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INTRODUCTION

Two practical, often-encountered aspects about chicken soup are to be considered here. the first one concerns the American custom of feeding chicken soup to patients with head colds, to "help cure" the cold. Although this might seem to be an "old wives' tale", there might be some scientific foundation to it, as pointed out in an issue of popularly-written "Good Housekeeping." Dr. Alan Nourse wrote in this issue that workers at the Mount Sinai Medical Center in Miami Beach, Florida, found that the mvoement of mucus out of the nasal passages is hastened after administering hot chicken soup to the patient. This appears to help by carrying the cold viruses along with it, thus diminishing their chances of attaching more nasal cells. Cold water retards this flow of mucus, whereas sipping hot water is only about two-thirds as fast as the soup itself. It is specualted by researchers as to whether it is something in the chicken soup itself that cuases this relief, or if it is simply the hot vapors and extra intake of liquid.

Secondly, one might wonder why it is not possible to thicken chicken soup with readily-available household thickeners, for example, wheat flour or cornstarch. This might be due to the presence of a heat-insensitive amylase which causes partial liquefication of the amylose and/or due to the individual or combined effects of pH and the salts present in the broth, thereby preventing the soup from thickening.

The objective of this preliminary study was to begin looking at this phenomenon by comparing the thickening ability of unsalted chicken broth (stock) to that of redistilled water, to see whether thre is, in fact, less thickening found with the broth, judging from Brabender amylograph measurements of viscosity changes; and, if so, to try to establish a possible reason for this phenomenon.

MATERIALS AND METHODS

Materials

Chicken broth (stock). Chicken broth was prepared by covering "Fircrest" stewing hens with cold water in a large saucepan, bringing it to the boil and simmering it for a few hours, to extract as many nutrients and flavor compounds as would be customary for homemade soup. NaCl was omitted. The broth thus obtained was strained through a metal sieve, allowed to cool, and as much fat skimmed off as possible, before being bottled in 450 mL amounts, labelled and frozen for later use. Only as much as was required was thawed at a time. It was mostly thawed in the incubator set at 25C, for improved slurry mixing.

Distilled water. Triple distilled water was prepared for the Brabender calibration starch mixture and double distilled water was used for the thickening tests without the broth.

Cornstarch. A homogenous mixture of "Argo" foodservice pure corn starch (Best Foods, Div. of CPC International Inc., General Offices, Englewood Cliffs, N.J. 07632) was used for the entire experiment. It was stored in well-sealed, screw-top bottles, to ensure no moisture-uptake from the atmosphere.

Cornstarch amylase substrate. A 2% (w/w) "Argo" cornstarch mixture was prepared and gelatinized by autoclaving for 68 minutes at 15 psi, for alpha-amylase tests. it was freeze-dried, sealed and stored at room temperature.

Methods.

Total Moisture. the total moisture content determination of the cornstarch was done according to the official AACC Moisture Method 44-40. duplicate samples from each of the four jars of starch were taken. A similar determination was made at the end of the study, to ascertain whether or not a significant moisture content change had taken place.

"VISCO/amylo/GRAPH" (C.W. Brabender Instruments Inc., P.O. box 2127, South Hackensack, new jersey 07606) was used for the starch thickening experiments.

due to previous mechanical problems with the Brabender, and also out of convention, a fresh calibration check kit was obtained and run twice within the month it is valid for, to check on the calibration of the amylograph.

Due to previous mechanical problems with the Brabender, and also out of convention, a fresh calibration check kit was obtained and run twice within the month it is valid for, to check on the calibration of the amylograph.

the thermoregulator was set at 25C and the control lever of the termoregulator was set in the "UP" position. the timer was set for 45 minutes and the water cooling device was switched off. The pen was checked and set at zero, and the slurry prepared according to the VISCO/amylo/GRAPH Calibration Check Procefure, #76/32(1983). It was quanititatively transferred to the Brabender bowl, the stirrer installed, instrument head and cooling probe lowered into position, turned on and revolutions per minute checked and adjusted to 75. Once the 45 minute timer had run, it was reset to 15 minutes for the "hold" cycle, the thermoregulator set in the neutral position and the Brabender again switched on. The 700 cmg sensitivity head was used for most of the runs, but the 350 cmg one was also tried in order to obtain more senitive readings.

The amount of calibration starch to be used was approximately 9.53% (w/v) and so the same percentage was used for the 700 cmg head, and reduced to 7% (w/v) for the 350 cmg head.

