Study Of The Extraction, Purification, Structural Characteristics And Physicochemical Property Of Black Pigment From Semen Sesami Nigrum

Semen sesami nigrum, black seeds of the Pedaliaceae Sesamum, is one of the chief oilseed crops in the world, cultivated in many countries from Asia and South and Central America. Being a big producer of sesame, China is called “the Kingdom of Sesame” for leading the world in production. Semen sesami nigrum can be used as homology of medicine and food, and contains abundant nourishments. Black pigment from Semen sesami nigrum not only is a kind of natural black pigment, but also has nutritional value and pharmacological action, especially the strong anti-oxidation activity. In recent years, as the improvement of food safety awareness of the consumers, they have already paid much more attention to pure natural, nutrient-rich and healthy food. Therefore, to develop the black pigment extracted from Semen sesami nigrum meets the pursuit of consumers. This paper mainly researched the extraction, purification, structural characteristics and physicochemical property of black pigment from Semen sesami nigrum with alkaline solution. The main research content and relevant results were as follows:(1) First, the absorption spectra of black pigment extracted from Semen sesami nigrum was examined and the maximum absorption wavelength was obtained. Then, based on single-factor experiments, response surface methodology was used to optimize extraction conditions of black pigment with the corresponding color value as an index. The results showed that the maximum absorption of extraction was at 228 nm and that the optimal extraction conditions were: extraction temperature 30℃, concentration of NaOH solution 11.4g/L, extraction time 20 min, ratio of material to solvent 1:3, the solution acidified pH1.0 and a single extraction. Under the above conditions, the color value of black pigment extraction was 326.(2) Black pigment extracted from Semen sesami nigrum was hydrolyzed by three proteases, respectively, namely alkaline protease, a specialized enzyme 1 for vegetable protein hydrolysis and a specialized enzyme 2 for vegetable protein hydrolysis. With the rate of deproteinization as an index, the best enzymatic hydrolysis conditions were obtained through orthogonal test. The results showed that a specialized enzyme 2 for vegetable protein hydrolysis was the best enzyme and that the optimum conditions were: hydrolysis temperature 55℃, pH8.0, dosage of enzyme 0.5%, and hydrolysis time 20 h, while the rate of deproteinization of black pigment was up to 32.9%.(3) Black pigment was further treated by alkali extraction and acid precipitation, hydrochloric acid hydrolysis and organic solvent, respectively. The results showed that purification effects on black pigment were not good except hydrochloric acid hydrolysis while high concentrations of hydrochloric acid could lead to the failure of structures and that black pigment was further purified only by 2mol/L hydrochloric acid hydrolysis. In addition, ultraviolet-visible absorption spectra of the purified black pigment showed that its absorption was the highest in ultraviolet region and that the maximum absorption was at 213 nm, namely absorption value 0.830 and color value 415, and that its absorption turned weak with the increasing of the wavelength, which were in line with typical ultraviolet-visible absorption of melanin; infrared spectroscopy showed that black pigment not only had typical infrared signature of melanin, meaning it belonged to melanin, but also consisted of benzene ring with most hydrogens replaced, alkyl, carboxyl, hydroxyl and amidogen and so on.(4) Black pigment from Semen sesami nigrum was easily dissolved in alkaline solution. When pH value of the aqueous solution was less than 5.0, turbidity, even precipitate would appear; when pH value was no less than 7.0, it would have good stability. In alkaline condition, it was relatively stable to light and heat; it had a certain extent of anti-oxidization and anti-reduction; sodium chloride and saccharose had little effects on its stability; metal ions, such as Ca2+, Mg2+, Al3+ and Zn2+, had no obvious effects, while Fe2+, Fe3+ and Cu2+ had some degree of protection or hyperchromism.