The input I received from Dr. Charles to have students work in pairs to make things Carpenter of Utah State University for the first edi- go faster. The information on hazards and precautions in testing the experimental procedures written for the use of the chemicals for each experiment is not first edition. For this second edition, I want to espe- comprehensive, but should make students and cially thank my graduate student, Cynthia Machado, a laboratory assistant aware of major concerns for her assistance and offering advice based on her in handling and disposal of the chemicals.
It is recommended in the text of the experi- Food Analysis laboratory course. The Nutrition Labeling and Education Act man- On the left hand side of the web page, click on the Food dated nutritional labeling of most foods. As a result, a Analysis Students link located under the services heading. A food labeling guide and since the publication of this laboratory manual and any changes in the procedures described below will also be found on this links to the complete nutritional labeling regulations web page.
As an example, a small Procedure change in the amount of an ingredient may determine if a product can be labeled low fat. As a result, the abil- 1. Enter the ity to immediately approximate how a formulation Nutrition Labeling section of the program. In some cases, the opposite situation may occur 2. Enter the ingredients for formula 1 listed in and a concept called reverse engineering is used.
In Table Click on the Add Ingredients button, reverse engineering, the information from the nutri- then select each ingredient from the ingredient list tional label is used to determine a formula for the window and click on the Add button, click on the X product. Caution must be used during reverse engi- to close the window after all ingredients have been neering. In most cases, only an approximate formula added.
Enter the percentage of each ingredient for for- vided by the nutritional label may be necessary. Enter the serving size common household unit described earlier.
In this laboratory, you will use a and the equivalent metric quantity and number computer program to prepare a nutritional label from of servings. First, click on the Serving Size button a product formula, determine how changes in the for- under Common Household unit, enter 8 in the window, mula affect the nutritional label, and observe an exam- click on OK, select oz from the units drop down list; ple of reverse engineering. Nutrition labeling. Nielsen Ed. Owl Software.
Condensed skim milk Enter a name and save formula 1. From the yogurt formula 1. After contacting several suppliers, File menu, select Save Formula. View the nutrition label and select label options. The composi- tein; the daily value footnote and calories conver- tion of the Dairy Calcium you will add is shown sion chart will be displayed unless Hide Footnote in Table Add and enter the name of the new ingredient 7.
Edit the ingredient declarations list. Click on the to the database. Answer yes to the question, top window and the ingredient declaration can be and click OK.
Enter the new ingredient composition Table Copy and paste the nutritional label and ingredi- under the edit ingredient file tab, the row will turn ent declaration list for formula 1 in a Word file. Edit the ingredient declaration which will paste the label, click Return on the label window.
To appear on the ingredient list for the new copy and paste the ingredient list for formula 1, ingredient. Click on the Return button. Component Amount Enter a name and save formula 2. Save the changes to the ingredient file. Click on View and print the nutritional label for the new the Finish Edit button, answer Yes to the question.
Follow the 5. Select close ingredient file. Open food analysis formula 1 in the Formula handout. Development Section of the program. From You will have to perform this calcula- 7. Add the new Dairy Calcium ingredient tion yourself following the example in Step 8. In this example, the program will automatically go through the reverse engineering process. Enter the amount of calcium required in the for- iron are entered. The minimum and maximum levels of each except skim milk and Dairy Calcium Find nutrient are calculated on a g basis.
Comment: calcium in the Properties column and enter in The program uses the rounding rules to determine the the Minimum and Maximum columns for calcium. This lets the program know that you want to have 3. The information about nutrient minimum and mg of calcium per g. In both the Min and maximums is transferred into the Formula Max columns of the formula ingredients enter Com- for milk 3. This lets the program adjust the amount of skim milk 4.
Ingredients used in the formula are then selected and Dairy Calcium calcium phosphate and based on the ingredient declaration statement on keeps the amount of all the other ingredients con- the nutrition label.
Comment: Selecting the right stant. Click on the Formulate button, click OK. Enter a name and save the modified formula. Restrictions on the amount of each ingredient the X to close the window, select Save Formula from in the formula are imposed whenever possible. Comment: This is a critical step that requires knowl- Open the new formula on the nutritional label- edge about the typical levels of ingredients used in the ing section.
