Effect of Processing Methods on Amino Acid and Fatty Acid Composition of Parkia biglobosa Seeds

Abstract

Parkia biglobosa (PB) is among the various underexploited nutritious plants. A comparative study was conducted on the effect processing PB has on the amino and fatty acid composition. Fermented (FPB), defatted (DPB), and protein isolates (PI) samples were prepared from Parkia biglobosa seeds using various processing methods, and evaluated using standard analytical protocols. The PI showed the highest significant total non-essential amino acids, essential amino acids, and conditionally essential amino acids when compared with FPB and DPB. In addition, the PI showed the highest significant (p < 0.05) total neutral amino acids, basic amino acids, total aromatic amino acids, and the lowest percentage cystine ratio of total sulphur amino acids and total amino acids in comparison with FPB and DPB. The PI also showed a better-predicted protein efficient ratio, essential amino acid index, biological value, protein content, and nutritional index than FPB and DPB. Furthermore, PI amino acid composition was compared favourably with the reference scores for a whole hen’s egg, preschool child, and provisional scoring pattern. Arginine and histidine values of PI were higher than the recommended values. The FPB (42.29%) showed the highest polyunsaturated fatty acids compared with the DPB (41.94%) and PI (26.7%). The dominant saturated, monounsaturated, and polyunsaturated fatty acids were stearic acid (15.1 DPB), linoleic acid (42.29 DPB), and oleic acid (14.05 PI). The DPB (1.84) showed a better polyunsaturated to saturated (P:S) ratio than FPB (1.74) and PI (0.91). The results revealed that the processing methods improved the relative amino acid composition, whereas the fatty acid composition improved in DPB. Therefore, PI could serve as an alternative in the formulation of complementary foods.

1. Introduction

Food insecurities are estimated to increase to ten billion by 2050, which are driven by the prevailing global population pressure and demand for more sustainable underexploited nutrition plants, especially with high protein and essential fatty acid content [1]. Proteins are a source of essential amino acids, which play a major role in tissue growth and the production of hormones, haemoglobin, enzymes, and energy. A deficiency in any of the essential amino acids could lead to disease conditions [2]. The main dietary proteins are either from animal or plant origin. Animal proteins are known to possess the full spectrum of essential amino acids, whereas proteins of plant origin are deficient in one or more essential amino acids [2]. In addition, the high level of biological values and predicated protein efficiency ratio further showcases animal protein as the preferable source of quality protein. Biological values denote how the body utilises the protein; meanwhile, the predicted protein efficiency ratio stresses the usage of protein for growth [2]. Despite animal protein providing a complete protein and numerous vitamins and minerals, there are still health concerns about the consumption of animal protein, due to the high-saturated fatty acid composition [3]. Fatty acids are a good source of energy [4]. Polyunsaturated fatty acids such as linolenic, linoleic, and arachidonic acid improve the normal physiology of the body system, whereas saturated fatty acids have been implicated in cancer and some other metabolic diseases such as cardiovascular diseases and diabetes mellitus [5]. Therefore, the search for a highly nutritive and cheaper source of protein of plant origin with lower saturated fatty acids is an inevitable alternative to existing animal sources.

Legumes are a good and cheap choice of plant protein in place of animal protein in the developing world [6]. It has also been reported that legumes are about 18–35% protein, which acts as a good complement to cereals in supplementing the needed minerals and vitamin B complex [7]. Legumes are a good replacement for animal protein as zinc, protein, and iron sources. They also increase the intake of folate and fibre above the recommended level, which are commonly low in the Western diet [8]. Consumption of legumes has several health benefits [9]. The nutritive value and functional properties of some legumes, such as soybean and cowpea seeds, have been evaluated [10].

Parkia biglobosa (Jacq.), commonly known as the African locust bean, is widely distributed within the savannah belt of West Africa [11]. As a legume, it has both nutritional and medicinal uses. It is claimed to treat diseases such as diabetes mellitus, pain conditions, malaria, infections, and inflammation [12]. The toxicity of Parkia biglobosa in mice show no lethality, hence, highlighting its safety [12]. Its fermented seeds are widely used as a spice for nutritional meals [11,13]. The emerging food processing technologies are an alternative to thermal traditional processes to enhance nutritional composition, especially protein quality [14]. It was observed that selected processing methods could alter the protein structure and eliminate antinutritional factors [15]. However, the amino acid and fatty acid composition of P. biglobosa using different processing techniques has rarely been investigated. In the present study, the effect of amino acid and fatty acid composition of P. biglobosa using different processing methods, including fermented, defatted, and protein isolates, were investigated. Our findings could lead to the discovery of an adequate processing method for an alternative source of complementary foods.

