Mechanism And Applied Study Of Processing High Strength Agar From Gracilaria Species

The effect and mechanism of alkali-treatment, the acidifying bleaching mechanism, the interactions and mechanism between electrolytes, food gums and agar during the process of agar from Gracilaria species were profoundly studied in this thesis, the mechanism of processing high strength agar from Gracilaria was explored. Moreover, the nutritive composition of Gracilaria species was investigated and the processing technology of health food from Gracilaria was also primarily explored.The results from the gel strength of agar, the yield of agar extraction, the physicochemical and Theological properties, the chemical composition before and after the alkali-treatment of 15 different Gracilaria species showed that the Gracilaria agar gel strength depended mainly on the chemical composition, the structure of the Gracilaria agar and the reasonable processing technology. The gel strength of Gracilaria agar was strongly negative correlated with SO₄^2- content, and positive with 3.6-AG content, the absolute viscosity of agar, the increasing amplitude of 3.6-AG content and the decreasing amplitude of SO₄^2- content before and after the alkali-treatment. The reasonable alkali-treatment decreased and increased significantly SO42" and 3.6-AG contents, respectively, promoting partialtransformation of agar pectin into agarose without degrading the agar molecules (the absolute viscosity remained constant), consequently, the gel strength of agar increased substantially, furthermore, the solidifying and melting point of agar increased generally, and the loss of agar during the alkali-treatment was limited.The average increase of gel strength was 13.71-times with maximum 31.6-times and minimum 5.83-times by high temperature-dilute alkali treatment of 15 different Gracilaria species, moreover the loss of agar was minimum. The two principal indices achieved or became superior to those of concentrate alkali treatment. The optimum conditions of processing were as follows : with 8% NaOH at 85 C during 2 hr for "hard" Gracilaria and with 10% NaOH at 80 C during 2 hr for "soft" Gracilaria.The results obtained from the optimum bleaching conditions of Gracilaria by NaClO,KMnO₄ and H₂O₂ showed that bleaching with NaClO and H₂O₂ should becarried out in dilute alkaline conditions, followed by acidifying so as to not only achieve the better bleaching effect and facilate the extraction of agar, but also avoid the structrural destruction of agar molecules during the bleaching process and obtain the high strengh Gracilaria agar. Under the optimum bleaching conditions of the methods concerned above, the NaClO bleaching process showed the highest gel strength of agar and that of KMnO₄-H₂C₂O₄ showed the least, while the lattermethod showed the highest yield of agar and that of H₂O₂ showed the least. Thereasonable acidifying bleaching process must not only destruct essentially the Gracilaria pigment and degrade the compact Gracilaria. cell wall, but also should protect the agar molecules from destruction, so as to solve the contradictary between...