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21 Cards in this Set
- Front
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To extract the fat from a food sample,you have the choice of using ethyl ether or petroleum ether as the solvent, andyou can use either a Soxhlet or a Goldfish apparatus. What combination of solvent and extractionwould you choose? Give all the reasons for your choice. |
Petroleumether (vs. ethyl ether) - More selective for more hydrophobic lipids - Less hygroscopic - Less flammable - Cheaper Soxhlet extraction (vs. Goldfish) - Doesn't cause channeling - Soaks sample - Doesn't heat sample |
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Itemize the procedures that may be required to prepare a food sample for accurate fatdetermination by a solvent extraction method (e.g., Soxhlet method). Explainwhy each of these procedures may be necessary. |
Predrying sample - Fats cannot be efficiently extracted from moist foods with ethyl ether; ether saturated with water is inefficient for fat extractions; dried samples are easier to grind. Particle size reduction - Increases the efficiency of extraction Acid hydrolysis- Breaks covalently and ionically bound lipds (Bound to proteins and carbs) so lipid is extractable |
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Youperformed fat analysis on a new superenergy shake (high carbohydrate andprotein) using standard Soxhlet extraction. The value obtained for fat content was much lower than that expected. What could have caused the measured fatcontent to be low and how would you modify the standard procedure to correctthe problem? |
The proteins and carbs in the shake interact with the fat (causing it to be bound tightly), which makes it difficult to extract. Results may be lower than expected. Modify the procedure by adding an acid digestion prior to standard fat extraction
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Whatis the purpose of the following chemicals used in the Mojonnier method? |
a. Ammonium hydroxide - Neutralizes the acidic sample and dissolves protein b. Ethanol - Prevents possible gel formation c. Ethyl ether - Dissolves the lipid d. Petroleum ether - Removes moisture from the ehtyl ether extract and dissolves more nonpolar lipid |
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What if the key application of the GCmethod and what does it specifically quantify? |
Application -Nutrition labeling
Quantifies each individual fatty acid (sum is total fat content) |
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Whatis the purpose of the following procedures used in Babcock method? |
a. Sulfuric acid addition - Digest protein, generates heat and releases the fat b. Centrifugation and addition of hot water - Separates the fat from the rest of the sample and brings it to the graduated portion of the test bottle so it can be quantitated. |
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Whichof the following methods are volumetric and which are gravimetricdeterminations of lipid content: Babcock, Soxhlet, Mojonnier, Gerber? |
Babcock– Volumetric Soxhlet – Gravimetric Mojonnier – Gravimetric Gerber – Volumetric |
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Explainand contrast the principles (not procedures) involved in determining the fatcontent of a food product by the following methods. Indicate for each method thetype of sample and application that would be appropriate for analysis |
a. Soxhlet Principle - Fat is extracted, semicontinuously, with organic solvent. Fat content is measured by weight loss of sample or weight of fat removed Type of Sample and Application - Dry to semi-dry sample; extract fat before GC analysis; Defat before fiber analysis; Product development; Verify fat content < 0.5 g/serving; Quality b. Babcock Principle: -Sulfuric acid digests protein, generates heat, and releases fat. After centrifugation of samples, fat content is measured volumetrically. Types of sample and application - Liquid samples; Official analysis c. Mojonnier Principle - Fat is extracted with mixture of ethyl ether and petroleum ether. The extracted fat is dried to constant weight and expressed as percent fat by weight. Type of sample and application - Solid or liquid sample; Same as Soxhlet d. GC analysis Principle - Sample is treated by acid and/or alkaline hydrolysis, then fat is extracted with ether and methylated to form foatty acid methyl esters (FAMEs). The FAMEs are separated by gas chromatography and quantitated with the aid of an internal standard. Type of sample and application - Nutrition Labeling |
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You want to compare several fat/oilsamples for the chemical characteristics listed below. For each characteristic, name one test (givefull name, not abbreviation) that could be used to obtain the informationdesired: |
a. Degree of unsaturation - Iodine Value b. Predicted susceptibility to oxidativerancidity - Schaal oven storage, oil stability index, active oxygen method test, oxygen bomb c. Present status with regard to oxidativerancidity - Peroxide value, anisidine value/totox value, hexanal, thiobarbituric acid number d. Average fatty acid molecular weight - Saponification number e. Amount of solid fat at various temperatures - - Solid fat index f. Hydrolytic rancidity - Free fatty acid |
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Your analysis of an oil sample gives thefollowing results. What does each ofthese results tell you about the characteristics of the sample? Briefly describe the principle for eachmethod used: |
a. Large saponification number - Short fatty acid chain length + The mg KOH required to saponify triglycerides in the fat is related to average fatty acid chain length b. Low iodine value - Low degree of unsaturation (Highly saturated) + The amount of iodine absorbed by a quantity of fat or oil is related to amount of unsaturation; more iodine absorbed, iodine value is higher as is degree of unsaturation c. High TBA number - High level of oxidative rancidity + Malonalydehyde generated lipid oxidation react with TBA to give colored end product that can be quantitated by absorbance. d. High FFA content - High level of hydrolytic rancidity + The mg KOH required to neutralize free fatty acids present in a quantity of fat or oil reflects the amount of fatty acids hydrolyzed from triacylglycerol
e. High OSI- High stability to oxidative rancidity + When fat or oil is held at high temperature and has air bubbled through it, acidic volatiles (primary formic acid) due to lipid breakdown are trapped in deionized water and measured by conductivity |
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Define solid fat content, and explain theusefulness of this measurement. |
It is the actual precent solid fat in sample. It can be determined using either continuous wave or pulse NMR. Useful in products such as margarine and shortenings, because the proportion of solids to liquids in a fat, and how quickly the solids melt, have an impact on functional properties such as mouthfeel |
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Peroxide value, TBA number, hexanalcontent all can be used to help characterize a fat sample. a. What do the results of these tests tell youabout a fat sample? b. Differentiate these three tests as to whatchemical is being measured. |
a. Measure present status regarding lipid oxidation b. Peroxide value - Measure formation of peroxide or hydroperoxide groups TBA test - Measure malonaldehyde Hexanal - Mesure formation of hexanal |
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What methods would be useful indetermining the effectiveness of various antioxidants added to an oil? |
Accelerated tests such as Schaal oven storage test, oil stability index, active oxygen method or oxygen bomb.