2. Materials and Methods

2.1. Plant Material

The fermented seeds of Parkia biglobosa (Jacq.) (African locust beans) were purchased from a local market in Ijebu-Ode, Ogun state, Nigeria. The seeds (voucher IB3) were authenticated at the Department of Botany, University of Zululand, and deposited at the University Herbarium.

2.2. Method for the Preparation of Deffated and Protein Isolate Samples

The fermented seeds were thoroughly rinsed with diluted water and oven-dried using a laboratory oven (AP 60L 230-OGH 60, Tmax Laboratory Equipments, Fujian, China) at 50 °C. The dried seeds were milled into a fine powder using a Tencan Lab Stirred Ball Mill (JM-1) (Adolf Kuhner, Birsfelden (Basel), Switzerland) and stored in a dry place prior to use. For the deffated sample, 100 g of fine powder was defatted by the maceration method using hexane (5L × 3) and a Lab shaker (LAB1ST, Shanghai, China) (200 rpm). The solution was filtered using Whatman filter paper (Merck KGaA, Drmstadt, Germany), and concentrated with a rotor evaporator (200 rpm, 40 °C). Portions of the residue from defatted samples were air dried and treated with butanol (1:10 w/v) to remove anti-nutrients. The protein isolate of the Parkia biglobosa samples was prepared following the method described by Nkosi and colleagues [16]. The treated fermented sample was re-suspended in distilled water at pH 10. The resultant suspension was filtered, and the filtrate was adjusted to pH 5 using a buffer solution. The filtrate was then centrifuged using a ThermoFisher centrifuge (ThermoFisher, Waltham, MA, USA) (5000 rpm) for 15 min at 4 °C. Following the centrifugation, the supernatant was discarded, and the pellets containing the protein isolate were lyophilised using a ZZKD Freeze dryer (ZZKD Machinery, Zhengzhou, China) (FD-O4H) and kept at −80 °C for further use.

2.3. Amino Acid Analysis

The amino acid composition of the samples was determined by using the ion-exchange chromatography method [17] using a Technicon Sequential Multi-Sample Amino Acid Analyser (TSM) (Technicon Instruments Corporation, Dublin, Ireland). The reported amino acid values are the means of two determinations and are expressed as a percentage of the total protein. Tryptophan was not determined.

2.4. Determination of the Quality Parameters

Dietary protein quality was determined using the essential amino acid scoring pattern [18]. The amino acid score for essential and non-essential amino acids was based on a whole hen’s egg amino acid profile [19]. The essential amino acid score was based on the suggested preschool child requirement [20]. The essential amino acid score was also determined on the basis of a provisional amino acid scoring pattern with the following formula: Amino acid score (AAS) = amount of amino acid per test protein in [mg/g]/amount of amino acid per protein in reference protein [mg/g].

Amino acid index (EAAI) = 10 logEAA

logEAA = 0.1[log(a1/als × 100) + log(a2/a2 × 100) + log(an/ans × 100)]

2.5. Determination of the Predicted Protein Efficiency Ratio (P-PER)

The predicted protein efficiency ratio (P-PER) of the samples was calculated from their amino acid composition using the equation of Alsmeyer et al. [21].

P-PER₁ = −0.684 + 0.456(Leu) − 0.047(Pro)

P-PER₂ = −0.468 + 0.454(Leu) − 0.105(Tyr)

2.6. Biological Values

The biological values of the samples were estimated using the suggested equation of Oser [22].

BV = 49.09 + 10.53 (PER₂)

BV = 1.09 × essential amino acid index (EAAI) − 11.7

2.7. Essential Amino Acid Index (EAAI)

The essential amino acid index was estimated (EAAI) using the equation from Machado et al. [23]: EAAI = where: [lysine, tryptophan, isoleucine, valine, threonine, leucine, phenylalanine, histidine and methionine] a in the test sample and [lysine, tryptophan, isoleucine, valine, threonine, leucine, phenylalanine, histidine and the sum of methionine and cystine] b the content of the same amino acids in standard protein (%) (egg/casein), respectively. The nutritional index of the sample was also determined using the Crisan and Sands method [24] with the following formula: Nutritional index [%] = EAAI × % protein/100.

Determination of Other Protein Quality Parameters

The ratio of the total essential amino acids (TEAA) to the total amino acids (TAA), i.e., (TEAA/TAA), total sulphur amino acid (TSAA), percentage of cystine in TSAA (% Cys/TSAA), total aromatic amino acid (TArAA), total basic amino acid (TBAA), total acidic amino acid (TAAA), total neutral amino acid (TNAA), and the Leu/Ile ratios was calculated [24].

