Progress 09/01/05 to 08/31/08
Outputs
OUTPUTS: Soymilk and tofu consumption have been increasing in Western countries in recent years, while being popular for many centuries in Asian countries. The renewed consumer interest in these products is largely due to: i) the soy protein health claim approved in 1999 by the U.S. Food and Drug Administration, and (ii) the abundant body of literature on the health benefits of soy protein and isoflavone consumption. Thermal treatment is applied to soymilk to assure its safety and increase its shelf life. Thermal treatment also decreases antinutritional trypsin inhibitors content by 90 percent, and inactivates lipoxygenase, an enzyme responsible for soymilk off-flavor. However, the thermal process can decrease the nutritional quality of soymilk as well as add undesirable off-flavors; therefore identification of an alternative process might benefit soymilk quality. The outputs of this project are to identify processing conditions using high-pressure technology, combined or not with mild temperature treatment, to produce more healthy and functional foods. Our findings were disseminated to national and international presentations and publications. PARTICIPANTS: Dr. Murphy (ISU), Dr. Bala Balasubramanian (OSU). Dr. Cadwallader (University of Illinois) and Dr. de Lamballerie-Anton (France) collaborated on different part of this project. Three students and two post doctoral research associates participated in the research of this project. Many oral presentations were performed to national and international meetings, including regional NC1023 meetings. TARGET AUDIENCES: The results of this project can be used to provide healthier food using alternative processing to the consumers in general, and it will certainly help the soy industry by promoting soybase products with unique characteristics and the HPP industry by providing innovative data showing potential application of this non traditional technology to soy products. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
We first studied how processing conditions affected both lipoxygenase and trypsin inhibitors. While soymilk lipoxygenase can be inactivated by pressures greater than 400 MPa, trypsin inhibitors required a combination of high pressure and mild thermal treatment, i.e., 65*C, to be destroyed. These processing conditions, however, use lower temperatures or shorter treatment times than conventional heat treatments. Using these conditions, soymilk vitamin B6 content was retained as well. We also determined that short-term exposure (1 or 5 min) of soymilk to high pressure (600 MPa) applied at 25 and 75*C increased the refrigerated shelf life of this product to 3 and 4 weeks, respectively. This is a major advantage for this highly perishable product. Sub-lethal injury in surviving populations of spoilage microorganism and resuscitation of sub-lethally injured cells were observed during refrigerated storage of soymilk. The content and profile of isoflavones, key soy compounds for health, are maintained after treatment up to 800 MPa at 25*C. HPP treatment at initial temperature of 75*C changes the isoflavone profile, which has been related to the adiabatic heating during treatment. Clear understanding of the health benefit of each isoflavone isoform will determine if pressure-induced changes in soymilk isoflavone profile might have health benefits. Pressurization of soybeans was, however, inefficient in increasing extractability of isoflavones into water during soymilk production. As expected, soy proteins are affected by pressure treatment and this can lead to an undesirable change in soymilk appearance. By adequately adjusting the pH and soybean-to-water ratio, the appearance and viscosity of soymilk can be maintained while its emulsification properties are enhanced. Soymilk with reduced trypsin inhibitors content, inactivated lipoxygenase, extended shelf life, enhanced isoflavone and vitamin B6 contents, viscosity similar to fresh soymilk, and improved functionality can therefore be obtained with HPP. The pressure-induced changes in soymilk protein significantly impact the textural properties of tofu. HPP could be used as a soymilk pretreatment before thermal production of tofu or as an alternative to thermal treatment for tofu making. Either way, use of HPP allows production of tofu with unique properties.
Publications
- Jung, S., Mahfuz, A. Low temperature dry extrusion and high-pressure processing prior to enzyme-assisted aqueous extraction of full fat soybean flakes Food Chemistry, accepted October 2008.
- Jung S., Murphy P.A., Sala I. Conversion and water-extractability of isoflavones during high-pressure processing of soymilk and soybeans, Food Chemistry, http://dx.doi.org/10.1016/j.foodchem.2008.04.025, 2008.
- Lakshmanan R., de Lamballerie-Anton M., Jung S. Effect of soybean-to-water ratio and pH on pressurized soymilk properties, Journal of Food Science 71:E384-391, 2006.
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Progress 09/01/06 to 08/31/07
Outputs
The objective of this work is to determine whether high-pressure processing (HPP) could qualify as an alternative to the conventional thermal treatment of soymilk and tofu. We investigated the effect of pressure alone and combined with a mild thermal treatment on soymilk key enzymes, nutritional factors, protein/functional properties and microbiological attributes. Outputs: Soymilk was pressurized at 400, 500, and 600 MPa at 25 and 75˚C for 1 and 5 minutes. Total bacterial counts (TBC), psychrotrophs, Enterobacteriaceae, and injured cells were quantified during 28 days of aerobic and anaerobic storage at 4˚C. A 106 log CFU mL-1 was considered as the spoilage level. Immediate mesophile reductions ranged from 2.5 to 4.5 log CFU mL-1 depending on treatment conditions. The control reached the spoilage level after 11 days of chilled storage while the psychrotrophic counts were lower than the spoilage level after 28 days. No Enterobacteriaceae growth was observed
for treated samples throughout the storage study. The TBC after 28 days of aerobic and anaerobic storage for treated samples was less than the control at day 7. Untreated samples had a pH level of 3.4 with a 35% precipitate after storage, while pressurized samples' pH and stability were maintained during storage. High pressure with thermal treatment stored anaerobically gave the least TBC after 28 days of storage while yielded the most neutral pH and least precipitate. Effect of soybean variety (lipoxygenase free and Vinton 81) on flavor profile of soymilk was determined.
