DMT20053 - FOOD CHEMISTRY LAB MANUAL LAB 1: DETERMINATION OF MOISTURE CONTENT Objective: At the end of the laboratory session, students will be able to: 1. Apply different methods to determine total moisture content. 2. Handle specific equipments. 3. Determine the suitability of method for a specific sample. 4. Adhere to all safety measures. A. OVEN DRYING METHOD Introduction: In oven drying methods, the sample is heated under specified conditions, and the loss of weight is used to calculate the moisture content of the sample. The amount of moisture determined is highly dependent on the type of oven used, conditions within the oven, and the time and temperature of drying. Principle: Weighed samples are placed in an oven for a specified time and temperature (e.g. 3 hours at 100oC) and their dried mass is determined, or they are dried until they reach constant mass. The thermal energy used to evaporate the water is applied directly to the sample via the shelf and air that surrounds it. Equipment: Drying oven, metal dishes, digital balance, desiccators, spatula Procedure: 1. Prepare food samples in the right pre-sampling method. (i.e. if the sample is in the form of solid, blend it). 2. Put 2 metal dishes with cover in an oven (100 – 105°C) for 20 minutes. Transfer them into desiccators for 10 minutes. 3. Weigh each metal dish and record the reading (Wo). 4. Weigh 5g of dry food sample or 10g of wet food sample in each metal dish. Record the reading (W1). 5. Put them in an oven for an hour uncovered. 6. Transfer them into desiccators for 10 minutes. Weigh them and record the reading (W2). 7. Put the metal dishes in an oven for another an hour. Put again in the desiccators for 10 minutes and weigh them. Record for every reducing in weight. 8. Repeat step 5-6 until the reading is constant. Calculation: % moisture content = W1 – W2X100 W1 – Wo Where; Weight of metal dish = Wo Weight of metal dish + sample = W1 (before drying) Weight metal dish + sample = W2 (after drying)
DMT20053 - FOOD CHEMISTRY LAB MANUAL B. VACUUM OVEN METHOD Introduction: Drying oven is not suitable if the product to be assayed has a high concentration of volatiles such as oil and fat, vegetables, fruits, and milk products. By drying under reduced pressure, one can obtain a more complete removal of water and volatiles without decomposition within a 3 – 6 hour drying time. Vacuum ovens need a dry air purge in addition to temperature and vacuum controls to operate. Principle: Weighed samples are placed under reduced pressure (typically 25-100 mm Hg) in a vacuum oven for a specified time and temperature and their dried mass is determined. Equipment: Oven vacuum, digital balance, metal dishes, spatula, desiccators Procedure: 1. Prepare food samples with the right pre-sampling methods. 2. Put 2 metal dishes in an oven (105°C) for 30 minutes. 3. Transfer them into desiccators and weigh them (Wo). 4. Weigh 5g of dry food sample and 10g of wet food sample in the metal dishes (W1) 5. Put it in a vacuum oven for 3-6 hours. 6. Transfer them into desiccators and weigh them (W2). 7. Repeat step 5-6 until the reading is constant. Calculation: % moisture content = W1 – W2X100 W1 – Wo Where; Weight of metal dish = Wo Weight of metal dish + sample = W1 (before drying) Weight metal dish + sample = W2 (after drying) Result: Refers to Food Chemistry Lab Sheet C. INFRARED SCALE METHOD Introduction: The sample to be analyzed is placed under an infrared lamp and its mass is recorded as a function of time. The water molecules in the food evaporate because they absorb infrared energy, which causes them to become thermally excited. Principle: Infrared drying involves penetration of heat into the sample being dried, as compared to heat conductivity and convection with conventional ovens. Such heat penetration to evaporate moisture from the sample can significantly shorten the required drying time, to 10 – 25 minutes. The infrared lamp used to supply heat to the sample results in a filament temperature of 2000 – 2500K.
