Classification and Authentication of Paprika by UHPLC-HRMS Fingerprinting and Multivariate Calibration Methods (PCA and PLS-DA).

In this study, the feasibility of non-targeted UHPLC-HRMS fingerprints as chemical descriptors to address the classification and authentication of paprika samples was evaluated. Non-targeted UHPLC-HRMS fingerprints were obtained after a simple sample extraction method and C18 reversed-phase separation. Fingerprinting data based on signal intensities as a function of m/z values and retention times were registered in negative ion mode using a q-Orbitrap high-resolution mass analyzer, and the obtained non-targeted UHPLC-HRMS fingerprints subjected to unsupervised principal component analysis (PCA) and supervised partial least squares regression-discriminant analysis (PLS-DA) to study sample discrimination and classification. A total of 105 paprika samples produced in three different regions, La Vera PDO and Murcia PDO, in Spain, and the Czech Republic, and all of them composed of samples of at least two different taste varieties, were analyzed. Non-targeted UHPLC-HRMS fingerprints demonstrated to be excellent sample chemical descriptors to achieve the authentication of paprika production regions with 100% sample classification rates by PLS-DA. Besides, the obtained fingerprints were also able to perfectly discriminate among the different paprika taste varieties in all the studied cases, even in the case of the different La Vera PDO paprika tastes (sweet, bittersweet, and spicy) which are produced in a very small region.

Targeted UHPLC-HRMS (Orbitrap) Polyphenolic and Capsaicinoid Profiling for the Chemometric Characterization and Classification of Paprika with Protected Designation of Origin (PDO) Attributes.

Society's interest in the quality of food products with certain attributes has increased, the attribute of a Protected Designation of Origin (PDO) being an effective tool to guarantee the quality and geographical origin of a given food product. In Spain, two paprika production areas with PDO (La Vera and Murcia) are recognized. In the present work, targeted UHPLC-HRMS polyphenolic and capsaicinoid profiling through the TraceFinderTM screening software, using homemade accurate mass databases, was proposed as a source of chemical descriptors, to address the characterization, classification, and authentication of paprika. A total of 126 paprika samples from different production regions-Spain (La Vera PDO and Murcia PDO) and the Czech Republic, each including different flavor varieties, were analyzed. UHPLC-HRMS polyphenolic profiles showed to be good chemical descriptors to achieve paprika classification and authentication, based on the production region, through principal component analysis and partial least squares regression-discriminant analysis, with classification rates of 82%, 86%, and 100% for La Vera PDO, Murcia PDO, and the Czech Republic, respectively. In addition, a perfect classification was also accomplished among the flavor varieties for the Murcia PDO and Czech Republic samples. By employing the UHPLC-HRMS polyphenolic and capsaicinoid profiles as chemical descriptors, acceptable discrimination among La Vera PDO flavor varieties was also achieved.

Determination of Phenolic Compounds in Paprika by Ultrahigh Performance Liquid Chromatography-Tandem Mass Spectrometry: Application to Product Designation of Origin Authentication by Chemometrics.

An ultrahigh performance liquid chromatography-electrospray-tandem mass spectrometry method was developed for the determination of 36 phenolic compounds in paprika. The proposed method showed good method performance with limits of quantitation between 0.03 and 50 µg/L for 16 compounds and between 50 µg/L and 1 mg/L for 12 compounds. Good linearity (R2 > 0.995), run-to-run and day-to-day precisions (%RSD values < 12.3 and < 19.2%, respectively), and trueness (relative errors < 15.0%) were obtained. The proposed method was applied to the analysis of 111 paprika samples from different production regions: Spain (La Vera PDO and Murcia PDO) and Czech Republic, each one including different flavor varieties (sweet, bittersweet, and spicy). Phenolic profiles and concentration levels showed to be good chemical descriptors to achieve paprika classification and authentication according to the production region by principal component analysis and partial least squares regression-discriminant analysis. In addition, perfect classification among flavor varieties for Murcia PDO and Czech Republic samples was also obtained.

Non-Targeted HPLC-UV Fingerprinting as Chemical Descriptors for the Classification and Authentication of Nuts by Multivariate Chemometric Methods.

