INVESTIGATION OF SOLVENT EXTRACTION KINETICS OF ANTIOXIDANTS FROM GRAPE MARC
Special Symposium - Innovations in Food Technology (LMC Congress)
Innovations in Food Technology - Poster Session (Food - P2)
Keywords: Antioxidants, grape, kinetics, marc, solvent-extraction
INVESTIGATION OF SOLVENT EXTRACTION KINETICS OF ANTIOXIDANTS FROM GRAPE MARC
Giorgia Spigno*, Lorenza Tramelli, Dante Marco De Faveri
Institute of Oenology and Food Engineering, Università Cattolica Sacro Cuore, Via Emilia Parmense, 84 – 29100 Piacenza, Italy
*e-mail: giorgia.spigno@unicatt.it, Tel: +390523599181, Fax: +390523599232
Some previous researches (1) had shown the feasibility and goodness of a one solvent-one-step extraction (compared to other literature results obtained with similar, longer or more complicated systems), to recovery phenolic compounds from grape marcs, which are a typical waste of wine-making production. The first optimisation experiments had led to the choice of solvent (ethanol), working temperature (60°C) and time (less than 5 h). In fact, it was observed that ethanol, besides being a safe solvent in view of food application of the extracts, allowed for high recovery yields; while, considering both final yield and economical aspects, it was suggested to work at 60°C for less than 8h. Trend of phenols yield could be well described by a first order kinetics up to a 5h time, but a detailed study on extraction rate and its relationship with temperature and antioxidant power of extracts will allow scaling-up and design of the process.
Aim of the present work was to investigate the effect of water addition to ethanol on recovery yield, since mixtures of alcohols and water have revealed to be more efficient than the corresponding mono-component solvent system(2). Then the extraction rate at 60°C up to 5h was studied to evaluate the influence of stirring variation on phenols extraction, together with the eventual influence of extraction time on quality of extracted phenols in terms of composition (percentage of tannins on total phenols) and antioxidant power.
Raw materials were pressed marcs (by Barbera and Pinot nero red grape) collected in the 2005 and 2006 vintages from two wine-making factories in northern Italy. They were oven dried at 60°C up to moisture content of about 2-4%, and milled through a 2mm sieve (final size ≤ 2mm). Dried marcs were extracted in a thermostatic rotary shaker (at 80 rpm) or by using a heated magnetic stirrer (corresponding to a higher stirring rate), with a 4/1 (w/v) ratio solvent/sample. Total phenols content was determined by direct reading at 280nm, and expressed as gallic acid equivalents (GAE) by means of a calibration curve. Percentage of tannins was estimated by the PVV method(3), and the antioxidant power (AOP) was assessed according to the ABTS assay(4).
Results showed that addition of water improved extraction rate, but above 40% water content an increased concomitant extraction occurred, leading to lower phenols contents in the extracts.
Experimental data obtained by both the stirring modalities could be described accurately by the use of the characteristic function in the general case of a polydispersed anisotropic solid(5): Cl = A – B•exp(-H∙t); where Cl is the liquid phase concentration, and t is the time (r2 and constants evaluated by non linear regression analysis, SPSS v.11.5) The increase in stirring rate, however, allowed to almost duplicate the phenol concentration (9.36 g/l versus 4.69 g/l at 5h). Tannin analysis revealed a constancy of composition of the extracted phenols over the time (between 67.9 and 72.8%), which was also supported by the ABTS assay: all the samples showed the same trend of AOP as a function of GAE concentration.
Further experiments for characterisation of structural changes of the solid phase by porosimetry during extraction, are needed to obtain the values of the kinetic coefficients (effective diffusion coefficient and external mass transfer coefficient), followed by the sizing up of the extraction unit.
(1) Spigno G.,& De Faveri D.M. (2007), J. Food. Eng. 78, 793-801.
(2) Yilmaz Y, & Toledo RT. (2006) J. Food Comp. Anal. 19, 41-44.
(3) Makkar H.P.S., Bluemmel M., Borowy N.K, & Becker K. (1993) J. Sci. Food Agric. 61, 161-165.
(4) Re R., Pellegrini N, Proteggente A., Pannala A., Yang M., & Rice-Evans C. (1999) Free Rad. Biol. Med. 26(9/10), 1231-1237.
(5) Simeonov E., Tsibranska I., & Minchev A. (1999) Chem. Eng. J. 73, 255-259.
Presented Thursday 20, 13:30 to 14:40, in session Innovations in Food Technology - Poster Session (Food - P2).
