Seaweed proteins - how to get to them? Effects of processing on nutritional value, bioaccessibility and extractability

Abstract

As a consequence of the expected population growth towards 2050, the demand for food, and in particular proteins, will increase. Due to limited resources of arable land and freshwater, this increase cannot come in the agricultural sector alone. At present, the utilization of marine environments for food production is low and should be increased. Seaweeds are fast-growing plants occurring in marine environments worldwide and some of them have proven to be rich in proteins. Living in oceans, they neither need arable land nor freshwater in order to grow and as primary producers they absorb inorganic compounds from their surroundings and convert them into macronutrients. The overall aims of this project were to examine the nutritional quality, along with effects of processing on bioaccessibility and extractability of seaweed proteins, and to evaluate their suitability as food, feed or ingredients in such. The specific goals were limited to i) document the nutritional composition in ten different seaweed species, ii) study the impact of heat treatment on the bioaccessibility of seaweed proteins, and iii) study the effect of enzymatic treatment on the bioaccessibility and extractability of seaweed proteins. The lipid contents in seaweeds were generally low, while mineral contents were high. The protein contents were generally higher in red seaweeds than in the other classes. However, the variation in protein contents within the brown and green seaweeds were large. The protein contents were generally lower than presented in many other studies, most likely due to methodological differences. However, also seasonal and geographical variations may have influenced this. The proteins in several of the analysed seaweeds were found to be complete proteins, as they contained sufficient amounts of the essential amino acids in order to cover the human requirements. Both protein content and quality of dulse (Palmaria palmata) were higher compared to that of wheat, corn and rice. In P. palmata, heat treatment increased the amount of accessible amino acids and the amount of amino acids liberated during a simulated gastrointestinal digestion model. The contents of essential amino acids were not negatively affected as a result of the process. For winged kelp (Alaria esculenta), no equivalent changes were observed. Also enzymatic treatment of P. palmata increased the amount of accessible amino acids and the amount of amino acids liberated during a simulated gastrointestinal digestion model. Enzymatic treatment also increased the protein extractability.