Study On Corn Flour By Wet Milling And Its Properities

The study was based on corn wet-milling process, and the laboratory wet-milling procedure was established. The protease was used to hydrolyze the protein which combined with starch in the endosperm. The relationship between the ganule of corn flour with the properties of corn flour were studied. The corn flour blended with cassava starch and xanthan gum in order to modify the quliaty of corn flour. The relationship between corn flour with corn food was established.A 50-g laboratory wet-milling procedure was established in order to reduce sample requirement for determining the milling characteristics of corn samples and analyzing of process conditions. Corn steeped in the steep solution containing 0.20 %(w/w) sulfur dioxide and 0.50 %(w/w) lactic acid at 52 ℃ for various times(40 h, 48 h, 56 h, 64 h, 72 h). corn was wet-milled and the wet-milled fractions were recovered. The optimal result of corn starch of yield was 62.56 % when steeping time was 48 h. The starch granules were an angular and circle conformation, and great homogeneity in size distribution of starch granules were reached by using various times. The result of DSC showed △H had a significant increase from 12.69 J/g to 14.09 J/g with increasing steeping time from 48 h to 72 h(P<0.05). twelve replicates of the hybrid corn averaged 62.83 % starch yield with standard deviation of 0.58 %.Enzymatic milling was a modified wet millig process that used protease to hydrolyze protein which combined with starch in the endosperm. Preparation of corn flour were optimized by single factor and response surface experiments. The optimum conditions were that the first soaking, enzyme addition and hydrolyzed time were 6h, 0.35 mL(the protease activity at 1.27×105 U/mL) and 7h, respectively. The surface characteristics, pasting properties, thermal properties and rheological properties of there corn flours(enzymatic-milled corn flour, dry-milled corn flour, wet-milled corn flour) were mearsured. Compared with dry-miled corn flour and wet-milled corn flour, the enzymatic-milled corn flour had smaller average particle size(16.74 μm), and great homogeneity in size distribution of granules. The pasting properties showed that the highest peak viscosity and final viscosity of 2997 c P and 3300 cP, respectively, were observed for enzymatic-milled corn flour, whereas dry-milled corn flour showed the lowest value for the same. The thermal properties by differential scaning calorimetry showed enzymatic-milled corn flour had higher △H and lower To, Tp and Tc of 13.43 J/g, 68.54 ℃, 72.89 ℃ and 78.41 ℃, respectively, compared with dry-milled corn flour, which had △H, To, Tp and Tc of 6.59 J/g, 69.99 ℃, 75.36 ℃ and 79.32 ℃, respectively(P<0.05). Enzymatic-milled corn flour gel(6%, w/w) exhibited slightly superior viscoelastic properties to dry-milled corn flour gel and wet-milled corn flour gel as evidenced by their higer G’ and lower tanδ over the enter frequency range(0.1 rad/s~100 rad/s).The additions of ingredients were optimized by orthogonal test when the corn flour blended with cassava starch, xanthan gum and guar gum in order to modify the quliaty of corn flour. The optimal ingredient additions were that xanthan gum and cassava starch were 0.5 % and 5 %, respectively(w/w, g/100 g basis flour). The properties of different basic formulations made of flours(enzymatic-milled corn flour, dry-milled corn flour), cassava starch and xanthan gum, to make tortillas and the tortillas were mearsured to study the relationship between corn flour with tortillas. The pasting properties of formulations showed that pasting properties of enzymatic-milled corn flour was increased after adding xanthan gum and cassava starch. After adding cassava starch and xanthan gum, the G’ of enzymatic-milled corn flour gel(6%, w/w) was increased, but the G ’ of dry-milled corn flour gel was slight changed. Dynamic viscoelastic measurement of tortillas indicated that after adding cassava starch and xanthan gum, the tortillas which were made by enzymatic-milled corn flour had lower value of G’, G’’ and tanδ than the tortillas which were made by dry-milled corn flour over the enter frequency range(0.1 rad/s~100 rad/s). The SEM results showed that the gel structure of tortillas which were prepared by enzymatic-milled corn flour had many pores, and great homogeneity indistribution of pores.