| Carrageenan is applied to kinds of food such as jelly as food gelling agent.And it forms different gel types by interaction with micromolecules,for example kappa-carrageenan can form a stiff and crisp gel with the appearance of K+,iota-carrageenan can form a soft and elastic gel with the appearance of Ca2+ or stevioside.Recently,the study on the effects of micromolecules on carrageenan gels has attracted much attention,and some researches indicated amino acids can affect the gel properties of potato starch.However,the study on interaction of amino acid with carrageenan has not been reported.This paper aimed to investigate the effects of alanine and glutamine on gel properties and interaction with iota-carrageenan through the rheomer,the low field nuclear magnetic resonance,infrared spectroscope,differential thermal analysis and scanning electron microscope,and to further interpret the interaction mechanism.Firstly,we examined the effects of different added content of alanine,pH on the rheology of iota-carrageenan gel and the sodium chloride,calcium chloride on iota-carrageenan/alanine gel system respectively.The results showed that the maximum of the G’ and the minimum of tan(δ)of iota-carrageenan/alanine gel system was observed both at ratio of 5:1(iota-carrageenan:alanine)and in pH=7,in which the G’ and the tan(δ)was stable with the frequency increasing,and the highest gel-sol transition temperrature of 31 ℃ and 35 ℃occurred in both conditions presented above respectively.The interaction of sodium chloride and iota-carrageenan was contributed by the alanine,but the alanine had no effect on the interaction of sodium chloride and iota-carrageenan.Secondly,we investigated the effects of different added content of glutamine,pH on the rheology of iota-carrageenan gel and the sodium chloride,calcium chloride on iota-carrageenan/glutamine gel system respectively.The results indicated that the maximum of G’ and the minimum of tan(δ)of iota-carrageenan/glutamine gel system occurred both at the ratio of 5:1(iota-carrageenan:glutamine)and in pH=7,in which the G’ and the tan(δ)was stable with the frequency increasing,and the highest gel-sol transition temperrature of 37℃and 36.5℃ was observed in both conditions mentioned above respectively.The interaction of sodium chloride and iota-carrageenan was contributed by the glutamine,but the glutaminehad no effect on the interaction of sodium chloride and iota-carrageenan.The value of G’ of iota-carrageenan/glutamine gel is higher than that of iota-carrageenan/alanine gel in the same ratio of iota-carrageenan to alanine or glutamine,and the gel properties of iota-carrageenan/glutamine gel is better.Lastly,the interaction of iota-carrageenan with alanine,glutamine was analyzed by the low field nuclear magnetic resonance,infrared spectroscope,differential thermal analysis and scanning electron microscope.The results of low field nuclear magnetic resonance showed that alanine and glutamine affected the mobility of free water,that the relaxation time T23 of iota-carrageenan/alanine gel and iota-carrageenan/glutamine gel was shorter than iota-carrageenan gel which was 787.63-1436.12 ms,596.92-1371.27 ms respectively.The free water was embedded firmly in the gel network by alanine and glutamine,and it’s combination with iota-carrageenan/amino acid gel was enhanced by sodium chloride and calcium chloride to some extent;the results of infrared spectroscope revealed that the hydroxyl group vibrational stretching band of iota-carrageenan turned to lower wave number because of the formation of hydrogen bonds between iota-carrageenan and alanine,glutamine;the curves of differential thermal analysis indicated that the oxidation-thermal decomposition temperature of iota-carrageenan was improved from 210 ℃ to 240 ℃ and 218.9 ℃ by alanine and glutamine respectively,but it decreased owe to the addition of sodium chloride and calcium chloride;the results of scanning electron microscope uncovered that the structure of iota-carrageenan films was changed by alanine and glutamine,the structure of iota-carrageenan/alanine was like flake,and the structure of the iota-carrageenan/glutamine was like silkiness.The interaction mechanism of alanine,glutamine with iota-carrageenan was speculated based on the results of the rheology,the relaxation time,the infrared spectroscope,the differential thermal analysis and the scanning electron microscope.That is the formation of hydrogen bonds between the hydrogen of hydroxyl of iota-carrageenan and the oxygen of carboxyl of alanine and glutamine,and between the nitrogen and hydrogen of the amine of alanine,glutamine,then the formation of the double helix structure of iota-carrageenan contributed by the amino acids,then the formation of the gel following the twisting,intertwining,aggregation of the double helix structure.However,the effects of the glutamine were better than alanine because of the more formation of hydrogen bonds due to the moreamines of glutamine. |
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