| The predominant processing methods of sesame are pressing and roasting-assisted aqueous extraction processing,which focus on oil production,resulting in protein-rich by-products can only be used as feed and fertilizer.Aqueous extraction processing is environment-friendly,and it has great potentials to be used for the comprehensive utilizations of sesame lipids and proteins.Sesame milk can be made by wet grinding and filtration of sesame seeds.By centrifugation,the sesame milk can be divided into three parts: floating(oil body concentrate),skim,and precipitate fractions.The previous studies in our laboratory has confirmed the high proteolytic activity in the sesame oil body concentrate,which was used to demulsify oil bodies to obtain sesame oil.Therefore,in this study,the composition,distribution and hydrolysis conditions of endogenous proteases in the skim and precipitate were examined.In addition,the sesamin is an important functional component in sesame seeds.It is instructive to investigate the distribution of sesamin in sesame seeds for the preparation of sesame oil in aqueous extraction processing.The main research contents and results are as follows:Firstly,the sesame milk(prepared by grinding)was separated into three fractions by centrifugation(3000g,15 min).In the floating,skim,and precipitate fractions,the distribution percentages of proteins were 9.56%、18.51% and 71.93%.They were 87.40%、6.87% and5.73% for lipids,and 73.97%,20.37% and 5.66% for sesamin.The results showed that lipids were mainly distributed in the floating,while proteins(90.44%)were mainly distributed in the skim and precipitate.Through the correlation analysis,it was found that the distribution of lipid and sesamin showed a significant positive correlation.Secondly,the distribution of sesamin in sesame seed cells was examined.Firstly,more than 97% of sesamin was distributed in the peeled sesame seeds,and the residuals in the sesame skin.Due to the shearing effects during grinding was likely to destroy the microstructure of oil bodies,the sesame milk was prepared by stone milling.In addition,in order to make all oil bodies float up,the centrifugal conditions were as follows: the sesame milk(p H 11,20% sucrose solution)was centrifuged at high speed(42500g,60 min).The results showed that approximately 95% of total lipids in peeled sesame seeds were in the form of oil bodies,approximately 95% of sesamin was distributed in the oil bodies,and the residuals in the bio-membrane such as endoplasmic reticulum.Finally,based on the results above,the effects of different methods for sesame oil was investigated.The results showed that the sesame oil directly prepared from oil bodies(such as freezing-thawing method)had a higher sesamin content than that from pressing methods,which was consistent with the results above.Then,the composition of endogenous proteases in the floating,skim,and precipitate fractions was investigated by LC-MS/MS,and the relative abundance of each protease was calculated by the label-free quantification intensity of LC-MS/MS.The results showed that the predominant proteases in the floating fraction were aspartic endopeptidases,tripeptidyl-peptidase 2 and serine carboxypeptidases.The skim predominantly contained aspartic endopeptidases,aminopeptidases,tripeptidyl-peptidase 2,cysteine endopeptidases,serine carboxypeptidases and serine endopeptidases,and glutamate decarboxylase.The precipitate fraction predominantly included aspartic endopeptidases,tripeptidyl-peptidase 2,serine carboxypeptidases,cysteine endopeptidases and serine endopeptidases.And 93.41% of endogenous proteases were distributed in the skim and precipitate fractions.Then,the hydrolysis conditions and activity of endogenous proteases in the skim,precipitate and skim-precipitate mixture were investigated.The results showed that the endogenous proteases in the precipitate exerted proteolytic activity at 50℃ and p H 3～p H 5,which was predominantly contributed by the aspartic endopeptidases and serine carboxypeptidases.the endogenous proteases in the skim had higher proteolytic activity at p H3.5～p H 5.As for the skim-precipitate mixture,the endogenous proteases exhibited activity at40℃～70℃ and p H 3.5～p H 6,and optimal at 50℃～60 ℃ and p H 4.5～p H 6.By incubation at50℃ and p H 4.5 for 6 h,the TCA-NSI value in the skim-precipitate mixture reached to approximately 38%,and the free amino acids was 3148 mg/L,accounting for approximately15% of the total proteins.The thermal stability test showed that the exopeptidases were more sensitive to heat than the endopeptidases.The exopeptidases were obviously inactivated at70℃,while the exopeptidases and endopeptidases were substantially inactivated after boiling water bath treatment.Finally,the applications of endogenous proteases in sesame were investigated.It was found that the sesame endogenous proteases also could effectively hydrolyze the soybean and peanut proteins,especially their heat-denatured ones.Sesame protein hydrolysate cool beverage was prepared by the skim-precipitate mixture hydrolysate which was incubated at50℃ and p H 4.5 for 6 h.The bitterness of hydrolysate could be effectively covered up by adding 0.13 g/kg sucralose and 1% erithritol.The sterilized products remained stable and tasted good after 3 months at room temperature. |
