Evaluation of the volatile composition and sensory properties of five species of microalgae

Characterizing and decoding the key odor compounds of Spirulina platensis at different processing stages by sensomics

Processing is an indispensable technology in the preparation of Spirulina platensis (S. platensis). The key odorants in liquids, muds, and powders from S. platensis (NM and GZ) were characterized. A total of 90 odorants were identified and 41 odorants were sniffed with the flavor dilution (FD) factors ranging from 1 to 729. Among them, nonanal, decanal, d-limonene, β-cyclocitral, and β-ionone with FD factors ≥1 were detected in S. platensis during the whole processing stages. In addition, heptanal, (E, E)-2,4-nonadienal, trans-4,5-epoxy-(E)-2-decenal, 1-hepten-3-one, isophorone, 3-ethyl-2,5-dimethylpyrazine, and α-ionone exhibited higher odor activity values in powders; β-myrcene, methional, and S-methyl methanethiosulphonate were key odorants in muds; while trans-3-penten-2-ol was key odorant in liquids. Besides, the GZ-mud presented stronger earthy and fishy odor than NM-mud. S. platensis powders have the stronger grassy odor, roasted odor, and marine odor than S. platensis muds. Overall, drying process promotes the formation of aldehydes, heterocyclic compounds, and terpenoids.

The Volatile Compounds Change during Fermentation of Saccharina japonica Seedling

It is important to eliminate the fishy odor and improve the aroma quality of seafood. In this study, the Saccharina japonica (S. japonica) seedling, which is a new food material, was investigated for the effects of fermentation with Saccharomyces cerevisiae (S. cerevisiae) through sensory evaluation, GC-MS, and odor activity value (OAV) analysis. GC-MS analysis revealed the presence of 43 volatile compounds in the unfermented S. japonica seedling, with 1-octen-3-ol, hexanal, and trans-2,4-decadienal identified as the main contributors to its fishy odor. After fermentation with S. cerevisiae, 26 volatile compounds were identified in the S. japonica seedling. Notably, the major malodorous fish compounds, including 1-octen-3-ol, hexanal and trans-2,4-decadienal, were no longer present. The results indicate that fermentation with S. cerevisiae is an effective method for removing fishy malodor compounds and enhancing the volatile components with fruity, sweet, green, and floral notes in the Saccharina japonica seedling. This process facilitates the elimination of fishy malodor and enhance the fruity, sweet, green, and floral notes of S. japonica seeding and other seaweeds.

Volatile Profiling of Spirulina Food Supplements

Spirulina, a cyanobacterium widely used as a food supplement due to its high nutrient value, contains volatile organic compounds (VOCs). It is crucial to assess the presence of VOCs in commercial spirulina products, as they could influence sensory quality, various processes, and technological aspects. In this study, the volatile profiles of seventeen commercial spirulina food supplements were determined using headspace solid-phase microextraction (HS-SPME), coupled with gas chromatography-mass spectrometry (GC-MS). The identification of volatile compounds was achieved using a workflow that combined data processing with software tools and reference databases, as well as retention indices (RI) and elution order data. A total of 128 VOCs were identified as belonging to chemical groups of alkanes (47.2%), ketones (25.7%), aldehydes (10.9%), alcohols (8.4%), furans (3.7%), alkenes (1.8%), esters (1.1%), pyrazines (0.8%), and other compounds (0.4%). Major volatiles among all samples were hydrocarbons, especially heptadecane and heptadec-8-ene, followed by ketones (i.e., 4-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3-buten-2-one, β-ionone, 2,2,6-trimethylcyclohexan-1-one), aldehydes (i.e., hexanal), and the alcohol oct-1-en-3-ol. Several volatiles were found in spirulina dietary supplements for the first time, including 6,10-dimethylundeca-5,9-dien-2-one (geranylacetone), 6,10,14-trimethylpentadecan-2-one, hept-2-enal, octanal, nonanal, oct-2-en-1-ol, heptan-1-ol, nonan-1-ol, tetradec-9-en-1-ol, 4,4-dimethylcyclohex-2-en-1-ol, 2,6-diethylpyrazine, and 1-(2,5-dimethylfuran-3-yl) ethanone. The methodology used for VOC analysis ensured high accuracy, reliability, and confidence in compound identification. Results reveal a wide variety of volatiles in commercial spirulina products, with numerous newly discovered compounds, prompting further research on sensory quality and production methods.

Dairy, Plant, and Novel Proteins: Scientific and Technological Aspects

Alternative proteins have gained popularity as consumers look for foods that are healthy, nutritious, and sustainable. Plant proteins, precision fermentation-derived proteins, cell-cultured proteins, algal proteins, and mycoproteins are the major types of alternative proteins that have emerged in recent years. This review addresses the major alternative-protein categories and reviews their definitions, current market statuses, production methods, and regulations in different countries, safety assessments, nutrition statuses, functionalities and applications, and, finally, sensory properties and consumer perception. Knowledge relative to traditional dairy proteins is also addressed. Opportunities and challenges associated with these proteins are also discussed. Future research directions are proposed to better understand these technologies and to develop consumer-acceptable final products.