2.8. Fatty Acid Determination

The fatty acids of the samples and their methyl ether were estimated by gas chromatography, adopting the modified official method of AOAC 965.49. The separation of methyl ether was conducted using an HP 6890 Gas Chromatography analyser powered by HP Chem Station Rev A 09.11(1206), Hewlett-Pakard Enterprise, Johannesburg, South Africa.

2.9. Data Analysis

The experiments were conducted in triplicate and expressed as mean ± standard deviation (SD). Coefficient percentage (CV) was calculated using SPSS (Version 24). One way ANOVA and comparison analysis by Tukey post hoc was carried out using a Graph prism (version 6). p < 0.05 was considered as statistically significant.

3. Results

3.1. Amino Acid Compositions of Fermented, Defatted, and Protein Isolates of Parkia biglobosa Seeds

The amino acid composition of fermented (FPB), defatted (DPB), and protein isolate (PI) of Parkia biglobosa is presented in

Table 1. Amino acid compositions (mg/100 g protein) of fermented, defatted, and protein isolates of Parkia biglobosa seeds. Different alphabet (^a, ^b, ^c) showed a significant difference of p < 0.05. ND (not determined), SD (Standard deviation, CV % (coefficient of variation).

Non-Essential Amino Acids
Amino acids	FPB	DPB	PI	Mean	SD	CV%
Alanine	2.94 b	4.32 a	4.81 a	4.02	0.97	24.13
Aspartic acid	6.90 b	9.41 a	10.40 a	8.90	1.80	20.22
Serine	2.78 b	3.71 a	3.88 a	3.46	0.59	17.05
Glutamic acid	11.0 b	16.06 a	17.27 a	14.78	3.33	22.53
Total	23.62 b	34.49 a	35.37 a	31.16	6.54	20.98
Conditionally essential amino acids
Proline	3.22 b	4.84 a	4.86 a	4.17	0.84	20.14
Glycine	3.38 b	3.69 b	4.81 a	3.96	0.75	18.94
Arginine	3.49 b	4.43 a	4.59 a	4.17	0.59	14.15
Cystine	0.19 c	0.25 b	0.50 a	0.31	0.16	51.61
Tyrosine	4.46 c	5.01 b	6.02 a	5.16	0.79	15.31
Total	14.74 b	19.41 a	19.59 a	31.16	6.54	20.98
Essential amino acids
Lysine	5.36 b	5.75 b	8.44 a	6.52	1.68	25.77
Threonine	2.31 b	2.86 b	3.44 a	2.87	0.57	19.86
Valine	4.68 c	5.89 b	6.57 a	5.71	0.96	16.81
Methionine	0.50 c	0.69 b	0.83 a	0.67	0.17	25.37
Isoleucine	2.97 b	4.35 a	4.37 a	3.90	0.80	20.51
Leucine	5.75 c	7.10 b	8.11 a	6.99	1.18	16.88
Phenylalanine	4.81 c	5.31 b	6.16 a	5.43	0.68	12.52
Histidine	1.98 c	2.26 b	3.69 a	2.64	0.92	34.85
Trptophan	ND	ND	ND	ND	ND	ND
Total	28.36c	34.93b	40.89a	34.73	6.27	18.05

. The total non-essential amino acid was observed to be highest in the protein isolate sample (35.37 mg/100 g) compared to the defatted (34.49 mg/100 g) and fermented (23.62 mg/100 g) samples. In addition, PI showed the highest significant glutamic acid value (17.3 mg/100 g), whereas FPB showed the lowest serine values (2.8 mg/100 g) in the category of the tested non-essential amino acid. The PI (19.59 mg/100 g) also showed the highest total conditionally essential amino acid composition compared to DPB (19.41 mg/100 g) and FPB (14.74 mg/100 g) samples. However, tyrosine (6.02 mg/100 g) in DPB was the highest in total conditionally essential amino acids of the samples, whereas cystine (0.19 mg/100 g) in FPB showed the lowest. The PI (40.89 mg/100 g) showed the highest significant total essential amino acid composition compared to DPB (34.93 mg/100 g) and FPB (28.36 mg/100 g) samples. By comparing lysine and methionine, lysine (8.44 mg/100 g) in PI dominated the essential amino acid composition, whereas methionine (0.50 mg/100 g) in FPB showed the lowest value.

