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Algal taste and odor
... Similar to odor threshold concentrations (OTCs), critical cell density (CDC), defined as the minimum algal density at which people can perceive odor or algal capita VOC production exceeding its OTCs, is sometimes used as a criterion to evaluate the potential impact of algal species on aquatic odor levels. Watson (2010) summarized CDCs for Dinobryon (3 Â 10 3 to 4 Â 10 5 cells/mL), Asterionella (3 Â 10 3 cells/mL), Cyclotella (2 Â 10 3 cells/mL), Melosira (3 Â 10 3 cells/mL), Synedra (3 Â 10 3 cells/mL), and Cryptomonas (1 Â 10 3 cells/mL), and, although these CDC values might be misleading for several reasons, they can be used as general guidelines for preliminary assessment of water quality. In this study, the ratio of algal cell number to CDC values for the six typical fishy odor producing algae at each sampling site were calculated, as shown in Fig. 2. Fishy odor intensity generally exhibited an increasing trend with the increase in algal cell number/CDC value, suggesting that the fishy odor in the source waters might be associated with these algae. ...
... This might be associated with the high density of Chlorophyta (expressed as "others" in Table 4). Chlorophyta is not a typical fishy odor producing genera, but is commonly associated with "grassy" odors (Watson, 2010). Its presence might have enhanced the fishy odor produced by Synedra. ...
... Therefore, even though the levels of these aldehydes were lower than their respective OTCs, co-existence of these compounds and other unknown ones might have contributed to the overall fish-like odors. Notably, some amines, such as butanolamine, ethanolamine, methylamine, and trimethylamine, are thought to be associated with fishy odors in the aquatic environment (Watson, 2010). These amines have low OTCs and can be formed through the bacterial degradation of some amino acids in water (Mallevialle and Suffet, 1987). ...
Yellow River source water has long suffered from odor problems in winter. In this study, odor characteristics, potential odorants, and algae in the source water of six cities (Lanzhou, Yinchuan, Hohhot, Zhengzhou, Jinan and Dongying) along the Yellow River were determined in winter (February to March 2014). According to flavor profile analysis (FPA), moderate to strong fishy odors occurred in all cities, except for Lanzhou. At the same time, mild earthy/musty odors and septic/swampy odors were also detected. The strong fishy odor (FPA intensity, 8.5) in Yinchuan was attributed to the abnormal growth of Dinobryon (cell density, 5.7 × 10(4) cells/mL), while the fishy odors in Hohhot, Zhengzhou, Jinan, and Dongying might be caused by Melosira and Cyclotella, Cryptomonas, Dinobryon, and Synedra, respectively. Unsaturated aldehydes, which have been reported to cause fishy odors, were not detected in all samples. However, some saturated aldehydes, including hexanal, heptanal, nonanal, decanal, and benzaldehyde, were detected with a total concentration range of 690 ng/L to 2166 ng/L, and might have partly contributed to the fishy odors. In addition, 2-MIB (5.77-21.12 ng/L) and geosmin (2.26-9.73 ng/L) were responsible for the earthy/musty odors in the Yellow River source waters, and dimethyl disulfide (648.2 ng/L) was responsible for the rancid/swampy odor (FPA intensity, 8.0) episode in Yinchuan. This is a comprehensive study reporting on the occurrence and possible reasons for the odor issues in the Yellow River source water during winter.
... The unpleasant odor in algal oil is mostly caused by DHA oxidation, however, oxidation of other fatty acids also plays role (Wen et al. 2022). High PUFA concentrations in diatoms, Chrysophytes and Synurophytes results in the production of volatile organic compound derivatives with fishy odor and cucumber smelling (oxylipins) odor upon cell rupture (Watson 2010). Natural or synthetic antioxidants are added to enhance the stability of algal oil. ...
Omega-3 fatty acids have gained attention due to numerous health benefits. Eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) are long chain omega-3 fatty acids produced from precursor ALA (α-linolenic acid) in humans but their rate of biosynthesis is low, therefore, these must be present in diet or should be taken as supplements. The commercial sources of omega-3 fatty acids are limited to vegetable oils and marine sources. The rising concern about vegan source, fish aquaculture conservation and heavy metal contamination in fish has led to the search for their alternative source. Microalgae have gained importance due to the production of high-value EPA and DHA and can thus serve as a sustainable and promising source of long chain omega-3 fatty acids. Although the bottleneck lies in the optimization for enhanced production that involves strategies viz. strain selection, optimization of cultivation conditions, media, metabolic and genetic engineering approaches; while co-cultivation, use of nanoparticles and strategic blending have emerged as innovative approaches that have made microalgae as potential candidates for EPA and DHA production. This review highlights the possible strategies for the enhancement of EPA and DHA production in microalgae. This will pave the way for their large-scale production for human health benefits.
... In turn, the sulfides are themselves affected by the pH of the water (Buerkens et al. 2020). Watson (2010) provides a comprehensive list of these odorous compounds. The fishy odors in untreated surface waters can range from cod liver oil-like, clam shells, dead crab, rotten fish, ammoniacal, to fishy (Suffet et al. 1996), and thus could be affected by changes in pH. and within some green algae. ...
