The Scope of Food Microbiology

Microbiology is the science which includes the study of the occurrence and significance of bacteria, fungi, protozoa and algae which are the beginning and ending of intricate food chains upon which all life depends. These food chains begin wherever photo synthetic organisms can trap light energy and use it to synthesize large molecules from carbon dioxide, water and mineral salts forming the proteins, fats and carbohydrates which all other living creatures use for food.

Within and on the bodies of all living creatures, as well as in soil and water, micro-organisms build up and change molecules, extracting energy and growth substances. They also help to control population levels of higher animals and plants by parasitism and pathogenicity.

When plants and animals die, their protective antimicrobial systems cease to function so that, sooner or later, decay begins liberating the smaller molecules for re-use by plants. Without human intervention, growth, death, decay and regrowth would form an intricate web of plants, animals and micro-organisms, varying with changes in climate and often showing apparently chaotic fluctuations in populations of individual species, but inherently balanced in numbers between producing, consuming and recycling groups.

In the distant past, these cycles of growth and decay would have been little influenced by the small human population that could be supported by the hunting and gathering of food. From around 10000 BC however, the deliberate cultivation of plants and herding of animals started in some areas of the world. The increased productivity of the land and the improved nutrition that resulted led to population growth and a probable increase in the average lifespan. The availability of food surpluses also liberated some from daily toil in the fields and stimulated the development of specialized crafts, urban centres, and trade – in short, civilization.

1.1 MICRO-ORGANISMS AND FOOD

The foods that we eat are rarely if ever sterile, they carry microbial associations whose composition depends upon which organisms gain access and how they grow, survive and interact in the food over time. The micro-organisms present will originate from the natural micro-flora of the raw material and those organisms introduced in the course of harvesting/slaughter, processing, storage and distribution (see Chapters 2 and 5). The numerical balance between the various types will be determined by the properties of the food, its storage environment, properties of the organisms themselves and the effects of processing. These factors are discussed in more detail in Chapters 3 and 4.

In most cases this microflora has no discernible effect and the food is consumed without objection and with no adverse consequences. In some instances though, micro-organisms manifest their presence in one of several ways:

(i) they can cause spoilage; (ii) they can cause foodborne illness;

(iii) they can transform a food's properties in a beneficial way – food fermentation.

1.1.1 Food Spoilage/Preservation

From the earliest times, storage of stable nuts and grains for winter provision is likely to have been a feature shared with many other animals but, with the advent of agriculture, the safe storage of surplus production assumed greater importance if seasonal growth patterns were to be used most effectively. Food preservation techniques based on sound, if then unknown, microbiological principles were developed empirically to arrest or retard the natural processes of decay. The staple foods for most parts of the world were the seeds – rice, wheat, sorghum, millet, maize, oats and barley – which would keep for one or two seasons if adequately dried, and it seems probable that most early methods of food preservation depended largely on water activity reduction in the form of solar drying, salting, storing in concentrated sugar solutions or smoking over a fire.

The industrial revolution which started in Britain in the late 18th century provided a new impetus to the development of food preservation techniques. It produced a massive growth of population in the new industrial centres which had somehow to be fed; a problem which many thought would never be solved satisfactorily. Such views were often based upon the work of the English cleric Thomas Malthus who in his 'Essay on Population' observed that the inevitable consequence of the exponential growth in population and the arithmetic growth in agricultural productivity would be over-population and mass starvation. This in fact proved not to be the case as the 19th century saw the development of substantial food preservation industries based around the use of chilling, canning and freezing and the first large scale importation of foods from distant producers.

To this day, we are not free from concerns about over-population. Globally there is sufficient food to feed the world's current population, estimated to be 6000 million in 1999. World grain production has more than managed to keep pace with the increasing population in recent years and the World Health Organization's Food and Agriculture Panel consider that current and emerging capabilities for the production and preservation of food should ensure an adequate supply of safe and nutritious food up to and beyond the year 2010 when the world's population is projected to rise to more than 7 billion.

There is however little room for complacency. Despite overall sufficiency, it is recognized that a large proportion of the population is malnourished. The principal cause of this is not insufficiency however, but poverty which leaves an estimated one-fifth of the world's population without the means to meet their daily needs. Any long-term solution to this must lie in improving the economic status of those in the poorest countries and this, in its train, is likely to bring a decrease in population growth rate similar to that seen in recent years in more affluent countries.

In any event, the world's food supply will need to increase to keep pace with population growth and this has its own environmental and social costs in terms of the more intensive exploitation of land and sea resources. One way of mitigating this is to reduce the substantial pre-and post-harvest losses which occur, particularly in developing countries where the problems of food supply are often most acute. It has been estimated that the average losses in cereals and legumes exceed 10% whereas with more perishable products such as starchy staples and vegetables the figure is more than 20% – increasing to an estimated 25% for...