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IntroductionAttenuated total reflection (ATR)–Fourier transform infrared (FTIR) analysis is a rapid tool and represents a snapshot of all molecules present in a (plant) sample. Most alternative techniques for biochemical analyses of plant biomass require destructive sampling, complex and laborious sample pre-treatment, and precise and costly analysis. These analyses are often limited to soluble compounds instead of all compounds present. Such complicated procedures are not efficient for manipulative studies that involve repeated sampling and rapid nutrient changes over time, such as in agro-industrial cultivation studies.MethodsIn our study, the green seaweed species Ulva laetevirens (Chlorophyta) was cultivated under different nutritional regimes in onshore cultivation tanks. The regimes were nitrogen and phosphorus repletion, nitrogen depletion, phosphorus depletion, and light limitation. Samples were taken and tested according to common laborious analysis methods to determine the biochemical composition of polysaccharides, proteins, carbon, and nitrogen. These results were compared with the potential of ATR-FTIR spectroscopy combined with multivariate analysis to allow for prediction of biomass composition.ResultsStatistical analysis of the spectra showed that the samples were clustered according to the nutritional regime during the incubation of U. laetevirens. This made it possible to deduce which abiotic factors were replete or deplete during cultivation. Furthermore, partial least square regression analysis proved the most suitable method to predict carbohydrate concentration and nitrogen content present in the biomass.Discussion/conclusionOn the basis of these findings, it is concluded that ATR-FTIR spectroscopy is an efficient and rapid alternative tool for qualitative and quantitative determination of the biochemical composition of U. laetevirens that can be used in industrial cultivation setups.

The microalgae Rhodomonas sp. is known as an excellent feed source for live feed organisms such as copepods. The main benefits of feeding Rhodomonas to live feed animals are attributed to the relative high polyunsaturated fatty acid (PUFA) level, the combination of containing both docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), and the ratio between these fatty acids (FA). It has been shown that microalgae are able to accumulate valuable metabolites, such as lipids, under adverse conditions. The easiest and most inexpensive method to induce stress to microalgae is through nitrogen (N) starvation. In this study, the effect of N-starvation on biomass concentration, cell volume, and cellular composition, such as fatty acid concentration and composition, and phycoerythrin (PE) concentration of Rhodomonas sp. during a period of 8 days, was investigated. The research was divided into two stages. In the first (growth) stage, Rhodomonas sp. was cultivated in small 400 ml photobioreactors (Algaemist-S) under optimal conditions in turbidostat mode, which reached a biomass concentration of 1.5 gDW L–1 and dilution rate of 1.3 d–1. Samples were taken every 24 h for cell density and volume and productivity measurements in order to ensure a healthy and stable culture. In the next stage (N-starvation), the biomass was washed and transferred in a reactor filled with N-depleted medium. During N-starvation, samples were taken for biomass concentration, cell volume, PE and FA composition. The results of this study demonstrate that the lipid content increased significantly from 9% (t = 0 h) to 30% (t = 120 h) of the dry weight. After 120 h of N-starvation, the total FA content of Rhodomonas sp. remained stable for the remainder of the experiment (next 72 h). The highest increase of the FA concentration was represented by C16:0, C:18:1, C18:2, and C18:3, with highest concentrations after 120 h of starvation. The maximum EPA and DHA concentrations were observed after 48 h of starvation, while the maximum DHA to EPA ratio was detected at the end of the starvation.