Handbook of Food Spoilage Yeasts, Second Edition (Contemporary Food Science)

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Lu, Xuewen. McKellar and Xuewen Lu Preface The field of food microbiology is a broad one, encompassing the study of microor- ganisms that have both beneficial and deleterious effects on the quality and safety of raw and processed foods. Accumulating sufficient data on the behavior of microorganisms in foods requires an extensive amount of work and is costly.

One way this link can be made is through the use of mathematical models. In its simplest form, a mathematical model is a simple mathematical description of a process. Models have been used extensively in all scientific disciplines. They were first used in food microbiology in the early 20th century to describe the inactivation kinetics of food-borne pathogens during thermal processing of foods.

Since then, with the advent of personal computers and more powerful statistical software packages, the use of modeling in food microbiology has grown to the point of being recognized as a distinct discipline of food microbiology, termed predictive microbiology.

Food microbiology notes pdf

This concept was introduced and extensively discussed with partic- ular reference to growth of food-borne pathogens by McMeekin and his colleagues at the University of Tasmania. Extensive research in recent years has shown, however, that the most important application of predictive microbiology is in support of food safety initiatives. It has been argued, however, that predictive microbiology is a misnomer, for predictive microbiology does not actually make predictions at all.

To examine this further, we need to first look at some definitions of modeling. Food Technol 49 12 Farrer, K. Who invented the brine bath?

Food Technol. Goldblith, S. A condensed history of the science and technology of thermal processing. Joslyn, and J. Introduction to Thermal Processing of Foods, vol.

Jensen, L. Man's Foods, chaps.

Champaign, IL: Garrard Press. Pederson, C S. Microbiology of Food Fermentations. Schormiiller, J. Die Erhaltung der Lebensmittel. Stuttgart: Ferdinand Enke Verlag. Stewart, G. Introduction to Food Science and Technology, chap. New York: Academic Press. Tanner, F. The Microbiology of Foods, 2d ed. Food-Borne Infections and Intoxications. PART II Habitats, Taxonomy, and Growth Parameters Many changes in the taxonomy of foodborne organisms have been made during the past decade, and they are reflected in Chapter 2 along with the primary habitats of some organisms of concern in foods.

See the following for more information: Deak,T. Handbook of Food Spoilage Yeasts. Detection, enumeration, and identification of foodborne yeasts. Doyle, M. Beuchat, TJ. Montville, eds. Food Microbiology—Fundamentals and Frontiers. Food spoilage as well as foodborne pathogens are covered in this page work along with general growth parameters. Microorganisms in Foods. All of the foodborne pathogens are covered in this page work with details on growth parameters. Well referenced. CHAPTER 2 Taxonomy, Role, and Significance of Microorganisms in Foods Because human food sources are of plant and animal origin, it is important to understand the biological principles of the microbial biota associated with plants and animals in their natural habitats and respective roles.

Although it sometimes appears that microorganisms are trying to ruin our food sources by infecting and destroying plants and animals, including humans, this is by no means their primary role in nature.

Food Properties Handbook

In our present view of life on this planet, the primary function of microorganisms in nature is self-perpetuation. During this process, the heterotrophs carry out the following general reaction: All organic matter carbohydrates, proteins, lipids, etc. This, of course, is essentially nothing more than the operation of the nitrogen cycle and the cycle of other elements Figure The microbial spoilage of foods may be viewed simply as an attempt by the food biota to carry out what appears to be their primary role in nature.

This should not be taken in the teleological sense.

World Health Day: 7 April 2015

In spite of their simplicity when compared to higher forms, microorganisms are capable of carrying out many complex chemical reactions essential to their perpetuation. To do this, they must ob- tain nutrients from organic matter, some of which constitutes our food supply. If one considers the types of microorganisms associated with plant and animal foods in their natural states, one can then predict the general types of microorganisms to be expected on this particular food product at some later stage in its history.

Results from many laboratories show that untreated foods may be expected to contain varying numbers of bacteria, molds, or yeasts, and the question often arises as to the safety of a given food product based on total microbial numbers. The question should be twofold: What is the total number of microorganisms present per gram or milliliter and what types of organisms are represented in this number? It is necessary to know which organisms are associated with a particular food in its natural state and which of the organisms present are not normal for that particular food.

It is, therefore, of value to know the general distribution of bacteria in nature and the general types of organisms normally present under given conditions where foods are grown and handled. Many of the new taxa have been created as a result of the employment of molecular genetic Nitrogen Atmospheric Nitrogen fixation Denitrification Atmospheric nitrogen fixed by many microorganisms, e.

Ctostridium, Azotobacter etc.

World Health Organization, Food Safety: What you should know

Reduction of nitrates to gaseous nitrogen by bacteria, e. Source: From Microbiology by MJ. Pelczar and R. The methods that are the most powerful as bacterial taxonomic tools are outlined and briefly discussed below. First, the prokaryotic ribosome is a 70S Svedberg unit, which is composed of two separate functional subunits: 5OS and 30S. When the singlestranded DNA is made in the presence of dideoxynucleotides, DNA fragments of various sizes result that can be sequenced by the Sanger method.

It was through studies of 16S rRNA sequences that led Woese and his associates to propose the establishment of three kingdoms of life-forms: Eukaryotes, Archaebacteria, and Prokaryotes. The last include the cyanobacteria and the eubacteria, with the bacteria of importance in foods being eubacteria. Sequence similarities of 16S rRNA are widely employed, and some of the new foodborne taxa were created primarily by its use along with other information. Nucleotide catalogs of 16S rRNA have been prepared for a number of organisms, and exten- sive libraries exist.

Sequences -mers of bases are produced and separated, and similarities SAB Dice-type coefficient between organisms can be compared. The sequencing of 16S rRNA by reverse transcriptase is preferred to oligonucleotide cataloging, as longer stretches of rRNA can be sequenced. The latter group is referred to as the Clostridium branch of the eubacterial tree. It has been noted that the ideal reference system for bacterial taxonomy would be the complete DNA sequence of an organism.

In the meantime, changes in the extant taxa may be expected to continue to occur. Some of the important genera known to occur in foods are listed below in alphabetical order. Some are desirable in certain foods; others bring about spoilage or cause gastroenteritis. Each genus has its own particular nutritional requirements, and each is affected in predictable ways by the parameters of its environment.

Eight environmental sources of organisms to foods are listed below, and these, along with the genera of bacteria and protozoa noted, are presented in Table to reflect their primary food-source environments. Soil and Water. These two environments are placed together because many of the bacteria and fungi that inhabit both have a lot in common.

Soil organisms may enter the atmosphere by the action of wind and later enter water bodies when it rains. They also enter water when rainwater flows over soils into bodies of water. Aquatic organisms can be deposited onto soils through the actions of cloud formation and subsequent rainfall. This common cycling results in soil and aquatic organisms being one and the same to a large degree. Some aquatic organisms, however, are unable to persist in soils, especially those that are indigenous to marine waters.

Alteromonas spp. The bacterial biota of seawater is essentially gram negative, and gram-positive bacteria exist there essentially only as transients.