Ilse Fraeye

Flocculation of Chlorella vulgaris induced by high pH: Role of magnesium and calcium and practical implications

Microalgae hold great potential as a feedstock for biofuels or bulk protein or treatment of wastewater or flue gas. Realising these applications will require the development of a cost-efficient harvesting technology. Here, we explore the potential of flocculation induced by high pH for harvesting Chlorella vulgaris. Our results demonstrate that flocculation can be induced by increasing medium pH to 11. Although both calcium and magnesium precipitated when pH was increased, only magnesium (≥0.15 mM) proved to be essential to induce flocculation. The costs of four different bases (sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide and sodium carbonate) were calculated and evaluated and the use of lime appeared to be the most cost-efficient. Flocculation induced by high pH is therefore a potentially useful method to preconcentrate freshwater microalgal biomass during harvesting.

Antioxidant potential of microalgae in relation to their phenolic and carotenoid content

In the past decades, food scientists have been searching for natural alternatives to replace synthetic antioxidants. In order to evaluate the potential of microalgae as new source of safe antioxidants, 32 microalgal biomass samples were screened for their antioxidant capacity using three antioxidant assays, and both total phenolic content and carotenoid content were measured. Microalgae were extracted using a one-step extraction with ethanol/water, and alternatively, a three-step fractionation procedure using successively hexane, ethyl acetate, and water. Antioxidant activity of the extracts varied strongly between species and further depended on growth conditions and the solvent used for extraction. It was found that industrially cultivated samples of Tetraselmis suecica, Botryococcus braunii, Neochloris oleoabundans, Isochrysis sp., Chlorella vulgaris, and Phaeodactylum tricornutum possessed the highest antioxidant capacities in this study and thus could be a potential new source of natural antioxidants. The results from the different types of extracts clearly indicated that next to the well-studied carotenoids, phenolic compounds also contribute significantly to the antioxidant capacity of microalgae.

Comparative study of the cell wall composition of broccoli, carrot, and tomato: Structural characterization of the extractable pectins and hemicelluloses

This study delivers a comparison of the pectic and hemicellulosic cell wall polysaccharides between the commonly used vegetables broccoli (stem and florets separately), carrot, and tomato. Alcohol-insoluble residues were prepared from the plant sources and sequentially extracted with water, cyclohexane-trans-1,2-diamine tetra-acetic acid, sodium carbonate, and potassium hydroxide solutions, to obtain individual fractions, each containing polysaccharides bound to the cell wall in a specific manner. Structural characterization of the polysaccharide fractions was conducted using colorimetric and chromatographic approaches. Sugar ratios were defined to ameliorate data interpretation. These ratios allowed gaining information concerning polysaccharide structure from sugar composition data. Structural analysis of broccoli revealed organ-specific characteristics: the pectin degree of methoxylation (DM) of stem and florets differed, the sugar composition data inferred differences in polymeric composition. On the other hand, the molar mass (MM) distribution profiles of the polysaccharide fractions were virtually identical for both organs. Carrot root displayed a different MM distribution for the polysaccharides solubilized by potassium hydroxide compared to broccoli and tomato, possibly due to the high contribution of branched pectins to this otherwise hemicellulose-enriched fraction. Tomato fruit showed the pectins with the broadest range in DM, the highest MM, the greatest overall linearity and the lowest extent of branching of rhamnogalacturonan I, pointing to particularly long, linear pectins in tomato compared with the other vegetable organs studied, suggesting possible implications toward functional behavior.

Influence of organic matter generated by Chlorella vulgaris on five different modes of flocculation

Microalgae excrete relatively large amounts of algal organic matter (AOM) that may interfere with flocculation. The influence of AOM on flocculation of Chlorella vulgaris was studied using five different flocculation methods: aluminum sulfate, chitosan, cationic starch, pH-induced flocculation and electro-coagulation-flocculation (ECF). The presence of AOM was found to inhibit flocculation for all flocculation methods resulting in an increase of dosage demand. For pH-induced flocculation, the dosage required to achieve 85% flocculation increased only 2-fold when AOM was present, while for chitosan, this dosage increased 9-fold. For alum, ECF and cationic starch flocculation, the dosage increased 5-6-fold. Interference by AOM is an important parameter to consider in the assessment of flocculation-based harvesting of microalgae.

The occurrence of N-nitrosamines, residual nitrite and biogenic amines in commercial dry fermented sausages and evaluation of their occasional relation.

Regarding food borne intoxications, the accumulation of biogenic amines must be avoided in all kinds of food products. Moreover, biogenic amines can function as precursors for the formation of carcinogenic N-nitrosamines when nitrite is present. To estimate the food safety of the dry fermented sausages available on the Belgian market, a screening of the residual sodium nitrite and nitrate contents, biogenic amines and volatile N-nitrosamine concentrations was performed on 101 samples. The median concentrations of residual NaNO2 and NaNO3 were each individually lower than 20mg/kg. In general, the biogenic amine accumulation remained low at the end of shelf life. Only in one product the amounts of cadaverine and putrescine reached intoxicating levels. Concerning the occurrence of N-nitrosamines, only N-nitrosopiperidine and N-nitrosomorpholine were detected in a high number of samples (resp. 22% and 28%). No correlation between the presence of N-nitrosamines and the biogenic amines content was observed. Although the N-nitrosamines could not been linked to specific product categories, the occurrence of N-nitrosopiperidine could probably be attributed to the use of pepper.

