Subject: Human Nutrition Laboratory 1 Food Processing: Food Qualities and Additi
ID: 274832 • Letter: S
Question
Subject: Human Nutrition
Laboratory 1
Food Processing: Food Qualities and Additives
Introduction Much of the food eaten today, whether in restaurants or at home, has been processed in some way by the food industry. Commercial processing of foods, such as freezing, canning, and drying, is done to extend the useful shelf life. Compounds (food additives) are added to food to impart favorable color, texture, and flavor. These include stabilizers and emulsifiers, which keep ingredients in foods such as mayonnaise and peanut butter from separating, thickeners that improve the texture of foods such as soups, desserts, and jams, and natural and artificial colors and flavors that improve appearance and taste. Other additives enhance the nutritional value of foods. Examples are the addition of vitamins A and D to milk, B vitamins and iron to cereals, and calcium to orange juice. Benzoates, sorbates, and proprionates protect foods from microbial contamination, and antioxidants such as ascorbate (vitamin C), BHA, and BHT prevent oxidation of the fatty acids in foods (rancidity). Food processing and the use of preservatives are not a recent phenomenon. For thousands of years people have preserved food by smoking, drying, and adding salt, sugar, and spices. More than 700 food additives have been used for a long enough period of time to be considered safe for human consumption without having to go through the lengthy testing required of new food additives. These additives are included on the GRAS (generally recognized as safe) list. Additives on the GRAS list are subject to further scrutiny if evidence is presented that indicates they may be harmful. Saccharine is an example.
In Part A of this lab assignment, the chemical and physical properties of three commonly used thickening agents will be examined. Modified food starch, cornstarch, and guar gum, are used in a number of ways, including thickening milkshakes, preventing creamy salad dressing from separating, and stabilizing frozen desserts. The effect of modified food starch is to stabilize and thicken foods. This is accomplished by the cross-linking of glucose chains in the starch. Natural food starches, such as cornstarch, are also used to thicken foods. However, modified starches tend to have higher solubility and greater stability, so are preferred by food processors for certain uses. Emulsifiers allow the mixing of two or more liquids that are immiscible. Guar gum acts as a stabilizer and emulsifier in the same manner as bile. One end of the structure attracts water (is hydrophilic), and the other end attracts oil (is hydrophobic). This property of guar gum is demonstrated in Part A, as well as its ability to thicken solutions. Guar gum is similar to pectin, a soluble fiber and polysaccharide. It cannot be digested by the body, and therefore cannot be broken down to produce energy. Starches, however, are foods in and of themselves, and have nutritive and caloric value. Part B of this lab examines the effect of storage conditions on the nutritive quality of foods. Your class will have three samples of orange juice that have been stored differently. Vitamin C, ascorbic acid, is one of the many chemicals difficult to measure directly. You will be using a semi-quantitative method to determine how much Vitamin C is in your sample. Vitamin C is easily destroyed in air through oxidation. It breaks down in the presence of oxygen. This is why you put lime juice in guacamole. The Vitamin C in the lime absorbs the oxygen more readily than the avocado does, keeping the avocado from turning brown as quickly. This is also why it is difficult to maintain the Vitamin C content of preserved and processed foods. You will be using Quantofix® test sticks to measure the concentration range (in mg/L) of ascorbic acid in your sample. When the end of the test stick is placed in a solution containing Vitamin C, a color change occurs based on how much ascorbic acid is present. The color indicated on the test stick is then compared to the test color chart to determine the ascorbic acid concentration range (in mg/L) for that solution. You will also be using long range pH paper to measure the pH of your sample. pH is the measure of acidity or alkalinity of a solution. By measuring the pH 3 of your sample you will be able to determine if the amount of Vitamin C, ascorbic acid influences the pH of the orange juice. Part C examines the use of enzymes in food production. Enzymes are essential for our bodies to digest and absorb the food that we consume. They are also used to prepare foods, such as cheese. Cheese is the solid portion of milk (curd) that has been separated from the liquid portion (whey). It has been one of the most important sources of food for thousands of years because it keeps better than milk and has much of milk's food value. Adding the enzyme, rennin, to milk makes cheese. The rennin coagulates the milk proteins into a curd form. Rennin is an enzyme found in the lining of calves’ stomachs. It is also isolated from bacteria that have been genetically engineered to produce it. Many foods are produced utilizing the enzymatic byproducts of bacteria and yeast, for example, bread and beer or wine.
Experimental Procedures Part A - Comparison of food thickeners The following materials will be necessary: ! Scale with weigh boats ! Vegetable oil ! 2 stir sticks ! Corn starch ! 2 10 mLtransfer pipets ! Modified food starch ! Guar gum ! Vinegar ! 4 sample vials ! Marking pens Food starch investigation: 1. Obtain 2 sample vials. Label each of sample vials identifying its contents, as cornstarch or modified food starch. 2. Weigh out 0.3 g of cornstarch and 0.3 g of modified food starch, using 2 weigh boats. 3. Using a pipet, add 10 mL of vinegar to each vial. 4. Add 2 mL of vegetable oil to each vial. 5. Transfer the cornstarch and modified food starch to the labeled vials. 6. Cap and shake vigorously for 15-20 seconds. 7. Examine the contents and record your observations in Table 1.
Table 1: Food starch investigation Substance Observations With oil and vinegar after shaking Cornstarch Modified Food Starch.