DMT20053 - FOOD CHEMISTRY LAB MANUAL Equipment: Infrared moisture analyzer, aluminum dishes, spatula Procedure: 1. Prepare food samples with the right pre-sampling method. 2. Weigh 5g dry food sample or 10g wet food sample on the aluminum drying dish. 3. Let the drying process complete and record the reading. Notes: No infrared drying moisture analysis techniques are approved by AOAC currently. However, because of the speed of analysis, this technique is suited for qualitative in-process use. Discussion: The following should be in your discussion: State the results by quoting significant data. Do not re-write all the data! Give the advantages and disadvantages of each analysis that is carried out. Suggest steps that need to be taken to prevent decision error on the analyzed sample. Conclusion: The following should be in your conclusion: State the objective/purpose. Was the objective/purpose achieved? If so, explain how and if not explain why not. State what you learned in this activity. Summarize your result. Questions: Refers to Food Chemistry Lab Sheet
DMT20053 - FOOD CHEMISTRY LAB MANUAL LAB 2: DETERMINATION OF CARBOHYDRATES USING PHYSICAL METHOD Objective: At the end of the laboratory session, students will be able to: 1. Identify the types of sugar in food samples using polarimeter. 2. Determine sugar concentration in food using refractometer and hydrometer. A. REFRACTOMETER Introduction: Refractometry is a technique that measures how light is refracted when it passes through a given substance, in this case, an unknown compound. The amount by which the light is refracted determines the refractive index. Refractive index can be used to identify an unknown liquid compound, or it can be used as a means of measuring the purity of a liquid compound by comparing it to literature values. The closer the refractive index is to the literature values, the purer the sample. Refractive index is defined as the ratio of the velocity of light in air to the velocity of light in the medium being measured. Principle: When a beam of light is passed from one medium to another and the density of the two differs, then the beam of light is bent or refracted. Bending of the light beam is a function of the media and the since of the angles of incidence and refraction at any given temperature and pressure and is thus a constant. Equipment: Hand refractometer, Abbe refractometer, spatula, dropper Sample: Sucrose, glucose and fructose solution Procedure: 1. Place a drop of sample on the measuring surface of the refractometer. 2. Look through eyepiece. 3. Take the reading at the point where the contrast line (difference between light and dark areas) crosses the scale. 4. Do the correction using the table enclosed. B. POLARIMETRY Introduction: Polarimetry measures the extent to which a substance interacts with plane polarized light (light which consists of waves that vibrate only in one plane); whether it rotates plane polarized light to the left, to the right, or not at all. If the substance rotates plane polarized light to the left or to the right, it is called optically active. To be optically active, a compound must have a chiral center. A chiral center is a carbon that has 4 different groups attached to it. Depending on the orientation of these four different groups about the chiral carbon, the compound may rotate plane polarized light to the left or to the right. If a compound does not have a chiral center, it will not rotate light at all. The number of degrees and the direction of rotation are measured to give the observed rotation. The observed rotation must be corrected for the length of the cell used and the solution concentration. Comparing the corrected observed rotation to literature values can aid in the identification of an unknown compound. Principle: Carbohydrates can rotate the plane of polarized light through an angle that depends on the nature of the compound, the temperature, the wavelength of the light and the concentration of the compound. The concentration of the compound can be determined from a value known as the specific optical rotation.
DMT20053 - FOOD CHEMISTRY LAB MANUAL Equipment: Polarimeter Sample: Sucrose, glucose and fructose solution Procedure: 1. Switch on the light source. 2. Set the polarimeter to zero degrees and view the selected object through the polarimeter. 3. Rotate the lens of the polarimeter filter slowly until you have rotated it in a complete circle. Check for any changes in brightness. The light is unpolarized if its brightness does not change as you rotate the lens. 4. Locate the polarimeter setting at which the light is brightest. Note: This will generally require you to rotate the lens back and forth a few times to find the setting of maximum brightness. 5. Read the setting that produces the maximum brightness. Settings of zero and 180 degrees indicate a completely vertical polarization, and settings of 90 and 270 degrees indicate complete horizontal polarization. 