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.
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