Volume 11
Issue 4
Food Science and Technology
JOURNAL OF
POLISH
AGRICULTURAL
UNIVERSITIES
Available Online: http://www.ejpau.media.pl/volume11/issue4/art-11.html
CHARACTERISTICS OF FAT FROM AFRICAN OSTRICH STRUTHIO CAMELUS
Marcin Frontczak, Krystyna Krysztofiak, Agnieszka Bilska, Waldemar Uchman
Institute of Meat Technology,
University of Life Sciences in Poznań, Poland
For well over a decade now interest in farm rearing of African ostrich (Struthio camelus) has been growing both in Poland and worldwide. Ostrich meat has an excellent taste and high nutritive value. For this reason it is exceptionally valuable source of meat and may be used to obtain various meat products. But there is a problem with optimal utilization of ostrich fat. Most studies concern intramuscular fat, while only scarce studies investigate reserve fat. In Poland depot fat collected during slaughter of ostriches is treated as waste. The aim of this study was to determine the chemical composition and basic physico-chemical properties of subperitoneal fat obtained from African ostrich (Struthio camelus) bred in Poland for the assessment of its potential utilization in food industry. Experimental material was ostrich subperitoneal fat – fat lining the abdominal cavity and porcine subcutaneous fat – backfat. The se preliminary prepared material were subjected to chemical and physical analyses. The se following parameters were determined: fat content, water content, acid number, peroxide value, melting point, solidification point and composition of fatty acids. Statistical analysis of obtained results showed a statistically significant effect of the type of fat on water content, acid number and melting point of analyzed samples. Ostrich fat was characterized by higher contents of total monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) in comparison to backfat. All these results indicate a higher nutritive value of ostrich fat than porcine fat. Thus a manner of its utilization as food material should be considered.
Key words: ostrich, Camelus, meat, fat, quality, nutritive value, fatty acids.
INTRODUCTION
One of the basic raw materials obtained during slaughter of slaughter animals is the lipid fraction. Its composition and properties vary depending on the species of animals [2, 12, 23], their age and sex [12] and management conditions [1, 12].
Depending on the chemical composition and physico-chemical properties this raw material is utilized in different ways [23].
For well over a decade now interest in farm rearing of African ostrich (Struthio camelus) has been growing both in Poland and worldwide. This increasing popularity of ostrich farming is connected with the versatile utilization of this species and adaptability to changing climatic conditions. The se animals provide high quality leather, feathers, eggs, and first of all excellent meat [9, 11, 14].
Ostrich meat has an excellent taste and high nutritive value, as well as low calorie content at a very low cholesterol content. For this reason it is exceptionally valuable from the point of view of dietetics [4] and may be used to obtain various meat products [3, 5, 6, 8, 14]. Ostrich skin is a raw material in the production of luxury leather goods, while feathers are in demand by theatres, variety shows and cafes. Eggs are valuable reproduction material, but they are also used in bakery industry and for everyday consumption [9, 24].
The re is a problem with optimal utilization of ostrich fat. Relatively few studies have been conducted on its chemical composition and properties [7, 9, 10, 21]. Most studies concern intramuscular fat, while only scarce studies investigate reserve fat. Its composition varies considerably and is dependent on many factors, e.g. species, management conditions, age of animals, etc. It results from available information that it is a raw material for the production of cosmetics [24], oil [4], etc.
In Poland depot fat collected during slaughter of ostriches is treated as waste. Assuming that mean body weight of an ostrich is 55 kg, then subperitoneal fat constitutes approx. 7% this weight (4 kg). Breeders either throw it away or use it as feed for fox farms [9, 24]. Characteristics of the composition and properties of this fat may be used when determining its utilization.
The aim of this study was to determine the chemical composition and basic physico-chemical properties of subperitoneal fat obtained from African ostrich (Struthio camelus) bred in Poland for the assessment of its potential utilization in food industry.
MATERIAL AND METHODS
Experimental material was ostrich subperitoneal fat – fat lining the abdominal cavity and porcine subcutaneous fat – backfat.
In order to collect the experimental material required for the study both types of fat (subperitoneal ostrich fat and backfat) were subjected to preliminary comminution using an electric grinder with mesh size of 3 mm. Such pre-treated materials were rendered in a glycerin bath at different temperatures (65°C, 75°C, 85°C, 95°C, 105°C) and the quality of rendered fat and cracklings was subjected to sensory examination. Cracklings should be golden-coloured and at the same time fat should be clear and white when solidified. Rendered lard was separated from cracklings and its percentage proportion in relation to fat prior to rendering was determined. Such prepared material was subjected to chemical and physical analyses.
Methodology
Determination of fat content according to Soxhlet
The Soxhlet method belongs to the group of extraction gravimetric methods [17]. Fatty substances determined using this method include first of all proper fats (glycerides), waxes, higher fatty acids, carotenoids, vitamins A, D and E as well as essential oils, alkaloids and organic acids (e.g. lactic acid).