There is general agreement that pH is an important parameter in many drinking water treatment and control processes such as taste and odor (T&O) control. However, pH is not usually targeted as a primary control parameter and its effects on T&O are often overlooked in favor of other treatment issues. When it comes to T&O control, treatment alternatives typically focus on oxidation and adsorption processes. Whether within these processes or separately, pH plays an important role and the effects on T&O should be considered. For example, pH plays a role in the speciation of odorous chemicals in the environment, some of which arise in wastewater treatment and others from the occurrence of metals in water. During blooms of algae and cyanobacteria in surface water, pH is an important parameter affecting water quality and T&O. Finally, as pH is important for the sample preservation and analysis of T&O compounds, pH is important in the fate and control of T&O. The objective of this article is to better understand the various ways that pH can influence T&O production, control, and analysis of odorants in water and encourage advancement in the state of the science of pH optimization for T&O control.
... The list of volatile organic compounds (VOC) produced by the bloom species is extensive. A summary of the 30+ specific VOCs can be found in Watson (2010) and are summarized in Table 1. Many descriptive terms have been used to characterize chrysophyte T&O: ammonia, black currant leaves, earthy, fishy, flowery, fresh, fruity, garlic, green-leafy, herbaceous, honey, lavender, mushroom, orange, orange-rose, putrid, rancid, rotten fish, septic, smoky/moldy, swampy, sweet, and tobacco. ...
... Trace concentrations of various odorous metabolites produced by bacteria may change the organoleptic properties of water and act as chemical attractants or repellents in the aquatic food web for invertebrates, fish, and humans (Höckelmann et al., 2004;Watson et al., 2007). In freshwater environments, Cyanobacteria have been known as the major producers of odorants Watson, 2010;Watson et al., 2008). Off-flavor compounds, such as MIB and GSM, which deteriorate the quality of water, are often associated with seasonal blooms of Oscillatoria, Anabaena flos-aquae, Planktothrix, and Microcystis aeruginosa (Hayes & Burch, 1989;Li et al., 2007;Su et al., 2015), where decaying blooms can release many odorous metabolites (Ma et al., 2013;Smith et al., 2008) and other bioactive compounds like cyanotoxins (Smith et al., 2008). ...
Occurrences of odorous bacterial metabolites, 2‐methylisoborneol (MIB) and geosmin (GSM), in drinking water supply reservoirs are considered as a nuisance by the water industry and a source of
complaints from customers. In Eagle Creek Reservoir, routine monitoring programs of MIB and GSM highlight intense odorous outbreaks during the spring season when high inflow discharges occur. Cyanobacteria have always been assumed to be source of these metabolites even if no known producers are present in raw water. A copper‐based algaecide is often used to terminate the metabolite production and the algal growth in the reservoir. The current study was designed to investigate and identify other biological
sources involved in the biosynthesis of MIB and GSM metabolites as well as environmental factors that could be important triggers for the growth of bacterial producers. The community structure of the bacterioplankton was determined using a 16S rRNA gene sequencing technique, which showed that not only Cyanobacteria but Actinobacteria also were involved in the reservoir internal production. Planktothrix species was identified as the main source of GSM (p < 0.001) while Streptomyces (Actinobacteria) was very likely responsible of MIB (p < 0.01). Application of an algaecide disrupted GSM and the growth of Planktothrix but was less effective against MIB and Streptomyces. Statistical analyses revealed that MIB‐ and GSM-causing bacteria were found abundant when the water was enriched with nitrogen, temperature cooler, and the water column mixed.
... showed similar olfactometry profiles, with 20 and 21 odor peaks identified, respectively (Tables S2 and S3). Among them, five odor peaks were characterized as fishy/cod liver oil/fatty/ rancid descriptors (Cotsaris et al., 1995;Hartvigsen et al., 2000;Frank et al., 2009;Watson, 2010). The odor peaks from GC-O analysis were then matched to the chromatographic peaks from GC-TOFMS analysis using RIs. ...
Fishy odor has become one of the most often encountered aesthetic water quality problems in drinking water. While fresh water algae living in colder water can produce offensive fishy odors, their environmental behaviors remain poorly understood. In this study, two chrysophyte species (Synura uvella and Ochromonas sp.), which are often associated with fishy odor events, were selected to investigate the effect of temperature (8, 16, and 24 C) and light intensity (10, 41, and 185 mmol photons m À2 s À1) on algal growth and odorant production. Five polyunsaturated aldehyde derivatives, including 2,4-heptadienal, 2-octenal, 2,4-octadienal, 2,4-decadienal, and 2,4,7-dectridienal, were identified as fishy/cod liver oil/fatty/ rancid descriptors in the cultures of the two algae based on gas chromatography-olfactometry-mass spectrometry and comprehensive two-dimensional gas chromatography mass spectrometry. While biomass yield increased with the increase in temperature for both species, significantly higher odorant yields (production of odorants per cell) were obtained at 8 C. The total odorant production and cell yield of the odorants decreased with the increase in light intensity from 10 to 185 mmol photons m À2 s À1. The biodegradation half-lives for the released odorants were 6e10 h at 8 C and 2e4 h at 24 C, whereas the volatilization half-lives were 36e97 d at 8 C and 6e17 d at 24 C, suggesting that temperature-dependent biodegradation was an important factor controlling the fate of fishy compounds in aquatic environments. The results of this study will help clarify why most fishy odor events occur in cooler seasons, and provide knowledge related to cold water persistence for the management of fishy odor problems associated with algae.
