Onion is associated with micro-organisms which are capable
of causing spoilage. Onions with rots were examined microscopically. A
solution of it was made and the serial dilution of
1:10-1 to 1:1-5 were made from 10ml of the onions
sample. From the dilution, 1ml of each diluent was plated on nutrient
and saboor and dextrose agree to permit the grouth of the common
bacterial and fungi, from the roffen onions. Duplicate plates were
performed for each dilution. The plates was sivirled of gently to ensure
even distribution of diluent and was incubated in inverted position of
370 c for 24 hours. After 24 hours, the colorues were counted, with
vales yielding 30 to300 (to avoid TFTR and TNTC), the viable count per
ml was defermined by multiplying the average number of colories of the
duplicate plates by the corresponding factor (MPN table). Gram staining
was carried out on the colories and examined microscopically.
Representative colories were seperately sus-cultored on nutrient agar
slopes for confirmatory characterization of the organism present
Biochemical test for identification was also carried out. The result
showed a mixed flora of bacterial and fungi including moulds as the
organism responsible for spoilage of onions. The fungi isolated
were Mucor spp rhizopus spp, Aspergilus spp and saccharomycis spp. The
bacteria isolated from the sample
were staphylococcus aureus, streptococcus pyogenes and Bacillus spp.
LIST OF TABLES
Table 2: Composition of Raw onion Components
Table 2: total plate counts
Table 3: Isolate from onions
Sample Table 4: Identification
of Bacterial isolates From onoins sample Table 5: Biochemical test
for identification of bacterial isolates
TABLE OF CONTENT
1.1 Background information
1.2 Aims of this research project
1.3 Statement of problems
1.5 Significance of study
1.6 Limitation of this project
2.0 literature review
2.2 Species of onions
2.3 Composition of raw onions
2.4 Dehydration of onions and uses of dehydrated onions
2.5 Basic principles involve in preventing microbial spoilage of onions
2.6 Spoilage of micro organisms
3.0 Materials and method
3.1 sample collection
3.2 materials used for the preparation of the medium
3.3 preparation of media
3.4 Preparation of sample
3.5 Microbial counts staining and microbiological work
3.5.1 Biochemical test for identification
3.5.2 Motility test
3.5.3 Sugar fermentation test
4.0 Result discussion
5.0 conclusion and recommendation
1.1 BACKGROUND INFORMATION
Onions is a vegetable crop and ancient in nature if is
through to have been domesticated in the central Asia. It is one of the
oldest vegetable cultivated by man for food. In the world onion buld are
found in ancient Egypt, India, China and Europe during the middle ages,
and in the late sixteenth or early seventeenths centuries, it spread to
the new world by the Spaniards. The crop is now wide spread in both
temperate and tropical regions with Europe as the largest producers
(cobley and Steele, 1976).
In the tropic most onions are grown with irrigation during
the relatively cool dry season in semi arid region, they are not good
crop for hot wet tropic. Onions can be grown under a wide range of
climatic condition but they succeed best in a mild climate without
excessive rainfall or great extremes of heat and cold. They are not
suitable to regions with heavy rainfall in the lowland humid tropics.
Cool conditions with an adequate moisture supply are most suitable for
early growth followed by warm drier condition for maturation, harvesting
and curing. They can be grown on a variety of soils, but the soil
should be retentive of water, non – packing and rich in nutrient, a good
fertile loam usually gives the best result. They may be grown
successfully on peat soils. The soil optimum pH is about 6.0 – 7.0
(alkaline) (carl and Hall, 1986).
In storage a specific environment must be provided for the
onions, if a high quality product is to result. Storage losses are a
function of storage environment as well as the condition and cultural
practices used during the growing season. Proper control of storage
environment can however, significantly extend the storage season from
that which would result from storage environment that were not matched
to the condition of the onions when placed in storage (carl & Hall,
Onions may be stored in bulk or may be placed in palletised
bins that are stacked in a storage structure. The use of bins may make
handling of onions convenient but it does make ventilation of the onions
more difficult. Improved bins design may alleviate the ventilation
problems in future (cobley and Steele, 1976).