As soon as the Brabender's cooling/holding period had ended, the heated bowl was removed and samples for scanning electron micrographs (SEMs) taken. The standard procefure for the preparation of starch samples suitable for SEMs was taken from the Department of Foods and Nutrition's Laboratory Manual (Appendix 1) and the method published by Holmes and Soeldner (1981).

the liquid nitrogen-frozen drops were not quite successfully freeze-dried initially and were therefore kept frozen at -18C for later professional evaluation and discussion. Scanning electron micrographs were prepared by the Electron Microscope Unit, Oregon State University, Corvallis, almost a year later. Particular attention was paid to the surface morphology of the starch granules and etched, "pits," "eaten away" or attacked parts were scutinized more closely. Initially, overall views and more detailed views were photographed, mainly considering 200x, 700x, and 3000x magnifications.

RESULTS AND DISCUSSION

Total moisture: The results averaged out at 12.35 +- 0.08% total moisture initially, and 12.66+/- 0.12% after the experiment was ended. This slight increase probably did not affect the Brabender results significantly.

Cornstarch amylase substrate. The alpha-amylase tests were not carried out, due to time constraints and lack of opportunity. Purified porcine or chicken alpha-amylases could have been used, but it seemed more advantageous to analyze the broth directly for the enzymes, rather than to test for the amount of glucose released by possible enzymes present in the stock, as compared to these commercially-prepared standards.

Pomeranz and Shellenberger (1962) say that the amylolytic breakdown of the starch molecule entails liquefaction, detrinization and saccharification. This brekdown can be classified according to molecular length or size (largest to smallest, in the order as stated above) and each of these stages can be used to measure the extent to which amylase activity has taken place in the starch. total saccharification leads to the formation of a true solution of glucose which is not viscous at all. quantitative glucose tests are readily available.

Brabender Amylograph Tests. Table 1 lists the most important results and summarizes the percentage starch (w/v) used, type of starch, type of liquid, amount of cheesecloth straining (if any) that had taken place before running the tests, sensitivity head used when not 700 cmg, date done (for record purposes and not for publication purposes), the Brabender units after 45 minutes heating and then the value reached after the 15 minute cooling period. (Appendix 2 contains the total list of runs.)

figures 1A through 1 G show the respective Branbder charts for 1A Code #1), 1B (code #3), 1C (code#4), 1D (code #7), 1E (code #8), 1F (code#10) and 1G (code #11). The code nujmbers used for identification have been maintained, so that there is less confusion, as numbers on graph legends correspond to those in the Table 1. Initially problems were experienced with the Brabender equipment, and so run #2, using water and cornstarch was exclused from the discussion. The third run's values are lower as less starch (9.1 vs 9.5% cornstarch) was used, mainly as it was till testing the noise level of the machine, but is taken into consideration here, as there are no other water-control runs, using the 700 cmg head. Runs #7 and 8 (9.5% starch) have a mean value of 620 Brabender Units (B.U.') after the initial 45 minute heating period and 605 B.U.'s after the 15 minute holding period. this is lower than both the corresponding values for the cornstarch-water mixtures (700 and 655 respectively). this would indicate that the starch mixture made with chicken stock was indeed less viscous or 'thickened" than the ones of similar starch concentration and redistilled water.

An interesting phenomenon is the apparent "outlier" (#4) made with 9.53% cornstarch and broth. it varied from 50 to 220 B.U.'s and was noticebaly thinner than the others. It was excluded from the above-mentioned means. Had the starch been liquefied to such a degree by a possible heat-insensitive alpha-amylase that it had lost so much of its thickening power, or was the instrument malfunctioning (not heating proprely at the rate of 1.5C per min.), or had the weights been incorrectly measured or read? This broth had only been strained through two layers of cheesecloth, whereas the others had been through eight layers. Did this perhaps cause a thinning effect? if so, what had cause it , what had been removed or how did it work? More discussion follows under the SEMs and it would appear that it is not an "outlier" in this case.

Code 8 (9.54% cornstarch), made from broth that had been stored for two days at 25C, did not appear to alter the thickening ability of the starch to the extent that the freshly-defrosted and strained broth did. this leads to speculation about the sensitivity of the elusive enzyme or condition(s) such as pH, electrolyte content and/or ionic strength of the stock that could have caused this to happen at this 25C temperature region, and/or its loss of activity under these conditions. the pH of the broth used for code 11 (7.00% cornstarch) was 6.6. Unfortunately the pH of the stored stock was not measured, as this might have hinted at what changes might have occurred.

