Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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