(597e) Modeling of High Speed Continuous Flow Subcritical Water Extractions

The use of water near or over its boiling point under compression (i.e. subcritical water) has seen increasing use for the potential extraction of naturally-derived substrates utilized in the food and nutraceutical industries.  Whereas hot subcritical water extraction (SWE) can provide an alternative to the use of organic solvent media for such extractions, it has the potential for also converting and hence degrading the extracting solutes.  Thus alternative and rapid methods of performing SWE have been reported and optimized [1].  The modeling of such very rapid extractions (<10 min.) is important since partial extraction (~75-80 % of the desired solutes) may be deemed sufficient in order to minimize degradation and dilution of the resultant extracts.  This is particularly in the case when applying SWE for the valorization of agricultural waste streams such as grape pomace which are laden with natural antioxidants [1].

In this study, we have applied several different modeling concepts to better understand the rate of polyphenolic extraction as a function of time, both close to and above the boiling point of water.  A particular focus has been on predicting the “break point” in the extraction rate curve by employing combined thermodynamic-kinetic models [2], the “one or two-site” kinetic desorption models [3, 4 ], as well as mass transfer intensive models [5, 6] for optimizing SWE.  The latter can also include the effect of thermal degradation of the targeted solutes [6] as a mitigating factor in regulating the time of the SWE.  Our recently reported “hot-cold” method of applying SWE [1] can also be interpreted in terms of a model developed for explaining multiple “expresso”-based extractions [7].

A particularly simple model developed for predicting the extraction rate of natural antioxidants from foodstuffs [8] may also be applied to gain a better understanding of the process described in [1].  Here the extraction rate utilizes the sorption model advanced by Peleg [9] involving water sorption on both dry and wet substrates can be applied to predict the rapid extraction of antioxidant-laden extracts.  This presentation will conclude with an inter-comparison of the above models applied to the SWE of naturally-derived substrates.

References:

[1] J. K. Monrad, K. Srinivas, L. R. Howard, and J. W. King, J. Agric. Food Chem., 2012, 60, 5571-5582.

[2] J-W Kim and G. Mazza, j. Agric. Food Chem., 2006, 54, 7575-7584.

[3] A. Kubatova, B. Jansen, J.-F. Vaudoisot, and S.B. Hawthorne, J. Chromatogr., 2002, 975, 175-188.

[4] S.M. Ghoreishi, R. G. Shahrestani, and S.H. Ghaziaskar, World Acad. Sci. Eng. Techhnol., 2008, 100-110.

[5] M. Khajenoori, A.H. Asi, and F. Hormozi, Chinese J. Chem. Eng., 2009, 17, 359-365.

[6] L. Duan, Ph.D. Thesis, University of Arkansas, (2005).

[7] L. Navarini, E. Nobile, F. Pinto, A. Scheri, and F. Suggi-Liveran, Applied Thermal Eng., 2009, 29, 998-1004.

[8] S. Jokic, D. Velic, M. Bilic, A., Bucic-Konc, M. Planinic, and S. Tomas, Czech J. Food Sci., 2010, 28, 206-212.

[9] M. Peleg, J. Food Sci., 1988, 53, 1216-1219.