Food Analysis - Laboratory Manual

Objective Determination of Moisture contents Determine the moisture content using moisture balance analyzer versus forced draft oven versus of rice flour and liquid milk.. Using forced

INTERNATIONAL UNIVERSITY

FOOD ANALYSIS LAB MANUAL

Instructor: Assoc Prof Pham Van Hung Teaching Assistant: BEng Nguyen Dang Tam

CONTENTS

Session 1 1

Determination of Moisture contents 1

Session 2 3

Determination of Ash contents 3

Session 3 5

Determination of Lipid Content 5

Session 4 7

Determination of Protein Content in Food 7

Session 5 9

Determination of Total Carbohydrate in foods 9

Session 6 11

Determination of Crude Dietary Fibre in Foods 11

Session 7 13

Determination of Total Flavonoid Content (TFC) 13

Session 8 14

Determination of Vitamin C in foods 14

I Objective

Determination of Moisture contents

Determine the moisture content (using moisture balance analyzer versus forced draft oven versus)

of rice flour and liquid milk

II Materials

• Rice flour, 50 g

• Fat-free liquid milk, 50 ml

• Volumetric pipette, 10 ml

• Plastic gloves

• Tong

• Spoon

• Aluminium pan

• Tray

• Desiccators

• Analytical balance

• Moisture balance analyzer

• Forced draft oven

III Method

A Moisture content determination

a1 Using moisture balance analyzer

*Note: test rice flour and liquid milk separately

Follow operating instructions from manufacturer

• Milk: pipette 5mL into the aluminium disk

• Rice flour: weigh 2 g

• Turning on the power switch and waiting for instrument warming up

• Specifying settings

o Automatic operation mode for both rice flour and liquid milk

• Placing an aluminium pan in the tester

• Tarring the tester

• Placing test material on the pan (record the weight)

• Start the measurement

• Obtain results

a2 Using forced draft oven

• Milk:

o Label and weigh the crucible

o Pipette 10mL into a crucible

o Evaporate majority of water on a hot stirring plate

o Place the crucible containing samples in a forced draft oven at 130oC

o Weigh the crucible after each 30 min until no change in weight observed

• Rice flour:

o Label and weigh the crucible

o Weigh 5 g of sample

o Place samples in the crucibles

o Place crucibles containing samples in a forced draft oven at 130oC

o Weigh the crucible after each 30 min until no change in weight observed

• Store samples in a desiccator until samples are weighed

• Weigh

IV Questions

1 What is the difference between moisture content and water activity measurements? (20%)

2 Why the milk sample was partially evaporated on a hot plate before being dried in the hot oven? (20%)

3 Compare the rice flour and liquid milk moisture content results obtained by moisture balance analyzer and forced draft oven methods Explain any differences (40%)

4 What are advantages and disadvantages of each method? (10%)

5 What do we need to pay attention during sample preparation in order to limit errors? (10%)

References

AOAC International (2007) Official methods of analysis, 18thedn, 2005; Current through revision 2,

2007 (On-line).AOAC International, Gaithersburg, MD

Bradley RL Jr (2010) Moisture and total solids analysis, Ch.6.In: Nielsen SS (ed) Food Analysis,

4thedn Springer, New York

Nielsen SS (2010) Determination of moisture content, Ch.3.In: Nielsen SS Food analysis

laboratory manual, 2ndedn Springer, New York

Determination of Ash contents

I Objective

Determine the ash content of rice flour and liquid milk using muffle furnace

II Materials

• Rice flour, 50 g

• Fat-free liquid milk, 50 ml

• Volumetric pipette, 10 ml

• Plastic gloves

• Tong

• Spoon

• Aluminium pan

• Tray

• Crucible (preheated at 550oC for 24 h)

• Desiccators (with dried desiccant)

