Food-preservation processes, role

The plants and animals we have chosen to use as foods naturally contain, as we have already noted, thousands of chemicals that have no nutritional role, and when we eat to acquire the nutritionally essential chemicals we are automatically exposed to this huge, mostly organic, chemical reservoir. Of course, human beings have always manipulated foods to preserve them or to make them more palatable. Processes of food preservation, such as smoking, the numerous ways we have to cook and otherwise prepare food for consumption, and the age-old methods of fermentation used to make bread, alcoholic beverages, cheeses and other foods, cause many complex chemical changes to take place, and so result in the introduction of uncounted numbers of compounds that are not present in the raw agricultural products. 

Preservatives or antimicrobial agents play an important role in today s supply of safe and stable foods. Increasing demand for convenience foods and reasonably long shelf life of processed foods make the use of chemical food preservatives imperative. Some of the commonly used preservatives—such as sulfites, nitrate, and salt—have been used for centuries in processed meats and wine. The choice of an antimicrobial agent has to be based on a knowledge of the antimicrobial... 

The ability to store large quantities of food has played a pivotal role in mankind s development. Evidence of food preservation dates back to the postglacial era, from 15,000 to 10,000 BC, and the first use of biological methods has been traced back to 6000 to 1000 BC, with evidence of fermentation processes used in producing beer, wine, vinegar, bread, cheese, butter, and yogurt (Soomro, Masud, and Anwaar, 2002). 

During the last three decades water activity, has played a major role in many aspects of food preservation and processing. It is defined as the ratio of the vapor pressure of water P in the food to the vapor pressure of pure water Pq at the same temperature (fl = P/Pq). Next to temperature, it is now considered as probably the most important parameter having a strong effect on deteriorative reactions. The effect of water activity was studied not only to define the microbial stability of the product but also on the biochemical reactions in the food system and its relation to its stability. It has become a very useful tool in dealing with water relations of foods during processing. 

As an interesting aside, the reader may recall that the conversion of cytosine to uracil (Equation 14.1) is accomplished by deamination through nitrosation and that the deamination shown in Figure 14.7 might raise questions about the role of nitrites in food preservation. It is difhcult to estabhsh whether the deamination process occurred as commonly prior to the widespread use of nitrites. 

Water molecules are constantly in motion, even in ice. In fact, the translational and rotational mobility of water directly determines its availability. Water mobility can be measured by a number of physical methods, including NMR, dielectric relaxation, ESR, and thermal analysis (Chinachoti, 1993). The mobility of water molecules in biological systems may play an important role in a biochemical reaction s equilibrium and kinetics, formation and preservation of chemical gradients and osmotic pressure, and macromolecular conformation. In food systems, the mobility of water may influence the engineering processes — such as freezing, drying, and concentrating chemical and microbial activities, and textural attributes (Ruan and Chen, 1998). 

In Chapters 4 and 6, considerable emphasis is placed on the environmental significance of biotransformation as opposed to biodegradation. It therefore seems appropriate to draw brief attention also to their use in biotechnology. Microorganisms play important roles in widely diverse technical processes ranging from the leaching of ores and the preservation of food, to the production of antibiotics and food additives. It is worth drawing attention to some features of these applications. 

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