Food Science

Food Processing
Unit of Operations

NFS 3323

Unit operations of food processing

• Number of __Operatio __
____steps______required in the processing
and manufacture of the multitude of available
food products is huge.

• Exact procedures vary from company to
company and from country to country due to
the technology available.

Unit operations of food processing

• Underlying principles and systematic activities
of unit operations provide uniformity to the
processing of food.

• Unit operations are the broad categories of
_____common processing operation in
practice in the food industry.

Unit operations of food processing

• There are about a dozen categories of unit
operations

• Most cover a wide variety of products and
applications

Unit operations in food

• QA/QC
• Materials handling
• Separating
• Cleaning
• Disintegrating
• Pumping

• Mixing
• Heat exchange
• Evaporation
• Drying
• Forming
• Packaging

Primary unit operation

• Defined by many different activities or actions.

• For example, the unit operation of __Mixing___
encompasses all of the following actions:
– Agitating
– Emulsifying
– Beating
– Homogenizing
– Blending
– Whipping

Quality assurance – Quality control

• __Monitor __ the __entire__ __Process_ from
raw materials through
– processing and packaging,
– checking specific quality parameters (moisture,

pH, color, %Brix, nutrient content)

QA or QC personnel have the authority to shutdown
a production line if anything deviates from the
product standard until corrective actions are taken.

Quality control

• Extremely important factor in any food
processing facility

• For health and safety reasons

• ___Prodict_ __Uniformity___

Unit of operations –
Materials handling

• Refers to the manner in which raw
commodities such as crops and animals and
animal by-products are harvested and
transported to a food processing facility.

• i.e. eggs are a by-product of hens, and
material handling of eggs includes;
– Gathering of the eggs
– Transporting them to an egg processing facility

Unit of operations – separating

• __Isolates a desirable part of raw food from another
part______

• A solid food part can be removed from another solid
part, or a liquid is taken from a solid food.

• i.e. removing the skin of potatoes in preparation for
frozen french fry production (solid from solid
separation)

• Pressing orange juice from oranges to make frozen
concentrated juice.

Unit of operations – cleaning

• Straightforward – removal of surface dirt,
debris, and associated bacteria

• Can include filtration (liquid beverages),
trimming (fruits, vegetables, hard cheeses)
and centrifugation from milk, fruit juices, and
syrups to remove spores, bacilli, yeasts, and
molds

Unit of operations – Disintegrating

• Refers to __Particle size___ __reduction__ of
foods

• i.e. – cutting of meat into smaller pieces,
grating of cheese, and dicing of fruits and
vegetables.

Unit of operations – pumping

• Involves the __Mechanical__ method of
_moving _ ___food___
__material____during processing

• Can be semisolid foods such as yogurt and
chunky soups and liquid foods such as syrups,
beverages, and liquid or dispersed ingredients

Unit of operations – mixing

• The __Blending__ of food ingredients to
create a food product

• Emulsifying a mixture of oil, water, and flavor
creates a stable salad dressing

• Homogenizing is a process applied to milk
• Carbonation of water – mixing of a gas with

liquid

Unit operations of food processing

• The _Heat exchange___ process (heating) is
used in each of these product operations:
– Pasteurizing milk
– Baking cookies
– Roasting peanuts or coffee
– Commercially sterilizing canned tuna

Unit of operations – heat exchange

• ____application or removal of heat
formation__________

• Roasting of coffee and the freeze drying of
coffee

• Removal of field heat from fresh produce

Unit of operations – evaporation

• Removal of moisture __ from a food to
_Concentrated__ its solid content

• Accomplished through__Controlled___
_Heating____

• Used for processing cane sugar into white
crystalline sugar, evaporated milk, and
concentration of fruit juices for freezing

Unit of operations – drying

• A more extensive approach to moisture
removal

• Product moisture is reduced to a mere few
percent

• Spray-drying is the method of choice for
liquids and tunnel drying or vacuum freeze-
drying for raw food pieces

Unit of operations – Forming

• Foods are __Formed___ into Specific_
_Shapes___during processing

• Breakfast cereals, confectionery, pasta, bread

Unit of operations – packaging

• Protects products from the environment

• Offers ____ convenience____

• Primary concern – prevention of
contamination by microbes and protection
from oxygen, moisture, light, unwanted flavor
and odor transfer and pest access

Meat example / hot dog – frankfurter

• Are a processed, emulsified meat product

• Made by mixing chopped meat with curing
ingredients, flavorings, and colorings

• Chopped meat is stuffed into casings, cooked,
removed from casing and packaged for
consumer.

Meat example – frankfurter

• Made from a variety of meats, mostly 100% beef,
but can be blend with pork. Poultry franks
(chicken or turkey)

• Though high in protein, franks may contain up to
30 percent fat.

• Water added (up to 10%) to create a uniform
meat emulsion and contribute to a juicy texture.

Meat example – frankfurter

• Begins with inspection of meat

• Assessed for moisture percentage, odor, pH and
appearance

• Then chopped and mixed in stainless steel
container to reduce particle size

• Other ingredients are added to blend until a fine
emulsion (termed “batter”) is formed

Meat example – frankfurter

• During processing, the meat is mixed with a curing
solution to improve taste and increase the shelf life

• Typically a mix of:
• Water – helps in curing
• Salt – inhibits microbial growth, contributes to flavor
• Sodium nitrate – retards development of rancidity and

stabilize meat color
• Accelerators, sodium ascorbate or sodium erythorbate

– preserve the color of meat during storage

Meat example – frankfurter

• Batter is pumped into a stuffer machine forming
the product into the familiarly shaped links

• Links are actually cellulose casings, twisted at
precise points to produce hot dogs of equal size.

