...Am I seeing Yamaoka actually go " this storebought thing is just fine and yall are overreacting "
....Is he well? Who is this stranger?
I know there are differences between American and Japanese mayo, so I deliberately did not want to comment on anything because I don't know much of anything about Japanese mayo, but here in the US, the reason mayo doesn't spoil easily is not really to do with chemical additives, really. It doesn't spoil because:
1. It's acidic. Here in the US, lemon juice and vinegar are added and that puts the PH balance at like 4 or 4.1, which makes it harder for bacteria to grow.
2. The raw eggs are pasteurized. Now, I know from the chapter where Tomii's son wouldn't drink milk that Kariya already seems not to trust the process of pasteurization.
3. The oil to water ratio is very high. Bacteria need the water to multiply and have a harder time when the moisture is bound by oil.
4. Now, this is something where Kariya was probably rubbing his hands together, but yes, mayo does have additives, but those additives tend to be things like seed oil or xanthan gum, which are natural additives rather than chemical ones (xanthan gum, for those that don't know is a very common binding agent made by fermenting simple sugars like glucose).
I don't know what answers Yamaoka will get in the next chapter yet, but those are the answers as to why it's shelf stable.