Extruded snack foods

Extruded Snack foods:
Extruded Snack foods Vandana Mishra , Neelam Yadav and Vinita Puanik Centre of Food Technology University of
Allahabad
PowerPoint Presentation:
Extrusion is a process which combines several unit operations including mixing, cooking, kneading, shearing, shaping
and forming.
Extrusion cooking (HTST) is a popular means of preparing snacks and ready to eat foods. Its advantages include
energy efficient, lack of process effluents and versatility with respect to ingredient selection, and the shapes and
textures of products that can be produced. Extrusion processing is used for processing of starch as well as
pertinacious material. It is an important food processing technique for preparation of nutritious food
Snack foods: The snack food processes, which use extrusion cooking, include the production of direct expanded
extrudate and extruded pellets or half products of the third generation snacks. The extruded half products require a
secondary puffing step. Prior to consumption, the third generation snacks are puffed in a fryer, or expanded in hot air
or a microwave oven. Snack food technology of direct expanded, and shaped snacks is similar to RTE cereals
processes, but normally performed at lower moistures, so that a higher energy input from mechanical sources occurs.
In general, direct expanded products are made using high-shear extruders. Other categories of the direct expanded
foods are crisps or flat breads, which are produced using the twin-screw extruder technology. Also, twin-screw
extruders can be used for cracker production.
Types of Snack Foods Each snack processor may use a specific unit operation and somewhat different technologies
to produce unique snacks. There are many ways to classify snacks. Manufacturers use three main terms to identify
snacks: First generation snacks : Simply Extruded Snacks In this category all the natural products used for snacking,
nuts, potato chips and popped popcorn are included. Second generation snacks : ExpandedSnacks The majority of
the snacks fall in this category. All the single ingredient snacks, simple shaped products like corn tortilla chips and
puffed corn curls and all directly expanded snacks are included in this category . Third generation snacks , half
products ” or pellets In this category, multi ingredient form ed s nacks and pellets , made by extrus ion cooking are
included.
Most snack manufacturers use some form of existing technology as the basis for creating snack products, but
incorporating variation is very necessary, especially to increase the snack’s health image appeal by lowering fat and
calories or adding nutrients. This variation can be accomplished by using extrusion technology. :
Most snack manufacturers use some form of existing technology as the basis for creating snack products, but
incorporating variation is very neces s ary, es pecially to increas e the s nack’s health image appeal by lowering fat and
calories or adding nutrients. This variation can be accomplished by using extrusion technology. Simply Extruded
Snacks This category has the greatest potential for growth among snack foods. These snacks can be made to
produce innovation, which captures consumer imagination. Some examples are three-dimensional snacks, a variety
of animals , cartoon, and alphabets s hapes etc. Raw material cos ts play an important role in the finis hed product’s
selling price. Therefore it is advantageous to use the lowest cost raw material to produce a successful snack.
ExpandedSnacks The majority of extruded s nacks are in this category. This group is als o referred to as “collet” or
“s econd generation s nacks”. Expanded s nacks are made on high -shear extruders. These are high-fiber, high-protein,
and low calorie snacks. Some examples are corn curls, onion rings, three dimensional snacks and potato sticks.
These types of snacks can be seasoned with a variety of different flavors, oils, salt, sugars, etc. The quality of an
expansion-cooked product depends upon the conditions of operation of the extruder and the main raw material used
in the formulation.
Fried Collets These are the most familiar extruded snacks in the market. A special die arrangement gives the product
a twisted, puffed shape. These collets are made on collet extruders. The product is then fried in vegetable oil, and
coated with cheese and some other flavor. During frying, the moisture level in the product reduces from 8 percent to
1-2 percent. The most common material used for fried collet is corn meal. Some other cereal grains can also be used
for this type of product.

Baked Collets Baked collets are another example of extruded snacks. This includes products such as baked corn
curls, onion rings and potato sticks. Baked collets can be made with different cereal grains and tuber flours. Protein,
fibers, cellulose, and bran can be blended with cereal grain up to 20 percent to make healthy snacks. Potato sticks
are usually made by mixing potato flour with corn or rice flour.
Third-Generation Snacks These are extrusion cooked, and formed at low pressure to prevent expansion, and then
dried to a final moisture content of about 10 percent to form a glassy pellet. To create formed or pelletized products, a
high moisture dough is used at a lower temperature. When the extrudate is forced through the forming die, the
product takes the shape of the die, instead of expanding. The result is a dense intricately-shaped pellet
Flow diagram for the production of second and third generation snacks
Second generation snacks or expanded snacks, where most extruded snacks are classified, are usually low in bulk
density and are often marketed as high-fibre, low-calorie, high protein and nutritional products. Different raw materials
used to produce these kinds of snacks (i.e. flours and/or cereals and tubers starches and proteins) are processed in a
extruder resulting in a continuous mass, that is cut into pieces of uniform size, being afterwards dried, flavoured and
stored.
Third generation snacks or pellets are produced almost the same way as second generation snacks, however, when
the product exits the extruder, it has the form of the die, that is, it is not expanded, being dried in this form. The
expansion of the product occurs afterwards through frying, heating by hot air or in a microwave oven. This kind of
product presents a low moisture content (between 7 and 10%), high density and stability to be stored for a long time
without microbial damage.
Co-Extruded Snacks This is a relatively new technology introduced in 1984 to the snack food industry. Coextrusion is
a process that combines two different extruded streams to obtain two-component products characterized by a dual
texture and/or color. The two materials can come from two extruders or from one extruder and one pump. This
process can produce a snack with two different flavors, or two textures or two colors. The most common snack
produced by co-extrusion is a cereal-based outer tube with a cheese filling inside. There are three basic types of co-extruded
snacks in the market; cereal-based tubes with cereal-based fillings, cereal-based tubes with fat-based
fillings, and cereal-based tubes with water-based fillings.
Fats and oils play an important role in frying, coating and filling of the extruded snack foods. Coating with oil and
seasonings is the final processing step in the production of snack foods. The seasonings allow the manufacturer to
create a variety of flavors. The oil is the carrier of seasonings and gives the extrudate a better mouth feel. The oil and
seasoning coating usually makes up to 35% of the finished product. The shelf life of these snacks is limited, because
of migration of moisture and/or oil from the filling to the outer shell.
Common Ingredients Extrusion technology, have led to more diverse and complex formulations for snack foods. The
most common source of ingredients is corn, wheat, rice, potato, tapioca, and oats. A major ingredient in snack
formulation is starch. In its natural form, the starch is insoluble, tasteless, and unsuited for human use. To make it
digestible and acceptable, it must be cooked.
CerealSources Almost any cereal can be extruded, but if expansion is a major objective, the numbers of functional
cereals are limited to de-germed corn/grits and rice. Cereals that have high amounts of lipids are more difficult to
expand due to dough slippage within the extruder barrel. This type of cereal usually requires high moisture and high
temperature before significant puffing will occur. In general, starches with 5-20 percent amylose content will
significantly improve expansion as well as the texture of snack foods.

