Download fat content on nutrition label

Natalie Harris
HSN 104 Fat and Protein Analysis
Coversheet
HSN 104 The Science of Food
Laboratory report 1- Fat and Protein Analysis
Natalie Harris*/Caitlyn Hack
Laboratory Class: 1/8/12 and 8/8/12 Wednesdays at 3pm-6pm
Word Count (excluding text in table and graphs): 909 words
Abstract
212375709
Natalie Harris
HSN 104 Fat and Protein Analysis
212375709
Protein, fat and nitrogen content was measured using the Kjeldahl nitrogen method, Soxhlet
method and modified Bligh and Dyer method. The outcomes were compared to claims made on
the original product packaging, that being 5.9g/100g protein and 12g/100g fat. After completing
the methods 5.99g/100g protein, 5.4g/100g (Soxhlet) and 6.52g/100g (Bligh and Dyer) was
calculated, showing a differences between claims.
Key Words
Kjeldahl nitrogen method, Soxhlet and modified Bligh and Dyer method, fat, protein,
carbohydrate, dietary fibre, total energy.
______________________________________________________________________
1. Introduction
During laboratory sessions, nutritional panels of biscuits were used to compare the calculated
protein and fat results of the three different methods. This included applying the Kjeldahl
nitrogen method, Soxhlet, and modified Bligh and Dryer method. The Kjeldahl nitrogen method
entails filling a tube with biscuit and concentrated sulphuric acid. The tubes move to the Kjeldahl
distillation unit and titrated to determine the nitrogen and protein content (Faculty of Health,
2012). Fat can be determined either by the modified Bligh and Dyer method or the Soxhlet
method. Each of the methods demonstrate different concepts, thus leading to varied results. The
Soxhlet method recovers lipids poorly in water rich foods, so it is best to use on relatively dry
products. Soxhlet is completed by biscuit and petroleum ether running trough the Soxhlet fat
extractor. Foods higher in water content are more accurately measured using the modified Bligh
and Dyer method, where added chloroform is removed using a rotary evaporator then the weight
is measured and compared to the original weight after drying (P. Manirakiza, A. covaci, P.
Schepends, 2002). The method presents different results from repeated experiments, so result’s
can be inaccurate The aim of the sessions is to determine if nutritional labels are accurate, all
while applying the knowledge of macronutrients and methods to determine these. It is important
to prepare representative samples for the use of analysis because human error could make the
results differ from the true value.
2.Results and discussion
(i)Kjeldahl distillation (Nitrogen and Protein determination):
Figure 1, Wednesday 3pm class data, including class Mean for protein per 100g
Biscuits
(group #)
Protein
claims on
nutrition
table (per
100g)
Nitrogen in
sample (%)
Protein in
sample (%)
per 100g
Mean
6.319g/100g
1
5.9g
-
-
-
2
5.9g
-
-
-
Natalie Harris
HSN 104 Fat and Protein Analysis
Biscuits
(group #)
Protein
claims on
nutrition
table (per
100g)
Nitrogen in
sample (%)
Protein in
sample (%)
212375709
per 100g
4 (*)
5.9g
1.0515
5.9937
5
5.9g
-
-
6.39
6
5.9g
-
-
6.39
8
5.9g
-
-
6.07
Mean
6.426
Figure 2, Personal data**
Food
Biscuits
Conversi
on factor
Weight Volume Volume
of
0.1M
sample
HCL for
(g)
blank
Nitrogen
content
of
sample
(%)
Protein
content
of
sample
(%)
Protein
on
Nutrition
label
5.70
1.039
1.0515%
5.9937
%
5.9g/100
g
8.2mL
0.4mL
There are limitations of the Kjeldahl distillation process, one being certain foods nitrogen cannot
be easily measured. Products containing refractory compounds cannot be evaluated accurately,
they contain nitrogen in a oxidized form. If pre-treated properly, like addition of a reducing
agent, refractory compounds can include measurement of nitrogen in its analysis.(J.A. Persson,
2012) A blank is required for the Kjeldahl method to compare the two final products. Without a
blank, there really is nothing to compare nitrogen and protein content to. A blank is used to
ensure the end product legitimacy. Human error is always a possibility. In this case, false
measurement of the distillation process may easily occurred. As observed from the results
(Figure 2), the date calculated is a relatively higher to the protein on the label (6.426g/100g vs
5.9g/100g), this could be due to possible error or misinterpretation of the manufactures.