6. Determine the degree of polarization. Locate the setting where the light is faintest and estimate the brightness of the faintest setting as a percentage of the brightest light. If no light at all can be seen on this setting, the light is completely polarized. If the brightness doesn't change, the light is completely unpolarized. Calculation: ()D20 = 100 /lc Where: ()D20 = specific rotation of sugar at sodium D line 20 0C = degree of rotation l = tube length (dm) c = concentration of sugar (g/100 ml) C. SPECIFIC GRAVITY Introduction: Specific gravity is defined as the ratio of the density of a substance to the density of a reference substance (usually water), both at a specified temperature. The concentration of a carbohydrate solution can be determined by measuring the specific gravity of the solution then referring to appropriates specific tables (Table 1). Table 1: Specific gravity for glucose, fructose and sucrose at 20°C CONCENTRATON SPECIFIC GRAVITY (%/w) Glucose Fructose Sucrose 5 1.01769 1.01803 1.01824 10 1.03769 1.03853 1.03901 20 1.07981 1.08162 1.08270 30 1.12475 1.12760 1.13000 Principle: Hydrometer used an approach to measuring specific gravity based on Archimedes’ principle, which states that a solid suspended in a liquid will be buoyed by a force equal to the weight of the liquid
DMT20053 - FOOD CHEMISTRY LAB MANUAL displaced. The weight per unit volume of a liquid is determined by measuring the volume displaced by an object of standard weight. A hydrometer is a standard weight on the end of a spindle, and it displaces a weight of liquid equal to its own weight. The Brix hydrometer is a type of saccarometer used for sugar solutions such as fruit juices and syrups, and one usually directly reads the percentage of sucrose at 20°C. Equipment: Hydrometer, measuring cylinder 500 ml Sample: Sucrose, glucose and fructose solution Procedure: 1. Sanitize the hydrometer and measuring cylinder. 2. Place measuring cylinder on flat surface. 3. Fill the measuring cylinder with enough liquid to just float the hydrometer - about 80% full. 4. Gently lower the hydrometer into the cylinder; spin the hydrometer as you release it, so no bubbles stick to the bottom of the hydrometer. (NOTE: This can affect readings). 5. Make sure the hydrometer isn't touching the sides of the test jar and is floating freely, 6. Take a reading across the bottom of the meniscus and record the reading. 7. Do the correction using the table enclosed. Result: Refers to Food Chemistry Lab Sheet Discussion: The following should be in your discussion: State the results by quoting significant data. Do not re-write all the data! Give the advantages and disadvantages of each analysis that is carried out. Suggest steps that need to be taken to prevent decision error on the analyzed sample. Conclusion: The following should be in your conclusion: State the objective/purpose. Was the objective/purpose achieved? If so, explain how and if not explain why not. State what you learned in this activity. Summarize your result. Questions: Refers to Food Chemistry Lab Sheet
DMT20053 - FOOD CHEMISTRY LAB MANUAL
DMT20053 - FOOD CHEMISTRY LAB MANUAL LAB 3: MICROSCOPIC TEST FOR STARCH GRANULE Objective: At the end of the laboratory session, students will be able to: 1. Locate the presence of starch granules. 2. Identify different types of starch granules. Introduction: Starches are widely distributed in nature and in many processed foods. Important commercial starches include those extracted from cereals (e.g., corn, rice, wheat) and roots and tubers (e.g., potato, tapioca). Starch molecules arrange themselves in the plant in semi-crystalline granules. Each plant species has a unique starch granular size: rice starch is relatively small (about 2μm) while potato starches have larger granules (up to 100μm). Principle: The size and shape of starch granules are characteristic of the plant source and can be identified microscopically. The birefringent pattern of the granules seen under polarized light assists in identification. Equipment: Microscope, slide, filter paper Sample: Sediment of potato, rice, corn, sago, tapioca, and wheat flour Procedure: 1. Put a drop of sample sediment on a slide. 2. Using the appropriate technique, determine the structure and distribution of the starch granules. 3. Repeat the process for the other starch samples. 4. Compare the size and distribution of all the samples. Result: Refers to Food Chemistry Lab Sheet Discussion: The following should be in your discussion: Discuss the characteristics of each granule. Suggest steps that need to be taken to prevent decision error on the analyzed sample. Conclusion: The following should be in your conclusion: State the objective/purpose. Was the objective/purpose achieved? If so explain how and if not explain why not. Summarize your result. Questions: Refers to Food Chemistry Lab Sheet
