Grain physical properties

Chapter 3 Grain properties and the nutritional composition of Bambara groundnut and

3.6 Results and discussion

3.6.1 Grain physical properties

CIE colour values (Hunter L*, a* and b*) of the whole grain, oven dried grains and flours of each grain variety are presented in Table 5.

112 Table 5. The CIE colour values (Hunter L*, a* and b*) of the whole grains, oven dried grains and flours of white maize, PABM, brown and red BGN varieties

Sample

Mean ± SD

L a* b*

Whole grains

White maize (reference) 70.58 ± 0.19^a 3.19 ± 0.02^a 25.98 ± 0.17^a Yellow PABM (control) 65.68 ± 0.21^b 13.86 ± 0.17^b 38.42 ± 0.47^b

Brown BGN 44.34 ± 0.18^c 13.33 ± 0.08^c 23.65 ± 0.10^c

Red BGN 28.62 ± 0.11^d 20.33 ± 0.05^d 15.02 ± 0.26^d

Oven dried grains

White maize (reference) 68.91 ± 0.12^a 1.67 ± 0.05^a 33.70 ± 0.02^a Yellow PABM (control) 62.78 ± 0.05^b 10.11 ± 0.09^b 46.61 ± 0.30^b

Brown BGN 30.85 ± 0.12^c 10.60 ± 0.06^c 14.14 ± 0.14^c

Red BGN 23.95 ± 0.14^d 11.04 ± 0.08^d 7.11 ± 0.24^d

Flour

White maize (reference) ) 75.11 ± 0.01^a 4.11 ± 0.01^a 12.80 ± 0.01^a Yellow PABM (control) 67.25 ± 0.02^b 6.17 ± 0.01^b 15.33 ± 0.01^b

Brown BGN 65.26 ± 0.01^c 6.22 ± 0.02^c 12.65 ± 0.00^c

Red BGN 75.10 ± 0.01^d 4.11 ± 0.01^d 12.80 ± 0.01^d

L* Measure of lightness (0 = black to 100 = white) a* Measure of redness and (+a = redness; -a = greenness) b* Measure of yellowness (+b = yellowness; -b = blueness)

a, b, c, d denotes that there was significant difference (p<0.05) amongst the means

113 There was a significant difference (p<0.05) between the L*, a* and b* of the whole grains, oven dried grains and the flours of each grain variety, respectively. Confirming visual appearance of the whole and oven dried grains, the reference sample (white maize) had the highest L* values followed by the control sample (yellow PABM), brown BGN and red BGN grains, although the L* values of the oven dried grains were slightly lower than those of the whole grains. However, in terms of a* values, the red BGN variety had the highest L* values whereas the reference sample grain had the lowest a* values. The whole and oven dried grains of the control had the highest b* values followed by the reference c, brown BGN and red BGN. When compared with whole and oven dried grains, the L* values of the flours were higher. In general, all the flours had higher L* values and lower a* values which is desirable in developing instant porridges.

The L*, a* and b* values of the yellow PABM of the current study were slightly higher than the values reported by Pillay et al. (2011) and Beswa et al. (2015). The L* and b* values of the white maize in this study were however higher whereas a* values lower than those reported Beswa et al. (2015). The L*, a* and b*colour values of the PABM grain studied by Pillay et al.

(2011) ranged from 53.6 to 57.0; 16.5 to 25.7 and 29.3 to 37.5 whereas those studied by Beswa et al. (2015) ranged from 36.4 to 42.3, 11.5 to 19.8 and 24.0 to 33.6, respectively. The L*, a* and b* values of the white maize studied by Beswa et al. (2015) were 46.3, 6.3 and 24.6, respectively.

There was however no literature found on the L*, a* and b* values for the whole grains, oven dried grains and flours of the BGN varieties and that of the oven dried grains and flours of both of the maize varieties.

The lower L* and a* values of the oven dried grains compared to those of the whole grains could have been attributed to the reactions that took place during drying such as evaporation and Millard reactions which causes some changes in the colour (i.e. browning) of the grains. The high L*, a* and b* of the control, red BGN and yellow PABM is expected since the grains are white, red and yellow in colour, respectively. Hence the high degree of lightness, redness and yellowness in the respective grains. The yellow colour of the biofortified maize is due to PVA carotenoids. The high L* values of the flours in this study could have been attributed to milling which reduces the particle size of the grain. The smaller particles of the flours cause low light

114 absorption and more spectral response contributing to the whiteness L* attenuation (Galvez and Resurreccion 1993). Hence, the flours in this study are suitable for developing instant porridges since they generally have high L* and low a* values which is desirable in porridge making.