3.2. Nutritional Quality of the Fermented, Defatted, and Protein Isolates

The nutritional quality of the fermented, defatted, and protein isolates of Parkia biglobosa seeds is presented in

Table 2. Concentration of essential, non-essential, acidic, neutral, sulphur, aromatic acid (mg/100 mg), protein efficient ratio (PER), biological value (BV), iso-electric point (Pi), Leu/Ile ratio, Leu/Ile difference in fermented, defatted, and protein isolates of Parkia biglobosa seeds. Different alphabet (^a, ^b, ^c) showed a significant difference of p < 0.05. SD (Standard deviation), CV% (coefficient of variation).

Amino Acids	FPB	DPB	PI	Mean	SD	CV%
Total amino acid (TAA)	66.72 b	89.89 a	94.79 a	83.64	14.82	17.7
Total non-essential amino acid (TNEAA)	34.87 b	50.53 a	49.31 a	44.90	8.71	19.4
Total essential amino acid (TEAA) with His	31.85 c	39.36 b	45.21 a	38.74	6.60	17.0
Total essential amino acid (TEAA) with no His	29.87 b	37.10 a	41.31 a	36.09	5.77	15.9
% TNEAA	44.77 b	56.21 a	52.29 a	51.09	5.81	11.4
% TEAA with His	47.74 a	43.79 a	47.71 a	46.41	2.27	4.9
% TEAA with no His	44.76 a	41.27 a	43.80 a	43.28	1.80	4.2
Total neutral amino acid (TNAA)	37.99 b	50.77 a	51.21 a	46.66	7.51	16.1
% TNAA	53.94 a	54.30 a	56.48 a	55.91	1.41	2.52
Total acidic amino acid (TAAA)	17.90 c	26.68 b	20.46 a	24.21	5.51	22.8
% TAAA	26.82 b	29.68 a	28.06 a	28.19	1.43	5.1
Total basic amino acid (TBAA)	10.83 b	12.44 a	13.84 a	12.37	1.51	12.2
% TBAA	14.68 b	13.84 b	16.23 a	14.92	1.21	8.11
Total sulphur amino acid (TSAA)	0.94 c	1.33 b	0.69 a	0.99	0.32	32.3
% TSAA	1.03 a	1.48 a	1.00 a	1.17	0.27	15.8
% Cys/TSAA	27.54 a	37.59 b	26.60 a	30.58	6.09	19.9
Total aromatic amino acid (TArAA)	9.27 b	10.32 b	12.18 a	10.59	1.47	13.9
% TArAA	13.89 a	11.48 b	12.91 a	12.76	1.21	9.48
P-PER1	1.67 a	2.23 b	2.58b	2.16	0.46	21.30
Leu/Ile ratio	1.94 a	1.63 a	1.86a	1.81	0.16	8.84
Leu/Ile ratio (difference)	2.78 b	2.75 b	3.74a	3.09	0.56	14.36
% Leu/Ile (difference)
EAAI	73.06 c	78.95 b	82.15 a	78.05	4.61	5.91
BV	67.94 c	74.46 b	77.84 c	73.38	5.02	6.84
P-PER2	1.79 c	2.40 b	2.73 a	2.41	0.48	20.80
NI	28.06 c	36.79 b	48.80 a	38.88	10.41	26.83
Protein	38.4 c	46.6 b	59.4 a	48.13	10.58	21.98

. The PI (94.79) sample showed the significantly highest total amino acids when compared with the DPB (89.89) and FPB (66.72) samples. The DPB (56.21%) sample showed the highest total percentage of non-essential amino acids (% TNEAA) when compared with PI (52.29%) and FPB (44.77%) samples. The total essential amino acid percentage (% TEAA) values with histidine were 47.74%, 47.71%, and 43.79% for FPB, PI, and DPB, respectively, whereas the values for the total essential amino acid percentage (% TEAA) without histidine were 44.76%, 43.80%, and 41.27%, respectively. In comparison, PI (51.21) showed the significantly highest total neutral amino acid (TNAA), compared with DPB (50.77) and FPB (37.99) samples. The DPB (26.68) sample showed better total essential amino acid (TAAA) than the PI (26.46) and FPB (17.90) samples. The basic amino acid values (TBAA) were 13.84, 12.44, and 10.83 for the PI, DPB, and FPB samples respectively. The value of the DPB (1.33) sample for total sulphur amino acid (TSAA) was higher in comparison with the PI (0.94) and FPB (0.69) samples. The DPB (37.59%) sample showed the highest percentage cystine ratio of the total sulphur amino acid (% Cys/TSAA) when compared with the FPB (27.54%) and PI (26.60%) samples. The highest total aromatic amino acid (TArAA) was recorded in PI (12.18) when compared with DPB (10.32) and FPB (9.27). The predicted protein efficiency ratio (P-PER₁ and P-PER₂) of the samples was 1.67, 2.23, 2.58 to 1.79, 2.40, 2.73 for FPB, DPB, and PI, respectively. The values for the Leu/Ile ratio were 1.94, 1.86, and 1.63 for FPB, PI, and DPB, respectively. The PI (3.74) sample for the Leu/Ile ratio (difference) was higher compared with FPB (2.78) and DPB (2.75). The PI (82.15%) sample for the essential amino acid index (EAAI) showed the highest significant value compared to the DPB (78.95%) and FPB (73.06%) samples. The PI (77.84) sample showed the highest significant biological value (BV) compared to the DPB (74.46) and FPB (67.94) samples. The nutritional index (NI) of the PI (48.80) sample showed the highest significant values compared to the DPB (36.79) and FPB (28.06) samples. The PI (59.4) sample showed the highest significant protein content compared to the DPB (46.6) and FPB (38.4) samples.