Click on the Labeling Menu tab, select product. In this example, the amount of click open. Make sure you have the correct serving size gelatin is limited to 0. The program calculates an approximate formula. Assume you added enough Dairy Calcium to 7. Comment: This information is yogurt? Make a nutrition label using the chocolate chip cookie section of the program accessed by selecting View recipe and other information in Table Conversion fac- Reverse Engineering Section then Label to Spec from tors to get the weight of sugars and salt can be found in the Reverse Engineering menu.
Based on the labels you produced for yogurt formula 1 and 2 in Method A, what nutrient content claims could Resource Materials you make for each formula a description of nutrient content claims is found in Tables and in the Nielsen Metzger LE Nutrition labeling.
Food analysis, 4th edn. Springer, New York 2. Background It is generally required that reported values minimally include the mean, a measure of precision, Volumetric glassware, mechanical pipettes, and balances and the number of replicates.
The number of are used in many analytical laboratories. If the basic significant figures used to report the mean reflects skills in the use of this glassware and equipment the inherent uncertainty of the value, and it needs are mastered, laboratory exercises are easier, more to be justified based on the largest uncertainty in enjoyable, and the results obtained are more accurate making the measurements of the relative precision of and precise.
Measures of accuracy and precision can the assay. The mean value is often expressed as part be calculated based on the data generated, given the of a confidence interval CI to indicate the range glassware and equipment used, to evaluate the skill of within which the true mean is expected to be found. Determining mass using an analytical balance is A procedure or instrument is generally not deemed the most basic measurement made in an analytical inaccurate if the CI overlaps the standard value.
Accurately weighing reagents is the first step needs improvement. In the case of testing the accuracy in preparing solutions for use in various assays. All analytical laboratories use volumetric coefficient of variation CV. Calculations of precision glassware and mechanical pipettes. Mastering their are largely independent of the number of replicates, use is necessary to obtain reliable analytical results.
This laboratory includes of commonly used laboratory equipment. However, assessment of the accuracy and precision of automatic for more general acceptance of procedures, they are pipettors. An example application is determining the validated by collaborative studies involving several accuracy of automatic pipettors in a research or qual- laboratories.
Collaborative evaluations are sanctioned ity assurance laboratory, to help assess their reliability by groups such as AOAC International, AACC Inter- and determine if repair of the pipettors is necessary. Such collaborative studies are prerequisite to pipettors to determine if they accurately dispense procedures appearing as approved methods in manu- the intended volume of water.
To do this, water dis- als published by these organizations. Introduction to food analysis. S, Nielsen Ed. Evaluation of analytical data.
Repeat this proce- Analysis, 4th ed. Note that the total Familiarize, or refamiliarize, oneself with the use volume will be 60 ml. It is not necessary to of balances, mechanical pipettes, and volumetric empty the beaker after each pipetting. Do six determinations. Analytical balance and buret. Principle of Method a Repeat the procedure as outlined in Step 2a, Proper use of equipment and glassware in analytical but use a ml beaker, a ml or ml tests helps ensure more accurate and precise results.
It is not necessary to buret empty the beaker after each addition. Analytical balance and mechanical pipette. It is not necessary to empty the beaker after each pipetting. Notes 5. Total content TC versus total delivery TD. Before or during the laboratory exercise, the instructor is Tare a ml volumetric flask on a top loading encouraged to discuss the following: 1 Difference between balance.
Fill the flask to the mark with water. Now tare a ml 2 difference between markings on a ml versus a or beaker and pour the water from the volumetric ml buret. Weigh the water delivered from the volumetric flask. Readability versus accuracy.
Record the observed weight. Use gloves Record data in tables that follow. Check the temperature of least two other top loading balances, recording the water with a thermometer. Analytical balance and volumetric pipettes. Are these results consistent with what would be expected?
In a titration experiment using a buret, would you expect to use much less than a ml volume in each titration? Which is a volumetric pipette? This laboratory was developed with inputs from Dr 7.
From your results from Part 6 of this lab, would you now Charles E. Carpenter, Department of Nutrition and assume that since a balance reads to 0. What sources of error human and instrumental were evident or possible in Parts 2—4, and how could these be reduced or eliminated? Resource Materials 9.