Effect of seawater on the biomass composition of Spirulina produced at a pilot-scale

The microalga Arthrospira platensis BEA 005B was produced in 11.4 m3 raceway photobioreactors and a culture medium based on commercial fertilisers and either freshwater or seawater. The biomass productivity of the reactors operated at a fixed dilution rate of 0.3 day-1 decreased from 22.9 g·m-2·day-1 when operated using freshwater to 16.3 g·m-2·day-1 when the biomass was produced using seawater. The protein content of the biomass produced in seawater was lower; however, the content of essential amino acids including valine, leucine and isoleucine was higher. Seawater also triggered the production of carotenoids and altered the synthesis and accumulation of fatty acids. For example, the biomass produced using seawater showed a 319% and 210% higher content of oleic and eicosenoic acid, respectively. The results demonstrate that it is possible to produce the selected microalga using seawater after an adaptation period and that the composition of the produced biomass is suitable for food applications.

Enriched Pea Protein Texturing: Physicochemical Characteristics and Application as a Substitute for Meat in Hamburgers

There is currently a growing trend towards the consumption of vegetable protein, even if it shows some deficiencies in essential amino acids. It has been driven by consumer passion for health and wellness, environmental sustainability, animal welfare and the flexitarian lifestyle. However, the formulation of plant protein food analogues to meat products is complicated by the technological properties of isolated plant protein. One of the processes used to improve these properties is the texturisation of the protein by extrusion, as well as the use of other plant materials that can enrich the formulation. Therefore, the aim of this study was to evaluate the effect of pea protein (PP) enriched with lucerne (L), spinach (S) and Chlorella (C) in powdered and texturised forms on the physicochemical properties and extrusion parameters, and to evaluate its technological and sensory quality as a meat analogue in vegetal hamburgers. Texturisation reduced the number of soluble components released, thus reducing the molecular degradation in extruded material. The texturised samples were significantly (p < 0.05) less hygroscopic than the non-textured samples. Once the properties of the powder and texturised had been analysed, they were used to prepare vegetal hamburgers. The addition of vegetable-enriched texturised samples with high chlorophyll content led to more intense colour changes in the vegetal hamburgers during cooking, with PP+C providing the darkest colouring, and also resulted in a final product more similar to a traditional meat hamburger, with higher overall and meat odour/flavour intensity, hardness, juiciness and chewiness, and less legume and spice odour and flavour. Overall, texturisation improved the technological properties of the enriched protein isolate, allowing for more efficient production of vegetal hamburgers.

A review of volatile compounds in edible macroalgae

Seaweeds (green algae, red algae and brown algae) are rich in nutrients, and incorporating algae into the human diet can provide important health benefits. However, consumer acceptance of food is closely related to its flavor, and in this respect, volatile compounds are key factors. This article reviews the extraction methods and composition of volatile compounds from Ulva prolifera, Ulva lactuca, Sargassum spp. and economically valuable cultured seaweeds such as Undaria pinnatifida, Laminaria japonica, Neopyropia haitanensis and Neopyropia yezoensis. Research found that the volatile compounds of the above seaweeds were composed mainly of aldehydes, ketones, alcohols, hydrocarbons, esters, acids, sulfur compounds, furans and small amounts of other compounds. Volatile compounds such as benzaldehyde, 2-octenal, octanal, β-ionone and 8-heptadecene have been identified in several macroalgae. This review argues that more research on the volatile flavor compounds of edible macroalgae is required. Such research could aid new product development or widen applications of these seaweeds in the food or beverage sectors.

Perspective: Multiomics and Machine Learning Help Unleash the Alternative Food Potential of Microalgae

Food security has become a pressing issue in the modern world. The ever-increasing world population, ongoing COVID-19 pandemic, and political conflicts together with climate change issues make the problem very challenging. Therefore, fundamental changes to the current food system and new sources of alternative food are required. Recently, the exploration of alternative food sources has been supported by numerous governmental and research organizations, as well as by small and large commercial ventures. Microalgae are gaining momentum as an effective source of alternative laboratory-based nutritional proteins as they are easy to grow under variable environmental conditions, with the added advantage of absorbing carbon dioxide. Despite their attractiveness, the utilization of microalgae faces several practical limitations. Here, we discuss both the potential and challenges of microalgae in food sustainability and their possible long-term contribution to the circular economy of converting food waste into feed via modern methods. We also argue that systems biology and artificial intelligence can play a role in overcoming some of the challenges and limitations; through data-guided metabolic flux optimization, and by systematically increasing the growth of the microalgae strains without negative outcomes, such as toxicity. This requires microalgae databases rich in omics data and further developments on its mining and analytics methods.

