PHYSICO-CHEMICAL CHARACTERISTICS OF PEARL MILLET CULTIVARS GROWN IN NORTHERN NIGERIA

ABSTRACT

Thirty-one millet cultivars grown in Northern Nigeria were evaluated for physical properties and chemical composition. The physico-chemical characteristics were also correlated. There were wide variations in thousand-kernel weight (8.1–12.1 g) and volume (5.8–10.0 ml), grain hardness (30.3–68.0 N), per cent floaters (31.0–95.0%), in addition to considerable variations in protein (9.6–12.7%), fat (3.3–5.2%), crude fibre (1.2–4.4%) and tannin (0.0–2.8% catechin equivalent) contents. The grain hardness correlated positively with crude protein (r=0.687, P<0.01). Crude protein content correlated positively with grain major diameter (r=0.538, P<0.01), thickness (r=0.529, P<0.01) and correlated negatively with carbohydrate (r=−0.473, P<0.01). The density of the grain showed significant positive correlation, with grain hardness (r=0.435, P<0.01), grain thickness (r=0.568, P<0.01) and moisture content (r=0.430, P<0.01) but negative correlated (r=−0.403, P<0.01) with per cent floaters.

Keywords:

• Pearl millet
• Crude protein
• Grain hardness
• Grain thickness
• Density

INTRODUCTION

Pearl millet is an indispensable food for millions of people inhabiting the semi arid tropics, and is more important in the diet of poor. It is used primarily for human food and remains a major source of calories and a vital component of food security in the semi arid areas in the developing world [1]. The crop can be produced on light, well-drained soils that are poor in organic matter and low rainfall [1].

The states that produce millet in large quantities in Nigeria are Borno, Yobe, Kano, Sokoto, and Jigawa [2]. As the desert encroachment persist, more states may be involved in the production of millet, being desert resistant crop 3-4. Pearl millet is the most common grain produce in those states in Nigeria where maize and sorghum cannot be grown due to drought and poor sandy soils.

Pearl millet is processed in so many ways for preparation of various food products. Some of the primary processes employed are de-hulling and milling in order to produce flours, grits and de-hulled whole grains. These intermediate products are used to prepare staple foods like cooked whole grain, thin and thick porridges, steam cooked products, for example couscous, burabosko, kunun zaki, preparation of tuwo and fura [3]. Millet can also be malted to produce alcohol/non alcoholic beverages and weaning foods 5-7. Relative little information on specific types of pearl millet that have optimum properties for each of these food systems in Nigeria is currently available. The knowledge of physical characteristics and chemical composition of millet cultivars is very important to food processors and nutritionist. The food processors need to understand what they are working with and what happen to the quality of the gains when they are subjected under various conditions of food processing. The nutritionists are interested in the nutrient composition of the food products in order to determine its nutritional value. Therefore, the present paper reports the physical characteristics and chemical composition of 31 millet cultivars and the relationships between them.

MATERIALS AND METHODS

Thirty-one [31] millet cultivars, comprising of local and improved ones were obtained from International Crops Research Institute for the Semi Arid Tropics (ICRISAT) experimental station at Bagauda, Kano and Lake Chad Research Institute, Maiduguri, Nigeria.

Sample Preparation

The Pearl millet grains were cleaned manually of broken seeds, dust and other extraneous materials. Experimental samples were taken using the quartering procedures of Lees [8].

Physical Characteristics

One thousand kernels of the whole grains were manually counted and their weights determined. One thousand kernels volume was measured by Archimede's principle. Based on weight and volume, the density was calculated. Major diameter, minor diameter and thickness of the grains were measured with vernier calliper, vernier calliper and micrometer screw guage respectively, as described by Sefa-Dedeh and Stanley [9]. Grain hardness was measured with hardness tester (Erweka, BH 30, made Germany). Percent floaters were determined based on the floatation of kernels in a solution of sodium nitrate of known density 10-11.

