Valorization of red grape pomace for sustainable food packaging: Development of pectin/kidney bean protein based biocomposite films enriched with grape pomace polyphenols

Red grape pomace (GP), as an underutilized waste of wine and juice production units, was utilized as a valuable source of pectin (GPP) and extract (GPE). The co-extraction of GPP and GPE was performed using ultrasound-microwave assisted technique and the process factors were co-optimized using response surface methodology, which yielded 20.25% GPP and 21.51% GPE. The compositional characterization of the ingredients indicated a low-methoxyl galacturonic acid-rich structure for GPP and a wide range of phenolic compounds for GPE. The obtained GPP was then employed in the fabrication of a novel biocomposite film with red kidney bean protein isolate (KPI) and the prepared films were evaluated using physicochemical, hydration, barrier, mechanical, thermal and structural analysis. The results revealed that a 50/50 ratio of GPP/KPI improved hydration, barrier and mechanical properties, with water solubility of 14.96%, water vapor permeability of 1.86 x 10(-10) g/m.s.Pa, tensile strength (TS) of 36.20 MPa and elongation at break (EB) of 17.90%. The results from FTIR spectroscopy, X-ray diffraction and scanning electron microscope images suggested high compatibility between KPI and GPP and improved structural properties for the composite films. Furthermore, the thermogravimetric analysis presented improved thermal properties for GPP/KPI (50/50) films. Additionally, biodegradability monitoring of GPP/KPI films showed that they begin to deteriorate within eight days when exposed to vegetal compost. Finally, the incorporation of GPE in GPP/KPI (50/50) films in different ratios enhanced TS (up to 45.41 MPa), antioxidant and antibacterial properties, while negatively impacting EB and barrier properties.