Influence of Temperature and Drying Time on Extraction Yield of Phenolic Compounds from Grape Pomace Variety “Portogizac”

Sustainable food production is one of the main goals of the modern world. Nowadays, there is a growing interest in the exploitation of the by-products generated from agriculture and food production as raw materials for obtaining high-value products, which can be used for various purposes in the pharmaceutical, cosmetics and food industries. During the winemaking process, about 20 % of the grapes1–3 remains as a solid waste by-product (grape pulp, seeds, skin and stems), representing a rich source of various value-added products, such as ethanol, sugars, proteins, fruit acids, oils, hydrocolloids, dietary fibres and phenolic compounds. Phenolic compounds are particularly important due to their beneficial effects on human health, and their application in improvement of flavour, colour and stability of food4–8. Besides polyphenols, grape waste contains proteins, polysaccharides and lignin, which are associated with functional groups responsible for metal ion adsorption, thus making this agricultural waste a good alternative to expensive synthetic adsorbents. Chand et al.9 tested cross-linked grape waste gel for the adsorption and separation of Cr(VI) ions from synthetic aqueous solution. Grape pomace has so far been investigated as a fertilizer or soil conditioner10–13, as biomass for biofuel production14–16 and as animal feed17–20. Wet grape pomace is a highly perishable material subject to uncontrolled microbial spoilage owing to its high moisture content (~60 %wb) and water activity. Therefore, the dehydration process is an important step in extending the shelf life of raw material and keeping its native properties before utilization for different purposes. The selection of the dehydration method depends on raw material properties, the desired characteristics of the dried product, the restriction on the operating conditions and costs. Sun drying is still a favourable method for drying some plant materials (fruits, vegetables, herbs, etc.) due to lower drying temperature and costs. However, its main drawbacks are dependence on weather conditions, often-poor product quality, long duration of process, possibility of material contamination with dust, soils, insects, etc. Otherwise, convection drying based on heated air in different designed drying devices (cabinet driers, tunnel driers, fluid-bed driers), vacuum drying, freeze-drying, and alternative methods, such as infrared drying and microwave drying, ensure better process control, shelf-stability and microbiologically safe dried product, with minimal degradation of nutrients and sensory quality21,22. Influence of Temperature and Drying Time on Extraction Yield of Phenolic Compounds from Grape Pomace Variety “Portogizac”