When the resulting extract was then encapsulated by spray drying in an alginate–xanthan gum matrix, the powder retained far more of its phenolic compounds, flavonoids, condensed tannins, and radical-scavenging activity during two weeks of storage and throughout a standardized simulated digestion than a non-encapsulated counterpart.

The research team, working with seed powder supplied by a Tunisian date-processing company, compared three green extraction strategies: ultrasound-assisted extraction (UAE), high-pressure autoclave extraction (HPAE), and a sequential combination of the two. One gram of seed powder was suspended in 10 milliliters of distilled water for each treatment. Sonication was carried out at 30°C in a 47 kHz ultrasonic bath, while the autoclave treatment ran at approximately 120°C and 1.0 bar gauge pressure for either 15 or 30 minutes, followed by rapid ice-bath cooling to limit thermal degradation. Extracts were filtered, centrifuged, and analyzed for total phenolic content, total flavonoid content, total condensed tannins, and antioxidant capacity using DPPH and ABTS assays.

Thirty minutes of high-pressure autoclave extraction delivered 133.71 ± 1.14 mg gallic acid equivalents per gram of dry matter in total phenolic content, roughly four times the 31.68 ± 0.16 mg GAE/g obtained with 30 minutes of ultrasound and more than double the 63.78 ± 0.83 mg GAE/g from the sequential UAE15–HPAE30 treatment. Flavonoids followed the same hierarchy, peaking at 44.96 ± 0.18 mg quercetin equivalents per gram for HPAE30. Condensed tannins reached 551.40 ± 3.86 mg catechin equivalents per gram under the same condition. Pearson correlations between phenolic measures and antioxidant assays were positive and moderately strong, with r values between 0.718 and 0.772, supporting the view that polyphenols are major contributors to the extracts’ radical-scavenging capacity.

Notably, the sequential ultrasound-then-pressure approach did not outperform pressure alone, contradicting the hypothesis that acoustic cavitation pre-treatment enhances solvent accessibility during subsequent high-pressure extraction. The authors suggest that oxidative degradation under some ultrasound conditions may be one contributing mechanism, though this was not directly tested. Based on its overall performance, HPAE30 was selected for the encapsulation stage, where the extract was combined with alginate and xanthan gum at a 1:3 weight ratio and spray dried at an inlet temperature of 160°C with an outlet between 70°C and 80°C.

Physicochemical characterization revealed meaningful differences between the encapsulated powder (EP) and the non-encapsulated powder (NEP). Powder yield rose from 2.50% for NEP to 6.15% for EP. Water activity dropped from 0.65 to 0.35, and moisture content fell from 1.713% to 0.428%, both favorable for shelf stability. Water solubility index was significantly lower for EP (3.088%) than for NEP (9.560%), and the encapsulated powder appeared darker and less yellow in color measurements. Encapsulation efficiency was 34.26%, which the authors acknowledge is modest compared with the 81% to 98% values reported for other spray-dried phenolic systems using maltodextrin, gum arabic, or alginate-gelatin blends, and they call for further optimization of wall-material composition and drying parameters.

Phytochemical analysis of the finished powders showed that encapsulation was associated with higher measured levels of all three compound classes. Total phenolic content was 45.816 ± 0.17 mg GAE/g in EP versus 39.013 ± 0.33 mg GAE/g in NEP, an increase of about 17.4%. Flavonoids rose roughly 136%, from 0.745 to 1.76 mg QE/g, and condensed tannins climbed from 256.683 to 360.85 mg CE/g. DPPH and ABTS activities were also slightly higher in the encapsulated material. The authors caution that these increases may reflect improved extractability and analytical accessibility as much as genuine chemical preservation, since individual compounds were not profiled chromatographically.

Storage trials over 14 days under light, darkness, 25°C, and 40°C showed a consistent descriptive pattern of greater retention in the encapsulated powder. Under continuous light, EP retained approximately 95.0% of its initial phenolic content at Day 14, while NEP retained only 77.3%. At 40°C the gap widened further: EP held about 91.3% of its phenolics and 93.3% of its DPPH activity, whereas NEP dropped to 65.1% and 74.9% respectively. Condensed tannin retention at 40°C was 84.7% for EP versus 56.6% for NEP. The authors emphasize that these storage findings are interpreted descriptively, without new inferential statistics, because replicate-level data for such analysis were not available.

Simulated gastrointestinal digestion using the internationally harmonized INFOGEST 2.0 protocol—covering oral, gastric, and intestinal phases with verified enzyme activities—showed that measurable phenolic, flavonoid, and tannin levels declined progressively in both formulations. Yet the encapsulated powder retained higher concentrations at every stage. By the intestinal phase, EP held 30.24 ± 0.25 mg GAE/g in total phenolics compared with 22.63 ± 0.30 mg GAE/g for NEP. The TPC-based intestinal bioaccessibility index was approximately 66% for EP and 58% for NEP, though the authors note this difference should be confirmed statistically using independent replicate-level values. Antioxidant activity followed the same trajectory, with EP retaining 55.47 μM Trolox/g in DPPH and 68.51 μM Trolox/g in ABTS at the intestinal stage, versus 48.15 and 58.48 μM Trolox/g for NEP.

The study’s limitations are clearly stated. All work was done at laboratory scale, storage was limited to 14 days, and phytochemical characterization relied on global spectrophotometric assays rather than compound-specific chromatographic methods such as HPLC-DAD or LC-MS. The sequential extraction was not evaluated in a full factorial design, so no synergistic interaction between ultrasound and pressure can be established. Morphological and particle-size characterization of the powders was not performed, and the INFOGEST model, while physiologically relevant, does not reproduce intestinal absorption, metabolism, or in vivo biological effects.

Subject of Research: Green extraction and spray-drying encapsulation of date seed bioactive compounds

Article Title: Green Extraction Coupled With Spray‐Drying Encapsulation Enhances Stability and In Vitro Bioaccessibility of Phoenix dactylifera Seed Bioactives

Article References: Rebai, O., Raboudi, F., Temessek, M. B., Gatri, R., & Fattouch, S. (2026). Green Extraction Coupled With Spray‐Drying Encapsulation Enhances Stability and In Vitro Bioaccessibility of Phoenix dactylifera Seed Bioactives. Food Science & Nutrition, 14(11), Article e72488. https://doi.org/10.1002/fsn3.72488

Image Credits: AI Generated

DOI: 10.1002/fsn3.72488

Keywords: date seed, Phoenix dactylifera, green extraction, high-pressure autoclave extraction, ultrasound-assisted extraction, spray drying, encapsulation, polyphenols, antioxidant activity, bioaccessibility, INFOGEST 2.0, food waste valorization