Effet Of Ultrasound Treatment On Enzymatic Hydrolysis Characteristics Of Casein

With the enzymatic hydrolysis of casein without ultrasounic treatment as the control test,the effect of ultrasound treatment on enzymatic hydrolysis characteristics of casein from theangle of the change of molecular weight distribution, partical size distribution, sufacestructure, the second structure of casein and its hydrolysates. We tried to discuss themechanism of the influence of denaturation before hydrolysis on the characteristics of proteinenzymolysis.The effects of ultrasound on degree of hydrolysis (DH) and contents of souble-N,amino–N and peptide-N in the hydrolysates in the casein-trypsin system during hydrolysiswere investigated. The results showed that the DH and the content of amino–N of thesystem significantly increased after ultrasonic pretreatment, but there is no obvious differencebetween two treatment powers (160W and400W); More, compared with blank test,400Wultrasonic power pretreatment caused significant increase in souble-N in hydroylasates of thecasein-trypsin system.The influence of ultrasound on molecular weight distribution of casein and itshydrolysates was studied by high-performance size exclu-sion chromatography (HPSEC) andSDS-PAGE. The results showed that, the molecular weight decreased rapidly when thecasein was hydrolysised by trypsin in10min, and with the development of enzymatichydrolysis, the content of high molecular weight (>20kDa) reduced gradually,while the lowmolecular weight increased gradually. Compared with the control test, the content ofpeptides with high molecular weight decreased after the ultrasound treatment of160W and400W. Moreover, the molecular weight of the hydrolysates was lower than the control atthe same time of hydrolysis, and400W treatment produced the effect greater than160W.The surface strcture of casein was observed by scanning electronic microscope (SEM),the result showed that, the surface of casein became loose and porous after enzymatichydrolysis and ultrasound treatment, the400W caused significant change. This makes iteasier for the contact of trypin and casein. Besides, the hydrolysis induced a rapid decreaseof partical size in the solution. The content of big size partical dropped after the160W and 400W ultrasound treatment, and the partical size of hydrolysates was lower than the controltest.The effects of ultrasound on the second structure of casein and its hydrolysates wasinvestigated by Fourier transform spectroscopy (FTIR). Followed the160W and400Wultrasound treatment on casein for1h, the ratio of α-helix and β-sheet was decreased, itshowed that the ultrasound treatment makes an increase in pliability of casein to behydrolysised easily. The pliability of the hydrolysates increased after the enzymatichydrolysis, and it happened after the160W and400W ultrasound treatment compared withthe control at the same hydrolysis time.