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The use of insects as feed and food can be part of the solution towards a circular economy, in case the safety of insect products is assured. Black soldier fly larvae (BSFL, Hermetia illucens) can be reared on different waste streams. However, before BSFL can be legally reared on these streams, the safety of BSFL for feed and food should be assessed thoroughly. This study aimed to investigate several food safety aspects of BSFL grown on waste streams. Therefore, BSFL were reared for 7 days on substrate mixtures of waste streams with similar protein and moisture content. These waste streams included fast food waste (FF), mushroom stem (MS), pig manure solids (PS), poultry meal (PM) and slaughter waste (SW). The substrates, BSFL and the frass were analysed for the presence of metals and veterinary drugs. The substrates and BSFL were also analysed for presence of DNA of ruminant, pig and chicken. Some of the metals accumulated in BSFL, although the concentrations in BSFL (as these would be manufactured as feed) were below maximum limits for feed. Only traces of some of the analysed veterinary drugs were found in the BFSL and no accumulation thereof was observed. DNA of ruminant and pig was traced back in BSFL samples, however, chicken was not. A good understanding of the presence of food safety hazards and possible variance thereof in potential substrates, such as waste streams, and their possible residues in insects is necessary for implementation of this circular way of insect feeding in the food chain.

Insects are receiving increasing attention as a possible ingredient for feed and/or food production. When used efficiently, insects can provide a sustainable and economically favourable contribution to global food security. Housefly larvae (HFL) can grow on a variety of organic side streams and upgrade them by partial conversion into high-quality protein. Organic side streams may be chemically contaminated by naturally occurring toxins, e.g. mycotoxins, therefore, effects on insect survival and biomass as well as other feed and/or food safety issues should be investigated. In this study, the HFL were exposed to a feed substrate spiked with aflatoxin B1 (AFB1), deoxynivalenol (DON) or zearalenone (ZEN) at concentrations of either 1 or 10 times the maximum levels or guidance values set for feed materials by the European Commission. Mortality and biomass of HFL were recorded over five days of exposure. LC-MS/MS analysis was used to determine the concentration of the mycotoxins in the substrate offered, the larvae and the residual feed material. A molar mass balance was calculated to estimate how much of the spiked mycotoxins (and several metabolites), was recovered in the larval body and the residual material. Exposure to either of the three mycotoxins did not affect larval mortality and biomass, and accumulation in the larval body did not take place. Metabolism does seem to occur for AFB1 and ZEN as the molar mass balance revealed an unrecovered fraction of ca. 40-50%. Little DON metabolism occurred as most of the initially present DON was found back unchanged. The results of this study support the potential for safe use of HFL as food- and/or feed when reared on mycotoxin contaminated side-streams, as accumulation of the tested mycotoxins did not take place in HFL. Further research is needed to identify the fate of the unrecovered fractions of AFB1 and ZEN.

Risk-based monitoring of veterinary drug residues requires a prioritisation based on the potential occurrenceof these residues as well as their human health effects. Previously, decision trees have been drafted to include these elements allowing for a prioritization of substances into low, medium or high priority to be included in the National Residue Control Plan (NRCP). One decision tree focuses on unauthorised substances (group A) and another on authorised substances (group B). These decision trees have been used previouslyto prioritise veterinary drug residues in livestock production animals. The aim of the current research was to rank the substances for products derived from aquaculture, farmed game, rabbits and honey. The latest draft Implementing Regulation available at the time of the research (i.e. SANTE 11987-2017 Rev 9) was used to determine which substance groups for which animal species needed to be included in the NRCP. Available monitoring data from national monitoring, the rapid alert system for food and feed (RASFF) andEFSA reports were used as input for the prioritisation. Furthermore, potential use of veterinary drugs was assessed based on regulations in relevant import countries, availability of VMP online and internet research on potential use in the specified animal species (e.g. based on internet fora). The current evaluation revealed that limited monitoring data were available for the animal products studied in comparison to the earlier studied animal species. This resulted in a high number (59% of all substance-animal product combinations)of unauthorised substances prioritised as medium or high for precautionary reasons (marked with a proviso). Likewise, for the authorised substances, the conclusion for many substances (77%) was to perform a survey since data were lacking. For 28% of these substances, internet search indicated a potential use and for 1.5%of these substances non-compliances were found in related species.According to the lates

