Introduction: The growing consumption of plant-based foods and their byproducts has gained global attention. People are choosing plant-based diets for health benefits, reducing their carbon footprint, and supporting sustainable food production. To keep up with these trends, the food industry must use advanced analytical techniques to improve extraction methods while preserving bioactive compounds. In this context, plant-based byproducts should be carefully examined for bioactive compounds, particularly prebiotic glycans (oligosaccharides and polysaccharides). This presentation explores combined omics and method optimization to study the carbohydrates of grape pomace, with an emphasis on mass spectrometry.
Methods: Naturally occurring monosaccharides and oligosaccharides were extracted using water and purified via filtration and solid phase extraction. The remaining solids, containing polysaccharides, were fractionated into water-insoluble and soluble polysaccharides. The advantages and disadvantages of various extraction and derivatization methods were tested and compared before mass spectrometry analyses. NanoLC-chip-QTOF-MS was employed to investigate the oligosaccharide structures, while LC-QQQ-MS was used to quantify the extracted and/or purified free monosaccharides, oligosaccharides, and polysaccharides.
Results: Chardonnay pomace contains an interesting diversity of carbohydrates, including monosaccharides (~300 mg/g raw materials), oligosaccharides (~4 mg/g), and polysaccharides (~76 mg/g). Fructose (139 mg/g) and glucose (134 mg/g) dominated the free monosaccharide profile, followed by glucosamine (11 mg/g) and arabinose (10 mg/g). A total of 178 oligosaccharides (including isomers/anomers) based on 27 primary structures and 14 monosaccharide building blocks were characterized in Chardonnay pomace, with an oligomerization degree ranging from 3-9. The optimal hydrolysis time of polysaccharides was 4-7 hours. Total polysaccharides were mainly composed of xylose (~25mg/g), arabinose (~10 mg/g), galacturonic acid (~8 mg/g), glucose (11 mg/g), and galactose (~10 mg/g). The boiling water extraction was effective at separating the xylose- and arabinose-enriched polysaccharides thanks to solubility difference.
Conclusions: The discovery of these diverse carbohydrates in side streams can promote their valorization as natural sweeteners, prebiotics, and ingredients for functional food/beverage/skincare products.

Lydia Gu

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