Iron Bioaccessibility and Speciation in Microalgae Used as a Dog Nutrition Supplement

SIMPLE SUMMARY: In recent years, the microalga market has grown due to its interesting nutritional profile, characterised by high quality proteins, bioactive molecules, and essential trace elements. Therefore, it is of vital importance to study how different species of microalgae can be used in animal nutrition, assessing how they are digested and what percentage of valuable nutrients is really absorbed. Iron is an essential trace element and the availability of natural sources of this nutrient may be useful in dog nutrition. This study investigated the iron content in four microalgae (Chlorella vulgaris, Arthrospira platensis, Haematoccocus pluvialis, and Phaeodactylum tricornutum) with emphasis on the iron bioaccessibility in dogs. The present results show that, in C. vulgaris, a high percentage (30%) of iron was available to be absorbed by the canine gastrointestinal system, suggesting that this microalga could be used as valuable iron supplementation in dog nutrition. ABSTRACT: Chlorella vulgaris, Arthrospira platensis, Haematoccocus pluvialis, and Phaeodactylum tricornutum are species of interest for commercial purposes due to their valuable nutritional profile. The aim of this study was to investigate the iron content in these four microalgae, with emphasis on their iron bioaccessibility assessed using an in vitro digestion system to simulate the process which takes place in the stomach and small intestine of dogs, followed by iron quantification using atomic absorption spectrometry. Furthermore, the extraction of soluble proteins was carried out and size exclusion chromatography was applied to investigate iron speciation. Significant differences (p < 0.004) in iron content were found between C. vulgaris, which had the highest (1347 ± 93 μg g(−1)), and H. pluvialis, which had the lowest (216 ± 59 μg g(−1)) iron content. C. vulgaris, A. platensis, and H. pluvialis showed an iron bioaccessibility of 30, 31, and 30%, respectively, while P. tricornutum showed the lowest bioaccessibility (11%). The four species analysed presented soluble iron mainly bound to proteins with high molecular mass ranging from >75 to 40 kDa. C. vulgaris showed the highest iron content associated with good bioaccessibility; therefore, it could be considered to be an interesting natural source of organic iron in dog nutrition.