Insect proteins are expected to be increasingly used for food and feed. Black soldier fly larvae (BSF, Hermetia illucens) can convert low quality organic substrates, such as manure, into protein-rich ingredients for food and feed. However, pig and chicken manure can contain residues from antibiotics and anti-parasitic drugs, resulting from treatments of the animals for diseases. This study aimed to evaluate the possible effects of veterinary drugs on black soldier fly larvae rearing, including growth and survival, as well as on the presence of residues in the larvae. The study focused on regularly found veterinary drugs in manure. Five-days old larvae were exposed to either 0.05 and 0.5 mg/kg flubendazole (FLUB), 0.05 and 0.5 mg/kg ivermectin (IVM), 0.5 and 5 mg/kg doxycycline (DOX), 0.5 and 5 mg/kg flumequine (FLUM) or 0.5 and 5 mg/kg sulfadiazine (SULF) for one week. The growth of larvae reared on substrate with IVM (0.5 mg/kg) was significantly lower than the control, while the survival of the larvae was not affected. The growth and survival of the larvae was not affected by the other treatments. Chemical analyses showed that concentrations of the veterinary drugs in the larvae, after exposure, were generally low. Only DOX concentrations in the larvae were high; these levels would exceed the European Commission maximum limit for DOX in meat products. Mass-balance calculations showed possible degradation or metabolism of veterinary drugs by the larvae, except for SULF. In conclusion, when using manure as substrate for BSF rearing, the possible presence of veterinary drugs in manure should be carefully controlled to ensure optimal insect growth and safety of the insect products.

Novel protein sources for animal feed are needed, and the use of insects as feed ingredient is explored. The insect production sector offers opportunities for a circular and sustainable approach to feed production by upgrading waste or side streams into high-quality proteins. However, potential food or feed safety issues should be studied in advance. Mycotoxins, such as aflatoxin B1, are natural contaminants commonly found in agricultural crops and have proven to be detrimental to the agricultural industry, livestock, and human health. This systematic review aims to provide a comprehensive overview of the published evidence on effects of mycotoxin exposure on insect growth and survival, mycotoxin accumulation within the insect body, and metabolization of various mycotoxins by insects. The review includes 54 scientific articles published in the past 55 years, in total covering 32 insect species. The main findings are the following: (1) Insects of the order Coleoptera show lower mortality after exposure to aflatoxin B1 when compared to Lepidoptera and Diptera; (2) effects of mycotoxins on larval growth and survival are less detrimental in later larval stages; (3) accumulation of mycotoxins was low in most insect species; (4) mycotoxins are metabolized within the insect body, the degree of which depends on the particular mycotoxin and insect species; (5) cytochrome P450s are the main family of enzymes involved in biotransformation of mycotoxins in some insect species. Results of this review support an optimistic outlook for the use of mycotoxin-contaminated waste streams as substrate for insect rearing.

Insects are a promising future source of sustainable proteins within a circular economy. Proving the safety of insects for food and feed is necessary prior to supplying them to the market. This literature review provides a state-of-the-art overview of the chemical food safety hazards for insects reared for food and feed, focusing mainly on transfer of contaminants from the substrate. Contaminants covered are: heavy metals, dioxins and polychlorinated biphenyls, polyaromatic hydrocarbons, pesticides, veterinary drugs, mycotoxins, and plant toxins. The twelve insect species reported as having the largest potential as feed and food in the EU are included. Transfer and bioaccumulation of contaminants depend on the chemical, insect species, life stage, and source of contaminant (spiked vs natural), as well as the particular substrate and rearing conditions. The heavy metals lead, arsenic, mercury, and cadmium can accumulate, whereas mycotoxins and polycyclic aromatic hydrocarbons (PAHs) seem not to accumulate. Mycotoxins and veterinary drugs could be degraded by insects; their metabolic routes need to be further investigated. Data are generally limited, but in particular for PAHs, plant toxins, and dioxins and dioxin-like polychlorinated biphenyls. Further research on chemical safety of different edible insects is therefore warranted.

