Slip melting point

Apart from butter or butter oil most fats that are used in biscuits are defined in terms of their physical and chemical properties. Fat suppliers are skilled at producing products with controlled physical and chemical properties from a range of raw materials. The baker can either buy fat on a physical and chemical specification, e.g. solid fat index, slip melting point, and not to contain lauric fat, or on an origin basis, e.g. to be coconut oil. The advantage of the botanical specification is that the item is a commodity and can be obtained from numerous sources. The disadvantage of this approach is that the product is tailored for a particular use. 

Interesterification of blends of milk fat and palm kernel olein by a mycelium-bound lipase from Rhizomucor miehei or a commercially immobilized enzyme preparation resulted in a lower slip melting point and solid fat content. An interesterified product made from a 70 30 mixture of palm kernel olein and anhydrous milk fat was considered to be suitable for use in ice cream (Liew et al., 2001). 

By capillary action, molten fat sample is drawn into the tube, which is open at both ends. The fat is solidihed by chilling and then melted in water at a regulated rate of increase in temperature. The temperatures at which the fat shps and appears clear in the liquid state are noted as its slip/melting points or melting range. 

Shortening Slip melting point (°C) Polymorphic form Days of storage ... 

Those for crude oils include the free fatty acids (FFA), iodine value (IV), saponification value (SV), refractive index (RI), specific gravity (SG), unsapo-nifiable matter (US), and moisture plus impurities (M I). These are intended to give a quick impression of the authenticity of the oil and the likely losses in refining. For refined oils, the values also usually include the colour, peroxide value (PV), slip melting point (SMP) and solid fat content (SFC), if appropriate. These are indications of quality and behaviour in use. As the SFC test relies on nuclear magnetic resonance, these values are also known as NMR or N values. The Malaysian standard for crude and refined CNO (MS 1987) is shown in Table 6.7 and the Codex (2001) draft standard in Table 6.8. 

Widely used methods in the past were the Wiley mp in the US and the complete fusion in Europe but more recently, the AOCS method Cc 3-25 for the slip melting point (SMP), has been rapidly gaining acceptance, especially in international transactions. Unfortunately, although there is a broad correlation between the results of the various methods, there is no exact conversion equation valid for all oils, because each method measures a different point on the melting curve and the curves have different slopes. 

Although only three basic products are normally made from PKO (PKO itself, PKOo and PKOs), there are also hydrogenated and blended versions, which complicate the picture considerably. The simplest way to distinguish between them is from their iodine value/slip melting point relationships, and a more certain characterisation can be made by examining their SFC profile and fatty acid composition. 

Cocoa butter substitutes are prepared by separating out a middle melting fraction from palm oil and blending the resulting product with other exotic tropical fats. These fats are called palm mid-fractions. The slip melting points and iodine values of a few such fats are also plotted in Fig. 8.2 for added interest. It is unlikely that palm oil will ever be adulterated or contaminated with a palm mid-fraction as these fractions command a high price and are traded separately from the conventional bulk oils. 

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