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

PÉREZ C.D; DE’NOBILI M.D.,; LEÓN P; GERSCHENSON L.N.; ROJAS A.M

ANAHEIM, CALIFORNIA, USA.

Congreso; IFT 2009 ANNUAL MEETING + FOOD EXPO; 2009

Institute of Food Technologists

Edible films based on gellan or high methoxyl pectin were developed to support L-(+)-ascorbic acid (AA) for antioxidant protection of foods. Kinetics of AA-destruction and subsequent non-enzymic browning (NEB) development were studied and their relationship with the microstructure, at molecular level, was analyzed. 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 adjusting pH to 3.1.Each solution was poured onto polystyrene plates and air-dried (casting technology). Peeled films were stored, at 25ºC, over saturated solutions of known water activity: MgCl2 (aW 0.333), NaBr (aW 0.577) or NaCl (aW 0.752), for equilibration. Samples were evaluated during storage for AA content as well as NEB change, which was evaluated through the Yellow Index (YI). Water mobility was assessed through 1H-NMR spin-spin relaxation (T2). Constant rates of AA destruction and NEB increased with relative humidity of storage and were higher in gellan network. 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 and microstructure of film network in the presence of remaining and available water, which was involved in the anaerobic mechanism of AA-hydrolysis that prevailed during storage. 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. Results obtained can help to optimize food quality.