Behaviour of corn and water chestnut flour blends for the development of extruded products
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Date
2015
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Investigations on “Behaviour of corn and waterchestnut flour blends for the development of extruded products” were carried out during 2012-13 and 2013-14 in the Division of Post Harvest Technology, SKUAST-Kashmir, Shalimar. Corn var. C8 and waterchestnut cv. local were taken for investigation. Both of them were ground to coarse flour and blends were prepared by replacing corn with waterchestnut flour as 10, 20, 30, 40 and 50 per cent. The experiment I was laid down by studying physicochemical and rheological properties of both individual flours and their blends. The extrusion of product was carried out at the Department of Food Science & Technology, Punjab Agriculture University, Ludhiana. Response surface methodology (RSM) was used to study the effect of water chestnut incorporation (10-50%), moisture content (12-20%), barrel temperature (125-185oC) and screw speed (200-600 rpm) on expansion index, bulk density (g/cc), water absorption index (g/g), water solubility index (%), colour (L*, a*, b*, hue angle and chrome), hardness and SME of blended extrudates. The experiment II was laid down by carrying out extrusion in a clextral twin screw extruder with variable screws and heaters following a 4K central composite rotatable design that required 30 extrusion runs. Second order polynomial regression models were established and the adequacy of regression model was checked by correlation coefficient. Lack of fit test was used to judge the adequacy of model fit. All the functional properties of the extrudates affected product responses significantly (P≤0.01). Feed moisture had a significant effect on all product responses except WAI and WSI. Screw speed and barrel temperature had a significant effect on bulk density, expansion index, hardness and SME of the product. Optimized processing parameters for preparation of extruded product were water chestnut incorporation (40%), feed moisture (14%), screw speed (300rpm) and barrel temperature (170oC). The 2nd order polynomial was adequate in modeling the dependence of bulk density, WAI, WSI, expansion index, hardness and SME on the extrusion variables. Predicted values were very close to the experimental values making the model ideal for prediction of the dependence of the extrudate functional properties on the extrusion variables. Nutritional profile of optimized treatment was checked. The experiment III was carried out by preparing flat bread (chapatti) from optimized treatment wherein thickness (mm), diameter (cm), cutting force (N) and colour coordinates of chapatti were studied. On the basis of sensory evaluation (over all acceptability scores) of fried product, best flour blend containing 40% waterchestnut flour was selected to study the effect of tomato pomace on extrusion behaviour of blended flour. The experiment IV was carried out to develop the health food by incorporating tomato pomace. The experiment was laid down in the same manner as in experiment II except replacing blending percentage with pomace percentage at five levels viz; 5, 10, 15, 20 and 25 per cent. The study revealed that bulk density, WSI, a* value, and hardness increased with the increase in pomace level. However, WAI, expansion index, hue angle and L* value decreased with the increase in pomace level. Other factors showed same effect as in experiment I. The storage studies revealed that free fatty acid (%), peroxide value (meq/kg) and moisture (%) increased, while as iodine value (%) decreased in both the packaging materials though less increase was observed in case of aluminium laminate (AL). Organoleptic evaluation showed that product packed in low density polyethylene (LDPE) was accepted upto 60 days only as compared to product packed in aluminium laminate which was acceptable even up to the 120 days of storage. Therefore, it was concluded that the samples blended with 10 per cent tomato pomace and with 14 per cent feed moisture extruded at 170oC barrel temperature and 300 rpm screw speed showed the best consumer acceptance. Moreover, the fried snack can be stored in aluminium laminate upto 120 days at ambient conditions.