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Food and beverages, Marine biology
Seaweeds or marine macroalgae are renewable living resources which are also used as food, feed and fertilizer in many parts of the world. They are able to produce a great variety of secondary metabolites characterized by a broad spectrum of biological behavior such as antibacterial and antioxidant activities. The effect of heat treatment was investigated on the level of bioactive compounds and changes in the overall antioxidant capacity of edible Irish brown seaweeds namely Himanthalia elongata, Laminaria saccharina and Laminaria digitata. In order to make the seaweeds safe and edible, they were heated at 85, 95, 100, 110 and 121°C for 15 min using an autoclave and the samples were extracted with 60% methanol. The total phenolic content (TPC), proanthocyanidin content (PC) and total radical scavenging capacity (RSC) against DPPH• increased as the heating temperature increased to 95°C. Heating at 95°C significantly increased (p<0.05) the TPC (1.6, 1.8 and 1.9-fold), PC (1.9, 2.0 and 2.6-fold) and RSC (2.0, 1.4 and 2.1-fold) as compared to raw H. elongata, L. saccharina and L. digitata, respectively. However, reducing antioxidant power (FRAP) significantly increased by 2.6, 2.4 and 2.8-fold as compared to the raw samples at 110°C. A high and statistically significant (p<0.05) correlation was observed between TPC and RSC. The polyphenol content and antioxidant capacity in the water soluble extract of processed seaweeds were in the order of H. elongata > L. saccharina > L. digitata. The overall changes by processing could be attributed to the complete breakdown or modifications of cellular components by heat and pressure. These compounds usually present in bound states as conjugate with sugars, fatty acids or proteins. It could be anticipated that heating around 100°C could be responsible for the disassociation of conjugate phenolic forms in seaweeds as their outer cell wall is much harder and heating at 100°C or above results in their deterioration. Results showed that the heat processing not only enhanced the contents of biologically active compounds in seaweeds but also the biological activity associated with these compounds as compared to the unprocessed seaweeds.
Rajauria, G., Gupta, S., Abu-Ghannam, N. and Kumar, A. (2010). Antioxidant capacity and polyphenol content of brown seaweeds after heat processing. Poster presented at the 2nd International Chester Food Science and Technology Conference, Chester, UK, 22nd - 24th March 2010.