CANNED FOODS - PowerPoint Presentation

Slide1

CANNED FOODSSlide2

CANNINGCanning

 is a method of preserving food in which the food contents are processed and sealed in an airtight container.

Canning provides a typical shelf life ranging from one to five years, although under specific circumstances a freeze-dried canned product, such as canned, dried lentils, can last as long as 30 years in an edible stateTo prevent the food from being spoiled a number of methods are used:

pasteurisation

, boiling (and other applications of high temperature over a period of time), refrigeration, freezing, drying, vacuum treatment, antimicrobial agents are usedSlide3

Safe Canning MethodsThe boiling water bath method is safe for tomatoes, fruits, jams, jellies, pickles and other preserves. In this method, jars of food are heated completely covered with boiling water (212°F at sea level) and cooked for a specified amount of time

Pressure canning is the only safe method of preserving vegetables, meats, poultry and seafood. Jars of food are placed in 2 to 3 inches of water in a special pressure cooker which is heated to a temperature of at least 240° F. Slide4

This temperature can only be reached using the pressure method. A microorganism called Clostridium botulinum

is the main reason why pressure processing is necessary. Though the bacterial cells are killed at boiling temperatures, they can form spores that can withstand these temperatures. The spores grow well in low acid foods, in the absence of air, such as in canned low acidic foods like meats and vegetables. When the spores begin to grow, they produce the deadly

botulinum toxins(poisons)Slide5

Foods that are low acid have a pH of more than 4.6 and because of the danger of botulism, they must be prepared in a pressure canner.The low acidic foods include:meatsseafood

poultrydairy productsall vegetablesSlide6

High acid foods have a pH of 4.6 or less and contain enough acid so that the Clostridium botulinum spores can not grow and produce their deadly toxin. High acidic foods can be safely canned using the boiling water bath method.

The high acidic foods include:fruitsproperly pickled vegetablesSlide7

FACTORS THAT LIMIT THE SHELF LIFE OF CANNED FOODS Cans or glass jars with metal lid can get rusted if not used properly 

Cans could even corrode, if food will chemically react with metal container. Especially highly-acid food like canned tomatoes and fruit juices gets easily corroded. Temperatures over 100 degrees Fahrenheit are harmful for canned foods. If the storage temperature rises, the risk of spoilage of

food, jumps sharply. There are high chances of loosing nutrient of the caned food, if stored at above 75 degree for very long periodSlide8

SPOILAGE OF CANNED FOODSThe most important kind of chemical spoilage of canned foods is hydrogen swell, resulting from the pressure of hydrogen gas released by the action of acid of a food on the iron of the can

Hydrogen swells favored by:Increase in acidities of foods

Increase in tempratures of storageImperfections in the tinning and lacquering of the interior of the can

Presence of soluble

sulphurs

and phosphorus compoundsSlide9

TYPES OF SPOILAGE OF CANNED FOODSThree most important kinds of biological spoilage of commercially canned foods are:

flat sour spoilage

TA spoilage putrefacation

A fourth kind of spoilage caused by the action of food on the iron of the

can,results

in hydrogen swellSlide10

FLAT SOUR SPOILAGE

This kind spoilage occurs when canned food remain flat during souring or by development of lactic acid in the food by the flat sour bacteriaThis spoilage occurs chiefly in low acid foods such as peas and corn and is caused by species of Bacillus Flat sour spoilage of acid foods like tomatoes or tomato juice is caused by special

facultatively thermophillic species bacillus

coagulansSlide11

Various species of bacillus that are able to form acid without gas in food may be mesophilies,facultative

thermophilies or obligate thermophiliesThe spores of mesophilies are less heat resistant and killed by heating process and hence are rarely concerned with flat sour spoilage

the spores of thermophilies are more heat resistant and may survive the heat process and cause flat sour spoilageSlide12

TA SPOILAGEThis is a

thermophillic spore forming anaerobe that forms acid and gas in foodsThe gas(mixture of carbon dioxide and hydrogen) swell the can if it is held long enough at a high

temprature and may eventually cause burstingThe spoiled food usually has a sour odour

. Sources are same as for flat sources bacteriaSlide13

SULFIDE OR SULFUR STINKER SPOILAGE

Spoilage caused by Desulfotomaculum nigrificansFound in low acidic foods such as peas and corn

Spores of this bacterium are less heat resistant than those of flat sour and TA bacteriaThe organism is an obligate thermophile and therefore also requires poor cooling of heat processed foods or hot storage for its developmentSlide14

TYPES OF SPOILAGE BY MESOPHILIC SPORE FORMING BACTERIAMOST SPOILAGE BY MESOPHLIC MICROORGANISMS THAT RESULTS FROM UNDERPROCESSING IS CAUSED BY SPORE FORMING BACTERIA OF THE GENERA

BACILLUS AND CLOSTRIDIUMSlide15

SPOILAGE BY MESOPHILIC clostridium species:Sugar fermenting species of clostridium –eg-

c.butyricum and c.pasteurianum causes butyric acid fermentation in acidic foods by release of

carbon dioxide and hydrogenOther species such as C.

sporogenes

,C.

putrefaciens

,C.

botulinum

are

proteolytic

or putrefactive decomposing proteins with the production of malodorous compounds such as hydrogen

sulfide,ammonia,indole

and

skatoleSlide16

Putrefacative anaerobes also produce carbon dioxide and

hydrogen,causing the can to swellCanned acid foods such as

pineapple,tomatoes and pears have been found spoiled by C.pasteurianumPutrefactive

anerobes

grow best in the low acid –canned foods such as

peas,corn,meat,fish

and poultrySlide17

SPOILAGE BY MESOPHILLIC bacillus SPECIES:Spores of various species of Bacillus

differ considerably in their heat resistanceSpores of many of the mesophillies are killed in a short time 100 C` or less but few can survive the heat treatments employed in steam-pressure processing

Many species of Bacillus are aerobic and therefore cannot grow in a well evacuated containerSlide18

Commercially canned foods have been spoiled by bacillus species,especially in poor evacuated cans

aerobacilli or gas forming bacillus species have been reported to cause spoilage of canned peas,asparagus,spinach,peaches and tomatoesSlide19

SPOILAGE BY YEASTCanned fruits,jams

,jellies, fruit juices , syrups and sweetened condesed milk have been spoiled by fermentative yeast with swelling of the cans by carbon dioxide producedFilm yeast may grow on the surface of jellied pickled

pork,repacked pickles or olives and similar products but their presence indicates contamination or lack of heat processing ,plus poor evacuationSlide20

SPOILAGE BY MOLDSMolds probably are the most common cause of the spoilage of home canned foods which they enter through a leak in the seal of the container

Jams , jellies, marmalades and fruit butters permit mold growth when sugar concentration are as high as 70 % and in the acidity usually present in these productsSome molds are fairly resistant to heat,especially

those forming tightly packed masses of mycelium called sclerotia.Byssochlamys

fulva

a pectin fermenting

mold,has

ascospores

that have resisted the heat processing of bottled and canned fruits and have caused spoilageSlide21

SPOILAGE OF CANNED MEAT AND FISHCanned fish and meat exhibits two chief types of spoilage by:

bacillus species resulting in softening and souring

Clostridium species producing putrid swellsLess commonly bacilli may produced acid and gas and swells the cans

Heat process given to Canned cured meats are insufficient for sterilization therefore it may be subjected to production of carbon

dioxide,nitrogen

oxide or nitrogen gas from

nitrate,sugars

and meat or they may subjected to

putrefacation

with gas produced by

Clostridium

species

Such species ordinarily is prevented by adequate refrigeration