| Grain amaranth (Amaranthus sp.) belongs to Amaranthceae, Amaranthus. It is a kind of annual herb that can be used as grain as well as fodder. " Grain amaranth" is a generic term for amaranth which is harvested for cereal use. Amaranthus hypochondriacus, A. cruentus and A. caudatus are the three most important varieties of grain amaranth. Grain amaranth is rich in nutrition, its starch has good qualities; It has a high protein content and amino acids composition are reasonable; Most of its lipids are unsaturated fatty acids, a kind of precious substance named squalene was found in grain amaranth; As the same time, it has been reported to has a considerable content of calcium, magnesium, iron, potassium, zinc and some other mineral elements; It still has a good digestion; What is more, stems, leaves and flower spikes of grain amaranth can be used to the extraction of natural pigments.This test employed K112(Amaranthus cruentus L.) collected from JingGuan town in ChongQing as raw material, using analysis equipment such as scanning electron microscope, laser particle size analyzer, X-ray diffractomer, differential scanning calorimeter, texture analyzer, Brabender viscometer,combined with some regular physical or chemical analytical method to study on the properties of starch extracted from grain amaranth seeds, some of these texts adopted corn starch, cassava starch and sweet potato starch to show a contrast. Based on single factor experiment, extraction process of grain amaranth flower spikes pigment was optimized by the experimental design of response surface method, effects of physical and chemical factors such as light, temperature, pH, REDOX to the stability of the pigment was observed. The main results are as follows:1. Properties of starch from grain amaranth seeds:(1) Researches on the granules properties of starch from grain amaranth seeds showed: most of the starch granules demonstrate irregular polyhedron, under SEM, it was found that the average diameter of the granules was 1.38μm, particle size was range from 0.65,μm to 1.92μm, the surface was smooth, the structure is undamaged relatively, a part of the fragments may be caused by damage to the starch granules; through laser particle size analyzer, it was known that the surface weighted mean D of the granules was 2.38μm, the volume weighted mean D was 8.13μm,50% of the starch granules was less than 2.91,um and 90% of them were less than 22.93/μm; there were three peaks in the X-ray diffraction pattern which located in 15.2°,17.5°,23.2°respectively, so the crystalline type belonged to type A, the crystallinity was 64.67%, which was higher than other origin starch.(2) Researches on the physical and chemical properties of starch from grain amaranth seeds showed:Starch content in grain amaranth seeds was 62.49% and there was about 6.12% amylopectin in its starch; Infrared spectroscopy showed that, there appeared some relatively strong absorption peaks located in telescopic vibration and variable Angle vibration peak of O-H in 3600-1cm-3200cm-1 and 1105cm-1; As well as telescopic vibration and the variable Angle vibration of-CH2-the C-H in 2926cm-1 and 1459cm-1, it can be inferred that the starch was primarily consisted by O-H and C-H, in addition, there exist a-D pyranoid ring with primary and secondary hydroxyl groups, these were consistent to normal origin starch; its starch paste has a poor transparency which was only 1.5, the lowest among four kinds of starch; settling velocity was the slowest of the four kinds of starch,24 hours after the settlement, the subsidence area 2.0mL, in the end of the process of settlement, the supernatant volume was 18.4mL; freeze-thaw stability of the starch paste was moderate, water separated after only once freeze-thaw process, rate of separated water was 27.52%, higher than the corn starch, lower than the sweet potato starch, and approximate with cassava starch; In a certain time, the retrogradation degree of starch paste was deepen by the increase of time, the higher the concentration was the more difficult to retrogradation, within 24 h, water chromatography rate of starch paste with the concentration of 4% was 20.61%, and 8% was 0.the starch has a poor solubility but a relatively strong swelling power, in a certain range, solubility and swelling power increased by the rising of temperature, swelling power were 3.81% and 13.68% respectively when temperature were 65℃and 85℃, a fast rising process can be seen in this period, which is a characteristic for restricted expansion starch; blue value