Banks and Brown (1975) point out that the ability of amylose to dissolve in a particular aqueous solvent system, is a function of both pH and the type of electrolyte present. Figure 2 shows how the presence or absence of electrolytes affected the viscosity of a waxy-maize amylopectin as a function of pH, in a similar way to that of amylose. it would therefore be suggested that one also examine the ionic strength of the various chicken broths used in experiments such as these.

when the sensitivity was changed to 350 cmg, there was a more definite difference between the two sets of readings, although both had actually stayed the same value, from when the heating period ended and the cooling period began, until the end of the cooling period. This was not so noticeable with the others. Unfortunately time constraints prevented more replications to be run, using the same stock batch at first, and then trying another.

Scanning electron micrographs

The micrographs in Figure 3A, 3B and 3C show the 200x, 700x and 3000x magnifications respectively for code #4, namely, the 9.53% "Argo" cornstarch mixture with broth at 25C strained through two layers of cheesecloth and resulting in the low viscosities ranging from 50 to 220 B.U.'s. In all three these magnifications holes are clearly visible, with a threadlike network noticeable in more than one place. Some surface dehydration could have taken place during the prolonged storage time at -18C, but it mostly seems to point to some enzyme action or etching, "biting" or "eating" away of molecules. This would result in an impaired ability to gelatinize and "hold the liquid phase together" and could explain why the viscosity readings were so low. Some surface irregularities are visible on Figure 3C and this might be more than impurities or artefacts found there. It does not look like imploded starch granules only, either.

Figure 4A, 4B and 4C are SEMs of code #7 with 9.53% "ARGO" cornstarch used with chicken stock at 28C, and which had been strained through 8 layers of cheeselcoth. A similar cavity-riddled appearance is evident in all the magnifications, although the surface ap0pears more smooth in the 7000x magnification. It does not seem to have much gelatinized starch holding it together and that the thin films between the cavities could readily give way to form one large one.

Figures 5A and 5B are SEMs of a 7.00% "ARGO" cornstarch-redistilled water mixture at 200x and 700x magnification, contrasted with Figures 5C and 5D are identical mixtures, with broth instead of water (codes 10 and 11, respectively). Figures 5A and 5B show a few small holes, but not as many nor as pronounced as Figures 5C and 45's. Figure 4 B seems to have intact granules pushing up from below, yet the appearance in Figure 5D is much more broken or irregular and unstable-looking.

Banks and Greenwood (1975) refer to work by Evers and McDermott (1970) in their book and publish their plate showing the "fracture face profile" of a commercial wheat starch granule after its incubation with wheat alpha-amylase. This seems to resemble this "holey" appearance found here.

CONCLUSIONS

this study seems to point to the fact that a heat-insensitive amylase could be present in chicken broth. Further research is necessaryt and some suggestions can be made as follows:

• Strain the broth through several layers of cheesecloth before bottling and freezing, as then one is assured of sufficient volume for the run that requires 420 mL.
• An ice layer placed between the cheesecloth helps to remove excess fat, providing the stock is not too hot at the time of straining. It is is too cold, it might gel, and this would also not help.
• Be careful about the source of broth-whether whole stewing hens are used, just backs, and whether or not the internal organs (sources of enzyme) are present or not (for example, chicken pancreas amylase is commercially available).
• how does the fat present affect the viscosity and possible enzyme action?
• Perhaps the use of the Brabender cooling device would prove beneficial in an experiments such as this, as the potential starch breakdown would have more time and opportunity to take place and one could perhaps test more efficiently for viscosity changes, and their corresponding microscopic changes.
• The structure of the mucoproteins and other (polysaccharide) constituents of mucus should be explored in greater detail to see whether or not there are structural similarities to starch (for example, glucosidic alpha 1-4 linkages) that could help to account for the releif found by cold suffers when consuming hot chicken soup.
REFERENCES
American Association of Cereal Chemists. 1982. Approved methods of AACC. The Association, St. Paul, MN.
Banks, W. and C.T. Greenwood. 1975. Starch and its components. Edinburgh University Press, 22 George Square, Edinburgh. Great Britian.
Brabender, C.W. 1983. CWB VISCO/amylo/GRAPH Calibration check procedure #76/32. C.W. Brabender Instruments, Inc., P.O. Box 2127, South Hackensack, N.J. 07606.
Evers, A.D. and McDermott, E.E. 1970. "Starke" 22: 23., quoted in Banks and Greenwood, 1975, plate 13, p. 307.
Holmes, Z.A. and A. Soeldner. 1981. Macrostructure of raw selected starches and heated starch dispersions. Journal American Dietetic Association 78: 153.
Nourse, A.E. 19?? Good Housekeeping. "Family Doctor." 187(5):92.
Pomeranz, Y. and Shellenberger, J.A. 1962. Starch-liquefying of alpha-amylase. 1. use of pregelatinized wheat starch as substrate. Cereal Chem. 29: 327.

Updated: Wednesday, June 20, 2007.