Determination of water content using the drier method
Determination consists in weighing an appropriately comminuted sample, its drying in an air electric dryer under normal pressure at 105°C and repeated weighing. Water content is calculated from the difference between sample weight before and after drying [16].
Determination of acid number
This method consists in the dissolution of the tested sample in a mixture of solvents in the presence of an indicator and titration with ethanol solution of potassium hydroxide [20].
Determination of peroxide value
Peroxide value is a measure of peroxide contents and is treated as an indicator of the oxidation state (rancidity) of fat. Peroxide value (PV) was determined according to the respective standard PN – ISO 3960 [19]. Peroxide value was expressed in active oxygen milliequivalents per kg sample.
Melting point
Fats, due to their chemical composition, do not exhibit a rapid transition from the solid to liquid state. This transition occurs over at least several degrees. Thus we determine both the temperature, at which an analyzed fat substance starts to enter the liquid state and the temperature, at which it is completely melted and clear.
This method is based on the determination of temperature, at which as a result of melting the column of fat rises in a cappillary tube open at both ends [18].
Solidification point
Similarly as melting point, solidification point is not clear-cut. In analyses solidification point is defined as the temperature recorded at self-cooling of fat, which is maintained and occasionally rises for a short period of time as a result of emitted heat of solidification. A detailed description of this method is given in the respective Polish standard [15].
Assay of fatty acids
The composition of fatty acids was determined using gas chromatography (Hewlett-Packard 6890 Series Gas Chromathograph). Contents of individual fatty acids were expressed as the percentage of contents of all fatty acids with chain lengths of 12 to 20 carbon atoms.
Results of fatty acids assays were used to evaluate nutritional value of both types of fat.
Statistical analysis of results
All recorded results of analyses were subjected to basic statistical analysis. Significance of dependencies was determined at p = 0.05.
RESULTS AND DISSCUSION
The aim of preliminary analyses was to determine fat rendering temperature and time. It was found that ostrich fat rendered at 75°C for 60 min and lard rendered at 105°C for 120 min should be selected for further analyses.
In such prepared samples the following parameters were determined: contents of water and fat, acid number and peroxide value, as well as melting point and solidification point. Obtained results are presented in Tables 1a and 1b.
Type of determination | Ostrich fat | Backfat | Fobl. (Ftab=18.512) |
---|---|---|---|
Fat content in native material (%) | 93.10 | 93.70 | 1.440- |
Water content in native material (%) | 2.60 | 1.95 | 13.000- |
Type of determination | Ostrich fat | Lard | Fobl. (Ftab=18.512) |
*** – significance at p≤0.05 - – no significant differences at P≤ 0.05 |
---|---|---|---|
Proportion of lard (%) Proportion of cracklings (%) |
92.50 7.50 |
1.95 88.00 |
16.200 |
Water content (%) | 1.30 | 0.20 | 121.000*** |
Acid number | 0.803 | 1.150 | 20.512*** |
Peroxide value | 3.522 | 1.400 | 7.759- |
Melting point (°C) | 30.50 | 36.25 | 529.000*** |
Solidification point (°C) | 25.25 | 25.75 | 2.000- |
When analyzing data presented in Tables 1a and 1b we may observe differences, although statistically non-significant, in contents of fat and water in ostrich fat and in backfat in their native state. In turn, in lard from ostrich fat the content of water was found to be 5 times higher.
Statistical analysis showed a statistically significant effect of the type of fat only on acid number and melting point of tested samples. It needs to be stressed that ostrich fat has a lower acid number that porcine fat. Ostrich fat has also a lower melting point in comparison to porcine fat, although from the technological point of view the difference is not big enough to be used.
In the analyses of fats, multicomponent mixtures with a complex chemical structure, one of the primary directions of investigations is to determine the composition of fatty acids. Means from the determined composition of fatty acids for ostrich fat and backfat are presented in Table 2.
