MICROBIAL EXAMINATION OF SPOILT AVOCADO FRUIT
THE ORIGIN OF AVOCADO FRUITS
The avocado pear, otherwise known as persea Americana miller originated from south America where it has been an important part of diet for thousands of years. The fruit of various species of persea, a genus nature to Mexico, Guatemala, and other central American countries, has been used for food by the inhabitants of those countries for countries. Selections from those wild trees, of California, Florida and Texes. World production is nearly 2 million tonnes, of which a small proportion is grown for export, mainly in California (Lee and young 1984)
Cultivars vary greatly in size, shape and colour of their fruits, fuerte (a guntermalen type) is thick, woody and knobbed, turning purplish black as the fruit ripens. Common to all avocado is a rich, smooth, oily pulp which is eaten as a nutritious savoury. The centre is a large stone, the seed . In warm and humid areas such as south east Florida and all world low lands near the Equator, only the West Indian race is well adapted but West Indian Xguatemalan hybrides are doing well and becoming increasingly important in extending the harvest season
2.1 USES OF AVOCADO FRUITS
Avocado fruits persea Americanna, is a delicious fruits the fruits is very useful in fruit juice production. Many manufacturing companies see Avocado fruit as very important raw material for the production of fruit juice. The sale of avocado fruits yield revenue to local fanuas.
It is consumed as a good source of mineral or vitamin.
2.2 PRESERVATION OF AVOCADO FRUIT
Avocado fruit is highly nutrition, there a re many ways it can be preserved and retained it potential nutrients.
Drying method: Avocado fruits can be diced into bits and dried in an open air oven or in air depends on the concentration of the heat. This dried avocado fruit may be grind into fine powered and use as a food supplement.
Frozen method: This is by use of refrigerator preserved avocado fruit, it is use when need
Canned method: this is another method of preservation most applicable to fruit juice industries. dried avocado
- WAYS AVOCADO FRUIT CAN BE PRONE TO CONTAMINANTS
As soon as avocado fruits are gathered into boxes, lugs, baskets or trucks during harvesting, they are subjected to contamination with spoilage organisms from each other and from the container unless these have been adequately sanitized. During transportation into market or the processing plants. Mechanical damage may increase susceptibility to decay and growth of micro-organisms may take place. Pre-cooling of the product and growth of micro-organisms. Washing the avocado fruit may involve a preliminary soaking, may be by agitation in water or preferably, by a spray treatment soaking and washing by agitation tend to distribute spoilage organisms from damaged to whole fruits recalculation or reused water is likely to add organisms and the washing process may moisten surface enough to permit growth of organisms during a holding period. Avocado washed with detergent or gerundial solution have reduce number of micro-organisms on them (shepherd, 1990).
Sorting spoiled fruits or firming spoilage may result in mechanical damage (Kotze, 1992) when these products are sold in the retained market without processing, they are not ordinarily subjected to much further contamination except for storage into the market in contaminated bins or other containers, possibly contact with decaying products, handling by sales people and customers, and perhaps spraying with water.
In the processing plant the fruits are subjected to further contamination and changes for growth of microorganisms or numbers of kids of organisms may be reduced by some procedures. Adequate washing at the plant causes a reduction in number of micro-organisms on the peelings, cutting and various methods of disintegration may add contaminants from the equipment involved. Infact every piece of equipment coming in contact with fruit can be a significant source of micro-organism unless it has been cleaned and sanitized adequately. Modern metal equipment with smooth surfaces and without cracks dead ends etc.,, is made to facilitate such treatments. Examples of possible sources of contamination of fruits with micro-organisms are trays, bins tanks, pipes, flumes, tables, aprons and filters.
Building of populations of micro-organisms on equipment as the result of microbial growth in the exudes and residences from fruits may greatly influence the amount of contamination of the fruit and the growth of the contamination. Not only is there the possibility of the addition of large numbers of organisms from this source, but ther is also the likelihood that these will be organisms in their logarithnic phase of growth and therefore able to continue rapid growth.
Inclusion of decayed parts of fruits increase the number s of microorganism in avocado fruit juices. Number in the juice, for example, and the numbers of coliforms are increased greatly by the inclusion with soft vots.
2.4 MICROBIAL SPOILAGE OF AVOCADO FRUIT
The deterioration of fruits may result from physical factors, action of their own enzymes, microbial action, or combinations of these agencies. Animals, birds or insects, or from bruising, wounding bursting, cutting freezing, or other mishandling may predispose towards increased enzymatic action or the entrance and growth of micro-organism previous damage by plant pathogens may make the part of the plant used as food until for consumption or may open the way for growth of saprophytes and spoilage and increasing the wastage. Improper environment conditions during harvesting transit, storage, and marketing may favour spoilage. The fitness of fruit for consumption is judged partly on their maturity. If the designed stage of maturity s greatly exceeded, the fruit may be considered inedible or even spoiled. An example is an over-ripe avocado, with its black skin and brown mushy interior.
