From the Wikipedia article (with sources):
Prior to 2007, the company website of Jamba Juice claimed that “Jamba” derives from the “African” word “Jama,” which means “to celebrate, taking care of body, mind and soul is a way of celebrating life.” The etymology has since been removed from the company’s website. Direct e-mails to the company claim it to be of West African origin, but they do not specify from which of the estimated 1800 African Languages it derives. “Jamba” means “fart” in Swahili. Additionally, there is a town named “Jamba” in Angola, which may be related to the word “jamba,” meaning “Elephant” in Umbundu, a language spoken in southern Angola. The town became relatively well-known as the headquarters of UNITA during the Ronald Reagan Administration in the USA.