Conservación de alimentos

FOOD AND INDUSTRIAL MICROBIOLOGY
Food Preservation Dr. Rakesh Kumar Gupta
Reader, Department of Microbiology, Ram Lal Anand College, Dhuala Kuan, New Delhi-110021 (10-Aug-2006) Revised 17-Sep-2007

CONTENTS Introduction Principles of food preservation Physical methods of food preservation Asepsis Removal of Microorganisms High Temperature Drying Low Temperature Irradiations High HydrostaticPressures Ultrasound Pulsed Electric Fields Chemical Methods of Food Preservation Organic Acids and their Salts Nitrite Sulfur Dioxide NaCl and Sugars Gases Biopreservatives

Keywords
Microorganisms, preservation, packaging, physical preservation, chemical preservation, biopreservatives, nisin, UHT, irradiation, drying, freezing, blanching, canning, hurdle technology, aseptic packaging,bactofuge, ultrasound, pulsed electric field, high hydrostatic pressures.

Introduction Most foods deteriorate in quality following harvest, slaughter or manufacture, in a manner that is dependent on food type, its composition and storage conditions. The principal quality deterioration reactions of foods may be Microbiological The microorganisms present in a food may be contributed by its own naturalmicroflora or from the processing conditions like in the course of harvesting/manufacturing, storage, and transport. In some cases the microflora has no discernible effect on the food quality and food safety while in others, this may affect the quality in several ways like causing food spoilage, food borne illness or food fermentations. While food fermentations are desirable transformations of foodbut food spoilage, food borne infections and intoxications may result into huge economic losses as in cases where a particular batch of food has been found to be involved in an outbreak of a disease or has low shelf life as desired and hence the complete batch has to be recalled back from the market and destroyed. In developing countries like India, losses due to microbial spoilage have beenestimated between 10-25% in various types of foods, which adds to the problems of acute shortage of food supply in these countries. Enzymatic Enzymes native to plant and animal tissues or from microorganisms are responsible for changes in the texture, color, smell and appearance of foods e.g. microbial enzymes cause hydrolytic reactions, rancidity and browning in foods, and plant enzymes may causeover ripening of fruits and vegetables rendering them unsuitable for consumption. Chemical Chemical reactions like oxidative rancidity, oxidative and reductive discoloration, non enzymatic browning and destruction of nutrients contribute to the deterioration of foods if not stored in a proper environment. Physical Physical changes are responsible for loss of texture, flavors and structural damage.The most serious forms of quality deterioration include those due to microorganisms, following the survival and/or growth of spoilage, infectious pathogenic bacteria or the growth of toxinogenic ones. In this chapter we are going to study how these losses due to microbial spoilage of foods can be minimized and how foods are made safe for our consumption. The techniques employed to achieve thesetargets are called food preservation. Principles of food preservation The food preservation methods by which the microbial decomposition of foods can be delayed or prevented include 1. Restrict access of microorganisms to foods (packaging and aseptic packaging), 2. Removal of microorganisms (by filtration or centrifugation),

2

3. Slow or prevent the growth and activity of microorganisms(reduction in temperature, water activity and pH, removal of oxygen, modified atmosphere packaging and addition of preservatives) and 4. Inactivation of microorganisms (by heat, radiations, high hydrostatic pressures, ultra sound and pulsed electric fields). These methods usually are also effective against enzymatic activity or chemical reactions in the food, responsible for its self-decomposition....