Diseases of avocado fruits may results from the growth of an organisms that obtains its food from the host and usually damages it or from adverse environmental conditions and cause abnormalities in functions and structures of the fruits.
Fungal spoilage of avocado fruit I. Scab, a very important diseases of avocado causes by the fungus sphacelous persea, which attacks both foliage and fruit. This fungus caused corky, raised, brownish oral shaped spot on the fruit. As the spots become older they may coagulace and give the fruit a resettled appearances may develop cracks that permit entry of other fruit rotting organisms. Scabby deforming lessons are also formed on leaves, leaf petrioles and twings.
- Autractnose, caused by Glomerella angulata is characterized by sunk as black spots on the fruit, the spots being nearly circular in outline and one-fourth to one-half inch in diameter. Signs of anthrocnose typically appear when the fruit begins to soften and infected ripening fruits begins to soften and infected spots on the skin while the flesh beneath undergoes rapid decay costs and Ramalto, 1970.
- Cercospora spot or blotch, causes by Cercospora purpurea appears as small, catttered, brown, slightly smiken spots that have a definite outline but irregular shap. Grayish spone bearing structural of the fungus appear on the spots in humid weather. These fruit spots, which are one – eight of one – fourth inch in draine later denecope cracks or tissues, which permit the entry of other fungi that cause fruit decay.
- Dorthiorella rot, the most important rot of avocado fruit is caused
by the fungus Botryosphaera ribis (imperfect stage Dothiorella gregaria). The fungus is commonly present on dead wool, dead leaf tips, and debris. It enters the fruit sometimes before harvesting. After entering the fruit sometimes before until the fruit begins to soften, by which time it has reached the consumer.
The fact that there is no method of detecting fruit that will develop this is no method of detecting fruit that will develop this rot and culling it out in the packing house creates a difficult marketing problem. This rot commonly appear first as small brown or purplish – brown spots on the green fruit surface. The spots gradually enlarge until much of the surface may be involved. In early stages there is little involvement of the flesh. As the disease progresses, however, the fungus invades the flesh and causes a brown discolouration and an offensive odour. Occasionally the fungus indives a stem and rot. It may also invade fruit pedicles, causing the fruit to drop. The fungi Diplodia and Phomopsis are also involved in stem and rot of fruit.
Other fungi associated with avocado are Blue mold rot caused by penicillium expansum fusarium rot example E pallidoreseum, pestalotiopsis rot caused by pestalotiopsis versicolor phytophthora ciltricda and pink mold rot caused by Rhizopus stolonifer. Black mold rot caused by strated non-parasitic disease brought about either by deficiencies or excesses o certain elements occasionally are found on the avocado. One of the most common is zinc deficiency, which results in a little condition mottling of the leaves, and often a deforming of the fruit. If the deficiency is prolonged, the branches may due off. Bacteria spoilage of avocado fruit. As a result of the wide effect of bacteria, biologist have investigated and described both the adverse and useful side effects of bacteria. However, research is still in progress to harness and control the organism that a few types of bacteria make their own food. They make use of energy from the breakdown of in organic compounds. Most bacteria, however, take in ready-made food. Other, they break down food present in dead organisms and absorb it.
Among the important bacteria that causes spoilage of avocado are
- Gall diseases of avocado caused by A grobacterium uumefacies
- Food poisoning disease: caused by poisoning by the formation of
poisonous substances or toxins in the food. The bacteria which cause the spoilage of food are usually harmless when taken by mouth. The dangerous bacteria or pathogens are those, which harm man but do not usually change the appearance, taste or small of food. However, when there is shortage of water, some bacteria can produce resting bodies, which are called spores.
- CONTROL OF BACTERIAL AND OTHER DISEASE SOF AVOCADO FRUITS AND FRUITS PRODUCTS.
Microorganisms on the surfaces of freshly harvested avocado fruits include not only those of the normal surface flora but also those soil and water and perhaps plants pathogens Genera of bacteria usually present includes Pseudomonas sp, Alcalgenes sp, Bacillo Sp, Chromoba sp, Enterobacter sp, flavobacterum sp, lactobicillus sp, Leuconostar conostoc sp, Staphylococcus sp st others plus perhaps genera containing plant pathogens, such as Erwinia sp and Xanthomionas sp. Any of a number of kinds of molds also may be there and some times a few yeast. It the surfaces are moist or the outer surface has been damaged, growth of some microorganisms may take place between harvesting and processing, or consumption of the fruit. Adequate control of temperature and humidity will reduce such growth. Best results for control have been obtained with sprays, some other methods for the control of the disease of avocado are
- Asepsis: Avocado fruit may be subjected to contamination between harvesting and processing from containers and from spoiling fruits, and care should be taken to avoid such contamination as much as possible.
