| Refined wheat flour is a staple food in northern China.It is produced by wheat after removing most of its cortex and germ,resulting in the loss of a large amount of high-quality protein,dietary fiber,and phenolic substances in wheat.Whole wheat flour,a whole grain food,contains all the nutrients of wheat.However,the hard texture of the wheat cortex interferes with the formation of continuous gluten structures during the formation of whole wheat flour dough,resulting in poor processing quality of whole wheat flour.At the same time,the high activities of lipase,lipoxygenase,and polyphenol oxidase in the wheat cortex and embryo are prone to enzymatic hydrolysis and oxidative rancidity,leading to poor storage quality of whole wheat flour.These factors restrict the development and utilization of whole wheat flour.Existing studies have shown that reducing the particle size of wheat bran can improve the processing quality of whole wheat flour,but there are no reports on the relevant mechanisms.High voltage pulsed electric fields have the characteristics of short processing time,low energy consumption,and insignificant temperature rise.They have been widely used to improve the extraction rate of active ingredients,reduce energy consumption for freeze drying,and control enzyme activity,but have not been used to improve the storage quality of whole wheat flour.Therefore,this article uses micronization and high-voltage pulsed electric field to treat wheat bran,mainly exploring the impact of micronization on the physicochemical properties of wheat bran and the processing quality of whole wheat flour,as well as the impact of high-voltage pulsed electric field on the physicochemical properties of wheat bran and the storage quality of whole wheat flour,with a view to promoting the development and utilization of whole wheat flour.The main conclusions of this article are as follows:(1)The quality of whole wheat flour was compared by using direct pulverization method and feed back method.The results showed that the whole wheat flour prepared by the feed back method had low damaged starch content,long shelf life,and better texture characteristics and sensory quality of the whole wheat noodles.Reducing the particle size of the added wheat bran can weaken the interference of wheat bran on gluten protein polymerization,form a relatively continuous gluten structure,reduce the breaking rate and cooking loss rate of whole wheat noodles,and improve the texture characteristics and sensory quality of whole wheat noodles.However,reducing the grain size of the added wheat bran played no significant impact on the shelf life of whole wheat flour.(2)The mean particle size(D50)of wheat bran ranged 26.05~46.08 was prepared by using an ultra-fine pulverizer.The physicochemical properties of wheat bran and the processing quality of whole wheat flour were compared.The results showed that with the decrease in the D50 of wheat bran from 46.08 μm to 26.05μm,the dissolved amounts of protein,total flavonoids,and total phenols in wheat bran increased by 6.72%,23.47%,and 19.07%,respectively;The adsorption capacity,cation exchange capacity,and in vitro antioxidant activity of cholesterol and sodium nitrite were enhanced.With the D50 of wheat bran decreased from 46.08 μm to 26.51 μm.The degree of encapsulation of wheat bran particles by the protein starch matrix increased,the continuity of the gluten structure increased,and the dough formed a relatively loose structure,which improved the cooking characteristics,texture characteristics,and sensory quality of whole wheat noodles.But with the D50 of wheat bran decreased from 26.51 μm to 26.05 μm,the dough formed a more compact structure,resulting in poor quality of whole wheat noodles.These above results indicated that the optimal D50 of wheat bran in the production of whole wheat flour for noodles by the feed back method was 26.51 μm.(3)The microstructure of wheat bran and gluten was analyzed to reveal the mechanism of the impact of micronization on the physicochemical properties of wheat bran and the processing quality of whole wheat flour.The results showed that with the decrease in the D50 of the wheat bran from 34.93 μm to 26.05μm.The degree of fiber fragmentation in wheat bran increased,the crystallinity index decreased,and more active groups were exposed,promoting the release of active ingredients and improving functional properties.Wheat bran with the D50 of wheat bran decreasing from 34.93 μm to 26.51 μm promoted the polymerization of gluten proteins through disulfide bonds and hydrophobic interactions,resulting in an increase in molecular weight and a more continuous network structure of gluten,which improved the cooking characteristics,texture characteristics,and sensory quality of whole wheat noodles.With the decrease in D50 of wheat bran from 26.51 μm to 26.05 μm,active substances exposed on the surface can affect the polymerization between gluten proteins through non covalent interactions with gluten proteins,resulting in a relatively loose network structure of gluten,leading to poor quality of whole wheat noodles.(4)Wheat bran was treated with a pulsed electric field of 10~50 k V/cm to compare the physicochemical properties of wheat bran and the storage quality of whole wheat flour.The results showed that as the electric field intensity(E)increased from 10 k V/cm to 20 k V/cm,the total flavonoids and total phenols in wheat bran increased by 14.95% and 3.90%,respectively;When E>20 k V/cm,the structure of total phenols and flavonoids was destroyed or combined with other substances,resulting in a decrease in the dissolution amount.As E increased from 10 k V/cm to 40 k V/cm,α– 1,4 or α– The 1,6 glycosidic bond was destroyed,the molecular weight decreased,and more active groups are exposed,which enhanced the adsorption and exchange capacity of wheat bran;When E>40 k V/cm,polysaccharides bound to proteins to form conjugates,leading to a decrease in the adsorption and exchange capacity of wheat bran.Pulsed electric fields with an E ≥ 20 k V/cm played inhibitory effects on the activities of lipase,lipoxygenase,catalase,and multiple oxidase in wheat bran,which can be applied to extend the shelf life of whole wheat flour.Among them,the lipase activity in wheat bran had the strongest correlation with the shelf life of whole wheat flour(r2=-0.9286,P<0.05).(5)Using electric field intensity,pulse frequency,and duty cycle as independent variables,the relative extraction rate of active ingredients and the inactivation rate of endogenous enzymes as dependent variables,establishing a comprehensive evaluation index to optimize the processing parameters of highvoltage pulsed electric field treatment of wheat bran by response surface methodology.The results showed that the electric field intensity played the greatest impact on the comprehensive score,followed by the duty cycle and pulse frequency.Based on the optimal combination analysis of Design-Expert 8.0.6 software and feasibility analysis,the combination of process parameters with the highest comprehensive score was determined as follows: electric field intensity 40 k V/cm,pulse frequency 670 Hz,and duty ratio 27%.Under these conditions,the measured comprehensive score of wheat bran was 0.5801,and the cooking and texture characteristics of whole wheat noodles were also better than those of the untreated group.(6)In order to reveal the mechanism of the effect of high-voltage pulsed electric field treatment on the storage quality of whole wheat flour,the effects of 10 to 50 k V/cm pulsed electric field on the characteristics and microstructure of lipase were analyzed.The results showed that a pulsed electric field with E=10 k V/cm disrupted the secondary bonds that maintain the spatial structure of lipase,exposing more aromatic amino acids such as tryptophan,presenting a more extended and ordered structure.The binding sites with the substrate increased,and the enzyme activity increased.A pulsed electric field with an E ≥ 20 k V/cm promotes the reaggregation of enzyme molecules through hydrophobic interactions.The hydrophobic groups on the surface of the lipase are re encapsulated within the molecule,reducing the binding sites with the substrate,leading to a decrease in enzyme activity. |
