CHAPTER
ONE
1.1 INTRODUCTION
Tomato (Solanum lycopersicum L.) is a berry annual, short–lived herbaceous plant of the solanaceae family. It is a flag-ship species that belongs to the genus of lycopersicon which includes more than 3,000 species with chromosome number of 24; it usually sprawls on the ground, and could reach about 1-5m height (Wogu and Ofuase, 2014). It has a weak woody stem covered with glistering yellow to reddish glandular hairs, rarely vine over other plants.
Tomato plant is cultivated in the savanna agro-ecological zone of Nigeria during cropping season and dry season, under furrow irrigation. The plant usually produces higher yield and better fruit qualities with minimal foliar diseases under irrigation compared to those cultivated during the cropping season. In Nigeria the major producing areas lie between latitudes 7.50N, 130N and 250C to 340C (Umeh et al., 2002). Global production estimate is put at approximately 130 million metric tons annually on 118.71 million hectares of land (FAO, 2010). In Nigeria it is mostly cultivated in the semi-arid region during the cool dry season using irrigation, high temperature limits the production of tomato to the cooler period of the year.
The fruit is one of the most consumed
vegetables in the world, after potatoes and onions, cassava and also the
preferred garden crop, ranking 1st in the world for vegetables, with
production estimate of approximately 160 million tones, cultivated on 4.8
million hectares in the year 2011 (FAOSTAT 2011, Ogunbawo et al., 2014). Nutritionally, the fruit contains calcium, niacin, flavonoids,
lycopene, beta-carotene, derivatives of hydroxycinnamic acid, high amount of
water and vitamins, specifically A, C, and E which are very vital in metabolic
activities of humans (Greenberg et al.,
2015).
The fruit is a versatile health product
and due to its equally versatile preparation option, the fruit is consumed as
vegetable, dietary supplement, eaten raw as salad and for cooked food or
condiment garnishing, contributing to a healthy well-balanced food. Raw,
ripened tomato fruit is valuable in food industries and its constitutes of 100g
constituents of carbohydrates 4g, energy 75kg (18k) dietary fiber 1g, sugar
2.6g, fat 0.2g, vitamin C (22%, 13 mg), protein 1g, and water 95g (Ijato et al., 2011).
The foods that we take in are rarely if ever stance, they carry
microbial associations whose composition depends upon which organisms gain
access and how they grow, survive and interact in the food overtime. The microorganisms present will originate
from the natural micro-flora of the raw material and those organisms introduced
in the harvesting/slaughter, processing, storage and distribution. In most
cases, this micro-flora has no discernible effect and the food is consumed
without objection and with no adverse consequences. As these micro-organisms manifest their
presence in some instances they can cause spoilage, food borne illness and also
transform a food’s properties and compositions in a beneficial way food
formation.
Food spoilage is a metabolic process
that causes foods to be undesirable or unacceptable for human consumption due
to changes in sensory characteristics (properties and composition).
Spoiled
foods may be safe to eat, i.e. they may not cause illness because there are no
pathogens or toxins present, but changes in smell, taste or appearance or cause
them to be rejected.
Micro-organisms are living entities
of microscopic size and include bacteria, viruses, yeasts and molds (designated
together as fungi), algae and protozoa.
Tomatoes
have evolved many strategies to survive the predation of herbivores and
omnivores, including humans, and these strategies include, not only protective
mechanisms to protect vegetative parts such as leaves, stems and roots, but
also the development of rich succulent fruits to encourage animals to help in
the dispersal of seeds.
Most microorganisms that are
initially observed on whole fruit surfaces are soil inhabitants. Vectors for disseminating these microbes
include soil particles, airborne spores, and irrigation water. Most bacteria and fungi that arrive on the developing
crop plant either completely begin to cause damage to crop’s health or, in many
situations provide a natural biological barrier to infestation by the subset of
micro-organisms responsible for crop damage (Janisiwicz and Korsten, 2002).
Spoilage
micro-organisms can be introduced into the crop itself, during crop growth in the
field, during harvesting and postharvest handling, or during storage and
distribution. The same types of soil –
borne spoilage microbes that occur in produce are the same spoilage
micro-organisms that are present on harvesting equipment, on handling equipment
in the packing house, in the storage facility, and on food contact surfaces
throughout the distribution chain.
