Effect of hydrothermal processing on chemical composition and quality of Saccharina latissima cultivated in Norway for human consumption - Decreasing iodine content by two heat processing methods and determining the possible loss of quality compounds
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The brown seaweed Saccharina latissima contains high levels of iodine, which in excess intake can cause adverse human health effects. Norwegian cultivated S. latissima were blanched to attempt reduction of iodine content to ensure a safe food product. Two experiments were executed, one with focus on the two blanching methods; steam and water at the three temperatures 60, 80 and 95°C for 300 seconds. Second experiment focused on the process variables; time and temperature within water blanching. The process temperatures were 30, 45, 60 and 80°C and processing time were 0, 30, 120 and 300 seconds, where 0 seconds were an immerging into the water. Moreover, the nutritional compositions together with quality compounds (amino acids and total phenols) were screened to evaluate their loss during processing. Water blanching was more efficient to reduce iodine than steam and lowered the iodine content below the threshold value of 2,000 mg I/kg dry weight. The process variables interacted with each other from which it could be concluded that both process time and temperature has an influence on the iodine reduction, although around 350 mg I/kg dry weight was the reduction going towards a constant level. The water blanching at the tested process variables affected water, ash and calculated carbohydrates, but not lipid or protein concentration significantly. It was found that a processing time above 30 seconds would decrease the total phenolic content significantly. Regarding protein quality was no significant changes found when evaluating by essential amino acid to amino acid ratio and amino acid score. However, a significant decrease of the amino acids alanine, aspartic and glutamic acid occurred, which could lead to a change of flavor. Low processing temperature and time such as 45°C for 30 seconds is recommended due to nutritional and quality aspects of the final product, additionally due to economical and environmental impacts. At these process variables the safe intake of S. latissima is 4.3 g wet weight according to recommended intake of iodine for adults.