Taxonomic identification of Monostroma from the Zhanjiang coastal area and nutritional ingredient analysis of typical sample

Monostromatic green algae with fronds consisting only of horizontally arranged single cell layers are widely distributed from temperate to tropical seas worldwide. Monostroma Thuret 1854, Gayralia Vinogradova 1969, and Protomonostroma Vinogradova 1969 are among the main monostromatic green algal genera. Monostroma (Chlorophyta, Ulvophyceae) is cosmopolitan and comprises 55 species, of which only 32 are currently taxonomically confirmed. A number of Monostroma species are attracting global attention due to theirs economic importance, mainly in the food and cosmetic industries. In addition, chemicals with antiviral and anticoagulant properties were recently isolated from some species of the Monostroma genera. Zhanjiang city is bounded on three sides by the sea with a long coastline (2325.9 km), rich in wild resources of Monostroma species. In order to determine the identity of Monostroma species from Zhanjiang coastal area and analyze their nutritional composition from typical sampling site, this study examined the morphological characteristics (thallus type, size, color; cell size, shape and arrangement, chloroplast shape, position, and pyrenoid number) and nuclear-encoded Internal Transcribed Spacer (ITS) phylogenetics of collected Monostroma species, and then their main nutrient composition (crude protein, ash, moisture, crude fat), amino acid content and mineral composition were determined by the national standard method to evaluate their nutritional values. The results of morphological observation showed that Monostroma thalli with similar morphology presented a green or light green color, had a single-cell layer; the thallus were approximately 9.19-11.12 cm long, 6.85-8.16 cm wide and 35.20-38.80 μm thick; the surface cells were irregular, polygonal, rounded polygons with a size of 11.14-11.42 μm long and 7.25-8.48 μm wide, containing mainly one (≥88%), rarely two (≤8%) or three (≤4%) pyrenoids. The ITS sequences analysis showed that the Monostroma species had an identical nrITS sequence to M. nitidum (AF415170) from Fangchenggang of Guangxi, China, support value on Bayesian posterior probabilities, ML bootstrap and NJ distance bootstrap was 0.99, 88% and 99% respectively. Therefore, all the Monostroma species in Zhanjiang coastal area should be regarded as Monostroma nitidum. Nutrient composition analysis showed that the M. nitidum were high in water content (16.26%), moderate in ash (16.17%), crude protein (10.50%) and crude fat (1.37%) contents. There are many kinds of fatty acids in M. nitidum, including saturated fatty acids (78.57%) and unsaturated fatty acids (21.43%). The amino acid varieties were abundant, including essential amino acids (39.02%) and flavor amino acids (47.93%), which meet the requirements of FAO / WHO standard model. Therefore, the M. nitidum along Zhanjiang coastal area has a great economic value in the food and pharmaceutical industries because of theirs rich nutrients and high nutritional value. These data increase our understanding of the nutrient value of M. nitidum and will promote a healthy and rapid growth of M. nitidum industry.