You are considering adopting a new analytical method in your lab to measure the moisture content of cereal products. Nielsen SS Introduction to food analysis, Ch. Springer, New York and compare it to the old method? In: or estimate the accuracy of the new method? Nielsen SS ed Food Analysis, 4th edn. Moisture is an important factor in food quality, preservation, and resistance to deterioration.
Principle of Method Determination of moisture content also is necessary The sample is heated under specified conditions and to calculate the content of other food constituents on the loss of weight is used to calculate the moisture a uniform basis i. The dry matter content of the sample. Instructors may want to have students compare results Near infrared X with and without these fiberglass covers. Moisture and total solids analysis, information, or record container information linker to Ch.
Use gloves or tongs when handling sam- New York. These pans and crucibles have been dried and stored in desiccators prior to weighing. Overall Objective They will pick up moisture by sitting on the counter, The objective of this experiment is to determine and so remove them from the desiccator only just before compare the moisture contents of foods by various use. Open desiccators slowly to avoid damage and methods of analysis.
After cooling in a desiccator, the crucibles containing I. Moisture in Corn Syrup ashed milk would be weighed and the ash content 1. Label dried pans disposable aluminum calculated. Place 5 g of sample in the pan and weigh IV. Moisture of Nonfat Dry Milk accurately. Because corn syrup is very 1. Weigh accurately the dried pan with lid. Place 3 g of sample in the pan and weigh syrup. Store in a desiccator until samples are 4.
Store in a desiccator until samples are weighed. Label dried pans disposable aluminum 1. Weigh accurately dried pan with lid. Note identifier number on pan and lid. Place 3 g of ground sample in the pan and 2. Place 2—3 g of sample in the pan and weigh weigh accurately. Be sure metal covers are ajar, to allow 4.
Store in a desiccator until samples are water loss. Remove from oven, realign covers to 5. Data and Calculations III. Note identified num- wt of wet sample ber on crucible. Place 5 g of sample in the crucible and weigh accurately. Label weighing pans i. Fresh basil 1 4. Store in a desiccator until samples are cooled 2 to ambient temperature.
Label weighing pan, add 10 g dried sand and stirring rod, then weigh accurately. Add 5 g of sample and weigh accurately. Mix with stirring rod being careful not to spill any of the Objective sample. Leave the stirring bar in the pan. Bleed dried air into the vacuum oven method, with and without the addition oven as vacuum is released. Store in a desiccator until samples are cooled to ambient temperature. Hazards Determine the moisture content of corn flour using a Toluene Harmful, highly flammable rapid moisture analyzer.
Continue refluxing until two consecutive readings 15 min apart show no change. Toluene is highly flammable and is harmful if Dislodge any water held up in the condenser inhaled. Use adequate ventilation. Wear safety glasses with a brush or wire loop. Rinse the condenser and gloves at all times.
For disposal of toluene carefully with ca. Dislodge any waste, follow good laboratory practices outlined by moisture droplets adhering to the Bidwell— environmental health and safety protocols at your Sterling trap or toluene trapped under the institution. For this, use the wire. Rinse wire with a small amount 10 ml of toluene Supplies before removing from apparatus. Flask, condenser, and receiver must be scrupulously length with a T. For example, the apparatus, including ling trap, T.
No open flame! It should be long enough to extend the Bidwell—Sterling trap. Flatten the 2. A correction blank for toluene must be conducted loop on the buret brush and use this brush, periodically by adding 2—3 ml of distilled water to ml of toluene in the distillation flask, then inverted, as a wire to dislodge moisture drops following the procedure in Steps 2—6 above.
Data and Calculations Procedure 1. Grind the fresh basil with a small table-top food grinder. Pulse grind the sample in 5—10 s Wt. Avoid long pulses and excessive grinding to prevent frictional heat. Weigh approximately 40 g of sample basil or NFDM accurately amount chosen to yield 2—5 ml water. Transfer sample quantitatively to distilling flask. Add sufficient toluene to cover the sam- Objective ple completely not less than 75 ml.
