Whole mulberry leaves as a promising functional food: From the alteration of phenolic compounds during spray drying and in vitro digestion

This study investigated the potential of processing whole mulberry leaves as nutraceutical foods rich in phenolic compounds by spray drying with different drying aids. The results indicated that the spray-dried product 6 (24.2% whey protein isolate [WPI], 33.3% mulberry leaves solid, 38.7% maltodextrin, 3.8% soybean lecithin) with high WPI/mulberry leaves solid ratio possessed the best physical properties, the highest total phenolic compounds level and antioxidant capacity among all the products. Specifically, free chlorogenic acid and rutin were increased by two to three times, but free isoquercitrin and astragalin lost more than 50% in product 6 compared with fresh mulberry leaves. For in vitro digestion, rutin, isoquercitrin, and astragalin (the antioxidative phenolic compounds in mulberry leaves) showed higher bioaccessibility than chlorogenic acid (p < 0.05) in product 6. Meanwhile, the phenolic compounds bioaccessibility of product 6 was 10-20 times higher than that of fresh whole mulberry leaves. Considering the increased level and bioaccessibility of phenolic compounds, whole mulberry leaves could be developed as potential functional foods by spray drying under the protection of WPI. PRACTICAL APPLICATION: The spray-dried whole mulberry leaves can be consumed as a beverage, meal replacement powder, or used as additive during food processing.