What is the fine-grained topic of the following text: Snackfood firm Rhythm Superfoods has closed a $6m Series D financing round filled through the CircleUp platform, with 301 INC - General Mills' new business development and venturing unit - as the lead investor (additional investors include Blueberry Ventures and the CircleUp Growth Fund). Only return the topic.
Rhythm Superfoods' Series D financing round closure