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News 840 views last update:6 Aug 2012

Citrus peel shows promise in fish feed

South Korea produces an annual 40,000 tonnes of citrus peel as a by-product from fruit processing. Together with the dead fish waste from aquaculture production, the citrus peel can provide a valuable fish feed according to scientists.

The compounds found in citrus peel, known as polymethoxylated flavones (PMFs), are antioxidants that belong to a group of plant chemicals called flavonoids. Flavonoids exist in a variety of fruits and vegetables, as well as tea and red wine. This fact made a research team at Cheju National University look for producing high valuable fish meal from the citrus peel and the fish waste. The research was led by Dr Seon-Heui Cha of the University's Faculty of Applied Marine Science.

Antioxidant activities
Dr Cha and his team made two kinds of functional fermented fishmeal (FFM) from the dead fish and citrus peel. One contained citrus peel, the other contained rice bran but no citrus peel.
Statistical trials showed that the FFM containing the citrus peel showed strong antioxidant activities against the DPPH free radical (about 95%) and hydrogen peroxide (around 80 %) in a concentration of 4 mg/ml. The FFM containing citrus peel also exhibited enhanced protection to flounder leukocyte against H2O2-mediated DNA damage.

Tested in fish
Two experimental diets were formulated for olive flounder (also named Japanese flatfish). One pellet was a normal raw fish moisture pellet. The second diet was the same but contained 7% FFM containing citrus peel. The feeds including FFM enhanced the growth and significantly decreased the mortality of the fish. Fish fed FFM had significantly higher lysozyme activity and NBT reduction. Dr Cha considered that the results suggest citrus peel containing FFM increased the immune response of cultured olive flounder.

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