Comparison of Carbohydrate, Pigment, pH, and Enzyme Levels of Light, Regular, and Fresh Squeezed Orange Juices

By Laura Stolle, Ian Gannon, and Sarah Janisse

Abstract

ÊÊÊÊÊÊÊÊÊÊÊ In recent years, low-carb diets (i.e. Atkins and South Beach) have shifted the common view of healthy foods. Orange juice, which has always been a part of a balanced, nutritious breakfast, is now considered to be unhealthy by Atkins and South Beach diets.Ê The goal of this study is to compare carbohydrate and photosynthetic pigment content along with enzyme and pH levels of three different types of orange juice: fresh squeezed (from South Africa Navelate Oranges), Tropicana regular orange juice with calcium and Tropicana Light ÎN Healthy. Four tests were used to identify the carbohydrates present (Benedictâs, Barfoedâs, Selivanoffâs, and Bialâs). Paper chromatography was performed for the three juices to identify photosynthetic pigments. Juice pHâs were tested with a pH meter. The Bradford Assay and the presence of PPO (Polyphenoloxidase) was performed for the three juices. Using the above experiments, we hoped to prove that the carbohydrate content is lowest in the fresh-squeezed juice; the processed juices have the greatest enzyme concentration; the fresh squeezed juice has the highest pH; and none of the juices will contain photosynthetic pigment.

The carbohydrate results showed little or no difference between the sugar content of each juice; however, the Light ÎN Healthy did react differently on Benedictâs test. None of the juices contained photosynthetic pigments; therefore, the R_f value of the paper chromatography was 1.Ê The fresh orange juice had the lowest pH with Light and Regular being slightly higher. None of the samples had PPO and Regular had the highest enzyme content.

Discussion:

Carbohydrate Testing

ÊÊÊÊÊÊÊÊÊ Benedictâs test tests for reducing sugars.Ê The aldehyde is oxidized; copper is reduced.Ê Reduced copper precipitates and blue color changes to orange/red. (Sayed, 2003) Our results shown in photo 1 displays that the Fresh, and Regular orange juices turned orange, while the Light orange juices turned orange/red.Ê The positive control, glucose, turned red, and the negative control, water, stayed blue. The darker precipitate in the light juice means that there may have been more sugars or other chemicals that reduced with Benedictâs reagent. Possibly, the surcralose in Light may react better than any of the other reducing sugars.

The Barfoedâs test, tests for reducing sugars that are monosaccharides.Ê Only monosaccharides will reduce copper and change color due to formation of orange/red precipitate. (Sayed, 2003)Ê Figure 2 shows that all of the juices formed a red precipitate.Ê The positive control, glucose, formed a red precipitate, and the negative control, water, remained unchanged with a blue color. Both of the processed juices were darker, which may mean that the processed juices had glucose added to them. The darker color may also mean that the fresh orange juice contained more water, which may cause the lighter color.

The Selivanoffâs test determines a ketose from an aldose sugar.Ê Color turns red fastest if the sugar is a monosaccharide ketose, and turns red at about 1 min if it is a disaccharide ketose sugar, any longer than one minute and the sugar is an aldose. (Sayed, 2003)Ê ÊOur results show that all of the orange juices formed a red precipitate, and therefore there must be a ketose sugar present.Ê The positive control, fructose, turned red, and the negative control, water, stayed clear. All of the juices changed color at approximately the same time (about 1 min), which means all three juices most likely, contains sucrose. This is expected since sucrose is extremely common in fruits. (Oregon State, 2004)

The Bialâs test determines if there is a furanose ring.Ê Yellow color turns greenish if the sugar is a furanose.Ê If the sugar is a pentose-furanose the color turns an olive green.Ê If the color turns a muddy brown if the sugar is a hexose-furanose.Ê If there is no color change the sugar is a pyranose. (Sayed, 2003)Ê Photo 4 indicates that both Fresh and Regular orange Juice turned a muddy brown color therefore indicating the presence of a hexose-furanose (i.e. sucrose).Ê The Light orange juice turned more of an olive green color indicating the presence of a pentose-furanose (i.e. xylose).Ê The positive control, sucrose, also was an olive green color, and the negative control, water, stayed yellow. Since the Light was an olive green color, it seems possible that it contains xylose, which is a pentose-furanose. This may also help explain why the Light reacted differently in Benedictâs test.Ê Overall, the hypothesis about the fresh juice containing a smaller variety of carbohydrates was only partially true. Throughout all of the tests, the regular and fresh juices basically reacted the same. The light juice may contain a wider variety of sugars or compounds that react like sugar in order to make it behave like it did in each of the tests.

