Calle Niemi’s research while affiliated with Swedish University of Agricultural Sciences and other places

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Publications (9)


Fatty acid analysis in microalgal mono- and polycultures using diffuse reflectance infrared Fourier transform spectroscopy coupled with partial least squares analysis
  • Article

June 2024

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8 Reads

Heliyon

Calle Niemi

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Francesco G. Gentili

Fatty acids are of particular interest for industrial applications of microalgal feedstock, as these have a wide array of different uses such as pharmaceuticals and biofuels. Fourier transform infrared (FTIR) spectroscopic techniques used in combination with multivariate prediction modeling are showing great potential as analytical methods for characterizing microalgal biomass. The present study investigated the use of diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) coupled with partial least squares regression (PLSR) to estimate fatty acid contents in microalgae. A prediction model for microalgal samples was developed using algae cultivated in both Bold's basal medium (BBM) and sterilized municipal wastewater under axenic conditions, as well as algal polycultures cultivated in open raceway ponds using untreated municipal wastewater influent. This universal prediction model was able to accurately predict microalgal samples of either type with high accuracy (RMSEP = 1.38, relative error = 0.14) and reliability (R2 > 0.92). DRIFTS in combination with PLSR is a rapid method for determining fatty acid contents in a wide variety of different microalgal samples with high accuracy. The use of spectral characterization techniques offers a reliable and environmentally friendly alternative to traditional labor intensive techniques based on the use of toxic chemicals.


Biochemical and spectral characterization of micro- and macroalgae

January 2024

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20 Reads

Algae contain many compounds which are of interest to the pharmaceutical, agricultural and food industries, among others. Despite the potential for many applications, a quick, accurate and inexpensive method for characterising algae is lacking. The objective of this thesis was to investigate the ability to determine protein, carbohydrate and fatty acid contents in algae, using infrared spectroscopy. Algal samples were analysed using some of the most accurate chemical methods, by hydrolysing proteins and polysaccharides and quantifying the resulting amino acid and monosaccharide contents using chromatography techniques. Fatty acid contents were similarly quantified by extraction followed by gas chromatography. This data was subsequently used to calibrate spectral prediction models, using different infrared spectroscopies. The accuracy of protein prediction by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and near-infrared spectroscopy (NIR) using partial least squares regression (PLSR) was compared to traditional methods like N-protein ratios and colorimetric assays. DRIFTS, attenuated total reflectance (ATR) Fourier transform infrared spectroscopy (ATR) and NIR were also comparatively used to characterise seaweed carbohydrates. Fatty acid contents were studied using DRIFTS in both microalgae and seaweeds. Infrared spectroscopy coupled with PLSR was shown to be highly accurate in characterising algal biomass, provided a sufficiently robust library of calibration samples. These methods require little or no chemicals and are rapid and easy to use, making them both environmentally and economically attractive.



Fig. 1. Representative spectra of a brown and a red seaweed species. A. esculenta (dark blue line) from the Faroe Islands and P. palmata (light red line) from Bodø, Norway. a) Processed DRIFTS spectra. The overlapping bands of from proteins (Amide I) and alginate C--O stretches at approximately 1665 and 1620 cm 1 , respectively, are indicated. b) SNV-corrected NIR spectra. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Seaweed samples used for prediction modelling (total n = 45).
Linear and PLS regression protein prediction results.
Rapid and accurate determination of protein content in North Atlantic seaweed by NIR and FTIR spectroscopies
  • Article
  • Full-text available

October 2022

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205 Reads

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48 Citations

Food Chemistry

Calle Niemi

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[...]

