Chapter 1: 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. Most food chains begin wherever photosynthetic 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. About 10 000 years ago 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.

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 microflora 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:

• they can cause spoilage;

• they can cause foodborne illness;

• they can transform a food’s properties in a beneficial way – food fermentation.

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 such concerns, although globally there is sufficient food to feed the world’s population, estimated to be 8 billion in 2023, and world grain production has managed to keep pace with population growth. But there is little room for complacency as food supply chains can quickly be disrupted by war, political upheavals and other events.

Despite today’s overall sufficiency, it is recognized that worldwide 828 million people are affected by hunger and that 45% of deaths in children under the age of 5 years are linked to undernutrition. 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, projected to reach 9 billion by 2050, and this will have 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. According to data from the UN’s Food and Agricultural Organization (FAO), food losses from harvest up to, but not including, retail have remained fairly steady in the period 2016–2020, at just above 13%. The UN Environmental Programme has estimated subsequent losses at the retail and consumer level as 17%. This is broadly in line with an earlier report for the FAO, which arrived at a similar overall figure of roughly one-third of global food production being either lost or wasted, amounting to 1.3 billion tonnes per year.

In low-income countries losses were mostly concentrated in the earlier stages of the food chain, where they were typically of the order of 20–30% for commodities such as cereals, fish, meat products, oilseeds and pulses, but were higher for root crops and tubers, and up to 50% for fruits and vegetables.¹ 

Clearly reduction in such losses can make an important contribution to feeding the world’s population. While it is unrealistic to claim that food microbiology offers all the answers, the expertise of the food microbiologist can make an important contribution. In part, this will lie in helping to extend the application of current knowledge and techniques, but there is also a recognized need for simple, low cost, effective methods for improving food storage and preservation in developing countries. Problems for the food microbiologist will not however disappear as a result of successful development programmes. Increasing wealth will lead to changes in patterns of food consumption and changing demands on the food industry. Increased income among the poor has been shown to lead to increased demand for the basic food staples, while in the better-off it leads to increased demand for more perishable animal products. To supply increasingly affluent and expanding urban populations will require further extension of existing global food supply chains and will place great demands on the food microbiologist.

In addition to its undoubted value, food has a long association with the transmission of disease. Regulations governing food hygiene can be found in numerous early sources, such as the Old Testament, and the writings of Confucius, Hinduism and Islam. Such early writers had at best only a vague concept of the true causes of foodborne illness and many of their prescriptions probably had only a slight effect on its incidence. Even today it is very difficult to get a true picture of the burden of foodborne disease and it was not until 2015 that the World Health Organization (WHO) produced its first global estimate. The report, looking at foodborne disease caused by 31 agents – bacteria, viruses, parasites, toxins and chemicals – concluded that each year as many as 600 million, or almost 1 in 10 people in the world, fall ill after consuming contaminated food. Of these, 420 000 people die, including 125 000 children under the age of 5 years.

The various ways in which foods can transmit illness, the extent of the problem and the principal causative agents are described in more detail in Chapters 6, 7 and 8.

Microbes can, however, play a positive role in food. They can be consumed as foods in themselves, as in the edible fungi, mycoprotein and algae. They can also effect desirable transformations in a food, changing its properties in a way that is beneficial. The different aspects of this and examples of important fermented food products are discussed in Chapter 9.

Food microbiology is unashamedly an applied science and the food microbiologist’s principal function is to help assure a supply of wholesome and safe food to the consumer. This must accommodate the impact of social and other changes taking place, such as greater affluence, increasing consumption of food away from the home, reduced frequency of food shopping, increased international travel and the development of new food processing technologies. To do this requires the synthesis and systematic application of our knowledge of food microbiology to practical situations, to ensure the consistent production of safe, stable and affordable foods. How we attempt to do this is described in Chapter 11.