Recovery of polyphenols from the by-products of plant food processing and application as valuable food ingredients

• Food processing by-products serve as rich sources of high-value phenolic compounds
• Simultaneous recovery of pectin and polyphenols from apple pomace
• Isolation of phlorizin for dietary and pharmaceutical purposes
• Novel process for recovering phenolic colorants and antioxidants from grape pomace
• Combined recovery of proteins and polyphenols from sunflower expeller

Residues from plant food processing are valuable sources for the recovery of polyphenols, pectins, and proteins. These compounds may be used as natural antioxidants and functional food ingredients. The present review exemplifies innovative strategies for the valorization of by-products originating from apple, grape and sunflower processing. Apple pomace is an important starting material for pectin extraction. The color of apple pomace and of the pectins recovered therefrom is caused by oxidative browning of phenolic compounds. This limits the use of apple pectins as food gelling agents in very light-colored products. Consequently, a patented process for the simultaneous recovery of pectin and phenolic compounds from apple pomace has been developed. Phlorizin, the most abundant phenolic compound in apple pomace extracts, is the basic structure of a new class of oral antidiabetic drugs. Type 2 diabetes mellitus may be treated by the inhibition of sodium-glucose co-transporter-2 (SGLT 2). In a recently patented process, dihydrochalcones are enriched and purified from undesired ortho-dihydroxy phenol compounds being prone to oxidation and covalent binding to proteins.While pigments from apple pomace are obtained by enzymatic oxidation of phlorizin using fungal polyphenoloxidases, anthocyanin-based pigments may be extracted from grape skins without using sulfite applying a novel enzyme-assisted process. Consequently, anthocyanins and phlorizin oxidation products are valuable alternatives for the replacement of synthetic azo dyes, some of which have been associated with health risks.De-oiled sunflower press cake is a promising source of food protein as an alternative to soy and egg protein being devoid of toxic substances and low in antinutrients. Conventional alkaline protein extraction yields dark-colored products having reduced nutritional and functional quality. Therefore, a novel process for the production of light-colored sunflower protein isolates has been developed, combining mild-acidic protein extraction with subsequent adsorptive removal of phenolic compounds.