| Maize is an important cash crop and its production output rankes the second, next to wheat and rice, Starch content in maize is about70%; nutrients are comprehensive and maize has certain health functions. Therefore, maize is one of the main grains in the people’s life. However, most nutrients in maize can not be directly absorbed by human body. There are many defects in maize starch, which limit using. Germination have a positive effect on improving the amino acid composition in seed and utilization of protein, increasing B vitamins content, reducing the level of anti-nutritional factors, and improving the processed characteristics of starch.In this paper, three maize varieties:normal maize (Suyu24, SY-24), waxy maize (Zihua waxy maize, ZY) and sweet maize (Jingjing3, TY) were used as the research materials. Composition differences and the changes of main physio-biochemical properties and carbohydrate components of the three maize varieties during different periods of germination were investigated. The changes of maize starch properties from different germination stage, such as morphological structure, thermodynamics and rheology were observed and analyzed. The starch from different maize germination stages, as fat replacers used in processed cheese. The fat replacement rate was analyzed and assessed. The main results and findings were summarized as follows:Chemical compositions of maize varieties were analysised. There were some composition differences among the three maize varieties. SY-24showed the highest1000kernel weight and amylose content. Amylose was not detected in ZY. There was no significant difference between SY-24and ZY in starch content. ZY showed the highest contents of moisture, reducing sugar, soluble sugars, Mg, Na and Ca; TY showed the highest the contents of carotenoids, soluble protein, free amino acids, ash, crude fat, Zn and K. However, Ca was not detected in SY-24. Fe content was no significant between TY and SY-24(P>0.05), while were significantly higher than ZY (P<0.05), which was4.69times and1.04times, respectively, as compared with TY and SY-24.In the process of germination, the content of dry matter decreased; shoot length and germination rate gradually increased; amylase activity gradually increased, meanwhile, β-amylase activity was significantly higher than a-amylase. With the effect of amylase, the starch content and granule decreased. There was no amylose produced during germination of ZY. Amylase content of SY-24and ZY were fist increased then decreased, and reached the maximum at24h and36h, which were3.10times and1.46times as compared with that of non-germinated, respectively. Soluble sugars showed a fluctuation change among SY-24, ZY and TY. Reducing sugar in ZY and SY-24were gradually increased. However, TY was fist decreased then increased and reached the minimum at12h with15.44%lose compared to that of non-germinated.With the bases of composition and germinated characteristics in three maize varieties, SY-24was germinated and starch from it was extracted. The results showed that:Starch morphology of maize that was germinsted was studied. It has little effect on microstructures with a short time of germination with polarizing microscope, scanning electron and XRD. However, cracks, holes and debris on the surface of starch granules were increased with the germination time. Moreover, it changed maize starch’s ratio of crystallization and non-crystalline regions, destructed the microstructure of starch and reduced the size of starch granules.Starch characteristics of germinated maize were analysised. Raw starch, germination24h and96h there were "gel-sol" transition temperature, but48h,72h and120h did not have "gel-sol" transition temperature. Hardness, springiness, cohesiveness, chewiness and gel-strength reached the minimum value and adhesiveness reached the maximum value at72h. It was the turning point of gel properties.Temperature range and emulsion activity of maize starch was not changing significant in germinated0～120h. However, it significantly impacted the value of the enthalpy (△H). With the effect of germination, the emulsion stability reduced; the cracks and holes on the surface of starch granules and the dispersion of starch in water increased; swelling power, water-absorption capacity and freeze-thawing stability of starch increased; improving the water-absorption capacity of starch gel, reducing the light transmittance and oil-absorption capacity of starch paste.In the process of germination, starch films’ elongation was first decreased then increased, and reached the minimum at96h. Tensile strength, transparency and solubility were first increased and decreased, and the first two reached the maximum at96h, solubility reached the maximum at72h. Water vapor permeability (WVP) increased, gradually. Starch films were stable in the acid. Lye reduced the stability of starch films because of destructing the hydrogen bonds among molecules. Germination reduced the stability of starch films in alkaline solution. Therefore,72h and96h were key points of starch films.Maize starch was applied on processed cheese as fat substitute. There was no significant difference between adding and non-adding72h germinated starch as replacement rate below15%. Adding it could improve the meltability and organizational structure and overall sensory evaluation of the processed cheese. The sensory evaluation of25%fat replacement rate was lower than15%. However, the sensory evaluation of25%was still in the range of acceptable. Therefore, it could replace25%fat in the processed cheese with72h germinated maize starch. |
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