Food Factors in Health Promotion and Disease Prevention - American

Chapter 34

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Structural Modification to Improve Psyllium Functionality Liangli Y u Department of Food Science and Human Nutrition, Colorado State University, Fort Collins, C O 80523-1571

A novel procedure was developed to improve psyllium functionality by conducting a solid-state enzyme reaction. The procedure requires no special equipment/operation (such as freeze dry) and could be carried out without using any additional chemicals. To evaluate the solid-state enzymatic procedure, modified psyllium preparations were produced under selected reaction conditions, and analyzed for their water-absorbing capacity, gelling capacity, particle surface structure, and soluble and insoluble fiber contents. The results showed that structural modification improved psyllium functionality. Modified psyllium preparations had reduced water-absorbing capacity and less gelling ability. The reduced water-absorbing capacity may be explained by the decreased surface area of psyllium particles. In addition, the solid-state enzymatic treatments had much less effects on soluble fiber contents than the liquid phase enzymatic reactions.

Psyllium, the seed husk of the plant Plantago genus, is an excellent source of soluble and insoluble dietary fibers. Previous studies have shown that psyllium is a highly branched acidic arabinoxylan (/). The xylan backbone has both (l->4) and ( l - » 3 ) linkages. Other monosaccharides presented in psyllium

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© 2003 American Chemical Society In Food Factors in Health Promotion and Disease Prevention; Shahidi, F., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.


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include D-rhamnose, D-galactose, D-galacturonic acid, 4-O-methyl-Dglucuronic acid, and 2-0-(2-D-galactopyranosyluronie acid)-L-rhamnose (2). A number of studies have been conducted to investigate the health benefits of psyllium and its applications in food and other consumer products such as hairsetting lotions (2). In addition to its cholesterol-lowering activity, psyllium also has laxative effects, can reduce the risk of colon cancer, treat gastric hypoacidity, and may be helpful in weight control (3-7). The application of psyllium in functional foods have received more attention since F D A approved that psyllium containing foods may have a health claim of reducing the risk of heart disease. However, its extremely strong water-uptaking and gelling capacities have limited the incorporation of psyllium in foods as well as its other applications. There have been several physical/mechanical means developed to improve the functionality and sensory properties of psyllium, including controlling the range of particle size (8), mixing and extruding with other food ingredients (9), and coating and granulating psyllium with polyvinylpyrrolidone and polyethylene glycol (10). These previous investigations have indicated the potential possibility of improving the physicochemical/sensory properties of psyllium and to promote its applications in foods. However, none of them could sufficiently solve the strong gelling and extreme water-uptaking problems of psyllium. No structural modification has been conducted to improve the functional properties of psyllium until Y u and others (/) disclosed an enzymatic procedure to produce novel psyllium preparations with a reduced water-uptaking capacity and different gelling properties. Unfortunately, this procedure is not practically applicable since a freeze-dry step has to be involved to remove the water added for the enzyme reaction. In this chapter, a solid-state enzymatic procedure for psyllium modification and the novel psyllium preparations with improved functionalities is discussed. This procedure requires no special operation, equipments and hazardous chemicals. This procedure also produces no chemical wastes.

Materials and Methods

Solid-state Enzymatic Reaction A known amount of enzymes was added to 50 g raw psyllium (98% purity, 40 mesh, JB Laboratories). The enzyme preparations may contain cellulases, xylanases, hemicellulases, pentosanses, aribanases, and beta-glucanases but substantially free of amylase and protease activities (/). The reaction was conducted at 40-50°C and terminated by inactivating enzymes. The enzymes

In Food Factors in Health Promotion and Disease Prevention; Shahidi, F., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

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were inactivated according to the method described previously (1). The final product of the solid-state reaction was obtained after grinding the material through a 20 mesh sieve. Controls were performed using the above procedure without addition of enzymes.


Water Absorbing Capacity Water absorbing capacity was determined gravimetrically using a modification of the method described by Elizalde et al. (11), with some modification. Briefly, all samples were equilibrated in a 10% relative humidity (RH) chamber for 48 hours. Then, samples were transferred into a 98% R H chamber and exposed to moisture for 5 min. The dry matter and the absolute amount of absorbed water were determined. A l l measurements were made in triplicate. The results were expressed as the mean ± SD in mg water absorbed by per gram of psyllium per minute.

Gelling Property Gelling properties were analyzed using a T A - X T 2 texture analyzer (Texture Technologies Corp, Scarsdale, N Y ) , with a 25 mm diameter probe (72). 1.50 g of each psyllium preparation was added into 30 ml distilled deionized water and stirred for 30 seconds. After setting for 24 hours, gel samples were subjected to a double compression test. Measurements were performed with a pretest speed of 2.0 mm/sec, a test speed of 5.0 mm/sec, a post test speed of 5.0 mm/sec, and a distance of 6 mm. A l l measurements were made in triplicate. The results were expressed as the mean ± SD in gram force for Hardness and Adhesiveness.

Fiber Contents Soluble and insoluble fiber contents in modified and raw psyllium were measured using a commercial kit purchased from Megazyme International Ireland Ltd (Wicklow, Ireland) according to the previously reported procedure (13).

Surface Structures Scanning electron microscope (SEM) analysis was conducted to determine the surface structures of modified psyllium preparations using a Philips S E M 505 instrument (Holland).


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Results and Discussion A solid-state enzymatic procedure was developed for psyllium modification to improve the functionalities of psyllium and consequently to promote it applications in functional foods. Modified psyllium products from the solidstate reactions were powdered solid (Figure 1A) and required no additional steps for water removal. In contrast, a free-dry step has to be involved to remove water from the final gel materials (Figure IB) obtained from the conventional liquid-phase enzymatic reactions (/). The weight based yield of the solid-state procedure is about 100%, which is much higher than that of the liquid-phase reactions (/).