The recovery of bioactive products with green processes is a critical topic for the research and industry fields. In this work, the application of solid–liquid (SLE), microwave-assisted extraction (MAE) with aq. ethanol 90% v/v and supercritical fluid extraction (SFE) with CO2 for the recovery of biocomponents from Scenedesmus obliquus is studied. The effects examined were temperature (30–60 °C), time (6–24 h), and solvent-to-biomass ratio (20–90 mLsolv/gbiom) for SLE, temperature (40–60 °C), time (5–25 min), solvent-to-biomass ratio (20–90 mLsolv/gbiom), and microwave power (300–800 W) for MAE, and temperature (40–60 °C), pressure (110–250 bar), solvent flow rate (20–40 gsolv/min), and cosolvent presence (0, 10% w/w ethanol) for SFE in relation to the extract’s yield, phenolic, chlorophyll, carotenoid content, and antioxidant activity. The optimum extraction conditions determined were 30 °C, 24 h, and 90 mLsolv/gbiom for SLE, 60 °C, 5 min, 90 mLsolv/gbiom, and 300 W for MAE, and 60 °C, 250 bar, and 40 gsolv/min for SFE. Additionally, a kinetic SFE study was conducted and the obtained results were satisfactorily correlated using Sovová’s model. The comparison between the methods proved MAE’s efficiency in all terms compared to SLE. Moreover, SFE was accompanied with the lowest yield and chlorophyll content, yet led to an increased carotenoid content and improved antioxidant activity. Finally, the cosolvent addition significantly improved SFE’s yield and led to the most superior extract.
The production of bioactive products from microalgae biomass with efficient and environmentally friendly technologies is a field of great research interest. The present work focuses on the recovery of high-added value bioactive components from Chlorella vulgaris through microwave-assisted extraction (MAE) with aq. ethanol 90% v/v. The effect of extraction temperature (40–60 °C), duration (5–25 min), solvent-to-biomass ratio (20–90 mLsolv/gbiom), and microwave power (300–800 watts) was investigated regarding the extraction yield, extract’s chlorophyll, carotenoid and phenolic content, and antioxidant activity. MAE optimization at 60 °C, 300 watts, 14 min, and 22 mLsolv/gbiom led to 11.14% w/w yield, 63.36 mg/gextr total chlorophylls, 7.06 mg/gextr selected carotenoids of astaxanthin, lutein and β-carotene, 24.88 mg/gextr total carotenoids, 9.34 mgGA/gextr total phenolics, and 40.49 mgextr/mgDPPH IC50 (antioxidant activity indicator). Moreover, the conventional solid-liquid extraction (SLE) with aq. ethanol 90% v/v, the supercritical fluid extraction (SFE) with CO2, as well as SFE with cosolvent addition (10% w/w ethanol), were also performed for comparison purposes. The results revealed that SLE presented the highest yield. However, the non-conventional methods of MAE and SFE led to extracts of competitive or even better quality under significantly shorter extraction duration.
Microalgae are well-known for their high-added value compounds and their recovery is currently of great interest. The aim of this work is the recovery of such components from Chlorella vulgaris through supercritical fluid extraction (SFE) with CO2. The effect of the extraction temperature (40–60 °C), pressure (110–250 bar), and solvent flow rate (20–40 g/min) was tested on yield, the extract’s antioxidant activity, and the phenolic, chlorophyll and carotenoid content. Thus, data analysis indicated that the yield was mainly affected by temperature, carotenoids by pressure, while the extract’s phenolics and antioxidant activity were affected by the synergy of temperature and pressure. Moreover, SFE’s kinetic study was performed and experimental data were correlated using Sovová’s mass transfer-based model. SFE optimization (60 °C, 250 bar, 40 g/min) led to 3.37% w/w yield, 44.35 mgextr/mgDPPH antioxidant activity (IC50), 18.29 mgGA/gextr total phenolic content, 35.55, 21.14 and 10.00 mg/gextr total chlorophyll, carotenoid and selected carotenoid content (astaxanthin, lutein and β-carotene), respectively. A comparison of SFE with conventional aq. ethanol (90% v/v) extraction proved SFE’s superiority regarding extraction duration, carotenoids, antioxidant activity and organoleptic characteristics of color and odor despite the lower yield. Finally, cosolvent addition (ethanol 10% w/w) at optimum SFE conditions improved the extract’s antioxidant activity (19.46%) as well as yield (101.81%).
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