Chemical Composition

AOAC [12] methods were used to determine the moisture, fat (Petroleum ether extract), ash, crude fibre and protein by Kjeldahl method. Soluble carbohydrate was determined by difference. Tannin content was determined based on the reduction of ferric ions to ferrous ions by tannins and other polyphenols followed by the formation of a coloured ferricyanide-ferrous complex known as Prussian blue [13]. The intensity of the colour formed enables the tannin content to be determined, using a set of standard solutions as reference.

All the determinations were done in triplicate and reagents were of analytical grade.

Statistical Analysis

The mean and standard deviations were calculated for each parameter based on 31 millet cultivars. Analysis of Variance (ANOVA) was used to determine differences among cultivars and means compared using Duncan Multiple Range Test (DMRT). The correlation coefficients among the various physical characteristics and chemical composition were also determined with computer using statistical programme, statistix, version 4.1, U.S.A [14].

RESULTS AND DISCUSSION

Physical Characteristics

Table 1 shows the physical characteristics of the 31 millet cultivars. The major diameter, minor diameter and thickness of the grains ranged from 2.8 to 3.7 mm, 1.7 to 3.3 mm and 1.4 to 1.9 mm respectively. The density of grains ranged from 1.1 to 1.3 g/ml, while grain hardness ranged from 30.3 to 68.0 N and per cent floaters ranged from 48.3 to 95.0%. Wide variations in thousand kernel weight, volume and hardness of millet grains have also been reported 15-16.

Table 1. Physical Characteristics of Millet Cultivars^1,2

	Parameter
Millet Cultivar	Major Diameter (mm)	Minor Diameter (mm)	Thickness (mm)	1000 Grain Weight (g)	1000 Grain Volume (ml)	Density (g/ml)	Grain Hardness (N)	Percent Floaters (%)
GB 8735	3.09^bcde	2.05^abcdefgh	1.69^k	8.91^s	7.83^l	1.14^q	43.67^d	79.33^de
SOSAT C-88	3.70^a	2.13^abcdef	1.80^cd	12.06^a	9.83^b	1.23^h	44.67^d	95.00^a
ICMV-1S 89305	3.27^abcde	2.06^abcdefg	1.75^fg	9.75^m	8.83^f	1.15^p	51.00^c	80.00^de
BUDUMA	3.25^abcde	1.74^h	1.44^q	7.15^x	5.83^s	1.23^h	34.67^ef	58.00^i
ICMV-1S 86330	3.22^abcde	2.16^abcdef	1.81^c	10.33^i	8.67^g	1.20^m	30.33^f	94.33^a
INMV 83	3.24^abcde	2.09^abcdef	1.84^b	8.85^t	7.17^o	1.24^hg	51.67^c	71.33^gh
IKMV 8201	3.37^abcd	1.87^fgh	1.66^l	10.17^k	8.33^i	1.22^ij	47.33^cd	82.33^cd
GWAGWA	3.42^abcd	2.10^abcdef	1.76^f	9.58^n	7.83^1	1.22^hi	35.33^e	68.00^h
EX-BORNO	3.43^abc	1.75^gh	1.50^op	8.32^w	6.67^q	1.25^g	41.00^d	80.33^de
BAGAUDA LOCAL	3.23^abcde	2.11^abcdef	1.81^c	11.58^c	9.33^d	1.24^h	50.67^c	68.33^h
LCRI-IC 9701	3.06^bcde	2.02^abcdefgh	1.73^gh	8.92^s	7.00^p	1.28^cd	39.00^de	39.33^m
LCRI-IC 9702	3.25^abcde	2.31^a	1.81^c	11.50^d	10.00^a	1.15^p	68.00^a	79.00^de
LCRI-IC 9703	3.09^bcde	1.98^bcdefgh	1.71^ij	9.73^m	8.00^k	1.22^jk	40.33^d	51.00^jkl
ZATIB	2.97^cde	1.99^bcdefgh	1.77^f	8.99^r	7.00^p	1.28^b	44.33^d	23.00^fg
G.I. 14-9	3.24^abcde	2.08^abcdef	1.73^gh	10.46^h	8.17^j	1.28^b	41.33^d	31.00^n
ICMV-1S 88305	3.24^abcde	2.13^abcdef	1.74^fg	9.38^o	7.17^o	1.31^a	65.00^ab	55.00^ij
ICMV-1S 90309	3.26^abcde	1.91^efgh	1.51^o	9.71^m	8.17^j	1.19^n	38.67^e	77.00^ef
ICMV-1S 94208	3.28^abcde	2.26^abc	1.81^c	10.59^g	8.83^f	1.20^m	49.33^c	58.00^i
ICMV 86-3	2.96^cde	2.06^abcdefg	1.82^c	9.28^P	7.33^n	1.27^ef	59.67^b	38.33^m
ICMV-1S 94206	3.14^bcde	2.20^abcde	1.85^ab	10.90^f	8.83^f	1.23^g	52.33^c	58.67^i
G.I. 297-1	2.91^de	2.29^ab	1.79^de	10.26^j	8.50^h	1.21^l	58.00^b	39.00^m
ICMV 93501	2.84^e	1.93^defgh	1.57^n	9.20^q	7.67^m	1.20^m	44.33^d	53.00^ik
ACC 364-1	3.14^bcde	2.09^abcdef	1.80^cq	8.70^k	7.17^o	1.21^kl	60.67^b	48.33^l
ACC 680-5	3.54^ab	2.07^abcdef	1.80^cq	10.58^g	8.33^i	1.27^de	53.00^c	38.00^m
INMV 89	2.81^e	1.97^cdefgh	1.72^hi	8.93^rs	7.00^P	1.28^b	59.00^b	49.00^kl
PM 573	3.06^bcde	2.24^abcd	1.82^c	9.99^l	8.17^j	1.22^hi	37.00^e	78.00^e
PM 584	3.19^abcde	2.14^abcdef	1.84^b	10.43^h	9.00^e	1.18^o	34.00^f	93.33^a
PM 596	3.29^abcde	2.03^abcdefgh	1.72^hi	11.03^e	9.00^e	1.23^hi	52.33^c	68.00^h
PM 601	3.29^abcde	2.17^abcdef	1.82^c	10.30^ij	8.33^i	1.24^hg	41.67^d	87.33^b
PM 608	3.22^abcde	2.23^abcd	1.87^a	11.92^b	9.67^c	1.23^g	38.00^e	87.33^b
ZANGO	3.02^cde	2.08^bcdef	1.73^gh	8.63^v	6.83^q	1.26^f	48.33^c	86.33^bc

