Seaweeds are a renewable natural source of valuable macro and micronutrients that have attracted the attention of the scientists in the last years. Their medicinal properties were already recognized in the ancient traditional Chinese medicine, but only recently there has been a considerable increase in the study of these organisms in attempts to demonstrate their health benefits. The extraction process and conditions to be used for the obtention of value-added compounds from seaweeds depends mainly on the desired final product. Thermochemical conversion of seaweeds, using high temperatures and solvents (including water), to obtain high-value products with more potential applications continues to be an industrial practice, frequently with adverse impact on the environment and products’ functionality. However more recently, alternative methods and approaches have been suggested, searching not only to improve the process performance, but also to be less harmful for the environment. A biorefinery approach display a valuable idea of solving economic and environmental drawbacks, enabling less residues production close to the much recommended zero waste system. The aim of this work is to report about the new developed methods of seaweeds extractions and the potential application of the components extracted.

Electric field-based technologies for extraction processes have been gaining importance due to sustainability concerns. This work aims to assess the potential of ohmic heating as an efficient and feasible tool for the extraction of different biocompounds from Gracilaria vermiculophylla and its effect on the extracts' composition. Different ratios of water/ethanol (0 to 75% ethanol, v/v) were used to target different families of biocompounds. The ohmic heating-based extraction was performed at 82 • C under electric field and frequency of 2-8 V/cm and 25 kHz, respectively. Conventional extractions without the presence of electric field were made keeping a temperature profile identical to the ohmic heating treatments, thus addressing the potential occurrence of electrical (non-thermal) effects. Extraction yields and extracts composition (content in polysaccharides, proteins, phenolic compounds and pigments) were evaluated. Further, as agar is the major commertially exploited compound from Gracilaria spp., the effect of ohmic heating on the extracted agar in terms of yield, carbohydrates' composition, monosaccharides profile, and gelling ability was also envisaged.Overall, significant differences in the extraction of each family of compounds between ohmic and conventional extractions were observed, being more pronounced at the best solvent for each compound (100% water for carbohydrates, 75:25 water/ethanol for proteins, 75:25 and 50:50 water/ethanol for phenolic compounds and 25:75 water/ethanol for pigments). Higher extraction yields were achieved for ohmic heating at 1 h, except for 100% water, probably indicating accelerated extraction kinetics promoted by the presence of electric field effects. Furthermore, the gelling ability of agar and the antioxidant activity were not impaired by the use of moderate electric fields. Therefore, ohmic heating is an interesting alternative, with reduced energy consumption and improved extraction performances, to recover functional ingredients or additives from seaweeds for the food industry.

Este livro de Ema Sofia Leitão, baseado na tese de doutoramento que a autora desenvolveu na Universidade de Cardiff, Reino Unido, constitui um excelente contributo para os estudos das crianças e da televisão...

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