ABSTRACT
Control of the storage pest Larger Grain Borer (LGB) (Prostephanus
truncates) and aflatoxin contamination by the mould Aspergillus spp. are
the major challenges to maize storage in Africa. In this study, the
effect of hermetic storage on LGB and Aspergillus spp. during maize
storage was evaluated. A 2 x 3 factorial experiment of two storage atmospheres
(hermetic and non-hermetic) and infestation levels (LGB, Aspergillus spp.
and uninfected control) were evaluated during the storage of ‘Obatampa’
maize. LGB and Aspergillus spp. were each introduced into 1.5 kg of the
maize grains in hermetic and non-hermetic bags and stored alongside uninfected
grains of same weight. Oxygen depletion in the hermetic bags was significant (p
= 0.012) while temperature in both hermetic and non-hermetic bags remained
fairly constant at 26.99 ºC and 27.4 ºC, respectively. Relative humidity,
moisture content, grain damage and weight loss percentages were significantly
different in the various bags ( p < 0.001). There was 100 % LGB
mortality in the hermetic storage after 52 days. Aspergillus flavus
contamination in the non-hermetic bags was highly significant compared to the
hermetic bags (p = 0.002). The aflatoxin group B2 was found in both
storage systems. While the aflatoxin group G1 was not detected, the G2 group
was only detected at the concentration 0.1 ppb in the hermetic storage. The
double layer hermetic SuperGrainbag better preserved the quality and shelf life
of the maize grains and maintained seed viability ( p < 0.001) much
longer than the non-hermetic polypropylene bag.
CHAPTER ONE
INTRODUCTION
Background to the Study
Maize is a member of the grass family; Poaceae (Gramineae)
(Piperno Flannery, 2001). It is further organized in the genus Zea, a
group of annual and perennial grasses native to Mexico and Central America (Buckler & Stevens, 2005). Maize
is currently the world’s third most important cereal
after wheat and rice (Belfield &
Brown, 2008). It is, however, the most important cereal in most African
countries including Sub-Sahara Africa (Du Plessis, 2003). It also serves as a staple food for some
200 million people in developing countries, especially in Sub-Sahara Africa
(SSA) (Hussein, Metwally, Farghaly, & Bahawirth, 2011). Maize is used for
three main purposes; food for mankind, raw material in brewing industries and
for animal feed. According to Onimisi, Omage, Dafwang and Bawa, G. S. (2009),
seventy percent (70 %) of maize produced worldwide is also used for livestock
feed and as staple food for more than 1.2 billion people in SSA and Latin
America. In Sub-Saharan Africa, maize is consumed by 50 % of the population and
is the preferred food for one-third of all malnourished children and 900
million poor people worldwide. By 2025, maize will be the developing world’s
largest crop and between now and 2050, the demand for maize in the developing
world is expected to double. By 2050, global maize consumption is expected to
increase from 32 to 52 kilograms per person per year (http://maize.org/why-maize/ Accessed on
April 9, 2015).
Despite the importance and place of maize in Africa, its
production is subject to high post-harvest losses due to poor handling and
inadequate storage techniques. Losses after harvest of both quantity
(weight losses) and quality (bio deterioration) are brought about by insect
pests, mould growth, fungi, rodents and sometimes, birds which deprive farmers
of the full benefits of their labour (Boxall, 2001).
Traditionally, maize grain is stored by African farmers for consumption and
sold later depending on the quantity produced per household. The stored maize
is usually destroyed by several pests which eventually leads to deterioration
in quality forcing farmers to sell at reduced prices and below the production
cost. The value of storage protection to a market-oriented grower is a function
of price seasonality, value loss prevention, and their opportunity costs of
capital (Jones, Alexander, & Lowenberg-DeBoer, 2011).