DMT20053 - FOOD CHEMISTRY LAB MANUAL LAB 4: DETERMINATION OF CRUDE FIBER Objective: At the end of the laboratory session, students will be able to: 1. Handle appropriate method to determine crude fiber content. 2. Calculate crude fiber content in food sample. 3. Compare crude fiber content in food sample. Introduction: Crude fiber is a non digestible carbohydrates of foods found in foods such as whole grain products, fruits, vegetables, and legumes (such as dry beans and peas) that may promote regularity and as part of a healthy diet may decrease your risk for some diseases. Principles: Crude fiber is determined gravimetrically after chemical digestion and solubilization of other materials present. The fiber residue weight is then corrected for ash content after ignition. Equipment: Crucibles, drying oven, heating plat, digital balance, muffle furnace Chemical solution: 5% sulphuric acid, 40% and 25% NaOH, 1% HCl, phenoftalein, ethyl alcohol, boiled water Procedure: 1. Blend sample. 2. Weigh accurately 2.00g of the dried and fat free sample into round flask 500ml. 3. Add 50ml H2SO4 (5%) and 150ml distilled water. 4. Place the round flask under the condenser and reflux for 30 minutes. 5. Add 5ml NaOH (40%) solution and neutralize the excessive acid using NaOH solution (40%) (Use phenoftalein as indicator) and add 10ml NaOH (25%) solution. 6. Reflux for 30 minutes again. 7. After reflux exactly for 30 minutes,filter through filter paper in a Buchner funnel using suction and wash well with HCl (1%) solution. 8. Wash acid using boiling water (use litmus paper). 9. Wash twice with alcohol, dry 2 hours at 100 °C, cool and weigh. 10. Ignite slowly over a Bunsen flame until no more fumes are evolved. 11. Transfer the crucibles to muffle furnace set at 550oC 12. Incinerate the sample until it is free of black carbon particle (2 hours) (until it is white in color). 13. Remove the crucibles in desiccators and weigh after cooling. 14. Repeat until no further loss in weigh is indicated. Calculation: Crude fiber (%) = (S-K)-A x 100 W Where; Weight of crucible +ashless paper + dried residue = S Weight of ashless filter paper = K Weight of crucible + ash = A Weight of dried and fat free sample = W
DMT20053 - FOOD CHEMISTRY LAB MANUAL Result: Refers to Food Chemistry Lab Sheet Discussion: The following should be in your discussion: State the results by quoting significant data. Do not re-write all the data! Give the advantages and disadvantages of this analysis. Suggest steps that need to be taken to prevent decision error on the analyzed sample. Conclusion: The following should be in your conclusion: State the objective/purpose. Was the objective/purpose achieved? If so, explain how and if not explain why not. State what you learned in this activity. Summarize your result. Questions: Refers to Food Chemistry Lab Sheet
DMT20053 - FOOD CHEMISTRY LAB MANUAL LAB 5: DETERMINATION OF PROTEIN CONTENT Objective: At the end of the laboratory session, students will be able to: 1. Determine the protein content in foods samples using Kjeldahl method. 2. Calculate protein content in various food samples. 3. Compare protein content in various food samples. Introduction: Proteins are an abundant component in all cells, and almost all except storage proteins are important for biological functions and cell structure. Food proteins are very complex. They are composed of elements including hydrogen, carbon, nitrogen, oxygen and sulfur. Nitrogen is the most distinguishing element present in proteins. However, nitrogen content in various food proteins ranges from 13.4% to 19.1% due to the variation in the specific amino acid composition of proteins. Generally, proteins rich in basic amino acids contain more nitrogen. Principle: In the Kjeldahl procedure, proteins and other organic food components in a sample are digested with sulfuric acid in the present of catalyst. The total organic nitrogen is converted to ammonium sulfate. The digest is neutralized with alkali and distilled into a boric acid solution. The borate anions formed are titrated with standardized acid, which is converted to nitrogen in the sample. The result of the analysis represents the crude protein content of the food since nitrogen also comes from non-protein components. Equipment: Digestion unit, distillation set, digestion tubes, and measuring cylinders. Chemical solution: Concentrated sulfuric acid, 32%NaOH, 40% NaOH, 2% boric acid, 0.02N HCl, protein catalyst (mixture of 0.15g CuSO4, 5.5g K2SO4, 0.03g selenium), protein indicator (0.016g red metil and 0.083g green bromocresol dissolve in 100ml alcohol). Procedure: Method 1: Micro Kjedahl : a. Digestion 1. Weigh 0.15-0.2g food sample in a digestion tube. 2. Add in 0.8g protein catalyst and 5ml concentrated H2SO4. 3. Digest the mixture in the digestion unit until the process is complete. 4. Repeat all the steps above for blank (without sample). BEWARE FOR UNSTABIL REACTION FOR THE FIRST 30 MINUTES b. Distillation 1. Transfer ALL the content of the digestion tube into a distillation tube by adding 5ml of distilled water. 2. Add 15ml NaOH 32% into the tube. 3. Measure 10ml of boric acid in 100ml conical flask together with a few drops of protein indicator. Put the conical flask at the end of the condensor. Make sure the end-tip of the condensor is IN the solution. 4. Distill the sampel for 15 minutes. Adjust the end-tip of the condensor just above the solution and distiil it for another 2 minutes. 5. Wash the end tip with distilled water. c. Titration 1. Titrate the content of conical flask with 0.02N HCl until the color of the solution turns pinkish.