• Some manufacturers leave the casings on, others
remove them.

Making hot dogs

• https://www.youtube.com/watch?v=2NzUm7
UEEIY

Breakfast cereal
puffed, flaked, extruded

• W.K. Kellogg and C.W. Post will forever be
associated with breakfast cereal.

• Kellogg invented the first
precooked flaked cereal

Breakfast cereal

• Post was the first to market breakfast cereal as
health foods.

Over the years the image of their products has
transformed from health food to quick, convenient
and tasty breakfast food.

Breakfast cereal

• Common knowledge the most important
material for any breakfast cereal is the grain
source.
– Corn
– Wheat
– Oats
– Rice
– Barley

Breakfast cereal

Majority of breakfast cereals
contain other ingredients – salt,
yeast, sweeteners, flavoring
agents, coloring agents, vitamins,
minerals and preservatives.

Breakfast cereal
• Whether cereal is of the flaked variety, such as

corn flakes, or the puffed variety, like wheat
puffs, it all starts with grain

• The grain is received at the cereal factory, as
which time it is inspected and cleaned

Breakfast cereal

• Whole grains or partial grains (such as corn
grits) are then mixed with flavoring agents,
vitamins, minerals, sweeteners, salt and water
in a large rotating pressure cooker.

• The time, temperature, and speed of rotation
vary with the type of grain being cooked.

Breakfast cereal

• The cooked grains are then moved to a drying oven,
to remove moisture that still allows for a soft, solid
mass suitable for forming into shapes.

• Grains are ground into flour and placed in a cooking
extruder, which is a device consisting of a long screw
within a heated housing.

Breakfast cereal

• As the screw turns, it mixes the flour with
water, flavorings, salt, sweeteners, vitamins,
minerals, and sometimes food colorings.

• To ensure proper cooking and shaping, the
temperature and moisture content of the
cereal are constantly monitored.

Breakfast cereal

• At the output of the extruder, the cooked
product emerges as a ribbon and a rotating
knife (or die) cuts the ribbon into extruded
and shaped pellets.

• After shaping, can add sugar frosting,
vitamins, minerals, etc. if not added to the
original flour.

Breakfast cereal

• Puffed cereals are made by using one of two
methods:
– Oven-puffing –usually made from rice that is cooked,

cooled, and dried.

– The product is moved between metal rollers and
partially flattened (“bumping”)

– Bumped rice is dried again and placed in very hot
oven – increase in temperature generates internal
steam causing each grain piece to swell or puff.

Breakfast cereal

• Gun puffing – rice or wheat grains or extruded
pellets are used

• The grain is placed in the gun (a very small
vessel that can hold very hot steam and
handle very high pressure)

• The gun is opened quickly to reduce the
pressure suddenly, which puffs the grain.

Soy Tofu

• Tofu – derived from soybeans, a type of legume.

• Soybeans are pulses – plants having a symbiotic
relationship with bacteria that emit nitrogen
through nodules in the plant’s roots.

• Nutritious plant product that are unusual for their
protein and amino acid content and quality.

Soy Tofu

• First introduced in US in 1970s, but meet with
resistance because of bland, beany and
astringent taste.

• Changed this flavor by breeding soybeans with
lower content of lipoxybenase

Soy Tofu

• Production of tofu consists of two main steps:
– The preparation of soymilk
– The coagulation of soymilk to form curds that are

subsequently pressed to form tofu cakes

Soy Tofu
QC/QA – cleaning

First step – soak soybeans
__extracting___the soymilk (~12
hours)

Soaked beans are mashed with
stone grinders or metal blades.

Soymilk is extracted with aid of
roller press, to separate it from the
pulp.

Add ___coagulant__ (Ca++ sulfate
or magnesium chloride

Soy Tofu
Coagulant lowers pH over
20 minutes, curdling the milk.

Once curd is formed, the tofu
is pressed into the desired shape
and the liquid is drained off.

The final water content of the
tofu determines the texture (soft,
Firm, extra-firm)

Cut into desired shape, packaged,
And pasteurized.

Questions?

Crystallization

NFS 3323

Sugar crystal

• In a sugar crystal, the sucrose molecules are
arranged in a repeating pattern that extends
in three dimensions.

• All of these molecules are attracted to each
other by intermolecular forces – a type of
interaction that binds molecules together and
is weaker than the bonds between atoms in a
molecule.

Crystallization

• When you add granulated sugar to water, some
of the sucrose molecules start separating from
one another because they are __Attracted to
water molecule___.

• When water and sucrose molecules are close to
each other, they interact through intermolecular
forces that are similar to the intermolecular
forces between sucrose molecules

Crystallization

• The dissolving process involves two steps:

• First, the water molecules bind to the sucrose
molecules;

• Second, the water molecules pull the sucrose
molecules away from the crystal and into the
solution.

Crystallization

• In general, only a certain amount of a solid can be
dissolved in water at a given volume and
temperature.

• If we add more than that amount, no more of
that solid will dissolve.

• At this stage, we say that the solution
is __saturated___. The additional solid just falls
to the bottom of the container.

Crystallization

• The final texture of a candy is determined by the
way in which sugar molecules are made into a
solid structure

• If the sugar forms a few large crystals, then the
candy texture will be coarse and grainy.

• If it forms millions of microscopic crystal that are
lubricated by just the right amount of syrup, then
the candy will be smooth and creamy.