Protein Isolates from Bambara Groundnut (Voandzeia Subterranean L.): Chemical Characterization and Functional Properties

Figures & data

Table 1 Chemical composition of Bambara groundnut flour and protein isolates from three replicate analysis

	Bambara groundnut flour		Bambara groundnut protein isolates
Parameters (g/100 g)	White variety	Brown variety	White variety	Brown variety
Moisture	5.64 ± 0.10^a	6.82 ± 0.24^a	2.11 ± 0.10^b	2.72 ± 0.24^a
Dry matter	94.36 ± 0.56^a	93.18 ± 0.11^a	95.36 ± 1.56^a	96.18 ± 1.11^a
Protein	29.53 ± 0.27^a	30.37 ± 0.36^a	90.0 ± 1.27^a	91.0 ± 1.36^a
Lipid	9.65 ± 0.16^a	9.69 ± 0.47^a	ND	ND
Ash	4.50 ± 0.16^a	4.36 ± 0.06^a	5.04 ± 0.17^b	5.26 ± 0.23^b
Crude fiber	2.20 ± 0.06^a	3.00 ± 0.02^ab	0.02 ± 0.00^a	0.01 ± 0.00^a
Carbohydrates*	44.94 ± 0.25^b	46.76 ± 0.35^b	ND	ND
Reducing sugars (mg/100 g)	334 ± 3.61^c	430 ± 4.04^b	ND	ND
Non-reducing sugars (mg/100 g)	2.56 ± 0.34^b	3.78 ± 0.45^a	ND	ND
Starch	39.45 ± 0.31^a	40.76 ± 0.23^a	ND	ND
Gross energy (MJ/kg)	21.7 ± 0.23^b	21.75 ± 0.45^b	ND	ND
The results are mean ± SD of triplicate analysis. Means followed by different superscripts in each row indicates significant differences at P < 0.05. ND implies not detectable (i.e., below detectable limit); ND implies not determined. Results are expressed as mg/100 g.
*Carbohydrates by difference as 100 − (moisture + crude protein + lipid + ash).

Table 2 Protein yield and content of Bambara groundnut isolates obtained by isoelectric precipitation (IEP) or micellization (MP) and soybean isolate

	Bambara white variety		Bambara brown variety		Soybeans
Type of isolate	Protein yield	Protein content	Protein yield	Protein content	Protein yield	Protein content
IEP	56.30	90.0	58.2	91.0	56.6	92.0
MP	14.4	75.0	15.6	78.0	16.2	72.0

Table 3 Amino acid (g/100 g protein) composition of Bambara groundnut

Amino acid	Bambarra groundnut (white)*	Bambarra groundnut (brown)	Soybeans	FAO/WHO (children)	Reference pattern
Isoleucine ^a	3.98 ± 0.80	4.10 ± 0.90	4.0	2.8	1.3
Leucine ^a	6.70 ± 0.44	6.48 ± 0.14	7.80	6.6	1.9
Lysine ^a	5.93 ± 0.22	6.10 ± 0.43	6.40	5.8	1.6
Methionine ^a	1.40 ± 0.15	1.40 ± 0.75	1.40	2.5	1.7
Phenylalanine ^a	4.73 ± 0.24	5.28 ± 0.40	5.20	6.3	1.9
Tyrosine	7.12 ± 0.16	7.42 ± 0.51	3.80	Na	Na
Threonine ^a	5.10 ± 0.12	4.68 ± 0.21	4.10	3.4	0.9
Valine ^a	5.10 ± 0.89	4.98 ± 0.39	5.00	3.5	1.3
Histidine	2.42 ± 0.41	2.62 ± 0.65	2.80	1.9	1.6
Arginine ^a	8.06 ± 0.19	7.79 ± 0.51	7.70	Na	Na
Alanine	3.84 ± 0.73	3.67 ± 0.32	4.30	Na	Na
Aspartic acid	12.34 ± 0.09	11.90 ± 0.07	11.60	Na	Na
Glutamic acid	15.34 ± 0.94	15.08 ± 0.06	19.10	Na	Na
Glycine	2.38 ± 0.69	2.55 ± 0.05	4.70	Na	Na
Serine	5.56 ± 0.50	5.71 ± 0.59	5.60	Na	Na
TAA	90.00	89.76	93.50
TEAA	41.00	40.81	41.60
TNEAA	49.00	48.95	51.90
%TEAA/TAA	45.56	45.47	44.49
%TNEAA/TAA	54.44	54.53	55.51
^aEssential amino acids, FAO/WHO (children), and reference pattern are not available for non-essential amino acid.
*Mean values ± standard deviation of replicate analysis. Na: Not available.