• Analytical balance

• Muffle furnace

III Method

A Moisture content determination

• Milk:

o Label and weigh the crucible

o Pipette 10mL into a crucible

o Evaporate majority of water on a hot stirring plate

o Place the crucible containing samples in a forced draft oven at 130oC

o Weigh the crucible after each 30 min until no change in weight observed

• Rice flour:

o Label and weigh the crucible

o Weigh 5 g of sample

o Place samples in the crucibles

o Place crucibles containing samples in a forced draft oven at 130oC

o Weigh the crucible after each 30 min until no change in weight observed

• Store samples in a desiccators until samples are weighed

• Weigh

B Ash content determination

• Re-weigh crucible containing dried sample

• Primary burning the content of materials by flame in a fume hood

• Place all the crucibles in muffle furnace at 550oC for 3h until only white matters can be

seen

• Cool crucibles in a desiccator

• Weigh

IV Questions

1 What is ash? What does ash consist of? Give examples to illustrate your answer (30%)

2 How many types of ashing procedures? What are they? (30%)

3 Calculate percentage ash (wt/wt) as shown on the table below Refer your findings to the ones in literature (20%)

Sample Rep Crucible

(g)

Crucible + Wet sample (g)

Crucible + Ashed

Rice flour

1

2

3

𝑿 =

SD =

Liquid

milk

1

2

3

𝑿 =

SD =

4 Why do the samples need to be placed in desiccators, but not outside, before weighed? (10%)

5 What do we need to pay attention during performing this experiment in term of lab safety? (10%)

References

AACC International (2010) Approved methods of analysis, 11thedn (On-line) AACC International,

St Paul, MN

AOAC International (2007) Official methods of analysis, 18thedn, 2005; Current through revision 2,

2007 (On-line).AOAC International, Gaithersburg, MD

Bradley RL Jr (2010) Moisture and total solids analysis, Ch.6.In: Nielsen SS (ed) Food Analysis,

4thedn Springer, New York

Nielsen SS (2010) Determination of moisture content, Ch.3.In: Nielsen SS Food analysis

laboratory manual, 2ndedn Springer, New York

Wehr HM, Frank JF (eds) (2004) Standard methods for the examination of dairy products, 16thedn American Public Health Association, Washington

Determination of Lipid Content

I Objective

Determine the lipid content of snack foods and rice bran by the Soxhlet method

II Materials

• Rice bran, 30g

• Snack food, 30 g

• Hexane

• Aluminium weighing pan, pre-dried in 70oC oven over night

• Filter paper, pre-dried in 70oC oven over night

• Plastic gloves

• Spatula

• Tape

• Tongs

• Beaker, 250 ml

• Graduated cylinder, 500 ml

• Desiccators

• Mortar and pestle

• Pumice

• Analytical balance

• Soxhlet extractor, with glassware

• Forced draft oven

III Method

• Record the fat content and serving size of snack food product as shown on the package

label

The fat content on the label

Name of Snack Food Label g fat / serving Label serving size (g) Label g fat / 100 g product

• Grind approx 10 g sample with mortar and pestle

• Correct moisture content:

o Determine moisture content of 3 g sample using moisture balance analyser

• Weigh filter paper

• Prepare samples: place 3 g of snack or rice bran in the pre-weighed filter paper Tightly

wrap it up and reweigh

• Prepare 1 control

• Place the wrapped filter paper in a Soxhlet extractor Put 300 ml hexane in the flask Add

some 3 – 5 pumices Extract for 6 h

• Remove wrapped filter paper from the Soxhlet extractor using tongs, air dry overnight in a hood, and thenopen filter paper to expose the content; dry in a drying oven at 70oC for 24

h

• Cool dried samples in a desiccator then reweigh

IV Questions

1 Calculate % moisture and % fat and report on the tables below (25%)

Data from Soxhlet extraction

Sample Filter

paper (g)

Wet sample (g)

Wet sample + Filter paper (g)

Dried sample + Filter paper (g) % moisture % fat

Snack

1

2

𝑿 =

SD =

1

2

𝑿 =

SD =

1

2

𝑿 =

SD =

1

2

𝑿 =

SD =

1

2

𝑿 =

SD =

1

2

𝑿 =

SD =

Rice

bran

1

2

𝑿 =

SD =

1

2

𝑿 =

SD =

1

2

𝑿 =

SD =

1

2

𝑿 =

SD =

1

2

𝑿 =

SD =

1

2

𝑿 =

SD =

2 Compare your findings to fat content reported on the nutrition label Explain any

similarities and/or differences between the two (30%)

