ABSTRACT
BACKGROUND: Pesticide quantitation in foods relies on the availability of matrix reference materials, which, however, are scarce because of the general instability of pesticides. In particular, no avocado reference material has been developed. OBJECTIVE: This research aimed to develop a reference material to support the determination of pesticide residues in avocado. METHOD: Avocado was spiked with 11 selected pesticides at levels of 0.01-0.35 mg/kg. The production process included the assessment of between-unit heterogeneity, stability during dispatch, and best storage conditions according to ISO 17034. Reference values were estimated through an interlaboratory comparison study involving laboratories of demonstrated competence and adhering to ISO/IEC 17025. The corresponding expanded uncertainties were calculated as 4-19% in compliance with the Guide to the Expression of Uncertainty in Measurement. RESULTS: The reference material was sufficiently homogeneous and stable at 4°C during the entire study period (365 days) for most of the pesticides, and at 40°C during 10 days, but it was unstable at 50 and 60°C during 10 days. Four pesticides showed downward trends; however, this behavior was considered in the uncertainty budget. As this material complied with all requirements of proficiency testing, it was used in an interlaboratory proficiency test designed to investigate analytical performance and assist laboratories in improving the quality of measurement results. CONCLUSIONS: The presented material can be used for the development of novel analytical methods or in-house reference materials and adds to the scarce supply of reference materials for the determination of pesticides in vegetable matrixes with high oil contents and intermediate water contents. HIGHLIGHTS: A novel reference material has been developed for the reliable and accurate quantitation of multiple pesticides in avocado, allowing researchers to avoid the preparation of in-house reference materials for this purpose.
Subject(s)
Persea , Pesticide Residues , Pesticides , Laboratory Proficiency Testing , Persea/chemistry , Pesticide Residues/analysis , Pesticides/analysis , VegetablesABSTRACT
Resumen Los metabolitos secundarios producidos por hongos son ampliamente diversos en estructura y función, lo que provee una fuente de compuestos con actividad biológica para aplicaciones en agricultura, farmacia y procesamiento de alimentos. Entre los metabolitos secundarios se encuentran compuestos orgánicos volátiles (COVs) a los cuales se atribuye un papel determinante en la comunicación entre microorganismos. En este trabajo empleamos una cámara de ensayos comunicada por el espacio de cabeza para evaluar la actividad debida únicamente a COVs. Los resultados indican que los COVs liberados por T. viride afectan el crecimiento de los hongos fitopatógenos evaluados. En el caso de Fusarium sp. se afectaron los halos de crecimiento y para Colletotrichum gloeosporioides se observaron cambios morfológicos en su color. Para identificar los COVs responsables de esta actividad, se usaron 3 técnicas de extracción: Headspace dinámico (HSD), headspace estático (HSE) y extracción líquido-líquido (ELL) y el análisis por cromatografía de gases acoplada a espectrometría de masas (GCMS). Mediante el muestreo del HSD y HSE se encontraron alcoholes y lactonas, mientras que en ELL los compuestos mayoritarios fueron alcoholes y varios ácidos orgánicos. Entre los compuestos determinados por las tres técnicas se encuentran alcohol bencílico, alcohol 2-feniletílico, 6-pentil-2H-piran-2-ona y gama-butirolactona. Esta última identificada por primera vez en T. viride. La comparación de las tres técnicas de extracción permitió establecer que HSD es el método de extracción de COVs que mejor simula la situación presentada en la cámara de evaluación de actividad biológica, permitiendo así identificar los COVs responsables de la actividad antifúngica detectada.
Abstract The secondary metabolites produced by fungi widely vary in structure and function, providing a rich source of biologically active compounds with applications in farming, pharmacology and food processing. Volatile organic compounds (VOCs) are a biologically relevant class of secondary metabolites, since they are suspected of playing a crucial role in the communication between microorganisms. In this work, we use a test headspace chamber to evaluate the VOCs mediated antifungal activity of T. viride against Fusarium sp. and Colletotricum gloeosporiodes. We observed that VOCs produced by T. viride interact with both fungi affecting the growth halos of Fusarium sp. and modifying the colour of Colletotricum gloeosporiodes. The VOCs responsible for this activity were identified using three extraction techniques: Dynamical Headspace (DHS), Static Headspace (SHS) and liquid-liquid extraction (LLE), all of them analyzed via gas chromatography coupled to mass spectrometry (GCMS). DHS and SHS identified alcohols and lactones as VOCs, while with LLE we found a large number of alcohol components and several organic acids. All three techniques identified benzyl alcohol, 2-phenylethyl alcohol, 6-pentyl-2H-pyran-2-one and, for the first time associated to T. viride, gama-butirolactone. After comparison between these extraction techniques, we established that DHS provides the most accurate simulation of biological activity in the test chamber, which reflects in a reliable identification of the VCOs with antifungal activity.