Recently, the authenticity of food products has become a great social concern. Considering the complexity of the food chain and that many players are involved between production and consumption; food adulteration practices are rising as it is easy to conduct fraud without being detected. This is the case for nut fruit processed products, such as almond flours, that can be adulterated with cheaper nuts (hazelnuts or peanuts), giving rise to not only economic fraud but also important effects on human health. Non-targeted HPLC-UV chromatographic fingerprints were evaluated as chemical descriptors to achieve nut sample characterization and classification using multivariate chemometric methods. Nut samples were extracted by sonication and centrifugation, and defatted with hexane; extracting procedure and conditions were optimized to maximize the generation of enough discriminant features. The obtained HPLC-UV chromatographic fingerprints were then analyzed by means of principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA) to carry out the classification of nut samples. The proposed methodology allowed the classification of samples not only according to the type of nut but also based on the nut thermal treatment employed (natural, fried or toasted products).

Cooking with elaborate recipes can reduce the formation of mutagenic heterocyclic amines and promote co-mutagenic amines.

Heterocyclic amines (HCAs) are foodborne carcinogens for which their formation is highly dependent on cooking conditions. HCAs have been commonly quantified in food items prepared with simple procedures. This approach is suitable for elucidating HCAs' formation, but it only partially reflects the contamination in consumed food. In the current investigation, the generation of HCAs has been investigated in fried beef items prepared with elaborated cooking recipes, and their occurrence has been compared with control beef fried without the addition of ingredients other than oil. The food recipes that included a variety of food ingredients had lower yields of mutagenic HCAs (≥47% reduction, with individual HCA levels ranging between 0.01 and 2.22 ng/g) with respect to the control beef. In contrast, the co-mutagens norharman and harman were formed generally at greater levels (up to three times the contamination in the control fried beef) in the items prepared including a greater variety of ingredients.

Detection and Quantitation of Frauds in the Authentication of Cranberry-Based Extracts by UHPLC-HRMS (Orbitrap) Polyphenolic Profiling and Multivariate Calibration Methods.

UHPLC-HRMS (Orbitrap) polyphenolic profiling was applied to the characterization, classification, and authentication of cranberry-based natural and pharmaceutical products. Fifty three polyphenolic standards were characterized to build a user-accurate mass database which was then proposed to obtain UHPLC-HRMS polyphenolic profiles by means of ExactFinder software. Principal component analysis results showed a good sample discrimination according to the fruit employed. Regarding cranberry-based pharmaceuticals, discrimination according to the presentation format (syrup, sachets, capsules, etc.) was also observed due to the enhancement of some polyphenols by purification and preconcentration procedures. Procyanidin A2 and homogentisic, sinapic, veratric, cryptochlorogenic, and caffeic acids showed to be important polyphenols to achieve cranberry-based products discrimination against the other studied fruits. Partial least-squares regression allowed the determination of adulterant percentages in cranberry-fruit samples. Very satisfactory results with adulteration quantification errors lower than 6.0% were obtained even at low adulteration levels.

Furan in commercial baby foods from the Spanish market: estimation of daily intake and risk assessment.

The occurrence of furan in commercial baby food samples from the Spanish market was evaluated using an automated headspace solid-phase microextraction method coupled to gas chromatography-mass spectrometry (HS-SPME-GC-MS). A total of 76 baby food samples including infant formula, baby cereals, fruit in cans and/or jars, vegetables, meat, and fish, were surveyed for furan content. The lowest concentration of this compound was found in infant formula (<0.02-0.33 ng ml-1), and cereal-based food (0.15-2.1 ng g-1) while baby food containing fish showed the highest concentrations (19-84 ng g-1). Following recommendation of the European Food Safety Authority (EFSA), the effect on furan content was evaluated of consumer home preparation of foods, heating and handling. Furan concentrations were reduced by up to 35% when samples were heated in a dish using microwave oven and by up to 53% when a hot water bath was used. Finally, we estimated the furan intake from baby food consumption (0.002-1.18 µg kg-1 body weight day-1) and we calculated the margin of exposure (MOE) from samples as purchased and also after home preparation of the food. For infant formula and cereal baby foods, the MOEs (26,278-412,776) indicated no infant health concern or priority, while for meat and fish-based baby foods the values pointed to a potential public health risk, even considering the furan losses during preparation at home.

