FOOD PRESERVATION

ASEPSIS,TEMPERATURE, DRYING, RADIATION AND CHEMICALS

INTRODUCTION

• Food preservation can be defined as the process of treating and handling food in such a way as to stop or greatly slow down spoilage and prevent foodborne illness while maintaining nutritional value, texture and flavour.
• Among the oldest methods of preservation are drying, refrigeration, and fermentation.
• Modern methods include canning, pasteurization, freezing, irradiation, and the addition of chemicals.

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Importance of Food Preservation

• Food preservation gives the food more variety.
• Food preservation extends food's shelf-life.
• Food preservation expands the supply of food.
• Food preservation cuts down on food waste.
• Food preservation helps to reduce dietary deficiencies.

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Food preservation also make food more resistant to microorganism growth and slow the oxidation of fats.

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ASEPSIS

• Process of preventing contamination of food by spoilage micro-organisms is called asepsis.
• Inner tissue of healthy animal and plants do not contain micro-organisms and if present they usually do not spoil food.
• Most spoilage micro-organisms enter into the food by contamination from external sources like water, air etc.
• Several foods like egg contains natural covering around food that prevent entry of spoilage organism into the food.
• Nowadays, variety of such artificial barrier are made around the food to prevent contamination.
• For.eg. fruits and vegetables are stored for years by coating the wax around them.
• Some other artificial barriers that prevent the contamination includes wrappers, cartoons and cans. Safe handling of food and good personal hygiene of food handler are important method to minimize contamination of food by spoilage organisms.

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Some techniques that preserve food by removing microorganisms include:

• Filtration:
• It is only one successful method for removing micro-organisms from contaminated food.
• Unfortunately, this method is applicable only for clear liquid like clear fruit juice, beverages etc.
• To remove micro-organisms, liquid food is filtered through sterile bacterial filter.
• Centrifugation/ sedimentation:
• Centrifugation removes some but not all micro-organisms from contaminated liquid food.
• When liquid food is centrifuged suspended particle, debris and some micro-organisms settle to the bottom which is later separated and remove from the food.
• This technique is commonly used for milk in dairy industries.

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By removing microorganisms from contaminated food�

• Washing:
• This method is commonly used for vegetable and fruits. Dusts and micro-organisms present on the surface of whole vegetable and fruits are removed by washing with sterile water.
• One limitation of washing is that it increases water activity of some food and hence facilitates growth of remaining spoilage organisms.
• Furthermore, if washing water is not sterile, it adds spoilage organisms in food.
• Trimming:
• Trimming is the process of removing spoiled parts of food like vegetables and fruits by cutting.
• Trimming prevents spread of micro-organisms from spoiled part into inner healthy tissue.

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�Maintenance of anaerobic conditions�

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• A preservative factor is sealed. Packaged foods may be in the anaerobic conditions in the container.
• A complete fill, evacuation of unfilled space or replacement of the air by co2 or by inert gas such as N2 will bring about anaerobic conditions.
• Spores of some aerobic organisms are especially resistant to heat and may survive in canned foods, but will not be able to germinate under anaerobic conditions.
• Production of C02 and during fermentation and its accumulation at the surface will serve to make conditions anaerobic there and prevent the growth of aerobes.

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�Use of high temperatures�

Pasteurization:

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• Process of slow heating is known as Pasteurization. It can kill some microorganisms but not all.
• Usually involves the application of temperature below 100 degree Celsius.
• The heating can be done by means of steam, hot water, dry heat and electric currents.
• Time and temperature used in this process depends upon the method employed and the product treated.
• The high temperature-short time method employs comparatively higher temperatures for a short period of time.
• The low temperature-long time method uses a lower temperature for a longer time.
• Example: Grape wine pasteurization for 1min at 82-85 degree Celsius in bulk.

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�Use of low temperature�

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At lower temperatures, chemical reactions, enzyme action and

microbial growth will be much slower.

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Chilling/Cold storage:

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• In this temperature is not far above freezing.(-1 degree Celsius)
• Generally refrigerators are used at 0-8 degree Celsius for preserving food products.
• Most perishable foods like eggs, dairy products, meat, and seafood can be held in chilling storage refrigerators for a limited time with a very little change from their original condition.
• Process of Enzymatic and microbial changes in food cannot be prevented by this method, but the process is slowed down to great extent.

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Freezing or Frozen storage:

• The rate of freezing of foods depends on the method employed, temperature used, circulation of air and the type of food to be freeze.
• The temperature is usually -23.3 degree Celsius or (lower to -15 to -29 degree Celsius) and takes 3-72 hours for the process.

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Drying�

Solar Drying:

• It is limited to climates with high temperatures and dry atmosphere and to certain types of fruits like apricots, peaches and pears.
• This process takes longer time than other processes.

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Mechanical Drying:

• Involves passage of hot air with controlled relative humidity over the food to be dried.
• The simplest dryer is the evaporator or Kiln, where the natural draft from the rising of hot air brings about drying of food.

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Freeze drying: 

• Freeze drying or sublimation of water from a frozen food by means of vacuum and applied heat at drying shelf can be used in number foods like meat, poultry, seafood, vegetables and fruits.

�Preservation by Radiation�

• This method can also be called as cold sterilization.
• Surface contamination of several foods can be prevented or reduced by this method. Radiations like UV rays, X-rays and gamma rays are used to kill microorganisms.
• Example: low level of radiations can be used on fruits and vegetables to kill insects and prevent food from spoilage.

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�Preservation by food additives�

• Food additives are specifically added to prevent decomposition or deterioration of food. The food additives used for this purpose are called as chemical preservatives.
• They inhibit microorganisms by inhibiting their cell membrane, enzyme activity or their genetic mechanism.
• Factors that influence effectiveness of chemical preservatives in inhibiting microorganisms are: concentration of chemical, temperature, time, chemical and physical characteristics of substrates in which organism is found.
• Food additives added include organic acids, salts, sugars and spices.
• Salting helps in preserving fruits for a longer duration.
• Sodium benzoate, vinegar, and sodium metabisulphite which are known as synthetic preservatives can also be added.

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Canning

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• Canning can be defined as preservation of food in sealed containers and usually implies heat treatment as the principle factor.
• Canning is done using Tin cans or in glass containers.
• Raw food for canning is freshly harvested, properly prepared, graded and washed thoroughly before used for canning.
• Many vegetable foods are blanched briefly by hot water or steam before packaging.
• Blanching washes the food further, sets color, and kills microorganisms.

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OVERVIEW OF FOOD PRESERVATION METHODS

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THANK YOU

BY

M.JERLINE

Head and Assistant Professor

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Department of Biochemistry

Dr.R.A.N.M Arts and Science College

Erode.