Effects of storage conditions on viability, germination and sugar content of pearl millet (pennisetum glaucum) grains

Effects of storage conditions on viability, germination and sugar content of

pearl millet (Pennisetum glaucum) grains

Keywords: Pearl millet, viability, germination, storage container, storage period, sugar content, post-harvest.

ABSTRACT: Pearl millet (Pennisetum glaucum) is the most widely grown type of millet in Africa and Asia. Pearl millet is well adapted to growing in areas characterized by drought, low soil fertility, and high temperature. It grow well in soil with high salinity or low pH. In northern Namibia, pearl millet grains are stored in wooden, plastic and cement containers for future consumption and also seeds for the next planting season. This study looked at viability, germination and sugar content of pearl millet grains in different containers after 0-16 months post-harvest. Germination and viability of pearl millet grains decreased as the period of storage increased, and this was more obvious especially in cement and wooden containers. Viability in wooden container ranged between 64-50% after 8-16 months post-harvest compared to 83-74% in plastic container and 30-12% in wooden container after a similar period of storage. Pearl millet grains were found to contain high amounts of starch and sucrose for the first four months and it decreases as storage time increase. As the duration time of storing the pearl millet grain increased, the amount of starch and sucrose decreased. This happened in all storage containers but there was a rapid loss in starch and sucrose content in cement storage than in the other storage facilities.

088-092 | JRA | 2012 | Vol 1 | No 1

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Journal of Research in

Agriculture An International Scientific

Research Journal

Authors:

Marius Hedimbi1,

Natalia K. Ananias1 and

Martha Kandawa-Schulz2.

Institution:

1. Department of Biological

Sciences, University of

Namibia, P/Bag 13301,

Windhoek, Namibia.

2. Department of Chemistry

and Biochemistry,

University of Namibia,

P/Bag 13301, Windhoek,

Namibia.

Corresponding author:

Marius Hedimbi..

Email:

[email protected]/

[email protected].

Phone No:

(+264) (61) 206 3425.

Fax:

(+264) (61) 206 3791.

Web Address:

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documents/AG0018.pdf.

Dates: Received: 01 Feb 2012 Accepted: 09 Feb 2012 Published: 16 Jun 2012

Article Citation: Marius Hedimbi, Natalia K. Ananias and Martha Kandawa-Schulz. Effects of storage conditions on viability, germination and sugar content of pearl millet (Pennisetum glaucum) grains. Journal of Research in Agriculture (2012) 1: 088-092

Original Research

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INTRODUCTION

Pearl millet (Pennisetum glaucum) is a

traditional staple food crop of the semi-arid tropical

zones of Africa and Asia, and it is cultivated in areas

with a rainfall ranging from 150 mm to 800 mm per

annum. It has a high nutritional value compared to other

cereals like maize, wheat or rice, it is digested more

slowly and thus delays hunger, it has a higher lipid and

protein content, and its amino acid balance is better than

that of other cereals (Labetoulle, 2000). Pearl millet is

one of the most drought tolerant cereals and can grow in

soil with low fertility which is unsuitable for other

cereals. Being particularly resistant to moisture stress

and adapted to high temperatures, it has a low yield,

which also explains its high nutritional value compared

to other cereals. In the dryer parts of Southern Africa

(Angola, Namibia, Zimbabwe, Botswana, Zambia and

South Africa) pearl millet is traditionally grown as a

staple food crop (Mallet and du Plessis, 2001).

Pearl millet is a principal source of energy,

protein, vitamins, and minerals for millions of people in

the regions where it is cultivated as the dominant crop

(Hulse et al., 1980). Pearl millet, like sorghum, is

generally composed of 9-13% protein but large

variations in protein content, ranging from 6-21%, have

been observed (Baker, 2003). Pearl millet grains are

usually made up of 70% carbohydrates and consist

almost exclusively of starch. The starch itself is

composed of two third amylopectin and one-third

amylase (USAID, 1971). It has no husk, no tannin,

contains 5-7% oil, and has higher protein and energy

levels than maize or sorghum. Pearl millet is also rich in

B vitamins, potassium, phosphorus, magnesium, iron,

zinc copper and manganese (Baker, 2003).

Pearl millet is the most important cereal crop in

Namibia and over 60% of Namibia population depends

on it as their staple food (Ipinge, 1998). It is widely

grown in seven regions of Namibia such as Caprivi,

Kavango, Oshikoto, Ohangwena, Oshana, Omusati and

Kunene covering about 355200 hectors of land (Ipinge,

1998). In Namibia more pearl millet are produced

annually, and the farmers store pearl millet till the next

rain season. A number of storage facilities are used to

store pearl millet in Namibia (Goussault and Adrian,

1977) such as wood containers, cement buildings, and

plastic containers. Pearl millet stored in some of the

facilities such as cement and wooden containers have

been observed to have deteriorated in their physical

appearance, mainly due to pest invasion. However it is

not clear if these reductions in physical appearance also

translate into reduced viability, germination and sugar

content of the grains. Therefore this study was conducted

to find out the effect that different storage facilities have

on viability, germination and sugar content of pearl

millet grains after various period of storing the grains

post-harvest.

MATERIALS AND METHODS

Sample collection

Pearl millet grain samples were collected from

the northern part of Namibia, in the Omusati region

(Oikokola village), Ohangwena region (Endola village)

and Oshikoto region (Omupupa village). Samples were

collected every four months for 16 months post-harvest.

Three samples from each storage facility from each

village were collected. Samples that were not used

immediately were kept in plastic containers and stored at

4ºC in the dark until use.