Biotechnological Approaches for Biomass and Lipid Production Using Microalgae Chlorella and Its Future Perspectives

Heavy reliance on fossil fuels has been associated with increased climate disasters. As an alternative, microalgae have been proposed as an effective agent for biomass production. Several advantages of microalgae include faster growth, usage of non-arable land, recovery of nutrients from wastewater, efficient CO₂ capture, and high amount of biomolecules that are valuable for humans. Microalgae Chlorella spp. are a large group of eukaryotic, photosynthetic, unicellular microorganisms with high adaptability to environmental variations. Over the past decades, Chlorella has been used for the large-scale production of biomass. In addition, Chlorella has been actively used in various food industries for improving human health because of its antioxidant, antidiabetic, and immunomodulatory functions. However, the major restrictions in microalgal biofuel technology are the cost-consuming cultivation, processing, and lipid extraction processes. Therefore, various trials have been performed to enhance the biomass productivity and the lipid contents of Chlorella cells. This study provides a comprehensive review of lipid enhancement strategies mainly published in the last five years and aimed at regulating carbon sources, nutrients, stresses, and expression of exogenous genes to improve biomass production and lipid synthesis.

Production and Analysis of Beer Supplemented with Chlorella vulgaris Powder

The microalgae Chlorella vulgaris is a cheap source of nutrients and bioactive compounds, and thus is used in many interventional studies. This study evaluated the potential effects of C. vulgaris powder on fermentation parameters; sensory, phytochemical, and antioxidant activity; and the abundance of volatile organic compounds (VOCs) of treated versus control beers. A German Pilsner-style lager beer (GPB) was brewed and supplemented with C. vulgaris at various levels (3.3, 5, and 10 g/L) after primary fermentation. The apparent °Brix and pH was used to monitor the progress of fermentation. The 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydrogen peroxide (H2O2) was used to measure the antioxidant activity of beers. Addition of C. vulgaris increased the concentration of total polyphenols, total flavonoids, and antioxidant activity of treated beers (CGB) compared to the control (GPB). Treatment had no effects (p > 0.05) on higher alcohols such as 3-methyl-1-butanol, 2-hexanol, and phenylethyl alcohol. An increase in the concentration of C. vulgaris had no significant effects on sensory perception of enriched beers. The results showed that C. vulgaris could be used as a potential ingredient for designing functional beer with improved health benefits.

Active aroma compounds assessment of processed and non-processed micro- and macroalgae by solid-phase microextraction and gas chromatography/mass spectrometry targeting seafood analogs

The odor of four algae was investigated and compared to evaluate the potential of these algae to mimic shrimp aroma. Solid-phase microextraction followed by gas chromatography analysis coupled with sensory analysis was used for performance assessment. The volatile organic compounds were determined in non-processed, raw samples (r), and processed cooked (c) and cooking water (w) samples for two microalgae [Nannochoropsis oceanica (NO) and Tetraselmis chuii (TC)], two macroalgae [Ulva rígida (UR) and Saccharina latíssima (SL)], and shrimp Vannamei cong (SH). The results showed significant differences in the composition of volatile compounds between macroalgae and microalgae. The key odorants in macroalgae were octanal, 2-octenal, nonanal, and β-ionone, and in microalgae were 1,5-octadien-3-ol, hexanal, 2,4-decadienal, 2-octenal, octanal, nonanal, 3,5-octadien-2-one, and terpenes. The PCA analysis of GC-MS data showed odor similarities between the studied samples, which were divided into five main groups: (1) TC(c) and TC(w); (2) TC(r) and NO(c); (3) NO(r), NO(w), and SL(w); (4) SL(c), UR(r), UR(c), and UR(w); and (5) SL(r). The data from the sensory analysis show bigger similarities between the macroalgae and the shrimp odor. Overall, the data provided indicate that the cooking water and cooked samples are very similar in key components of odorants. These features allow the possibility to use algae and their processed resulting products as a shrimp flavor replacement in non-animal-based food formulations, thus decreasing the pressure on seafood crops and aquaculture-associated issues leading to more sustainable livestock. Furthermore, circularity and waste reduction may be further enabled by the use of otherwise wasted cooking water as an odorant agent.

Algal volatiles - the overlooked chemical language of aquatic primary producers

Volatiles are important 'infochemicals' that play a crucial role in structuring life on our planet, fulfilling diverse functions in natural and artificial systems. Algae contribute significant quantities to the global budget of volatiles, but the ecological roles of aquatic volatiles are not well understood. In this review, we discuss the current knowledge of volatile compounds from freshwater and marine microalgae and marine macroalgae, with a focus on their ecological roles. We highlight the multiple reported functions of biogenic volatiles, ranging from intraspecific communication for reproduction, intra-bloom signalling and antioxidant functions, to various interspecific signal exchanges that may allow herbivores to locate them and function in defence against competitors and predators. Beyond reviewing our current understanding, we specifically highlight major knowledge gaps and emerging questions for algal volatile research. These novel perspectives have the potential to improve our understanding of aquatic ecosystems and thus need to be addressed in future research. Filling these gaps and addressing these questions will facilitate humanity's efforts to exploit aquatic volatiles in various applications.

