Carbohydrate, Pigment and Protein Tests display Soy Milk is more nutritious than Whole Milk

By:
“The Catalysts”
Joanna Freeman
Glenn Murray
Alyssa Seaton
Laurel Wangler

 

Our project explores the differences in nutrition based on chemical makeup between whole and soy milk. To assist in this exploration, various carbohydrate, photosynthetic, and enzyme tests were used.
First, we utilized five different tests to determine various types of carbohydrates: Benedict’s, Barfoed’s, Selivanoff’s, Bial’s and Iodine tests. Whole milk tested positive for reducing sugars and ketoses. Soy milk tested positive for ketoses, hexose furanose rings and starches. From these results, it seems that soy milk has a greater variety of carbohydrates, possibly making it more complex.

Next, we analyzed the photosynthetic elements within whole and soy milk through the paper chromatography and the absorption spectrum tests. These tests provided us knowledge of pigments specific to the two milk specimens and also a soybean solution. The chromatography for both milk solutions showed no pigments. The absorption spectrum test used a spectrophotometer to measure the absorbency of different pigments in the milk by inducing the milk specimen to various visual wavelengths of light. For all three specimens, red light (400nm) was absorbed the most and descended to purple light (700nm). We observed that whole milk had the greatest overall absorbencies, for all wavelengths, followed by soy milk and the soybeans solution.

The last portion of our experiment examined the protein concentrations of whole and soy milk by means of the Bradford Assay test. The readings from whole and soy milk were compared to a standard protein curve to determine its protein concentration, showing whole milk with greater concentration than soy milk.

Discussion
By Glenn Murray
Revised by Laurel Wangler
2nd Revision by Joanna Freeman and Laurel Wangler

In our experiment, we were investigating whether Meijer whole milk (3.25% milkfat) or plain Silk soy milk was more nutritious, based on the difference in chemical makeup. The amount of nutrition will be determined by the presence of carbohydrates, protein concentration, and absorption of light at different wavelengths. Carbohydrates are a source of energy for the body and protein provides amino acids for forming body proteins for building and repairing tissues (Columbia Encyclopedia, 2003). Carbohydrates and protein are important aspects when discussing proper nutrition (Columbia Encyclopedia, 2003). Whole or soy milk will have to have a greater content of carbohydrates and concentration of protein in order to be considered more nutritious than the other.

Before starting experimentation, we believed that whole milk was going to have more variety in chemical makeup because of the source it is being derived from. Cow milk consists of proteins, fat, salts, and milk sugar, or lactose (Columbia Encyclopedia, 2003). Soy milk comes from soybeans that are broken down into liquid form (U.S. Soyfoods Directory, 2003). We believe that many chemical compounds are broken up during this process. We conducted tests that range from simple indication techniques, used for carbohydrate detection, to the Bradford Assay test, which is commonly used for determining protein concentration. We also performed chromatography and absorption tests, which analyzed pigments present and light absorbed. Our first series of experiments utilized indicators to analyze the carbohydrate composition of whole milk and soymilk.

Our first indication test (Benedict’s Test) evaluated the carbohydrates found in soy and whole milk for either a free ketone group or an aldehyde group. If a free ketone or aldehyde group was present during Benedict’s test, then our two milk solutions contained reducing sugars. Common reducing sugars include glucose and fructose based on results from a previous lab found in the lab manual. In a normal benedict’s test, a red precipitate should form in the presence of reducing sugars. During our trial tests, none of the dilutions of either soy or whole milk resulted in a red precipitate (Figures 1, 2; Table 1). All the soy milk dilutions resulted in a blue solution which indicates no change. Therefore, these results showed the lack in presence of reducing sugars in soy milk. As for whole milk, both the 10 percent and 25 percent dilution solutions resulted in an opaque green solution and the 50 percent dilution had a burnt orange. These results support that the 10 percent and 25 percent solutions did not have reducing sugars present. On the other hand, we can not refute that the 50 percent dilution did not have a red precipitate. It is quite possible that the opaque white color of milk influenced the results of the test and quite possibly masked the results. Also, since the positive control started out as a clear solution and the milk is a white opaque solution it is hard to compare the results of the two. Therefore there possibly could be reducing sugars present in the 50 percent dilution of whole milk but they were disguised by the opaque white color of the initial solution.

The second test we did under the reducing sugars category was the Barfoed’s Test, which indicates the presence of either monosaccharides or disaccharides. The Barfoed-milk solution was only allowed to react for two minutes, because if more time was permitted, disaccharides would have had time to hydrolyze into monosaccharides. When the Barfoed’s test was performed on our various dilution levels of both soy and whole milk, the results showed no change for all repetitions (Figures 3,4; Table 2). However, unlike the negative control, sucrose, all the repetitions had white precipitate particles that formed along with the no change in blue color. More likely than not, this white precipitate is curdled milk that formed from the combination of heating the milk solutions with the Barfoed’s solution. Based on our test results we support that both soy and whole milk contain di- and polysaccharides. This did not necessarily mean that monosaccharide were not present in soy and whole milk, it was just that they did not show in this particular test.

