Higher molecular weight pectin inhibits ice crystal growth and its effect on the microstructural and physical properties of pectin cryogels

Understanding the formation of ice crystals is essential for tailoring the microstructure and physical properties of cryogels. This study investigated the effects and mechanisms of pectin molecular weight (Mw) on impacting ice crystal formation. Pectin fractions various Mw (10.13-212.20 kDa) were prepared by hydrothermal method. The solution of high Mw pectin fractions exhibited higher contact angle, lower water freedom, and stronger adsorption of water molecules. The splat experiment and molecular dynamic (MD) results confirmed that higher Mw pectin have stronger ice crystal growth inhibition activity than lower Mw pectin. Furthermore, the pore size distribution of the cryogel increased from 98-203 μm to 105-267 μm as the molecular weight decreased from 212.2 kDa to 121.0 kDa. Additionally, in the higher Mw pectin cryogel, stronger mechanical strength was observed. These findings suggested that changing the molecular weight of pectin has the potential to regulate the ice crystal growth, microstructure and physical properties of frozen products.

Solution characterization of a hyperbranched polysaccharide carbamate derivative and specific phase separation behavior due to chain branching

A hyperbranched polymer consisting of rigid helical part chains was prepared as highly branched cyclic dextrin tris(phenylcarbamate) (HTPC) with the weight-average molar masses of 880 and 590 kg mol-1. Small-angle X-ray scattering (SAXS) measurement and viscometry were performed on the samples in good and poor solvents to determine the dimensional and hydrodynamic properties in solution. The HTPC molecule has a much more compact conformation than the linear chain with the same molar mass as expected for the hyperbranched architecture. While the corresponding linear polymer is soluble in methyl acetate (MEA) over a wide temperature range, HTPC is only soluble in the solvent at low temperatures. A typical LCST-type phase diagram was observed for the HTPC-MEA system, indicating that the interactions between the polymer segment of HTPC and the MEA molecules are substantially different from those of the linear chains. This is most likely due to the bending helical chains near the branching point of HTPC having different interactions with solvent molecules.

Self-Assembly of Amphiphilic Amylose Derivatives in Aqueous Media

Six amylose derivative (C₁₂CMA) samples with hydrophobic dodecyl ether groups and hydrophilic sodium carboxymethyl groups were synthesized from an enzymatically synthesized amylose for which the weight-average molar mass is 50 kg mol^-1 to realize amylose-based amphiphilic polymer micelles. The degree of substitution of hydrophobic (DS_C12) and hydrophilic (DS_CM) groups ranges between 0.076 and 0.39 and between 0.35 and 1.83, respectively. Static and dynamic light scattering, small-angle X-ray scattering (SAXS), and fluorescence measurements with pyrene as a probe were carried out for the samples in 150 mM aqueous NaCl to characterize the higher-order structure in solution. The fluorescence from pyrene showed that all six samples have hydrophobic environment, while the hydrophobicity tends to increase with rising DS_C12. All six samples have high scattering intensity owing to the relatively large concentrated droplets ranging in the hydrodynamic radius from 50 to 110 nm, whereas the weight fraction of such large particles is substantially small except for the highest DS_C12 sample. Most polymer chains for relatively low DS_C12 of 0.076 were molecularly dispersed with a very small amount of large droplets. The dispersed chain has a slightly smaller helix pitch per residue and a more rigid main chain than those for amylose in dimethyl sulfoxide, suggesting that the amylosic main chain of C₁₂CMA has a helical structure with dodecyl groups at least locally. On the other hand, an anisotropic shaped micelle-like structure is only found for relatively high DS_C12 (0.23 and 0.39) samples, which was detected by the SAXS profile at a high scattering vector range. The micelle structure for high DS_C12 samples is consistent with the high chain stiffness.

Rigid Cyclic Polymer in Solution: Cycloamylose Tris(phenylcarbamate) in 1,4-Dioxane and 2-Ethoxyethanol

Six cyclic amylose tris(phenylcarbamate) (ATPC) samples have been prepared from enzymatically synthesized cyclic amylose ranging in the number of repeat units N from 24 to 290. Synchrotron-radiation small-angle X-ray scattering measurements were made for the samples in 1,4-dioxane (DIOX) and 2-ethoxyethanol (2EE) to determine the z-average radius of gyration ⟨S²⟩_z and the particle scattering function P(q). Molar mass dependencies of ⟨S²⟩_z in the two solvents were successfully explained by the current theories for the wormlike ring with the same parameters for linear ATPC in the corresponding solvent, that is, the helix pitch h (or contour length) per residue and the Kuhn segment length λ^-1 (stiffness parameter, twice the persistence length). The latter parameter λ^-1 is 22 and 16 nm in DIOX and 2EE, respectively. Except for the low-q region, P(q) was also explained by the rigid ring having the same contour length Nh as that for linear ATPC. Further, their local conformation estimated from circular dichroism spectra is essentially unaltered from that for linear ATPC at least when N ≥ 24.

Solvent-dependent conformation of amylose tris(phenylcarbamate) as deduced from scattering and viscosity data

The z-average mean-square radius of gyration S(2)(z), the particle scattering function P(k), the second virial coefficient, and the intrinsic viscosity [eta] have been determined for amylose tris(phenylcarbamate) (ATPC) in methyl acetate (MEA) at 25 degrees C, in ethyl acetate (EA) at 33 degrees C, and in 4-methyl-2-pentanone (MIBK) at 25 degrees C by light and small-angle X-ray scattering and viscometry as functions of the weight-average molecular weight in a range from 2 x 10(4) to 3 x 10(6). The first two solvents attain the theta state, whereas the last one is a good solvent for the amylose derivative. Analysis of the S(2)(z), P(k), and [eta] data based on the wormlike chain yields h (the contour length or helix pitch per repeating unit) = 0.37 +/- 0.02 and lambda(-1) (the Kuhn segment length) = 15 +/- 2 nm in MEA, h = 0.39 +/- 0.02 and lambda(-1) = 17 +/- 2 nm in EA, and h = 0.42 +/- 0.02 nm and lambda(-1) = 24 +/- 2 nm in MIBK. These h values, comparable with the helix pitches (0.37-0.40 nm) per residue of amylose triesters in the crystalline state, are somewhat larger than the previously determined h of 0.33 +/- 0.02 nm for ATPC in 1,4-dioxane and 2-ethoxyethanol, in which intramolecular hydrogen bonds are formed between the C==O and NH groups of the neighbor repeating units. The slightly extended helices of ATPC in the ketone and ester solvents are most likely due to the replacement of those hydrogen bonds by intermolecular hydrogen bonds between the NH groups of the polymer and the carbonyl groups of the solvent.