Assemble the apparatus as shown in Chap. Fill the trap with toluene flour by the Karl Fischer KF method. Insert a loose nonabsorbing cotton When the sample is titrated with the KF reagent, plug into the top of the condenser to prevent which contains iodine and sulfur dioxide, the iodine condensation of atmospheric moisture in the is reduced by sulfur dioxide in the presence of water condenser. The water reacts stoichiometri- 5.
Bring to boil and reflux at about two drops per cally with the KF reagent. The volume of KF reagent second until most of the water has been col- required to reach the endpoint of the titration visual, lected in the trap, then increase the reflux rate conductometric, or coulometric is directly related to to ca. Hazards several samples exact number depends on type Karl Fischer reagent Toxic of sample.
Remember that this entire appara- 2-Methoxyethanol tus is very fragile. To prevent contamination Pyridine from atmospheric moisture, all openings must Sulfur dioxide be closed and protected with drying tubes. Iodine Harmful, dangerous to the environment II. Normally, this needs to be done only once a day, or when changing the KF reagent supply.
Reagents 1. Put the magnetic stir bar in the vessel and for 2 h turn on the magnetic stirrer. Remove the caps if any from drying tube. Hazards, Cautions, and Waste Disposal Turn the buret stopcock to the filling posi- tion.
Hold one finger on the air-release hold Use the anhydrous methanol in an operating hood in the rubber bulb and pump the bulb to fill since the vapors are harmful and it is toxic. Otherwise, the buret. Close the stopcock when the KF adhere to normal laboratory safety procedures.
Use reagent reaches the desired level at posi- appropriate eye and skin protection. The KF reagent tion 0. Titrate the water in the solvent anhydrous hazardous wastes. Allow the solution to stabilize at the Equipment endpoint on the meter for at least 1 min before proceeding to the next step. Berkeley, CA, Aquametry Apparatus 6.
Fill the buret with the KF reagent, then titrate the water in the sodium tartrate Procedure dihydrate sample as in Step II. Record the Instructions are given as for a nonautomated unit, and volume ml of KF reagent used. If using an automated unit, 7. Calculate the KF reagent water moisture follow instructions of the manufacturer. Prepare samples for analysis and place in S reaction vessel as described below. Use an extra Volume piece of weighing paper to form a cone- Wt.
Weigh the syringe with sample Wt. The color of the solution in the vessel should change to Principle light yellow and the meter will register Specific frequencies of infrared radiation are absorbed below the KF zone on the meter. The concen- sample as in Step II. Record the tration of moisture in the sample is determined by volume ml of KF reagent used.
After titrating energy absorbed. Explain your answers. For each method, what would you have to do to the corn flakes Follow instructions from manufacturer for use of the before measuring the moisture content? You have been asked to Data and Calculations evaluate the feasibility of switching to new methods the specific one would depend on the product for measuring moisture content.
Questions What are the advantages of each of these methods over the hot air oven method in the proposed use? In separate tables, summarize the results from the various What disadvantages or potential problems might methods used to determine the moisture content of each you encounter with the other two methods? Include in each table the following for each method: a Data from individual determinations, b Mean value, c Standard deviation, d Acknowledgments Observed appearance, etc.
This experiment was developed in part with 2. Calculate the moisture content of the liquid milk samples materials provided by Dr Charles E. Montecalvo, Jr. Arizona Instrument Corp. Forced draft oven Microwave drying oven ReSource Materials 3. Why was the milk sample partially evaporated on a hot plate before being dried in the hot air oven? Of the various methods used to measure the moisture 11th edn. Paul, MN content of corn syrup, based on concerns for accuracy AOAC International Official methods of analysis, and precision, what method would you choose if you 18th edn, ; Current through revision 2, On-line.
In: 5. What is the difference between moisture content and Nielsen SS ed Food analysis, 4th edn. Springer, New York water activity measurements? What method would you use to measure the moisture examination of dairy products, 17th edn.
Solvent drips onto the sample and soaks it to extract the fat. At 15—20 min Background intervals, the solvent is siphoned to the heating flask, to start the process again. Chemicals The lipid content of a food determined by extraction with one solvent may be quite different from the lipid content as determined with another solvent of differ- CAS No.