Characterisation of the volatile profile of microalgae and cyanobacteria using solid-phase microextraction followed by gas chromatography coupled to mass spectrometry

Microalgae and microalgae-derived ingredients are one of the top trends in the food industry. However, consumers’ acceptance and purchase intention of a product will be largely affected by odour and flavour. Surprisingly, the scientific literature present a very limited number of studies on the volatile composition of microalgae and cyanobacteria. In order to fill the gap, the main objective of the present study was to elucidate the volatile composition of seven microalgal and cyanobacterial strains from marine and freshwaters, with interest for the food industry while establishing its potential impact in odour. Among the seven selected strains, Arthrospira platensis showed the highest abundance and chemical diversity of volatile organic compounds (VOCs). Aldehydes, ketones, and alcohols were the families with the highest diversity of individual compounds, except in Arthrospira platensis and Scenedesmus almeriensis that showed a profile dominated by branched hydrocarbons. Marine strains presented a higher abundance of sulfur compounds than freshwater strains, while the ketones individual profile seemed to be more related to the taxonomical domain. The results of this study indicate that the VOCs composition is mainly driven by the individual strain although some volatile profile characteristics could be influenced by both environmental and taxonomical factors.

Effect of formulations and fermentation processes on volatile organic compounds and prebiotic potential of gluten-free bread fortified by spirulina (Arthrospira platensis)

Gluten free (GF) foods, designed and marketed for the needs of people who are unable to metabolize gluten, in recent years have aroused growing interest that has led to the conquest of important market segments, with a strongly growing trend. Given the low protein content of standard GF flours, it is particularly important to fortify GF foods, and to study the effect that this process exerts on functional and sensorial characteristics. In this work, fortification of GF bakery goods was done with the addition of Arthrospira platensis (spirulina) flour. Two different dough formulations (with and without fortification) were fermented by four different processes, including spontaneous, single strains and sourdough starters. The baked products were then subjected to "consumer's tests". During the process, fermentation performances, prebiotic activity, and the VOC (Volatile Organic Compound) profiles were analyzed and compared through robust multivariate statistics. The results obtained evidenced that fortification led to a product with more abundant (medium organic acids) and exclusive bioactives (thymol, borneol, and nicotinic acid), which were correlated to the prebiotic activity of spirulina breads. This work, for the first time indicates that spirulina can be used to fortify GF bakery, improving also its functional potential.

Algae as a Source of Natural Flavors in Innovative Foods

As a result of their nutritive values, algae have been used as a food resource for centuries, and there is a growing interest to use them as enrichment ingredients in food products. However, food product acceptance by consumers is strongly linked to their organoleptic properties, especially the aroma, taste, and a combination of the two, flavor. With regard to edible algae, "fresh seashore", "seafood-like", "cucumber green", and "earthy" are descriptors commonly used to define their aromas. Several families of molecules participate in the diversity and peculiarities of algal aromas: pungent sulfur compounds and marine halogenated components but also herbaceous fatty acid derivatives and fruity-floral terpenoids. In both macroalgae (seaweeds) and microalgae, these compounds are studied from a chemistry point of view (identification and quantification) and a sensorial point of view, involving sensorial evaluation by panelists. As a whole food, a food ingredient, or a feed, algae are valued for their nutritional composition and their health benefits. However, because the acceptance of food by consumers is so strongly linked to its sensorial features, studies have been performed to explore the aromas of algae, their impact on food, their evolution through processing, and their ability to produce selected aromas using biotechnology. This review aims at highlighting algal aromas from seaweed and microalgae as well as their use, their handling, and their processing in the food industry.

A chemometric approach to characterize the aroma of selected brown and red edible seaweeds / extracts

BACKGROUND

Information pertaining to the aromatic profile of seaweeds and seaweed extracts can provide evidence regarding their potential suitability as ingredients in processed foods. To date only limited material has been available on the volatile profiles of some seaweed species. Others in this study have not previously been described. The volatile profiles of dried brown (Himanthalia elongata, Undaria pinnatifida, Alaria esculenta) and red (Porphyra umbilicalis, Palmaria palmata) seaweeds, and a brown seaweed extract (fucoxanthin) from Laminaria japonica were investigated using a chemometric approach to collate data from volatile gas chromatography - mass spectrometry (GC-MS), direct sensory aroma evaluation, and gas-chromatography - olfactometry (GC-O) to obtain a better understanding of their volatile profile and sensory perception.