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Francesco G. Gentili

Seaweed is considered a potentially sustainable source of protein for human consumption, and rapid, accurate methods for determining seaweed protein contents are needed. Seaweeds contain substances which interfere with common protein estimation methods however. The present study compares the Lowry and BCA protein assays and protein determination by N-ratios to more novel spectroscopic methods. Linear regression of the height or the integrated area under the Amide II band of diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to predict seaweed protein with good prediction performance. Partial least squares regression (PLSR) was performed on both DRIFTS and near-infrared (NIR) spectra, with even higher prediction accuracy. Spectroscopy performed similar to or better than the calculated N-ratio of 4.14 for protein prediction. These spectral prediction methods require minimal sample preparation and chemical use, and are easy to perform, making them environmentally sustainable and economically viable for rapid estimation of seaweed protein.

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Cold stress stimulates algae to produce value-added compounds

July 2022

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55 Reads

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8 Citations

Bioresource Technology Reports

Two cold-tolerant microalgae, Chlorella vulgaris and Scenedesmus sp., were grown at 22 and 5 °C. At the lower temperature, the microalgae showed substantial biochemical and morphological changes. The soluble sugar profile in response to low-temperature cultivation was very different in the two strains. C. vulgaris increased both the sucrose and raffinose family oligosaccharides (RFOs) content at 5 °C while Scenedesmus sp. drastically reduced the sucrose content. Both strains increased the total fatty acid methyl ester (FAME) content when grown at 5 °C. However, the FAME profiles were very different: C. vulgaris mainly increased C18:1 and less so C18:3, while Scenedesmus sp. decreased C18:1 but greatly increased C18:3. The morphology of C. vulgaris changed slightly at the lower temperature, while Scenedesmus sp. showed substantial changes in the size and shape. Low temperature triggered the synthesis of unsaturated fatty acids that are essential for human nutrition.


Extraction Technologies for Functional Lipids

July 2021

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32 Reads

Algal functional lipids are a group of compounds that have recently attracted a lot of interest both from a scientific and an economic point of view. Microalgae are particularly rich in functional lipids such as omega‐3 polyunsaturated fatty acids and carotenoids. These interesting compounds are often tightly entrapped inside the algal cells; hence they need to be extracted to be collected. Generally extraction can include different steps such as pretreatment (dehydration, cell disruption), extraction, and post‐treatment (separation/fractionation). Extraction methods can be divided into conventional and nonconventional or novel methods. Conventional methods are based on traditional organic solvents, while novel methods include new greener and environmentally friendly solvents such as ionic liquid and/or methods such as supercritical fluid (CO2) extraction. In this chapter conventional and novel extraction methods and the most common cell disruption techniques are discussed. Among the novel methods, the chapter focuses on ionic liquid, supercritical fluid extraction, and pressure liquid extraction.


The use of natural organic flocculants for harvesting microalgae grown in municipal wastewater at different culture densities

March 2021

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114 Reads

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15 Citations

Physiologia Plantarum

Harvesting microalgae from liquid culture is a difficult issue to solve and is most commonly done through settling. However, settling is a slow process on its own and generally needs to be induced chemically or by introducing stress to the culture. Polymeric, cationic substances, such as cationised starch and chitosan, are often used for flocculation and settling. These large, positively charged molecules form large clusters with suspended particles in the liquid medium. In the present study, three natural organic flocculants (cationic starch, chitosan and acacia tannin S5T) were tested to harvest microalgal cultures grown in wastewater. Two microalgal species, one strain of Chlorella vulgaris and one strain of Scenedesmus obliquus, were cultured in municipal wastewater for different lengths of time, and settled using either cationic starch, chitosan, or acacia tannin S5T. Results indicated that S5T worked with approximately the same efficiency in the two assayed species, although it requires a relatively high dosage to function (about 300 mg/L), while the other two flocculants varied from species to species. This article is protected by copyright. All rights reserved.