Characterization, classification and authentication of fruit-based extracts by means of HPLC-UV chromatographic fingerprints, polyphenolic profiles and chemometric methods.

HPLC-UV was applied to the analysis and characterization of fruit-based and fruit-processed products. A Kinetex C18 reversed-phase column was proposed under gradient elution for the determination of 17 polyphenols. Acceptable sensitivity (LODs below 0.16mg/L), and good linearity (r2 higher than 0.995), precision (RSD below 6.8%), and method trueness (relative errors below 11%) were obtained. Data corresponding to polyphenolic peak areas and HPLC-UV chromatographic fingerprints were then analyzed by exploratory principal component analysis (PCA) to extract information of the most significant variables contributing to characterization and classification of analyzed samples regarding the fruit of origin. HPLC-UV chromatographic data was further treated by partial least square (PLS) regression to determine the percentages of adulteration in cranberry-fruit extracts. It was found that even mixture samples containing low percentages of adulterants could be distinguished from genuine cranberry extracts. Highly satisfactory results were obtained, with overall errors in the quantification of adulterations below 4.3%.

Determination of polyphenolic profiles by liquid chromatography-electrospray-tandem mass spectrometry for the authentication of fruit extracts.

Liquid chromatography-electrospray-tandem mass spectrometry (LC-ESI-MS/MS) was applied to the analysis and authentication of fruit-based products and fruit-based pharmaceutical preparations. A Kinetex C18 reversed-phase column under gradient elution with 0.1 % formic acid aqueous solution and methanol mobile phases was used for the simultaneous determination of 26 polyphenols, allowing an acceptable separation in less than 22 min. Instrumental quality parameters such as limits of detection (LOD, values between 12 and 14 µg/L for 19 of the 26 analyzed polyphenols), linearity (r (2) > 0.991), run-to-run and day-to-day precisions (relative standard deviation (RSD) values lower than 9.9 and 13.5 %, respectively), and accuracy (relative errors lower than 8 %) were established. A simple extraction method, consisting of a sample sonication with acetone/water/hydrochloric acid (70:29.9:0.1 v/v/v) and centrifugation, was proposed. Two calibration procedures, external calibration using standards prepared in water and standard addition, were evaluated for polyphenol quantification in several grape and cranberry fruits and processed fruit products. For a 95 % confidence level, no statistical differences were observed between the two calibration methods (p values between 0.06 and 0.95), denoting that external calibration was suitable enough for the quantitative analysis of polyphenols in fruit-based products. The proposed LC-ESI-MS/MS method was then applied to the analysis of polyphenols in 23 grape-based and cranberry-based natural products and pharmaceutical preparations. Polyphenolic concentration data was then analyzed by principal component analysis (PCA) to extract information of the most significant profile data contributing to authentication of natural extracts according to their fruit of origin.

Characterization of fruit products by capillary zone electrophoresis and liquid chromatography using the compositional profiles of polyphenols: application to authentication of natural extracts.

Capillary zone electrophoresis (CZE) and high performance liquid chromatography (HPLC) were applied to the authentication of fruit products based on the compositional profiles of polyphenols. Various sample treatments were used to maximize the overall recovery of polyphenols or specific fractions, such as phenolic acids or anthocyanins. The resulting CZE and HPLC data were treated with Principal Component Analysis (PCA) showing that samples were mainly clustered according to the fruit of origin, with cranberry- and grape-based products clearly separated in groups. A possible adulterated cranberry extract was analyzed more deeply by high resolution mass spectrometry (HRMS) in order to identify the presence of A-type proanthocyanidins, which are characteristic and more abundant in cranberry-based products. In accordance with PCA interpretation, HRMS results indicated that the suspicious sample was not a cranberry-based product, allowing us to validate and demonstrate the suitability of both CZE- and HPLC-proposed methods for the characterization of fruit-based products.

Identification of seafood as an important dietary source of heterocyclic amines by chemometry and chromatography-mass spectrometry.

