Physicochemical, nutritional, and antimicrobial properties of wine grape (cv. Merlot) pomace extract-based films

Wine grape pomace (WGP) (cv. Merlot) extract-based films were studied in terms of their physicochemical, mechanical, water barrier, nutritional, and antibacterial properties. Pomace extract (PE) was obtained by hot water extraction and had a total soluble solid of 3.6% and pH 3.65. Plant-based polysaccharides, low methoxyl pectin (LMP, 0.75% w/w), sodium alginate (SA, 0.3% w/w), or Ticafilm (TF, 2% w/w), was added into PE for film formation, respectively. Elongation at break and tensile strength were 23% and 4.04 MPa for TF-PE film, 25% and 1.12 MPa for SA-PE film, and 9.89% and 1.56 MPa for LMP-PE film. Water vapor permeability of LMP-PE and SA-PE films was 63 and 60 g mm m(-2) d(-1) kPa, respectively, lower than that of TF-PE film (70 g mm m(-2) d(-1) kPa) (P<0.05). LMP-PE film had higher water solubility, indicated by the haze percentage of water after 24 h of film immersion (52.8%) than that of TF-PE (25.7%) and SA-PE (15.9%) films, and also had higher amount of released phenolics (96.6%) than that of TF-PE (93.8%) and SA-PE (80.5%) films. PE films showed antibacterial activity against both Escherichia coli and Listeria innocua, in which approximate 5-log reductions in E. coli and 1.7- to 3.0-log reductions in L. innocua were observed at the end of 24 h incubation test compared with control. This study demonstrated the possibility of utilizing WGP extracts as natural, antimicrobial, and antioxidant promoting film-forming material for various food applications.

WGP extract-based edible films with the addition of a small amount of commercial polysaccharides showed attractive color and comparable mechanical and water barrier properties to other edible films. The films also demonstrated their potential antioxidant and antimicrobial functions. Hence, they may be used as colorful wraps or coatings for food, pharmaceutical, or other similar applications.