Time-temperature effects on the stability of a monoglyceride-oil-water low saturated fat shortening alternative

Figure 3. Principle of MAG gel formation and structure

Abstract
The stability of an opened container of a monoglyceride-oil-water shortening alternative (MAG gel) containing 4.5% monoacylglycerol, 0.22% stearic acid, canola oil and 30, 35 or 40% water was monitored for a period of 5 weeks at 22˚C or 8˚C. The dropping point (DP) of the 40% water-containing samples stored at RT remained constant at ~75˚C while the DP of cold-stored samples decreased by 10 degrees in the 5-week period.

The DP of RT stored samples remained constant during the 5-week storage period. The DP of cold-stored samples decreased by 9 degrees and 12 degrees for the samples containing 35% and 30% water, respectively. The peak melting temperature determined by DSC did not change in the 5-week period for any of the samples. Water syneresis was observed only in the cold-stored samples after 3 weeks and reached 8%, 6.5% and 3% (w/w) for samples containing 40%, 35% and 30% water, respectively.

These results are consistent with the notion that H-bonding between MAG hydroxyl groups is strengthened at cold temperatures, causing shrinkage of the inter-lamellar region, resulting in syneresis. This is partially responsible for the destabilization of the MAG multilayers and the observed decrease in DP.
Introduction
A novel, structured oil was recently developed at the University of Guelph, to be utilized as a trans fat free low saturated fat shortening alternative. This material is a cellular-solid structure as an oil-in-water emulsion with water-swollen MAG multilamellae surrounding 1-5 micrometer oil globules.

The globules are in contact with each other via hydrogen bonding. The co-surfactant aids in both emulsion formation and water-binding. This experiment attempts to mimic the handling conditions experienced by the material after a package of such material is opened and material removed for use.
Materials and Methods
Sample Preparation: The gels were produced by vigorously mixing a hot oil-monoglyceride solution with alkaline deionized water. The water and oil portions are heated to ~ 75˚C and blended with an immersion blender for one minute. The blended samples were then passed through the Komax static mixer at a pump speed of five to ensure a homogeneous white paste is obtained. Canola oil was used in these studies, although any edible oil is suitable.

The monoglyceride used was Danisco’s commercially available HSK-A (10% monopalmitin, 90% monostearin) distilled monoglyceride and cosurfactants such as stearic acid in a 20:1 (w/w) ratio. The mixture contained 4.5% (w/w) distilled monoglyceride for proper gel formation. The resulting gel is firm and spreadable as shown in Fig 1A.Dropping Point: The dropping point is an indication of the thermal stability of the product. The higher the dropping point the more energy required to alter the structure and thus the more thermally stable the sample is.
Samples were inserted into the Mettler FP 83 Dropping Point Cell at an initial temperature of 40.0°C. Samples were then heated a rate of 5.0°C/min until the dropping point temperature. Five replicates of each sample were completed.

 Differential Scanning Caliorimetry (DSC): Approximately 10 micrograms of fat was placed in hermetic alodined pans supplied by TA Instruments. Pans were loaded into the DSC and samples were heated from an initial temperature of 35.00°C to 65.00°C at a rate of 5°C/min.

Centrifuge Test: The centrifuge test is used to determine the amount of water and oil separation in the samples when placed under gravitational force.
Approximately one gram of each sample was placed into a centrifuge tube using a syringe. The samples were then placed in the centrifuge for five minutes. After five minutes water separation was determined by visual approximation, and oil separation was determined by removing the oil and reweighing the centrifuge tube.

Figure 2. Polarized light image of MAG gel- Microscopy images over the 5 week storage period did not show evidence of flocculation or coalescence between any of the samples

 Results

Figure 4. Melting points determined by DSC curves of room temperature (RT) and cold storage samples over the 5 week storage period. Melting points remained within a few degrees of each other throughout the 5 week storage period. Cold storage samples have lower melting points then RT samples (n=2).

Figure 5. Dropping points of room temperature samples over the 5 week storage period (n=5).

Figure 6. Dropping points of cold storage samples over the 5 week storage period. Fluctuation between DP’s more evident for cold storage then RT samples (n=5).

Figure 7. Water separation of cold storage samples over the 5 week storage period. Syneresis begins during week 3 of storage. The RT samples did not show any signs of syneresis. Oil separation was too little to be quantified for all samples (n=3).

Conclusions
The melting point of all the samples remains constant throughout the 5 week storage period indicating that there is no change in the state of the sample.

The variability in the dropping point can lead to the conclusion that there is a structural change taking place in the refrigerated samples.

These results are consistent with the notion that H-bonding between MAG hydroxyl groups is strengthened at cold temperatures, causing shrinkage of the inter-lamellar region, resulting in syneresis.

This is partially responsible for the destabilization of the MAG multilayers and the observed decrease in DP. Storage at room temperature is more advantageous as the product appears to behave more consistently throughout the five week storage period.