Guar gum investigation: 1. Label each of two sample vials identifying the contents - 0.2 g guar gum, 2.0 g guar gum. 2. Weigh out 0.2 g and 2.0 g of guar gum, using 2 weigh boats. 3. Add 10 mL vinegar to each vial. 4. Add 2 mL vegetable oil to each vial. 5. Transfer 0.2 g of guar gum to one vial, and add 2 g to the other. 6. Cap and shake vigorously for 15-20 seconds. 7. Examine the contents after shaking and then 5-10 minutes later. 8. Record your observations in Table 2.
Table 2: Guar gum investigation Guar gum Observations after shaking 0.2 g + oil and vinegar 2 g + oil and vinegar.
Part B: Vitamin C (ascorbic acid) Testing This station should have the following materials: • Quantofix Test • Vials of unknown orange juice samples • Long range pH paper • 3 test tubes Procedure 1. The Quantofix Test Kit will be used to determine the concentration of ascorbic acid (Vitamin C) in the provided orange juice samples, labeled 1, 2, and 3. Remove 3 test strips from the container and reseal. DO NOT TOUCH THE TEST PAPER ZONE. 2. Pipet approximately 15 mL of each orange juice sample into individually labeled test tubes (1, 2 and 3). 3. Dip the test strip into each of the 3 orange juice samples for no more than 5 seconds, place on paper towel for 30 seconds. 4. Compare the test paper zone with the color scale to determine the concentration range of ascorbic acid in each sample (measured in mg/L). The paper will turn green to blue in the presence of ascorbic acid. 5. Record the values in Table 3. 6. To determine the pH of each sample, use the pH paper. Tear off a small piece of paper and dip it into each of the samples for approximately 2 seconds. 7. The color change reaction will occur immediately. 8. Compare the color change of the paper to the color scale to determine the pH of the 3 samples. 9. Record the values in Table 3.
Table 3: Ascorbic Acid Concentration and pH Sample Number Concentration of Ascorbic Acid (mg/L) pH 1 2 3
Part C: Use of Enzymes to Produce Cheese Only the initial stage of cheese making will be performed in lab: the formation of curds from milk and the separation of the whey. The incredible variety of cheeses results from the different way the curds are handled i.e. temperature of the environment, whether they are kneaded, pressed or placed in a mold, how long they are aged, and what other flavorings or microorganisms are added. Materials ! 37ºC water bath ! Milk treated with buttermilk ! Small bottle of 5% rennin ! Spatula ! Cheesecloth ! Graduated cylinder ! 4 50-100 mL beakers Procedure 1. Measure 20 mL of the milk into 2 beakers. This milk has been pretreated with buttermilk to lower the pH. Why? Hint: What information have you learned about the pH of the different parts of your digestive system? 2. Label 1 beaker 37 ºC and 1 beaker 25ºC 3. Add 8 drops of the rennin to each beaker and stir well. 4. Place the 37 ºC labeled beaker in the water bath and leave the 2nd beaker on your work station countertop (25ºC is approximately room temperature). 5. Let the mixtures stand for 15 min or till gel like. 6. Carefully break the curd up into pieces with the spatula. Pour the mixtures into beakers lined with 2 layers of cheesecloth. 7. Pour the liquid whey into the graduated cylinder. Record the volume in the spaces below. 37 ºC Beaker 25ºC Beaker Liquid fraction (whey) _________ Liquid fraction (whey) _________ Original volume ________ Original volume ________ To determine the percent efficiency of your cheese making operation: • Divide the whey portion by the original volume and multiply that value by 100 • Subtract the % whey from 100 to determine the percent useable cheese. • Which method produces the greatest volume of useable cheese. 8 Report Guidelines 1. Lab report format is to follow Scientific Method; therefore, the report must include the following sections: a. Introduction- Describe the background information relevant to the overall experiments conducted and objective/purpose for the experiments conducted (parts A, B and C). b. Methods- describe the procedures performed for each test (parts A, B and C). Be sure to mention that all observations or measurements were made and recorded for analysis and any specific tests used to conduct the experiments. c. Results i. Present tables including data for experiments performed (parts A, B and C). ii. Tables should include titles that adequately describe the experiment. That is, if an individual knew nothing about your experiment he/she should be able to get a basic idea of what your group did by just looking over the tables. Include appropriate units for measure. iii. Show all calculations for part C. d. Conclusions i. This is where you write up the interpretations of the data that obtained from the experiment. ii. DO NOT simply restate the results- interpret them using the data from the results, including answers to the questions stated below. ALWAYS SUPPORT FINDINGS WITH DATA DISCUSSION. iii. Part A: Thickening Agents: If these thickening agents were used to produce a salad dressing, which of the samples tested would retain the same consistency after shipping from a manufacturing plant? Why? Answer question using descriptions of findings from the tests conducted. What if a manufacturer decided to produce a low-calorie line product, what thickener should be used and why? iv. Part B: Vitamin C Analysis: Which sample had the greatest Vitamin C concentration? Be sure to list all numbers obtained and what the samples were. Would a 4 oz (120 mL) serving of this sample meet the RDA daily requirement for Vitamin C? Were there any differences in the pH of the 3 samples? 9 v. Part C: Efficiency of cheese production: Which method produced the MOST useable cheese? Use values obtained from results to discuss the answer. vi. Were there any limitations of the experiment? Remember, there are always limitations in any scientific study.
Explanation / Answer
A)
B.