Hazards ent polarity. Fat content is determined often by solvent extraction methods e. The method of choice depends on a variety of factors, including the nature of the sample Hazards, Precautions, and Waste Disposal e. Otherwise, adhere to normal This experiment includes the Soxhlet, Goldfish, laboratory safety procedures. Wear gloves and safety Mojonnier, and Babcock methods. If samples analyzed glasses at all times. Petroleum ether and ether liquid by these methods can be tested by an instrumen- wastes must be disposed of in designated hazardous tal method for which equipment is available in your waste receptacles.
Snack foods are suggested for analysis and compari- Supplies son by the Soxhlet and Goldfish methods, and milk by the Mojonnier and Babcock methods. Fat analysis. Wearing plastic gloves, remove three predried cellulose extraction thimbles from the desic- Data from moisture analysis: cator. Place the three samples in a Soxhlet extractor. Cool dried samples in a desiccator then 1 reweigh. The Soxhlet extraction procedure utilized petroleum ether. What were the advantages of using the Soxhlet extraction Name of Snack Food: method rather than the Goldfish extraction method?
Solvent continuously Rep g Thimble g wool g g wool g drips through the sample to extract the fat. Fat con- 1 tent is measured by weight loss of sample or weight 2 of fat removed.
Follow Steps 1—4 in Soxhlet procedure. Place the thimble in the Goldfish condenser bracket. Push the thimble up so that only about 1 cm. Follow Steps 6 and 7 in Soxhlet procedure. If the fat content 1. What would be the advantages of using ethyl ether rather of the food you analyzed was given on the label, report than petroleum ether in a solvent extraction method, such this theoretical value.
Label serving size g : 3. Make triplicate determinations on both the sample and reagent blanks. The Principle procedure given here is for fresh milk. Other samples may need to be diluted with distilled water in step 2 and require Fat is extracted with a mixture of ethyl ether and petro- different quantities of reagents in subsequent steps. Consult leum ether. The extract containing the fat is dried and the instruction manual or AOAC International Official Methods expressed as percent fat by weight.
The assay uses not only ethyl ether and petroleum ether, but also ammonia and ethanol. Ammonia dis- Procedure solves the casein and neutralizes the acidity of the Instructions are given for analysis in triplicate. Ethanol prevents gela- tion of the milk and ether, and aids in the separation 1.
Turn on power unit and temperature controls of the ether—water phase. Ethyl ether and petroleum for oven and hot plate on the fat side of the ether serve as lipid solvents, and petroleum ether Mojonnier unit. Warm milk samples to room temperature and mix well. Chemicals 3. CAS No. Hazards Handle dishes from this point on with tongs or gloves. Use three dishes for each type of milk Ammonium Corrosive, dangerous for the samples, and two dishes for the reagent blank.
Cool dishes in cooling desiccator for 7 min. Weigh dishes, record weight of each dish and its Petroleum Harmful, highly flammable, identity, and place dishes in desiccator until use. Weigh samples accurately ca. If weighing rack is used, fill curved pipettes and place in rack on the balance. Weigh Hazards, Precautions, and Waste Disposal each sample by difference.
Add chemicals for the first extraction in the Ethanol, ethyl ether, and petroleum ether are fire haz- order and amounts given below. After each ards; avoid open flames, breathing vapors, and contact addition of chemicals, stopper the flask and with skin.
Ether is extremely flammable, is hygro- shake by inverting for 20 s. Ammonia is a corrosive; avoid contact and breathing vapors. Oth- erwise, adhere to normal laboratory safety procedures. First extraction Second extraction Wear gloves and safety glasses at all times. Petroleum Chemicals Step Amount ml Step Amount ml ether and ether liquid wastes must be disposed of in designated hazardous waste receptacles.
The aqueous Ammonia 1 1. Carefully pour off the ether solution of each Notes sample into a previously dried, weighed, and Reagents must be added to the extraction flask in the follow- cooled fat dish. Most or all of the ether layer ing order: water, ammonia, alcohol, ethyl ether, and petroleum should be poured into the dish, but none of the ether. The burets on the dispensing cans or tilting pipets are remaining liquid must be poured into the dish.
