No, the noun 'tahini' is a common noun, a general word for any tahini of any kind.
A common noun is capitalized only when it is the first word in a sentence.
A proper noun is always capitalized. A proper noun is the name or title of a specific person, place, or thing.
A proper noun for the common noun 'tahini' is the name of a specific brand of tahini; for example, Joyva Tahini or Nuts To You Tahini.