DMT20053 - FOOD CHEMISTRY LAB MANUAL Method 2: Macro Kjedahl a. Digestion 1. Add 2 – 5g sample with 20ml concentrated sulfuric acid and 8g of catalyst. 2. Digest the mixture in the digestion unit until the process is complete. 3. Repeat the entire step above for blank (without sample). b. Distillation 1. Transfer the content of digestion tube to the distillation tube. Wash the tube with 40ml distilled water. 2. Attach the tube to the distillation set. Add 60ml of 40% NaOH. 3. Measure 50ml of 2% boric acid in 500ml conical flask. Add in a few drops of protein indicator. 4. Distill the sample for 3 minutes. 5. Replace the first tube with another tube filled with 100ml distilled water. 6. Continue the distillation process for another 2 minutes. 7. Wash the end tip of the condenser with distilled water. c. Titration 1. Titrate the solution with 0.5N H2SO4 until the color changes to pinkish. Calculation: Nitrogen content = (titration sample –titration blank) X Normality HCl X 1.4007 weight of sample ( gm ) % protein = Nitrogen content X factor Table 1: Factor for conversion of nitrogen value to protein in various food samples (per g N) Source Factor Vegetable oil 5.40 Wheat flour 5.70 Cereal 5.90 Vegetable leaf 6.60 Animal/fish 6.25 Milk and milk products 6.38 Gelatine 5.55 Coconuts 5.30 • Where a specific factor is not listed, 6.25 should be used until a more appropriate factor has been determined. Result: Refers to Food Chemistry Lab Sheet Discussion: The following should be in your discussion: State the results by quoting significant data. Do not re-write all the data! Give the advantages and disadvantages of this analysis. Suggest steps that need to be taken to prevent decision error on the analyzed sample.
DMT20053 - FOOD CHEMISTRY LAB MANUAL Conclusion: The following should be in your conclusion: State the objective/purpose. Was the objective/purpose achieved? If so, explain how and if not explain why not. State what you learned in this activity. Summarize your result. Questions: Refers to Food Chemistry Lab Sheet
DMT20053 - FOOD CHEMISTRY LAB MANUAL LAB 6: DETERMINATION OF CRUDE FATS Objective: At the end of the laboratory session, students will be able to: 1. Perform crude fat content in food samples using Sohxlet apparatus. 2. Calculate total fat content in selected food samples. 3. Compare total fat content in selected food samples. Introduction: Lipids are one of the major constituents of foods and are important in our diet for a number of reasons. They are a major source of energy and provide essential lipid nutrients. Nevertheless, overconsumption of certain lipid components can be detrimental to our health, e.g. cholesterol and saturated fats. In many foods the lipid component plays a major role in determining the overall physical characteristics, such as flavor, texture, mouth feel and appearance. Principle: According to the Soxhlet’s procedure, oil and fat from solid material are extracted by repeated washing (percolation) with an organic solvent, usually hexane or petroleum ether, under reflux in a special glassware. Equipment: Round flask 250ml, cotton wool, desiccators, thimbles, soxhlet extractor, digital balance, 2-face condenser, heating mantle Chemical solution: Petroleum ether (boiling point 40 – 60°C), boiling chips Procedure: 1. Put a few boiling chips in a 250ml round flask. Let it dry in an oven (105°C) for 30 minutes. Transfer the flask into desiccators and weigh it. 2. Weigh 1-2 g of dry sample in a thimble and put a piece of wool on top of it. 3. Measure 150ml petroleum ether in a 250ml round flask and attach it to the extractor and distillation unit. 4. Let the reflux process run for 8 hours. 5. Take off extractor from the flask and take out the thimble from the extractor. Let it distill until the minimum level of petroleum ether in the flask. 6. Dry up the excess petroleum ether in the flask using a heating plat. 7. Put the flask in an oven (105°C) for an hour. Transfer it into desiccators and weigh it. 8. Do it in duplicate. Calculation: % Crude fats = (W3 – W2) X 100 W1 –Wo Where; Weight of thimble = Wo g Weight of thimble + sample = W1 g Weight of flask + boiling chips = W2 g Weight of flask + boiling chips + fats = W3 g
