Pengembangan model matematik proses dekafeinasi biji kopi robusta dalam reaktor kolom tunggal

Abstract

Consumers drink coffee not as nutrition source, but as refreshment drink. For coffee consumers who have high tolerance for caffeine, coffee may warm up and refresh their bodies. However high caffeine content in coffee beans may cause health problems to consumers who are susceptible to caffeine. One of the efforts for coffee market expantion is product diversification to decaffeinated coffee. The general objective of this research was to optimize decaffeination process of robusta coffee in single column reactor with leaching method. The specific objectives of this research were to study process characteristic of Robusta coffee decaffeination in single column reactor using acetic acid as solvent, to develop mathematical model for predicting decaffeination time with leaching method, and to optimize process decaffeination of robusta coffee using developed model. Temperature (T) and concentration (c) of solvents were both variables analysed in decaffeination process. Mathematical model validation was checked by comparing prediction time (t-predict) versus observation time (t-obsr). Mathematical model was valid if the result showed that determination coefficient value (R2) > 0.75. Coffee decaffeination was processed using vertical single column reactor. A simple mathematic model for caffeine kinetic description during the extraction process (leaching) of coffee bean was developed. A non-steady diffusion equation coupled with a macroscopic mass transfer equation for solvent was developed and then solved analytically. The kinetic of caffeine extraction from coffee bean was expressed by:         - =- - - + - - 0.3 0.3 ).(4.4106. exp )( 3.3319 10.302)) ln 2 (det) (( 0 0.01282 ( 1041.82 / ) 1 2 A T AS c c c d d t p where d was coffee beans diameter (m), c was solvent concentration (%), T was solvent temperature (K), and cAS was caffeine content at-t (%). In the first step of decaffeination process, coffee beans was steamed during 1.5 hours using water vapour, and continued with leaching process using acetic acid, effluent of fermented cocoa beans, and tertiary solution of fermented cocoa pulp as solvents. Linier regression analysis showed that t-obsr = 0.8914. t-predict + 0.5045 with R2 0.9326 for acetic acid, t-obsr = 0.771.t-predict + 2.8137 with R2 0.9556 for effluent of fermented cocoa beans, and t-obsr = 0.8825.t-predict + 2.8354 with R2 0.7727 tertiary solution of fermented cocoa pulp as solvents. Response Surface Methodology (RSM) showed that optimum condition for coffee beans decaffeination was 0.4976%/hours decaffeination rate and 4.99 hours decaffeination time with 100oC solvent temperature and 69% solvent concentration using acetic acid as solvent; 0.3426%/hours decaffeination rate and 5.68 hours decaffeination time with 100oC solvent temperature and 55% solvent concentration using effluent of fermented cocoa beans as solvents; and 0.3016%/hours decaffeination rate and 6.57 hours decaffeination time with 100oC solvent temperature and 70% solvent concentration using tertiary solution of fermented cocoa pulp as solvent. The developed mathematical model can be used in designing single column reactor for coffee decaffeination process, to predict decaffeination time and rate, and decaffeination process in optimum condition using acetic acid, effluent of fermented cocoa beans, and tertiary solution of fermented cocoa pulp.

Kopi diminum oleh konsumen bukan sebagai sumber nutrisi melainkan sebagai minuman penyegar. Untuk penikmat kopi yang memiliki toleransi tinggi, kafein akan membuat tubuh menjadi lebih segar dan hangat. Tingginya kadar kafein di dalam biji kopi diduga dapat menyebabkan keluhan terutama bagi penikmat kopi yang memiliki toleransi rendah terhadap kafein. Tujuan umum dari penelitian ini adalah melakukan optimasi proses dekafeinasi biji kopi robusta dalam reaktor kolom tunggal dengan metode pengurasan (leaching). Tujuan khusus penelitian adalah karakterisasi proses dekafeinasi biji kopi robusta dengan pelarut asam asetat dalam reaktor kolom tunggal, pengembangan model matematik pendugaan waktu proses dekafeinasi biji kopi robusta dengan metode pengurasan (leaching), optimasi laju pelarutan kafein biji kopi robusta dengan menggunakan model matematik yang dikembangkan. Suhu (T) dan konsentrasi pelarut (c) adalah variabel yang diteliti dalam proses dekafeinasi. Validasi dilakukan dengan membandingkan data waktu proses prediksi (t-prediksi) yang diperoleh dari hasil model matematik yang dibangun dengan data waktu proses observasi (t-observasi) yang diperoleh dari hasil percobaan. Model simulasi dikatakan valid apabila diperoleh nilai koefisien determinasi (R2)>0.75. Proses dekafeinasi biji kopi dilakukan dalam reaktor kolom tunggal berbentuk silinder tegak. Model matematik untuk menggambarkan kinetika kafein selama proses ekstraksi (pengurasan) dalam biji kopi telah dikembangkan. Persamaan difusi pada kondisi tak mantap (non steady) yang berkaitan dengan persamaan perpindahan massa makroskopik untuk pelarut telah dikembangkan dan diselesaikan secara analitis. Kinetika ekstraksi kafein dari dalam biji kopi dapat diekspresikan dengan persamaan berikut :         - =- - - + - - 0.3 0.3 ).(4.4106. exp )( 3.3319 10.302)) ln 2 (det) (( 0 0.01282 ( 1041.82 / ) 1 2 A T AS c c c d d t p Dalam hal ini d adalah diameter biji kopi (m), c adalah konsentrasi pelarut (%), T adalah suhu pelarut (K), dan cAS adalah kadar kafein yang pada kondisi-t (%).