¹Mean of several determinations. ²Means with each column not followed by the same letter are significantly different (P<0.05)

Physical characteristics of grains are determined for various reasons. Grain dimensions are very important in cleaning, specifically threshing operations. In these operations, screens are necessary, because it allows the passage of specific size of the grains and various unwanted materials [17]. Grain density is a useful information for transporters, marketers and percent floaters is an indirect method of determining grain density, which is also a measure of hardness.

Grain hardness is very important factor in determining grain quality. Milling quality is influenced by grain hardness. Harder grains give higher milling yield and also influence water absorption, which in turn has an effect on diastatic enzyme activity [18].

Chemical Composition

The chemical compositions of the 31 millet cultivars are shown in Table 2. Moisture content of the millet cultivars ranged from 5.9 to 7.7% and protein from 9.6 to 5.2%, whereas the ash content from 1.2 to 1.6%. Crude fibre and soluble carbohydrate contents ranged from 1.5 to 4.4% and 71.9 to 76.4% respectively. Mean values of the chemical composition were similar to those reported by Kurien et al. [19], Subramanian et al. [20] and Hadimani et al. [16]. Tannin content of the millet cultivars reported as per cent catechin equivalent (% C.E.) ranged from 0 to 2.8. The values were similar to values reported by Khetarpaul and Chauhan [21].