DMT20053 - FOOD CHEMISTRY LAB MANUAL Result: Refers to Food Chemistry Lab Sheet Discussion: The following should be in your discussion: State the results by quoting significant data. Do not re-write all the data! Give the advantages and disadvantages of this analysis. Suggest steps that need to be taken to prevent decision error on the analyzed sample. Conclusion: The following should be in your conclusion: State the objective/purpose. Was the objective/purpose achieved? If so explain how and if not explain why not. State what you learned in this activity. Summarize your result. Questions: Refers to Food Chemistry Lab Sheet
DMT20053 - FOOD CHEMISTRY LAB MANUAL LAB 7: DETERMINATION OF FAT CONTENT IN MILK PRODUCT Objective: At the end of the laboratory session, students will be able to: 1. Perform total fat content in selected food samples using Majonnnier, Gerber or/and Babcock method. 2. Calculate total fat content in selected dairy products. 3. Compare total fat content in selected dairy products, A. MOJONNIER METHOD Introduction: The Mojonnier test is an example of the discontinuous solvent extraction method and does not require removal of moisture from the sample. It can be applied to both liquid and solid samples. It has been applied primarily to dairy food but is applicable to other foods. Principle: Fat is extracted with a mixture of ethyl ether and petroleum ether in a Mojonnier flask, and the extracted fat is dried to a constant weight and expressed as percent fat by weight. Equipment: Mojonnier tubes and rack, oven at 100°C, distillation flasks or conical flasks Chemical solution: 0.880 ammonia, ethyl ether, petroleum ether (40 – 60), 95% ethanol Procedure: 1. Weight accurately about 10 g of milk into a Mojonnier extraction tube. 2. Add 1 ml of 0.880 ammonia and mix well. 3. Add 10 ml of ethanol, mix and cool. 4. Add 25 ml of ethyl ether, stop the tube and shake vigorously for 1 min. 5. Cool, remove the stopper and with 25 ml petroleum ether, shake vigorously for 30 seconds. 6. Allow the tube to stand in the rack for 30 minutes or until the ether layer has completely separated. (If necessary, add distilled water to bring the interface between the two liquids to the narrowest part of the tube). 7. Decant as much as possible of the ether layer into a previously weighed flat-bottomed distillation flask or conical flask. 8. Repeat this extraction three times using a mixture of 5 ml ethanol, 25 ml diethyl ether and 25 ml petroleum ether, adding the extract to the distillation or conical flask. 9. Distil off the solvent from the distillation flasks (or remove the solvent from the conical flask on a steam bath), dry the flask for 1 h at 100°C and reweigh. 10. Calculate the percentage fat content of the milk sample. Calculation: % Fat content of milk = W2 – W1 X 100 W3 Where; Weight of empty flask (g) = W1 Weight of flask + fat (g) = W2 Weight of milk taken (g) = W3
DMT20053 - FOOD CHEMISTRY LAB MANUAL Result: Refers to Food Chemistry Lab Sheet Discussion: The following should be in your discussion: State the results by quoting significant data. Do not re-write all the data! Give the advantages and disadvantages of this analysis. Suggest steps that need to be taken to prevent decision error on the analyzed sample. Conclusion: The following should be in your conclusion: State the objective/purpose. Was the objective/purpose achieved? If so explain how and if not explain why not. State what you learned in this activity. Summarize your result. Questions: Refers to Food Chemistry Lab Sheet
DMT20053 - FOOD CHEMISTRY LAB MANUAL LAB 8: DETERMINATION OF VITAMIN C IN FOOD SAMPLES Objective: At the end of the laboratory session, students will be able to: 1. Handle dichlorophenol indophenols (DCPIP) indicator titration method to calculate vitamin C content. 2. Calculate vitamin C content in food samples. 3. Compare vitamin C content in food samples. Introduction: The chemical name for vitamin C is ascorbic acid. Ascorbic acid is a good reducing agent and therefore it is easily oxidised. Methods for the detection of vitamin C involve titrating it against a solution of an oxidising agent. Principles: A blue substance called 2, 6-dichlorophenolindophenol (DCPIP) acts as an indicator. DCPIP solution can be used to test for the presence of vitamin C in foods. During titration, when all the ascorbic acid in the solution has been used up, the solution will remain pink. Equipment: Volumetric acid 100ml and 250ml, conical flask, pipet 10ml, biuret Chemical solution: 1. 