Heterocyclic amines (HCAs), which are formed during the cooking of protein-rich foods, are potent mutagens and a risk factor for human cancers. Levels of HCAs have been extensively investigated in meat products but not in fish products. Here, we report levels of HCAs in fried salmon, tuna, hake, sardine, angler fish, cod, sole, swordfish, squid, and cuttlefish. The HCA levels of some of these foods have not been previously analyzed. We employed multivariate factor-analysis tools, including principal components analysis (PCA) and partial least-squares (PLS) regression, to study the effects of cooking weight loss and levels of creatine, glucose, and free amino acids on HCA levels. The highest concentrations of mutagenic HCAs, 159.3 ng·g(-1) total, where 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) accounted for 121 ng·g(-1), were found in fried swordfish (cooking loss of 51.8%). These levels are higher than those generally found in fried chicken, which is typically cited as the most contaminated food item. Thus, swordfish is among the richest known sources of HCAs. The other cooked seafood items contained from 0.4 to 35.4 ng·g(-1) HCAs, comparable to concentrations typically reported for meat. Chemometric analysis showed that the fish species is the most influential parameter on the formation of HCAs such as DMIP, PhIP, and norharman. Concentrations of histidine, lysine, creatine, and glucose, as well as weight loss, also influence the yield of HCAs. These results suggest that seafood is an important dietary source of HCAs. The formation of HCAs in fish is influenced by multiple factors, some of which remain unknown.

Biomonitoring of dietary heterocyclic amines and metabolites in urine by liquid phase microextraction: 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a possible biomarker of exposure to dietary PhIP.

Heterocyclic amines (HCAs) are mutagenic/carcinogenic compounds formed at ng/g levels during frying meat or fish. The effect of the normal intake of dietary HCAs in humans and their involvement in the etiology of cancer are currently unknown. In this work, a new extraction method, liquid phase microextraction (LPME) with hollow fibers, and LC-MS/MS have been used for the first time to determine HCAs and metabolites in nonspiked human urine following a single meal of chicken cooked at 180 °C for 6 min. The total intake of HCAs was estimated to be 6 µg, of which 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) accounted for about 1 µg. The concentrations of PhIP in nonhydrolyzed urine samples ranged from 11.7 to 59.4 pg/g. The total amount of PhIP in urine ranged between 9.3 and 21.1 ng, which corresponds to 0.91-2.1% of the ingested PhIP. In addition, the urine levels of 4'-OH-PhIP (2-amino-1-methyl-6-(4'-hydroxy)phenylimidazo[4,5-b]pyridine) and 5-OH-PhIP (2-amino-1-methyl-6-(5-hydroxy)phenylimidazo[4,5-b]pyridine) also showed a narrow variation between the samples. The analysis of urine samples after acid hydrolysis did not give additional information but showed a notable increase in norharman in some cases. The obtained results suggest PhIP in urine as a possible biomarker of exposure to HCAs and the LPME and LC-MS/MS method as an appropriate strategy to biomonitor HCAs in urine.

Determination of polyphenols in Spanish wines by capillary zone electrophoresis. Application to wine characterization by using chemometrics.

A capillary zone electrophoresis (CZE) method for the simultaneous determination of 20 polyphenols in wine was developed. The separation was performed using fused-silica capillaries of 75 µm i.d. and a 30 mM sodium tretraborate buffer solution at pH 9.2 with 5% isopropanol as a background electrolyte. A capillary voltage of +25 kV with pressure-assisted (3.5 kPa) separation from minute 18 was applied, thus achieving a total analysis time of <25 min. Instrumental quality parameters such as limits of detection (LOD, values between 0.3 and 2.6 mg/L), linearity (r(2) > 0.990), and run-to-run and day-to-day precisions (RSD values lower than 6.5 and 15.7%, respectively) were established. Three different calibration procedures were evaluated for polyphenol quantitation in wines: external calibration using standards prepared in Milli-Q water, standard addition, and pseudomatrix-matched calibration using wine as a matrix. For a 95% confidence level, no statistical differences were observed, in general, between the three calibration methods (p values between 0.11 and 0.84), whereas for some specific polyphenols, such as cinnamic acid, syringic acid, and gallic acid, results were not comparable when external calibration was used. The CZE method using pseudomatrix-matched calibration was then proposed and applied to the analysis of polyphenols in 49 Spanish wines, showing satisfactory results and a wide compositional variation between wines. Electrophoretic profiles and other compositional data (e.g., peak areas of selected peaks) were considered as fingerprints of wines to be used for characterization and classification purposes. The corresponding data were analyzed by principal component analysis (PCA) to extract information on the most significant features contributing to wine discrimination according to their origins. Results showed that a reasonable distribution of wines depending on the elaboration areas was found, tyrosol and gallic, protocatechuic, p-coumaric, and caffeic acids being some representative discriminant compounds.

