| Whey protein is capable of self-assembling into amyloid fibrils under certain denaturing conditions,such as high temperature with low pH and low ionic strength.The process can be divided into the lag,elongation and saturation phases.Homogeneous nuclei with high free energy were formed during the lag phase and secondary nuclei with fibril structure were formed during elongation and saturation phases.There is a lack of comparative study on the nucleation-inducing capability for WPC fibrillation and functional properties between homogeneous nuclei and secondary nuclei.Therefore,the research aimed to compare the difference between the two types of nuclei regarding the nucleation-inducing capability for WPC fibrillation and functional properties.The research,selecting whey protein concentrate?WPC?as raw material,measured the change of Th T fluorescence intensity,TEM,protein aggregation,kinetic parameters of fibril aggregation reactions and aggregation driving force during heat treatment to compare the difference in the nucleation-inducing capability for WPC fibrillation between the two types of nuclei.The two types of nuclei whether still had the nucleation-inducing capability for WPC fibrillation after hydrolysis and centrifugal treatment and the difference between them.And the effect of the two types of nuclei on the functional properties of WPC was investigated.The results of the study are as follows:Comparation of the nucleation-inducing capability between homogeneous and secondary nuclei The two types of nuclei could accelerate WPC fibrillation and increase the amount of fibrils compared with WPC self-assembling into amyloid fibrils,the amount of fibrils formed by adding homogeneous nuclei was higher than that obtained with secondary nuclei.Secondly,the two types of nuclei could enhance the rate of polymerization,reduce the lag time and the time of fibrils formation,secondary nuclei had a faster nucleation-inducing capability for WPC fibrillation than homogeneous nuclei.The aggregation rate?df/dt?of WPC reached a maximum value in the third hour,whereas those of WPC mixed homogeneous nuclei and WPC mixed secondary nuclei reached maximal values in the second and first hours,respectively;The lag time of WPC mixed homogeneous nuclei and WPC mixed secondary nuclei was shorten by 41.4%and 55.2%,respectively.The time of fibril formation was significantly shortened from 10 h to 2 h.Meanwhile,the surface hydrophobicity is the main driving force during fibrillation process,the aggregation driving force of WPC mixed nuclei was rapid change for accelerated fibril formation to compare with spontaneously formation during the early stage?0–2 h?.Comparation of the nucleation-inducing capability of WPC fibrillation between homogeneous and secondary nuclei hydrolysate The two types of nuclei after hydrolysis treatment had nucleation-inducing capability for WPC fibrillation,but there was different change in comparison with nuclei without hydrolysis.The nucleation-inducing capability of homogeneous nuclei was weaken after hydrolysis treatment,but still remain 89.2–91.4%and stronger than WPC self-assembly fibrillation.On the contrary,the nucleation-inducing capability of secondary nuclei was enhanced after hydrolysis treatment and reached to 104.6–112.3%.Secondly,the aggregation rate?df/dt?of WPC induced by nuclei hydrolysate did not changed,which was consistent with the change regulation of unhydrolyzed nuclei.The aggregation rate?df/dt?of WPC mixed secondary nuclei hydrolysate reached a maximum value in the first hour,whereas those of WPC mixed homogeneous nuclei hydrolysate and WPC reached maximal values in the second and third hours,respectively.Comparation of the nucleation-inducing capability of WPC fibrillation between homogeneous and secondary nuclei hydrolysate fragment The two types of nuclei hydrolysate after centrifugal treatment still had nucleation-inducing capability for WPC fibrillation.Compared with the nucleation-inducing capability of unhydrolyzed nuclei,the nucleation-inducing capability of homogeneous and secondary nuclei hydrolysate was reduced after centrifugal treatment,but still remain 84.1–85.8%and 94.1–96.3%,stronger than WPC self-assembly fibrillation,respectively.Meanwhile,the aggregation rate of homogeneous and secondary nuclei hydrolysate after centrifugal treatment was reduced,which was consistent with the change regulation of WPC self-assembly fibrillation,the aggregation rate?df/dt?of them reached a maximum value in the third hour.But there was different in the value of?df/dt?max,the value of secondary nuclei hydrolysate fragment was most,the next was homogeneous nuclei hydrolysate fragment,WP C hydrolysate fragment was least.The effect of nuclei on gel properties of WPC The gelling time of WPC with added nuclei was significantly shortened compared with that of WPC?pH 2.0/6.5?at a final protein concentration 7.0%?w/v?,from 10 h?WPC?pH 2.0/6.5??to 4 h?WPC+HN?to 2 h?WPC+SN?.The hardness of the gel composed of WPC with added nuclei was significantly modified,and the viscosity and chewiness showed little improved,and the springiness slightly descreased.Compared with WPC?pH 2.0?gel,the hardness of WPC+HN and WPC+SN gels was increased by137.3%and 161.0%,respectively.There was the greatest influence on the hardness of WPC gel after hydrolysis and centrifugal treatment.Compared with unhydrolyzed gel,the hardness of WPC and WPC+HN gels was descreased after hydrolysis treatment,the descend degree was 20.5–23.7%and 12.4–15.1%,respectively.But the the hardness of WPC+SN gel was increased after hydrolysis treatment,the decreasing degree was 10.6–13.1%.The hardness of WPC induced by nuclei hydrolysate was descreased after centrifugal treatment,descend degree from small to large was secondary nuclei hydrolysate,homogeneous nuclei hydrolysate and WPC hydrolysate,the degree was 8.9–10.3%,16.2–19.2%and 24.1–28.2%,respectively.The effect of nuclei on water distribution of gels Mixed the two types of nuclei could not only improve the hardness of WPC gel,but also enhance the water holding capacity of WPC gel,the water holding capacity of WPC gel induced by homogeneous nuclei was better than that of WPC gel induced by secondary nuclei.The proportion of T23 distributions?PT23?in the WPC gel induced by nuclei was lower than WPC?pH 2.0?gel.The content of evaporated water in the WPC gel induced by nuclei was lower than WPC?pH 2.0?gel when the samples were heated for 6 h after gelling.The evaporation of water lower,the water holding capacity of WPC gel better.The effect of nuclei on foaming properties of WPC The foaming property of WPC induced by nuclei was much higher than that of WPC spontaneous fibrillation.The two types of nuclei after hydrolysis and centrifugal treatment also could improve the foaming property of WPC.Hydrolysis treatment would decrease the foaming property of WPC spontaneous and WPC induced by homogeneous nuclei,increase the foaming property of WPC induced by secondary nuclei.Secondly,centrifugal treatment would decrease the foaming property of WPC hydrolysate spontaneous and WPC induced by two types of nuclei hydrolysate,the descend degree of secondary nuclei hydrolysate was lowest among them.Foam stability of secondary nuclei could improve through the two ways between hydrolysis and induction,and the improvement degree of induction was higher than hydrolysis treatment.However,the combination hydrolysis and induction was the most beneficial to improve the foam stability,reaching 12.9%. |
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