| Whey protein is the most commonly used functional protein in food industry,which has unique hydrophilicity,fat emulsification,foaming and mild taste.But the stability of whey protein is poor,which is easily affected by ambient pressure,such as temperature,pH value,salt and so on.Therefore,the modification of whey protein to make it maximize its functional characteristics has always been a high topic for scholars at home and abroad.Maillard reaction is one of the most widely studied methods at present.By covalently coupling protein with sugar,it improves the functional properties of protein,making them a better food ingredient.In this study,whey protein and inulin were used as study objects.The purpose of this study was to investigate the effects of glycosylation conditions on the physicochemical properties of whey protein,including heating process?dry and/or moist heating?and inulin addition before or after heating treatment.The physicochemical properties of the products of glycosylation reaction were detected by elisa reader,ultraviolet spectrophotometer and nano particle size meter.The surface hydrophobicity and secondary structure changes of the products were detected by Circular dichroism,Fourier Transform Infrared Spectroscopy,fluorescence spectra and glycoprotein electrophoresis.In order to determine the safety of the product of glycosylation reaction,the content of acrylamide for moist heating samples was detected by high performance liquid chromatograph?HPLC?.Antioxidative properties changes of the heated protein-inulin complexes were also assessed involving DPPH,ABTS+and ORAC using chemical assays.The main results were as follows:?1?This study aims to investigate physiochemical and structural properties of whey protein?10%,w/v?and inulin?8%,w/v?under controlled heating process?dry and/or moist heating?with inulin addition before or after heating treatment,such as WPI-inulin d?WPI/inulin d?WPI-inulin d+h+h and so on.The results indicated that dry heating and moist heating both led to physiochemical and structural changes of samples.Moist heating of whey protein resulted in more significantly negative zeta potential values than dry heated samples with or without inulin?p<0.05?.Inulin increased the magnitude of zeta-potential for all samples regardless of the heating method and addition manner.Dry heating significantly decreased the hydrophobicity of whey protein followed by combining dry and moist heating.Dry-heating may cause whey protein denaturation to less degree than moist heating.It seemed that different inulin addition manners affected the properties of dry-heated whey protein significantly.?2?Mixtures of whey protein and inulin at varying weight ratios of 1:0,3:1,2:1,1:1 1:2,and 1:3 were dry heated at 60?for 5 days under the relative humidity of63%.No significant color change was observed for heated samples by determining absorbance at 420 nm?p>0.05?.Compared with control,average diameter of all complexes significantly decreased with inulin proportion increased?p<0.05?.Zeta potential of all samples after dry-heating was significantly decreased in comparison with native samples?p<0.05?.Samples after dry-heating showed lower intensity in surface hydrophobicity and attachment by inulin caused much lower values.The changes in secondary structure were confirmed by the FT-IR and CD spectra.Compared with native samples,dry heated samples showed significantly higher DPPH scavenging ability when mass ratios were 1:2,1:3 for whey protein and inulin complexes?p<0.05?.Dry heated samples at all ratios showed significantly higher antioxidant capacities in both ABTS+and ORAC-FL tests in comparison with native samples?p<0.05?.?3?Whey protein and inulin solutions were heated at various mass ratios of 1:0,3:1,2:1,1:1,1:2 and 1:3 with constant sample concentration of 10%?w/v?at pH 7-9and heating temperature of 80-100?in oil bath for 1 h.Absorbance of mixtures at420 nm significantly decreased with inulin proportion increased?p<0.05?.Compared with other alkaline conditions,all the samples showed higher diameter values at pH 9.Comparison of WPI and WPI-inulin mixture indicated that the mixture in the ratio of3:1 showed the minimum zeta-potential value?p<0.05?.Compared with WPI alone,all the samples for mixtures of whey protein and inulin at various ratios showed higher surface hydrophobicity.All the samples were determined for acrylamide contents and the results showed that no acrylamide was detected for all samples using the current method.The ABTS+free radical scavenging rate of moist-heating samples was positively correlated with pH and temperature. |
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