Effect of different drying methods and storage time on the retention of bioactive compounds and antibacterial activity of wine grape pomace (pinot noir and merlot)

The effects of different drying methods (40 °C conventional and vacuum oven, 25 °C ambient air and freeze dry) on the stability of two red wine grape (Pinot Noir, PN and Merlot, M) byproducts, pomace containing skins and seeds (P) and pomace containing skins only (S) were investigated. Freeze dried samples retained the highest bioactive compounds with total phenolic content (TPC) of 21.19-67.74 mg GAE/g d.m., anthocyanin content (ACY) of 0.35-0.76 mg Mal-3-glu/g d.m., DPPH antiradical scavenge activity (ARS) of 22.01-37.46 mg AAE/g d.m., and total flavanol content (TFC) of 30.16-106.61 mg CE/g d.m., followed with ambient air dried samples. All samples lost significant amount of bioactive compounds during 16 wk of storage at 15 ± 2 °C, in which ambient air and freeze dried samples had TPC reduction of 32-56% and 35-58%, respectively, but ARS in PN-P and M-P still remained more than 50 mg TE/g d.m. Overall, TPC, ARS, and TFC were higher in PN than in M, and higher in pomace than in skins, while reverse results were observed in ACY. Pomace extracts showed higher antibacterial efficiency against Listeria innocua ATCC 51142 than Escherichia coli ATCC 25922 with minimal inhibition concentration (MIC) of 3%, 6%, 4%, and 9% against E. coli, and 2%, 7%, 3%, and 8% against L. innocua for PN-P, PN-S, M-P, and M-S samples, respectively. Dietary fiber content of samples was 57-63% of total dry matter. This study demonstrated that Pinot Noir and Merlot pomace are good sources of antioxidant dietary fibers and may be incorporated into various food products as a functional ingredient. Practical Application: Wine grape pomace (WGP), the byproduct of wine making, is a good source of polyphenols and dietary fibers and may be incorporated into various food products as a functional ingredient. This study reported the effect of four drying methods and storage at 15 ± 2 °C up to 4 months on the retention of polyphenols and antioxidant activity in two types of red WGP (with and without seeds). Antibacterial activity, dietary fiber content and the basic physicochemical properties of dried pomace powder were also reported. The information is essential for developing specific applications of the pomace.