FOOD PROCESSING

History
Formerly, production and small scale processing
done on farms & homes
Present days, centralized processing
Development from cottage & community
program to large scale
Early days - grain milling, milk processing and
sugar and candy processing
Steps taken from product to consumer involved
quality of the product and its value to end user
Types of food processing
a) Refining and milling:
- Sugar obtained from cane or beets
converted to common food product by
various processes known as refining
- Milling: convert grain into flour by
mechanical means
- Modern milling industry innovations in
measuring, metering, weighing, conveying,
blending, applying power & sanitation
b) Canning:
- Fresh food eg. Fruit, vegetables, meats,
fish preserved for long term storage by
heat treatment and sealing into air-tight
containers
- Containers may be metal, usually tinted or
untinned steel often plastic-lined,
aluminium or special strength glass
- Raw food packed in container, sealed and
heat treated to cook the food and sterilize
both container and contents
- Heat treating in steam pressure vessel @
121
o
C for time dependent upon size of
container and nature of contents
- Acid food (pH < 4.5): less time to process
than food with pH 4.5 7.0
- Toxins prod. By microorganism toxic to
humans hence processing severe enough
to destroy organism
- Heating degrade odor and taste of food
and other chemical changes take place
drg canning
- In general, short time high temp. cause less
deterioration than long time low temp. process
- Agitated cookers used to ensure good heat
penetration usg. short time treatment
- Agitation increases rate of heat transfer from
container to product
- Agitated cooker consists of preheater, cooker
and cooler
- Cans placed in individual compartments, rotated
by revolving reel on spiral track
- Track guides the compartments from inlet to
outlet continuously
c) Concentration
- Method of preservation: foodstuffs contain
high % of water partially dehydrated
- Eg. evaporated milk and fruit juice
- Usu. practice: reduce volume to of
original volume
- Three main processes:
i. evaporation with evaporators
ii. Reverse osmosis
iii. Freeze concentration
- The three processes are competitive
- Choice depends on nature of food
- Evaporation most common and
economical
- RO used for separation & concentration
eg. separation of lactose from whey
- Freeze concentration very limited high
cost, eg. wine, beer, coffee, apple and
orange juices, skim milk & vinegar
- Advantage: color & flavor retained
compared wt. heat treatment
d) Freezing
- Preservation by freezing possible if food can be
frozen v. quickly (supercooled) and maintained
at low temp. preventing ice crystal formation
- Quality not greatly deteriorated and
microorganisms will not increase
- Ordinary slow freezing large ice crystals in
cells of food rupture cells and cause structure
breakdown, hence allows undesirable enzyme
reactions at L temp. (-18
o
C) to take place
- Prevention: inactivation of enzymes by heat
treatment (blanching) prior to freezing
- Quality of final product improved if amt. of water
reduced bef. Freezing
- Frozen food either packaged or unpackaged
- Unpackaged food freezes faster but dehydration
become serious problem
- Actual freezing accomplished by:
i. either still or forced air
ii. direct contact with metal surface cooled by a
refrigerant
iii. immersion in liquid nitrogen
- Freezing only inactivate microorganism however
on thawing the organisms are reactivated and
food spoiled faster
- Freezing retained nutrients in food
e) Drying
- Method practice since ancient times
- Common technique : sun drying to preserve
fruits
- Dried food easy to transport & store bec. occupy
1/10 volume of fresh food
- Microbial growth control bec. amt. of water not
sufficient for growth
- Mold will grow if water content 12% or higher
although few mold grow at 5% moisture
- Most bacteria require at least 30% moisture
- Nutritive value of dried food is unchanged but
vitamin content generally reduced
- Sun drying cheapest drying method but
contamination of product by dust, insects, birds
and rodents
- Dried fruits changed color from bright to dark
brown unless fruit treated with SO
2
before drying
- Moist dried fruit, glycols are used to rehydrate
and soften harder sun or mechanically dried
prodt without adding moisture which allow
growth of microbes
- Freeze dehydration utilizes vacuum conditions
at triple point of water water molecules pass
from solid to gaseous phase with passing
through liquid phase, esp. for meat drying
f) Pasteurization and sterilization
- Pasteurization: HTST method exposes
milk to 73
o
C for not less than 16 s followed
by rapid cooling
- Purpose: kill pathogenic microorganisms,
eliminating food-borne disease, inactivate
enzymes to improve storage and keeping
quality
- Prodt kept refrigerated bec. method does
not kill all bacteria present
- Sterilization: eg. milk sterilization ie.
conditions severe enough to kill or
completely inactivate all microorganisms,
pathogenic and nonpathogenic, consists of
more intense heat treatment
- Sterilized product placed in sterile
container under aseptic conditions and
sealed
- Milk treated can be stored for several
months at room temperature
g) fermentation:
- Food processing and preservation methods
aims at destroying microorganisms but not all
organisms are detrimental
- Humans utilized microbes and yeast in wine
making, bread baking, cheese making and
salting of foods
- Fermentation: decomposition of carbohydrates
- Putrefaction: action of microorganisms on
protein
- Fermentation produces CO2 but no putrid odor,
while putrefaction produces sulfur-containing
protein prodts and HS
h) irradiation:
- Effects of radiation on various forms of life vary
with complexity of living organism
- However, proven that radiation can be used to
preserve food, esp. protein food eg. Meat
without causing undesirable protein denaturation
or altering in taste and without leaving any
residual radioactivity in food
- Using low doses of radiation, less loss of
vitamins in foods than that seen in canning,
freezing or drying
i) packaging:
- purpose: shipping and storing food far from
place of production and preventing deterioration
drg. storage by insects, molds, yeast,
microorganisms and enzymes
- For many foods, container is filled before food is
processed
- Eg. Rigid metal cans, glass containers and
plastic pouches
- Container sealed to avoid contamination and
food spoilage
- Cardboard boxes with inside liners of waxed or
plastic-coated paper commonly used for dry
foods packaging eg. cereals, flours, dried fruits
- Food sterilized before placed in container
necessitated development of aseptic packaging
- Advantages of aseptic processing and
packaging: longer shelf-life, ability to store
perishable food without refrigeration
- Packaging usually rigid, rectangular cardboard
construction, sterilized by hydrogen peroxide
and heat
Food processing equipment
Sanitary design and materials of construction
- Liquids, solids and combinations must be
handled without deterioration of product or
damage to equipment
- Sanitary conditions additional consideration
beyond normal unit operation
- Chemical and biological properties usu. play
predominant role than mechanical properties in
designing equipment for food industry together
with corrosion resistant materials
- Good appearance must be maintained and pH
of fluid products is the major factor in materials
selection