087/2012

Melting Point M-565

Slip Melting Point Determination of Palm Stearin

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SHORT NOTESHORT NOTESHORT NOTESHORT NOTE Slip Melting Point Determination of Palm Stearin

Palm stearin, the solid fraction of palm oil, is a natural source of hard fat. The melting characteristic of palm stearin is an important quality parameter and depends on its content of different fats. The melting temperature of palm stearin is usually determined by the slip melting point (SMP). We report a SMP of 50.7±0.1 °C for a palm stearin sample provided by New Britain Oils Ltd. Obtained results confirm that the M-565 is a reliable tool to measure the SMP for palm stearin samples. The melting process was recorded and analysed without modification of the instrument.

Introduction

Palm stearin is a mixture of fats, fractionated from palm oil. It is a mixture of different fully natural ingredients [1] and mainly used as an edible, trans-fat free and thus healthy alternative to partially hydrogenated plant oils [2].

The melting point of fats is described using empirical methods, usually by the slip melting point (SMP). The SMP is defined as the temperature at which a sample rises in an open capillary upon heating under defined conditions as illustrated in Figure 1 [3].

A facile, quick, and reproducible method to measure the slip melting point (SMP) of palm stearin using the M-565 is reported.

Figure 1. Illustration of the palm stearin sample preparation (steps 1-3) and

the rising sample (step 4).

Experimental

About 1 g of palm stearin sample was carefully melted at 60 °C in a glass beaker using a heating plate. When completely melted the liquid sample was filled into a capillary that is open on both ends, by dipping the capillary into the solution. The height of the palm stearin sample in the capillary was 9 to 10 mm. To harden the sample it was cooled overnight at 4 °C.

Then, the sample capillary was immersed in a boiling point tube containing water (Figure 1). When inserted, the water level in the boiling point tube was 20 mm above the upper edge of the sample. The total height of the water was 30 mm (Figure 1).

The palm stearin sample was placed in the M-565 (boiling point sample place) and heated applying a temperature gradient of 1.0 °C/min. The melting process was recorded from 45-55 °C using the Melting Point Monitor software. Data were recorded without supervision and analysed after each run.

Results

Six measurements of the palm stearin sample were performed as described. An average SMP of 50.7±0.1 °C was measured. Observed SMP is well comparable to the SMP of palm stearin found in literature, ranging from 44.8-53.4 °C, and measured following the ISO 6321 or the AOCS CC 3-25 protocols [4].

A typical melting progress is shown in Figure 2. During heating the sample plug changed its appearance from white to semi-transparent. The slip melting point temperature was recorded when the complete sample started to move upwards in the capillary (Figure 2 middle).

Figure 2. Snapshots of the palm stearin sample during the melting process.

The SMP determined for six samples was 50.7±0.1 °C.

Conclusion

It was demonstrated that the SMP of palm stearin can be determined using the M-565. Reproduction of the measurements was performed with a standard deviation of only 0.1°C.

Clearly, found results confirm that the M-565 can be applied to perform the SMP measurements, in addition to its conventional use for the determination of melting- and boiling points. No modifications of the instrument are necessary rendering the M-565 an economic and versatile instrument for the quality control in the palm oil industry.

References

[1] Malaysian Palm Oil Board, www.mpob.gov.my/en/faqs

[2] K.G. Berger , Czech J. Food Sci. Vol., 25, No. 4, p. 174–181, 2007.

[3] J. Beare-Rogers et al, Pure Appl. Chem., Vol. 73, No. 4, p. 685–744, 2001.

[4] International Standard, ISO 6321, Animal and vegetable fats and oils – Determination of melting point in open capillary tubes (slip point), second edition, 2002-2-15.

087/2012

Melting Point M-565

Application Note 087/2012 Version A, Copyright © 2012 Büchi Labortechnik AG 3/6

1 Introduction

A facile, quick, and reproducible method to measure the slip melting point (SMP) of palm stearin using the M-565 is reported.

Palm stearin, the solid fraction of palm oil, is a completely natural source of hard fat. It is mainly used as an edible, trans-fat free and thus healthy alternative to partially hydrogenated plant oils [1]. It is also considered as a sustainable feedstock to substitute fossil fuels [2].

Table 1. Chemical formula, structure and melting points of fatty acids found in palm stearin.

Sources: *J. Beare-Rogers et al, Pure Appl. Chem., Vol. 73, No. 4, pp. 685–744, 2001, **Sigma-Aldrich, MSDS

The typical fatty acid composition of palm stearin includes palmitic-, linoleic-, oleic- and stearic acids, hence, it is a mixture of different natural compounds [3]. The relative content of the ingredients, influenced by the raw material and the fractionation process, greatly affect the melting point [4]. Briefly, the melting point increases with a greater content of long chain fatty acids, increasing double-bond saturation, and transformation from cis isomers to trans isomers (see Table 1).

To measure the SMP, also known as the open capillary tube method or the rise melting point method, the sample is solidified in a capillary and heated in a water bath. At a certain temperature the sample rises in the capillary, this temperature is called the SMP temperature.