RESULTS

More than 100 volatile compounds were identified by static headspace solid phase micro-extraction (HS-SPME) and thermal desorption gas chromatography - mass spectrometry (TD GC-MS). Brown seaweeds were characterized by 'grassy/herbal/floral', 'fruity', and 'fatty' aromas, red seaweeds by 'green/vegetable', 'mushroom/earthy' and 'sweet/buttery' aromas, and the fucoxanthin extract by 'rancid' and 'nutty' aromas with an overall lower intensity. Heptanal appeared to be a major odor-active compound in all samples. Other volatiles were more characteristic of each individual seaweed: hexanal, (E,Z)-2,6-nonadienal and 2-pentylfuran for H. elongata; ethyl butanoate and 2,3-butanedione for U. pinnatifida; 6-dimethylpyrazine, (E,Z)-2,6-nonadienal and sulactone for P. palmata; 1-octen-3-ol for P. umbilicalis, heptanone for A. esculenta, and 2-furanmethanol for fucoxanthin.

CONCLUSION

Brown and red seaweeds had distinct sensory properties with individual seaweeds having differing volatiles and odorants. This study provides additional information that can contribute to the development of products incorporating dried seaweeds / extracts that are more acceptable to the consumer. © 2020 Society of Chemical Industry.

Solid-State Fermentation of Arthrospira platensis to Implement New Food Products: Evaluation of Stabilization Treatments and Bacterial Growth on the Volatile Fraction

Arthrospira platensis is a cyanobacterium widely used in food formulation and mainly consumed as a food supplement because of its high amount of proteins, vitamins and minerals. Different probiotic food supplements are present in the market, and a lactic acid fermented food product like dried spirulina could be useful not only to introduce lactic acid bacteria (LAB) with beneficial effects to the diet of consumers, but also to improve or change the aromatic profile of the substrate. Therefore, the aim of this study was the evaluation of lactic acid fermentation of A. platensis biomass, focusing on the consequent changes in the aromatic profile. For this purpose, two different stabilization treatments (UV light treatment and sterilization) were applied prior to fermentation with two LAB strains, Lacticaseibacillus casei 2240 and Lacticaseibacillus rhamnosus GG. The biomass proved to be a suitable matrix for solid-state fermentation, showing a LAB growth of more than 2 log CFU/g in 48 h. The fermentation process was also useful for off-flavor reduction. In particular, the fermentation process significantly influenced the concentration of those compounds responsible for aldehydic/ethereal, buttery/waxy (acetoin and diacetyl), alkane and fermented aromatic notes (isoamyl alcohol). The heat treatment of the matrix, in addition to guaranteed safety for consumers, led to an improved aroma after fermentation. In conclusion, a fermented spirulina powder with a different aromatic profile was obtained with the applied heat treatment. Fermentation with lactic acid bacteria can be an interesting tool to obtain cyanobacterial biomasses with more pleasant sensory properties for potential use in food formulations.

Performance and Milk Composition of Nubian Goats as Affected by Increasing Level of Nannochloropsis oculata Microalgae

Fat supplementation affects the lactational performance of goats and dramatically changes milk nutritive value. In the present experiment, two levels of Nannochloropsis oculata microalgae, a natural source of rumen-protected eicosapentaenoic acid (EPA), were studied in the diet of Nubian goats. Using quintuplicated 3 × 3 Latin square design, fifteen lactating goats, (14 ± 2 months old and 33.0 ± 1.3 kg) after kidding, were randomly assigned into three treatments in an 84-d assay. Goats were offered a basal diet comprising berseem clover, wheat straw and concentrates in 3:2:5, respectively, (control treatment-no supplementation). The other two treatments were supplemented with N. oculata microalgae at 5 g (NOM5 treatment) or 10 g (NOM10 treatment)/doe/d. Without affecting intake, treatments improved (p < 0.01) nutrient digestibility. Supplementations had no effect on ruminal pH and ammonia-nitrogen, however, NOM5 and NOM10 linearly improved (p < 0.05) total volatile fatty acids and propionic acids. N. oculata supplementation linearly increased (p < 0.01) milk yield and lactose content. Supplementation reduced atherogenic index (p = 0.004) and enhanced the concentrations of unsaturated fatty acids and C20:5n3 (EPA). Conclusively, feeding Nubian goats on diet supplemented with N. oculata at 5 and 10 g improved milk production and the nutritive value. No improvements in the performance were observed when N. oculata dose was increased from 5 g to 10 g/doe; thus, 5 g dose is recommended for use.

Low Molecular Weight Volatile Organic Compounds Indicate Grazing by the Marine Rotifer Brachionus plicatilis on the Microalgae Microchloropsis salina

Microalgae produce specific chemicals indicative of stress and/or death. The aim of this study was to perform non-destructive monitoring of algal culture systems, in the presence and absence of grazers, to identify potential biomarkers of incipient pond crashes. Here, we report ten volatile organic compounds (VOCs) that are robustly generated by the marine alga, Microchloropsis salina, in the presence and/or absence of the marine grazer, Brachionus plicatilis. We cultured M. salina with and without B. plicatilis and collected in situ volatile headspace samples using thermal desorption tubes over the course of several days. Data from four experiments were aggregated, deconvoluted, and chromatographically aligned to determine VOCs with tentative identifications made via mass spectral library matching. VOCs generated by algae in the presence of actively grazing rotifers were confirmed via pure analytical standards to be pentane, 3-pentanone, 3-methylhexane, and 2-methylfuran. Six other VOCs were less specifically associated with grazing but were still commonly observed between the four replicate experiments. Through this work, we identified four biomarkers of rotifer grazing that indicate algal stress/death. This will aid machine learning algorithms to chemically define and diagnose algal mass production cultures and save algae cultures from imminent crash to make biofuel an alternative energy possibility.

