Antioxidant and rheological properties of guava jam with added concentrated grape juice

BACKGROUND Guava jam enriched by the addition of concentrated grape juice in the proportion of 30% (w/w) ( ENR ) was studied for its antioxidant potential and rheological behavior. Total phenolics content, 1,1‐diphenyl‐2‐picrylhydrazyl radical ( DPPH • ) scavenging activity and β ‐carotene–linoleic acid coupled oxidation assays were used to evaluate the antioxidant properties of the samples during storage for 90 days at room temperature (25°C) . RESULTS The ENR showed a total phenolic content of 11.09 g GAE kg −1 of jam at production, more than two‐fold the phenolic content presented by the standard formulation ( STA ). For the ENR formulation the antioxidant capacity increased in almost 20% ( P ≤ 0.05) with time on the β ‐carotene assay and decreased with time on the DPPH assay. The enriched guava jam exhibited a non‐Newtonian shear‐thinning behavior at temperatures ranging from 25 to 55°C, and, moreover, presented higher stability than the standard formulation when exposed to temperature variation . CONCLUSION ENR constitutes an original food product with a notable antioxidant potential, even greater than the potential presented by the standard guava jam, worldwide appreciated delicacy. © 2013 Society of Chemical Industry