Product Characteristics as Factors of Process Parameters in Starch Phosphates Preparation by Twin-screw Extruder

이축압출성형기로 인산전분 제조시 Process Parameters에 따른 제품의 특성

Starch phosphates were prepared from the corn starch mixed with 2% sodium tripolyphosphate by twin-screw extruder with a feed rate of 20 kg/hr and an extrusion temperature of $130^{\circ}C$, and the effects of extrusion variables on the physicochemical properties (target parameters) of starch phosphates were investigated. Interrelations of system parameters (specific mechanical energy and extrudate moisture) and rheological properities of starch was analyzed by using the response surface analysis. Degree of substitution (DS) was increased with increasing the feed moisture, and showed the maximum value at the screw of near 250 rpm, Degree of gelatinization was proportionally increased with increasing the screw speed and decreasing the feed moisture. Apparent viscosity of the paste was increased with increasing the feed moisture, but it was not significantly affected by the screw speed. It was found by scanning electron microscopy that the starch microgranules were much more degradaded, and as consequent result, the intrinsic viscosity was decreased, whereas, water solubility index was increased. The rate of retrogradation of the gels was retarded with increasing DS and decreasing viscosity.

Twin-screw extruder를 사용하여 인산제분 제조실험을 실시하였다. 옥수수 전분에 sodiumtripolyphosphate(STPP) 수용액을 분무하여 전분건물에 STPP 함량이 2%가 되도록 혼합하고, 원료투입속도 20 kg/hr 및 extrusion 온도 $130^{\circ}C$의 조건하에서 추가가수하여 조절한 process parameters 중 원료수분함량(23,25,30,35%) 및 스크류 회전속도(200,250,300,350 rpm)변화에 따라 압출되면서 측정한 system parameters(기계적 소모에너지, 압출물의 수분함량)와 압출된 인산전분의 특성인 target parameters(치환도, 호화도 및 분산액의 점도 및 겔 특성)와의 관계를 반응표면 분석하여 인산전분 제조공정을 검토하였다. 이 때 치환도는 수분함량이 클 수록 증가 하였고 스크류 회전속도 250rpm에서 최고의 값을 나타내었다. 호화도는 수분함량이 감소하고 스크류 회전속도가 증가할 수록 높았다. 주사전자현미경에 의한 전분입자의 미세구조는 입자의 붕괴가 크게 일어났으며 결과적으로 고유점도가 감소되었으나 용해도는 증가하였다. 또한, 겔의 노화속도는 치환도가 크고 점도가 낮을수록 지연되는 결과를 보였다.