The Effects Of Extrusion On The Food Industry

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INTRODUCTION
Extrusion technology which had emerged in 19th century was initially used to blend the rubber scraps and reuse them with an economical aspect. Thomas Hancock had developed the first extruder which was not known as extruder at that time and was rather known as the rubber masticator (GogosC.G., 2006). In later stages, extrusion came as an emerging technology for manufacturing of plastics - mainly, after the development of twin screw extruder in Italy (RauwendaalC., 2001). Along with the plastic manufacturing, extrusion technology had begun to establish its place in food industry with the production of sausages in 1870s. This was the first time when extruder was designed with the intent to be used in food industry (KarweM.V., 2008). …show more content…

The dry ingredients are supplied through the hopper and drops down to barrel with or without preconditioning (depend on the specifications of final product). The food is moved forward with the help of the augur. This augur has flights on it and the pitch decreases with increase in length of the screw. As we move ahead, the diameter of the augur is increased and furthermore, the space for the food is reduced which in turn results in higher compression, pressure and temperature. Since the food is being compressed, mechanical energy is dissipated and there is also an option to provide external thermal energy. Though, the manufacturers may not use the external energy provided the pre-set conditions can be achieved by the dissipation of mechanical energy, shear and the friction developed. When the food emerges out of the extruder from high pressure and temperature (generally above 100ᵒC) to relatively low pressure and temperature (room temperature), the moisture is whizzed off as steam resulting in the expansion of the final product (GangulyS., 2014). The expansion of extruded food product majorly depends upon the difference between the vapour pressure of water and the pressure just outside the extruder that is the atmospheric pressure along with the capability of expanding of that particular food stuff (SinghR.K.R., …show more content…

While, the temperature in feed zone (input) and the output zone is generally the same which is lower than the temperature of cooking section. Such a setting is done as it favours the mechanism of extrusion that is cooking of extrudate. For example in the following study where the barrel temperature is mentioned as 75-140ᵒC , the temperature in the input and output zone would be 60-90ᵒC (Aguilar-PalazuelosE. Z.-M. H.-B., 2012). The high barrel temperature (75-140ᵒC) effect is subjugated over the effect of high feed moisture (16-30%) resulting in higher expansion ratio and hence lower bulk density when the potato starch was used upto 50%. The suspected reason for such behaviour is the formation of complex amylose-lipid complexes (Aguilar-PalazuelosE., 2006). The best expansion ratio is found when the barrel temperature is 123-140ᵒC and feed moisture can be even up to 27-30% (Aguilar-PalazuelosE. Z.-M. H.-B., 2012). This is only possible in the case of high quality starch like in potato which is known as the ‘king of vegetables’. 65-80% of dry matter of potato tuber consists of potato starch which further consists of approximately 21% amylose content (ChhabraP.,

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