ABSTRACT
La formación de los compuestos volátiles durante la maduración de la guayaba (Psidium guajava L.) ha sido un aspecto ampliamente estudiado; sin embargo, se desconocen los cambios de estos compuestos en variedades blancas de los cultivos colombianos como Guavatá Victoria (GV), Regional Blanca (RB) y Ráquira (RQ). Se utilizó el método Headspace-Microextracción en Fase Sólida (HS-MEFS) para comparar los perfiles olfativos de tres variedades de guayaba blanca de la región de la hoya del río Suárez (Santander, Colombia) durante tres etapas de maduración (verde, pintón y maduro). En las tres variedades se presentó un comportamiento similar, los aldehidos C-6 (hexanal, (Z)-3-hexenal y (E)-2-hexenal) responsables de la nota verde disminuyen durante la maduración, mientras que el contenido de ésteres (acetato de hexilo y acetato de (Z)-3-hexenilo) aumenta produciéndose las notas dulce y frutal características de la fruta madura. Los compuestos ácidos, furánicos y alcoholes se observan en bajas proporciones durante las tres etapas. El análisis de los compuestos volátiles mediante HS-MEFS permitió establecer una relación entre la transformación de compuestos aldehídos C6, responsables de la nota verde, en ésteres análogos, a los cuales se les atribuye la nota frutal característica durante el proceso de maduración.
The composition of volatile compounds during guava ripening (Psidium guajava L.) has been an aspect broadly studied. However, the changes of these compounds in representative white varieties from Colombia, like Guavatá Victoria (GV), Regional Blanca (RB) and Ráquira (RQ) are still unknown. Comparison of the aroma profiles was done using heads-pace-Solid Phase Micro Extraction (HS-SPME) for three white guava varieties from the Suárez River Basin region (Santander, Colombia) during three maturation stages (green, half-ripened and ripen). The three varieties presented a similar behavior, the C6- aldehydes (hexanal, (Z)-3-hexenal and (E)-2-hexenal) characterized for a green note diminished during ripening, while ester amounts (hexyl acetate and (Z)-3-hexenyl acetate) increase, producing sweet and fruity notes characteristics in a ripen fruit. The acids, furanics and alcohol compounds are present in low proportions at the three stages. Through HS-SPME analysis, we established a relation between C6-aldehy-des compounds transformation, responsible of the green note, into analogue esters that contribute to the fruity note during the ripening process.
A formação dos compostos voláteis durante o processo de amadurecimento da goiaba (Psidium guajava L.) tem sido muito estudada. Entretanto, pouco se conhece sobre as mudanças desses compostos nas variedades brancas representadas pela Guavatá Victoria (GV), Regional Blanca (RB) e Ráquira (RQ) na região do rio Suárez (Santander-Colômbia). O emprego da técnica HS-MEFS (Heads-pace-Microextração em fase sólida) para comparar o perfil olfativo durante as etapas da maturação (verde, semimaduro e maduro) mostrou um comportamento similar nas três variedades de goiaba branca: os aldeídos C-6 (hexanal, (Z)-3-hexe-nal e (E)-2-hexenal), caracterizados por uma nota verde, diminuíram ao longo do amadurecimento, enquanto que o conteúdo de ésteres (acetato de hexilo e acetato de (Z)-3-hexenilo) aumentou, produzindo as notas doces e frutal caracteristicas da fruta madura. Os compostos ácidos, furânicos e alcoólicos foram observados em baixas concentrações nas três etapas de maturação. Por fim, a técnica HS-MEFS permitiu detectar a rápida transformação dos compostos aldeídos C6, causadores da nota verde em ésteres análogos que causam a nota frutal durante o processo da maturação.
