L. deMan

Short spacings and polymorphic forms of natural and commercial solid fats: A review

Short spacings refer to the cross sectional packing of the hydrocarbon chains. They are independent of chain length. Short spacings are widely used for characterizing the various polymorphic forms. Fats can crystallize into four polymorphic forms, i.e., sub-α, α, β′ and β. These polymorphic forms differ in their chain packing and thermal stability. The β′ form is also known to exhibit several intermediate polymorphic forms. The nomenclature for the polymorphic forms has generated a great deal of confusion over the years. Several researchers have reported on the polymorphic forms of pure triglycerides. Similar polymorphs have sometimes been described by different names. Currently, the nomenclature proposed by Larsson [Larsson, K.,Acta Chem. Scand. 20:2256 (1966)] is being widely used. Much of the earlier work on polymorphism has been obtained by studying simple purified substances. The listing of short spacings for natural and commercial fats presented in this paper will be beneficial to researchers working in this field.

Formation of short chain volatile organic acids in the automated AOM method

The end point in the automated AOM stability test for fats is related to the rapid production of volatile acids at the end of the induction period and usually measured by conductivity of an aqueous solution of the exit gases. It has been postulated that the reaction involves the transitory presence of a diperoxide which decomposes into two aldehydes and formic acid. The volatile acids produced by several oils were composed mainly of formic acid and significant amounts of acetic acid. In addition, acids with three or more carbon atoms, including propionic, butyric and caproic, were detected. It was found that the temperature of the water in the receiving jars was important in relation to retention of the formic acid. At temperatures above 20 C significant losses may occur. The relationships between peroxide value of the oils, the conductivity of the exit gas solutions and the organic acid content was investigated for the following fats and oils: sunflower, canola, olive, corn, peanut and soybean oil, triolein, lard and butterfat.

Polymorphic behavior of some fully hydrogenated oils and their mixtures with liquid oil

Fully hydrogenated soybean oil, beef fat, rapeseed oil, a rapeseed, palm and soybean oil blend, cottonseed oil and palm oil were characterized by fatty acid composition, glyceride carbon number and partial glyceride content, as well as melting and crystallization properties. The latter were established by differential scanning calorimetry. Polymorphic behavior was analyzed by X-ray diffraction of the products in the flake or granulated form and when freshly crystallized from a melt. The hard fats were dissolved in canola oil at levels of 20, 50 and 80% and crystallized from the melt. Palm oil had the lowest crystallization temperature and the lowest melting temperature; rapessed had the highest crystallization temperature and soybean the highest melting temperature. All of the hard fats crystallized initially in the =00 form. When diluted with canola oil, only palm oil was able to maintain β′ stability.

Chemical and physical properties of the high melting glyceride fractions of commercial margarines

The fat obtained from nine commercial mar-garines purchased from Canada and the U.S.A. were crystallized from acetone at 15, 10, 5 and 0°C. The high melting triglyceride (HMG) fractions at 15°C contained high levels of palmitic and stearic acids. The 18:1 levels increased as fractionation temperature decreased. Triglyceride analysis re-vealed that the 11MG fractions contained high 1ev-els of carbon 54 and 52. The levels of trans iso-mers increased, whereas the trans levels in the 18:1 decreased with fractionation temperature. Mar-games made from canola oil exhibited β charac-teristics whereas canola-paim, soybean and corn margarines showed β1 crystals. The fractions as crystallized from acetone, showed numerous X-ray short spacings, characteristic of β1, β and in-termediate forms. Upon heating and cooling, the 15°C fraction showed β1 or a and β1 characteris-tics regardless of the polymorphic form present in the original margarines. The differential scan-ning calorimetry (DSC) melting points of these fractions varied from 53 to 50° C. The difference between the β and β1 margarines could be related to the 16:0 and carbon 54 content of the 15°C frac-tion. In the β tending margarines the 16:0 content was below 11%, in the β1 tending margarines above 17%. The carbon 54 content in the 15°C fraction of the β tending margarines was close to 70% and that of the β1 tending margarines around 50%. The triglyceride C54 in the 15°C fraction is β tending and therefore should be kept as low as possible. In canola margarines this can be achieved by in-corporation of palm oil, preferably in a slightly hydrogenated form.

