Comparative studies of the sample decomposition of green and roasted coffee for determination of nutrients and data exploratory analysis

Abstract

Os teores de vários nutrientes foram determinados em 35 amostras de cafés verdes e torrados, por espectrometria de absorção atômica em chama (Ca, Mg, Fe, Cu, Mn e Zn), fotometria de emissão atômica em chama (Na e K) e pelo método Kjeldahl (N) após preparação das amostras por dois procedimentos de decomposição via úmida: i) sistema aberto (bloco digestor) e ii) sistema fechado (forno de microondas convencional com controle de pressão e temperatura). A exatidão dos procedimentos foi verificada analisando-se três materiais de referência certificados do National Institute of Standards and Technology (SRM 1573a Folha de Tomateiro; SRM 1547 Folha de Pessegueiro; SRM 1570a Espinafre). A análise dos dados após a aplicação do teste-t mostrou que os resultados obtidos no procedimento que empregou decomposição assistida por microondas em frascos fechados foram mais exatos do que os obtidos por bloco digestor com frascos abertos no nível de 95% de confiança. Além da exatidão, outras características favoráveis encontradas foram menores valores de branco analíticos, menor consumo de reagentes e menor tempo de decomposição das amostras. Análises exploratórias dos dados empregando-se Análise por Componentes Principais (PCA) e Análise por Agrupamentos Hierárquicos (HCA) mostraram que os elementos Na, K, Ca, Cu, Mg e Fe foram os principais responsáveis na diferenciação das amostras de cafés verde e torrado.The contents of some nutrients in 35 Brazilian green and roasted coffee samples were determined by flame atomic absorption spectrometry (Ca, Mg, Fe, Cu, Mn, and Zn), flame atomic emission photometry (Na and K) and Kjeldahl (N) after preparing the samples by wet digestion procedures using i) a digester heating block and ii) a conventional microwave oven system with pressure and temperature control. The accuracy of the procedures was checked using three standard reference materials (National Institute of Standards and Technology, SRM 1573a Tomato Leaves, SRM 1547 Peach Leaves, SRM 1570a Trace Elements in Spinach). Analysis of data after application of t-test showed that results obtained by microwave-assisted digestion were more accurate than those obtained by block digester at 95% confidence level. Additionally to better accuracy, other favorable characteristics found were lower analytical blanks, lower reagent consumption, and shorter digestion time. Exploratory analysis of results using Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) showed that Na, K, Ca, Cu, Mg, and Fe were the principal elements to discriminate between green and roasted coffee samples. Keywords: sample preparation, coffee, nutrients, exploratory analysis IntroductionCoffee is an important commodity due to the high consumption of its beverage by people worldwide.1 Since the value of coffee beans is based on quality, producers and traders have been motivated to make use of extra tools in order to confirm the geographic origin of the coffee. 2,3 In this context, inorganic chemical analyses of green and roasted coffees may be used to a...

Direct multielement determination of Cd, Pb, Fe, and Mn in ground coffee samples using energy dispersive X‐ray fluorescence spectrometry

“…Each sample of 250 mg was digested using 7.0 mL of concentrated HNO 3 and 1.0 mL of 30% (w/w) H 2 O 2 . [ 3,34–37 ] The microwave oven program used to digest the coffee samples is shown in Table 1.…”

The concentration of potentially toxic elements (PTEs) in the coffee products: a systematic review and meta-analysis

“…Moreover, Welna et al (2013) noted that the transfer of PTEs into brew might vary probably related to coffee type (instant and ground coffees). Amorim Filho et al (2007) also observed that the concentration of Fe and Cr is highest in steel grinders because of releasing these metals into the coffee samples via the mill overheating. Additionally, Nędzarek et al (2013) reported that potential contamination with PTEs may originate from packaging materials containing metals during coffee storage.…”

“…In the case of the brewing method, it is reported that the extraction levels of most PTEs are highest in the Turkish coffee method, in which coffee is boiled together with water (Nędzarek et al 2013;Şemen et al 2017). Regarding the type of coffee in terms of raw or roasted, it is noteworthy that the concentrations of PTEs in green coffee are typically lower than those determined in roasted coffees, probably due to removing water and volatile constituents (Amorim Filho et al 2007;da Silva et al 2017). Moreover, Şemen et al (2017) concluded that studied PTEs are leached to the infusion more difficult from roasted coffee than from green coffee.…”

Geographical Characterization of Beans Based on Trace Elements After Microwave-Assisted Digestion Using Diluted Nitric Acid

“…0.13-0.17 0.14-0.17 0.15-0.17 0.14-0.17 Tables 2 and 3 show that the concentration of analytes (major and trace elements) exhibited different orders of magnitude. Therefore, data were autoscaled before HCA and PCA in order to achieve independence on the factors of different scale of the element concentrations, in order to for all the factors to have the same importance (Amorim Filho et al 2007;Anunciação et al 2011).…”