3.3. Amino Acid Scoring Pattern

The amino acid scoring pattern of the samples, based on a whole hen’s egg is presented in

Table 3. Amino acid scores with respect to a whole hen’s egg (amino acids value were in mg/100 g’). FPB = fermented Parkia biglobosa, PI = protein isolate, DPB = defatted Parkia biglobosa. Different alphabet (a, b, c) showed a significant difference of p < 0.05. SD (Standard deviation), CV% (coefficient of variation).

Amino Acids	Hen Eggs	FPB	DPB	PI	Mean	SD	CV%
His	2.40	1.98 c	2.26 b	3.69 a	1.10	0.38	34.6
Ser	7.90	2.78 b	3.88 a	3.71 a	0.44	0.08	18.2
Arg	6.10	3.49 b	4.43 a	4.59 a	0.68	0.09	13.2
Gly	3.00	3.38 a	4.81 b	3.69 a	1.36	0.21	15.4
Asp	10.7	6.90 b	9.41 a	10.40 a	0.97	0.83	20.5
Glu	12.0	11.0 b	17.27 a	16.06 a	1.23	0.27	22.0
Thre	5.10	2.31 c	3.44 b	2.86 a	0.56	0.11	19.6
Ala	5.40	2.94 b	4.81 a	4.32 a	0.74	0.18	24.3
Pro	3.80	3.22 b	4.84 a	4.46 a	1.10	0.22	20.0
Cys	1.80	0.19 c	0.50 b	0.25 a	0.18	0.09	50.0
Lys	6.20	5.36 b	5.75 b	8.44 a	1.05	0.27	25.7
Met	3.20	0.50 b	0.83 a	0.69 a	0.09	0.02	22.2
Val	7.50	4.68 c	5.89 b	6.57 a	0.83	0.05	6.0
Ile	5.60	2.97 b	4.35 a	4.37 a	0.70	0.14	20.0
Leu	8.30	5.75 b	7.10 a	8.11 a	0.84	0.15	17.9
Phe	5.10	4.81 c	5.31 b	6.16 a	1.06	0.13	12.3
Tyr	4.00	4.46 c	5.01 b	6.02 a	1.61	0.25	15.5

. The PI sample showed the highest number of amino acid (Tyr > His > Lys > Glu > Gly > Phe > Pro) scores greater than one. The DPB sample also showed amino acid (Tyr > Gly > Glu > Pro > Phe) scores greater than one, whereas FPB showed two amino acid scores greater than one (Tyr > Gly). Methionine is the limiting amino acid for all the samples. The coefficient variation (CV%) ranges between 6.0 and 50.0. Cystine showed the highest CV% value.

3.4. Essential Amino Acid Scores Based on the Preschool Child Requirement

The essential amino acid scores of the samples, based on the preschool child requirement are presented in

Table 4. Amino acids scores with respect to preschool children’s requirements (amino acids value were in mg/100 g). Different alphabet (^a, ^b, ^c) showed a significant difference of p < 0.05. ND (not determined), SD (Standard deviation), CV% (coefficient of variation).

Amino Acids	Preschool	FPB	DPB	PI	Mean	SD	CV%
Leu	6.60	0.87 b	1.23 a	1.08 a	1.06	0.18	17.0
Ile	2.80	1.06 b	1.56 a	1.55 a	1.39	0.28	20.1
Met + Cys	2.50	0.28 c	0.38 b	0.53 a	0.40	0.13	32.5
Phe + Tyr	6.30	1.47 c	1.93 b	1.64 a	1.68	0.23	13.7
Thr	3.40	0.68 c	0.84 b	1.01 a	0.17	0.16	94.1
Val	3.50	1.34 c	1.88 b	1.68 a	1.63	0.27	16.7
His	1.90	1.04 c	1.94 b	1.19 a	1.39	0.48	34.5
Trp	1.10	ND	ND	ND	ND	ND	ND
Lys	5.80	0.92 a	1.46 b	0.99 a	1.12	0.29	25.9

