Studies On The Darkening Mechanism And Quality Improvement Of Whole-wheat Fresh Noodle

Whole-grain food has been considered to be one of the popular, natural, and functionalfoods. Whole-wheat food is one kind of whole-grain food which is mostly made ofwhole-wheat flour. Whole-wheat fresh noodle (WWFN), as one of whole-wheat food, canmeet modern people's requirement about food, and also lead to the improvement of people'sdietary pattern and the increase of functional materials intake. Darkening is always thetechnological difficulty in the production of WWFN, and the inhibition of darkening ofWWFN is of great value to improve the quality and prolong the shelf-life of WWFN; Theinclusion of wheat bran causes some adverse effects on the textural properties and sensoryqualities of whole-wheat food, the improvement technology of these properties is beneficial toincrease the popularity and extend the market of WWFN.The effects of two grinding techniques (bran-grinding and whole grain-grinding) on thecharacteristics of WWF and properties of WWFN were studied. As the results show, thereduction of wheat bran particle size could increase the PPO activity of WWF and darkeningof WWFN, the growth of the two indicators were positively correlated with correlation indexof0.92, however, the reduction of particle size improved the lightness of WWFN duringstorage, and increase the springiness and cohesiveness of WWFN; The particle size of WWFcould be significantly reduced by the whole grain-grinding technique, the minimum of MZcould be43?m, the color, cooking properties, textural properties, and microstructure ofWWFN were also improved by the reduction of particle size of WWF, but the excessivestarch damage (the maximum was26.03%in the study) produced during the grinding processcould exert adverse effect on the quality of WWFN; Compared to the bran-grinding technique,whole grain-grinding technique was more effective in decreasing the particle size of WWF,however, the cohesiveness and resilience of WWFN were more enhanced by bran-grindingtechnique than by whole grain-grinding.The darkening process curve of WWFN and the effect of temperature, moisture, pH,PPO activity and free phenols content on the darkening of WWFN were studied; themechanism of non-enzymatic darkening of WWFN was also discussed. As the results show,the darkening process could be divided into three stages: stage?(0-0.5h) and stage ?(4-24h) could be expressed by linear function, and stage ?(0.5-4h) could be expressed by aexponential function; When the temperature was between35?and40?, WWFN had themost discoloration, the growth of water addition level increased the enzymatic darkening; themost discoloration was caused when pH of whole-wheat dough was6, and when pH wasbelow5, the non-enzymatic darkening was significantly inhibited; PPO was the major reasonfor the stage?and stage ? of darkening in WWFN, the content of free phenols in wheatbran was one of the factors to affect the enzymatic darkening of WWFN; The relationshipcurve between the rate of non-enzymatic darkening and temperature was nearly a straight line,the R2of the fitting line was0.89; The furosine and HMF were detected in WWFN whenstored at around25?, indicating that mailard reaction was a part of non-enzymatic darkening of WWFN; the addition of tyrosine increased the discoloration in stage ?and stage ? withand without PPO activity in WWF, which demonstrated that the oxidation action of tyrosineinduced by PPO and ROS might be a part of the darkening mechanism in WWFN.The combination treatments of ultrasound and antioxidants were conducted to decreasethe enzymatic discoloration of WWFN, the non-enzymatic darkening of WWFN was alsosuppressed by changing the pH of dough and adding reducing agent. The PPO activity inwheat bran was significantly reduced by the combined treatment of ultrasound andantioxidants, the combination of ultrasound and ascorbic acid has been proved to be mosteffective, which decreased the PPO activity to be7.25%; the darkening of WWFN wassignificantly reduced after the treatments, which could be reduced by48%, some free phenolsin wheat bran were extracted by the treatment, but it had little effect on the antioxidantcapacity of WWF, only the content of Zn2+in WWF was affected when treated by ultrasoundfor3min; The inhibition ratio of non-enzymatic darkening reached42%and around50%,respectively, when pH was2in whole-wheat dough and the concentration of sulfite was0.125mol/L.The thermal mechanical properties of whole-wheat dough were studied by using Mixolaband the effect of enzymes and emulsifiers on the textural properties and sensory qualities werealso investigated. The development time of whole-wheat dough was shorter and toleranceindex was larger than white dough; Among the three kinds of enzymes, the addition of TGhad significant effect on the curve of mixolab curve, it increased the development time anddecreased the tolerance index and setback value of the dough; It has been proved to mosteffective in increasing the hardness, springiness, cohesiveness and resilience values andimproving the sensory qualities and microstructure of WWFN; As for the two kinds ofemulsifiers, the addition of SSL increased the viscosity of WWF, it also increased thedevelopment time and decreased the tolerance index of whole-wheat dough, the texturalproperties, sensory qualities and microstructure were also improved by the addition of SSL.The waxy whole-wheat flour (WWWF) was included to alter the ratio ofamylase/amylopectin in WWF, and the effect of the addition of WWWF on the rheolgicalproperties, combination state of water in whole-wheat dough and quality of WWFN were alsoinvestigated. The inclusion of WWWF significantly increased the content of amylopectin;During the scanning range of0.1-10Hz, the decreasing rank of storage modulus and lossmodulus were partial-waxy wheat group, control, and whole-waxy wheat group; The T21shifted toward to the left after the addition of partial-waxy wheat flour, which indicated thatthe combination of dough with water was enhanced, signal amplitude of every stage increasedafter the inclusion of whole-waxy wheat flour, but the ratio of bond water was notsignificantly affected; The inclusion of whole-waxy wheat flour had adverse effect on thetextural properties of WWFN, however, the springiness, cohesiveness, and resilience ofWWFN were improved by the addition of partial-waxy wheat flour.The effect of flour kinds of phosphate and two kinds of gum on the thermal properties,pasting properties of WWF and the qualities of WWFN were studied. The thermal propertiescurve of starch in WWF was shifted to the right and the gelatinization enthalpy increased afterthe addition of phosphate, STPP and SHMP have been proved to be more effective; The pasting viscosity also increased after the inclusion of phosphate, in which the peak viscosityand final viscosity increased by DSP and TSP; TSP has been proved to be most effective ininhibiting the darkening of WWFN; The cooking loss of WWFN was declined by the additionof STPP and SHMP and the textural properties of WWFN were also increased by theinclusion of STPP and SHMP; It was concluded that STPP was most effective in improvingthe quality of WWFN; The pasting viscosity of starch in WWF decreased after the addition ofArabic gum, in contrast, the inclusion of xanthan increased the pasting viscosity of WWF;The hardness of WWFN increased by Arabic gum, while the addition of xanthan increased thehardness, cohesinveness, and resilience of WWFN; Compared with Arabic gum, thecross-linking between protein matrix and starch granules was significantly enhanced by theinclusion of xanthan.