List possible causes for high and low results in a Mojon- Repeat the extraction procedure a second nier fat test. How would you expect the elimination of alcohol from the following the sequence and amount given in Mojonnier procedure to affect the results? Again, after each addition 3. How would you propose to modify the Mojonnier procedure of chemicals, stopper the flask and shake by to test a solid, nondairy product?
Explain your answer. Centrifuge the flasks again, as described above. If this is done, repeat the Principle centrifugation. Sulfuric acid is added to a known amount of milk Pour ether extract into respective fat dish sample in a Babcock bottle.
The acid digests the pro- i. Centrifugation poured into the same fat dish used for that and hot water addition isolate the fat into the graduated sample from the first extraction , taking care neck of the bottle. The Babcock fat test uses a volumetric to remove all the ether but none of the other measurement to express the percent of fat in milk or liquid in the flask. Complete the evaporation of ether, either very carefully on the hot plate this can be problem- Note atic and a fire hazard or open in a hood.
The specific gravity of liquid fat at that temperature is not fast enough to cause splattering. If the approximately 0. The calibration on the gradu- plate appears to be too hot and boiling is too ated column of the test bottle reflects this fact and enables one fast, only part of the dish should be placed to make a volumetric measurement, which expresses the fat on the hot plate.
If instead using an operating content as percent by weight. Chemicals When all the ether has been evaporated from the dishes, place the dishes in the vacuum CAS No. Sulfuric acid Corrosive Cool the dishes in the desiccator for 7 min.
Accurately weigh each dish with fat. Record weight. Hazards, Precautions, and Waste Disposal Concentrated sulfuric acid is extremely corrosive; avoid Data and Calculations contact with skin and clothes and breathing vapors. Calculate the fat content of each sample. Subtract the Wear gloves and safety glasses at all times. Otherwise, average weight of the reagent blank from the weight of adhere to normal laboratory safety procedures.
Sulfuric each fat residue in the calculation. Add glymol red reader to top of fat layer. Equipment Immediately use a divider or caliper to mea- sure the fat column to the nearest 0. Procedure 9. Reject all tests in which the fat column is milky Instructions are given for analysis in triplicate. Adjust milk sample to ca. The fat should be clear and spar- homogenous. Using a standard milk pipette, kling, the upper and lower meniscus clearly pipette After the pipette has emptied, blow out should be clear.
Record the readings of each test and determine bottle. Allow milk samples to adjust to ca. Dispense ca. Mix the milk and acid thoroughly. Be careful not to get 1 any of the mixture into the column of the bottle 2 while shaking. Be sure bottles are counterbalanced.
Position bot- Questions tles so that bottlenecks will not be broken in horizontal configuration. Be sure that the heater 1. What are the possible causes of charred particles in the fat column of the Babcock bottle? What are the possible causes of undigested curd in the 4.
Centrifuge the bottles for 5 min after reaching Babcock fat test? Why is sulfuric acid preferred over other acids for use in upon the diameter of the centrifuge head. Carefully permit the water to flow Resource Materials down the side of the bottle. Again, centrifuge the bottles for 2 min. In: Nielsen SS top graduation of the scale. Again, centrifuge ed Food analysis, 4th edn. Springer, New York the bottles for 1 min. Remove the bottles from the centrifuge and place examination of dairy products.
Hazards The protein content of foods can be determined by numerous methods. Both Hydrochloric acid, Corrosive methods are official for the purposes of nutrition conc. HCl labeling of foods. While the Kjeldahl method has Methyl red been used widely for over a hundred years, the recent Sodium hydroxide NaOH Corrosive availability of automated instrumentation for the Sulfuric acid, conc. Protein analysis. Add dd water Objective to make up to 4.
In a 4-L flask, dissolve g boric acid in ca. Mix and then add an additional 1. Principle of Method Cool to room temperature under tap water cau- The Kjeldahl procedure measures the nitrogen content tion: glassware may break due to sudden cooling of a sample. The protein content then, can be calculated or leave overnight. When using the rapid proce- assuming a ratio of protein to nitrogen for the specific dure, the flask must be shaken occasionally to food being analyzed.
