Introduction to Food Preservation Part I

Food spoilage and food preservation techniques:

The crop when harvested from the farm then the produce the post agricultural system. For the longer shelf life the harvested is to be processed which in general called Food Processing. The produce which is harvested has the many factors which could be deteriorated some of them are

a. Microorganism

i. Bacteria.

ii. Fungi

  • Yeasts
  • Moulds

b. Food Borne Diseases

c. Food Enzyme presence

d. Chemical Breakdown

e. Physical Damage during harvest or crop transportation

It’s been noticed that mostly the food is been spoiled or deteriorated by the microorganisms which is favored by two factors:

a. Intrinsic Factor (Internal Factor)

i. Moisture content
ii. pH
iii. nutrient content in food
iv. Oxidation reduction potential
v. Natural Inhibitory substances
vi. Structure and texture

b. Extrinsic Factor

i. Temperature of storage
ii. RH of environment
iii. Gas storage

Food Preservation by Blanching

Blanching is the heat treatment of the food for a short period of time. It’s normally done by dipping in the boiling water from few seconds to minutes depending upon the size of the produce to be blanched. Food/Plants contain many types of the enzymes present like example when apple is cut off into two halves the apple turn to red or brown due reaction of enzyme and sugar which is called enzymatic browning. Some of the general enzyme present in the plant/food are lipozygenase, polyphenoloxidase, polygalacturonase etc which is responsible for the loss of the flavor and nutrition and texture. A good example could be over ripened banana.

Benefits of blanching

The benefits of blanching are such as

a. To inhibit the enzyme action

Blanching inhibits the enzyme activity which prevents browning of the foods when cut off.

b. To expel the gases

Blanching reduces the intracellular gaseous spaces, pesticide and fungicide contaminants.

c. To reduce the microbial load and contaminants

Dipping in the hot boiling water prevents as well as reduces the microbial load, which ultimately prevents the microbial spoilage.

But there is the loss of the water soluble vitamins (B complex, C) during this process.

Food Preservation by drying

Drying is the oldest method of the food preservation. Gundruk is the natural food which is preserved by drying. Dehydration is the process of removal of the water by the application of heat.

Introduction to food preservation

Source: PJ Fellows Food Process Engineering

The frequently term used in drying is moisture content and water activity, mathematically it is defined as the:

Moisture content (MC)=

Water activity (aw) =
=

The range for moisture content is 0 to 100% whereas for the water activity is 0 to 1. Moisture content is useful in the food processing ( will be consulted in next day) whereas water activity is useful for studying microbial preference for their growth. Water activity is less than 0.65 than its safe from all sorts of the microorganisms. When the food is being dried there is change is texture, moisture content and color. Sekuwa, gundruk, sinki, potato chips are some of the examples of drying.

Low temperature storage

Freezing is another application of the food preservation. In general freezing the temperature of storage is below 5oC. The purpose of the freezing is to minimize the enzymatic activity, respiratory activity and microbial activity thus by enhancing the shelf life of the food. Cellar storage is also a principle of low temperature storage. Cellar is constructed below the ground with depth varying from 6ft to 8ft in hilly and mountainous region of the country. Generally cellar storage ranges from 4ft by 4ft to 4ft by 6ft. Deep freeze is also another type of low temperature storage where the temperature of storage is below -18oC. This type of storage is mostly suitable for meat and meat products like sausages, syrup, brines etc.

Food preservation by high temperatures

Food is also preserved by high temperatures like pasteurization, ultra high temperature (UHT), sterilization. Pasteurization are of two types namely low temperature low time (LTLT) which is 65oC for 30 minutes and high temperature short time (HTST) which is 73-75oC for 15 seconds. Sterilization temperature is 121oC at 15 psi pressure (pound per square inch). Ultra high temperature (UHT) is 135-140oC for few seconds. Normally fluid products are preferred in this process like milk, yoghurt, wine, beer, cream etc.

Food preservation by fermentation

Fermentation is process of breakdown from complex ones to simple ones with help of microorganisms or enzymes. Cut tear curl (CTC) tea is a good example of enzymatic fermentation whereas the yoghurt is another good example of microorganism. During
fermentation there are many changes like pH, texture, aroma etc. During the fermentation the pH of the food lowers as a result it becomes harder for microorganisms for growth. A good example could be taken as gundruk which has a typical aroma and texture.

Food preservation by preservatives

Preservation could be done by adding preservatives too. Natural preservatives like sugars, ethanol, honey, wood smoke, spices and essential oils, acetic acid or vinegar are used globally. They have no any side effects on health. Sugar candy (like तििोरा) or sugar coated fruit leather, wood smoke preservation like sukuti (सुकुटी), salt and spice preservation like titaura (तििोरा). Similarly there are other chemical preservatives like benzoic acid (used in the form of sodium benzoate), parabens, sulfur dioxide (used as potassium metabishulphite), sorbic acid, propionic acid, nitrates & nitrities, boric acid. These chemical preservatives have their own acceptable limit like for wine SO2 must not be more than 250 ppm.

 

 

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