3 What were the advantages of using the Soxhlet extraction method? Compare Soxhlet extraction method with another lipid extraction method you know to illustrate your answer (30%)

4 What do we need to pay attention in this experiment in term of lab safety? (10%)

5 How to treat the organic waste? (5%)

References

AOAD International (2007) Official Methods of Analysis, 18thedn, 2005 ; Current through Revision

2, 2007 (On-line) AOAC International, Gaithersburg, MD

Min DB, Ellefson WC (2010) Fat analysis.Ch.8.In : Nielsen SS (ed) Food analysis, 4thedn Springer, New York

Nielsen SS (2010) Determination of fat content, Ch.4.In: Nielsen SS, Food analysis laboratory manual, 2ndedn Springer, New York

Wehr HM, Frank JF (eds) (2004) Standard methods for the examination of dairy products 17thedn American Public Health Administration, Washington, DC

Determination of Protein Content in Food

I Objective

Determine the protein content of rice flour using the Kjeldahl method

II Materials

• Rice flour, 30 g

• NaOH 32% (wt/v)

• H3BO3 4% (wt/v)

• Tashiro indicator

• H2SO4, 0.1 N

• H2SO4, concentrated

• CuSO4

• K2SO4

• Digestion tubes

• Erlenmeyer flasks, 500 ml

• Spatula

• Weighing paper

• Analytical balance

• Burette with ring stand

• Kjeldahl digestion and distillation system

III Method

Digestion

*Note: Digestion takes place in a hood with fan on

• Turn on digestion block and heat up to 80% energy (about 370oC)

• To prepare sample

o Weigh approx 1 g rice flour Place rice flour in a digestion tube

o Add 0.2 g CuSO4, 1 g K2SO4, and 20 ml concentrated H2SO4to each tube with rice

flour

• To prepare blank:

o Add 0.2 g CuSO4, 1 g K2SO4, and 20 ml concentrated H2SO4to a tube with weighing

paper

• Place rack of digestion tubes on digestion block

• Let samples digest until white fumes can be seen Continue heating for about 60 – 90

minutes The samples should be clear with no charred material remaining

• Take samples off the digestion block and hang them on hanging rack and allow to cool

• Dilute digest with 50 ml of distilled water Swirl each tube

Distillation

• Start-up distillation system follows instruction manual

o Rinse the distillation block throughout using distilled water automatically pumped

by the system (Program 0)

• Add 50 ml H3BO3 4% into the 500 ml receiving flask

• Insert the digestion tube and receiving flask in to distillation block

• Start measurement (Program 1)

o Automatically pump 50 ml NaOHto digestion tube

o Heat the digestion sample to boiling point

o Distilling sample for 8 minutes

Titration

• Using a colorimetric endpoint:

o Fill 25 ml burette with H2SO4 0.1 N solution; record the initial volume

o Assemble burette into ring stand

o Place the receiving flask after distillation under the burette

o Titrate each sample and blank with the H2SO4 0.1 N solution to the colour before distillation process Record volume of H2SO4 0.1 N solution used

IV Questions

1 Calculate the percent nitrogen and the percent protein (wet weight basis (wwb) and dry weight basis (dwb)) (20%)

Assume moisture content of 10% Use 6.25 for the nitrogen to protein conversion factor

% 𝑁 = 𝑁𝑜𝑟𝑚𝑎𝑙𝑖𝑡𝑦 𝐻2𝑆𝑂4 × 𝑐𝑜𝑟𝑟𝑒𝑐𝑡𝑒𝑑 𝑎𝑐𝑖𝑑 𝑣𝑜𝑙 𝐿 × 14 𝑔 𝑁 × 100

𝑔 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒 𝑚𝑜𝑙

% Protein = % N X Protein Factor

2 Could phenolphthalein be used as an indicator in the Kjeldahl titration? Why or why not? (15%)

3 Describe the function of the following chemicals used in this determination (20%)

(a) Catalyst pellet

(b) Borate

(c) H2SO4

(d) NaOH

4 Why was it not necessary to standardize the boric acid solution? (20%)

5 For each of the disadvantages of the Kjeldahl method, give another protein analysis

method that overcomes that disadvantage (15%)

