and growth rate of rats fed on diets containing fermented products. The protein content in gari and fufu produced by different processes are compared in (Table3).⁴⁷ During fufu production, a 20% reduction in protein content was observed. At the end of 72 h, value dropped from 1.5% to 0.9% subsequently increasing to 1.2% which might be attributed to increased biomass production. A loss of about 70% protein during Lafun production has also been reported.³⁸

During fermentation of cassava meal, the protein and amino acid contents were reduced to half the original values (Table 16).⁷⁹ However, the amino acid composition did not show any noticeable change. It was also inferred that traditional fermentation caused only a minor reduction in chemical score of the tuber protein (3%) and biological value of the meal (from 58 to 56%). Because the protein content in the tuber meal itself is quite low, the reduction due to fermentation can be considered insignificant. In addition, fermentation did not drastically affect the sulfur-containing amino acids or the protein quality.

Table 16 : Changes in the Amino Acid Content of Cassava Tuber Meal and its Fermented Product

Composition g/g of dry matter
Amino acids	Unfermented Meal	Fermented Meal
Asparagine	1.33	0.68
Threonine	0.64	0.38
Serine	0.57	0.34
Glutamic acid	1.98	0.89
Glycine	0.58	0.34
Alanine	0.94	0.51
Cysteine	0.07	0.04
Valine	0.69	0.39
Methionine	0.11	0.05
Isoluecine	0.59	0.32
Leucine	0.88	0.49
Tyrosine	0.36	0.22
Phenylalanine	0.55	0.30
Histidine	0.34	0.16
Lysine	0.87	0.47
Arginine	0.58	0.34
Praline	0.52	0.28

Table 17 : Proximate Composition of Fresh and Fermented Cassava (%DM)

	Fermented Cassava	Control	Fermented
Protein (total n)	0.19	0.18	0.12
Crude fiber	1.92	1.98	1.54
Fat	0.72	0.63	0.39
Ash	2.50	2.66	1.08
Total Carbohydrates	94.67	94.55	96.87

Source: Bokanga⁵¹

The protein content and amino acid profile of fresh and fermented cassava using inoculum have been analyzed (Table 17).⁵¹ Fermentation decreased the total amino acids by about 42%. Only 10 out of the 17 amino acids decreased significantly. Praline was lost completely after 36 h. Glumatic acid was reduced by 48 and 44%, respectively. The fall in amino acid content commenced after 12h of incubation. Studies on the chemical score of the essential amino acids showed that there was a slight improvement in protein quality by the fermentation process.

The crude protein did not show any noticeable difference either in natural fermentation or in presence of added inoculum (Table 18)⁶⁷. The protein quality and quantity in flour from cassava tuber fermented with mixed culture inoculum have been examined in detail83 the results (Table 19) indicated a decrease in amino acid content of fermented flour compared with nonfermented flour. A decrease in arginine, histidine, and glutamine were quite clear. A considerable decrease in aspartic acid, alanine, leucine, and total lysine was observed in both sour and sweet fermented flours. The low amino acid content in the fermented flour might be due to leaching loss in step liquor. A considerable loss of bound amino acids was also observed either due to leaching or microbial utilization. Calculation of chemical scores revealed that only leucine and threonine were limiting in fermented sour flour, leucine and threonine in fermented sweet flour, while others exceeded FAO/WHO reference scores. The sulfur containing amino acids exceeded FAO/WHO reference score by 37% in fermented sweet flour. The results showed that although there was reduction in quantity of fermented flours was superior.

Table 18 : Proximate Composition of the Commercial, Native, and Fermented Cassava Starches

Type of cassava starch
Measured variablea	Commercial	Native	Fermented naturally	Fermented with culture
Total Carbohydrate (%)	0.1	0.1	0.1	0.3
apparent amylose (%)	2.3	1.0	2.0	2.2
total sugars (mg/ml)	1.9	2.3	1.4	1.3
crude fiber (%)	0.04	0.06	0.12	0.06
ash (%)	0.03	0.04	0.00	0.08
lipids (%)	0.02	0.03	0.03	0.01
crude protein (%)	0.03	0.01	0.01	0.01
cyanide (mg/kg)	0.19	0.00	ND	ND
acidity (g/d)asacetic acid	0.06	0.06	0.12	0.01

^a Values are expressed on a dry weight basis and each represents an average and a standard deviation of two runs, with each analyzed in triplicate. ND = not detectable.

Source: Numfor et al.⁶⁷ With permission.

Table 19 : Amino Acid Composition of Fermented and Nonfermented Cassava Floor

Amino acid	NFC	FSO	FSW
Aspartic acid	181.48	107.71	45.97
Threonine	83.31	49.91	25.33
Serine	100.30	51.36	28.40
Glutamic acid	470.11	162.29	73.64
Glycine	87.79	64.09	37.48
Alanine	155.76	97.08	36.97
Valine	106.91	67.46	39.09
Isoleucine	73.40	52.65	37.26
Leucine	122.96	76.80	42.90
Tyrosine	73.16	47.66	33.38
Phenylalanine	69.86	38.48	41.65
Histidine	396.95	156.17	31.70
Arginine	380.43	14.65	35.94
Proline	37.76	25.76	11.71
Total lysine	120.83	88.55	45.82
Cystine	39.18	25.12	15.66
Menthonine	29.03	24.79	19.54

Note: NFC, nonfermented cassava flour; FSO, fermented sour flour; FSW, fermented sweet flour; FSW fermented sweet flour.

Adapted from Padmaja et al.⁸³

In the view of low protein content in cassava, addition of cowpea or soyabean during fermentation has been attempted.⁶² Co-fermentation with soyabean/cowpea yielded products having higher overall protein from an initial value 1.8 to 13.1 and 7.7%, respectively. A method for production of fufu where protein content was in the range 1.0 to 2.2% has been outlined.35 Production of fufu by controlled fermentation was standardized using starter cultures, consisting of Citrobacter freundi, Geotrichum sp., and Saccharomyces sp., which considerably improved protein content.³²