What does 'low' mean? Low relative to what? Foreign broccoli crops? Broccoli seed or sprout extract supplements? Something else?
And what did you test? The entire plant including the stems? Or the florets only?
The published papers I've seen are reporting 89mg of glucoraphanin / 100g of broccoli florets. Is that what you consider 'low' or something else?
When you tested powdered mustard seed, what seed type did you use? Because from the published research I've read, yellow mustard seed has very little myrosinase in it. The only game in town is brown mustard seed. And when you say you tested 'powdered mustard seed' do you mean you ground and tested the resulting powder from the seed, or do you mean you just acquired already grounded powder meant to be added to cooked dishes, that might have been sitting on a warehouse shelf or inside a shipping container at room temperature for many months? All these factors appear to be very important...
With regard to fresh daikon what is your basis for a 1/4 cup? What's the ratio of myrosinase to glucoraphanin you're working off? 90% glucoraphanin to 10% myrosinase? Something else? What's the myrosinase content by weight for daikon?
So while I appreciate your input, nothing you're telling me is actionable yet, but I have my fingers crossed.
Will, you have set a huge 'assignment' here and as I'm chasing deadlines at the moment, I cant really take the time to answer all of these questions. What are the most pressing issues you want to address at the moment?
Here's one answer for now. I've attached the glucosinolate data for broccoli. This comes from UQ and the paper is from SA McNaughton "Development of a food composition database for the estimation of dietary intakes of glucosinolates, the biologically active constituents of cruciferous vegetables"
Keep note that this is an estimate of glucosinoltaes (GLS) - not glucoraphanin (GRN). The GRN is an unknown proportion of the GLS, so the GRN content will be significantly less than shown here.
Of equal importance is the fact that samples vary widely in their content of GLS and GRN, so that when you buy broccoli, you dont know which end of the range you have bought. If you use their median for 62mg GSL/ 100 g, the figure will be markedly less than the 89 mg you quoted. (Is this data fro a reliable source?)
As for florets vs stems, the florets are typically several times more concentrated than he stems. I also suggest avoiding stems as they tend to accumulate the agricultural chemicals.
When we tested samples in the lab, it was florets only and bought in a Brisbane supermarket brought into store from the markets that day - and the values we obtained were about 10% less than those listed in the USDA database.
A few points for you to think on for now perhaps?