The Kjeldahl procedure can be prevent recrystallization of the boric acid. Add basically divided into three parts: 1 digestion, 2 40 ml of bromocresol green solution mg distillation, 3 titration. In the distilla- ethanol. Dilute to 4 L with water and mix care- tion step, the digested sample is made alkaline with fully. The con- of ammonia nitrogen in this solution is quantified by tents of the flask should then be a neutral gray. A reagent blank If not, titrate with 0.
Calculate the amount of NaOH titrant required for this blank is subtracted from each solution necessary to adjust the boric acid solution determination. Fit the dispenser Add the calculated amount of 0. Mix well. Verify Kjeldahl tube. Set the bottle with dispenser on a tray the adjustment results by distilling a new blank to collect spills. Place adjusted solution into a bottle equipped with a ml repipettor. HCl to 4 L with dd water. Add 3—5 drops indicator Equipment 3 parts 0.
Note the acid volume used and calculate the normality as described below. Procedure Calculation to standardize HCl solution: Instructions are given for analysis in triplicate.
Digestion Write the normality of the standardized HCl 1. Turn on digestion block and heat to appro- solution on the stock container. Accurately weigh approximately 0. Record the weight. Leave in a drying digestion tube. Repeat for two more samples. Let cool in a desiccator. Add one catalyst tablet and appropri- a 1-L volumetric flask, dissolve 1. Dilute to volume. Concentrated sodium hydroxide is a corrosive. Place rack of digestion tubes on digestion Wear corrosion resistant gloves and safety glasses at block.
Cover digestion block with exhaust all times. Perform the digestions in an operating hood system turned on. Let samples digest until digestion is complete. Allow samples to cool in the hood before remov- The samples should be clear but neon green , ing the aspirating fume trap from the digestion unit.
Otherwise, adhere to normal laboratory safety proce- 6. Take samples off the digestion block and allow dures. The waste of combined sulfuric acid and sodium to cool with the exhaust system still turned on. Carefully dilute digest with an appropriate ensure it is pH 3—9 , so it can be discarded down the volume of dd water. Swirl each tube. However, for disposing any chemical wastes, follow good laboratory practices out- II. Distillation lined by environmental health and safety protocols at 1.
Follow appropriate procedure to start up your institution. In this distillation process, a set volume of NaOH solution will Blank 1 — — — — be delivered to the tube and a steam generator 2 — — — — will distill the sample for a set period of time. Upon completing distillation of one sample, Sample 1 proceed with a new sample tube and receiv- 2 ing flask. Titration Questions 1. Record the normality of the standardized 1.
H2SO4 was used to digest the sample, how many millili- 2. How to calibrate the instrument. Put a magnetic would your results have been changed if the alkali pump stir bar in the receiver flask and place it on a timer had malfunctioned and delivered only 15 ml of the stir plate. Molarity of conc. Could phenolphthalein be used as an indicator in the Kjeldahl titration? Why or why not? Titrate each sample and 3. Describe the function of the following chemicals used in blank to an endpoint pH of 4.
Record vol- this determination: ume of HCl titrant used. If using a colorimetric endpoint, put a b Borate magnetic stir bar in the receiver flask, place c H2SO4 it on a stir plate, and keep the solution stir- d NaOH ring briskly while titrating. Titrate each 4. Why was it not necessary to standardize the boric acid sample and blank with the standardized solution?
HCl solution to the first faint gray color. Explain how the factor used to calculate the percent pro- Record volume of HCl titrant used. Data and Calculations 6. For each of the disadvantages of the Kjeldahl method, give Calculate the percent nitrogen and the percent pro- another protein analysis method that overcomes at least tein for each of your duplicate or triplicate corn flour partially that disadvantage.
The corn flour sample you analyzed was not a dried sample. Use 6. Determine the protein content of corn flour using the nitrogen combustion method. In the assay, the the appropriate slot for the sample number. Sample and to release nitrogen gas and other products i. The other products are removed, and the nitrogen is quantitated by gas chromatography using Data and Calculations a thermal conductivity detector.