Since experimental factors, as heating rate, sample amount and sample preparation may influence the reproducibility of the SMP measurement an exact and reproducible procedure is necessary.

Here it is demonstrated how the SMP of a palm stearin can be accurately determined using the M-565 and the Melting Point software.

Application Note 087/2012 Version A, Copyright © 2012 Büchi Labortechnik AG 4/6

2 Equipment

− Melting Point M-565 − PC with Melting Point-Monitor Software − Analytical balance − Heating plate equipped with contact thermometer − Refrigerator set to 4°C − Beaker 50 ml − Syringe (2 ml) with needle

3 Chemicals and Materials

− Melting point capillaries, BUCHI, open on both ends (040808), Dimensions; Length: 80 mm, internal diameter: 1.10 mm, wall thickness: 0.225 mm

− Boiling point capillaries, BUCHI (019697) − Distilled water − Palm stearin: Sample 12/21, New Britain Oils Ltd, Liverpool UK

4 Procedure

4.1 Working Principle

The steps for SMP determination are shown in Figure 1. First, the sample has to be filled into a capillary that is open on both ends (Figure 1, step 1). The height of the material in the capillary should be about 10 mm as stated by normative procedures as the USP 741 Class II, or ISO 6321.

Second, another capillary, the boiling point capillary has to be filled with a few drops of distilled water (Figure 1, step 2). The boiling point capillary is open on one end only and filling of water is best done using a syringe with a thin needle.

Third, the capillary with the sample has to be immersed into the boiling point capillary as shown in Figure 1 step 3. According to the ISO 6321 norm, the total height of the water should be 30 mm [5].

Finally, the sample is placed in the M-565 – the position of the boiling point capillary is to be used. Upon heating, the sample material softens and expands. Also the water volume increases. When reaching the slip melting point temperature, the sample rises in its capillary (Figure 1 step 4).

Figure 1. Illustration of the sample preparation (steps 1-3) and the rising sample (step 4).

Application Note 087/2012 Version A, Copyright © 2012 Büchi Labortechnik AG 5/6

4.2 Experimental

4.2.1 Sample Preparation

About 1 g of palm stearin sample was carefully melted at 60 °C in a glass beaker using a heating plate. When completely melted the liquid sample was filled into a capillary that is open on both ends, by dipping the capillary into the solution. The height of the palm oil sample in the capillary was 9 to 10 mm. To harden the sample it was cooled overnight at 4 °C.

The sample capillary was immersed in a boiling point tube containing water (Figure 1). When inserted, the water level in the boiling point tube was 20 mm above the upper edge of the sample. The total height of the water was 30 mm (Figure 1).

4.2.2 Slip Melting Point Measurement

Before starting with the exact SMP determination, first, an experiment using a steep temperature gradient and a broad temperature range was performed. Therefore, the sample was placed in the boiling point position of the M-565 and heated from 30.0 °C to 65.0 °C using a heating rate of 2.0 °C/min.

From this experiment the SMP was determined to be around 50.0 °C. Based on this finding a slower heating gradient, 1.0 °C/min, was chosen in order to measure an exact SMP. The heating ramp started at 45 °C and stopped at 55 °C.

5 Results and Discussion

Six palm stearin samples of the same batch were measured as described. An average SMP of 50.7±0.1 °C was obtained. Observed SMP is well comparable to the SMP of palm stearin found in literature, ranging from 44.8-53.4 °C, and measured following the ISO 6321 or the AOCS CC 3-25 protocols [5].

A typical melting process of palm stearin is shown in Figure 2. During heating the sample plug changed its color from white to semi-transparent. Before slipping up the capillary, the sample expanded by volume, however, this is not considered the SMP. The SMP temperature recorded when the complete sample starts to move upwards in the capillary (see Figure 2 middle).

Figure 2. Snapshots of the palm stearin sample during the melting process. The SMP determined for six samples was

50.7±0.1 °C.

Application Note 087/2012 Version A, Copyright © 2012 Büchi Labortechnik AG 6/6

6 Conclusion

It was successfully demonstrated that the slip melting point of palm stearin can be determined using the M-565. Reproduction of the measurements was performed yielding a standard deviation only 0.1°C.

Clearly, found results confirm that the M-565 can be applied to perform SMP measurements, in addition to its conventional use for the determination of melting- and boiling points. No modifications of the instrument are necessary rendering the M-565 an economic and versatile instrument for the quality control in the palm oil industry.

7 Acknowledgement

New Britain Oils Ltd is thanked for providing the palm stearin sample.

8 References

[1] K.G. Berger , Czech J. Food Sci. Vol. 25, No. 4, p. 174–181, 2007.

[2] C.Y. May et al, Fuel, Vol. 84, p. 1717–1720, 2005.

[3] Malaysian Palm Oil Board, http://www.mpob.gov.my/en/faqs.

[4] J. Beare-Rogers et al, Pure Appl. Chem., Vol. 73, No. 4, pp. 685–744, 2001.

[5] International Standard, ISO 6321, Animal and vegetable fats and oils – Determination of melting point in open capillary tubes (slip point), second edition, 2002-2-15.

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