Evaluation of Microbial Load, Formation of Odorous Metabolites and Lipid Stability during Wet Preservation of Nannochloropsis gaditana Concentrates

Wet preservation of algae allows us to bridge the time period between algae harvest and processing while avoiding the costs and nutritional losses associated with algae drying. This study aimed to identify suitable storage conditions for the wet preservation of Nannochloropsis gaditana concentrates. The impact of storage temperature, time and the way of closing the storage recipient was evaluated using a full factorial design. The effect of acetic acid addition was tested for one storage condition. Storage temperature was the main factor determining the microbial count and had a vast impact on the formation of odorous metabolites. Storage at 20 °C in closed recipients led to rapid O2 consumption, accumulation of malodorous short-chain fatty acids above their odor thresholds, and the production of H2S and methanethiol. These odorous metabolites were not formed or to a much lower extent during 4 °C and 8 °C storage in closed recipients. Acetic acid supplementation (50 mM) suppressed the formation of short-chain fatty acids during 8 °C storage in unsealed recipients and reduced the aerobic microbial count and the number of yeasts and molds by approximately one log unit after 14 days. Yet, acetic acid addition also induced lipid hydrolysis and decreased chlorophyll levels when algae were stored for more than one week. This study demonstrated that temperature control is needed and that acetic acid addition is a promising approach when N. gaditana concentrates are stored for less than one week.

Sensory properties of aqueous dispersions of protein-rich extracts from Chlorella protothecoides at neutral and acidic pH

BACKGROUND

Water-soluble proteins extracted from the heterotrophically cultivated microalga Chlorella protothecoides have been shown to have a good solubility over a broad pH range, which makes them a promising candidate for beverage formulations. This study investigated the sensory properties of dispersions of a protein-rich extract from C. protothecoides at neutral and pH 3.

RESULTS

Sensory acceptance tests of the pure extract revealed an overall low acceptance at pH 7 without sucrose addition. Sensory acceptance was significantly (P ≤ 0.05) increased by lowering the pH to 3 with citric acid, and the addition of 50 g kg^-1 sucrose. Here, overall positive sensory acceptance ratings were achieved up to a protein extract concentration of 40 g kg^-1 . Basic taste evaluations showed only low bitterness scores and no significant (P > 0.05) increase in bitterness with decreasing pH.

CONCLUSION

It is suggested that protein-rich extracts from C. protothecoides have promising sensory properties in beverage formulations. © 2019 The Authors. Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Chemical Profiling of Volatile Organic Compounds in the Headspace of Algal Cultures as Early Biomarkers of Algal Pond Crashes

Algae ponds used in industrial biomass production are susceptible to pathogen or grazer infestation, resulting in pond crashes with high economic costs. Current methods to monitor and mitigate unhealthy ponds are hindered by a lack of early indicators that precede culture crash. We used solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry (GC-MS) to identify volatiles emitted from healthy and rotifer infested cultures of Microchloropsis salina. After 48 hours of algal growth, marine rotifers, Brachionus plicatilis, were added to the algae cultures and volatile organic compounds (VOC) were sampled from the headspace using SPME fibers. A GC-MS approach was used in an untargeted analysis of VOCs, followed by preliminary identification. The addition of B. plicatilis to healthy cultures of M. salina resulted in decreased algal cell numbers, relative to uninfected controls, and generated trans-β-ionone and β-cyclocitral, which were attributed to carotenoid degradation. The abundances of the carotenoid-derived VOCs increased with rotifer consumption of algae. Our results indicate that specific VOCs released by infected algae cultures may be early indicators for impending pond crashes, providing a useful tool to monitor algal biomass production and pond crash prevention.

Evolution of volatile compounds and sensory characteristics of edible green seaweed (Ulva rigida) during storage at different temperatures

BACKGROUND

Edible seaweeds are one of the most important resources that currently exist for their multiple uses and applications. Like other food types, during their storage there are significant changes in sensory characteristics associated with loss of freshness and with production and/or degradation of their volatile compounds. In this study, multiple headspace sorptive extraction (MHSSE) coupled with gas chromatography/mass spectrometry (GC/MS) detection has been applied to an edible green seaweed (Ulva rigida) in order to determine the evolution of volatile compounds during storage for 12 days at 4 or 16 °C.