This report describes the results of a literature review on chemical hazards in cereals, seeds and nuts produced and/or brought on the market in the Netherlands. Based on the literature review, a so-called ‘long list’ of chemical hazards was established: substances that may occur in cereals, seeds and nuts. From this long list, an ‘intermediate list’ of chemical hazards was derived. This intermediate list includes substances that were either frequently found in cereals, seeds and nuts and/or found in concentrations above EU legal limits. The intermediate list will provide the Dutch Food and Consumer Product Safety Authority with input for prioritizing future monitoring activities. When this list is combined with consumption data and toxicological information, a ‘short list’ of substances can be established: substances that may cause human health risks and as such should be included in the national monitoring program. The established intermediate list in this study is solely based on literature review. It is recommended to evaluate the Dutch monitoring data to confirm or adapt the intermediate list. Toxicological information was provided for the substances on the intermediate list or for substances identified as knowledge gap. Furthermore, trends were evaluated that may influence the presence of chemical hazards in cereals, seeds and nuts., Dit rapport beschrijft de chemische gevaren die voor kunnen komen in granen, zaden en noten die in Nederland zijn geproduceerd en/of op de markt gebracht. Op basis van het literatuuronderzoek is een zogenaamde ‘long list’ van chemische gevaren opgesteld: stoffen die mogelijk kunnen voorkomen in granen, zaden en noten. Stoffen die veel gevonden werden in granen, zaden en noten en/of boven Europese wettelijke limieten werden gevonden zijn opgenomen in de zogenaamde ‘intermediate list’. Deze lijst kan bijdragen aan de prioritering van chemische monitoringsprogramma’s in granen, noten en zaden door de NVWA. Door deze lijst te combineren met consumptiedata en toxicologische informatie kan een zogenaamde ‘short list’ opgesteld worden: chemische gevaren die een mogelijk risico kunnen vormen voor de mens en dus zouden moeten worden opgenomen in het nationale monitoringsprogramma. De intermediate list is uitsluitend gebaseerd op literatuuronderzoek. Het is daarom aan te bevelen de lijst aan te vullen met behulp van Nederlandse monitoringsdata. Voor de stoffen die op de intermediate list zijn aangegeven en voor stoffen die aangemerkt zijn als kennisleemte, is toxicologische informatie verstrekt. Daarnaast geeft dit rapport trends weer in granen, zaden en noten, die een invloed kunnen hebben op de aanwezigheid van chemische gevaren in deze voedselgewassen.

This report describes the results of a literature study performed for NVWA-BuRO in order to identify chemical hazards in bulbs, tubers, stem and root vegetables that are produced and/or consumed in the Netherlands. For the sake of convenience, these vegetables are referred to as underground vegetables in the remainder of this report. Potatoes were not included in this report since these were evaluated previously (Nijkamp et al., 2017). Search terms were predefined and used to obtain relevant scientific papers from the databases Scopus and Web of Science. Furthermore, the advanced search feature of Google was used to obtain relevant reports from the websites of four organizations (BfR, EFSA, FAO and FAVV). In case the number of hits for a certain chemical hazard group was limited or only experimental studies were found, an additional more specific literature search was performed for the particular hazard group. Based on title, keywords and abstract, the relevancy of the papers for the aims of our study was evaluated. Papers that were judged relevant were read in full and information from these papers on, amongst others, vegetables studied, chemical hazards included, country of origin, and reported concentrations, were extracted. This information was then stored in an Excel file. Long list of chemical hazards in underground vegetables The literature search in Scopus and Web of Science resulted in a total of 237 scientific papers. Of these, 97 were judged to be relevant. Additionally, 21 relevant hits were obtained using the Google search and 8 papers were included after the additional literature search. Most information was obtained for carrot, cassava and radish. Based on the information obtained, a long list of chemical hazards could be identified; this list contains chemical hazards that might be present in underground vegetables. The long list for underground vegetables includes heavy metals and essential elements, perfluorinated compounds, polycyclic aromatic hyd, Dit rapport geeft de resultaten van een literatuurstudie die voor NVWA-BuRO is uitgevoerd om de chemische gevaren in bol-, wortel- en knolgewassen en in stengelgroenten in kaart te brengen die in Nederland geproduceerd en/of geconsumeerd worden. Voor het gemak worden deze groenten in de rest van het rapport aangeduid met de term ‘ondergrondse groenten’. Aardappels waren geen onderdeel van deze studie, aangezien de chemische gevaren in aardappel beschreven zijn in een eerder rapport (Nijkamp et al., 2017). Scopus en Web Of Science werden gebruikt om met vooraf vastgestelde zoektermen artikelen te zoeken gerelateerd aan het onderwerp. Verder werd de geavanceerde zoekoptie in Google gebruikt om relevante rapporten te zoeken op de websites van 4 organisaties (BfR, EFSA, FAO en FAVV). Indien het aantal hits voor een bepaalde gevarengroep beperkt was of indien alleen experimentele studies werden gevonden, werd nog een additionele literatuurstudie uitgevoerd. Op basis van titel, keywords en abstract werd bepaald of een artikel relevant was. Relevante artikelen werden volledig gelezen en informatie uit deze artikelen (zoals de onderzochte groentes, de chemische gevaren, land van herkomst, gevonden concentraties) werden in een Exceltabel samengevat die apart bij dit rapport werd opgeleverd aan NVWA-BuRO. Long list van chemische gevaren in ondergrondse groenten In totaal werden 237 wetenschappelijke artikelen verkregen met Scopus en Web of Science. Hiervan waren 97 artikelen relevant. Verder werden in de Google search nog 21 relevante artikelen gevonden en 8 artikelen na een additionele literatuurstudie. De meeste informatie werd verkregen voor wortel, cassave en radijs. Op basis van de informatie uit de relevante artikelen werd een zogenaamde ‘long list’ van chemische gevaren opgesteld. Deze lijst bevat chemische gevaren die mogelijk kunnen voorkomen in ondergrondse groenten. De long list bevat zware metalen en essentiële elementen, perfluorverbindingen, polyaromatische kool

