Four later candidates, and where they land

In one paragraph. Two further rounds of research generated new candidates after the ranking above was set. None displaces the top category, but two change how it would be built, and one is a new entry near the top pending a single legal answer.

Candidate	Where it lands	Why
Koji biomass on food-grade side streams	Enters at or near the top, pending one legal answer	The only candidate that plausibly avoids the novel food gap entirely. Proven organism, proven substrate, existing Vietnamese practice, 30 to 40 percent protein. Carries a strain-safety burden: see 7.2
Duckweed on aquaculture effluent, fed back into aquafeed	Enters as a near-term feed candidate, roughly alongside the top category	The only candidate needing no fermentation tank. Thirty years of Vietnamese research, the highest protein yield per hectare in the study, and an existing nutrient stream at industrial scale. Feed only. Effluent-grown duckweed accumulates heavy metals and pathogens; food-grade duckweed needs closed cultivation on clean water and is a different business
Brewer's spent grain as substrate	Joins cassava pulp as a primary feedstock	Already protein-rich, concentrated at four brewery groups, large volume. Same constraint that it must be used where it is made
A working feed registration pathway	Not a candidate, an unlock	Raises everything aimed at feed by removing the regulatory unknown. Larger than it looked: the timeline is undocumented, not merely unconfirmed
Okara, the residue from making tofu and soy milk	Secondary feedstock	Real and large, but scattered across many small producers, and it recovers imported protein rather than displacing imports
Cultivated fish and shrimp cells	Stays last as an industry; enters as a research contribution	No food-grade production lines exist for the relevant species, though research lines do. Reframed, not promoted
Purple non-sulfur bacteria	Does not enter as a protein route	Productivity sits well below fungal systems; better understood as a wastewater technology with a saleable by-product
Methanotrophs on biogas	Unresolved	The search for this line failed to complete, which is not a negative result

The full assessment of duckweed is in chapter 11, and of the others in chapters 8 and 13.