Figure 1 (a) Protein solubility profile for two varieties of Bambara groundnut flours. (b) Protein solubility profiles of IEP isolate and MP isolate for the two varieties of Bambara groundnut.

Table 4 Functional properties of Bambara groundnut protein isolate in comparison with soybean protein isolate

	Bambara groundnut (white variety)		Bambara groundnut (brown variety)		Soy bean isolate
Properties	IEP	MP	IEP	MP	IEP	MP
Foaming capacity (%)	75 ± 1.2^a	78 ± 1.8^ab	72 ± 2.2^b	74 ± 1.8^bc	80 ± 1.3^ac	85 ± 1.1^a
Foaming stability (min)	52 ± 1.6^a	56 ± 2.0^b	50 ± 1.4^a	58 ± 1.2^ac	66 ± 1.2^c	68 ± 1.8^ab
Water absorption capacity (g/g)	6.0 ± 0.1^c	6.5 ± 0.2^b	5.8 ± 0.2^ab	6.7 ± 0.1^b	6.0 ± 0.3^a	6.6 ± 0.2^bc
Water absorption capacity (g/g)	6.9 ± 0.1^ac	7.2 ± 0.6^ab	6.6 ± 0.3^b	7.0 ± 0.4^a	6.2 ± 0.1^b	6.8 ± 0.2^c
Least gelation concentration (%)	8.0	6.0	8.0	6.0
Mean values ± standard deviation of replicate analysis, means followed by different superscript in each row indicates significant differences at P < 0.05. MP = Micelle protein; IEP = isoelectric protein.

Figure 2 (a) Emulsifying activity index of isoelectric isolate (IEP) and micellisation isolate (MP) of Bambara groundnut and soy protein isolate. (b) Emulsion stability index of isoelectric isolate (IEP) and micellisation isolate (MP) of Bambara groundnut and soy protein isolate (color figure available online).

Figure 3 Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) patterns of Bambara groundnut and soybean protein isolates: Lanes 2, 3, 4, 5, and 6 carried out without Dithiothreitol (DTT). Lanes 1, 7, and 13—Standard reference protein; Lane 2—Soy protein isolate (IEP); Lane 3—Bambarra isolate (IEP), white variety; Lane 4—Bambarra isolate (IEP), brown diversity; Lane 5—Bambarra isolate (MP), white variety; Lane 6—Bambarra isolate (MP), brown variety. Lanes 8, 9, 10, 11, and 12 with Dithiothreitol (DTT): Lane 8—Soy protein isolate (IEP); Lane 9—Bambarra isolate (IEP), white variety; Lane 10—Bambarra isolate (IEP), brown diversity; Lane 11—Bambarra isolate (MP), white variety; Lane 12—Bambarra isolate (MP), brown variety (color figure available online).

Figure 4 (a) DSC thermograms of the Bambara groundnut protein isolates produced by: (A) isoelectric precipitation (white variety); (B) micellisation (white variety); (C) isoelectric precipitation (brown variety); (D) micellisation (brown variety) (color figure available online).

Figure 4 (b) DSC thermogram of soybean protein isolate produced by isoelectric precipitation (color figure available online).