# Effects of Heat Treatment Processes: Health Benefits and Risks to the Consumer
## 6 Heat Treatment Influence on Chemical Structure  
The heat treatment of seaweed-based ingredients and foods regularly induces a major chemical modification on their compounds, such as nutrients and bioactive molecules [26]. One of the major changes is in the pigment compounds which give color to the seaweed and, after the heat treatment, change the seaweed's color, mostly in brown seaweeds [12]. Fresh seaweeds are very perishable and start to deteriorate very rapidly after harvest, thus drying is an essential path to working with seaweeds as whole food or at food industry [16]. The most commonly used drying method is sun-drying, which reduces bulk handling and microbial growth, maintaining the characteristics if the seaweed is not directly exposed to sunlight (UV rays interfere greatly with the biochemical structure of photo-sensible compounds, such as phenolic compounds and pigments) [27]. However, when this drying method and other methods are used, the high temperatures can cause a rapid dehydration during the drying process, which can result in undesirable changes in the whole biomass (shrinkage) and chemical compound changes caused by enzymatic and non-enzymatic reactions (such as oxidation) [28]. Additionally, the water flux changes the composition, with partial destruction of the seaweed tissue, releasing various compounds, nutrients and minerals into the solution, decreasing the compounds' yield and nutritional value [29; 30]. Only when considering the mineral part is the heat process important for diminishing the mineral intake to the recommended daily dosage [31]. It is well known that the bioavailability of vegetable compounds is conditioned by the species and abiotic factors (light, oxygen and temperature), and thus, their stability is essential for maintaining the bioavailability of the compounds and also changing the seaweed's nutritional profile. Heat treatment at low temperatures can also reduce the compounds availability in seaweed, as demonstrated by [PERSON] et al. [16], where _H. elongata_ lost nearly 30% of the compounds compared with seaweeds subject to 25 \({}^{\circ}\)C during rehydration. Mainly, the bioactive compounds are lost in direct response to the rise in the heat, due to their chemical structures' heat sensitivity. On the other hand, the antioxidant power also demonstrated a direct response, where the heat reduced the bioactivity, mostly to denaturation of the bioactive molecules and reduction of the compounds to low-molecular-weight compounds by hydrolysis [10; 32]. Thus, some heat processing methods have a different impact on antioxidant activity, as demonstrated by [PERSON] et al. : using blanching increased free radical scavenging in fruits [33]. The pigments also suffer chemical deterioration, and the sugars and polysaccharides are mainly solubilized, reducing the carbohydrates in the processed seaweed; the same happens to vitamins, amino acids (proteins) and minerals [34]. Although it is known that different heat treatments and temperatures significantly change the preservation of seaweed compounds, there is a general lack of knowledge about this complex topic using chemical characterization techniques, mainly spectroscopy and chromatography [10; 12]. Even when similar seaweeds were analyzed, their reaction to the same heat treatment method was very different due to the variation in the seaweeds' compounds and biochemical profile. This was demonstrated by [PERSON] et al. [35], using _Laminaria_ sp. and _Undaria pimnatifida_, where the same bioactive compounds and antioxidants were used. For example, the polyphenol compounds of _Laminaria_ sp. were more stable throughout the heat treatment compared with the polyphenols of _U. pimnatifida_[35]. In the case of proteins, one of the most important nutrients of seaweeds, the bioavailability and content depend on the species analyzed. [PERSON] et al.