2,6 –diklorofenol-indofenol (weigh 0.05g 2,6 diklorofenol-indofenol and make up to 100ml with distill water). 2. 20% metafosforik acid (weigh 20g metafosforic acid and make up to 100ml with distill water). 3. 5% metafosforik acid (weigh 5g of metafosforic acid and make up to 100ml with distill water). 4. Standard Vitamin C (weigh accurately 0.05g L-ascorbic acid in a beaker, add 60ml of 20% metafosforic acid and make up to 250ml with distill water). [Note: This solution must be freshly prepared for analysis]. Procedure: a. Standardization of 2,6-diklorofenol-indofenol 1. Pipette 10ml of ascorbic acid solution in a conical flask. 2. Titrate the solution with DCPIP until the color of the solution turns pinkish. Do it 3 times. b. Determination of Vitamin C (Sample: Juice, squash, fruits) 1. Pipette 10ml juice, squash in a graduated cylinder and add 10ml 5% metafosforic acid. Make up to 100ml with distill water. 2. Pipette 10ml juice solution into a conical flask and titrate it with DCPIP. 3. Do the titration for 3 times. c. Determination of Vitamin C (Sample: Vegetables or fruits) 1. Weigh 10g sample and crush it with mortal and pestle. Add 50ml 5% metafosforic acid gradually. 2. Filter the mixture into a beaker using muslin cloth. Wash it with distilled water. Make up to 100ml. Shake well. 3. Pipette 10ml of the solution and titrate with DCPIP. 4. Do the titration 3 times. Calculation: For standard Vitamin C 1 ml DCPIP = 1/ titration standard X 10/250 x 0.05g = x g = x x 1000mg = A mg
DMT20053 - FOOD CHEMISTRY LAB MANUAL Vitamin C of sample = titration sample x A x 10 x 10mg = B mg Result: Refers to Food Chemistry Lab Sheet Discussion: The following should be in your discussion: State the results by quoting significant data. Do not re-write all the data! Give the advantages and disadvantages of this analysis. Suggest steps that need to be taken to prevent decision error on the analyzed sample. Conclusion: The following should be in your conclusion: State the objective/purpose. Was the objective/purpose achieved? If so, explain how and if not explain why not. State what you learned in this activity. Summarize your result. Questions: Refers to Food Chemistry Lab Sheet
DMT20053 - FOOD CHEMISTRY LAB MANUAL LAB 9: DETERMINATION OF TOTAL ASH Objective: At the end of the laboratory session, students will be able to: 1. Handle appropriate method to determine total ash content. 2. Calculate total ash content in food samples. 3. Compare total ash content in food samples. Introduction: Ash content is a measure of the total amount of minerals present within a food, whereas the mineral content is a measure of the amount of specific inorganic components present within a food, such as Ca, Na, K and Cl. Principles: Dry ashing procedures use a high temperature muffle furnace capable of maintaining temperatures of between 500 and 600 oC. Water and other volatile materials are vaporized, and organic substances are burned in the presence of oxygen in air to CO2, H2O and N2. Most minerals are converted to oxides, sulfates, phosphates, chlorides, or silicates. Equipment: Crucibles, drying oven, heating plat/electric burner/Bunsen burner, digital balance, muffle furnace, spatula, and desiccators Procedure: 1. Blend sample. 2. Accurately weigh 5.00g of the powdered sample in a crucible. (If sample in liquid form, use 5.00 - 10.00g sample) 3. Ignite slowly over a Bunsen flame until no more fumes are evolved. 4. Transfer the crucibles to muffle furnace set at 550oC. 5. Incinerate the sample until it is free of black carbon particle (2 hours) (until it is white in color). 6. Remove the crucibles in desiccators and weigh after cooling. 7. Repeat until no further loss in weight is indicated. Calculation: Ash (%)=c - a X100 b Where; Weight of empty crucible = a Weight of sample = b Weight of ash + crucible = c
