| This study was funded by the Jilin Provincial Major Science and Technology Project"Key Technology and New Product Development for Separation,Extraction and Deep Processing of Non-oil Fraction of Tiger Nut"(20200502002NC).With the increase of the world population and the improvement of people’s living standard,the demand for high quality protein is increasing.It is imperative to develop new protein resources.Tiger Nut(Cyperus esculentus L.)is favored by the majority of researchers because of its adaptability,high yield,and complete range of protein amino acids.In this research,the Osborne extraction method was used to optimize the protein extraction process by single-factor and orthogonal experiments to obtain four tiger nut proteins,albumin,globulin,glutelin and prolamin.The nutritional analysis,physicochemical structure and functional properties of the four proteins were investigated.The effects of microwave and water bath heating on their digestibility,functional and structure properties were further investigated and characterized.Based on these studies,the tiger nut protein was added to the production of gluten-free bread in order to increase their nutritional and organoleptic properties.The specific research contents and results are as follows.(1)A study on the preparation and separation of tiger nut protein was carried out using tiger nut meal as raw material.The optimal extraction conditions were optimized by single-factor and orthogonal tests with protein extraction rate as the index:extraction time of 85 min,material-liquid ratio of 1:12 g/m L,salt concentration of 0.5 mol/L,alkali concentration of 0.12 mol/L and alcohol concentration of 70%.The yields of albumin,globulin,glutelin and alcoholic protein were 42.37%,6.23%,31.25%and5.10%,respectively.(2)The nutritional,structural and functional properties of tiger nut albumin,globulin,glutelin and prolamin were investigated.The results showed that the four tiger nut proteins contained 18 essential amino acids.Among the four proteins,albumin had the highest percentage of essential amino acids at 43.60%;globulin had the highest digestibility at 86.51%.The isoelectric points of the four proteins were p H 4.2,4.4,4.8,and 4.6,respectively.Albumin and globulin had similar molecular weight distributions in the range of 15-180 k Da,while glutelin and prolamin had molecular weight distributions in the range of 75-180 k Da.Theβ-folding was the main conformation of tiger nut albumin,glutelin,and globulin,andα-helix was the main conformation of prolamin.Glutelin has a larger maximum emission wavelength and higher surface hydrophobicity,contributing to protein functionality.The solubility,emulsifying and foaming properties of four proteins exhibited the lowest at the isoelectric point and showed better functional properties under alkaline conditions.Glutelin had emulsifying,foaming properties and water/oil holding capacity comparable to soybean protein,significantly higher than peanut and corn proteins.The albumin has higher thermal stability and glutelin has poor thermal stability.(3)The effects of microwave and bath heat treatment on the structural,functional and digestive properties of tiger nut glutelin were examined.At lower microwave frequencies and water bath temperatures,the surface hydrophobicity and fluorescence intensity of proteins increased with increasing treatment time,and the fluorescence absorbance spectra shifted red,exposing more hydrophobic groups and showing the promotion of functional properties.As the microwave power,water bath temperature and treatment time increased,the fluorescence absorbance spectra shifted blue,and the fluorescence intensity and surface hydrophobicity decreased,showing the inhibition of functional properties.The solubility,emulsifying,foaming and digestibility of the proteins showed a trend of increasing and then decreasing with the increase of microwave power,heating temperature and treatment time.The best solubility(68.88%)was obtained under the microwave heating condition of 40 s at 420 W.The best emulsification(9.61 m~2/g)was obtained under the microwave heating condition of 40s at 560 W.The best foaming(85.56%)was obtained for tiger nut glutelin in a water bath at 80°C for 20 min.The best digestibility of tiger nut glutelin was 78.58%at 560W microwave treatment for 40 s.(4)Tiger nut albumin was added to gluten-free bread as an emulsifier to research its effect on bread quality.The results showed that the addition of tiger nut albumin improved the dough characteristics,baking characteristics and sensory characteristics of gluten-free bread.The elastic modulus G’and viscous modulus G"increased with increasing protein addition,and G’was higher than G’’throughout the frequency range,and tanδvalues decreased.The baking loss was inversely proportional to the amount of protein added.The specific volume of bread showed the highest(2.22 cm~3/g)at 15%protein addition.The lower hardness was obtained at 10%and 15%protein addition.The color of crust and crumb core darkened with the addition of tiger nut protein,the red color deepened and the yellow color diminished.At 15%protein addition,the gluten-free bread showed good sensory properties while ensuring low baking losses,yielding a nutritious gluten-free bakery product rich in protein. |
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