단백질의 어떠한 가열변성 정도에서 소화율 저하에 영향을 미치는 lipid-protein complex가 가장 많이 형성되는 가를 구명하기 위하여 도다리(Pleuronichthys cornutus) 육단백질을 가열변성시키고 four-enzyme system을 이용하여 in vitro digestibility를 측정하였으며, 여기에 도다리 육에서 추출한 지질을 첨가하여 lipid-protein complex가 형성되는 현상을 조사한 결과는 다음과 같다. In vitro digestibility는 5분간 자숙하였을 때 생시료가 $88.09\%$, 탈지시료가 $90.56%$이었으며, 40분 후에는 각각 $85.95\%,;86.17\%$를 나타내었다. Microwaving의 경우 1분 가열 후의 소화율은 생시료가 $87.41%$, 탈지시료는 $91.47\%$이었고, 7분 가열 후에는 $3{sim}4\%$ 정도가 감소하였다. lipid-protein complex 생성에 기인된 것으로 생각되는 trypsin indigestible substrates(TIS)는 가열시간, 첨가되는 지질의 양, 상호작용시간에 따라 증가하는 경향을 나타내었다. 도다리 육에서 추출한 지질의 주요 지방산은 $C_{16:0},;C_{16:1},;C_{18:1},;C_{20:5},;C_{22:6}$이었고, 가열시간에 따른 지방산 조성의 변화는 거의 없었으며. 불포화지방산의 함량이 $67\%$ 정도를 차지하였다. POV, COV의 증가와 함께 갈변물질의 생성이 증가하였고, 단백질 용해도는 microwaving하였을 때 가장 낮았다($19.l9\%$). lipid-protein 상호작용에서 지질의 함량이나 산화정도가 효소적 소화에 가장 큰 저해인자로 작용하였으며, 생시료 및 탈지시료에 지질을 섞어 가열처리하면서 반응시킨 것과 단백질을 가열변성시킨 후 지질을 첨가하여 반응시킨 것을 비교하면 lipid-protein 상호작용으로 인하여 전자가 후자보다 낮은 소화율을 나타내어 단백질과 지질의 상호작용은 단백질 변성현상과 동시에 일어날 가능성이 높음을 알 수 있었다.
The present work aims to estimate the effect of heat treatment on the in vitro protein digestibility and formation of trypsin inhibitor or trypsin indigestible substrate(TIS) of raw and defatted flounder. It was also carried out to assess the formation of lipid-protein complexes under the conditions of different ratio of lipid addition. The in vitro protein digestibility increased when steamed for 5 min showing $88.09\%$ in raw and $90.56\%$ in defatted samples, respectively. After 40 min steaming, the digestibility decreased by $2{sim}4\%$. As for microwaving, heating for 1 min resulted in slight increase of digestibility, however, heating for 7 min did decrease of digestibility by $3{sim}4\%$ for both raw and defatted materials. There was no difference in fatty acid composition found with heat treatment. The major fatty acids of flounder meat were $C_{16:0},;C_{16:1},;C_{18:1},;C_{20:5},;C_{22:6}$ and the ratio of the unsaturated to saturated was 67.3:32.6. Fat oxidation and nonenzymatic browning were enhanced by heat treatment and protein solubility decreased necessarily as the brown pigment formation increased. On the other hand, the effects on the digestibility and TIS of the complexes formed from interaction of lipid and myofibrillar or meat protein of flounder were examined. The interaction of protein with lipid was considered to mostly contribute to the drop of digestibility of fish products. The digestibility of myofibrillar protein was $93.72\%$ for flounder, and it generally decreased as the amount of lipid added to protein and reaction time increased. Also mixed and heated samples were more active in digestibility decline than those mixed after heating. The result probably indicated that lipid-protein interaction was involved in the drop of digestibility which coincided with protein denaturation.
