Twin 2021 in vitro studies of cruciferous sprout bioaccessibility, with the first addressing hydroxycinnamic acids and flavonols:

“The present work studies effects of physicochemical and enzymatic characteristics of gastrointestinal digestion on two major groups of phenolic compounds – flavonols and cinnamoyl derivatives – on red radish, red cabbage, broccoli, and white mustard sprouts. Effects of gastrointestinal digestion on release and stability of phenolic compounds depends on different factors, such as physicochemical traits of the food matrix, pH, temperature, or enzymatic activity.

Although initial concentrations of phenolic acids in red radish were lower than in other sprouts, their bioaccessibility after digestion was higher, followed by red cabbage, white mustard, and broccoli. Most degradation of phenolic compounds corresponded to the flavonol fraction, which was almost erased during digestion (with the exception of digestion products of broccoli sprouts, which retained around 30% of the original flavonol concentration):

Red radish sprouts exhibited the greatest bioaccessibility.

Gastric digestion prepares the food matrix for more efficient polyphenol extraction during intestinal digestion, in which the highest release and stability of these compounds takes place. Hydroxycinnamic acids reach higher concentrations than flavonols, making them tentatively more available to be absorbed at the intestinal level.”

https://www.mdpi.com/2072-6643/13/11/4140/htm “In Vitro Evidence on Bioaccessibility of Flavonols and Cinnamoyl Derivatives of Cruciferous Sprouts”

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A cited predecessor used similar methods to study glucosinolate breakdown products like sulforaphane, iberin, and indole-3-carbinol:

“Significantly higher bioaccessibility of isothiocyanates (ITCs) and indoles from glucosinolates (GSLs) of red cabbage sprouts were observed. Bioaccessibility of GSLs from Brasicaceae sprouts is not exclusively associated with initial content of these compounds in plant material (almost negligible), but also with release of GSLs and ongoing breakdown reactions during gastric and intestinal phases of digestion, respectively:

The intestinal phase was the most relevant for bioaccessibility of ITCs. Aliphatic GSLs provided higher bioaccessibility of their corresponding ITCs in comparison to indolic and aromatic GSLs.”

https://www.mdpi.com/1422-0067/22/20/11046/htm “Evidence on the Bioaccessibility of Glucosinolates and Breakdown Products of Cruciferous Sprouts by Simulated In Vitro Gastrointestinal Digestion”

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Gastric and intestinal simulations were instructive. But rather than depending on digestion for ITCs, I “enzymatically convert to SF before oral intake” per A follow-on study to 3-day-old broccoli sprouts have the optimal yields.

Regarding phenolic compound digestion, my focus this year has been to give my gut microbiota what they want. I expect and get reciprocity from treating them well with whole oats, broccoli-red cabbage-mustard-oat sprouts, blackberries-blueberries-strawberries, quercetin from capers, etc. polyphenols. Not to mention inulin, artichoke hearts, and yeast cell wall β-glucan. Haven’t considered sprouting red radish seeds.

Per Red cabbage effects on gut microbiota, a related research group had an in vitro system that included gut microbiota. Maybe these researchers will get together in a future study?