Two convenience store owners have been sentenced to federal prison, and nine other individuals have pleaded guilty following a two-year investigation into food stamp fraud. US Attorney Peter Neronha announced that three store owners pleaded guilty to food stamp fraud charges Friday and will be sentenced in May. Six store owners or employees have pleaded guilty and will be sentenced in coming months. Two Providence store owners have been sentenced to terms of one year and 18 months in prison. The two owners each must pay back nearly $400,000. Authorities say the schemes defrauded the federal benefit program of more than $3 million. They say store owners and employees allowed food stamp recipients to redeem benefits for cash in exchange for a cut of the proceeds.