Grapes (Vitis sp.) are the world’s largest fruit crop. Mainly used in winemaking, about 20-30% of the weight of processed grapes ends up as the by-product pomace, which consists of the skins, seeds and stems.
To the wineries this poses an environmental and disposal problem but the pomace is a rich source of polyphenols with widely-researched health benefits.
The polyphenol compounds are only partially extracted during the winemaking process, leaving flavonoids such as anthocyanins and catechins, phenolic compounds and stilbenes still present in the pomace.
Now researchers behind a study published in New Biotechnology say this by-product could be used as a functional ingredient.
"The present results support the possibility to exploit fruit processing by-products as a source of bioactive compounds in view of their application as ingredients of healthy, functional and innovative products in the nutraceutical, pharmaceutical or cosmetic fields," they concluded.
Anti-inflammatory and anti-microbial grape and wine phenols have been shown to have protective effects against chronic diseases such as cancer, cardiovascular disease and neurodegeneration.
After digestion, dietary phenols are modified and may appear in circulation in low concentrations. Previous studies which compared recovery methods showed solvent and fluid extraction and enzymatic digestion to be the most efficient methods for grape pomace polyphenol recovery.
Polyphenolic compounds were recovered from wet and dried red grape pomice supplied by Italian wineries, using enzymatic digestions and ethanol-based extraction methods.
Wet pomace samples released the highest amount of polyphenols using Fungamyl and Celluclast enzymes. Dried pomace released less polyphenols which was thought to be as a consequence of drying.
In vitro methods were used to analyse the biological activities of the best extracts; they showed antioxidant and cholesterol-lowering activities and contained high amounts of total polyphenols, flavonoids, tannins and anthocyanins.
The wet pomice extract was able to significantly induce transcription activity of the rate limiting enzyme in bile acid synthesis. The results were in accordance with previous animal studies that demonstrated the cholesterol-lowering effect of grape pomice and a beneficial effect on LDL/HDL (low density lipoprotein/high density lipoprotein) cholesterol ratio with phenols.
Preparation methods are important
Previous studies on berries showed the sample preparation method prior to extraction was important. The authors similarly found that drying out the pomace had a negative effect on the polyphenol content. They suggested it was preferable to treat the pomace straight after its production during the winemaking process.
Lengthier enzyme treatments also yielded less polyphenols, so longer-term incubation which causes degradation of metabolites should be avoided, they suggested. Overall, two-hour control at 24°C and two-hour 1% Celluclast proved to be the best treatments.
Source: New Biotechnology
Published online ahead of print http://dx.doi.org/10.1016/j.nbt.2015.12.004
“Recovery of polyphenols from red grape pomace and assessment of their antioxidant and anti-cholesterol activities”
Authors: M. Ferri et al.