Stability of L-(+)-ascorbic acid supported in edible gellan and high methoxyl pectin films.

PÉREZ CAROLINA D.; DENOBILI MARÍA D.; LEÓN PAULA G.; GERSCHENSON LÍA N.; ROJAS A.M.

Anaheim Orange County, California, USA.

Congreso; IFT 2009 Annual Meeting; 2009

Institute of Food Technologists (IFT)

Edible films based on gellan or high methoxyl pectin were developed to support L-(+)-ascorbic acid (AA) for antioxidant protection of foods, by leveraging its natural activity as a vitamin in humans. Kinetics of AA-destruction and subsequent non-enzymic browning (NEB) development were studied and their relationship with the microstructure, at molecular level, was analyzed. Films were made using casting technology. Film-forming solutions were prepared by dissolving either gellan or HM-pectin in water under shear, followed by heating. Glycerol (plasticizer), potassium sorbate (antimicrobial) and AA were added. Citric acid was necessary only in gellan system for pH = 3.1. Each solution was poured onto polystyrene plates and air-dried. Peeled films were stored over saturated solutions of known water activity: MgCl2 (aWº = 0.333), NaBr (0.577) or NaCl (0.752), 25ºC, for equilibration. For kinetics, samples were collected during storage and AA content as well as Yellow Index (YI) like NEB parameter, were determined. Water mobility was assessed through 1H-NMR spin-spin relaxation (T2). Constant rates of AA destruction and NEB increased with relative humidity of film storage and were higher in gellan network (1.35x10-5 to 4.20x10-5 min-1, 1.90x10-4 to 1.80x10-3 YI-min-1). Browning seemed to be associated to AA-degradation as indicated through the relationship between AA half-life time (t1/2) and the time for YI duplication (t2). AA and NEB constant rates were a linear function of T2a and T2b, respectively. Different AA-stability and browning rate at a given relative humidity were the result of system composition, as well as microstructure of film network in presence of the remaining and available water, which was involved in the mechanism of AA-hydrolysis in the anaerobic storage that herein prevailed. The film microstructure developed by HM pectin produced a better immobilization of water molecules in comparison with gellan based films, leading to a higher AA retention and lower browning.