EFFECT OF GERMINATION ON PHENOLIC BIOACCESSIBILITY DURING SIMULATED IN VITRO GASTROINTESTINAL DIGESTION OF WHITE LUPIN

Pulses are important sources of nutrients and bioactive compounds, including phenolics with antioxidant properties. White lupin (Lupinus albus L.) has gained interest for human consumption because of its high protein content and diverse phenolic composition, including isoflavonoids. Germination can enhance phenolic content and antioxidant activity through the release of matrix-bound compounds and de novo biosynthesis. However, the potential biological relevance of these compounds also depends on their stability and release during gastrointestinal digestion.

This study evaluated the effect of germination on phenolic bioaccessibility and the antioxidant properties of white lupin during gastrointestinal digestion. Seeds and seven-day sprouts were subjected to the standardized INFOGEST in vitro digestion protocol. Initial flours and fractions obtained after the oral, gastric, and intestinal phases were characterized for total phenolic content (TPC) and individual phenolic compounds by HPLC-DAD, while antioxidant activity was assessed by FRAP and ORAC-FL assays.

Germination significantly increased TPC from 148 to 456 mg GAE/100 g dry matter. Antioxidant activity also increased, with FRAP values rising from 369 to 1,169 μmol TE/100 g dry matter and ORAC-FL values from 2,865 to 23,772 μmol TE/100 g dry matter. During gastrointestinal digestion, the release of phenolic compounds varied across the different phases. In both seeds and sprouts, TPC generally decreased during the oral phase, increased under gastric conditions, and declined during the intestinal phase. At the intestinal stage, sprouts showed higher amounts of bioaccessible phenolic compounds than seeds, as indicated by TPC and HPLC-DAD analysis. This was accompanied by higher ORAC-FL activity in sprouts, whereas FRAP values were higher in seeds. Considerable phenolic content and antioxidant activity were also detected in the fractions remaining after intestinal digestion, indicating substantial retention of phenolic compounds within the insoluble food matrix. HPLC-DAD analysis showed marked differences in phenolic profiles between seeds and sprouts, with seeds characterized mainly by rutin and naringenin, whereas sprouts showed a greater abundance of the isoflavonoids genistin and genistein, which remained detectable during digestion.

Overall, germination markedly enhanced the phenolic content and antioxidant potential of white lupin and increased the absolute amount of bioaccessible phenolic compounds and antioxidant activity after digestion. However, digestive stability and release depended on phenolic characteristics and interactions with the food matrix. These results support germinated white lupin as a promising functional food and suggest that phenolic compounds remaining after intestinal digestion may also become available for colonic metabolism.