Onions are packed locally by using basket and jute bags
these packaging material come locally from palm; bamboo and fibrous jute
trees, also they have different sorts and sizes. These packaging
materials have the function for transportation and storability of the
onions. Again these packaging material are locally available and
relatively cheap. Apart from these few advantages mentioned they have no
barrier to dust, not suitable for measuring weight and can easily be
crushed which might lead to damage of the onions.
The deterioration of raw onions may result from physical
factors; actions of their own enzymes, microbial or combination of these
factors. Mechanical damage resulting from action of animals, birds or
insects or from brushing, wounding, bursting, cutting, freezing,
desiccation or other mishandling may predispose towards increased
enzymatic action or entrance, and growth of microorganisms. Also
previous damage by plant pathogens may make the part of the crop used as
food unfit for consumption or may open the way for growth of
saprophytes and spoilage by them. Contact with spoilage onions may bring
about transfer of organisms causing spoilage and increasing the
wastage. Improper environment condition during harvest, transit, storage
and marketing may favor spoilage.
Genera of bacteria usually present in onion
include pseudomonas spp, Bacillus spp, chromobacterium, Enterobacterium,
flavobacterium, lactobacillus serratia, staphylococcusspp, streptococcus spp and
others and perhaps genera containing plant pathogens, such as Erwinia
and xanthomomes. Grouwth of some micro-organisms may take place
between harvesting and processing or consumption of the vegetable.
Adequate control of temperature and humidity will reduce such growth
(frazier and westhoff, 1978).
1.2 AIMS OF THIS RESEARCH PROJECT
The aims of this research project are:
1 to isolate, identify and characterize the different
micro-organaniszs that are responsible for the spoilage of onions.
2 To categorize the pathogenic micro-organisms associated with the spoilage of onions.
1.3 STATEMENT OF PROBLEMS
The society is a place where a vegetable is been consumed everyday.
This project research goes a long way in identifying problems which is
encountered when spoilage occurs in onions; onion bulb that is
contaminated when consumed causes severe stomach ache (presence of
enterobacteriacea) because of the pathogenic micro-organisms present in
if and this inturn is hazardous to ones health. The pathogenic
micro-organisms present in the spoilage of onoins are deterimental to
humans e.g pseudomonas spp., staphylococcus spp, Erwinia etc.
Onions been a member of the vegetable group is used widely in
seasoning, flavouring and sometimes cured and stored as spicing agent.
The proper storage of onions makes it available for use all year round
and the effect of spoilagemicro-organisms afecting it has an adverse
efect on the society at large because if makes onions not readily
available to the society; that is why studies is been carried out in
this project research to minimize and or stop spoilage of onions.
HO-A mixed flora of bacteria and fungi is found in spoilt onions.
Hi-bacteria and fungi found in onion result in the onions own
enzymatic actions causing physical, microbial or combination of these
factors leading to entrance and or growth of micro-organisms.
1.5 SIGNIFCANCE OF STUDY
The justification of this project research is to ascertain the
different micro-organism responsible for the spoilage of onions. In this
process bacteria and fungi were isolated identified and characterized
because they are the microorganisms associated with the spoilage of
The deterioration of raw onions can also result from physical
factors, actions of their own enzymes, microbial action or combination
of these factors. In physical factors; the storage patter can affect the
raw onions that is if it is stored in bulk or may be placed in
palletized bins and this does not make ventilation of the onions easily,
so improved bins design may be of great help. In action of their own
enzymes; if the raw onions is crushed during packaging, handling, this
may inturn allow the penetration of micro – organisms which will now
alter the enzymatic action of the raw onions and may lead to spoilage of
the onions flesh which is meant for food and if consumed could be
hazardous to health.