Pectins applied to the development of antioxidant edible films: influence of the macromolecular structure in the L-(+)-ascorbic acid stabilization.

PÉREZ, C. D.; DE'NOBILI M. D.; FISSORE E. N.; BASANTA M. F.; GERSCHENSON L. N.; CAMERON R. G.; ROJAS, A. M.

Pectin: Chemical Properties, Uses and Health Benefits.

Nova Science Publishers, Inc.

Lugar: Hauppauge , NY ; Año: 2014; p. 159 - 186

Pectins of different nanostructure were assayed in their ability to develop film networks able to stabilize L-(+)-ascorbic acid (AA) to hydrolysis in view of antioxidant protection at interfaces, nutritional supplementation or therapy. Compartmentalization into edible films can permit not only to increase the AA stability but also to achieve localized antioxidant activity and controlled release. The AA hydrolysis was specifically studied in the present work. Hence, films were stored at controlled relative humidity (RH) in the absence of air. Films were made with each one of the enzymatically tailored (50, 70 and 80% DM) pectins (Cameron et al., 2008) or commercial high methoxyl pectin (HMP; 72% DM). A random distribution of demethylated blocks is expected to characterize commercial pectins whereas ordered patterns are obtained by enzymatic action. Calcium ions are necessary for crosslinking of low methoxyl pectins. Hence, the ability of Ca-mediated junction zones to stabilize AA into the edible films made with commercial pectins of low (LMP; 40%) or high (HMP; 72%) DM, at the same Ca2 concentration (film systems called Ca-LMP and Ca-HMP, respectively), was also evaluated. Glycerol was used for plasticization. Kinetics of AA loss and subsequent browning development were determined by film storage at constant 57.7% RH and 25ºC, in the dark. Since AA stability was dependent on water availability in the film network, determined by 1H-NMR, it was observed that the pectin nanostructure affected the AA kinetics. Higher AA retention and lower browning rates were achieved in HMP films than in enzymatically tailored pectin films, and the immobilization of water and consequent AA stability increased with the proportion of calcium-crosslinked junction zones present in the film network. As determined through tensile assays, the presence of Ca2+ in the film network produced significant decrease in elongation at fracture. This assay also revealed some sensibility of the HMP (commercial 72% DM pectin) to calcium ions. The glass transition temperature values of pectin films decreased (Tg  88 to 102ºC) with the moisture content increase, indicating the contribution of water to the network plasticization by glycerol. However, water was mostly confined in the Ca-LMP network (Tg  93.99ºC) followed by Ca-HMP (Tg  88.56ºC), as inferred from the water availability determined by the 1H-NMR. This was attributed to the water interaction at the Ca2+-junction zones. Random distribution of demethylated blocks in the HG chains in addition to the presence of some disordered (amorphous) regions of RG-I may produce better immobilization of water than more rigid networks like those developed from the tailored pectin macromolecules.