Rice as a S tarch Source:
Rice as a Starch Source Small, tightly packed starch granules that hydrate slowly Becomes sticky when it gelatinizes
Choose long grain varieties over medium and short grain varieties as they are much less sticky when cooked Rice is
very digestible even when cook values are low Rice bran may contain up to 40% starch
Corn as a S tarch Source:
Corn as a Starch Source Good expansion Excellent binding Sticky at high levels (>40%)
Wheat as a S tarch Source:
Wheat as a Starch Source Good binding Good expansion Can be sticky if overcooked Contains gluten (good binder)
Most widely available starch source Often utilized as wheat flour which has most of the bran removed
Tubers as a S tarch Source (Potato & Cassava):
Tubers as a Starch Source (Potato & Cassava) Excellent binding (at 5% levels) Requires less total starch in diet
Good expansion Often precooked Smooth pellet surface Increased cost
Factors influencing the degree of puffing of snacks during extrusion The amount of moisture in the feed material,
dough residence time in the extruder barrel and cereal particle size. To manufacture expanded products, the
pressure and temperature are increased, while the moisture level is accurately controlled. When the product exerts
the extruder through the forming die, the change in atmospheric pressure causes the internal moisture to turn to
steam. This puffs the fully-cooked dough into an expanded product.
The factors are- a) Raw materials The most used raw materials in the extrusion process are starch and protein based
materials. The structure of the extruded products may be formed from starch or protein polymers. In general, the
chemical or physicochemical changes in biopolymers that can occur during extrusion cooking include: binding,
cleavage, loss of native conformation, fragment recombination and thermal degradation. Thermally labile compounds
such as flavors and vitamins may be injected immediately before the die to minimize exposure to heat and shear.
Moisture If high expansion is required in a low moisture product, finely milled forms of harder endosperm types will
give excellent results. If the product requires low to medium expansion, some of the hard material may be replaced
by soft flour; and for low expansion in a dense product such as breading crumb, soft flour may be used. Maximum
expansion degree is closely related to starch content. Maximum expansion is obtained with pure starches (an
increase of 500% in product diameter), followed by whole grains (400%) and with lower expansions for seeds or germ
(150-200%); the starch content of these products is 100, 65-78, 40-50 and 0-10, respectively. The minimum starch
content for expansion is 60-70%. In the extrusion process of expanded products with low moisture, the expansion of
the final product is inversely related to the moisture of the raw material and directly related to the increase in
extrusion temperature; however, the effect of moisture is more significant
Superheated dough Product puffs as moisture flashes off
Fibre The physical presence of fibres in air cell walls reduces the expansion potential of the starchy film, larger
particles, such as bran, tend to rupture air cell walls of the extruded product, causing a reduction in expansion index.
Non-starch polysaccharides, such as fibres, may bind water more strongly than proteins and starch during extrusion.
This water binding capacity inhibits water loss at the die, that is, at the exit of the extruder, red ucing expansion. The
starch present cannot be totally gelatinized in the presence of fibre and is thus not capable of supporting expansion.
Lipids The presence of lipids in quantities lower than 3% does not affect expansion properties, however, in amounts
above 5%, reduction in expansion rate is considerable. The increase in lipid content can be corrected through the
reduction in conditioning moisture content, so as not to affect the expansion index of second generation products
(directly expanded snacks).
Temperature Another important parameter for extrudate expansion is process temperature. Products do not expand if
the temperature does not reach 100°C. Expansion increases with the increase in temperature when moisture content
of the material is close to 20%, due to lower viscosity, permitting a more rapid expansion of the molten mass, or due

to an increase in water vapour pressure. The reduction of expansion at very high temperatures is attributed to an
increase in dextrinization, weakening starch structure. . Expansion occurs in both radial and axial directions, at
different degrees, depending on the viscoelastic properties of the melt. Vaporization of moisture and cooling of the
extrudate serve to bring the product from a molten to a rubbery state; and further drying is usually used to produce
the brittle, fracturable texture typical of these products.
Conclusion:
Conclusion In the future science and technology of the extrusion field, scientists and engineers should focus on the
relationship between composition changes and product quality, evaluating and enhancing nutritional, sensory and
functional properties of extruded foods.
Thank you

Extruded snack foods

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