TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Compositions: Trivalent iron salt is ferric chloride, iron bromide, or iron acetate, preferably anhydrous ferric trichloride in which molar amount of trivalent iron salt and iodine is equal to dihydro flavanone molar amount, and amount of iodine can be reduced to 1/5, 1/10, or 1/100 of original amount but not 0. Acid is phosphoric acid, sulfuric acid, hydrochloric acid, hydrobromic acid, acetic acid, oxalic acid, citric acid, and/or tartaric acid, preferably hydrochloric acid, sulfuric acid, and phosphoric acid. Iron-removing agent is phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, or hydrosulfite, preferably phosphoric acid.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Processes: Filter cake is processed by adding alcohol solution of iron-removing agent, stirring until there is no iron complex color, preserving heat in water bath, filtering, washing, placing filter cake in alcohol solution of phosphoric acid, and washing 2-3 times. Preferred Components: Alcohol is monohydric alcohol, dihydric alcohol, and/or trihydric alcohol in which monohydric alcohol is methanol, ethanol, or propanol, dihydric alcohol is ethylene glycol, 1,2-propylene glycol, or 1,3-propylene glycol, and trihydric alcohol is glycerol, preferably ethylene glycol or glycerol. Pyridine and its derivative is pyridine, 2-methyl pyridine, 3-methyl pyridine, 4-methyl pyridine, 5-methyl pyridine, 6-methyl pyridine, or 2,6-dimethyl pyridine, preferably pyridine. Dihydro flavonoid is represented of formula (I), and its dihydro flavone compound is hesperidin, naringin, naringenin, hesperetin, or neohesperidin. Flavonoid is represented of formula (II), and its flavone compound is rhoifolin, apigenin-7-O-glucoside, apigenin, diosmin, or diosmetin.R1, R2, R3, R4, R5, R6, R7, R8, R9=H, OH, OCH3, glc, glucose, rutinose (rutoside glycosyl, O- beta -Dglucopyranosyl(6-1) rhamcopyranosy), or O- beta -Dglucopyranosyl(2-1) rhamcopyranosy (neohesperidin glycosyl).