Table 2. Chemical Composition of Millet Cultivars^1,2

	Parameter
Millet Cultivar	Moisture (%)	Protein (%)	Fat (%)	Ash (%)	Crude Fibre (%)	Soluble CHO (%)	Tannin C.E. (%)
GB 8735	6.04^lm	11.29^de	4.01^jkl	1.41^cd	4.32^ab	72.94^lmnop	0.00^l
SOSAT C-88	7.23^cde	10.91^efg	3.92^klm	1.29^fghij	1.38^opq	75.28^bcdef	0.00^l
ICMV-1S 89305	6.56^ghi	12.32^ab	3.79^lm	1.19^ik	4.20^b	71.94^pq	0.43^ef
BUDUMA	6.75^fg	10.53^ghi	4.20^hij	1.49^abc	1.61^lmn	75.50^abcde	0.37^fg
ICMV-1S 86330	5.88^m	10.23^hij	4.09^jk	1.41^cd	2.63^fg	75.77^abcd	0.47^e
INMV 83	7.39^bc	10.14^ijk	3.69^m	1.26^ghijk	1.29^pq	76.23^ab	2.83^a
IKMV 8201	6.45^hijk	11.15^def	4.44^efgh	1.31^efghi	2.43^ghi	73.19^klmno	0.47^e
GWAGWA	6.34^ijkl	9.69^jk	4.51^defg	1.46^bcd	2.52^gh	75.53^abcde	0.00^l
EX-BORNO	6.46^hij	12.05^bc	4.25^ghij	1.52^ab	3.56^a	72.17^opq	0.00^l
BAGAUDA LOCAL	6.37^ijkl	11.18^def	4.02^jkl	1.59^a	1.78^kl	75.07^cdefg	0.13^k
LCRI-IC 9701	7.37^c	10.50^ghi	4.81^bc	1.28^fghij	4.32^ab	71.74^q	0.00^l
LCRI-IC 9702	7.07^de	10.76^fgh	4.75^bc	1.35^defgh	2.45^ghi	73.63^ijklm	0.20^j
LCRI-IC 9703	6.60^ghi	9.73^jk	4.52^def	1.36^defgh	1.91^k	75.89^abc	0.13^k
ZATIB	6.43^hijk	10.14^ijk	5.17^a	1.37^def	2.54^gh	74.35^fghij	0.13^k
G.I. 14-9	7.66^a	10.53^ghi	4.63^bcd	1.28^fghij	3.21^e	72.64^mnopq	0.00^1
ICMV-1S 88305	7.32^cd	10.63^fghi	4.68^bcd	1.43^bcd	1.46^nop	74.83^defgh	1.33^d
ICMV-1S 90309	6.36^ijkl	11.28^de	4.88^b	1.31^efghi	2.27^ij	73.91^hijkl	0.37^fg
ICMV-1S 94208	6.81^fg	12.53^ab	4.58^cdef	1.41^bcde	1.74^klm	72.93^lmnop	0.00^1
INKMV 86-3	6.66^gh	9.60^k	4.61^cdef	1.27^fghij	3.82^c	74.05^ghijk	0.40^ef
ICMV-1S 94206	6.22^jklm	9.82^jk	4.55^cdef	1.47^bcd	1.57^mno	76.38^a	0.00^1
G.I. 297-1	6.76^fg	10.99^defg	4.21^hij	1.16^k	3.36^de	73.52^ijklmn	0.00^1
ICMV-1S 93501	6.19^jklm	10.22^hij	4.50^defg	1.51^abc	2.19^j	75.39^abcdef	2.17^b
ACC 364-1	6.11^klm	11.51^cd	4.67^bcd	1.42^bcd	4.42^a	71.88^q	0.20^i
ACC 680-5	7.19^cde	11.47^cde	4.32^hij	1.24^ijk	1.68^lm	74.54^efghi	1.67^c
INMV 89	7.23^cde	11.38^de	4.38^fghi	1.19^jk	3.31^e	72.51^nopq	0.43^ed
PM 573	7.53^c	9.77^jk	3.26^n	1.24^ijk	3.27^e	75.12^cdef	0.33^gh
PM 584	6.78^fg	12.69^a	3.30^n	1.23^ijk	1.21^q	74.80^defg	0.37^fg
PM 596	6.41^hijk	11.55^cd	4.62^bcd	1.43^bcd	2.40^hij	73.55^ijklmn	0.40^ef
PM 601	6.98^ef	11.95^bc	4.17^ijk	1.26^hijk	2.20^j	73.45^jklmn	0.30^hi
PM 608	6.35^ijkl	11.96^bc	4.25^ghij	1.44^bcd	2.77^f	73.24^klmn	2.83^a
ZANGO	7.63^ab	9.61^k	4.66^bcd	1.37^defg	2.30^ij	74.44^fghij	0.00^1