A literature study was performed to identify the chemical hazards that may be found in fruiting vegetables on the Dutch market. For this purpose, search terms were defined and used in Scopus and Web of Science for the period 2009-2019. Additionally, the advanced search feature of Google was used to retrieve relevant reports from EFSA, BfR, FAVV and Aecosan. Additional searches were performed on specific hazard groups in case limited number of hits were obtained or only experimental studies were retrieved. References were first evaluated on title, keywords and abstract. Those references that were seen as relevant were read in full and summarised in an Excel table that was submitted to NVWA-BuRO as additional file to this report. Long list of chemical hazards in fruiting vegetables The literature search in Scopus and Web of Science resulted in 350 hits of which 88 were seen as relevant. The Google search resulted in 17 relevant reports and the additional literature search resulted in 16 papers. The literature search showed that the most frequently mentioned fruiting vegetables were tomato, pepper and cucumber. Based on the information obtained, the following hazard groups were found to be present in fruiting vegetables: heavy metals and other elements, polycyclic aromatic hydrocarbons (PAHs), pharmaceuticals, dioxins and dl-PCBs, perfluorinated compounds, radionuclides, plant protection products (PPPs), mycotoxins, plant toxins, cleaning agents and disinfectants, and other chemical hazards such as phthalates, perchlorate and nitrate. These hazards were included in the so-called long list: chemical hazards that might be present in fruiting vegetables. Intermediate list of chemical hazards in fruiting vegetables Those chemical hazards that were found above legal limits, frequently encountered in fruiting vegetables or that led to an exceedance of a health-based guidance value (HBGV) were included on the so-called intermediate list. The heavy metals cadmium and lead were, Er is een literatuuronderzoek uitgevoerd om de chemische gevaren te identificeren die kunnen voorkomen in vruchtgroenten op de Nederlandse markt. Hiervoor werden zoektermen gedefinieerd en in Scopus en Web of Science toegepast voor de periode 2009-2019. Verder is de geavanceerde zoekoptie binnen Google gebruikt om relevante rapporten te zoeken op de websites van EFSA, BfR, FAVV en Aecosan. Indien een beperkt aantal hits werd verkregen voor een bepaalde gevarengroep of alleen experimentele studies werden gevonden, werd aanvullende literatuur gezocht. Referenties werden in eerste instantie beoordeeld op titel, abstract en zoektermen. Referenties die relevant leken, werden volledig gelezen en samengevat in een Exceltabel die als aanvullend bestand is aangeleverd aan NVWA- BuRO. Long list van chemische gevaren in vruchtgroenten De literatuuropdracht in Scopus en Web of Science resulteerde in 350 hits, waarvan er 88 als relevant werden gezien. De zoektocht in Google leverde 17 relevante rapporten op en het additionele literatuur- onderzoek 16 artikelen. Uit het literatuuronderzoek bleek dat de meest bestudeerde vruchtgroenten tomaat, paprika en komkommer waren. De verkregen informatie liet zien dat de volgende gevaren- groepen gevonden werden in vruchtgroenten: zware metalen en andere elementen, polycyclische koolwaterstoffen (PAK’s), geneesmiddelen, dioxinen en dl-PCB’s, perfluorverbindingen, radionucliden, gewasbeschermingsmiddelen, mycotoxinen, planttoxinen, reinigings- en disinfectiemiddelen, en overige chemische gevaren zoals ftalaten, perchloraat en nitraat. Deze gevaren werden opgenomen op de zogenaamde long list: chemische gevaren die mogelijk kunnen voorkomen in vruchtgroenten. Intermediate list van chemische gevaren in vruchtgroenten Chemische gevaren die boven de wettelijke limiet werden gevonden, regelmatig werden aangetroffen in vruchtgroenten of die leidden tot een overschrijding van een gezondheidskundige richtwaarden werden opgenomen op de zogenaamde inte