Hollow fibre-supported liquid membrane extraction and LC-MS/MS detection for the analysis of heterocyclic amines in urine samples.

Heterocyclic amines (HCAs) are potent mutagens/carcinogens to which humans are frequently exposed through the consumption of cooked meat and fish food. The effect of normal intake of HCAs and their role in the aetiology of human cancer is unknown. To some extent, limitations of the existing analytical methods in monitoring the low levels of HCAs in biological samples have hindered obtaining conclusive results. In this study, a method for the analysis of HCAs in human urine has been studied to detect HCAs and metabolites at levels resulting from consumption of food cooked at ordinary conditions. The analytical method consisted of extraction and clean-up by the novel technique liquid-phase microextraction combined with LC-MS/MS. The effect of pH during the extraction and hydrolysis step was examined. High sensitivity was achieved when the extraction was performed in raw urine adjusted to pH 5.5, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine being detected from 2 pg/g urine, levels comparable with a normal exposure. Good reproducibility and repeatability was obtained for 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline, below 9% using isotopic dilution. The performance of the method on 9H-pyrido[3,4-b]indole, 2-amino-1-methyl-6-(4'-hydroxyphenyl)imidazo[4,5-b]pyridine and 2-amino-1-methyl-6-(5-hydroxy)phenylimidazo[4,5-b]pyridine was also studied.

Quantification of heterocyclic amines from thermally processed meats selected from a small-scale population-based study.

Heterocyclic amines (HAs) are potent mutagens that form at high temperatures in cooked, protein-rich food. Due to their frequent intake, these compounds are considered a risk factor for human cancer. Cooking conditions and eating habits strongly influence the level of HA exposure. Thus, it is difficult to assess the intake of HAs in a large population. Food-frequency questionnaires (FFQs), designed to provide data on parameters that affect HA formation, were used to survey a small population (459 persons) from Barcelona (NE Spain). Subsequently, the most-consumed food items named were cooked according to the preferences of the population surveyed and analyzed for HAs using SPE and LC-MS/MS. In the population studied, the estimated intake via consumption of 13 meat dishes was 285.6 ng of mutagenic HAs per capita and day. PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) was the HA to which the population was most exposed, mainly from fried chicken and griddled beef. When the co-mutagens norharman and harman are included, the mean daily intake of HAs rises to 475.6 ng per capita and day. A novel putative DMIP regioisomer was detected in the cooked meats, which was analyzed in the present study by multistage MS.

CEC separation of heterocyclic amines using methacrylate monolithic columns.

Two methacrylate-based monolithic columns, one with a negatively charged group (sulfonic group) and another with a new monomer N,N-dimethylamino ethyl acrylate (DMAEA), were prepared and tested for the separation of basic compounds by CEC. This new monolithic stationary phase was prepared by the in situ polymerization of DMAEA with butyl methacrylate and ethylene dimethacrylate, using a ternary porogenic solvent consisting of water, 1-propanol and 1,4-butanediol. The performance of this column was evaluated by means of the analysis of a family of heterocyclic amines. Separation conditions such as pH, amount of organic modifier, ionic strength and elution mode (normal or counterdirectional flow) were studied. At the optimal running electrolyte composition, and using the counterdirectional mode, symmetrical electrochromatographic peaks were obtained, with the number of theoretical plates up to 30,000 and a good resolution between closely related peaks. The 2-acrylamido-2-methyl-1-propane-sulfonic acid column was used for CEC-MS, taking advantage of the compatibility of its elution mode (normal flow) with the MS coupling.

Effect of red wine marinades on the formation of heterocyclic amines in fried chicken breast.