¹Mean of several determinations. ²Means within each column not followed by the same letter are significantly different (P<0.05). CE=Catechin Equivalent. CHO=Carbohydrate.

There was good correlation between most of the physical characteristics and chemical compositions (Table 3). Per cent floaters was highly negatively correlated (P<0.01) with thousand kernels volume. Density, carbohydrate, major diameters were highly positively correlated (P<0.01) with grain thickness, while crude fibre was negatively correlated with soluble carbohydrate (P<0.01). No correlation was observed between tannin content with other parameters. Moisture content of the grains correlated (P<0.01) with ash. Similar results have been obtained by Hadimani et al. [16].

Table 3.Correlation Analysis Between Physical Characteistics and Chemical Composition of Millet Cultivars

	PFT														TGV	TGW	DEN	GHS	FBR	CHO	MJD	MND	TKS	TAN	ASH	FAT	MTR
TGV	0.330^a
TGW	0.125	0.717^b
DEN	−0.403^b	−0.401	0.012
GHS	−0.522^b	−0.202	0.076	0.435^b
FBR	−0.124	−0.048	0.423^b	−0.220	0.021
CHO	0.223	0.124	0.308	−0.076	−0.172	−0.585^b
MTD	0.361^a	0.242	0.610^b	0.331	0.202	0.101	0.723^b
MND	0.301	0.215	0.582^b	0.221	0.200	0.009	0.628^b	0.782^b
TKS	−0.423^b	0.124	0.432^b	0.568^b	0.112	0.263	0.621^b	0.681^b	0.723^b
TAN	0.102	0.111	0.321	0.210	0.262	−0.101	−0.200	0.008	0.006	0.028
ASH	0.105	−0.081	0.142	−0.003	−0.156	−0.145	0.162	0.021^b	0.513^b	0.482^b	−0.103
FAT	−0.531^b	−0.187	0.062	0.372	0.167	0.037	−0.214	0.582^b	0.331	0.432^b	−0.121	0.196
MTR	−0.199	−0.180	−0.009	0.430^b	0.259	−0.162	−0.032	0.210	0.125	0.128	0.105	−0.496^b	0.076
CPT	0.270	0.319	0.088	−0.305	0.687^b	0.028	−0.473^b	0.538^b	0.621^b	0.529^b	−0.120	−0.140	−0.338	−0.120

PFT; per cent floaters: TGV; 1000 grain volume: TGW; 1000 grain weight: Den; Density: GHS; Grain hardness: FBR; crude fibre: CHO; soluble carbohydrate: MJD; major diameter: MND; Minor diameter; TKS; Thickness; TAN; Tannin; MTR; Moisture: CPT; Crude protein. ^aSignificant at 5% level (P<0.05). ^bSignificant at 1% level (P<0.01).

CONCLUSION

Results obtained in this study revealed wide variations among the 31 millet cultivars with regard to physico-chemical characteristics. Crude protein was the only chemical constituent that influenced grain hardness. Grain hardness, grain thickness and moisture content had influence on density.

ACKNOWLEDGEMENTS

This study was supported in part by ROCAFREMI (A French word meaning, West and Central Africa Millet Research Network-WCAMRN). The technical support of Messrs I. Agarawai and E.O. Adejunio, both of Lake Chad Research Institute, Maiduguri, Nigeria, is gratefully acknowledged.