Phenolics, anthocyanins and antioxidant activity in red raspberry muffins

Maria U. Rosales Soto

Raspberries are a rich source of phenolic compounds, including flavonoids. Anthocyanins are the major group among flavonoids. Mixing and temperature baking influences on phenolics, antioxidant activity and anthocyanins from raspberry fruit were evaluated during the preparation of muffins. Frozen red raspberries (cv. Meeker) were processed to obtain raspberry juice. Red raspberry juice, control and raspberry batter and muffin samples were extracted using three solvents: 100% methanol, methanol:HCl and ethanol:HCl and analyzed for phenolics, antioxidant activity, and anthocyanins. Anthocyanins were also identified using HPLC with diode array detector. Change of the original pH of the fruit due to mixing with other muffin ingredients affected the final color of the batter and baked muffin product. Acidified methanol was selected as the solvent giving a greater amount of the parameters selected considering raspberry muffin as the product of interest. The largest phenolic content was obtained for raspberry batter (0.70 mg gallic acid equivalent (GAE)/g DM) compared to the phenolics given by the 2.4% solids of raspberry juice present in the raspberry batter dry sample (0.56 mg GAE/g DM). Raspberry muffin had a lower amount of phenolics (0.44 mg GAE/g DM) in comparison to the raspberry batter. On the contrary, antioxidant activity increased in the raspberry muffin (0.023 µmol Trolox equivalent (TE)/g DM) compared to the raspberry batter (0.012 µmol TE/g DM). Total anthocyanins were determined using a spectrophotometric method. Anthocyanin content decreased 42.5% from 0.080 mg of cyanidin-3-glucoside (CGE)/g DM present in the 2.4% solids of red raspberry juice to 0.046 mg of CGE/g DM found in raspberry batter. HPLC analysis showed the presence of four anthocyanins in red raspberry juice, cyanidin-3-sophoroside, cyanidin-3- glucoside, cyanidin-3-glucosylrutinoside, and pelargonidin-3-sophoroside. Pelargonidin3-sophoroside was undetectable in the raspberry batter and muffin products. This study confirmed that baking temperatures and batter mixing affect antioxidant activity, phenolic and anthocyanin content of red raspberry products. Possible approaches to protecting health benefiting phenolics in raspberry include using whole fruits with coatings.

Phenolics, anthocyanins and antioxidant activity in red raspberry muffins

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