Polymorphic stability of hydrogenated canola oil as affected by addition of palm oil

Palm oil was added to canola oil before and after hydrogenation and the effect of this addition on the polymorphic stability of the hydrogenated oils was investigated. Palm oil was added to canola oil at two levels to produce hydrogenated canola and palm oil blends containing 5 and 10% palm oil. The levels of palm oil added to hydrogenated canola oil were 5, 10 and 15%. Samples were subjected to temperature cycling between 5 and 20°C as well as storage at 5°C up to 56 days. X-ray diffraction and polarized light microscopy were used to follow the changes of polymorphic form and crystal growth, respectively, during cycling and storage. Theβ-crystal contents of the oils were quantified based on the relative density of the characteristic short spacings using a Soft Laser Scanning Densitometer. The delaying effect of palm oil on phase transition was observed using Differential Scanning Calorimetry. Palm oil showed no effect on the polymorphic stability of the temperature cycled selectively hydrogenated oil, however, it delayed the transition rate at a constant temperature of 5°C. Addition of palm oil at the 10% level before hydrogenation and the level after hydrogenation proved to be effective in delaying polymorphic instability of nonselectively hydrogenated canola oil. Theβ′ stabilization effect of palm oil on the polymorphic stability of hydrogenated canola oil is most likely due to a decrease of fatty acid chain length uniformity.

Physical and textural evaluation of some shortenings and margarines.

Solid fat content of shortening and margarine was estimated by pulsed NMR. These values were compared with those of the melted fats using different cooling methods. Solid fat content of shortenings measured at 10 and 20 C followed the same trend as those measured on the melted fat tempered at 30 C. Solid fat content of margarines followed the same trend as those measured on the nontempered fats. Softening points of the products were similar to the dropping points of the fats, as were the temperatures of the DSC major melting peaks. Compression tests of cylindrical samples provided more information about textural characteristics of the products than one penetration tests.

Soymilk and tofu properties as influenced by soybean storage conditions

Soybeans were stored at two temperatures, 20°C and 30°C, and two relative humidities, 65% and 85%. The amount of protein extracted into soymilk decreased by about 14% of the initial extractability in all cases after eight months of storage. The decline in protein extract-ability could not be explained by decreases in pH, nor by loss of solubility of certain protein components. Tofu made from beans that were stored at 85% relative humidity became less uniform in microstructure toward the end of the storage period. The volume of whey produced increased with bean storage time.

Automated AOM test for fat stability

A home-built version of the automated AOM test was used with Canola, corn, sunflower, olive and Crisco® oils, shortening and lard. The endpoint was found by measuring the conductivity of a solution of the exit gas from the reaction tube. Coefficients of variability of the samples ranged from 1.1% to 8.3%. The endpoint of the test was ca. 100 PV for Canola oil, ca. 200 PV for corn oil and 35 PV for lard. The aqueous solutions of the volatiles of three oils were used to determine the TBA value. Canola, sunflower and olive oil had TBA values ranging from 6–60 µg malonaldehyde/g at the end point. No apparent relationship was found between the TBA values of the volatiles’ solutions and the PV’s of the oils.

Melting-point determination of fat products

A variety of methods exist for the determination of the melting point (mp) of fats. These include the Wiley mp (AOCS Method Cc 2–38), open capillary slip point, softening point and Mettler dropping point. The conditions under which the tests are performed influence the values obtained. Several of these methods were compared using a variety of fats, including margarine and soft margarine oils, lard, butter and hydrogenated Canola oils. The Mettler dropping-point values were found to coincide with the extrapolated solid fat curves obtained using wide-line NMR for all fats except butterfat. The reproducibilities of the Mettler dropping point and softening point were excellent; that of the slip point was poor.

Textural and physical properties of north American stick margarines

Compression of cylindrical samples was found to be a sensitive method in detecting differences in textural attributes in stick margarines. Constant speed penetration by a probe was the second most sensitive method, while American Oil Chemists’ Society (AOCS) cone penetrometer was the least sensitive method. Canola margarines were significantly harder than soybean margarines. Solid fat content in the product is related to its texture only to a certain extent. The nature of the crystal network is also of importance. To estimate the solids in the final product by pulsed nuclear magnetic resonance it is best to use the AOCS cooling method with a tempering step at 25°C. The International Union of Pure and Applied Chemistry (IUPAC) cooling method results in much higher values.