Preparation And Flavor Characteristics Of Maillard Peptides Derived From Wheat Gluten

As the main by-product during the production of wheat starch,wheat gluten(WG)possesses the content of over 75% protein with various kinds of amino acids.WG has shown advantages in rich nutrition with competitive price and has been considered as the main source of vegetable protein.With the increase in the consumers' demand for wheat starch,there is a rising trend in the production of WG.However,the high amount of hydrophobic amino acids and the large hydrophobic region within molecules lead to its poor water solubility,limiting the application of WG in the food industry.Nowadays,the utilization of WG is confined to several food application fields,including fodder and bread;thus,it is extremely urgent to explore new areas to avoid the waste of WG and to create more values for food industry.This paper utilized wheat gluten meal as the raw material to prepare Maillard peptides with outstanding umami,thickly-mellow taste and stronger antioxidant activity by the methods of enzymatic hydrolysis and Maillard reaction technology;Maillard peptides derived WG,corn protein and sunflower seed protein were also compared to fully evaluate the sensory and flavor characteristics of WG Maillard reaction products.This research aimed to develop condiments which can meet different needs of consumers and also to clarify the application horizontal of different Maillard peptides in the current market.The main research contents are listed as follows:Based on the results of soluble solids extraction rate,degree of hydrolysis and sensory evaluation,protease A and protease D were selected to stepwise hydrolyze WG;the optimum conditions of enzymatic hydrolysis were determined as follows: WG solution was heated at 95°C for 30 min with a substrate concentration of 10%(w/v);after cooling down,the pH was adjusted to 8.0,then protease A was added with the concentration of 2200 U/g WG while the temperature was set at 60°C for 3 h.In the following step,the mixture with 400 U/g WG protease D was further digested for another 4 h at 50°C.Under above conditions,the soluble solids extraction rate of optimal WG hydrolysis was 88.50%,and the degree of hydrolysis reached 14.01%.Moreover,their Maillard reaction products possessed outstanding thicklymellow and umami taste with a good overall flavor characteristics.Maillard peptides were prepared using wheat gluten peptides(GP)-xylose-cysteine reaction system,in which GP was produced under the optimum conditions.Results of sensory evaluation were used as an index to examine the effect of reaction parameters on the flavor quality of Maillard peptides.The optimal Maillard reaction parameters were determined as follows: 25% of the reactants(xylose and cysteine)were added according to the total solids of hydrolysate.The ratio of cysteine and xylose was kept at 1:1.5 and the initial pH was adjusted to 7.0.Finally the mixture was heated at 120°C for 120 min.The Maillard reaction products obtained under above conditions possesses favorable umami and thickly-mellow taste as well as harmonious overall flavor attributes.Partial least squares regression(PLSR)was applied to analyze the correlation between Maillard reaction factors,volatile compounds and sensory indexes of MRPs.The results showed that the key flavor substance of WG Maillard peptides were 3-thiophenecarboxaldehyde,2,5-thiophene dicarboxaldehyde,4-amino-1-methyl-1H-benzotriazole,2-acetylfuran,3-methyl-thiophene,ethyl thioacetate,2-acetyl-thiophene,2-methyl-furan,1-hexanol,1-pentanol,2,5-dimethyl-thiophene,5-methyl-2-thiophenecarboxaldehyde,1,4,6-trimethyl-2(1H)-pyridone,1-ethylidene-1H-indene,3-heptanone,2-furfurylthiol,2-methyl-3-pentanethiol,heptanoic acid,hexanoic acid,thiirane,furfural.The antioxidant activity of MRPs derived from WG and its original enzymatic hydrolysates was compared and results suggested that when reaching the same reducing power,the concentration of hydrolysate was about 50 times that of MRPs.As for the DPPH radical scavenging ability,the enzymatic hydrolysates reached 91.88% at the concentration of 20 mg/m L while MRPs could reach 95.47% though the concentration was only 0.6 mg/m L.Obviously,the reducing power and DPPH radical scavenging ability were drastically improved after Maillard reaction.The WG,corn protein and sunflower seed protein Maillard peptides and their original enzymatic hydrolysates were compared in aspects of pH,color,volatile compounds,amino acids,nucleotides and sensory characteristics.The results showed that MGP with the highest degree of clarification had an outstanding umami taste,thickly-mellow taste and overallacceptance,while nitrogen containing compounds representing caramel-like flavor in MGP were also higher.These indicated that MGP was favorable for developing the light-colored foods with better umami,meat-like,thickly-mellow taste and caramel-like flavor.Furthermore,when compared with MGP and MSP,MCP possessed smallest color difference,stronger sweetness attribute and higher content of sweet amino acids,and this meant that MCP was desirable for the foods which require stronger sweetness and light color.Moreover,the content of bitter amino acids in MSP was low and the saltiness of MSP was quiet strong,which indicated that MSP was suitable to be added into salty foods to reduce the usage of salt.The electronic tongue can be objectively used to measure the characteristics of taste indicators including sourness,sweetness,bitterness,umami,salty,etc.Three different concentrations of MSG were compared with MGP(at the concentration of 3%)in terms of sourness,bitterness,umami and saltiness.The results showed that the umami intensity of MGP at the weight of 1.00 g was equivalent to 0.33 g MSG solution,which is of great significance for the further development of natural flavor enhancer.