K.V. Harish Prashanth

Characterization of chitin, chitosan and their carboxymethyl derivatives by differential scanning calorimetry

Abstract Chitin, chitosan and their O , N -carboxymethyl derivatives were characterized by differential scanning calorimetry (DSC) mainly focusing on changes in physical and chemical structures at different levels of acetyl and carboxymethyl contents. The thermograms were characterized by endo- and exotherms corresponding to water evaporation and decomposition of the polymer, respectively. However, each endo- or exothermic peak temperature and area changed as a function of primary and higher order structures of the macromolecule. It was found that the enthalpy value for endotherm increased with increase in amino and carboxymethyl contents. Further, in the case of carboxymethyl derivatives, no glass transition was observed despite the presence of substantial amount of amorphous content. During decomposition, the decomposition peak temperature and area changed as a function of molecular weight (MW), acetyl and carboxymethyl contents. A theoretical basis was adopted to correlate the heat of the reaction, Δ H , to the degree of deacetylation (%DD) and carboxymethylation (DS). A good correlation was obtained when the corresponding peak area and peak height were plotted against %DD and DS.

Studies on graft copolymerization of chitosan with synthetic monomers

Graft copolymerization of acrylonitrile and methylmethacrylate onto chitosan using potassium persulfate as an initiator was studied. Evidence for graft-copolymerization was obtained by infrared spectroscopy and CP-MAS 13C-NMR data. The appearance of nitrile (–CN) at 2244 cm−1 for chitosan-graft-polyacrylonitrile (C-g-PAN) and carbonyl (–CO) at 1730 cm−1 for chitosan-graft-polymethylmethacrylate (C-g-PMMA) confirmed graft-copolymerization. CP-MAS 13C-NMR showed the appearance of a signal at 33 ppm assigned to the N–CH group. With varying monomer concentration (40–180 mM), the percentage degree of substitution varied from 2 to 50. Maximum grafting efficiency was obtained with 120 mM acrylonitrile and 0.74 mM potassium persulfate at 65 °C for 2 h under nitrogen atmosphere for 1% chitosan solution and for C-g-PMMA 140 mM methylmethacrylate at 75 °C gave maximum substitution. X-ray diffraction showed changes in crystallinity pattern. Slightly different mechanisms in side chain substitution for these two copolymers were envisaged. DSC thermogram showed a decomposition peak for C-g-PAN at around 255 °C and a melting peak for C-g-PMMA at around 400 °C. C-g-PMMA could be thermopressed into films. Residual monomers were not found by HPLC in graft copolymers stored even for longer periods.

Structural analyses and immunomodulatory properties of fructo-oligosaccharides from onion (Allium cepa).

Onion (Allium cepa) is an immune-boosting food rich in fructans. The major aim of this study is to characterize and investigate the immunomodulatory properties of onion fructo-oligosaccharides (FOS). FOS was isolated from onion bulbs by hot 80% ethanol extraction (yield: ∼4.5 g/100 g fw) followed by gel permeation chromatography. NMR of onion FOS revealed unusual β-D-Glc terminal residue at the non-reducing end. TLC and ESI-MS analyses showed that onion FOS ranged from trisaccharides to hexasaccharides. Onion FOS (50 μg/mL) significantly increased (∼3-fold) the proliferation of mouse splenocytes/thymocytes vs. control. Further, onion FOS enhanced (∼2.5-fold) the production of nitric oxide by peritoneal exudates cells (PECs) from Wistar rats; intracellular free radicals production and phagocytic activity of isolated murine PECs were also augmented. Our structural and in vitro results indicate that onion FOS comprising of tri- to hexasaccharide units belongs to inulin-type fructans, and possess immunostimulatory activities towards murine lymphocytes and macrophages.

Bioactive chitosan based coatings: functional applications in shelf life extension of Alphonso mango – a sweet story

Abstract Chitosan-based coating (M4F2) was used successfully to delay ripening and prolong shelf-life of rapidly perishable and expensive Alphonso mango fruits stored at 30 ± 3°C and 40–50% RH for 15 days. Matured raw Alphonso mango fruits were simple dip treated/coated and air dried with our newly developed chitosan based formulation (for industry) with additives. Samples were taken at regular intervals for routine analysis of fruits. Results indicated that M4F2 coating could decrease the decay incidence loss along with delay the change in color of mango fruit during storage but not physiological steady weight loss. Interestingly, sensory evaluation indicated that quality of mango was enhanced slight significantly to more sweetness and better aroma by M4F2 coating compared to uncoated control fruits. Further, our M4F2 coating formulation may act as an important potentiator of flavor compounds of mango as well as controlling organic acids and sugars, which are key components in the perception of mango flavor. Understanding the chemical components that contribute to flavor perception of the fruit is necessary for post-harvest storage technology. This information is also important to study chitosan/derivatives elicitation in molecular level to improve mango flavor as well as in identification of genes responsible for flavor quality. The scientific story behind this effective chitosan based coating formulation development has been discussed.

In Vitro Antidiabetic Effects of Isolated Triterpene Glycoside Fraction from Gymnema sylvestre

A triterpene glycoside (TG) fraction isolated and purified from ethanolic extract of Gymnema sylvestre (EEGS) was investigated for blood glucose control benefit using in vitro methods. The HPLC purified active fraction TG was characterized using FTIR, LC-MS, and NMR. The purified fraction (TG) exhibited effective inhibition of yeast α-glucosidase, sucrase, maltase, and pancreatic α-amylase with IC50 values 3.16 ± 0.05 μg/mL, 74.07 ± 0.51, 5.69 ± 0.02, and 1.17 ± 0.24 μg/mL, respectively, compared to control. TG was characterized to be a mixture of triterpene glycosides: gymnemic acids I, IV, and VII and gymnemagenin. In vitro studies were performed using mouse pancreatic β-cell lines (MIN6). TG did not exhibit any toxic effects on β-cell viability and showed protection against H2O2 induced ROS generation. There was up to 1.34-fold increase in glucose stimulated insulin secretion (p<0.05) in a dose-dependent manner relative to standard antidiabetic drug glibenclamide. Also, there was further one-fold enhancement in the expression of GLUT2 compared to commercial standard DAG (deacylgymnemic acid). Thus, the present study highlights the effective isolation and therapeutic potential of TG, making it a functional food ingredient and a safe nutraceutical candidate for management of diabetes.