The next test we used to scrutinize the chemical composition of soy and whole milk was Selivanoff’s test. The Selivanoff test was used to distinguish between aldose and ketose compounds. Both aldose and ketose are monosaccharide sugars, but differ in structure. The whole milk dilutions were all negative; therefore, there was not any detection of either ketose or aldose in the solutions we used (Figure 5; Table 3). This does not mean that aldose or ketose were not present in whole milk it was just that for the set of dilutions and repetitions we carried out resulted in not detecting either. As for soy milk, the results of all the repetitions supported that ketoses and aldoses were present (Figure 6; Table 3). The positive control used for this test was fructose, which when combined with the Selivanoff’s reagent and heated produced a dark red color. In our experiment the 50 percent dilution yielded this exact dark red color. As for the 10 and 25 percent solutions they yielded a less intense red color, which we attribute to the fact that the milk was diluted down which could make the presence of both the ketoses and aldoses not as strong as in the 50 percent dilution. Nevertheless, whole milk had a negative detection of aldoses and ketoses while soymilk had a positive detection.

To further decipher the chemical makeup of soy and whole milk, Bial’s test was performed. Bial’s test primarily indicates furanoses (five-membered rings). Pentose furanoses will react with Bial’s reagent to create an olive green solution, whereas hexose furanose will react to form a darker olive color. The set of whole milk repetitions resulted in a negative detection for both pentose and hexose furanoses (Figure 7; Table 4). Whereas the 50 percent dilution soy milk solution resulted in a olive green solution which means the presence of hexose furanoses (Figure 8; Table 4). As for the 10 and 25 percent dilution soy milk solutions, the 10 present was a dark yellow and the 25 was a dark yellow with a tint of olive green (Figure 8; Table 4). We believe the less intense nature of coloring for the two percentages is caused by the dilution and that the presence of hexose furanoses is not strong enough to cause a reaction to create the olive green color.

Our final carbohydrate test tested for the presence of starch. Starch is a coiled polymer of glucose, and is classified as a complex sugar. The results for both soy and whole milk proved to be inconclusive; none of the solutions detected the presence of starch (Figures 9, 10; Table 5). For whole milk all the solutions resulted in a color similar to that of the negative control. On the other hand for soy milk the solutions resulted in very bizarre colors that neither supported the negative nor the positive control. To obtain more accurate results it might have been better to include a test that had 100 percent soy and whole milk solution which may have led to detection of any starches. It is possible that because of the dilutions the starch was too faint to detect any significant amount. Carbohydrates are abundant in most types of milk. Research in the types of carbohydrates, and their corresponding physiological effects, would be beneficial to pursue to better the nutritional value and the overall product of milk. For instance, raffinose oligosaccharides are the main contributors to the flatulence that follows the consumption of soy bean products, such as soy milk (Guimaraes, 2001). At the molecular level, flatulence, in monogastric mammals, occurs from the lack of the alpha-galactosidase enzyme (Guimaraes, 2001). If raffinose oligosaccharides can be illiminated from soy bean products, than soy beans would have a positive effect on the digestion of soy-based foods in monogastric mammals (Guimaraes, 2001). Another interesting aspect of our study dealt with analysis of whole and soy milk at the photosynthetic level.

The photosynthetic aspect of our experiment dealt with testing for which type of milk had the greater concentration of pigments and ability to absorb light. After completing a paper chromatography test, we detected slight amounts of pigments in soy milk and none in whole milk. Soy milk comes from the soybean, which is produced by the soybean plant. Soybean plants are photosynthetic and thus why there should be traceable amounts of photosynthetic elements in soymilk. We also conducted an absorption spectrum test which allowed us to observe the absorption of both soy and whole milk at different wavelengths. The results of this test showed absorption readings for all wavelengths because milk, having the white coloration absorbs all colors.

Our third portion of our experiment was the enzymic section. We tested for total protein concentration in whole and soy milk with a Bradford Assay. Both soy milk and whole milk had considerable concentrations of proteins. Soy products all contain the soy protein, so soy milk should have higher concentrations and absorbency numbers then whole milk. Whole milk should also have high protein concentration because it comes from a cow. Soy protein containing isoflavones affect the lipids found in postmenopausal women (Dalais, 2003). Lipids such as triacylglycerol and LDL are found to affect cholesterol levels (cholesterol levels affect nutrition) so research on soy bean protein and their link with lipids in postmenopausal women could have general applications in the fields of biological nutrition.

Figure 13: Bovine Serum Albumin (BSA) Standard curve. Absorbance readings were taken at 595 nm because CBBG (Coomassie Brilliant Blue G-250 Dye) binds to amino acids in the anionic form at this wavelength. As the concentration of BSA increases, so does the absorbance reading. A picture perfect standard curve should depict a linear relationship between protein concentration and absorbance.

In conclusion of the chemical compositions of whole and soy milk, our experimental data and results have pointed to an array of differences in chemical makeup. Based on testing results, soy milk seems to have higher protein concentration and greater number and variety of carbohydrates. Therefore, we have found support that soy milk is more nutritious than whole milk.