Figure 1. Modified psyllium products from solid-state enzymatic reaction vs. conventional liquid-state enzymatic reaction. A = modified psyllium at the end of solid-state reaction, and Β = modified psyllium at the end of liquid state enzymatic reaction. Psyllium preparation A requires no additional waterremoving step, while psyllium preparation Β requires additional step to remove water.

Psyllium prepared by the solid-state enzymatic procedure had reduced water-absorbing capacity (Figure 2). Increased levels of enzymes were not always associated with further reduction in water absorbing capacity. The lowest water-uptaking rate of modified psyllium by the solid-state procedure



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Figure 2. Effects of solid-state enzymatic treatment on water-absorbing capacity of psyllium. was 41% of that of the control sample under the experimental conditions. Reduced water-absorbing capacity is preferred for food applications of the psyllium preparations (1,8, 9). Solid-state enzymatic treatment reduced the gelling capacity of the modified psyllium preparations (Figure 3). Compared to raw psyllium, modified psyllium formed a weaker and less adhesive gel. Higher concentration of enzyme may further reduce the gelling capacity of modified psyllium (Figure 4). The psyllium preparations, with lower gelling ability, are much easier to incorporate into food formulae. These psyllium preparations also raise less concern about the undesirable sensory properties of the final food products containing significant levels of psyllium fibers. To better understand the solid-state enzymatic reactions, the surface structures of the modified psyllium were analyzed and compared to that of raw psyllium using a scanning electron microscope (SEM). S E M results showed that modified psyllium had a smoother surface than raw psyllium (Figure 5). In another words, solid-state enzymatic treatment reduced the total surface area of the psyllium particles. This reduction may explain the reduced water-uptaking rate of the modified psyllium preparations, but not the improved gelling properties. More studies are needed to evaluate the effects of solid-state enzymatic modification on gel forming properties of psyllium.


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Force

(g)

175.0-.


150.0- I

-5D.0-

Figure 3. Effects of solid-state enzymatic treatment on gelling capacity of psyllium.

Figure 4. Effects of enzyme amount on gel hardness.



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Figure 5. Surface structures of psyllium preparations determined by SEM. A = surface structure of raw psyllium, and Β = surface structure of modified psyllium. The soluble and insoluble fiber contents of the modified psyllium preparations were measured to estimate the effects of structural modification on the biological activities of psyllium including cholesterol-lowing activity, since the soluble fibers were believed to contribute to the cholesterol-lowing activity of raw psyllium (1, 8, 9). Compared to the liquid-phase enzyme reaction, solidstate enzymatic treatments showed less effect on soluble fiber contents of the modified psyllium preparations (Table 1), while both procedures had minor effects on insoluble fiber contents. Similar ratios of the selected enzyme resulted in about 15% reduction in soluble fiber content by the conventional liquid-phase enzymatic reaction (i), while only had less than 4% reduction in soluble fiber content under the solid-state reaction conditions. This is another advantage of the solid-state enzymatic procedure vs. the liquid-phase enzymatic reaction described previously by Y u et al. (i).

Table I. Soluble and insoluble fiber contents of modified psyllium Enzyme II (U)

Soluble fiber (g/100 g psyllium)

Insoluble fiber (g/100 g psyllium)

120 240 480 960 1800 Raw psyllium

72.9 77.3 75.9 73.1 68.3 79.6

12.4 12.6 13.2 11.9 12.3 12.4


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Acknowledgments


This study was supported by the Colorado Agricultural Experiment Station and the Colorado Wheat Research Foundation. The author would like to thank Dr. Mary Harris in the Department of Food Science and Human Nutrition at Colorado State University for her review of this manuscript.

References 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Y u , L . ; DeVay, G.; Lai, G.; Simmons, C.; Neilsen, S. 2001, U S Pat. 6248373. Chan, J.K.C.; Wypyszyk, V . Cereal Foods World 1988, 33,919-922. Park, H . ; Deib, P.A.; Chung, O.K. Cereal Chem. 1997, 74, 207-211. Hara, H . ; Suzuki, K.; Kobayashi, S.; Kasai, T. Nutr. Biochem. 1996, 7, 549554. Ganji, V . ; Kies, C. V. J. Food Sci. Nutr. 1996, 84, 595-597. Arjmandi, B . H . ; Craig, J.; Nathani, S.; Reeves, R.D. J. Nutr. 1992, 122, 1559-1565. Anderson, J.; Deakins, D.A.; Floore, T.L.; Smith, B.M.; Whitis, S.E. Crit. Rev. Food Sci. Nutr. 1990, 29, 95-146. Rudin, R. 1988, US Pat. No. Re. 32, 811. Wullschleger, R.D.; Creek B . ; Chen, S.C.; Bowman, F.A.; Hawblitz, L . V . 1993, US Pat. 5,227,248. Powell, D . R.; Patel, V . K . 1982, US Pat. No. 4,321,263. Elizalde, B.E.; Pilosof, A.M.R.; Bartholomai, G.B. J. Food Sci. 1996, 61, 407-409. Paraskevopoul, Α.; Kiosseoglou, V . J. Food Sci. 1997, 62, 208-211. Lee, S. C.; Rodriguez, F.; Storey, M.; Farmakalidis, E.; Prosky, L. J. AOAC Int. 1995, 78, 724-729.


Food Factors in Health Promotion and Disease Prevention - American

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