A Study On Reducing The Content Of Ash And Sulfate In Agar

The content of ash and sulfate is an important indicator to the quality of agar.Nowdays,the methods of ion-exchange resins,alkali and EDTA-Na₂ were mainly used to reduce the content of ash and sulfate in domestic researches.But their combination is still not systematic.In this paper,Gracilaria was chosen as a raw material.Cation-exchange resins,anion-exchange resins,alkali,EDTA-Na₂,and their combination were used to reduce the content of ash and sulfate.The effect of different techniques on the quality of agar was studied.The main results are as followed:?1?Powdered agar was treated with strong acid cation-exchange resins D001.A decrease in calcium concentration and ash content occurredwith a correlation between them.The optimum technical parameters for reducing the ash content in agar are that,the added amount of resins was5 g/g and the sample was treated at 60oC for 1 h.Moreover,the ash content was reduced to 0.15%in agar from resins.?2?The sulfate content of agar was analyzed by ion chromatography?IC?using the internal standard method.The result showed that the KNO₃ was more suitable than KH₂PO₄ as internal standard for a shorter determined time.The content of SO₄^2-exhibited well linearity in a range of10⁴5 mg/L?R²>0.999?,and the regression equation was Y=1.2740X-0.0987.Besides,the relative standard deviation was lower than 3%.The recoveries were 93.1%¹06.4%.?3?The sulfate content of the agar samples treated with D296 and D318 resins did not change.When alkaline treatment was applied,agar treated at 60oC had a lower sulfate content with a higher yield than those with treatment at 80oC.The agar powder treated with EDTA-Na₂exhibited a better ability to reduce the content of sulfate than the agar sol and agar gel treated with EDTA-Na₂.?4?Ash and sulfate content of samples treated from the different combination methods of cation-exchange resins,alkaline and EDTA-Na₂ was studied.As a consequence,it showed the lowest ash?0.31%?and sulfate?0.08%?content in the agar from alkaline method combined with cation-exchange resins.Besides,cation-exchange resins combined with alkaline and EDTA-Na₂were used to treat agar,in which the content of ash and sulfate were 0.38%and 0.12%.?5?The individual and combined methods of cation-exchange resins,alkali and EDTA-Na₂were used to prepare the agar.The results indicated that ash,sulfate,viscosity,gel strength,gelling and melting temperature were significantly reduced compared to the raw material?P<0.05?.Moreover,the transparency,colour and electrophoretic property were had improved slightly.The objective of this paper is to study the impact of individual and combined methods of cation-exchange resins,alkali and EDTA-Na₂ on the sulfate content in agar,which provides references to for producting agar with low content of ash and sulfate.