Seaweed is a source of protein that can help overcome the anticipated challenges of a growing world population and the current challenges for finding alternatives for animal proteins in the Western diet. Thus far, data on the safety of seaweed for feed and food purposes in the Western world are scattered. This study aimed to review the available knowledge on the presence of food safety hazards in seaweed, including factors influencing their presence, and to prioritize the hazards that may pose a risk to human health. Given current knowledge from the literature, data from the Rapid Alert System for Food and Feed, and results from a stakeholder survey, 22 food safety hazards were ranked into major (4), moderate (5), and minor (13) hazards. Arsenic, cadmium, iodine, and Salmonella were identified as major hazards. Hazards, where data gaps exist, should be carefully assessed. These include pesticide residues, dioxins and polychlorinated biphenyls, brominated flame retardants, polycyclic aromatic hydrocarbons, pharmaceuticals, marine biotoxins, allergens, micro- and nanoplastics, other pathogenic bacteria, norovirus, and hepatitis E virus. It is recommended to collect more data on these hazards in future studies. Many factors can affect the presence of hazards including seaweed type, physiology, season, harvest and cultivation environment, geography including the location of cultivation, alongside further processing. Moreover, when seaweed is cultivated near industrialized or anthropogenic activities, these activities may negatively influence water quality, which can increase the likelihood of hazards in seaweed. Results of the ranking prioritized hazards can be used to prioritize monitoring programs and adjusted given future additional knowledge covering the data gaps.

Summary Consumption of foods containing flavonoids is associated with a reduced risk of cardiovascular diseases (CVD), possibly by lipid-lowering effects. On the other hand, for one of these flavonoids, quercetin, also genotoxicity was shown especially in in vitro bioassays. Therefore, the first aim of this thesis was to identify mechanisms underlying potential beneficial health effects of flavonoids. The focus was on hepatic lipid metabolism and circulating lipids and a molecular and physiological approach was used. Secondly, we aimed to study the potential in vivo genotoxic effects of quercetin by transcriptome analyses in liver and small intestine, since these represent the tissues of first contact exposed to relatively high levels upon oral intake of flavonoids. Circulating lipids are important CVD-related risk markers, which are in general determined with commercially available enzyme-based assays. However, the usual enzyme in these assays, peroxidase, has previously been reported to be inhibited by flavonoids. Therefore, we have studied in chapter 2 whether these assays can adequately be used in flavonoid research. We observed that various flavonoid aglycones interfere with peroxidase used in triglycerides (TG) and free fatty acids (FFA) enzymatic assays, reporting incorrect lower TG and FFA levels than actually present. Furthermore, addition of metabolites such as isorhamnetin or quercetin-3-O-glucuronide, the major metabolite of quercetin in human and rat plasma, to murine serum also resulted in a significant reduction of the detected TG levels, while a trend was seen towards reduced FFA levels. It can be concluded that when applying these biochemical assays, vigilance is needed and alternative analytical methods assessing FFA or TG levels should preferably be applied for studying the biological effects of flavonoids on TG and FFA levels. In chapter 3 mechanistic and physiological effects of quercetin on hepatic lipid metabolism were studied. C57BL/6JOlaHsd

Dietary flavonoid intake is associated with reduced risk of cardiovascular diseases, possibly by affecting metabolic health. The relative potency of different flavonoids in causing beneficial effects on energy and lipid metabolism has not been investigated. Effects of quercetin, hesperetin, epicatechin, apigenin and anthocyanins in mice fed a high-fat diet (HF) for 12 weeks were compared, relative to normal-fat diet. HF-induced body weight gain was significantly lowered by all flavonoids (17–29 %), but most by quercetin. Quercetin significantly lowered HF-induced hepatic lipid accumulation (71 %). Mesenteric adipose tissue weight and serum leptin levels were significantly lowered by quercetin, hesperetin and anthocyanins. Adipocyte cell size and adipose tissue inflammation were not affected. The effect on body weight and composition could not be explained by individual significant effects on energy intake, energy expenditure or activity. Lipid metabolism was not changed as measured by indirect calorimetry or expression of known lipid metabolic genes in liver and white adipose tissue. Hepatic expression of Cyp2b9 was strongly downregulated by all flavonoids. In conclusion, all flavonoids lowered parameters of HF-induced adiposity, with quercetin being most effective.