. The following amino acid (Val > Pe + Tyr > His > Ile > Thr) values of the PI sample for EAAS are significantly greater than one with Met + Cys (0.53) as the limiting amino acid (LAA). Similarly, the DPB amino acid (His > Phe + Tyr > Val > Ile > Lys > Leu) values are greater than one with Met + Cys (0.38) as the LAA. FPB amino acids (Val > His > Lys > Phe + Tys > Ile > Leu) are also greater than one with Met + Cys (0.28) as the LAA. Histidine (34.5) was recorded as having the highest CV%, while Phe + Tyr showed the lowest.

3.5. Essential Amino Acid Scores (EAAS) Based on the Provisional Scoring Pattern

The essential amino acid scores (EAAS) of the samples, based on the provisional scoring pattern are presented in

Table 5. Amino acids scores with respect to provisional amino acid scoring pattern of FAO (amino acids values were in mg/100 g). Different alphabet (a, b, c) showed a significant difference of p < 0.05. ND (Not Determine), SD (Standard deviation), CV% (coefficient of variation).

Amino Acids	Scoring Value	FPB	DPB	PI	Mean	SD	CV%
Ile	4.00	0.57 b	1.09 a	1.09 a	0.92	0.30	32.6
Leu	7.00	0.82 c	1.01 b	1.16 a	0.99	0.17	17.2
Lys	5.50	0.97 c	1.05 b	1.53 a	1.18	0.30	25.4
Met + Cys (TSAA)	3.50	0.20 b	0.27 b	0.38 a	0.28	0.09	32.1
Phe + Tyr	6.00	1.55 c	1.72 b	2.03 a	1.77	0.24	13.6
Thr	4.00	0.58 b	0.86 a	0.72 a	0.77	0.14	18.2
Val	5.00	0.94 c	1.18 b	1.31 a	1.14	0.19	16.7
Trp	1.00	ND	ND	ND	ND	ND	ND

. The amino acid (Phe + Tyr > Val > Ile > Lys > Leu) values of the PI sample for EASS are greater than one with Met + Cys (0.38) as the LAA. The DPB amino acid values (Phe + Tyr > Lys > Val > Leu > Ile) are significantly greater than one while Met + Cys (0.38) served as the LAA. Phe + Tyr was the only amino acid value greater than one for FPB and Met + Cys (0.20) served as its LAA. A high CV% of 32.6 was recorded for Ile.

3.6. Fatty Acid Composition

The fatty acid composition of each sample is presented in

Table 6. Fatty acids composition of FPB, DPB and PI. Different alphabet (^a, ^b, ^c) showed a significant difference of p < 0.05. SD (Standard deviation), CV% (coefficient of variation).

		FPB	DPB	PI	Mean	SD	CV%
Fatty Acids
Lauric acid	C12.0	0.01 b	0.00 b	0.11 a	0.04	0.068	170
Mystic acids	C14.0	0.02 b	0.02 b	0.09 a	0.043	0.040	93
Palmitic acid	C16	9.5 c	8.76 b	14.64 a	10.97	3.202	29.2
Palmitoleic acid	C16.1	0.05 c	0.03 b	0.28 a	0.12	0.139	115.8
Stearic acid	C18.0	15.1 b	14.41 a	14.78 a	14.76	0.345	2.3
Oleic acid	C18.1	13.67 b	13.41 b	14.05 a	13.71	0.322	2.3
Linoleic acid	C18.2	42.29 b	41.94 b	26.7 a	36.98	8.902	24
Linolenic acid	C18.3	0.78 b	0.71 b	0.18 a	0.56	0.328	58.6
Arachidic acid	C20.0	11.33 b	12.05 b	9.37 a	10.92	1.387	12.7
Behenic acid	C22.0	0.08 b	0.03 b	0.27 a	0.13	0.127	97.7
Lignocenic acid	C24.0	0.05 b	0.04 b	0.39 a	0.16	0.199	124.4
Saturated Fatty Acid (SFA)
Myristic acid	C14.0	0.02 a	0.02 a	0.09 b	0.043	0.040	93
Palmitic acid	C16.0	9.5 b	8.76 b	14.64 a	10.97	3.202	29.2
Stearic acid	C18.0	15.1 b	14.41 a	14.78 a	14.76	0.345	2.3
Behenic acid	C22.0	0.08 b	0.03 b	0.27 a	0.13	0.127	97.7
Total		24.7 a	23.22 a	29.78 a	25.9	3.44	13.3
Polyunsaturated Fatty Acid (PUFA)
Linoleic acid	C18.2	42.29 b	41.94 b	26.7 a	36.98	8.902	24.1
Linolenic acid	C18.3	0.78 b	0.71 b	0.18 a	0.56	0.328	58.6
Arachidonic acid	C20.4	0.03 b	0.03 b	0.25 a	0.10	0.13	1.3
Docohexanoic acid	C22.6
Total		43.1 b	42.68 b	27.13 a	36.64	9.10	24.8
Monosaturated Fatty Acid (MUFA)
Palmitoleic acid	C16.1	0.05 a	0.03 b	0.28 a	0.12	0.139	115.8
Oleic acid	C18.1	13.67 b	13.41 b	14.05 a	13.71	0.322	2.3
Total		13.72 b	13.44 b	14.33 a	13.83	0.46	3.3
P:S		1.74 b	1.84 b	0.91 a

