High intensity ultrasound-assisted extraction of oil from soybeans

https://doi.org/10.1016/j.foodres.2004.02.016Get rights and content

Abstract

The application of 20 kHz high-intensity ultrasound during extraction of oil from two varieties of soybeans (TN 96-58 and N 98-4573) using hexane, isopropanol and a 3:2 hexane–isopropanol mixture was evaluated. In a simplified extraction procedure, ground soybeans were added to solvents and ultrasonicated between 0 and 3 h at ultrasonic intensity levels ranging from 16.4 to 47.6 W/cm2. Oil was recovered after distillation and yield and composition determined. Using hexane as a solvent, yield generally increased as both application time and intensity of ultrasound increased. Solvent type influenced the efficiency of the extraction, i.e., the highest yield was obtained using ultrasound in combination with the mixed solvent. Gas chromatography analysis of ultrasonicated soybean oil did not show significant changes in fatty acid composition. Results were attributed to mechanical effects due to ultrasonically induced cavitation increasing permeability of plant tissues. A comparison of scanning electron microscopy images of raw and ultrasonicated soybeans indicated development of microfractures and disruption of cell walls in ground soybean flakes. Our study suggests that high-intensity ultrasound may reduce time required to extract edible oils from plant sources and hence improve throughput in commercial oil production processes.

Introduction

Plant-based lipophilic compounds such as edible oils, phytochemicals, flavors, fragrances and colors are valuable products in the food, pharmaceutical and chemical industry. Extraction is one of the key processing steps in recovering and purifying lipophilic ingredients contained in plant-based materials (Liu, 1999). Classical extraction technologies are based on the use of an appropriate solvent to remove lipophilic compounds from the interior of plant tissues. The choice of a suitable solvent in combination with sufficient mechanical agitation influences mass transport processes and subsequently efficiency of the extraction. The most widely used solvent to extract edible oils from plant sources is hexane. Hexane is available at low cost and is efficient in terms of oil and solvent recovery (Mustakas, 1980; Serrato, 1981). More recently, the use of alternative solvents such as alcohols (isopropanol or ethanol) and supercritical carbon dioxide has increased due to environmental, health and safety concerns (Dunnuck, 1991). Alternative solvents are often less efficient due to a decreased molecular affinity between solvent and solute and costs for solvent and process equipment can be higher (Baker & Sullivan, 1983; Freidrich & Pryde, 1984; Karnofsky, 1981).

A potential new technology that may improve extraction of lipophilic compounds from plants is high-intensity ultrasound. High-intensity ultrasonication can accelerate heat and mass transport in a variety of food process operations and has been successfully used to improve drying, mixing, homogenization and extraction (Fairbanks, 2001; Mason, 1992; Mason, Paniwnyka, & Lorimera, 1996; Povey, 1998). Ultrasonication is the application of high-intensity, high-frequency sound waves and their interaction with materials (Luque-Garcı́a & Luque de Castro, 2003). The propagation and interaction of sound waves alters the physical and chemical properties of materials that are subjected to ultrasound (Mason & Lorimer, 1988). In the case of raw plant tissues, ultrasound has been suggested to disrupt plant cell walls thereby facilitating the release of extractable compounds and enhance mass transport of solvent from the continuous phase into plant cells (Vinatoru, 2001).

Hui, Etsuzo, and Masao (1994) utilized ultrasound to extract saponin from ginseng and observed that yield of total extraction increased by 15% and yield of saponin by 30%. Romdhane and Gourdon (2002) investigated extraction of pyrethrines from pyrethrum flowers and oil from woad seeds. In both cases, acceleration of extraction kinetics and increase in yield was observed, however less so in the case of woad seeds. Vinatoru et al. (1997) showed improved yields of lipophilic compounds extracted from herbs such as coriander and fennel.

Based on these studies, we hypothesize that application of high-intensity ultrasound may improve extraction of oil from soybeans. The objective of this study was to test this hypothesis by determining the influence of sonication time and intensity in combination with different solvents on the efficiency of oil extraction from soybeans.

Section snippets

Materials

Two soybean varieties, TN 96-58, a popular Tennessee variety, and N 98-4573, a North Carolina specialty variety, were obtained from the Crops Laboratory at The University of Tennessee. Compositional analysis of the two soybean varieties indicated a total lipid content of 19.6% for TN 96-58 and 19.1% for N 98-4573, a protein content of 42.2% for TN 96-58 and 42.7% for N 98-4573 and an ash content of 5.43% for TN 96-58 and 5.34% for N 98-4573 (Stassi, 2003). AOCS Mix No. 3, a fatty acid standard

Solvent extraction in the absence of high-intensity ultrasound

The oil extraction capabilities of three different solvents (hexane, isopropanol, and hexane:isopropanol mixture, 60:40%, v/v) at extraction times ranging from 30 min to 3 h are shown in Fig. 2. When the extraction time increased from 30 min to 3 h oil yield of TN 96-58 increased by 4.5%, 5.8% and 8.8% using isopropanol, hexane, and the mixed solvent. In general, oil yield increased with treatment time irrespective of the type of solvent used, but the mixed solvent was superior in terms of oil

Conclusions

The results obtained in this study have implications for the edible oil industry. Ultrasound has the potential to be used in oil extraction processes to improve efficiency and reduce processing time. During commercial solvent extraction, a series of time-consuming preparation steps is necessary to achieve the maximum oil yield. These key steps involve cleaning, dehulling, moisture conditioning, flaking and heating. Our study demonstrated that a simplified, short term extraction procedure that

Acknowledgements

The authors thank Dr. V. Pantalone for supplying the soybean varieties and Mrs. Amayeth Spencer and Mr. Rahul Seshadri for their support in the GC analysis. This project was supported by the Tennessee Agricultural Experiment Station (Project Nos. TEN 226 and TEN 230).

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