Quiz 5 Food Analysis Part All Sq

Front 1

Givethree reasons why carbohydrate analysis is important.

Back 1

- Qualitative analysis ensures that ingredient labels present accurate compositional info

- Quantitative analysis ensures that added components are listed in proper order on ingredient label and ensures that labeled amounts of specific components of consumer interest are proper

- Both types of analysis can be used to detect adulteration of products such as fruit juices

Front 2

“Proximatecomposition” refers to analysis for moisture, ash, fat, protein, andcarbohydrate. Identify which of thesecomponents of “proximate composition”are actually required on a nutrition label. Also, explain why it is important to measure the nonrequired componentsquantitatively if one if developing a nutrition label.

Back 2

Components of "Proximate composition" on nutrition label - protein, fat, carbs quantitate also moisture and ash so total carbs can be calculated as

% Total carbs = 100% - [%protein + %fat+ %moisture + %ash]

Front 3

Discusswhy mono- and oligosaccharides are extracted with 80% ethanol rather than withwater. What is the principle involved?

Back 3

Mono- and oligosaccharides are soluble in 80% ethanol and almost all polysaccharides and proteins are insoluble in hot 8-% ethanol. Mono- oligosaccharides, most polysaccharides and most proteins are soluble in water. Therefore, the extraction with 80% ethanol is rather specific for removing mono- and oligosacchraides.

Front 4

Define reducing sugar. Classify each of thefollowing as a reducing or nonreducing carbohydrate: D-glucose, D-fructose(Conditions must be described. Why?), sorbitol,sucrose, maltose, raffinose, maltotriose, cellulose, amylopectin, κ-carrageenan

Back 4

Definitionof reducing sugars:

-D-glucose- Reducing

-D-fructose - Reducing, under alkaline conditions (nonreducing under neutral or acidic conditions)

-sorbitol - Nonreducing

- sucrose - Nonreducing

-maltose - reducing

-raffinose - Nonreducing

-maltotriose - Reducing

- cellulose - Nonreducing

- amylopectin - Nonreducing

-κ-carrageenan - Nonreducing

The three polysaccharides have a reducing end unit but are nonreducing because of their high molecular weights

Front 5

To prevent hydrolysis of sucrose when sugars are extracted from fruits via a hot alcohol extraction (METHOD)

Back 5

Addition of calcium carbonate used to neutralize sample, so sucrose is not hydrolyzed.

Front 6

To remove proteins from solution for an enzymatic analysis (METHOD)

Back 6

Carrez treated used, which breaks emulsions, precipitates proteins, and absorbs some colors.

Front 7

To measure total carbohydrate (METHOD)

Back 7

Use phenol-sulfuric acid method

Front 8

To measure total reducing sugars (METHOD)

Back 8

Use Somogyi-Nelson method. Other methods re dinitrosalicylic acid, Munson-Walker

Front 9

To measure the sucrose concentration in apure sucrose solution by a physical method (METHOD)

Back 9

- Specific Gravity

-Refractive Index

Front 10

To measure glucose enzymically (METHOD)

Back 10

Coupled enzyme-catalyzed reactions utilizing glucose oxidase and peroxidase or combo of hexokinase and glucose 6-phosphate dehydrogenase.

Front 11

Tomeasure simultaneously the concentrations of individual free sugars (METHOD)

Back 11

HPLC or GC

Front 12

What are the principles behind totalcarbohydrate determination using the phenol-sulfuric acid method? Give an example of another assay procedurebased on the same principle.

Back 12

Oligo and polysaccharides are hydrolyzed to monosaccharides with hot acid solutions. Monosaccharides decompose to furan derivatives under similar conditions. The furan derivatives condense with phenol to form colored compounds that can be quantitated.

Addition of conc. H2SO4 to an aqueous solution generates a hot, strongly acidic solution.

Resorcinol, orcinol, alpha-naphthol, napthoresorcinol and various aromatic nitrogen compounds may be used in place of phenol.

