USING ACTIVATED CARBON FOR NONENZYMATIC BROWNING COMPOUNDS ADSORPTION IN PEACH PULP

Adsorption of dark coloured compounds onto granular activated carbon (GAC) was evaluated at different concentrations (0.01, 0.02, 0.03, and 0.04 g GAC/g of peach pulp at a temperature range of 30-60 C. The adsorption equilibrium was quantified by means of adsorption isotherms in the range from 30 to 60 C. Absorbance data at 420nm were used to plot all the isotherms which were best described by Langmuir isotherm model as compared to Freundlich model. Also, the efficiency of the adsorption process was studied for different GAC concentrations at different temperatures, from which it was observed that there was a notable improvement in efficiency as the GAC concentrations and temperature increased. INTRODUCTION Peaches are considered to be the most widely cultivated and consumed fruit crops. Processing of fruit juices may introduce some detrimental changes such as hydrolysis of carbohydrates, destruction of vitamins and amino acids, development of undesirable browning reactions, taste and odours, and the loss of volatile compounds (Gonzalez et al., 1988). Browning in juices and fruit pulps during processing and storage is of vital interest of these alterations (Toribio and Lozano, 1984), mainly due to nonenzymatic browning (NEB) processes that are caused by the Maillard reaction which takes place between carbonyl and free amino groups (Ibarz et al., 1989). Polyphenolic compounds with relatively low molecular weights have been found to be responsible for physico-chemical deterioration of some fruit juices and concentrates during storage (Constenla and Lozano, 1995; Wu et al., 1990). Further NEB not only undermines the sensorial characteristics but also causes the loss of nutrients and the formation of intermediate undesirable compounds, like furfural and 5hydroxymethylfurfural (Buedo et al., 2000). Different agents including activated carbon, gelatine/bentonite, casein, ion-exchange waxes and polyvenylpolypyrrolidone (PVPP) have been used for the removal of polyphenols from fruit juices (Giovanelli and Ravasini, 1993). Activated carbons are considered to be the best absorbent for colours and organic matters due to their excellent adsorption efficiency (El-Geundi, 1995; Hameed et al., 2008 and Landi et al., 2009). Activated carbon of high porosity and high surface area is frequently used in industry for purification and environmental remediation. Relatively, activated carbon exhibits high adsorption capacity for phenolic compounds. Several studies have been carried out to determine the equilibrium relationship of adsorption of phenolic compounds on activated carbon by using the isotherm model such as Freundlich and Langmuir (Tseng et al., 2003; Vol. ( 40 ) No. ( 2 ) 2011 ISSN: 2224-9796 (Online) Mesopotamia J. of Agric ISSN: 1815 – 316 X (Print) 10 Arslanôglu et al., 2005; Carabasa et al., 1998; Maarof et al., 2003 and Khan A. et al., 1997). Received 12 / 1 / 2011 accepted 9 / 5 /2011 However, studies on the adsorption of dark coloured compounds from peach pulp using activated carbon are few. The aim of this work was to focus on the adsorption behaviour of activated carbon for the dark compounds produced by browning reactions in peach pulp. This study was designed to (1) determine the adsorption isotherms at deferent temperatures by the retention onto granular activated carbon of the dark compounds in browned peach pulp, (2) obtain the Langmuir and Freundlich isotherm models to describe the adsorption processes. Adsorption isotherms: the adsorption isotherms describe the relationships between the equilibrium concentrations of the adsorbate in the adsorbing phase (m) and the fluid phase (S) at a fixed temperature. The correlation of the isotherm data by theoretical or empirical equations is desired for practical operation. The most common type of isotherm model is when a single adsorbate is retained in only one molecular layer. In this case the Langmuir isotherm to which many experimental data of different systems are well adjusted should be utilized: m/m0 = Kads S/ (1 + KadsS) (1) where, m0 is the maximum concentration retained by the adsorbent and Kads is the Langmuir adsorption equilibrium constant, both are dependent on temperature and adsorbate-adsorbent system type. Equation (1) can be expressed as: 1/m = 1/m0 + 1/KadsSm0 (2) Another common isotherm model is Freundlich model: