It seems most unlikely to me that food preservation techniques wouldn't continue to improve past TL 7. It seems to me that the lack of any improvement must be an oversight. ...
Well, let's explore that a bit and see where that takes us. On other subjects we've preferred to have a bit of science behind our far future assumptions - not consistently, and not always possible, but it seems to be the preference.
Let's start with freezing reduces the quality of many foods. Can we irradiate foods and keep them at the same level of quality, or will they wilt or otherwise suffer quality declines just as a result of time and chemical changes? I don't know much about irradiating foods. What other processes might be used to keep the food to the kind of quality that a good chef would respect? What speculative science are we drawing on to postulate improved far future food preservation techniques?
Reheating is often a problem too, though it depends on the food (I actually prefer leftover spaghetti over fresh-made). Modern microwaves are nice but a bit brute force - I get stuff fried on the outside and cold on the inside. A truly advanced microwave might use infrared sensors and more finely controlled microwave emitters to achieve more even heating. However, some foods will invariably lose additional moisture in the reheating, losing some quality in the process. Traditional cookery says get the food up to a germ-killing temp, but if you can eliminate the germ angle then it may be sufficient to bring it to palatable temps and find ways to minimize moisture loss. Still, there are foods that handle twice-heating quite well and others that suffer rather badly when you do it.
I'm looking at this, and it's occurring to me that there's a lot of effort here when I could just pick up a week's supply of fresh food before I leave port. It's not like I'm in an airplane with a galley the size of a broom closet - I've got decent room aboard for a proper galley and pantry. Time seems to be my only lack, and that only on the little tramp merchants. Then it occurs to me that there are some ports where that might be more difficult than others - or I might be limited to local foods that I'm not real familiar with and might want some more familiar fare, even if it's not fresh.
... The food fed to high passengers cost exactly the same as the food fed to middle passengers (exact same life support cost), so presumably there's no difference in quality. ...
Uh oh, I've been feeding the middle passage folk Hungry-man dinners to ease the workload on the steward. Hope nobody complains.