. The results revealed that linoleic acid dominated the fatty acid composition in FPB (42.29%), DPB (41.94%), and PI (26.7%), while lauric acid showed the least value. Stearic acid dominated the saturated fatty acid (SFA) composition in FPB (15.1%), DFB (14.41%), and PI (14.78%), while myristic acid was the least in all the samples. FPB (43.1%) was the highest total polyunsaturated acid (PUFA) when compared to DPB (42.68%) and PI (27.13%). Linoleic acid dominated the polyunsaturated fatty acid composition in the samples. Oleic acid had the highest concentration of monounsaturated fatty acid, with PI (14.05%), FPB (13.67%), and DPB (13.41%). FPB (1.84) had the significantly highest polyunsaturated/saturated (p:s) ratio, while PI (0.91) was the lowest. Lauric acid had the highest CV values.

4. Discussion

Food processing has an important role in achieving nutrition and food security [15]. The nutritional qualities of plant proteins are based on their amino acid and fatty acid composition [25]. In this study, the protein isolates from Parkia biglobosa exhibited a wider spectrum of the highest amino acid content when compared with the fermented and defatted samples (Table 1). The processing of food products has been demonstrated to improve their functional properties and nutritive values [26]. Our findings revealed that glutamic acid and aspartic acid are the most abundant amino acids in the PI sample. This finding is in accordance with that reported by Audu et al. [27] on black turtle beans, in which the legume contains a high level of glutamic and aspartic acids. Similarly, protein isolated from red kidney beans has been reported to contain a high level of glutamic acid and aspartic acid [28,29]. Glutamic acid plays a key role in cellular metabolism and brain function [30,31]. Glutamic acid is also a precursor of gamma-aminobutyric acid (GABA), which is found in abundance in the pancreas and cerebellum. During neurological syndromes, such as stiff-man syndrome, there is a decrease in the synthesis of GABA, triggering an autoimmune destruction of the pancreas that results in diabetes mellitus in the patient [32]. The detoxification and cardioprotective potential of glutamic acid have also been reported in plant seeds [33]. Aspartic acid also plays a major role in brain function, gluconeogenesis, and the stimulation of growth hormones [34]. The PI samples could, therefore, be used to ameliorate mental retardation, cardiovascular diseases, and other diabetic complications. Protein isolate samples from grains such as corn and wheat are reported to be lower in lysine. Lysine improves body mass and lowers anxiety, glucose, and osteoporosis [35]. The lysine value for the PI sample was observed to be within the range of the egg reference protein (6.3 g/100 g) [36]. The value (3.31–3.69 g/100 g) of lysine in the PI sample was better when compared to the value (5.36–8.44 mg/g) previously reported in respect of the Moringa oleifera tree [37]. This implies that the sample could serve as a good source of cereal fortification in weaning foods. Leucine has been reported to enhance protein synthesis, which plays a vital role in muscle building [38]. The value of leucine in the PI sample (8.30 g/10 g) was similar to pigeon peas (8.40 g/100 g) and higher when compared with Africa yam beans (7.45 g/100 g) (Table 3) [39]. Histidine plays an important role in child growth, while arginine has been reported to increase insulin sensitivity and vasodilation of coronary arteries [40,41]. Arginine and histidine values in the PI sample (Table 4) were observed to be higher than the recommended values for preschool children (2–5 years old) and adults [36]. Therefore, the sample could serve as a remedy for metabolic complications in child growth. Cystine values were observed to be the least concentrated amino acids in all the samples. This supports the previous report that cystine is the limiting amino acid in legumes [42].