Fatty acids | Chemical name | Customary name | Ostrich fat (%) |
Backfat (%) |
Fobl. (Ftab=18.512) |
*** – significance at p≤0.05 - – no significant differences at P≤ 0.05 |
---|---|---|---|---|---|
12:0 14:0 15:0 16:0 17:0 18:0 20:0 |
dodecanoic tetradecanoic pentadecanoic hexadecanoic heptadecanoic octadecanoic eicosanoic |
lauric myristic - palmitic margaric stearic arachidic |
0.020 0.620 0.115 24.98 0.130 5.340 0.050 |
0.065 1.295 0.040 24.675 0.380 13.675 0.205 |
3.240 28.974*** 225.000*** 0.081 6.250 251.324*** 106.778*** |
Total saturated fatty acids (SFA) | 31.255 | 40.335 | 31.926*** | ||
16:1 17:1 18:1 (cis) 18:1 (trans) 20:1 |
hexadec-9-enoic heptedec-9-enoic octadecenoic octedecenoic eicosenoic |
palmitoleic - oleic elaidic - |
5.890 0.090 42.760 2.305 0.490 |
2.600 0.385 43.220 2.810 0.835 |
43.858*** 11.880 0.189 11.959 26.304*** |
Total monounsaturated fatty acids (MUFA) | 51.535 | 49.850 | 12.719 | ||
18:2 18:3 20:2 20:3 20:4 |
octadecadienoic octadecatrienoic eicosadienoic eicosatrienoic eicosatetraenoic |
linoleic α – linolenic - dihomo-γ-linolenic arachidonic |
15.105 1.815 0.100 0.000 0.120 |
8.405 0.660 0.370 0.055 0.230 |
27.334*** 32.049*** 29.160*** 1.000 4.654 |
Total polyunsaturated fatty acids (PUFA) | 17.14 | 9.72 | 22.358*** |
From the point of view of nutrition physiology, the most important fatty acids are polyunsaturated fatty acids, first of all linolic and α – linolenic acids, as well as compounds from their family, e.g. arachidonic acid. Results of analyses showed (Table 3) that ostrich fat was characterized by higher contents of total monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) in comparison to porcine backfat. It was found that the content of total polyunsaturated fatty acids in ostrich fat is by approx. 57% higher than that of porcine fat and this difference was statistically significant. Ostrich fat was also characterized by a statistically significantly lower total saturated fatty acid content (SFA) than backfat.
Compared parameters |
Ostrich fat (%) |
Backfat (%) |
Fobl. (Ftab=18.512) |
---|---|---|---|
Total unsaturated fatty acids (UFA) Total saturated fatty acids (SFA) Ratio of unsaturated to saturated fatty acids (UFA:SFA) |
68.657 31.255 2.197 |
59.570 40.335 1.477 |
28.471*** 31.926*** 45.734*** |
Total monounsaturated fatty acids (MUFA) Total polyunsaturated fatty acids (PUFA) MUFA:PUFA |
51.535 17.14 3.007 |
49.850 9.72 5.129 |
12.719 22.358*** 9.602 |
Total cholesterol-reducing fatty acids DFA (UFA + stearic acid – C18:0) |
74.015 | 73.245 | 0.134 |
Total cholesterol-elevating fatty acids OFA (myristinic acid – C14:0 + palmitinic acid C16:0) |
25.600 | 25.970 | 0.096 |
DFA:OFA | 2.891 | 2.820 | 0.084 |
It was observed that the ratio of unsaturated to saturated acids was by 67% higher in ostrich fat. The presence of double bonds reduces melting point of fat. The more double bonds a fatty acid contains, the lower its melting point [13]. Analyses showed (results presented in Table 1b) that melting point of ostrich fat, in comparison to backfat, was statistically significantly lower and that this fat contains more fatty acids with double bonds.
Ostrich fat was also characterized by a higher total content of cholesterol-reducing fatty acids and a lower total content of cholesterol-elevating fatty acids in comparison to porcine fat. However, these differences were not statistically significant.
All these results indicate a higher nutritive value of ostrich fat than porcine fat. Thus a manner of its utilization as food material should be considered.
CONCLUSIONS
- Statistical analysis showed a statistically significant effect of the type of fat on water content, acid number and melting point of analyzed samples.
- Ostrich fat was characterized by higher contents of total monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA) in comparison to backfat.
- Ostrich fat has a more advantageous composition of fatty acids than porcine fat.
- The ratio of unsaturated to saturated acids was higher in ostrich fat.
- Ostrich reserve fat has a higher nutritive value than tested porcine fat (backfat).
- The above results of evaluation for ostrich fat indicate that it is advisable to undertake further studies on its utilization as food material.
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Marcin Frontczak
Institute of Meat Technology,
University of Life Sciences in Poznań, Poland
Wojska Polskiego 31, 60-624, Poznan, Poland
phone: (+48 61) 846 6086
Krystyna Krysztofiak
Institute of Meat Technology,
University of Life Sciences in Poznań, Poland
Wojska Polskiego 31, 60-624 Poznan, Poland
phone: (+48 61) 848 75 09
Agnieszka Bilska
Institute of Meat Technology,
University of Life Sciences in Poznań, Poland
Wojska Polskiego 31, 60-624, Poznań, Poland
phone: (+48 61) 846 72 61
email: abilska@au.poznan.pl
Waldemar Uchman
Institute of Meat Technology,
University of Life Sciences in Poznań, Poland
Wojska Polskiego 31, 60-624, Poznań, Poland
ph: (+48 61) 846 72 61
fax: (+48 61) 846 72 54
email: waluchm@au.poznan.pl
Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.