CANNING - FRUITS AND VEGETABLES

S.PRIYADHARSHINI 20086109

CANNING Canning is a method of preserving food in

which the food contents are processed and sealed in an airtight container.

Heat is the most common agent used. Removal of oxygen can also be used in

conjugation. Canning provides a typical shelf life

ranging from one to five years sometimes even more than that.

Principle of heat processing The basics for preservation of food by heat

is the destruction of living organisms which would cause spoilage of food.

Sometimes endanger the health of the consumer.

Consideration has to be given to the organoleptic and nutritional properties of the raw materials.

Heat processing regime It is influenced by number of factors Heat resistance of contaminating

microorganisms. Chemical and physical properties of

food. The rate at which heat penetrates the

product.

Classification by pH Acidity is the major factor in determining

the extent of heat process required to get commercial sterility, canned foods are classified as

Group1:low acid :pH 5 and above Group2:medium acid :pH 4.5 to 5.0 Group3:Acid: 3.7 to 4.5 Group4:High acid :pH 3.7 and below.

Most of canned vegetables fall under the category of medium and low acid group.

Risk factor is Clostridium botulinum, which causes botulism.

There are even spores in foods that are more heat resistant than C.botulinum.

Hence extended exposure of heat than the standard normal values.

Outline of the process- vegetables Canning of vegetables has following

process: Preparation of the food Filling Exhausting the container Sealing Thermal processing/sterilization Cooling the container and contents

Preparation of the food A number of processes are involved such

as washing, grading, peeling and blanching.

Washing – it involves agitating or tumbling the vegetables on moving belts or while they are immersed in water or subjected to water sprays.

Grading – products are size graded with screens of different diameters or parallel bars.

Peeling – it is an important preliminary operation.

In conjugation with washing it removes surface soiling and associated microbial contamination.

Methods – steam, mechanical, flame, abrasive, and lye peeling.

Blanching It is carried out due to following reasons To remove respiratory gases. To inhibit enzymatic reactions. To promote shrinkage of the product. To hydrate certain dry products. To pre-heat the product.

Different methods of blanching is done. The most common one is immersing the

vegetable in hot water at 85-950 C. Rotary immersion blancher, hydraulic-type

pipe blanchers. Hot water blanching causes loss of

nutrients and gives rise to large amount of waste water.

Filling Filling the material into glass or metal

container is accomplished by hand or mechanically.

The volume of headspace is important. Exhausting – it is the operation of removal

of air in the cans. It not only reduces the strain of the can

seams but also prevent internal corrosion and maintains quality.

Sealing – cans are closed by the formation of a double seam.

They may or may not be vacuum sealed. Thermal processing- sterilization of the

cans is done by heating accurately for predetermined time and temperature in heated water or steam air mixture.

Aseptic packaging –sterilized foods in bulk are filled in sterilized cans in aseptic conditions.

Storage – although canned food products are one of the most staple food products organoleptic and nutrient changes occur.

Rate of changes depend on >Storage temperature, nature of

packaging, product characteristics, severity of heat treatment.

Fruit canning process Needs for fruit processing – seasonal and

even modern transport systems are costlier.

Reasons for spoilage is biochemical activity and microorganisms.

The methods commonly used for long term canning, freezing etc.

Raw materials – must be sound, ripe and free from blemishes.

They are checked for quality before processing.

if they are picked during hot day must be processed without any delay – mould growth.

Process

Peeling – abrasion, lye and mechanical peelers.

Blanching – some fruits may require blanching prior to filling.

Softening and shrinkage helps filling. Hot filling reduces processing time.

Choice of cans depends on the raw material.

Filling – temperature of the product is highly important at the time of closing the can.

Syrup – fruits are always covered with sugar syrup from beet , cane , dextrose corn syrup, glucose syrup or invert syrup.

The UK canners code of practice defines light syrup, syrup, and heavy syrup.

These vary according to the type of fruit, a distinction being made between following three classes.

Class A : Apples, bilberries, blackberries, black currants, cherries… etc

Class B : Apricots, peaches, pears , pineapple, fruit salad, and fruit cocktail.

Class C : Prunes. Syrup: class A B C Light 15 15 10 Syrup 30 22 15 Heavy 40 30 20 Exhausting – it is the process of removing

air and entrapped gases from the can before closing.

A product containing a thin liquid will only rarely occlude gases below its surface.

Therefore it requires removal of air in the headspace.

Viscous or semi-solid products may contain a considerable amount of entrapped air when filled into can.

Fruit tissues also may contain Co2 .

The syrup is filled as hot as possible. Can closing is often preceded by steam-

flow closure. Processing – is almost similar to vegetable

processing. Prunes require extra heating for correct

texture. Fruits are processed in boiling water or

steam in atmospheric pressure.

They are correctly cooled at optimum conditions.

Sudden changes in ambient temperature should be avoided.

Checking of can vacuum, pH of end products and brix value of final syrup are general tests carried out.

References Fruit processingBy David Arthey, Philip. R. Ashurst Vegetable ProcessingBy David Arthey, Colin Dennis http://books.google.co.in/books?id

=d13ew2Du-gEC&pg=PA78&lpg=PA78&dq=Blanching,+exhausting,+processing+conditions&source=bl&ots=nPXDRaH8lx&sig=303vAO3DJyi4AH7b94TsCliJc2s&hl=en&ei=dHFgTtibOoXorQfJkOzwDw&sa=X&oi=book_result&ct=result&resnum=1&sqi=2&ved=0CB0Q6AEwAA#v=onepage&q&f=false

http://books.google.co.in/books?id=TvatVJxVTykC&pg=PA138&lpg=PA138&dq=Blanching,+exhausting,+processing+conditions&source=bl&ots=Pz0EuihLwg&sig=uV-s5ZTm3CERi6bw4YfYIEJJNlU&hl=en&ei=dHFgTtibOoXorQfJkOzwDw&sa=X&oi=book_result&ct=result&resnum=9&sqi=2&ved=0CFAQ6AEwCA#v=onepage&q&f=false

Thank you with canned fruit cocktail