Effects Of Recombinant Lipoxygenase On Wheat Flour Quality

Lipoxygenase (LOX) is classified as oxidoreductases, which extensively exists in animals, plants, alga and fungi. LOX can catalyze polyunsaturated fatty acid (PUFA) of cis, cis-1,4-pentadiene structure, resulted in the formation of hydroperoxides with a conjugated double bond. These hydroperoxides are of high activity and are the important intermediate in chemical reaction, which have great application value in food processing. Moreove, Lipoxygenase plays an important role in improving the quality of flour, due to the dual roles of bleaching and gluten strengthening, which has aroused extensive attention. At present, commercial grade lipoxygenase has not yet appeared, mostly soybean riched in LOX is used as the source of enzyme, but soybean contains many kinds of isozyme with complex components, poor enzyme purity, dark color and poor effect, which limited the wide application of LOX in food industry.Based on the expression recombinant lipoxygenase (ana-rLOX) in the laboratory, Yangmai 15 is used as matericals, this research is mainly about the effects of ana-rLOX on flour bleachment, gluten improvement and quality development of flour products. The results provide technical support for future bioprocess technology applications of ana-rLOX. Main study results are as following:1. Bleaching effect of ana-rLOX on wheat flour. High performance liquid chromatography (HPLC) was used to detect the effect of ana-rLOX on pigment degradation in flour, and A CIE-LAB color scale was used to detect the effect of ana-rLOX on flour bleaching. When the application rates were 50 IU/g in flour and dough, lutein decreased by 5.75%、20.23% respectively, β-carotene decreased by 15.22%、56.98% respectively. These results showed the bleaching effect of ana-rLOX on wheat flour was mainly by oxidation P-carotene, and the degradation rate in dough was higher than that in flour. The ana-rLOX treated samples of 10-30 IU/g flour initially showed increased whiteness (L* values) by 1.5-2.5 in 48 h at room temperature, and the whitening effect was very similar even if benzoyl peroxide was added to the flour. The L* values of flour dough treated with ana-rLOX increased by 2-3 in 5 h and the whitening effect was notable.2. Gluten strengthening effect of ana-rLOX on wheat flour. Though the investigation of dough farinograph, extensograph, dynamic rheological properties and structural characteristics, it could be found that the development time, stability time and tensile resistance of dough progressively increased after treated with ana-rLOX. When treated with ana-rLOX of 20 IU/g flour, the development time and stability time increased by 1.5 and 2.4 min respectively, the tensile resistance of dough increased by 9.8% and 9.9% at 90min/135min proofing time respectively, the G’ and G" of dough increased correspondingly. Simultaneously, the dough treated with enzyme showed a stronger and more resistant network than the control. The analysis of amino acid composition of gluten added 20 IU/g ana-rLOX showed that Glu and Asp increased by 15.66% and 66.06% respectively, Cys decreased by 1.9%. The essential amino acids like Thr, Val, Ile and Phe also increased, which is benifical to improve the nutritional value of gluten.3. Quality improvement of ana-rLOX on bread and noodle. By the application of ana-rLOX in bread and noodle making, the actual effect of ana-rLOX on flour quality improvement was evalued. The results showed that when treated with 20 IU/g ana-rLOX, the lightness (L* values) of the bread crumb increased by 1.65, the bread volume increased by 18.19%, the hardness, gumminess and chewiness of the bread was apparently decreased compared with the control, while the resilience was increased, so the bread textural properties were increased. The L* values of noodle increased by 2.34 compared with the control after storing 1h at room temperature. Shear force and viscous resistance of noodle was improved, the hardness, gumminess chewiness and springiness of the noodle was increased correspondingly. The gluten structures of noodle were more continuous and close, the starch granules were smaller and more uniform distribution, so the quality of noodle was improved. Those test results showed the effect of ana-rLOX on flour quality improvement is considerable with chemical gluten agent potassium bromate and benzoyl peroxide, and ana-rLOX can become a new biological flour improver.