(ii) Determination of fat by modified Bligh and Dyer method
Figure 3, Wednesday 3pm class data, including class Mean for fat per 100g
Biscuits
(Group #)
Fat %
Fat (saturated) on
label per 100g
1
-
5.7
2
-
5.7
4 (*)
5.379
5.7
Mean
6.547
Natalie Harris
HSN 104 Fat and Protein Analysis
Biscuits
(Group #)
Fat %
212375709
Fat (saturated) on
label per 100g
5
8.71
5.7
6
8.71
5.7
8
3.39
5.7
Mean
Figure 4, personal data from modified Bligh and Dyer method**
Food
Biscuit
Weight of
Flask (g)
5.050
Flask
weight in
step 4 (g)
97.082
Weight of
flask with
extracted
lipid (g)
Weight of
extracted
lipid (g)
97.408
0.326
Fat content
(%)
6.52
A possible error in the Bligh and Dyer fat determination could be “run off the lower
lipid/chloroform phase” (Faculty of Health, 2012), the upper phase could be run off accidentally.
This simple mistake could thwart all further results. The Bligh and Dyer method is more suited
for the determination of fatty acids, this is because the most fat is extracted in the process of
determination. This is the most reliable because it is able to extract fat from both water-based
and dry foods. (L. Xiao, 2010). The fat content calculated is a bit higher then that one the
packaging (6.52g/100g vs 5.7g/100g), this could be do to human error or mislabeling claiming to
have lower fat content.
(iii) Determination of fat by Soxhlet method
Figure 5, Class Data with mean fat per 100g
Biscuits
(Group #)
Total fat on label
(per 100g)
Fat %
1
12.0
-
2
12.0
-
4 (*)
12.0
6.52
5
12.0
12.65
6
12.0
12.65
8
12.0
7.07
Mean (Fat %)
9.7225%
Natalie Harris
HSN 104 Fat and Protein Analysis
212375709
Figure 6, personal data from Soxhlet method**
Food
Biscuit
Weight
empty
flask (g)
161.701
weight of
flask plus
fat (g)
weight of
dry food
sample
(g)
fat
content
on dry
basis (%)
fat
content
on “as
in” basis
(%)
161.852
2.731
5.529
5.379
fat
content
on
nutrition
label
12.0g
The Soxhlet method can be dangerous if safety measures are not followed. It is vital that when
using the petroleum ether you need to use a fume cupboard as this can be dangerous. Also, when
heating extracted fat, you leave a small amount of petroleum ether so that it does not burn, this
should also be done in a fume cupboard so no accidents occur. (Faculty of Health, 2012) As
mentioned earlier, the Bligh and Dyer method can give different results when repeated, that
means the Soxhlet method is more reliable. As seen from the Bligh and Dyer the results showed
6.52% fat, while the Soxhlet method showed 5.379%. It is predicted that more fat can be
extracted from the Soxhlet method because ether and chloroform are both non-polar, so more fat
can be extracted from the sample. Based of the calculations, Bligh and Dyer shows more fat in
the biscuits, this is predicted to human error as results differed class average. (P. Manirakiza, A.
covaci, P. Schepends, 2002).
Bligh and Dyer VS Soxhlet Method Figure 7
In Figure 7 we can see that the nutrition label is much lower then the Soxhlet and Bligh and Dyer
fat. The chart shows that the Soxhlet calculated fat is much lower then the mean of class data,
this could be due to possible error.
3. Conclusion
In terms of evaluation, this laboratory is a great hands-on experience for those pursuing a career
in the nutrition field. It is important to understand that you cannot always believe what labels
claims, it can be investigated using the three methods in determining fat and protein. In
summary, the Kjeldahl distillation yielded a 5.9937% protein, this is similar to the 5.9g/100g
claimed on the label showing little error. The nutrition panel gave us 12.0g/100g fat and
5.7g/100g saturated fat. Compared to the result’s from Bligh and Dyer and Soxhlet method,
Natalie Harris
HSN 104 Fat and Protein Analysis
212375709
(5.379g/100g and 6.52g/100g), we can see a difference in the presence of fat. Once again, errors
or misleading information could have led to this difference.
4. References:
(1) J.A. Persson, Handbook for Kjeldahl Digestion (2008). FOSS. Retrieved August 16, 2012,
from http://www.scancotec.com/publicfiles/brochures
(2) Faculty of Health (2012), The Science of Food [Laboratory one and two HSN 104].
Burwood: Deakin University.
(3) P. Manirakiza, A. covaci, P. Schepends, Comparative Study on Total Lipid Determination
using Soxhlet, Roese-Gottlieb, Bligh & Dyer, and ModifiedBligh & Dyer Extraction
Methods (2002), Journal of Food Composition and Analysis, Retrieved August 19 2012, from
http://www.sciencedirect.com/science/article/pii/S0889157500909724
(4) L. Xiao, Evaluation of Extraction Methods for Recovery of Fatty Acids from Marine
Products (2010). Master thesis of EMQAL project. Retrieved August 16, 2012, from
http://www.cursos.ualg.pt/emqal/documents/thesis/Liping_Xiao.pdf