- Removal of micro organisms thorough washing of avocado fruit servers to remove not only dirt and hence casual microorganisms but also poisonous sprays. Washing may be with water, detergent solution or even bactericidal solutions, such as chlorinated water. Trimming also removes micro-organisms. Clear fruits juice may be sterilized by filtration.
- Uses of preservatives: the use of chemical preservatives to lengthen the keeping times of avocado is done by applying chemicals and a clip or spray or impregnated in wrappers for the fruits. Among substances that have been applied to the outer surfaces of fruit are waxes, hypochlorites, biphenyl and alkaline sodium o-phenylphenate Korstan et al (1993).
- Biological control: Biological control of avocado fruit diseases using Bacillus substillis alone or integrated with prochloraz and applied with Tag-was was evaluated for the control of nthracnose Colletotrichum gloeosporiodes, Glomerella ingulata, the fruit rot complete. (Dothiorella aromatica and G. cingulata) and Thyronectria Pseudotrichia and phomopsis perseae: The biological and integrated treatments were as effective and the prochloraz. Tag wax treatment in controlling fruit rot on avocado (Duwen hage, 1993).
2.6 BIOCEHMICAL TESTS FOR BACTERIAL ISOLATES
Some of the biochemical test to identify the bacterial isolates are
- OXIDASE TESTS: Two or three drops of oxidae indicator (Jetramethyl – paraphenyldiamin) is placed or filter paper and smear with the test organisms. A pink to purple colour change within 10 seconds indicated positive result. This is use to identify oxidase enzymes producers.
- CATALASE TEST
A colony of pure culture is placed on the slide and 2-3 drops of 10% hydrogen peroxide (H2O2) is added to it. Occurrence of gas bubbles within 2-3 seconds shows a positive result. The test is used to distinguish catalase enzymes producers from non-producers. The enzymes catalyses the release of oxygen from H2O2. This test differentiates catalase producers.
- UREASE TEST
The test is performed using urea Agar. The organisms are inoculated using stabing and the bottles incubated at 370c for 24 hours light violet color is observed in urease positive cultures. This identified urease enzyme producers.
- HYDROGEN SULPHIDE TEST
This test showered the production of hydrogen sulphide (H2S) from sulphur containing amino acid by bacteria. The test organism is in cultured into sterile peptone broth and a piece of head acetate paper suspended by the help of the cotton plug. The set-up is incubated at 370c for 24 hrs. blackening of the head acetate paper mean positive result of H2S production. The test is used sto identify the organisms involved.
- NITRATE TEST
Yeast carbon base broth is used in this test. The medium is dissolved in specified quantify of distilled water and autoclaved at 1210c for 15 minutes the medium is divided into two portions before autoclaving. One portion contained nitrate and the control had peptone water. After cooling inoculate and incubate at 370c for 24 hours a cloudy growth is indicate nitrate assimiliation by the organism
- INDOLE TEST
A loopful of the stock culture of the isolate is inoculated into sterile bottles containing peptone water and incubate for 48 hrs at 370c. to this culture o.5ml of KOVACS reagent is added and thoroughly mixed and then allowed to stand for 10 minutes. A positive result indicated by the development of a deep red colour.
- METHYL – RED TEST
Glucose – phosphate broth is inoculate with the test organism and incubate at 370c for five days (5 days). To 5ml of this culture, 5 drops of methyl red indicator is thoroughly mixed. A red colour denoting acidic PH which is a positive result while a yellow colour meant negative result.
- VOGES – PROSICAER’S TEST (VP)
8ml of 5% alpha – naphtho; in absolute alcohol (alcoholic –napthol) and 1ml of 40% potassium hydroxide were added to a 5 – day old culture of the test organism is Glucose phosphate medium. Production of bright pink colouration after 2-5 minutes indicate a positive result while no colour change meant a negative result.
- CITRATE TEST
The test organism is inoculate on simmon’s citrate Agar and incubate at 370c for 96hrs. observation of streaks of growth and change of colour from green to blue indicate apositive result. A negative one is the maintenace of the original green colour and no growth. The test was to check the abilsity of the organism to utilize citrate as a sole carbon and energy source and ammonium salt as the sole nitrogen source. The test is important in identification of citrate utilizers.
- SUGAR FERMENTATION
The test is done using 1% sugar in peptone water medium. The medium is prepared using 1% in peptone water and two drops of Ardraide’s indicator solution. After thorough mixing, it was dispensed into bijoux bottles. Durhan tubes is dropped inverted into the bottles. The bottles then corked and sterile by autoclaving at 1210c and 15 minutes, the bottles are allowed to cool before inoculating with the test organisms and incubate at 370c for 24 hrs. each test organisms is inoculate into each sugar in duplicates. Gas prodium in the Durhan tube and change in colour of the medium from light yellow to pink indicate a positive acid and gas production. The test identifies organisms capable of using the sugar concerned and is used to identify the organisms involved.