Sulforaphane formation and bioaccessibility are more affected by steaming time than meal composition during in vitro digestion of broccoli.
Level 5 - mechanism / opinion, no new human data
In vitro laboratory digestion study without human subjects.
PubMed 27507513 · doi:10.1016/j.foodchem.2016.07.111
What was done
Researchers evaluated the formation and bioaccessibility of glucoraphanin breakdown products (sulforaphane and sulforaphane nitrile) using a multi-stage in vitro digestion model covering mouth, stomach, and intestine phases (excluding colonic digestion). They tested four broccoli preparations (raw, 1 min, 2 min, and 3 min steamed) and the effect of meal composition (addition of protein or lipid).
What was found
Primary formation of sulforaphane (SF) and sulforaphane nitrile (SFN) occurred during in vitro chewing, with no further hydrolysis occurring in subsequent phases due to irreversible gastric inactivation of myrosinase. SF concentrations after digestion were up to 10 times higher in raw and 1-min steamed broccoli compared to samples steamed for longer durations. The addition of protein or lipid had no influence on the formation or bioaccessibility of SF or SFN. Exact numerical baseline values were not reported in the abstract.
Why it matters
These findings indicate that myrosinase-dependent conversion of glucoraphanin to sulforaphane during oral processing is substantially preserved at one minute of steaming but drops sharply with longer cooking, irrespective of co-ingested macronutrients.
Limits
The study was performed entirely in an in vitro digestion model and did not measure in vivo human absorption, metabolism, or colonic microflora digestion. The abstract omits sample sizes, replicate counts, variance, and baseline chemical concentrations.
Cited by
- supports Chewing broccoli breaks plant cell walls to release the enzyme myrosinase, which converts glucoraphanin into sulforaphane.