Fish protein isolate (FPI) from by-products of Pangasius hypophthalmus has many technological features, can be applied in the food industry, sitch as: solubility, emulsifying, foaming, film-forming... However, one of its outstanding features is the emulsion ability. This study focused on surveying the emulsifying feature of FPI from catfish byproducts in hydrolysis at different conditions and optimized using response surface methodology to obtain FPI with the highest emulsifying ability. Then the components of protein molecules in the FPI were determined. The results show that the highest emulsifying ability of FPI is 31.80 percent with the hydrolytic conditions: pH 7.4
E/S ratio is 0.19 percent w/v, temperature at 62°C, hydrolysis time is 80 minutes. The result of HPLC analysis shows that molecular weight of proteins in FPI is relatively small and mainly focuses from 7 kDa to 10 kDa "3 kDa: 16.9 percent, from 3 kDa to 7 kDa: 13.9 percent, from 7 kDa to 10 kDa: 52.69 percent, from 20 kDa and above: 5.35 percent).