The maize weevil or Sitophilus zeamais and Prostephanus
truncatus or Larger Grain Borer (LGB) are the major primary pests of maize
during the drying and storage periods. They cause significant storage losses for
African maize producers, expressly in tropical and sub-tropical regions
(Anankware, Obeng-Ofori, Afreh-Nuamah, Oluwole, & Ansah, 2013). Maize
weevils and LGB can be extremely destructive to stored maize (Bbosa, Brumm,
Bern, & Rosentrater, 2014). Furthermore, inadequate storage protection
allows the entry of water and facilitates easy access by insects and rodents,
while in large-scale bag storage chemical browning reactions may lead to grain
discoloration called ‘stack-burn’. Maize kernels damaged by insects may be
contaminated with dangerous levels of aflatoxins apart from the actual nutrient
losses. The feeding activities of these insects also lead to the loss of seed
viability hence, low yields resulting in hunger and poverty (Anankware
& Bonu-Ire, 2013).
Fungi are the second significant cause of deterioration and
loss of maize next to insects. Fungi could cause about 50 % to 80 % of damage
on farmers’ maize during storage if conditions are favorable for their
development (Khosravi, Mansouri, Bahonar, & Shokri, 2007). Fungi infection
of maize grain before and after harvest remains a major problem of food safety
in most parts of Africa. Problems associated with this infection include loss
of germination, mustiness, mouldy smell (Sauer, 1992) and
aflatoxins contamination ( McAlpin, Wicklow, & Horn, 2002). Aflatoxin B1 is
one of the most potent naturally occurring animal carcinogens and found in all
cereal grains and other oil seeds. All animal species appear to be susceptible
to aflatoxins and susceptibility varies from species to species. Aflatoxins
were identified as the cause of epidemic liver cancer (hepatoma) in rainbow
trout. It was found that 4 µgkg-1 of diet fed for 16 months causes liver
cancer. The control of maize storage is therefore very important to boost maize
availability. Various approaches have been used over many decades to control
maize post-harvest losses. Among other methods, the integrated approach
involving the use of the narrow crib with appropriate pesticides or fumigants
is very popular (Affognon, Mutungi, Sanginga, & Borgemeister, 2015).
Major storage techniques utilized by small-holder producers
in Western Africa vary greatly, but include on field, open storage, jute bags,
polyethylene or polypropylene bags, raised platforms, conical structures with
thatched roofs, clay structures, and giant woven baskets (Addo, Birkinshaw,
& Hodges, 2002). Farmers may also store bags in their personal rooms, on
cobs above fireplaces, or simply heaped on floors (Ofosu, Compton, Magrath,
Acquaye, & Ayertey, 1995; Hell, Cardwell, Sétamou, & Poehling, 2000).
These are generally considered ‘traditional’ storage methods,
while improved covered structures or ‘cribs’ may be termed ‘semi-modern’, and
formal silos and warehouses termed ‘modern’ storage systems (Sekumade
& Akinleye, 2009). Though shelling of grain and
insecticide application is officially encouraged by many Ministries of
Agriculture, storage of maize on cobs (husked and de-husked) is almost
universal.
In recent years, there has been a rising interest in hermetic
storage systems as alternative methods for grain preservation against insects
that devour the stored grain. These methods are attractive to farmers as they
stop survival of the insects without the use of chemicals, and have less
destructive impact on the environment and human health. A quantity of these
technologies apply flexible plastic liners or bags that have low air
permeability properties, which enable them to secure modified atmosphere
involving low oxygen and high carbon dioxide concentrations around the grains
(Affognon et al., 2015). To avoid or reduce losses during those periods,
scientists have developed methods or technologies which nowadays give more
satisfaction in matters of cereal storage in general and maize grain in particular.
One of these methods and technologies is hermetic storage. Hermetic storage
isolates the storage ecosystem from the external environment while respiration
within the storage ecosystem causes O2 reduction and CO2 accumulation leading
to suffocation and dehydration of weevils (Navarro, Donahaye, & Fishman,
1994).
In line with this, the present study compares the effect of
hermetic and non-hermetic storage on the quality and shelf life of ‘Obatampa’
maize variety grain to determine which of the two is the most effective to
preserve grain quality and seed viability of maize.
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