Pigment Testing:

ÊÊÊÊÊÊÊÊÊ The results for the paper chromatography show that none of the sample juices contained any photosynthetic pigment. Since oranges are not green in color, it is not likely that they will contain chlorophyll a or b. Since the juice only was tested and photosynthesis normally takes place in cells close to the surface of the cell, it is extremely logical that orange juice does not contain any pigment identifiable by paper chromatography.

pH Testing:

ÊÊÊÊÊÊÊÊÊ The results for the pH test of the sample juices were contrary to our hypothesis, since the fresh juice actually had the lowest pH.Ê The freshness or ripeness of the processed juices or the fresh oranges; the difference in the type of oranges (i.e. Valencia and navelate), and the pH of the soil the oranges were grown in (Tropicana Inc., 2004). Also, the difference may be due to the processing of store-bought juices, which raises the pH by adding water. In short, the hypothesis that the fresh oranges would have the highest pH was disproved.

Enzyme Testing:

ÊThe results of the enzyme test show that the regular orange juice has the most mg of protein.Ê Fresh orange juice has an absorbance of .143 that corresponds to 11 mg of protein per 50 mL.Ê The light orange juiceâs absorbance corresponds to 15 mg of protein per 50 mL.Ê The regular orange juiceâs absorbance corresponds to 51 mg of protein per 50 mL.Ê The fresh orange juice had the least amount of protein, because it is not processed.Ê Often during processing the juice is enriched with chemicals.Ê The regular orange juice probably had the most mg of protein because it has the most juice and chemicals.Ê The light orange juice is only 45% juice, so it is watered down, but still has some chemicals.

Chart 1: ÊThis chart shows the standard curve for the Bradford Assay as well as the three points where the three different orange juices lie on the curve. ÊThe three points that are bold, red, and square represent the three different orange juices, and where they fell on the standard curve Fresh: Ê(11, .143), Light: (15, .192), and Regular: (51, .693). Ê

ÊÊÊ

References

Densupsoontorn N, Jirapinyo P, Thamonsiri N, Wongard R, Phosuya P, Tritiprat A, Patraarat S, Pidatcha P, Suwannthol L. Comparison of the nutrient content of fresh fruit juices vs commercial fruit juices. Journal Medical Association of Thailand. (all) Aug 2002.

Lord, Victoria. Brainfoods in Breakfast. Concious Choice. November, 1998. Last accessed Sept 16, 2004. http://www.consciouschoice.com/food/brainfood1106.html.

Oregon State , 2004. Food Resource: Sugars. Oregon State University Website.

ÊLast Accessed Sept 16, 2004. http://food.oregonstate.edu/sugar/name.html.

Sanchez-Moreno C, Cano MP, de Ancos B, Plaza L, Olmedilla B, Granado F, Martin A. Effect of orange juice intake on vitamin C concentrations and biomarkers of antioxidant status in humans. American Journal Clinical Nutrition. (all) Sept. 2003.

Sayed, Mimi. 2003. LBS 145 Lab Manual: Stream 1(Labs 1-3). Fall 2004 version.ÊÊÊÊÊÊÊÊÊÊÊÊÊÊ MichiganÊ State University.

Thompson Instruments, 2004 ãOrange Juice: Monosaccharides and Oligosaccharidesä. ÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊ ÊThompson Instruments Website.ÊÊ Last accessed September 8, 2004. ÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊÊ Êhttp://www.hplc.com/shodex/english/dc030228.htm

Tropicana Inc. 2004. ãTropicana Sourcingä . Tropicana, Inc Website. Last Accessed October 19, 2004 . http://www.tropicanafresh.com/sourcing.asp