Genotoxic heterocyclic amines (HAs) are formed via the Maillard reaction and free radical reaction mechanisms when meat or fish is cooked at usual cooking conditions. In this paper, the effect of the addition of red wine was tested to study if it interferes in HA formation. Fried chicken breast was the food item chosen, and three different red wines, characterized in terms of grape varieties, free amino acids, antioxidant properties, and metallic composition, were used to marinate meat prior to the heating process. Unmarinated samples and samples marinated with an ethanol-water mixture provided reference HA levels. The frying experiments were performed under well-controlled temperature and time conditions. The samples were analyzed for HA content using solid-phase extraction and LC-MS/MS. DMIP, PhIP, MeIQx, 4,8-DiMeIQx, IFP, TMIP, harman, and norharman were identified in fried chicken breast. Red wine marinades were found to reduce the formation of some of the HAs formed. PhIP, with a reduction of up to 88%, was the most minimized amine, although the formation of harman was enhanced.

Characterization of winemaking yeast by cell number-size distribution analysis through flow field-flow fractionation with multi-wavelength turbidimetric detection.

Yeasts are widely used in several areas of food industry, e.g. baking, beer brewing, and wine production. Interest in new analytical methods for quality control and characterization of yeast cells is thus increasing. The biophysical properties of yeast cells, among which cell size, are related to yeast cell capabilities to produce primary and secondary metabolites during the fermentation process. Biophysical properties of winemaking yeast strains can be screened by field-flow fractionation (FFF). In this work we present the use of flow FFF (FlFFF) with turbidimetric multi-wavelength detection for the number-size distribution analysis of different commercial winemaking yeast varieties. The use of a diode-array detector allows to apply to dispersed samples like yeast cells the recently developed method for number-size (or mass-size) analysis in flow-assisted separation techniques. Results for six commercial winemaking yeast strains are compared with data obtained by a standard method for cell sizing (Coulter counter). The method here proposed gives, at short analysis time, accurate information on the number of cells of a given size, and information on the total number of cells.

Microemulsion electrokinetic chromatography for the analysis of acrylamide in food.

The influence of microemulsion electrokinetic chromatography (MEEKC) operating conditions, such as the type of water-immiscible alcohol, aqueous phosphate buffer concentration, pH, as well as the addition of methanol and 2-propanol, on acrylamide migration has been studied. These parameters have been optimized taking into account the presence of matrix signals, in order to avoid the interference of these peaks in acrylamide determination. The best separations were achieved using a microemulsion consisting of 0.8% m/v n-amyl alcohol, 3.3% m/v sodium dodecyl sulfate (SDS), 6.6% m/v 1-butanol, and 89.3% m/v 40 mM phosphate buffer at pH 6.5 working at 15 kV in uncoated silica capillaries. Linear calibration curves over the range studied (1.25-125 microg x mL(-1)), the detection limit (0.70 microg x mL(-1)), and both run-to-run (up to 3.4% for concentration and 1.6% for time values) and day-to-day precision (lower than 11.6% for concentration) have been established. Finally, the applicability of the MEEKC method developed has been demonstrated by analyzing levels of acrylamide present in samples of home-made French fries.

Coupling gravitational and flow field-flow fractionation, and size-distribution analysis of whole yeast cells.

This work continues the project on field-flow fractionation characterisation of whole wine-making yeast cells reported in previous papers. When yeast cells are fractionated by gravitational field-flow fractionation and cell sizing of the collected fractions is achieved by the electrosensing zone technique (Coulter counter), it is shown that yeast cell retention depends on differences between physical indexes of yeast cells other than size. Scanning electron microscopy on collected fractions actually shows co-elution of yeast cells of different size and shape. Otherwise, the observed agreement between the particle size distribution analysis obtained by means of the Coulter counter and by flow field-flow fractionation, which employs a second mobile phase flow as applied field instead of Earth's gravity, indicates that yeast cell density can play a major role in the gravitational field-flow fractionation retention mechanism of yeast cells, in which flow field-flow fractionation retention is independent of particle density. Flow field-flow fractionation is then coupled off-line to gravitational field-flow fractionation for more accurate characterisation of the doubly-fractionated cells. Coupling gravitational and flow field-flow fractionation eventually furnishes more information on the multipolydispersity indexes of yeast cells, in particular on their shape and density polydispersity.