Front 13

What is the principle behind determination of total reducing sugars using the Somogyi-Nelson and similarmethods?

Back 13

In this method, they are subjected to a second oxidation-reduction reaction, generating a colored compound that can be measured spectrophotometrically. A standard curve, with either glucose or sugar being determined is used to quantitate the reducing sugar.

Front 14

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.

SIMILARITIES

Back 14

Similarities -

All 3 methods are based on reduction of cupric ions in alkaline solution to cuprous ions that precipitate as brick red cuprous oxide. All methods requires use of standard curve.

Front 15

Describe theprinciple behind AE-HPLC of carbohydrates.

Back 15

At a high pH, some of the hydroxyl groups of carbs become ionized, providing negative charges that bind to an anion-exchange column EX column that as a positive charge on surface of stationary phase

Front 16

Describethe general procedure for preparation of sugars for GC. What is required for this method to besuccessful?

Back 16

- Neutral sugars are reduced to alditols (sodium borohyride). The alditols are acetylated with acetic anydride to yield alditol peracetates, which can be subjected to analysis

- To be successful, 2 preps steps must be followed 1) Reduction of aldehyde groups to prime alcohol groups 2) Conversion of reduced sugars into volatile peracetate ester must be 100% complete.

Front 17

Whyhas HPLC largely replaced GC for analysis of carbohydrates?

Back 17

HPLC analysis requires no prior derivatization of carbs, as does GC. Derivatization is needed for GC analysis because carbs are nonvolatile. Each of the two steps involved in derivatization must be 100% complete.

Front 18

Whatis the advantage of an enzymic method? What is the limitation (potential problem)?

Back 18

Advantages:

- Usually specific for the substance being measured

- In some cases, available commercially as kits, with detailed instructions

- Generally have low detection limits

Limitations:

- May be interfering compounds present

- Not always 100% specific

- Not useful for measuring total carbs, a class of carbs or all carbs individually

Front 19

Describethe principles behind the enzymic determination of starch. What are the advantages of this method? What are potential problems?

Back 19

Principles:

- Starch is converted totally into D-glucose by enzymes specific for starch and D-glucose is quantitated by an enzymic assay

Advantages:

- Use of specific enzymes makes assay very specific so that the amount of starch in a complex, hetrogeneous food materials can be determined

- Kits for measuring glucose are available commercially

PotentialProblems:

- Amylases must be purified so D-glucose released is only from starch and to remove catalase which would destroy hydrogen peroxide

- Method may not be quantitative for high-amylose starch or samples high in resistant starch

Front 20

Describethe principles behind separation and analysis of water-soluble gums and starch.

Back 20

Water-solublegums -

Analysis relies on the extraction of gums and fractionation to remove free sugars and other water-soluble polysaccharides such as starch. The isolated gum is acid hydrolyzed and its constituent sugars are quantitated by HPLC or GC

Starch -

Analysis relies on removal of free sugars then enzymatic digestion of starch to D-glucose, and enzymatic quantitation of glucose

Front 21

Describetwo methods for determination of pectin.

Back 21

1. Pectin can be quantitated by precipitating the pectin as calcium pectate after de-esterifying it, then washing, drying and gravimetrically measuring the precipitate.

Front 22

Describe the principles behind and thelimitations of determining sugar (sucrose) concentrations by a) specificgravity determination and (b)

Back 22

Specificgravity

Principles

- The concentration of carbohydrate solution can be determined by measuring the specific gravity of the solution and referring to appropriate specific gravity tables. The specific gravity is the ratio of density of a substance to density of a reference substance, both at specific temperature

Limitations

- It can be used only on liquid samples.

- It is accurate only for pure sucrose or other pure solutions, but can be used for obtaining approximate values

Front 23

Define dietary fiber

Back 23

The sume of nondigestible components of a foodstuff or food product. Dietary fiber is the edible parts of plants or analogous carbs that are resistant to digestion and absorption in human small intestine with complete or partial fermentation in the large intestine.