RESULTS

The existing analytical methodology has been updated and validated for 18 additional compounds. At the end, 41 volatile compounds from different chemical families were quantified. Aldehydes, carboxylic acids and esters were the main classes found in U. rigida. Analytical and sensory data were submitted for statistical analysis. During storage, most volatile compounds were only affected by the number of storage days (P < 0.05), with significant decreases as storage time increased. Sensory analysis revealed significant changes in the samples stored for longer times (8, 10 and 12 days), with a clear influence of the boiled vegetable descriptor.

CONCLUSION

In order to get a successful preservation of seaweeds and to maintain their marine character during storage, both temperature and time should be carefully controlled. © 2019 Society of Chemical Industry.

The effect of partial substitution of rapeseed meal and faba beans by Spirulina platensis microalgae on milk production, nitrogen utilization, and amino acid metabolism of lactating dairy cows

Alternative protein sources such as microalgae and faba beans may have environmental benefits over rapeseed. We studied the effects of rapeseed meal (RSM) or faba beans (FB) as a sole protein feed or as protein feeds partially substituted with Spirulina platensis (spirulina) microalgae on milk production, N utilization, and AA metabolism of dairy cows. Eight multiparous Finnish Ayrshire cows (113 ± 36.3 d in milk; mean ± SD) were used in a balanced, replicated 4 × 4 Latin square with 2 × 2 factorial arrangement of treatments and 21-d periods. Four cows in one Latin square were rumen cannulated. Treatments were 2 isonitrogenously fed protein sources, RSM or rolled FB, or one of these sources with half of its crude protein substituted by spirulina (RSM-SPI and FB-SPI). Cows had ad libitum access to total mixed rations consisting of grass silage, barley, sugar beet pulp, minerals, and experimental protein feed. The substitution of RSM with FB did not affect dry matter intake (DMI) but decreased neutral detergent fiber intake and increased the digestibility of other nutrients. Spirulina in the diet decreased DMI and His intake. Spirulina had no effect on Met intake in cows on RSM diets but increased it in those on FB diets. Energy-corrected milk (ECM) and protein yields were decreased when RSM was substituted by FB. Milk and lactose yields were decreased in cows on the RSM-SPI diet compared with the RSM diet but increased in those on FB-SPI compared with FB. The opposite was true for milk fat and protein concentrations; thus, spirulina in the diet did not affect ECM. Feed conversion efficiency (ECM:DMI) increased in cows on FB diets with spirulina, whereas little effect was observed for those on RSM diets. The substitution of RSM by FB decreased arterial concentration of Met and essential AA. Spirulina in the diet increased milk urea N and ruminal NH₄-N and decreased the efficiency of N utilization in cows on RSM diets, whereas those on FB diets showed opposite results. Met likely limited milk production in cows on the FB diet as evidenced by the decrease in arterial Met concentration and milk protein yield when RSM was substituted by FB. The results suggest the potential to improve milk production response to faba beans with supplementation of Met-rich feeds such as spirulina. This study also confirmed spirulina had poorer palatability than RSM and FB despite total mixed ration feeding and lower milk production when spirulina partially replaced RSM.

Insight on a comprehensive profile of volatile compounds of Chlorella vulgaris extracted by two "green" methods

Some green extraction methods were selected and tested for the extraction of volatile compounds from different samples of the microalga Chlorella vulgaris: ultrasound-assisted liquid-liquid extraction using environment-friendly solvents (LLE) and solid-phase microextraction (SPME). The obtained profiles of volatile chemical compounds were different. Only one molecule was found in common to both extractions. Using the SPME method, the main chemical classes of identified volatile compounds were sulfuric compounds, aldehydes, and alcohols. Using the LLE method, the volatile profile was more balanced with alkanes, fatty acids, terpenes, alcohols, and aldehydes. Multivariate data analyses permitted discrimination among samples. Additionally, the relationship between the physicochemical properties of identified volatile compounds and the methods of extraction was studied. The results showed that the LLE extraction allowed the extraction of volatile compounds having a high boiling point (>160°C) and a high log P (>3). The SPME method was more effective to extract volatile compounds with a low boiling point (<160°C) and a low log P (<3). It is thus necessary to combine several extraction methods to obtain a complete view of the volatile profile for microalgae samples.

Deodorization of Arthrospira platensis biomass for further scale-up food applications

BACKGROUND

Given the importance of A. platensis as a potential food protein source, we describe an affordable deodorization process that does not significantly affect the nutritional value of algae biomass.

RESULTS

Ethanol, acetone or hexane were used to deodorize algae biomass and then to identify the profile of volatile compounds associated with its distinctive odor. Sensorial characteristics were improved in the biomass cake after the proposed solvent extraction. Panelists identified the ethanolic extract with the most pronounced algae-related odor. Gas chromatography-mass spectrometry analysis showed that a mixture of 20 different compounds derived from fatty acids and amino acids contributed to the characteristic smell of A. platensis biomass. The results of the present study show that the ethanol solvent-free A. platensis biomass contained > 600 g kg^-1 protein, < 10 g kg^-1  crude fat and > 65% in vitro protein digestibility, similar to the original biomass. The Fourier transform infrared spectroscopy secondary protein structure was comparable among samples, indicating that the only change after ethanol extraction was a reduction of the algae smell.

