Gelation of K-Carrageenan
The interaction ofK-currugwnan with locust bean gum and dextrun has been studied by rheologj: difkwntid scanning calorimrtry (DSC), und electron spin rcsonunce spectroscop)2 (ESR) . Rhrologicul inemirements show that the currageenun gel churactcrirtics arc grcatly enhanced in thc presence of locirst bean gum but not in the pressencc of dt.,utran. Curra~ecnan/lociist beun gum wixtiircs .show two peaks in the dsc cooling ci1rvc.s. The highcr tempcmturc pcak corrijsponds to thc temprrutiire qjkclation and its intensity incriwses at tho expense oflhe l o ~r r tcnipcrutrirr peuk as the proportion oflociwt bean gum in the mixtiirc increuses. Fiirthcrmore, the DSC hcaring c1irve.s shoi?. mhunced broadening w h m lociist beun gum is present, indicuting incrcusrd aggrqption. Thcw r t w l t s ure taken as evidence' of i,urragecnan/locii.st hcan giirn ussocialion. The gefution process hus also been ,fidlowtxi hy ESR ttsing ~~~~i n -l u h e l ~~d currugcenan. On cooling carrageenan .soliition.s. un immobile component appears in the ESR .spcictra signif.j,ing u l o s s of'sc~gmental moidity consistent with chain stlffkning d u ~
t o the coil + helix con fi)rinutionul trunsilion and helis uggregution. For curragPcnan/lociist hcan giirn mi.xtiirec, c'arrugccnun ordcring occiirs at tetnperatiires corresponding t o the highcr ternpcratrrrr DSC' .sotling pcak and the tcmperuturc c!fgclution. Similar st irdic..s using .spin-labeled locust hcan grim .shotzl that its mobility remuins virtiiully unufkctedditring fhcgelation process. It is rvident, thcwforc, [hat carrugwnan and Iociist bean gum interact on1.v weaklji. It is proposed thut ut IOM~ carrugecnan conwntrutions the gel net work con.si.st.s if currugcenun helices cross-linked by loc w t hean giiin chains. i l l high cart-agcwmn concentrations the network is enhanced b), thr additional .self&ggri>gution of' thti "csct'ss " carrugmmz moliwrles. For currag~~~~nun/dcdran tni.stirrc.s. only one p u k i s observed in the d.sc cooling curws. The onset qf'gelution shifts to higher tctnpcmtiircs onlv at w r ) ~ high (20%) dcstrun concentrutions and this is uttribiitcd t o voliimc csclusion e f k ~c f s . Fiirthermorc, thcre is no enhanced broadening of'thc peaks in rhc DSC' hrating cirrws as, f i v ~h c currug~~cnan/lociist bean gum systems. It is thcrtjii,rc conchided that currugrcnun/de,~-trun us.soc?ation does not occiir. The d ~f i w n c c in behavior bL.1vtvcn locii.~~ bean girin and dcstrun i s uttribiited to the greuterjlexibility qfthc di..strun chains.