have studied not only the effect on

have studied not only the effect on the elastic modulus at steady
state, but also on the gelation kinetics and the turbidity.
2. Materials and methods
2.1. Materials
The sodium -carrageenan used for this study is an alkali
treated extract from Eucheuma cottonii and was a gift from Cargill
(Baupte, France). Using NMR it was found that the sample contained less than 5% -carrageenan. A freeze-dried sample of -car
was dissolved by stirring for a few hours in Milli-Q water (70
◦
C)
with 200 ppm sodium azide added as a bacteriostatic agent. The
solution was extensively dialysed against Milli-Q water at pH 7
and subsequently filtered through 0.45 m pore size Anatop filters. The pH of the solution was adjusted to 7 by adding small
amounts of HCl 0.1 M. The -car concentration (CK) was determined by measuring the refractive index using refractive index
increment 0.145 mL/g. The molar mass (Mw) and radius of gyration
(Rg) were determined by light scattering as described elsewhere
(Meunier, Nicolai, Durand, & Parker, 1999): Mw= 2.1 × 10
5
g/mol,
Rg= 52 nm. The sample contained 5500 mg/100 g Na, 56 mg/100 g
Ca and 300 mg/100 g K.
2.2. Methods
The shear moduli were determined as a function of the frequency and the temperature using a stress imposed rheometer
(AR2000, TA Instruments) with plate – plate geometry (diameter
40 mm, gap 700 m). The temperature was controlled by a Peltier
system and the geometry was covered with paraffin oil to prevent
water evaporation. In all cases the measurements were done in the
linear response regime. For some systems we observed a decrease
of the shear modulus during gelation, which is caused by partial
detaching of the gels from the geometry. Here we only show results
of measurements where this did not occur and the results were
quantitatively reproducible.
Turbidity measurements were done as a function of the wavelength in rectangular air tight cells using a UV–visible spectrometer
Varian Cary-50 Bio. Different path lengths were used depending on
the turbidity of the samples in order to avoid saturation. Measurements were done at different temperatures that were controlled
within 0.2
◦
C using a thermostated bath.
3. Results
3.1. Pure potassium induced gelation
Fig. 1 shows the evolution of the storage shear modulus (G

) at
0.1 Hz during a cooling and subsequent heating ramp (2
◦
C/min) for
aqueous solutions of -car in 10 mM KCl at various -car concentrations between 2 and 13.5 g/L. For C > 4 g/L, G

increased steeply at
a critical temperature Tc≈ 18
◦
C. At lower concentrations, weaker
gels are formed and the initial steep increase of G

is below the
sensitivity of the apparatus. Therefore we observe for these solutions only the slower increase at lower temperatures. At lower
concentrations no significant increase of G

was observed during
the cooling ramp.
During subsequent heating, G

first increased weakly followed
by a decrease at significantly higher temperatures than Tccaused by
melting of the gel. The initial increase can be explained by the slow
gelation kinetics that initially dominates the effect of decreasing gel
strength with increasing temperature. As was reported elsewhere
(Meunier et al., 1999), the kinetics of gelation can be very slow,

Hasil (Bahasa Indonesia) 1:

telah mempelajari tidak hanya efek pada modulus elastis pada mantapnegara, tetapi juga pada gelation kinetika dan kekeruhan.2. bahan dan metode2.1. bahanNatrium-carrageenan digunakan untuk studi ini adalah alkalidiperlakukan ekstrak dari Eucheuma cottonii dan merupakan hadiah dari Cargill(Baupte, Perancis). Menggunakan NMR ternyata bahwa sampel mengandung kurang dari 5%-carrageenan. Sampel beku-kering - mobildibubarkan oleh aduk selama beberapa jam dalam Mili-Q air (70◦C)dengan 200 ppm natrium azide ditambahkan sebagai agen bakteriostatik. Thesolusi menyeluruh dialysed terhadap Mili-Q air pada pH 7dan kemudian disaring melalui 0.45 m pori-pori ukuran Anatop filter. PH larutan disesuaikan dengan 7 dengan menambahkan keciljumlah HCL 0.1 M. -Mobil konsentrasi (CK) ditentukan dengan mengukur indeks bias menggunakan indeks biaskenaikan 0.145 mL/g. Massa molar (Mw) dan radius gyration(Rg) ditentukan oleh cahaya menyebar seperti yang dijelaskan di tempat lain(Meunier, Nicolai, Durand, & Parker, 1999): Mw = 2.1 × 105g/mol,RG = 52 nm. Sampel terkandung 5500 mg/100 g Na, 56 mg/100 gCA dan 300 mg/100 g K.2.2. metodeGeser modul ditentukan sebagai fungsi dari frekuensi dan suhu menggunakan rheometer stres dikenakan(AR2000, TA instrumen) dengan piring-piring geometri (diameter40 mm, gap 700 m). Suhu dikendalikan oleh Peltiersistem dan geometri itu ditutupi dengan minyak parafin untuk mencegahwater evaporation. In all cases the measurements were done in thelinear response regime. For some systems we observed a decreaseof the shear modulus during gelation, which is caused by partialdetaching of the gels from the geometry. Here we only show resultsof measurements where this did not occur and the results werequantitatively reproducible.Turbidity measurements were done as a function of the wavelength in rectangular air tight cells using a UV–visible spectrometerVarian Cary-50 Bio. Different path lengths were used depending onthe turbidity of the samples in order to avoid saturation. Measurements were done at different temperatures that were controlledwithin 0.2◦C using a thermostated bath.3. Results3.1. Pure potassium induced gelationFig. 1 shows the evolution of the storage shear modulus (G) at0.1 Hz during a cooling and subsequent heating ramp (2◦C/min) foraqueous solutions of -car in 10 mM KCl at various -car concentrations between 2 and 13.5 g/L. For C > 4 g/L, Gincreased steeply ata critical temperature Tc≈ 18◦C. At lower concentrations, weakergels are formed and the initial steep increase of Gis below thesensitivity of the apparatus. Therefore we observe for these solutions only the slower increase at lower temperatures. At lowerconcentrations no significant increase of Gwas observed duringthe cooling ramp.During subsequent heating, Gfirst increased weakly followedby a decrease at significantly higher temperatures than Tccaused bymelting of the gel. The initial increase can be explained by the slowgelation kinetics that initially dominates the effect of decreasing gelstrength with increasing temperature. As was reported elsewhere(Meunier et al., 1999), the kinetics of gelation can be very slow,