Influence of irradiance, dissolved nutrients and salinity on the colour and nutritional characteristics of Gracilariopsis longissima (Rhodophyta)

Abstract

Colour is immediately perceived by the consumer and crucial for product attractiveness. In this study, the possibility of obtaining different colour schemes in the rhodophyte Gracilariopsis longissima using short cultivation protocols (i.e. 9 days) was explored. In a first factorial experiment, the effects of salinity (25‰, 35‰ and 45‰), irradiance (60 and 120 μmol photons m-1 s-1) and nutrient conditions (N&P enrichment, no enrichment) on the growth, pigment concentration and colour of G. longissima were assessed. The results indicated that growth rate and phycocyanin were influenced by the three variables, whereas the concentration of other pigments (cholophyll a, carotenoids and phycoerytrine) was significantly influenced by irradiance and nutrient conditions. The colour, defined as the RGB signal from the photographed thalli, was mainly affected by irradiance and nutrient conditions. In a second experiment, four culture conditions yielding the most contrasting colour schemes and growth rates were repeated scaling up the experiment to get enough biomass and analyze nutritional properties (lipids, fatty acids, proteins, tissue N and P). The colour schemes and the corresponding culture conditions selected were: i) dark red; high salinity, low irradiance, nutrient enrichment; ii) light red; medium salinity, high irradiance, nutrient enrichment; iii) brownish; low salinity, low irradiance; no enrichment; and iv) green-yellowish; low salinity, high irradiance, no enrichment. These conditions caused marked differences in the nutritional properties of the thalli. The light red colour showed the best nutritional characteristics. Overall, G. longissima was not a suitable source of omega 3 (maximum lipid content 1.6%; n-6/n-3 >10), but can be a source of Fe (0.34-0.53 mg g-1 DW) and K (161-103 mg g-1 DW) whereas its K:Na ratio can be enhanced under increasing salinity. The fast ecophysiological response, and its wide tolerance to environmental conditions, makes this species and excellent candidate for the development of short cultivation prococols.