The nutritive value of the protein source depends on its essential amino acid composition and ability to meet nitrogen demand [43]. The values of the percentage total essential amino acid (TEAA) with histidine for the PI sample (Table 2) were similar to some non-convectional animal sources, such as Achatina achatina, Achatina marginata, and Phaseolus vulcaris L. [43,44]. The PI % TEAA value is within the recommended standard for infants (26%) and adults (11%) [20]. The high content of essential amino acids in the PI sample implies that they could be used in the complementary treatment of protein malnutrition. Aromatic amino acids are the precursors of thyroxine and epinephrine, which are important in many biological functions [20]. The TArAA values of the PI sample are within the recommended ranges (6.8−11.8 g) for infant protein [25]. The PI value (Table 2) for TArAA was also higher than the value (3.9–5.3 g/100 g) previously reported by Audu et al. [27] on Phaseolus vulgaris L. but similar to the values (9.9–21.5) reported by Aremu et al. [30]. The PI samples are basic in nature because they have lower total amino acids (TAAA) and total sulphuric amino acids (TSAA) but with higher basic amino acids. Most plant proteins have a higher level of cystine/TSAA ratio, whereas in animal proteins the ratio is lower [45]. The cystine/TSAA ratio value (37.59 g/100 g) for the PI sample was observed to fall within the animal protein range. This finding was contrary to the previous report of Adeyeye [46] on fermented Parkia biglobosa seeds (44.4 g/100 g).

The predicted protein efficiency ratio (PER) is used in protein evaluation by measuring the effectiveness of protein through growth [17]. The PER value for the PI sample (Table 2) was observed to be higher than some reported legumes, such as cowpea (1.21) and millet (1.62), but similar to pigeon pea (1.82) and casein (2.7) [29]. This could imply that the sample is a good source of protein. The efficiency of protein utilisation in the body is determined by biological values (BV). Animal BV values are usually higher than plant sources due to the presence of limiting amino acids [29]. Our finding showed that the biological values (BV) for the PI sample (Table 2) compared favourably well with some BV reference standards such as wheat gluten (64), soy protein (74), and casein (77) [29]. The essential amino acid index (EAAI) is a useful tool in ascertaining food formulation for protein quality [47]. Despite that, it does not account for the difference in protein due to the various processing methods. The EAAI values for the PI sample (Table 2) compared favourably well with some standard references like soybeans (72.8), beef (74.3), fish (76.0), and milk (84.5) [48,49]. The Leu/Ile ratio of the samples (Table 2) was observed to be lower in comparison with the recommended value (2.36) [17]. The high level of leucine in a diet is known to impair niacin and tryptophan absorption in the gastrointestinal tract, which may lead to pellagra [41]. Hence, the sample could serve as an added advantage to amino acid balance in complementing cereals that are higher in leucine but low in leucine and tryptophan.

The amino acids scores (AAS) for the samples compared favourably with whole hen’s egg profiles, preschool child requirements, and provisional scoring patterns [20]. Met + Cys (TSAA) are the limiting amino acids (LAA) for all the samples (Table 5). This was in accordance with the previous reports by Audu et al. [27] and Aremu et al. [49]. This implies that Met + Cys (TSAA) could be supplemented with the samples to meet standard daily requirements.

The essential neutral fatty acids, stearic acid, and oleic acid dominated the saturated fatty acids and monounsaturated fatty acids of the samples, respectively (Table 6). Oleic acid has previously been reported to be the monounsaturated fatty acids dominant in some plant foods [50]. Oleic acids are also found predominately in olive, macadamia nut, peanut, and canola oils [51]. Essential neutral fatty acids have been demonstrated to not effect cholesterol. Abnormal cholesterol synthesis has been associated with cardiovascular diseases [52]. The polyunsaturated fatty acids showed the highest values when compared with saturated and monounsaturated fatty acids in the fatty acid composition (Table 6). Plant food, such as avocados, was reported to be rich in polyunsaturated fatty acids [50]. Linoleic acid is the dominant polyunsaturated fatty acid; this was validated previously in a report by Ijarotimi and Keshinro [50]. Adequate intake of essential fatty acids such as linoleic acid could prevent cardiovascular diseases and diabetes [37]. Due to the high rate of potential hazards attributed to the consumption of saturated fatty acids, emphasis is now laid on the consumption of food, which has a high polyunsaturated to saturated fatty acid ratio because of the potential health benefits [50].

5. Conclusions

This study revealed that processing significantly influenced the amino acid and fatty acid content of the samples. The PI sample possessed good nutritional value using the selected nutritional parameters compared to other tested samples. Therefore, PI could serve as a promising complementary food supplement or nutraceutical agent in the management of metabolic diseases in both infants and adults, especially in low-income earners. For future studies, the hypoglycaemic and hypolipidemic potentials of the samples need to be ascertained.