Extrusion Technology in Food Processing

Pratap Chakraborty and Susanta Bhattacharyya

Over the last few decades extrusion technology has played an increasingly important role in many industries such as food, feed and polymer. It has promising future. Extrusion is a multivariable unit operation i.e. mixing, shearing, cooking, puffing and drying in one energy efficient rapid continuous process. This process of High Temperature Short Time (HTST), extrusion bring gelatinisation of starch, denaturation of protein, modification of lipid and inactivation of enzymes, microbes and many anti nutritional factors. The extrudates are texturally and histologically restructured. Considerable efforts had been put for developing high protein rich extrudate from various sources, such as fish live-stocks, microbial cells and oil seeds only. But high production cost and low efficiency of protein conversion by live stock make plant protein more suitable for dietary protein intake. Thus the present challenge to the food technologists and scientists is how to present nutritive ingredients in the form of recognizable food stuffs from cheaper easily available plant sources. So the most plausible answer to use the newer food is characterized by its texture, which is determined by its micro-structure. Within technological limits the food technologist may control both the composition of starting material and processing variables to direct alteration for nutritional, textual and physical optimisation.

Extrusion Variables

Extruders provide the most efficient means of converting electrical and mechanical energy into thermal energy for cooking feed and food formulations. The quality of an extruded product determines its success, failure, or product life. Extrusion processing parameters and ingredients influence the product quality. Extrusion processing variables that directly control product quality attributes are called independent variables. Changes made to independent variables affect the functional properties of the extrudates and process dates i.e. dependent variables as such.

All this variables are given below:

Application of Extrusion Process in Food System

Extrusion is a new equipment which is a continuous conveyor reactor. This could be used as mixer, heat exchanger, pressure vessel, reactor, shearing device, and expander. This tool is applied in product areas such as expansion at high pressure of products.

Product profile :

	Infant food
	Dusoplings
	Pasta
	Instant beverage
	Pregelatinized starch
	3-generation
	Cooked whole grains
	Snack foods
	Quick cooking vegetable
	Textured vegetable protein
	Biscuits/ Bread
	Break fat cereals
	Meat analogues
	Tortillas
	Precooked flour
	Pet food
	Food bars
	Precooked grits
	Vegetable protein treatment
	Structured proteins
	Crisp breads
	Bread sticks
	Animal feed
	Confectionery
	Croutons
	Byproduct treatment
	Frozen produce
	Instant noodles
	Meat products
	Butter/marga rine
	Reaction hydrolysis

Protein supplemented food

Ordinarily cereal flours, tubers and their derivatives can be processed into snack food, breakfast cereals, confectionery items and precooked modified liquefied starches. Legumes and oil cakes based material can be transformed into texturized vegetable meat extenders, meat analogues. Mixture of cereals and protein sources like legumes oilcakes can be transformed into ready-to-eat or semi cooked food with higher protein level. After oil extraction the meals can be heat treated by extrusion cooking in order to increase their nutritional value by denaturation of protein and or inactivation of antinutritional factor.

In most of the cases powered raw materials of a particular meshsize are used. The powdered raw material are then sent for separation of the fine dust. The powdered materials from blending mixture are tempered by adding predetermined amount of water and mixed thoroughly to adjust feed moisture content in between (15-25%). The blending mixture are then allowed to equilibriate before extrusion. In general single screw extruder are used. The length to diameter ratio of the barrel is 20:1 and screw compression ration 1:1 to 1:4 is maintained. The extruder is provided with electrical brand heaters (over the barrel) and a temperature control facility. In general the temperature of the feed and comparison zones are kept constant, while metering zones temperature varies from 120oC to 200oC depending upon the products. A screw operated feed hopper fed the extruder at a variable screw speed. The extrudates are collected when the operation is at steady state as indicated by smooth extrudate production and constant barrel and product temperature.

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Authors are faculty member of Department of Food Technology and Biochemical Engineering, Jadavpur University, Calcutta.

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