DMT20053 - FOOD CHEMISTRY LAB MANUAL Result: Refers to Food Chemistry Lab Sheet Discussion: The following should be in your discussion: State the results by quoting significant data. Do not re-write all the data! Give the advantages and disadvantages of this analysis. Suggest steps that need to be taken to prevent decision error on the analyzed sample. Conclusion: The following should be in your conclusion: State the objective/purpose. Was the objective/purpose achieved? If so explain how and if not explain why not. State what you learned in this activity. Summarize your result. Questions: Refers to Food Chemistry Lab Sheet
DMT20053 - FOOD CHEMISTRY LAB MANUAL LAB 10: EFFECT OF HEAT AND pH ON PIGMENTS CHANGES Objective: At the end of the laboratory session, students will be able to: 1. Identify the influences of temperature, pH, oxygen and chemicals on pigments. 2. Discuss the measures to prevent pigment changes. Introduction: Colours contribute greatly to the aesthetic appeal of foods. The wide range of colours is attributable to the ability of pigments in fruits, vegetables, and meat to absorb certain light and reflect others. The chemical forms of some pigments are easily altered under conditions that may also affect the structural integrity of the tissue. High temperature, pH changes, and oxidation can affect pigment. Plant pigments may be categorized as carotenoids, chlorophyll, and flavonoids. Many plant pigments, especially chlorophyll and anthocyanins, are sensitive to heat and changes in pH. A. Plant pigment (chlorophyll, carotenoid, anthocyanins) Equipment: Blender, spatula, pH meter, beaker, test tubes Chemical solution: Sodium bicarbonate 1M, acetic acid 1M Sample: Green leaves, carrot, red cabbage Procedure: 1. Weight about 5g samples into each of the 50 ml beakers. 2. Add 20 ml solution/ water to the labelled beaker with: • Beaker I: acetic acid • Beaker II: sodium bicarbonate • Beaker III: Distilled water (heated) • Beaker IV: Distilled water (unheated 3. Heat each of the beakers except the unheated control (beaker IV) for 10 minutes. 4. Observe and record changes in the appearances of samples and the solution in each beaker during the heating treatment. 5. Allow the beaker to cool and drain the solution in graduated cylinder. 6. Pour the drained sample onto the labelled filter paper disc. 7. Determine and record the ph of each solution. 8. Observe and record the colour characteristic and the colour intensity for each drained solution. 9. Observe the changes in texture of sample with spatula or table fork. Record. B. Animal pigment (myoglobin) Equipment: Small (e.g., 100 mL) heat-resistant beakers, spoons or spatulas, test tubes, test tube rack, small funnels, thermometer, water bath, set at 90–100 °C, filter paper. Sample: Freshly minced beef, ~60 g, distilled water, ice cubes Procedure: 1. Place 10 g of meat into each of the six beakers. 2. Add 25 mL of distilled or deionised water to each beaker. 3. Place the beakers in a water bath set at about 90–100 °C.
DMT20053 - FOOD CHEMISTRY LAB MANUAL 4. Heat the samples, stirring them constantly with a spoon or spatula until they reach a final temperature of 50 °C, 60 °C, 65 °C, 70 °C, 75 °C or 80 °C. Use the thermometer to check the temperature regularly. 5. Once each sample has reached its final temperature, remove it from the water bath and cool it down immediately in an ice bath. Ensure that the beakers do not fall over — adjust the water level of the ice bath to the level of the content of the beakers or lower. 6. After cooling, filter each sample and collect the filtrate from each one in a separate test tube. 7. Evaluate the colour by eye (e.g., red, light brown, dark brown, brownish grey etc) and record your results in a table. Result: Refers to Food Chemistry Lab Sheet Discussion: The following should be in your discussion: State the results by quoting significant data. Do not re-write all the data! Give the advantages and disadvantages of this analysis. Suggest steps that need to be taken to prevent decision error on the analyzed sample. Conclusion: The following should be in your conclusion: State the objective/purpose. Was the objective/purpose achieved? If so explain how and if not explain why not. State what you learned in this activity. Summarize your result. Questions: Refers to Food Chemistry Lab Sheet