Optimization of sulforaphane bioavailability from a glucoraphanin-rich broccoli seed extract in a model of dynamic gastric digestion and absorption by Caco-2 cell monolayers†

Abstract

Broccoli is recognized for its health benefits, attributed to the high concentrations of glucoraphanin (GR). GR must be hydrolyzed by myrosinase (Myr) to form the bioactive sulforaphane (SF). The primary challenge in delivering SF in the upper gastrointestinal (GI) tract- is improving hydrolysis of GR to SF. Here, we optimized the formulation and delivery methods to improve GR conversion and SF bioavailability. We investigated whether the combination of GR-rich broccoli seed extract powder (BSE[GR]) with Myr-rich mustard seed powder (MSP[Myr]), ± ascorbic acid (AA, a co-factor of Myr), delivered as free powder or encapsulated powder, can: (i) facilitate GR hydrolysis to SF during dynamic in vitro gastric digestion and static in vitro small intestinal digestion, and (ii) increase SF bioavailability in Caco-2 cell monolayers, a model of human intestinal epithelium. Addition of exogenous Myr increased the conversion of GR to SF in free powder during small intestinal digestion, but not during gastric digestion, where Myr activity was inhibited by the acidic environment. Capsule delivery of BSE[GR]/MSP[Myr] (w/w ratio 4 : 1) resulted in a 2.5-fold higher conversion efficiency compared to free powder delivery (72.1% compared to 29.3%, respectively). AA combined with MSP[Myr] further enhanced the conversion efficiency in small intestinal digestion and the bioavailability of SF in Caco-2 cell monolayers. Bioavailability of GR as SF, SF metabolites, and GR was 74.8% in Caco-2 cell monolayers following 30 min gastric digestion and 60 min small intestinal digestion. This study highlights strategies to optimize GR bioconversion in the upper GI tract leading to enhanced SF bioavailability.