Screening Suitability of Northern Hemisphere Algal Strains for Heterotrophic Cultivation and Fatty Acid Methyl Ester Production

April 2020

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122 Reads

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9 Citations

Molecules

Rapid rises in atmospheric CO2 levels derived from fossil fuel combustion are imposing urgent needs for renewable substitutes. One environmentally friendly alternative is biodiesel produced from suitable microalgal fatty acids. Algal strains normally grow photoautotrophically, but this is problematic in Northern areas because of the light limitations for much of the year. Mixotrophic and particularly heterotrophic strains could be valuable, especially if they can be cultivated in municipal wastewater with contents of nutrients such as nitrogen and phosphorous that should be reduced before release into receiving water. Thus, the aim of this study was to screen for microalgal strains suitable for heterotrophic cultivation with a cheap carbon source (glycerol) for biodiesel production in Nordic, and other high-latitude, countries. One of the examined strains, a Desmodesmus sp. strain designated 2-6, accumulated biomass at similar rates in heterotrophic conditions with 40 mM glycerol as in autotrophic conditions. Furthermore, in heterotrophic conditions it produced more fatty acids, and ca. 50% more C18:1 fatty acids, as well as showing a significant decrease in C18:3 fatty acids, all of which are highly desirable features for biodiesel production.


Citations (6)


... The degree of methyl esterification (DME) was estimated by the ratio of moles of esterified D-galacturonic acid to the sum of the relative moles of unesterified and esterified D-galacturonic acid. The total sugar content was calculated from the sum of all monosaccharide residues determined in the GC/MS analysis, expressed as a percentage [56]. ...

Reference:

Extraction of Purple Prickly Pear (Opuntia ficus-indica) Mucilage by Microfiltration, Composition, and Physicochemical Characteristics
Quantitative and qualitative saccharide analysis of North Atlantic brown seaweed by gas chromatography/mass spectrometry and infrared spectroscopy
  • Citing Article
  • November 2023

International Journal of Biological Macromolecules

... Protein contents of the extracts were determined using the Pierce™ Bicinchoninic acid (BCA) Protein Assay Kit (Thermo Fisher Scientific Inc., Illinois, USA) complying with the manufacturer's recommendations as also followed in several studies [31][32][33]. Briefly, 25 μL of bovine serum albumin (BSA) standard (0-2 mg/mL) and sample extracts (2 mg/ mL) prepared in a similar way as in 2.3.1., were mixed with 200 μL of the BCA working reagent (50:1, Reagent A (mix of sodium carbonate, sodium bicarbonate, bicinchoninic acid and sodium tartrate in 0.1 M sodium hydroxide): Reagent B (4 % cupric sulfate)). ...

Rapid and accurate determination of protein content in North Atlantic seaweed by NIR and FTIR spectroscopies

Food Chemistry

... decreased(Xin et al., 2011).Lindberg et al. (2022) grew Scenedesmus sp. B2-2 at 5 C and observed an increase in the total fatty acid methyl ester content when compared to the control that was grown at 22 C(Lindberg et al., 2022). ...

Cold stress stimulates algae to produce value-added compounds
  • Citing Article
  • July 2022

Bioresource Technology Reports

... The most commonly employed large-scale method for collecting these byproducts involves coagulation-flocculation followed by gravitational sedimentation [16]. However, conventional coagulants can metal contamination from into the final products [17]. Consequently, recent studies have explored the integration of natural coagulants, such as those derived from plant tannins, into this method to ensure the safe reuse of the effluent and biomass generated [15,18,19]. ...

The use of natural organic flocculants for harvesting microalgae grown in municipal wastewater at different culture densities

Physiologia Plantarum

... The FTIR spectra of the L. nigrescens particles, the L. nigrescens particles after Cu 2+ adsorption, the seaweed residue and the seaweed residue after Cu 2+ adsorption are shown in Figure 2a. The peaks at 3431 cm −1 and 2924 cm −1 were associated with O-H stretching vibration and C-H antisymmetric stretching vibration [33,34]. The peak at 1033 cm −1 was due to the C-O-C stretching vibration from the carbohydrates in algal cell wall. ...

Screening Suitability of Northern Hemisphere Algal Strains for Heterotrophic Cultivation and Fatty Acid Methyl Ester Production

Molecules