1 april 2014, Item does not contain fulltext, SCOPE: Mice are usually housed at 20-24 degrees C. At thermoneutrality (28 degrees C) larger diet-induced differences in obesity are seen. We tested whether this leads to large differences in metabolic health parameters. METHODS AND RESULTS: We performed a 14-wk dietary intervention in C57BL/6J mice at 28 degrees C and assessed adiposity and metabolic health parameters for a semipurified low fat (10 energy%) diet and a moderate high fat (30 energy%) diet. A large and significant diet-induced differential increase in body weight, adipose tissue mass, adipocyte size, serum leptin level, and, to some extent, cholesterol level was observed. No adipose tissue inflammation was seen. No differential effect of the diets on serum glucose, free fatty acids, triacylglycerides, insulin, adiponectin, resistin, PAI-1, MMP-9, sVCAM-1, sICAM-1, sE-selectin, IL-6, ApoE, fibrinogen levels, or HOMA index was observed. Also in muscle no differential effect on mitochondrial density, mitochondrial respiratory control ratio, or mRNA expression of metabolic genes was found. Finally, in liver no differential effect on weight, triacylglycerides level, aconitase/citrate synthase activity ratio was seen. CONCLUSION: Low fat diet and moderate high fat diet induce prominent body weight differences at thermoneutrality, which is not paralleled by metabolic differences. Our data rather suggest that thermoneutrality alters metabolic homeostasis.

Contains fulltext : 144818.pdf (publisher's version ) (Open Access), Elevated circulating lipid levels are known risk factors for cardiovascular diseases (CVD). In order to examine the effects of quercetin on lipid metabolism, mice received a mild-high-fat diet without (control) or with supplementation of 0.33% (w/w) quercetin for 12 weeks. Gas chromatography and (1)H nuclear magnetic resonance were used to quantitatively measure serum lipid profiles. Whole genome microarray analysis of liver tissue was used to identify possible mechanisms underlying altered circulating lipid levels. Body weight, energy intake and hepatic lipid accumulation did not differ significantly between the quercetin and the control group. In serum of quercetin-fed mice, triglycerides (TG) were decreased with 14% (p<0.001) and total poly unsaturated fatty acids (PUFA) were increased with 13% (p<0.01). Palmitic acid, oleic acid, and linoleic acid were all decreased by 9-15% (p<0.05) in quercetin-fed mice. Both palmitic acid and oleic acid can be oxidized by omega (omega)-oxidation. Gene expression profiling showed that quercetin increased hepatic lipid metabolism, especially omega-oxidation. At the gene level, this was reflected by the up-regulation of cytochrome P450 (Cyp) 4a10, Cyp4a14, Cyp4a31 and Acyl-CoA thioesterase 3 (Acot3). Two relevant regulators, cytochrome P450 oxidoreductase (Por, rate limiting for cytochrome P450s) and the transcription factor constitutive androstane receptor (Car; official symbol Nr1i3) were also up-regulated in the quercetin-fed mice. We conclude that quercetin intake increased hepatic lipid omega-oxidation and lowered corresponding circulating lipid levels, which may contribute to potential beneficial effects on CVD.

Flavonoids are bioactive food compounds with potential lipid-lowering effects. Commercially available enzymatic assays are widely used to determine free fatty acid (FFA) and triglyceride (TG) levels both in vivo in plasma or serum and in vitro in cell culture medium or cell lysate. However, we have observed that various flavonoids interfere with peroxidases used in these enzymatic assays, resulting in incorrect lower FFA and TG levels than actually present. Furthermore, addition of isorhamnetin or the major metabolite of the flavonoid quercetin in human and rat plasma, quercetin-3-O-glucuronide, to murine serum also resulted in a significant reduction of the detected TG levels, while a trend was seen for FFA levels. It is concluded that when applying these assays, vigilance is needed and alternative analytical methods, directly assessing FFA or TG levels, should be used for studying the biological effects of flavonoids on FFA and TG levels.