6 What do we need to pay attention in this experiment in term of lab safety? (10%)

References

Chang SKC (2010) Protein analysis Ch 9 In : Nielsen SS (ed) Food analysis, 4thedn Springer, New York

AOAC International (2007) Official methods of analysis, 18thedn, 2005 ; Current through revision

2, 2007 (On-line) Method 960 :52 (Micro-Kjeldahl method) and Method 992.23 (Genetic combustion method) AOAC International, Gaithersburg, MD

I Objective

Determination of Total Carbohydrate in foods

Determine the total carbohydrate content of soft drinks and beers

II Materials

• Beer, regular; opened and stored in 10oC fridge over night

• Soft drink, regular; opened and stored 10oC fridge over night

• Erlenmeyer flask, 100 ml, for distilled water

• Erlenmeyer flasks, 500 ml, for beverages

• Bottle to collect waste

• Cuvettes for spectrophotometer

• Gloves

• Mechanical pipettes, 5000 µm, 1000 µm and 100 µm (or 200 µm), with plastic tips

• 20 Test tubes, 16-20 mm internal diameter

• Test tube rack

• Volumetric flasks, 1000 ml

• Volumetric pipette, 5 ml

• Volumetric pipettes, 10 ml

• Spectrophotometer

• Vortex mixer

• Water bath, maintained at 25oC

III Method

Prepare standard curve tubes:

• Using the glucose standard solution (100 µg glucose/ml) and distilled water as indicated in the table below

µg Glucose/10 ml

0 20 40 60 80 100

ml glucose stock solution (100 µg/ml) 0 2 4 6 8 10

ml distilled water 10 8 6 4 2 0

• Record caloric content from labels of soft drinks and beers

Prepare sample tubes:

• Dilute sample tubes as 1:2000 dilution by taking:

o 1ml sample + 9ml distilled water => 10ml A (dilute 10 times)

o 1ml A + 9ml distilled water => 10ml B (dilute 100 times)

o 0.5ml B + 9.5ml distilled water => 10ml C (dilute 2000 times)

• Pipette 1.0 ml sample and 1.0 ml of distilled water into a test tube

*Note: Phenol and H 2 SO 4 additions are carried out in a hood with fan on

• Phenol addition: add 0.05 ml 80% phenol to each tube of Standard curve tubes and

Sample tubes containing a total volume of 2 ml Vortex

• H2SO4 addition: after adding phenol, add 5.0 ml H2SO4 to each tube Mix on a Vortex test tube mixer Let tubes stand for 10 min and then place in to cool them to room temperature Vortex

• Reading absorbance: transfer samples from test tubes into cuvettes Do not rinse cuvettes with water between samples

• Zero the spectrophotometer with the blank

• Read absorbance of all other samples at 490 nm

IV Questions

1 Construct a standard curve for your total carbohydrate determinations, expressed in terms

of glucose (A490 versus µg glucose/ 2ml) Determine the equation of the line for the standard curve (20%)

2 Calculate the concentration of glucose in your soft drink samples and beer samples in terms of g/ L (20%)

3 Calculate the caloric content (based only on carbohydrate content) of your soft drink samples and beer samples in term of Cal/ L and compare to the label Explain any differences (30%)

4 Compare and explain any differences between the calories that carbohydrates contributed

to soft drinks and to beers (10%)

5 What are the advantages, disadvantages, and sources of error for this method to

determine total carbohydrates? (20%)

References

BeMiller JN (2010) Carbohydrate analysis Ch 10 In: Nielsen SS (ed) Food Analysis, 4thedn Springer, New York

Dubois M, Gilles KA, Hamilton JK, Rebers PA, Smith F (1956) Colorimetric method for

determination of sugars and related substances Anal Chem 28: 350 – 356

Nielsen SS (2010) Phenol-Sulphuric acid method for total carbohydrates, Ch.6.In: Nielsen SS, Food analysis laboratory manual, 2ndedn Springer, New York