Impacts
This project has provided significant knowledge on the effect of pressure level, temperature and treatment duration on soymilk quality. We demonstrated that key unwanted components of soymilk could be destroyed and inactivated while beneficial compounds could be maintained. Processing conditions inactivating enzyme responsible of off flavor, and destroying antinutritional factors were identified. We demonstrated that both vitamin and isoflavones content could be maintained even under the most drastic treatment conditions. Increase of shelf life of pressurized soymilks was proven while composition of soymilk leading to functionality improvement after high-pressure treatment was identified. This project, by significantly contributing to the development of non traditional food processing technology, will increase the use of this technology and increase consumption of soymilk.
Publications
- Ileana Sala. 2006. Effects of high-pressure processing on soymilk enzymes, proteins and isoflavones. Iowa State University Master thesis. May 2006, 146 p.
- Lakshmanan, R., de Lamballerie-Anton, M., Jung, S. 2006. Effect of soybean-to-water ratio and pH on pressurized soymilk properties. Journal of Food Science 71:E384-391.
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Progress 09/01/05 to 09/01/06
Outputs
The objective of this research work was to investigate whether high pressure processing (HPP) could qualify as an alternative to the conventional thermal treatment of soymilk based on its effects on some nutritional and quality aspects. Impact of HPP on soy enzymes and trypsin inhibitors activities In the conditions studied for buffer solutions of lipoxygenase, beta-glucosidase and trypsin inhibitors (Kunitz, KTI, and Bowman-Birk, BBI), thermal and pressure inactivation could be described by a first order kinetic model. Beta-Glucosidase was more thermostable than lipoxygenase but less pressure stable. This difference in heat and pressure stability suggested that the mechanism of action of pressure on proteins differs from that of temperature. While at 95 and 100 degrees C KTI was more thermolabile than BBI, at 120 degree C their inactivation rate constants were similar. BBI was more pressure stable than KTI at 600-800 MPa and 75 degree C. The differences in stability
of the enzymes and inhibitors may be attributed to their different disulfide bonds content. Raw soymilk was pressurized at 100-700 MPa for 10 min. Above 400 MPa, beta-glucosidase was more pressure stable than lipoxygenase. Pressure alone did not inactivate the inhibitors and combined pressure/temperature (75 degree C) treatments had to be applied. After soymilk was heated at 120 degree C for 10 min, the total trypsin inhibitor activity was 11 percent and that of BBI was 22 percent, suggesting that most of the activity left was due to BBI. Impact of HPP on soy milk attributes Neither change in color nor in rheological properties of pressurized soymilk was observed. Native electrophoresis showed changes in proteins greater than or equal to 300 MPa, suggesting dissociation into subunits and aggregation. Pressure denaturation occurred at 200 MPa for beta-conglycinin and 300 MPa for glycinin. When soymilk was pressurized at 75 degrees C, the distribution of isoflavones shifted from
6"-O-malonylglucosides towards beta-glucosides, possibly due to the effect of adiabatic heating. HPP of soaked soybeans increased the total isoflavone concentration of soymilk by 19% at 700 MPa. However, 6"-O-malonylglucosides and beta-glucosides decreased at 300 MPa. Impact of environmental parameters on pressurized soymilk attributes We showed that adequate combinations of pH and soybean-to-water ratio could be chosen to improve functionality of soymilk and to avoid drastic changes in soymilk viscosity.
Impacts
This project improves the understanding of the mechanisms that occur during high pressure processing (HPP). These advances will lead to new, soy protein products such as soymilk and tofu, which have been shown to have health benefits. HPP of soymilk and tofu will offer products with unique functional properties and extended shelf life. The development of high pressure processing responds to the increasing demand of the consumer for additive-free and more nutritional products. HPP may also allow for new opportunities to add value to soybean products. Understanding of mechanisms of HPP will help not only soybean processing, but all HPP processing that are faced with the problem of understanding some modifications occurring under pressure. The work may lead to improved commercialization of pressurized soy products.
Publications
- Ileana Sala. 2006. Effects of high pressure processing on soymilk enzymes, proteins and isoflavones. Iowa State University Master thesis. May 2006, 146 p.
- Lakshmanan, R., de Lamballerie-Anton, M., Jung, S. 2006. Effect of soybean-to-water ratio and pH on pressurized soymilk properties. Journal of Food Science 71:E384-391.
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