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Food Microbiology: Fundamentals and Techniques
Raina Jain, Prashant Bagade*, Kalpana Patil-Doke and Ganesh Ramamurthi
National Commodities Management Services Limited, Hyderabad, India
Abstract
Food microbiology is a broad subject encompassing study of both beneficial and harmful microorganisms in food, and their effects on the quality and safety of food. Beneficial microbes present in food offer an array of health benefits to humans and are important sources for fermentation, probiotics and bio- preservatives. Contrarily, harmful bacteria lead to food spoilage and a countless number of foodborne diseases which may even prove to be lethal, if uncontrolled. Food microbiology uses a number of testing methods to detect, enumerate and identify the microorganisms present in food. Conventionally, it involved culturing of microbes on suitable media and analyzing the results on the basis of physical or biochemical tests. However, such techniques are time-consuming and laborious. As a result, rapid and high-throughput techniques with use of advanced equipment and strategies have been developed to ensure quality and safety of food in real time. The chapter presents the long history of the development of Food Microbiology as a subject, along with classical and advanced techniques used to identify and quantitate foodborne microorganisms.
Keywords: Food microbiology, food spoilage, food microbes, food regulations, microbiological techniques, probiotics, AI and ML in food, biosensors
1.1 Introduction
Food microbiology is the study of microorganisms that colonize, modify, process or spoil food. It deals with foods and beverages of diverse composition, combining a broad spectrum of environmental factors, which may influence microbial survival and growth. A variety of microorganisms having beneficial or harmful effects on food quality and safety are studied in food microbiology. This includes spoilage, pathogenic, fermentative, and probiotic bacteria; molds and yeasts; viruses, prions, and parasites.
Microorganisms, viz., bacteria, molds and viruses can contaminate foods across the food value chain. Consumption of such foods can cause food-borne diseases. Effective intervention technologies are being developed and implemented to ensure safety of consumers against foodborne diseases. Food spoilage occurs due to growth of microorganisms in food or due to the action of microbial enzymes. Incidences of food contamination and spoilage are very frequent, and are being reported on a regular basis. Such incidences are partly due to consumers' changing palate in desiring undercooked, minimally processed, unpreserved foods, etc. Additionally, inadequate infrastructure along the supply chain, especially for temperature-sensitive foods, also plays a major role in food spoilage leading to economic losses.
Food bioprocessing is a technique of food and ingredient extraction, purification and production using processes that involve the application of enzymes and/or microorganisms. It is one the most primitive forms of food processing method, used by early Egyptians for production of wine, beer, and bread. Additionally, microbial enzymes were also being used to produce food and food additives. Since the past few years, by adoption of genetic recombination techniques and use of different microbial sources, enzymes of higher purity and activity are obtained. Nowadays, many types of additives from microbial sources are being developed and utilized in food processing. Some of these include single-cell proteins, essential amino acids, colour and flavour compounds, stabilizers, and organic acids [1]. Food bio-preservation through anti-microbial metabolites such as bacteriocins and organic acids like acetic, propionic and lactic acids are being developed and used, replacing preservatives of non-food origin. Probiotics - a rapidly emerging health food - contain live cells of bacteria that have apparent health benefits. The role of these bacteria for health and bacterial efficacy benefits are being researched upon.
1.2 Food Microbiology: A Historical Perspective
Foodborne disease and food spoilage have been part of the human experience since the dawn of our race. Several events spanning centuries led to the recognition of the role of microorganisms in foods. We are aware that early civilizations discovered and applied effective methods to preserve and protect their food. As far back as 7000 BC, Babylonians manufactured beer and wine. Egyptians, in 3000 BC, manufactured cheese and butter. Around the same time, use of salt to preserve meat and other foods became popular. In 1000 BC, the Romans discovered fermentation, salt, ice, drying and smoking to preserve shrimp and meat, though they did not know how these practices inhibited food spoilage or caused foodborne diseases. This was compounded by their belief that living things formed spontaneously from non-living matter.
In 1665, Francesco Redi demonstrated that maggots on putrefying meat did not arise spontaneously but were instead the larval stages of flies. This was the first effort opposing the doctrine of spontaneous generation. In 1765, Spallanzani disproved the theory of spontaneous generation of life by demonstrating that beef broth which was boiled and then sealed remained sterile. The French government offered 12,000 francs to anyone who could develop a practical way to preserve food in 1795. Nicholas Appert showed that meat could be preserved when it was placed in glass bottles and boiled. This was the beginning of food preservation by canning. Later, Schwann demonstrated that heated infusions remain sterile in the presence of air, again to disprove spontaneous generation. It is interesting to note that although Spallanzani and Schwann each used heat to preserve food, neither apparently realized the value of turning these observations into a commercial method for food preservation [2].
The first person to really appreciate and understand the cause- effect relationship between microorganisms in infusions and the chemical changes that took place in those infusions was Louis Pasteur. He convinced the scientific world through his experiments that all fermentative processes were caused by microorganisms. Later, he showed that souring of milk was caused by microbes and heat destroyed undesirable microbes in wine and beer. The later process is now used for a variety of foods and is called pasteurization. Because of the importance of his work, Louis Pasteur is known as the founder of food microbiology. Using his famous swan-necked flasks, he even demonstrated that air does not have to be heated to remain sterile, and this finally put an end to the theory of spontaneous generation. The knowledge that microbes were responsible for fermentation and putrefaction led Pasteur to argue that microbes were also causative agents in disease. These arguments eventually helped Joseph Lister to develop the first aseptic surgical procedures. Since that time, microbiological discoveries and developments began to proceed more rapidly, leading to implications of microbes in several diseases. This led governments to enact legislation to protect the quality of food.
Most of the food industries hesitated in adopting microbiological food safety norms in their routine procedures until they were economically affected by outbreaks of foodborne diseases in their products. One similar case occurred in 1920s with the outbreak of Botulism, which affected food canning industries. This resulted in adoption of the 12D process for heat treatment of C.botulinum. At about the same time, the dairy industry was driven to implement microbiological control over safety in milk production, because of several nasty outbreaks of milk-borne diphtheria, tuberculosis, typhoid fever, and brucellosis. Regulatory bodies made it compulsory to address the risks with focus on animal health, sanitation, and pasteurization - which had an immediate and very effective impact on the problems.
In one of the cases of early food microbiology, the US government had institutionalized a woman who came to be known as "Typhoid Mary". She was an asymptomatic typhoid carrier who worked as a cook for several families. Over 10 years, seven outbreaks of typhoid were directly traced to her and estimates suggest that she may have been responsible for 120 cases [3] of typhoid fever. New York authorities arrested her but eventually released her when she agreed never to work as a cook again. When another outbreak was traced to her a few years later, she was arrested as a threat to public safety and institutionalized until her death in 1938.
1.3 Beneficial Microbes in Food
The role of beneficial microbes is not given due recognition since it is a common perception to think of microbes only as harmful. Their presence in human gut play a significant role in maintaining human health by ensuring proper digestion apart from a range of benefits. The number of microorganisms that are present in the human GI tract is estimated to be over 1014 [4]. A recent study [5] has identified about 2,000 bacterial species in the human gut by using computational methods. However, these species are yet to be cultured in the lab. Beneficial microbes are used in the food industry for a variety of applications with simplest being in fermentation, which has been used since ancient times for production of wine, bread, cheese, etc., apart from a host of traditional dishes. Fermented foods are considered healthy due to the presence of various health promoting microorganisms. Based on the concept, a new trend that has taken over and is...
