Alterações químicas, sensoriais e microscópicas do café cereja descascado em função da taxa de remoção de água

Abstract

Este trabalho teve como objetivos avaliar o efeito de diferentes períodos de pré-secagem em terreiro e temperaturas de secagem, na taxa de redução de água, na composição química, na qualidade da bebida do café e alterações na estrutura das membranas e paredes celulares do endosperma de grãos de café cereja descascado (Coffea arabica L.). O café foi submetido a dois tempos de pré-secagem, 1 e 3 dias de terreiro. Após a pré-secagem, o produto foi submetido à secagem em três secadores experimentais com camada fixa de 13 cm de espessura, utilizando-se três temperaturas médias na massa de café 40°C, 50°C e 60°C, com fluxo de ar de 20 m3 m-1 m-2, com quatro repetições no tempo. Nos secadores, para o acompanhamento da perda de água e obtenção das curvas de secagem, as amostras foram pesadas a cada 1 hora. A secagem foi interrompida quando o café atingiu a massa correspondente ao teor de água de 11% (bu). As temperaturas da massa de café foram medidas a cada 30 minutos. Além das curvas de secagem, foram obtidas as curvas da taxa de redução de água. Observou-se que o tempo de secagem diminuiu com o aumento da temperatura e do período de pré-secagem e que a taxa de remoção de água foi menor para a temperatura de 40°C e 3 dias de pré-secagem. Para a avaliação da qualidade, foram realizadas as seguintes análises: condutividade elétrica, lixiviação de potássio, acidez graxa, açúcares totais, redutores e não-redutores. Verificou-se que a condutividade elétrica, a lixiviação de potássio e a acidez graxa aumentaram significativamente com a elevação da temperatura. O aumento no período de pré-secagem ocasionou redução na lixiviação de potássio e acréscimos nos valores de açúcares redutores. O período de três dias de pré- secagem possibilitou a obtenção de uma bebida de qualidade superior em relação a um dia de pré-secagem. Nas análises histoquímicas e ultra-estruturais para avaliar alterações na membrana plasmática, foi possível observar, nos grãos secados a 40°C, a manutenção da compartimentalização dos corpúsculos de óleo, os quais apresentaram-se distribuídos uniformemente em todo o perímetro interno da membrana; o espaço entre a membrana plasmática e a parede celular (lúmen) apresentou-se vazio. Em contraste, nos grãos de café secos a 60°C, observou-se a fusão dos corpúsculos de óleo formando grandes gotas no espaço intercelular, com total preenchimento do lúmen celular, indicando a ruptura da membrana plasmática e a ruptura e coalescência das vesículas celulares.

This work was intended to evaluate the effect of different temperatures and pre-drying periods on yard on the drying time, rate of water reduction, on the chemical composition, the quality of the beverage of coffee and cell alterations in the structure of the membranes and cell walls of the endosperm of peeled cherry coffee beans. The coffee was submitted to two pre-drying times, 1 and 3 days on yard. After the pre-drying, the produce was submitted to drying in three experimental dryers with fixed layer of 13 cm in thickness, by using three average temperatures in the coffee mass 40°C, 50°C and 60°C with an air flow of 20m3 m-1 m-2 with four replicates in time. In the dryers, for monitoring of water loss and attainment of the drying curves, the samples were weighed every 1 hour. Drying stopped when the coffee reached the mass corresponding to 11% of moisture (bu). The temperatures of the coffee mass were measured every 30 minutes. In addition to the drying curves, curves of water reduction rates were obtained. It was observed that the drying time diminished as both temperature and the period of pre-drying increased and that the water removal rate was lesser for the temperature of 40°C and 3 days’ pre-drying. For evaluation of quality, the following analyses were accomplished electrical conductivity, potassium leaching, fatty acidity, total sugars, reducing and non-reducing sugars and sensorial analyses. It was found that electrical conductivity, potassium leaching and fatty acidity increased significantly as temperature was risen. The increase in the pre-drying period caused reduction in the potassium leaching and increases in the values of reducing sugars. The 3-day pre-drying period enabled the obtaining of a beverage of superior quality in relation to one-day pre-drying. This work was intended to evaluate the effect of different temperatures and pre-drying periods on yard on the drying time, rate of water reduction, on the chemical composition, the quality of the beverage of coffee and cell alterations in the structure of the membranes and cell walls of the endosperm of peeled cherry coffee beans. The coffee was submitted to two pre-drying times, 1 and 3 days on yard. After the pre-drying, the produce was submitted to drying in three experimental dryers with fixed layer of 13 cm in thickness, by using three average temperatures in the coffee mass 40°C, 50°C and 60°C with an air flow of 20m3 m-1 m-2 with four replicates in time. In the dryers, for monitoring of water loss and attainment of the drying curves, the samples were weighed every 1 hour. Drying stopped when the coffee reached the mass corresponding to 11% of moisture (bu). The temperatures of the coffee mass were measured every 30 minutes. In addition to the drying curves, curves of water reduction rates were obtained. It was observed that the drying time diminished as both temperature and the period of pre-drying increased and that the water removal rate was lesser for the temperature of 40°C and 3 days’ pre-drying. For evaluation of quality, the following analyses were accomplished electrical conductivity, potassium leaching, fatty acidity, total sugars, reducing and non-reducing sugars and sensorial analyses. It was found that electrical conductivity, potassium leaching and fatty acidity increased significantly as temperature was risen. The increase in the pre-drying period caused reduction in the potassium leaching and increases in the values of reducing sugars. The 3-day pre-drying period enabled the obtaining of a beverage of superior quality in relation to one-day pre-drying.