Many fruits and vegetables present
nearly ideal conditions for the survival and growth of many types of
micro-organisms. The internal tissues
are nutrient rich and many, especially tomatoes/vegetables have a PH near
neutrality. The pH values of the tissues of many vegetables make them more
acceptable to bacterial invasion than fruits although there are also a number
of important spoilage fungi of stored vegetables.
The bacteria involved are usually
gram-negative bacteria. Clavibacter michiganensis
causes bacterial canker of tomato, Pseudomonas
syringae causes Bacterial speck, Xanthomonas
campestris causes Bacterial spot, Pseudomonas
conjugata and so much more (Geuttam, P. 2008). Tomato contains large amount of water which
makes them more susceptible to spoilage by the action of micro-organisms.
Tomatoes
and other vegetables are highly perishable products especially during the post harvest
phase, when considerable loss is due to microbial diseases, disorder,
transpiration and senescence can occur.
Another observed form of spoilage is
a softening of the tissue due to the pectinolytic activity of
micro-organisms. Pectin, the methyl ester
of x-1, 4-poly-D-galaturonic acid are major components of the middle lamella
between the cells making up plant tissues once it is broken down the tissue
loses its integrity and individual plant cells are more easily invaded and killed.
Food borne pathogens are wide spread
problems throughout the world. This
illness caused by food borne microbial pathogens, significantly affect people
health as well as being economically costly.
Food – borne pathogens are major threat to food safety, which have entered
the food chain, at some point from farm to fork. The detection and enumeration of pathogens in
food and on surfaces that come into contact with food are an important
component to ensure the safety of food throughout the food supply chain. Food companies use micro biological analysis
to monitor the state of contamination.
The identification of organism is fundamental to ensure high quality
standards for the food industry and market (Myers, 2011, Norak et al., 2004). These identification techniques are crucial
in food related diseases nut breaks for epidemiological investigations.
Classical microbiological taxonomy
has traditionally used morphological and physiological differences among the
species to discriminate between them.
Although, the tests could only differentiate only at the species level;
over the past twenty years, a significant number of DNA-Based techniques have
been introduced into the field of bacterial characterization and taxonomy. Today, biologists often use DNA sequences to
infer events that humans were not able to observe directly. These methods work
quite well for microbial classification and its main objective is in
discriminating or typing the different strains or genotypes of a species. DNA – based methods have specific DNA sequences
as markers, and can be divided into hybridization – based markers, and
Polymerase Chain Reaction (PCR) – based markers.
Therefore, the study aims at
identifying the bacteria pathogens involved in the post harvest decay of tomato
fruits.
1.2 STATEMENT
OF PROBLEM
Tomato production can serve as a
source of income for most rural and peri-urban producers in most developing
countries of the world. Scientific
research has been focused mainly on production whilst neglecting post-harvest
issues. Tomato producers have therefore
enjoyed good harvest in recent times, though the good harvests of those from
developing countries do not translate into profit as most are lost after
harvest. From this study, post-harvest
loss is a major challenge which deteriorates tomato production (Arah, et al., 2015). Tomato being a perishable crop as a result of
its high moisture content has short shelf life of about 48 hours (R.H. Muhammad
et al, 2011) under tropical
conditions. Tomato quality components
include appearance (color, size, shape, freedom form defects and decay),
firmness, flavor, and nutritional value.
These entire components are related to their composition at harvest and
compositional changes during postharvest handling.
The
post-harvest quality and shelf life of the fruit in some part will depend on
some post-harvest handling practices like harvesting, pre-cooling, cleaning and
disinfecting, sorting and grading, packaging, storing, and transportation all
play important roles in maintaining quality and extending shelf life and preventing
pathogens’ attack. Failure to adhere to these specialized handling practices
and treatment methods, there would be high amount of loss due to pathogens
The
purpose of this paper therefore is to identify bacteria that lead to the
reduction of the shelf life of harvested tomatoes caused by poor postharvest handling
practices sold in Ogbete and Artisan markets, Enugu, Enugu State, Nigeria.
1.3 SPECIFIC
OBJECTIVES
The
aspects of these studies are as follows;
- To isolate bacterial contaminants in selected tomatoes
- To identify bacterial contaminants based on morphological and biochemical characteristics.
BACTERIAL CONTAMINANTS IN SELECTED TOMATOES
