Ultrasound Assisted Extraction And Glycosylation Modification Of Brewer’s Spent Grain Protein

In the beer-brewing industry,brewers’ spent grain(BSG)is known as the most abundant by-product rich in protein.However,BSG is traditionally only used in animal feed or discarded directly,which not only results in pollution,but also makes it a waste of the protein-rich components.As barley storage protein,BSG protein is trapped tightly inside the crosslink of cellulose and lignin fragments,and thus makes it difficult to extract BSG protein with high yield.Previous researches have reported the application of ultrasound assisted extraction(UAE)in BSG protein recovery.However,the mechanism of the effects of key factors during ultrasound on the techno-functional properties of BSG protein have yet been discussed.Besides,the highly-denaturation structure and poor solubility limit the further application of BSG protein as functional ingredient.Up until recently,various modification methods have been reported in the improvement of functional properties of plant-based proteins.However,few studies have been done about modification of BSG protein to improve its foaming properties.Therefore,in the present work,BSG was used as the raw material to study the mechanism of UAE on BSG protein recovery firstly.Besides,different modification methods were adopted to improve the solubility and foaming properties of BSG protein.Meanwhile,the effects of modification methods on the structural and interfacial properties of BSG protein were clarified.The findings of this work could provide insight into the application of BSG protein in beer quality improvement.The main results are as follows:(1)The mechanism of UAE on BSG protein extraction enhancement was studied.The results demonstrated that UAE working at 250 W for 20 min under duty cycle of 60% could significantly improve the protein yield to 86.16%.The secondary structure of BSG protein was clearly modified under ultrasonication.Besides,SDS-PAGE pattern of protein was slightly strengthened.The enhancement in free sulfhydryl content and ultraviolet-visible spectra further indicated that exposure and unfolding of protein structure occurred.Therefore,the functional properties of BSG protein were enhanced,including fat absorption capacity,emulsifying and foaming properties.(2)The effects of ultrasound treatment,glycosylation and their combination impact on the structural and interfacial properties of BSG protein were clarified.BSG protein with high solubility and foaming property was obtained.The results showed that after modification,the secondary structure of BSG protein was modified with higher α-helix content and lower β-sheet content.The significant changes in infrared spectroscopy,free sulfhydryl content and disulfide bond content further confirmed rearrange of BSG protein molecules.Besides,disintegration of the network structure of protein led to decreased mean droplet diameters,and thus improved the interfacial properties of BSG protein.Solubility and surface hydrophobicity were enhanced,Zeta potential and surface tension were decreased.Therefore,the foaming capacity and foaming stability of BSG protein were both enhanced.(3)The effects of BSG protein addition during brewing process on the non-biological stability and foaming property of beer were tested.The results demonstrated that different kinds of BSG protein influenced the non-biological stability and foaming property of beer effectively.The proper addition time was selected as before mashing or after fermentation,and ultrasoundglycosylation modified BSG protein was a more effective foam-active protein adjunct.After addition,the foaming capacity and foaming stability of beer were improved,with little effects on its non-biological stability.Therefore,BSG protein could be utilized in the beer-brewing industry with high value.