Front 24

Listthe major constituents of dietary fiber.

Back 24

- Cellulose

- Hemicellulose

- Lignin

- Other non starch plant polysaccharides (pectin)

- Gums/Hydrocolloids

- REsistant starch

- Certain oligosacchraides (inulin)

Front 25

Explainhow measurement of dietary fiber relates to calculating the caloric content ofa food product.

Back 25

One method to calculate caloric content of a food for reporting on a nutrition label is to subtract the amount of insoluble dietary fiber from value for total carbs, before calculating calories based on protein, fat and carb contents

Front 26

Explain the purpose(s) of each of thesteps in the AOAC Method 994.13 for total dietary fiber listed below as appliedto determination of the dietary fiber content of a high-fiber snack food.

Back 26

a. Heating sample and treating with α-amylase

- Gelatinize starch and convert starch molecules to oligosaccharides that can be acted upon glucoamylase

b. Treating sample with glucoamylase

- Complete hydrolysis of starch to molecules that will not precipitate upon addition of alcohol

c. Treating sample with protease

- Hydrolyze protein to peptides with that will not precipitate upon addition of alcohol.

d. Adding four volumes of 95% ethanol to sample after treatment withglucoamylase and protease

- Precipitate soluble fiber

e. After drying and weighing the filtered and washed residue, heating oneduplicate final product to 525°C in a muffle furnace, and analyzing the otherduplicate sample for protein

- Correct fiber residue for ash content and protein content

Front 27

Whatis the physiological definition and the chemical nature of resistantstarch? What types of foods haverelatively high levels of resistant starch?

Back 27

Food with relatively high levels of resistant starch include cooked then cooled starch foods, such as potatoes and uncooked foods containing starch, such as carrots.

Front 28

Whatare some important considerations when selecting solvents to be used incontinuous and noncontinuous solvent extraction methods?

Back 28

Ideal characteristics:

-High solvent power for lipids

- Low solvent power for proteins, amino acids and carbs

- Evaporate relatively easily and leave no residue

- Have a relatively low boiling point

- Be nonflammable and nontoxic in both liquid and vapor states

- Penetrate sample particles readily

- Be in single component form to avoid fractionation

- Be inexpensive

- Be non hygroscopic

Front 29

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.

Back 29

Soxhlet extraction (vs. Goldfish)

- Doesn't cause channeling

- Soaks sample

- Doesn't heat sample

Front 30

Itemize the procedures that may be required to prepare a food sample for accurate fat determination by a solvent extraction method (e.g., Soxhlet method). Explain why each of these procedures may be necessary.

Back 30

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

Front 31

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?

Back 31

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

Front 32

Whatis the purpose of the following chemicals used in the Mojonnier method?

Back 32

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

Front 33

What if the key application of the GCmethod and what does it specifically quantify?

Back 33

Application -Nutrition labeling

Quantifies each individual fatty acid (sum is total fat content)

Front 34

Whatis the purpose of the following procedures used in Babcock method?

Back 34

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.

Front 35

Whichof the following methods are volumetric and which are gravimetricdeterminations of lipid content: Babcock, Soxhlet, Mojonnier, Gerber?

Back 35

Babcock– Volumetric

Soxhlet – Gravimetric

Mojonnier – Gravimetric

Gerber – Volumetric

Front 36

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

Back 36

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

Front 37

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:

Back 37

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

Front 38

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:

Back 38

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

Front 39

Define solid fat content, and explain theusefulness of this measurement.

Back 39

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

Front 40

What methods would be useful indetermining the effectiveness of various antioxidants added to an oil?

Back 40

Accelerated tests such as Schaal oven storage test, oil stability index, active oxygen method or oxygen bomb.

Front 41

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.

Back 41

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

Front 42

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.

Back 42

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

Front 43

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.

Back 43

- 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.

Front 44

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

Back 44

- 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.

Front 45

Describe the principles behind and thelimitations of determining sugar (sucrose) concentrations by RI measurement.

Back 45

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