3.6.1.2 Grain texture

The results for the texture of the whole grains of white maize, yellow PABM, brown and red BGN varieties determined at 20, 30 and 40% moisture content are shown in Table 6.

Table 6. The texture of the whole grains of white maize, yellow PABM, brown and red BGN grain varieties [Newtons (N)]

Grain variety

Moisture content

Firmness Toughness

Mean ± SD P value Mean ± SD P value White

maize (reference)

20% 19805.9 ± 3474.9^a

0.401

19406.9 ± 5686.8^a

0.107

30% 17688.7 ± 7035.3^a 25095.3 ± 3030.1^a

40% 15327.3 ± 3830.4^a 19759.1 ± 3838.3^a

Yellow PABM (Control)

20% 29101.2 ± 6708.9^a

0.027

25529.1 ± 7055.8^a

0.564

30% 19883.4 ± 7296.6^a 26945.7 ± 3072.8^a

40% 17227.7 ± 4461.4^b 23037.0 ± 6203.2^a

Brown BGN

20% 21908.2 ± 2567.8^a

0.139

70148.9 ± 14884.0^a

0.097

30% 15278.1 ± 1654.0^a 52430.9 ± 9447.5^a

40% 16589.0 ± 8362.8^a 66382.7 ± 12105.2^a

Red BGN 20% 19931.4 ± 4123.2^a

0.078

64408.8 ± 18205.9^a

0.042

30% 15605.8 ± 2266.0^a 60208.0 ± 6197.9^a

40% 14306.3 ± 4320.1^a 42003.2 ± 11788.0^a

a, b Means marked with different letters in the same column are significantly different (p<0.05)

115 The results in Table 6 above show that there was a significant difference (p<0.05) in the firmness of the yellow PABM (control) and in the toughness of the red BGN grains. The firmness of the white maize (reference), yellow PABM and red BGN decreased with an increase in moisture content of the grains from 20 to 40%. There was no clear-cut trend in the mean values for the firmness of the brown BGN grains with respect to an increase in moisture content from 20 to 40%. The toughness of the red BGN grain however decreased with an increase in moisture content whereas there was no cut trend in the toughness of the reference, control and brown BGN as the moisture content of the grain increases.

The findings of this study are different from those reported by Zhang et al. (2007) where there was a significant difference (p<0.05) in texture of the grains. The variations in texture of the grains in this study could be mainly due to genetic make-up, different environmental conditions in which the grains were exposed such as growth conditions, soil type and storage conditions. In terms of the genetic make-up, it was reviewed in Chapter Two that biofortification of maize with PVA carotenoids changes the texture of the grain and BGN has a hard testa hence poor WAC which contribute to the hardness of the grain. Grain size could have also contributed to the variations in texture as small grains have a tendency to be harder in texture than large-sized grains and thus require more processing time in making instant porridges, which causes high cost of production (Chen et al. 1993).

The correlation between grain colour and grain texture is shown in Table 7.

116 Table 7. The correlation between colour and texture of the whole grains of white maize, yellow PABM, red and brown BGN varieties

L* a* b* Firmness Toughness

L Pearson

Correlation 1 -0.836^** 0.786^** 0.357 -0.873^**

Sig. (2-tailed) 0.001 0.004 .282 0.000

a* Pearson

Correlation 1 -0.344 -.015 0.619^*

Sig. (2-tailed) 0.274 .964 0.032

b* Pearson

Correlation 1 .526 -0.632^*

Sig. (2-tailed) .079 0.028

Firmness Pearson

Correlation 1 -0.134

Sig. (2-tailed) 0.678

Toughness Pearson

Correlation 1

Sig. (2-tailed)

**. Correlation is significant at the 0.01 level (2-tailed).*. Correlation is significant at the 0.05 level (2-tailed)

As shown in Table 7, L* is significantly (p<0.01) and negatively correlated to a*, positively correlated to b* and negatively correlated to toughness. a* is significantly (p<0.05) and

117 positively correlated to toughness whereas b* is significantly (p<0.05) and negatively correlated to toughness. L* and b* had the highest correlation coefficient of 0.786 and L* and toughness had the lowest correlation coefficient of R=-0.873 at p<0.01. The lower correlation coefficient obtained in this investigation could have been attributed to the differences in texture and varieties of the grains. The findings of this investigation indicate that the genes controlling grain colour may be linked to those controlling grain texture. There was however, no literature found on the correlation between grain colour and grain texture. This suggest that grain texture which is tedious to measure can be predicted by measuring grain colour which is simple and rapid to do.

However, the sample size (n= 2) of the BGN varieties is too small to make a firm conclusion.