of the starch was 0.085,which was the lowest of four kinds of starch, a weak iodine bonding capacity implied a low amylose content; the maximum absorption wavelength of starch-iodine compound was 566nm, which was close with corn starch, it was 604nm and 579nm respectively for cassava starch and sweet potato starch, larger than the value of starch from grain amaranth seeds; enzyme hydrolysis resistibility was 0.41, lowest of four kinds of starch; in DSC determination, the starting pasting temperature was 66.5℃, the ending pasting temperature was 78.4℃, these were close to the values obtained in observation method which were 64℃and 80℃respectively, starch gel forming temperature was 72.2℃, pasting enthalpy variable value was 13.4J/g; hardness, springiness, cohesiveness and adhesiveness of the starch gel were 13.739g,0.624,0.386 and-19.982 respectively, those were in moderate level in the four kinds of starch, chewiness was only 3.279, which was poor; in Brabender viscosity determination, the peak value of viscosity was 181BU, pertain to starch of relatively low viscosity, breakdown value and return value were 2BU and 129BU, that implied good thermal stability and cold stability of the starch.2. Extraction technology and stability of pigment from grain amaranth flower spikes:(1) Researches on the extraction technology of pigment from grain amaranth flower spikes showed:Fresh grain amaranth material should be dried under a relatively low temperature as soon as possible in order to protect the pigment, the pigment was water soluble pigment and insoluble in organic solvent selected in the test, finally 10% ethanol was chosen as the extraction solvent, it showed sound effect and could save cost; single factor experiment showed that:to get a better extraction efficiency, solid-liquid ratio should be controlled around 1:50, extraction temperature should be controlled below 50℃, the ultrasonic intensity should not exceed 150W, extraction time controlled 60min or so is appropriate, the extraction times to 2 times was more reasonable; On the basis of single factor experiment, response surface methodology was introduced to optimize a optimum process:solid-liquid ratio 1:40, extraction temperature 23.1℃, extraction time 70 min, ultrasonic intensity 150W, extraction times twice, pigment extraction rate under abovementioned conditions in the verification test was 83.73%, error with the theoretical prediction was 0.19%, so the model established by response surface methodology proved to be reliable; in 6 months, the dry pigment could maintain a vivid color under room temperature with dry air.(2) Researches on the stability of pigment from grain amaranth flower spikes showed: the thermal stability of the pigment was disappointing, when the temperature was 80℃, the absorbance of the pigment decreased from 0.852 to 0.084 within 2 hours; low temperature was suitable for the preservation of the pigment, After 7 days kept in the refrigerator, the absorbance remains a high level and the color was ideal, natural light has slight effect to the pigment; the pigment put up relatively good stability when pH was 4-8, extreme pH can change the color of the pigment, when pH=10 and pH=11, the pigment solution appeared in reddish brown and brownish yellow; low concentration of oxidant and reducing agent did not make much difference on the stability of the pigment, but time went by, adverse effects also have a tendency to increase, when Vc concentration was more than 0.02%, the absorbance of the pigment was significantly decreased; when organic acid concentration was below 0.1%, the absorbance of the pigment solution showed a rapid downward trend, when the concentration was above 0.1%, the downward trend came to become mild; saccharides could provide a certain hyperchromic, color protecting effect, which was more obvious to the effect of glucose, when glucose concentration was greater than 10%, the absorbance value increased more significant; preservatives, the higher the concentration or the longer the storage time was, the degree of the damage to the pigment became more serious, when the concentration of sodium benzoate and potassium sorbate were above 0.06% and 0.02%, they showed obvious damage to the pigment after 24h; Ca2+, Zn2+, Fe2+, Fe3+ could muddy the pigment or even change its original color, low concentrations of Al3+ and Mg2+ played a certain hyperchromic role, the existence of Na+ and K+ result in a slight lessen in absorbance value of the pigment. |
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