Grape Marc Powder: Physicochemical and Microbiological Stability During Storage and Moisture Sorption Isotherm

Abstract

In the present work, the stability of grape marc powder was evaluated during its storage at room conditions for 6 months. Grape juice marc from Vitis labrusca cv. “Isabel” was dried to 8.8 ± 0.9 % moisture content (wet basis) in forced convection drying equipment at 70 °C, crushed and stored aseptically in dark polyethylene bags and kept at 25 ± 2 °C for up to 6 months. Grape marc powder was microbiologically safe, free of Salmonella sp., Bacillus cereus, and fecal coliforms. Total phenolic compounds with 1,1-diphenyl-2-pic-ryl-hydrazyl (DPPH) scavenging capacity and ferric reducing antioxidant power (FRAP) were stable, although monomeric anthocyanins and compounds with the capability of scavenging 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) radicals showed to be susceptible to degradation through the storage period. Moisture sorption isotherm at 25 °C for the powder material was determined by static gravimetric methodology. The sorption isotherm of the grape marc powder showed a sigmoidal shape (type II), typical of food materials. The experimental data was satisfactorily fitted by the GAB (Guggenheim–Anderson–de Boer) model, giving a monolayer moisture content (X m) of 6.75 % (dry basis). Results indicate that grape marc powder can be considered as a potential functional ingredient with an acceptable stability.