Low-Temperature Infrared Drying Preserves the Functional Quality of Grape Pomace: A Scalable Strategy for Sustainable Upcycling of Winery By-Products

Grape pomace, the main by-product of the wine industry, is a rich source of polyphenols and dietary fiber and has a high potential for functional food applications. However, its high moisture content promotes rapid deterioration, requiring stabilization before further utilization. Although freeze-drying effectively preserves thermolabile compounds, its high energy demand, long processing time, and operational costs limit industrial implementation. This study evaluated low-temperature infrared drying (IR, 40 °C) as a scalable and sustainable alternative to preserve the functionality of grape pomace from a Malbec-Pinot Noir blend (85:15, w/w). Resveratrol, total phenolic content (TPC), total flavonoid content (TFC), antioxidant capacity (ORAC), arabinoxylans content (AXC), and thermal stability by thermogravimetric analysis (DTG-TGA) were determined.

Both drying technologies produce samples with a final moisture below 5% and water activity below 0.4. The resveratrol content was effectively preserved, reaching an average value of 3.2 ± 0.1 mg Kg⁻¹ DW with both techniques. Freeze-dried samples had the highest content of TPC (6795,9 ± 549,4 mg GAE 100 g⁻¹ DW); whereas higher TFC and ORAC values were observed in IR-dried samples, with increases of about 53,7% and 15,6%, respectively, compared to freeze-dried samples. AXC remained unaffected by the drying method (5334.3 and 5147.8 mg XE 100 g⁻¹ DW respectively), suggesting the preservation of the dietary fiber fraction. DTG-TGA showed slightly higher thermal stability for freeze-dried samples, with an onset degradation temperature of 278.8 °C compared with 266.6 °C for IR-dried pomace, whereas maximum degradation temperatures were comparable (505.9 – 507.1 °C).

Overall, low-temperature IR drying effectively preserved the functional properties of grape pomace, maintaining resveratrol, flavonoids, antioxidant capacity, dietary fiber integrity, and storage stability at levels comparable to freeze-drying. Considering its lower energy demands, shorter processing time, and greater industrial scalability, IR drying represents a promising strategy for the sustainable upcycling of winery by-products.

Acknowledge to project ANID CREAS R23F0004.