Partial glycerides are commercially synthesized on a considerable scale every year for use as emulsifying agents in a wide range of foods. Monoglycerides in particular, which have superior emulsifying property than diglycerides, account for over 70% of the total world consumption of food emulsifiers. In general, the technical monoglycerides are not pure monoglycerides, but generally consists of a mixture of 40-48% monoglycerides, 30-40% diglycerides, 5-10% triglycerides, 0.2-9% fatty acids and 4-8% glycerol. Pure monoglycerides are available only after isolation by molecular distillation of the technical monoglycerides (Meffert, 1984). These pure monoglycerides are obviously more expensive as compared to the technical products. Their most important application is in food industry due to their excellent self-emulsifying and surface-active properties. Particular types of monoglycerides such as monolaurin, monocaprin and the like are in use as anti microbial agents or antiseptic agents, e.g. for foods and pharmaceutical industry.
Both monoglycerides and their derivatives, in addition to their excellent emulsifying properties, are also used in non-food applications such as emulsifiers, texturing agents, lubricants and plasticizers in pharmaceuticals, cosmetics and textiles etc. Depending on the chain length of the fatty acid monoglycerides, they are encountered in various formulations and usage in the non-food products and application.
Generally, there are two routes to the production of monoglycerides, namely the chemical and enzymatic synthesis. Glycerolysis of fats and oils or fatty acids are preferred since the partial esters of glycerol enjoy considerably more applications than those derived from glycol. On an industrial scale, monoglycerides are usually produced by glycerolysis of natural oils and fats with glycerol at temperatures greater than 220° C. in the presence of an inorganic catalyst, the reaction products are in an equilibrium mixture consisting of monoglycerides, diglycerides and triglycerides (Sonntag, 1982). However, in general, glycerides used as emulsifiers are required to contain at least about 90 mole % of monoglycerides. Hence, in the conventional production of such glycerides, it has been necessary to subject a glyceride mixture to molecular distillation or the like to enhance the content of monoglycerides. The yield of the conversion of triglycerides to monoglycerides is about 58%. Some studies using various solvents to improve the homogeneity of the reactants, i.e glycerol and fats have also been carried out. A total yield of 83% monoglycerides has been obtained using pyridine as a solvent for the glycerolysis of sunflower seed oil. Solvents offer the prospect of high yield of monoglycerides at relatively low temperature. But due to various drawbacks, glycerolysis involving solvent has not been studied extensively.
U.S. Pat. No. 6,127,561 discloses a process for the production of monoglycerides based on the glycerolysis of methyl ester derived from animal and vegetable fats and oils. The reaction was carried out at between 130 to 160° C. at a vacuum of 200 to 400 mbar, using an alkaline catalyst, stopping the reaction by fast cooling of the reaction mixture and the destruction of the catalyst when the quantity of glycerides has reached a concentration of mono and diglyceride of 40-60% and the ratio of concentration of mono and diglyceride lies between 3 to 10.
G.B. Patent 950,667 also discloses a process for the preparation of monoglycerides via glycerolysis of a mixture of glycerine and fatty acids or their esters or other mono- or polyvalent alcohols provided that the other alcohols are more volatile than glycerine at a temperature of at least 260° C. The reaction products comprising glycerine and a glyceride having high monoglycerides content are separated into two layers by cooling, one layer comprising glycerine which is removed. Residual glycerine is removed from the other layer by distillation and followed by water-washing to obtain the monoglycerides.
The production of monoglycerides via chemical synthesis can be further improved by engaging a suitable solvent to increase the solubility of glycerol in the oil and subsequently enhance the glycerolysis process.
For example, phenol was proposed by T. P Hilditch (1935) and J. G Riggs (1774). The reaction need to be carried out at a high temperature and in addition to that, it has been found out that phenol undergoes some condensation with stearic acid and glycerol, thus, giving rise to impurities which are not readily separated.
K. F Martill (1952) and R. J. Sims (1952) have proposed the use of tertiary aromatic amine such as pyridine, the picolines or isoquinoline as solvent for the reaction. However, these solvents caused difficulties due to odour and toxicity.
U.S. Pat. No. 2,789,119 discloses a process for the preparation of monoglycerides from naturally occurring fatty oil, fats or artificially prepared esters of higher fatty acids (which are substantially insoluble in water) in the presence of tertiary butyl alcohol and an alkaline catalyst. According to the patent disclosure, tertiary butyl alcohol is an excellent reaction medium and that is not esterified by fatty acid under the reaction condition. It is non-toxic, relatively odourless and has a low boiling point, making it readily removed from the reaction mixture. It is dehydrated under acid conditions and is therefore used in inter-esterification process between neutral fatty glycerides and glycerol with an alkaline catalyst.
In recent years, synthesis of monoglycerides using lipase enzymes has been actively investigated. Studies using a wide variety of different enzymes and substrates as well as conditions to improve the yield of partial glycerides have been carried out. U.S. Pat. No. 5,270,188 discloses a process of preparation of glycerides having a high content of monoglycerides with a lipase from Penicilium cyclopium ATCC 34613. Monoglycerides are produced by mixing glycerol and fatty acids with the lipase under agitation at a temperature of 20-55° C. for 1-50 hours.
Stevenson et al. (1993) have also investigated the glycerolysis of tallow with immobilized lipase. In ‘Glycerolysis of Tallow with Immobilised Lipase’ published in Biotechnology Lett. 15, 1043-1048, they have revealed the glycerolysis of melted tallow by using Lipozyme (immobilized Mucor meihei lipase) to synthesize monoglycerides. When reaction was carried out at 50° C., a maximum 35% yield of monoglyceride was obtained. Cooling before 42° C. resulted in monoglycerides crystallisation which improved the yield up to 50% but further yield was prevented by solidification of the reaction mixture. Although the present invention is embodied in several different aspects it will be clear from this broad background review that each aspect is so linked as to form part of the same inventive concept.