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Youare responsible for writing the specifications for vegetable oil purchased fromyour supplier for use in deep-fat frying several foods processed by yourcompany. Itemize the tests you shouldrequire in your list of specifications (specific values for the tests are notneeded). For each test, briefly statewhat useful information is obtained. |
Melting point - Reflects degree of saturation/stability
Smoke - Degree of hydrolysis, oxidation
Color - Improper refinement or abuse
Flavor and odor - Sensory acceptability/degree of oxidation
Free fatty acid - Degree of hydrolysis
SFC or SFI - Proportion of solid to liquid fat; influences mothfeel of finished product
Peroxide value - Degree of oxidation = Current status
OSI - Degree of oxidation = Predicts future stability
Linolentic acid - Amount of 18:3n-3 in oil
Trans fatty acids - Amount of trans acids in oil |
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TheNutrition Education and Labeling Act of 1990 (see Chapter 3) requires that thenutrition label on food products contains information related to lipidconstituents. In addition to the amountof total fat (see Chapter 8), thelabel must state the content of saturatedfat, cholesterol, and trans fat. a. Fora product such as traditional potato chips, explain an appropriate method forthe analysis of each of these lipid constituents. |
a. Fora product such as traditional potato chips, explain an appropriate method forthe analysis of each of these lipid constituents. Calories from fat - Calculation Total Fat- GC Saturated fat- GC Cholesterol - GC TRans fat - GC |
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You have developed a new buttercontaining added fish oil, which is high in PUFA. Before placing the product on the market, youneed to determine its shelf life. Whatmethod or methods would you use and why? |
Determine actual shelf life at ambient conditions of storage, might take months or years. If shelf life is defined as how long the product remains accpetable to the consumers, the best method is sensory analysis. Other methods for measuring oxidation such as peroxide value, TBA or hexanal must be correlated to sensory analysis.
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You work in quality control for a company that makespeanut butter. You received informationthat between July and August several lots of peanut butter may have been improperlystored and you are concerned about potential lipid oxidation in theproduct. A total of 50 lots of peanutbutter are involved. a. What test(s) would you use to measure lipid oxidation? Include your rationale for selecting the method. |
- The preferred method is sensory analysis. Other methods for measuring oxidation such as peroxide value of hexanal, may be used if correlated to sensory analysis of product. Rational: The consumer is the ultimate judge of product quality. conduction consumer taste panels will determine product acceptability. |
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The Munson-Walker, Lane-Eynon, and Somogyl-Nelsonmethods can be used to measure reducing sugars. Explain the similarities and differences among these methods with regardto the principles involved and the procedures used. DIFFERENCES |
- 3 methods differ in technique by which cuprous ions in the form of cuprous oxide are measured - In Munson-Walker method, cuprous oxide is measured either gravimetrically , by titration or electrolytically. - In Lane-Eynon method, cuprous oxide precipitated is determined by titration using methylene blue as indicator. - In Somogyi-Nelson, cuprous ions reduce as arsenomolybdate complex. The reduction of arsenomolybdate complex produces as intense blue color that is measured spectrophotometrically. |
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Describe the principles behind and thelimitations of determining sugar (sucrose) concentrations by RI measurement. |
Refractive index Principles - When light passes from one medium to another, it changes direction, being bent or refracted. The ratio of the sine of the angle of incidence to the sine of the angle of refraction is called the index of refraction or refractive index. By holding the nature of the compound, temperature, and wavelength of light constant, the concentration of the compound can be determined by measuring the refractive index. Limitations - It can be used only on clear liquid samples - It is accurate only for pure sucrose or other pure solutions, but can be used for obtaining approximate values |
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TheNutrition Education and Labeling Act of 1990 (see Chapter 3) requires that thenutrition label on food products contains information related to lipidconstituents. In addition to the amountof total fat (see Chapter 8), thelabel must state the content of saturatedfat, cholesterol, and trans fat. b. Comparedwith assays on traditional chips, how would the assays for total fat andsaturated fat differ for potato chips made with OlestraÒ? |
Use AOAC peer verified MEthod which uses lipase on lipid extract, to yield fatty acids and unreated Olestra. Fatty acids are converted to calcium soaps and Olestra is extract and discarded. The precipitated calcium soaps then are converted back to fatty acids so they can be analyzed by GC |
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You work in quality control for a company that makespeanut butter. You received informationthat between July and August several lots of peanut butter may have been improperlystored and you are concerned about potential lipid oxidation in theproduct. A total of 50 lots of peanutbutter are involved.b. How would you decide what to do with the peanut butter? |
If issue is whether or not product will be different than other samples, then run tests of oxidative stability: OSI, oven test or oxygen bomb. Using as the control a sample known to be of high quality, any differences will be apparent. To determine the degree tp which the samples may have been harmed would require correlation of such tests with sensory evaulation |
