Quality

What effect does quality have on items purchased for country use, such as vegetables, or tea?

it affects your country welfare. Under the Business and Trade Index, the Consumption Quality Index, is a measure of the Quality rating of you country supplies, that effects your country welfare

And what does the Country Welfare affect?

The production of corporations in your country.

exactly, the country welfare, along with corporate salaries, effects your corporation welfare

you can find the list of other things that effect country welfare, in the documentation. its pretty much spelt out for you