Partial interesterification of triacylglycerols

Details Partial interesterification of triacylglycerols Partial interesterification of triacylglycerols

1997-09-17

2001-05-29

Dawson, Robert (Department: 1712)

Chemistry: analytical and immunological testing

Testing of catalyst

C436S071000, C554S030000, C426S417000

Reexamination Certificate

active

06238926

ABSTRACT:

BACKGROUND OF THE INVENTION
Fats and oils constitute an important component of human diet. They are a source of essential fatty acids such as linoleic, linolenic and arachidonic acids, and act as vehicles for vitamins as well as being a source of calories. Fats and oils are also widely used to enhance the texture and palatability of foods. Their varied uses necessitate a wide range of melting and crystallization properties.
The physical properties of a fat or oil are determined by (i) the chain length of the fatty acyl chains, (ii) the amount and type (cis or trans) of unsaturation present in the fatty acyl chains, and (iii) the distribution of the different fatty acyl chains among the triacylglycerols that make up the fat or oil. Those fats with a high proportion of saturated fatty acids are typically solids at room temperature while triacylglycerols in which unsaturated fatty acyl chains predominate tend to be liquid. Thus, hydrogenation of a triacylglycerol stock (“TAGS”) tends to reduce the degree of unsaturation and increase the solid fat content and can be used to convert a liquid oil into a semisolid or solid fat. Hydrogenation, if incomplete, also tends to result in the isomerization of some of the double bonds in the fatty acyl chains from a cis to a trans configuration. Concerns over potential health implications of excessive consumption of fatty acids with trans double bonds (e.g., via margarines, shortenings or frying oils), has led to interest in the manufacture of low- or zero-trans spreadable fats.
By altering the distribution of fatty acyl chains in the triacylglycerol moieties of a fat, randomization can produce changes in the melting, crystallization and fluidity characteristics of a triacylglycerol stock. As well as leaving the overall degree of unsaturation (e.g., as measured by the Iodine Value) of a triacylglycerol stock unchanged, interesterification reactions typically do not generate additional trans double bonds.
With rising concerns over potential dietary effects of trans unsaturated fatty acids, interesterification provides an important alternative to partial hydrogenation in the production of plastic fats such as shortenings and margarines. Interesterification has been used in the oil industry for about a century, although the mechanism is still not well understood by the industry. Currently, interesterification is conducted with experimentally determined catalyst dosages and reaction times to reach a thermodynamic equilibrium (i.e., complete randomization) of the distribution of fatty acyl chains in a triacylglycerol stock. In practice, interesterifications are run with an excess of catalyst to ensure completion interesterification and the randomized product is then characterized by measurement of its physical properties, such as melting point and solid fat content. Herein the terms “randomization,” “complete interesterification” and “complete randomization” are used interchangeably.
Interesterification has been demonstrated as a method to prepare plastic fats and modify fat crystals. Stock oils and fats commonly available as raw materials for interesterification have varying qualities and levels of purity. Because of this, the experimental dosage of catalyst required for initiating or completing interesterification can vary widely. In some cases, because of inactivation reactions, the catalyst dosage may be insufficient to initiate or complete interesterification, resulting in production delays and cost increases. To overcome this limitation, interesterification reactions are typically run using a substantial excess of catalyst. The physical properties and/or composition of the reaction product must be assayed upon completion of the interesterification. While this approach can ensure initiation and completion of the reaction, it does not permit the degree of control of the reaction rate necessary to reproducibly achieve a specific level of partial esterification.
SUMMARY OF THE INVENTION
The present invention relates to triacylglycerol stocks, such as triacylglycerol mixtures derived from oilseeds, rendered beef tallow, fish oil, palm oil or other plant or animal sources. It particularly concerns modifications of selected triacylglycerol stocks to provide products with preferred properties for use, for example in the preparation of plastic fats such as shortenings and margarine.
A process for modifying a triacylglycerol stock, such as a vegetable oil stock, to enhance its physical properties (e.g., hardness or fluidity) in a controlled manner is provided herein. The process includes interesterifying the triacylglycerol stock in the presence of a basic catalyst. The triacylglycerol stock turns a reddish brown color upon initiation of the interesterification reaction. There is a direct correlation between the absorbance of the reaction mixture and the degree of interesterification which has been achieved, i.e., the absorbance is a reflection of the degree of interesterification of the mixture. While throughout this application reference is made to measuring the absorbance of a reacting interesterification mixture, it should be understood that in practical terms the transmittance of the mixture could also be measured. Since the absorbance and transmittance of a sample are arithmetically related (Absorbance=log(1/Transmittance)), either value could be measured and the second value calculated from the measurement of the first value. Throughout this application, it is to be understood the phrase “determining the absorbance” encompasses any measurement which involves the determination of the intensity of light passing through a sample relative to the intensity of the incident light source. Due to reactions with impurities in the triacylglycerol stock which can consume and/or inactivate the catalyst, the amount of active catalytic species generated from a fixed amount of catalyst can vary widely over different lots of triacylglycerol stock. Thus, although the same amount of catalyst can give different amounts of interesterification with different lots of starting triacylglycerol stock, by determining the absorbance of the mixture formed by addition of the basic catalyst to the triacylglycerol stock, it is possible to predict and monitor the degree of interesterification (partial or complete randomization) which will occur. Thus, according to the present invention, the partial interesterification of a triacylglycerol stock may be carried out by forming a mixture which includes the triacylglycerol stock and a basic catalyst. As the mixture is allowed to react, the absorbance of the reacting mixture is determined. The absorbance may be monitored at selected time intervals or continuously as a function of time. The reaction is allowed to proceed until the absorbance of the mixture reaches a preselected value, thereby forming a partial interesterification product. Once the absorbance has reached the preselected value, the reaction is typically stopped by the addition of a quenching solution.
Herein, when reference is made to the term “triacylglycerol stock,” the intent is to refer to a material comprising triacylglycerols, whether altered or not, derived from various plant, animal and synthetic sources, such as oil seed sources. The term at least includes within its scope: (a) such materials which have not been altered after isolation; (b) materials which have been refined, bleached and/or deodorized after isolation; (c) materials obtained by a process which includes fractionation of a triacylglycerol stock; (d) oils obtained from plant or animal sources and altered in some manner, for example through partial or complete hydrogenation; and (e) blends of any such materials. While the triacylglycerol stocks employed as starting materials in the present interesterification process may have been treated via a number of these processes, in most instances the starting triacylglycerol stock will have been bleached. “Bleaching” is a standard process used to remove color bodies from oils, typically via an adsorption/filtration process. It will be understood th

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