ANALYSIS OF DISPERSED PHASE OF COCONUT MILK EMULSION

Experiments were conducted to study the dispersed phase of coconut milk emulsion. They were optical microscopy analysis using a Nikon Microscope and particle size analysis using a Coulter Counter Multisizer. Particle size analysis using a Coulter Counter Multisizer on both original coconut milk and homogenized coconut milk at T = 19 °C indicated that they had a wide range of particle size with average value of 5.988 + 1 .0 pm and 6.696 + 1 . 1 pm in diameter respectively. Optical microscopy analysis showed that homogenization of coconut milk after it was heated in a water bath at T = 35 °C for about 15 minutes resulted in changes of particle size, the particle size became smaller. The result lead to a conclusion that the coconut milk emulsion may be considered as a polydisperse emulsion and it indicates that the system should not be sensitive to small variations in preparation or subsequent handling.


INTRODUCTION
other features of the behaviour of collo¬ idal suspensions.The rate of settling/ creaming, the ease with which they can The size and shape of colloidal particles are amongs their most important charac¬ teristics because they determine many 159 No. Artikel : 61/2000 (Kimia Fisik)  from creaming.Meanwhile, from time to time its particle size was analysed using a Coulter Multisizer apparatus.The ana¬ lysis was canned out by dispersing 1 to 2 drops of coconut milk in 15 mL Isoton 11 diluent and then analysing the particle si¬ ze.An orifice diameter of 50 pm was used.The full range menu of 128 chan¬ nel was applied.The coincidence correc¬ tion was made below 105 to ensure its precion and accuracy.About 40,000 particles were measured to ensure that there were a large number of perticles for statistical analysis.The procedure above was repeated for a homogenised coconut milk.It was obtained by homogenisation of coconut milk using a Silverson Emul¬ sifier at room temperature.

Optical Microscopy Analysis
Dispersions of coconut milk and homo¬ genised coconut milk in water were ma¬ de.They were prepared by adding one or two droplets of them to 100 mL water.The homogenised coconut milk was pre¬ pared by increasing the coconut cream temperature to 35°C in a water bath for about 15 minutes and homogenising it using Silverson Emulsifier at : (1.5 + 15%) x !Q3 cpm for about 5 minu¬ tes.The samples above were analysed using a Nikon Optical Microscope.be filtered, and their flow properties when poured or pumped through a pipe, all depend on particle size and shape 0' Coconut milk is widely used in Indonesia.It is used as a cooking ingredient.Tradi¬ tionally, It is used as raw material for producing coconut oil by evaporating the water content.
Coconut milk has an interesting behavi¬ our.When it is allowed to stand for a short time, it will form two layers, cream (upper part, rich of oil) and skim (lower part, rich of water) but not oil and water layers.This apparent behaviour which occurred during standing was the subject which led the author to carry out this project.The objective of this project is to study the colloidal particles of the coco¬ nut milk emulsion.Hopefully, the result will bring the author to an understanding of the emulsion system in coconut milk.

EXPERIMENTS Preparation of Coconut Milk
After removing the coconut pulp from its shell, the thin brown skin was peeled to get the white pulp.After that it was blen¬ ded with water (1:1 w/v) using a blender for about 15 minutes, so that it became a white juicy mixture.Finally, the coconut milk was obtained by filtering this mix¬ ture through a muslin cloth.Unless stated otherwise, the coconut milk used for all these experiments were obtained by this procedure.

Particle Size Analysis
The coconut milk emulsion was stored in a Tumbler apparatus at 24°C to prevent it RESULT

AND DISCUSSION
The results from the particle size analysis for both original coconut milk and homo¬ genised coconut milk at T --19°C indi¬ cated that they had a wide range of parti¬ cle size with the average value of 5.988 I) Hudiyanti:Analysis of Dispersed Phase of.+1.0 p.m and 6.696 + 1.1 pm in diameter respectively.
In analysing the diameter as a function of time, it appeared that the particles in the sample were growing bigger as the time changed figure 1. altered to smaller size.There are several possible explanations for these results.First af all, it is possibly because at tem¬ perature below the coconut oil melting point the oil is in its solid phase and the particle become hard and rigid so homo¬ genisation at a short time does not affect its particle size.But when heat is intro¬ duced to the sample, it changes the state of particles from solid to liquid droplets so the homogenisation can break them down and produce smaller droplets.Se¬ condly, smaller droplets increase the sur¬ face area to be covered by the emulsifier present in the dispersion so it may not be sufficient to cover all the smaller drop¬ lets surface resulted from homogenisati¬ on.The newly formed droplets do not have a full coverage of emulsifier, and so collisions between them during and after homogenisation leads to the formation of bridging flocculation<3) between the drop¬ lets by macromolqcules present in the system, such as: proteins or polysaccha¬ rideÿ.This result showed that eventhough the coconut milk was put in a Tumbler to prevent it from creaming, the preliminary process of breaking was still occurred either in the form of coalescence or flocculation.But this process happened very slow.
The results of optical microscopy indica¬ ted that homogenisation of coconut cre¬ am after it was put in a water bath at T = 35°C for about 15 minutes resulted in changes of particle size, the particle size became smaller.
The experiments show that the particle diameter do not change significantly be¬ fore and after homogenisation at tempe¬ rature below the coconut oil melting po¬ int range (T= 20-26°C)(2).But when the homogenisation was applied to coconut cream has been heated to T = 35°C for about 15 minutes, the particle size was As a result, the average droplet size dont alter significantly before and after homo¬ genisation, i.e. the droplet size is only a function of macromolecules (stabiliser)  conent and not of the preparation conditi¬ on.But when the homogenisation is ap¬ plied to a heated coconut cream, the heat affects the structure of stabiliser to be able to build bridges between the newly 161 No. Artikel : 61/2000 (Kimia Fisik)  formed smaller droplets, e.g.reduction of molecular weight.Hence the average droplet size become smaller after homo¬ genisation.

CONCLUSION
The results obtained in the present work provide evidence that the coconut milk emulsion may be considered as a poly- disperse system with average value of 5.988 + 1.0 pm pm in diameter at tempe¬ rature below the oil's melting point and homogenisation at temperature above the oil's melting point will lead to the forma¬ tion of bridging flocculation between the newly formed smaller droplets by macro¬ molecules present in the system.
Figure 1.Particle diameter as a function of time