MONTERREY, Mexico--(BUSINESS WIRE)--Fitch Ratings has upgraded Sigma Alimentos, S.A. de C.V.'s (Sigma) ratings as follows: --Long-term foreign currency Issuer Default Rating (IDR) to 'BBB' from 'BBB-'; --Long-term local currency IDR to 'BBB' from 'BBB-'; --National scale long-term rating to 'AA+(mex)' from 'AA(mex)'; --USD450 million senior notes due 2018 to 'BBB' from 'BBB-'; --USD250 million senior notes due 2019 to 'BBB' from 'BBB-'; --Local Certificados Bursatiles Issuances to 'AA+(mex)' fr