| Xylo-oligosaccharides(XO), are a kind of non-digestible oligosaccharides that can be produced by hydrolysis from a variety of xylan-containing raw materials. Their main constituents are 2-7 xylose molecules linked by β-1, 4 glucosidic bonds. XO have favorable technological features, including stability at acid p H, heat resistance, and stable at physicochemical property. XO are considered as prebiotic and they are widely used in the field of micro-ecological health. In addition, several animal experiments showed that XO were also antioxidative and could be used as hypolipidemic. However, as a kind of new food additive, there are only limited study focused on the structure modification and antioxidant activity of XO.Maillard reaction is a kind of modification method of lots of polysaccharides; this reaction will be started when carbonyl groups and amino acids are heated. In this paper, Maillard reaction derivatives were prepared by heating XO with two amino acids in different ratio of carbonyl group and amino group. We wish this research will provide new ideas for monitoring the character of the reaction, detecting the structures of derivatives and testing the antioxidant activities of Maillard derivatives. And hope these will be reference for developing natural, non-toxic and healthy antioxidants in food industry.In this paper, XO was heated with glycine and proline respectively, and XO was heated with glycine in the present of three kinds of metal ions as well. Then the p H, UV-Vis absorbance and fluorescence of the Maillard reaction products were monitored every 5 hours during the reaction. The structure of the Maillard derivatives was detected by FTIR, their molecular weight was measured by GPC(Gel Permeation Chromatography), and the content of reducing sugar and uronic acid was tested. Finally, the antioxidant activities of these derivatives were tested by evaluating their scavenging activity of superoxide anion and DPPH and their reducing capacity. The main conclusions of this paper are as follows:1. Maillard reaction process showed that with the reaction time prolongs, p H value decreased, UV-Vis absorbance(both 295 nm and 420nm) increased dramatically, and the fluorescence value(the excitation wavelength was 370 nm and emission wavelength was 440 nm) raised sharply. GPC test showed that the molecular weight of XO derivatives increased and FTIR indicated that XO characteristic absorption bands were reserved in XO derivatives, while amino groups disappeared after Maillard reaction. And the content of reducing sugar reduced while the content of uronic acid increased gradually.2. The Maillard derivatives XG were generated by heating XO and glycine. XG showed stronger antioxidant activity(including scavenging activity of superoxide anion radical and DPPH and reducing power) compared with XO. The longer reaction time lasted, the stronger antioxidant activity GX showed, in other words, XG prepared by heating 30 hours had the better antioxidant activity than 15 hours, and 5 hours derivatives showed the weakest antioxidant activity; XG with different ratio of carbanyl groups and amine groups showed different antioxidant activity, XG1:1 showed the best antioxidant activity; The content of reducing sugar declined and uronic acid increased as the reaction time prolongs, which indicated that antioxidant activity was connected with the content of uronic acid.3. The Maillard derivatives XP were generated by heating XO and proline. XP showed stronger antioxidant activity(including scavenging activity of superoxide anion radical and DPPH and reducing power) compared with XO. XP with different ratio of carbanyl groups and amino groups showed different antioxidant activity, 1:1 system showed the best antioxidant activity. The longer reaction time lasted, the stronger antioxidant activity XP presented. XP heated 30 hours showed the better antioxidant activity than 15 hours, and 5 hours derivatives showed the weakest antioxidant activity. Also, during the reaction, the content of reducing sugar declined while the content of uronic acid increased, which give the conclusion that the content of uronic acid might influence the antioxidant activity of derivatives.4. The comparison of antioxidant activity of two XO derivatives(glycine and proline with a 1:1 system and 5 hours heating time) indicated that two kinds of derivatives had better antioxidant activity than XO; and XG derivatives showed stronger antioxidant activity compared with XP; the derivatives prepared by smaller molecule amino acids had the better antioxidant activity. This might because the amine groups of amino acids with smaller molecule can easily attack carbonyl groups and accelerate Maillard reaction. The content of reducing sugar declined while the content of uronic acid increased.5. XO and glycine(1:1) were prepared by heating in three different metal ions(Fe3+, Cu2+ and Mg2+) solutions. Atomic absorption spectrum showed that there was no metal ions in derivatives; as the reaction time prolonged, the content of reducing sugar declined and uronic acid increased; three metal ions can influence the Maillard reaction in different ways, Fe3+ and Cu2+ can increase the absorbance of UV-Vis and fluorescence, and Fe3+ showed better ability to increase absorbance; while Mg2+ can reduce the absorbance; the test of antioxidant activity showed that derivatives generated in Fe3+ and Cu2+ solution showed better antioxidant activity than XG, while derivatives generated in Mg2+ solution had weaker antioxidant activity than XG, which is to say, the tendency of three kind of derivatives was XG-Fe3+ > XG-Cu2+ > XG > XG-Mg2+. The content of uronic acid is the key elements of antioxidant activity.The p H, UV-Vis absorbance and fluorescence of the XO Maillard products were tested in this paper. The structures of the XO derivatives were characterized by FTIR, GPC, and the content of reducing sugar and uronic acid was tested. And their antioxidant activity was compared in the condition of different ratio of carbonyl group to amino group, different type of amino acid, different heating time and metal ions solution. The result of this paper indicated that as the reaction time prolonged, the p H declined, UV-Vis absorbance and fluorescence had a sharp increase; the content of reducing sugar declined and uronic acid increased, which indicated that uronic acid was the key elements to the antioxidant activity of derivatives. Meanwhile, the antioxidant activity of the XO derivatives may be connected with the type of amino acid, the reaction ratio of carbonyl group to amine group, the reaction lasting time, as well as metal ions influence. It might be helpful to support the ideas for XO modification and the development of natural food antioxidants. |
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