Viability test

The method for viability test was modified from

that reported by Pelah et al., (2003). Ten pearl millet

grains from each storage facility were soaked in water

for 24 hours at room temperature to allow hydration and

initiate the germination process. Grains were then placed

in different petri dishes and covered with 1% of

2,3,5-triphenyltetrazolium chloride (TTC) solution. The

petri dishes were closed and covered with aluminium foil

and left in the TTC solution for 24 hours and the viability

089 Journal of Research in Agriculture (2012) 1: 088-092

Hedimbi et al., 2012

of the seeds were observed after 24 hours. Viable seeds

appeared pink to red inside.

Germination test

Plastic pots were filled with the growth media

(vermiculate). Twenty seeds from each facility were

sown per pot. The grains were watered every 2 days for

about three weeks and their ability to germinate was

recorded.

Starch test

Pearl millet grains were ground to fine powder

using the mortar and the pestle. The grounded powder

was placed in petri dishes. Approximately 1mL of iodine

solution was added to each petri dish. A dark blue colour

indicates the presence of starch.

Sucrose test

Pearl millet grains were ground to fine powder

using the mortar and the pestle. About 3g of fine powder

was transferred into different test tubes. About 5mL of

water was added to each test tube, and the test tubes were

swirled to mix the flour and water. About 5mL of

Benedict’s reagent was added to each test tube and the

test tubes were heated to boil in a water bath for few

minutes. If the solution turns green it indicates the

presence of sucrose.

RESULTS

Effects of storage facilities and duration on viability

and germination

In general, grains in storage facilities lost their

viability and germination chances as the duration of

storage post-harvest increases. The cement storage

container shows a rapid decrease of viability and

germination, especially between four and eight months

(Figure 1). Viability in wooden container ranged

between 64-50% after 8-16 months post-harvest

compared to 83-74% in plastic container and 30-12% in

wooden container after a similar period of storage. After

16 months post-harvest, viability and germination

remained high in plastic container (about 80%) compared

to cement container (less than 20%) and wooden

containers (20% germination and 60% viability)

(Figure 1).

Starch and sucrose content in pearl millet

As duration of storage increased, starch and

sucrose levels decreased in all storage containers. In

cement container, there was no sucrose detected after 16

months post-harvest. Starch and sucrose content was

better in the plastic and wooden storage facilities then in

the cement facilities from 8-16 months of storage

(Table 1).

DISCUSSION

Germination and viability of pearl millet grains

decreased as the period of storage increased, and this was

more obvious especially in cement and wooden

containers. There was a rapid loss of viability and

germination in the cement storage facility after four

months of storage and germination was less than 5%

after 16 months of storage in cement (Figure 1). The

rapid loss of viability and germination in cement can be

attributed to pest degradation due to the high pest

infestation associated with this storage facility. The level

of moisture content in the cement is likely to be high

compared to other storage facilities and might have

caused an increase in the amount of pest which in turn

Journal of Research in Agriculture (2012) 1: 088-092 090

Hedimbi et al., 2012

Figure 1: Viability and germination of pearl millet

grains in different storage containers after 0-16

months post-harvest.

would have resulted in low viability and germination in

the cement facility. Change in climate conditions has

been implicated as one of the reasons for increase in crop

pests by farmers in Rongai district, Kenya, in a study by

Ngeno et al., (2011). The main reason why farmers

regards pest infestation as the main reason for reduction

in agricultural output could be explained by the damage

and losses caused by different pests within a short period

(Ngeno et al., 2011).

Viability was higher than germination in all

storage facilities and this might be an indication of low

correlation between viability and germination, which

means not all viable grains are capable of germination. It

is possible that the low germination observed in this

study might be attributed to the artificial growth medium

(Vermiculate) used. However, no negative effect of the

growth medium used on germination has been reported

in the literature.

Pearl millet grains were found to contain high

amounts of starch and sucrose for the first four months

and it decreases as storage time increases. As the

duration time of storing the pearl millet grain increased,

the amount of starch and sucrose decreased. This

happened in all storage containers but there was a rapid

loss in starch and sucrose content in cement storage than

in the other storage facilities. Starch and sucrose content

remained better in plastic facility with medium (++)

amount after 16 months of storage compared to other

storage facilities which had low to no presence after the

same period of storage (Table 1). This study has shown

that pearl millets are rich in starch and sucrose. In a

similar study by Hulse et al., (1980), high amounts of

starch were found in sorghum and millets grains.

Plastic storage facility was the best in preserving

the grain qualities studied, but it is likely to be good at

absorbing heat which will cause proteins to change from

one form to another (Boora and Kapar, 1985).

Adu-Amankwa and Boateng (2011) carried out a study

on the postharvest loss of plantains (Musa spp. AAB,

ABB) in selected markets in Ghana and suggested that

high temperatures are likely to cause withering of

products due to high transpiration and respiration. The

study revealed that cement is not a good container to

store pearl millet grains as it results in significant loss of

viability, germination, starch and sucrose as compared to

other facilities. The high level of pest infestation, which

eats the inner core of the grains, is likely to be the cause

of loss of grain quality observed in this study.

REFERENCES

Adu-Amankwa PA and Boateng BA. 2011. Post-

harvest status of plantains in some selected markets in

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091 Journal of Research in Agriculture (2012) 1: 088-092

Hedimbi et al., 2012

Cement Wooden Plastic

Duration of storage (months) Starch Sucrose Starch Sucrose Starch Sucrose

0 (control) +++ +++ +++ +++ +++ +++

4 +++ +++ +++ +++ +++ +++

8 ++ + +++ +++ ++ +++

12 + + ++ + ++ ++

16 + - + + ++ ++

Table 1. Starch and sucrose content in pearl millet grains in different storage containers 0-16 months

post-harvest. +++=strong presence; ++=moderate presence; +slight presence; - = not detected.

Figure 2: Germination of pearl millet grains after 12

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From left to right: Cement, traditional and plastic

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