CONCLUSION

The various extraction procedures investigated in the present study were effective in deodorizing the algae biomass. The most effective protocol was the removal of odoriferous compounds with ethanol. This particular procedure yielded an algae biomass with an improved sensorial traits. The results of the present study should help with the identification of odoriferous compounds derived from fatty acids, pigments and proteins associated with A. platensis. © 2017 Society of Chemical Industry.

Aroma characterization of five microalgae species using solid-phase microextraction and gas chromatography-mass spectrometry/olfactometry

In this study, aroma compounds produced by three marine microalgae species (Crypthecodinium cohnii, Schizochytrium limacinum and Tetraselmis chuii) and two fresh water microalgae (Chlorella vulgaris and Chlorella protothecoides) important for nutritional applications were identified by means of solid-phase microextraction followed by gas chromatography-mass spectrometry (GC-MS), GC-olfactometry (GCO) and a sensory panel. Principal components analysis (PCA) was applied to the instrumental and sensory analysis data to visualize differences between the samples in terms of descriptive attributes and volatile compounds. Accordingly, C. cohnii was characterised by a high level of sulfur compounds (dimethyl sulfide, ethanethiol), and ester and alcohol compounds associated with distinct 'sulfur-cabbage', 'fruity', 'rosy', and 'boiled potato' aroma notes. While S. limacinum was characterised more by aldehydes and alcohol compounds associated with 'mushroom', 'cucumber', and 'fatty-grassy' aroma characteristics, the other three samples showed relatively higher levels of ketone and terpene compounds with 'woody' and 'cereal-like' sensory characteristics.

The role of algae and cyanobacteria in the production and release of odorants in water

This review covers literatures pertaining to algal and cyanobacterial odor problems that have been published over the last five decades. Proper evaluation of algal and cyanobacterial odors may help establish removal strategies for hazardous metabolites while enhancing the recyclability of water. A bloom of microalgae is a sign of an anthropogenic disturbance in aquatic systems and can lead to diverse changes in ecosystems along with increased production of odorants. In general, because algal and cyanobacterial odors vary in chemistry and intensity according to blooming pattern, it is necessary to learn more about the related factors and processes (e.g., changes due to differences in taxa). This necessitates systematic and transdisciplinary approaches that require the cooperation of chemists, biologists, engineers, and policy makers.

Volatile Metabolites Emission by In Vivo Microalgae-An Overlooked Opportunity?

Fragrances and malodors are ubiquitous in the environment, arising from natural and artificial processes, by the generation of volatile organic compounds (VOCs). Although VOCs constitute only a fraction of the metabolites produced by an organism, the detection of VOCs has a broad range of civilian, industrial, military, medical, and national security applications. The VOC metabolic profile of an organism has been referred to as its 'volatilome' (or 'volatome') and the study of volatilome/volatome is characterized as 'volatilomics', a relatively new category in the 'omics' arena. There is considerable literature on VOCs extracted destructively from microalgae for applications such as food, natural products chemistry, and biofuels. VOC emissions from living (in vivo) microalgae too are being increasingly appreciated as potential real-time indicators of the organism's state of health (SoH) along with their contributions to the environment and ecology. This review summarizes VOC emissions from in vivo microalgae; tools and techniques for the collection, storage, transport, detection, and pattern analysis of VOC emissions; linking certain VOCs to biosynthetic/metabolic pathways; and the role of VOCs in microalgae growth, infochemical activities, predator-prey interactions, and general SoH.

Change of volatile components in six microalgae with different growth phases

BACKGROUND

Head space solid-phase microextraction-gas chromatography-mass spectrometry has been applied to analyze the volatile components of six marine microalgae (Thalassiosira weissflogii, Nitzschia closterium, Chaetoceros calcitrans, Platymonas helgolandica, Nannochloropsis spp. and Dicrateria inornata) from Bacillariophyta, Chlorophyta and Chrysophyta, respectively, in different growth phases.

RESULTS

All volatile compounds were identified by database searching in the NIST08 Mass Spectral Library and analyzed by principal component analysis with SIMCA-P software (Umetrics, Umea, Sweden). The results clearly revealed that the volatile components of the six microalgae were significantly different in the exponential, stationary and declining phases. Aldehydes, alkanes, some esters and dimethyl sulfide significantly changed in different growth phases.

CONCLUSION

This is the first report on the comprehensive characteristics of volatile components in different microalgae and in different growth phases. The results may provide reference data for studies on the flavor of cultivated aquatic organism, odor formation in nature water, choice of feeding period and microalgae species selection for the artificial rearing of marine organisms. © 2016 Society of Chemical Industry.