Industrial byproduct pine nut skin factorial design optimization for production of subcritical water extracts rich in pectic polysaccharides, xyloglucans, and phenolic compounds by microwave extraction

Abstract

Pine nut skin (Pinus pinea L.) is a poorly explored industrial byproduct with potential to be utilized as a food ingredient. Subcritical water extraction (SWE), an eco-friendly extraction technique with higher efficiency than hot-water extraction (HWE), was studied to evaluate its suitability in producing extracts rich in soluble fiber and phenolic compounds. For this, a factorial design was developed considering temperature (120–180 °C), time (2–10 min), and mass/volume ratio (1–3 g/60 mL) under microwave irradiation. This design aimed to maximize the extraction of carbohydrates, while achieving the highest content of phenolic compounds and antioxidant activity. SWE produced higher yields (2.6-fold in relation to HWE) of extracts rich in polysaccharides, determined by methylation analysis, oligosaccharides, determined by GC-qMS as alditol acetates, and phenolic compounds, determined by HPLC-ESI-MS. SWE increased the recovery of pectic oligosaccharides (10-fold) and xyloglucans (2-fold), and allowed to recover pectic polysaccharides, type II arabinogalactans and insoluble-bound phenolic compounds. Mono-, oligo- and polysaccharides were not hydrolyzed during in vitro gastrointestinal digestion, showing potential prebiotic functionality. Although phenolic compounds suffered a 23 % (gallic acid equivalents) decrease, phenolic acids and aldehydes were released or conserved upon intestinal phase. These results highlight the potential of PNS valorization as functional food ingredients through the subcritical water solubilization of polysaccharides and phenolic compounds.