Record the percent nitrogen content for each of your duplicate or triplicate corn flour samples. Calculate Chemicals protein content from percent nitrogen data, and determine the average percent protein. The corn flour CAS No. Hazards sample you analyzed was not a dried sample. Report percent protein results on a wet weight basis wwb and Ethylenediaminetetraacetic acid, Irritant on a dry weight basis dwb. The other chemicals used are specific to each manufac- turer for the columns within the instrument.
Supplies Questions 1. What are the advantages of the nitrogen combustion Used by students method compared to the Kjeldahl method? If you analyzed the corn flour sample by both the Kjeldahl Equipment and nitrogen combustion methods, compare the results. Chang SKC Protein analysis. Springer, New York sample cup on an analytical balance.
Sample weight AOAC International Official methods of analysis, will be coordinated with sample number in autosam- 18th edn, ; Current through revision 2, On-line. Remove sample from Method Although the method detects almost all carbohydrates, the absorptivity of the different carbohydrates varies.
These compounds then react with phenol to produce a yellow-gold color. Wear gloves and safety glasses at all times, at nm. For products that are high in hexose sugars, and use good lab technique. The concentrated H2SO4 is glucose is commonly used to create the standard curve, very corrosive e.
The phe- and the absorption is measured at nm. The color nol is toxic and must be discarded as hazardous waste. In this experiment, you will create a standard curve with a glucose standard solution, use Supplies it to determine the carbohydrate concentration of soft drinks and beer, then calculate the caloric content of Used by students those beverages.
Carbohydrate analysis. Then, pipette 1. Dilute to volume with dd water. Seal flask with Para- Instructions are given for analysis in duplicate. Record caloric content from label: You will ana- volumetric flask, and dilute to volume lyze for total carbohydrate content: 1 a regular with dd water.
Seal flask with Parafilm and and diet soft drink of the same brand, or 2 a mix well. Before 5. Phenol addition: To each tube from Parts you proceed with the sample preparation and 1 and 4 containing a total volume of 2 ml, analysis, record the caloric content on the nutri- add 0. Mix on a Vortex test 3. Decarbonate the beverages: With the bever- tube mixer. Shake 5. The sulfuric acid reagent should gently at first try not to foam the sample if it be added rapidly to the test tube.
Direct the is beer and continue gentle shaking until no stream of acid against the liquid surface rather observable carbon dioxide bubbles appear. If than against the side of the test tube in order there is any noticeable suspended material in to obtain good mixing.
These reactions are the beverage, filter the sample before analysis. Sample tubes: So the sample tested will contain of H2SO4 to an aqueous sample. After ized. Mix on a Vortex test tube mixer. Let tubes dilution as indicated, pipette 1. Ana- for 10 min i. Vortex the test tubes again before reading the absorbance.
Dilution Volume assayed ml 7. Reading absorbance: Wear gloves to pour Soft drink samples from test tubes into cuvettes.
Do not Regular 1 rinse cuvettes with water between samples. Retain this blank sample in one Lite 1 cuvette for later use. Read your standard Sample table: curve tubes from low to high concentration i. Absorbance Spectra: Use one of the duplicate 18 Soft drink, 1: 1 ml 0. Determine the absorbance spectra from to nm by reading Sample calculation for soft drink, regular: the tube at 10 nm intervals. Construct a standard curve for your total carbo- ond table below.
Calculate the concentration of glucose in your into account the dilution and volume assayed. Note: Glucose equivalent 4. Plot the absorbance spectra obtained by measur- 11 Std. What are the advantages, disadvantages, and sources of diet error for this method to determine total carbohydrates? Your lab technician performed the phenol—H2SO4 analysis on 17 Beer, reg.
What most likely 6. Was it best to have read the absorbance for the standard caused these results? Describe what happened. Explain why a wave- 3. If you started with a glucose standard solution of 10 g length in this region is appropriate for this reaction.
Show all calculations. If you had not been told to do a fold dilution of This laboratory was developed with input from Dr a soft drink sample, and if you know the approximate Joseph Montecalvo, Jr. In: Nielsen content on the food label? Springer, New York ries explain any differences? The U. In The Food Lab, Kenji focuses on the science behind beloved American dishes, delving into the interactions between heat, energy, and molecules that create great food.
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