Effect of Temperature and High Pressure on the Activity and Mode of Action of Fungal Pectin Methyl Esterase

Pectin was de‐esterified with purified recombinant Aspergillus aculeatus pectin methyl esterase (PME) during isothermal‐isobaric treatments. By measuring the release of methanol as a function of treatment time, the rate of enzymatic pectin conversion was determined. Elevated temperature and pressure were found to stimulate PME activity. The highest rate of PME‐catalyzed pectin de‐esterification was obtained when combining pressures in the range 200–300 MPa with temperatures in the range 50–55 °C. The mode of pectin de‐esterification was investigated by characterizing the pectin reaction products by enzymatic fingerprinting. No significant effect of increasing pressure (300 MPa) and/or temperature (50 °C) on the mode of pectin conversion was detected.

Volatile N-nitrosamines in meat products: Potential precursors, influence of processing, and mitigation strategies

ABSTRACT Meat products can be contaminated with carcinogenic N-nitrosamines, which is ascribed to the reaction between a nitrosating agent, originating from nitrite or smoke, and a secondary amine, derived from protein and lipid degradation. Although in model systems it is demonstrated that many amine containing compounds can be converted to N-nitrosamines, the yield is dependent of reaction conditions (e.g., low pH and high temperature). In this article, the influence of the composition of the meat products (e.g., pH, aw, spices) and processing (e.g., ageing, ripening, fermentation, smoking, heat treatment and storage) on the presence and availability of the amine precursors and the N-nitrosamine formation mechanism is discussed. In addition, this article explores the current N-nitrosamine mitigation strategies in order to obtain healthier and more natural meat products.

Formation of naturally occurring pigments during the production of nitrite-free dry fermented sausages.

This study investigates the potential of producing red coloured dry fermented sausages without the addition of nitrite and/or nitrate. Therefore, the formation of zinc protoporphyrin IX (Zn(II)PPIX) as naturally occurring pigment, and the interrelated protoporphyrin IX (PPIX) and heme content were evaluated during nitrite-free dry fermented sausage production at different pH conditions. Zn(II)PPIX was only able to form in dry fermented sausages at pH conditions higher than approximately 4.9. Additionally, the presence of Zn(II)PPIX increased drastically at the later phase of the production process (up to day 177), confirming that in addition to pH, time is also a crucial factor for its formation. Similarly, PPIX also accumulated in the meat products at increased pH conditions and production times. In contrast, a breakdown of heme was observed. This breakdown was more gradual and independent of pH and showed no clear relationship with the formed amounts of Zn(II)PPIX and PPIX. A statistically significant relationship between Zn(II)PPIX formation and product redness was established.

APPLICATION OF ACCELERATED SOLVENT EXTRACTION (ASE) AND THIN LAYER CHROMATOGRAPHY (TLC) TO DETERMINATION OF PIPERINE IN COMMERCIAL SAMPLES OF PEPPER (PIPER NIGRUM L.)

In this preliminary study, an attempt was made to develop a simple yet reliable overall approach to quantification of piperine in pepper (Piper nigrum L.), and also in the other piperine-containing spice compositions. Such an approach can prove useful for rapid screening of the commercially traded pepper (and other spices) in a pulverized form, with piperine as a single adulteration marker. The main features of this approach consist in a rapid (ca. 40 min) and exhaustive (as proved in a recovery experiment) extraction of plant material with use of Accelerated Solvent Extraction (ASE), followed by an easy thin-layer chromatographic quantification of piperine in the obtained extracts. Within the framework of this approach, dichloromethane (DCM) was selected as an extracting agent and the extraction temperature was fixed at 70°C. With use of the piperine standard, the calibration curve was developed and applicability of the proposed approach was tested upon the commercial samples of white and black pepper in a pulverized and peppercorn form. The piperine levels obtained with the commercial pepper samples remained in agreement with the data available from the literature. Moreover, the assumed quantification approach correctly differentiates between the lower piperine levels in an unripe (black) pepper and the higher ones in a ripe (white) pepper, and also between the lower piperine levels extractable from the whole peppercorn and the higher ones extractable from the ground pepper. Now on the basis of this preliminary study, a completely validated method of quantifying piperine in botanical matter with use of the proposed approach can be elaborated.

DETERMINATION OF HEMIN, PROTOPORPHYRIN IX, AND ZINC(II) PROTOPORPHYRIN IX IN PARMA HAM USING THIN LAYER CHROMATOGRAPHY

An effort was undertaken to investigate a possibility to quantify hemin, protoporphyrin IX (PPIX), and zinc(II) protoporphyrin IX (Zn(II)PPIX) by means of thin-layer chromatography (TLC). All these porphyrins naturally occur in meat and meat products, and they are known for being metabolically interrelated in a not yet fully understood fashion. In view of the results of a current research in meat chemistry, it seems most likely that Zn(II)PPIX is responsible for the red color of Parma ham (a traditional Italian dry ham). This discovery prompted a novel concept that Zn(II)PPIX might replace sodium nitrite and potassium nitrate in the function of the red color-forming pigment, the latter two compounds traditionally used for the same purpose in meat industry, yet known for the formation of the carcinogenic N-nitrosamines as well. In this study, a novel analytical system was proposed for the successful baseline separation of hemin, PPIX, and Zn(II)PPIX, and a possibility was tested of quantifying these three porphyrins in Parma ham. To this effect, the calibration curves were established for the porphyrin standards. Due to the recognized photosensitivity of hemin, PPIX, and Zn(II)PPIX, extraction of these three compounds from Parma ham and the thin-layer chromatographic procedure were carried out in the darkness, although a complete blackout was not always possible. One problem remained unsolved in this study, namely the selection of a proper (preferably a visible light resistant, hence a nonporphyrin) internal standard (IS) for the performance of the recovery procedure for hemin, PPIX, and Zn(II)PPIX contained in the meat matrix. Finally, it was concluded that the elaborated TLC procedure can successfully be implemented to quantification of hemin and PPIX in Parma ham (and in the other meat products as well).