J.M. 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.

Photooxidation of milk and milk products: A review

Milk and other lipid containing products are susceptible to oxidative deterioration. Light from either natural or artificial sources catalyzes certain chemical reactions, resulting in the development of off‐flavors and the breakdown of pigments and vitamins. This review deals with the subject of light induced deterioration of foods and its various ramifications. Reaction pathways of light energy in model or natural systems are outlined. Mechanisms are presented, and the roles of lipids, proteins, and vitamins during photochemical reactions are discussed. Damaging effects of light on nutritional and organoleptic quality of milk and several fats or fat containing products are discussed and explained. Ways and means of preventing the occurrence of oxidation defects are covered involving the use of suitable containers and light barrier properties of packaging materials.

Determination of oil content of seeds by NIR: influence of fatty acid composition on wavelength selection.

The oil content of nine different types of oilseeds has been determined by near-infrared reflectance (NIR) spectroscopy. A Northstar computer was used to select the wavelengths that best represent the oil content in these seeds. Selected wavelengths were often in the same area of the spectrum, but calibrations differed with respect to the number of wavelength points required and their order of selection. Wavelength assignments for typical functional groups in fatty acids are discussed. The fatty acid composition and the predominant fatty acid component appeared to influence the wavelengths used for the estimation of oil content in each seed type. The mathematical treatments used appeared to affect absorption maxima of all seed types. Spectra of seed oils and their fatty acids indicated variation and closeness of absorption maxima.

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.

Consistency of fats: A review

The consistency of fats can be measured with the cone penetrometer (AOCS Method Cc 16-60). Several suggestions have been made to convert readings of penetration depth into parameters such as yield value, hardness or hardness index. This may extend the usefulness of the method. Motor-driven penetrating devices yield results in terms of force/area or stress. More basic information about the rheological properties of fats can be obtained with creep measurements. This includes the viscous flow component as well as instantaneous and retarded elastic components. Such methods are more suitable for research purposes than for quality control. Characteristics and application of various methods will be reviewed.

Texture — Strueture Relationships in Texturized Soy Protein II. Textural Properties and Ultrastructure of an Extruded Soybean Product

Abstract Thermoplastic extrusion was employed to produce an experimental texturized soybean product. Physical properties relative to process temperature were examined by test methods which yielded information on product density, shear strength, work of shearing, break elongation, breaking strength, stress relaxation and water regain. Light and scanning electron microscopy were employed to examine product structure. Shear force and work (Kramer Shear Press) and product density were affected markedly by process temperature, showing an increase in the former two and a decrease in the latter with increasing process temperature. Breaking strength (Instron), shear force (Warner-Bratzler Shear) and water regain were also affected but demonstrated more complex relationships. The photomicrographs obtained showed clearly the physical changes which occurred during processing and indicated that, under our experimental conditions, maximum texturization occurred between 175°C and 192°C.

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.

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.

Analysis of oilseeds for protein, oil, fiber and moisture by near-infrared reflectance spectroscopy.

Wavelength and mathematical treatments were optimized for the determination of oil, protein, moisture and crude fiber components in the ground seeds of nine oil-bearing crops [rape, flax, sunflower, safflower sesame, palm kernel, groundnut (peanut), soybean spectroscopy. Optimum wavelengths, selected for the estimation of various components, were influenced by the algorithm (math treatment) used and differed among crops. The second derivative math appeared to be better suited for the estimation of all constituents. Methods for sample preparation of all constituents. Methods for sample preparation and analytical results are discussed. The accuracy was quite satisfactory for routine quality control and evaluation purposes, and precision was equal to that of standard analyses.

Stability of edible oils and fats to fluorescent light irradiation

Butter, butterfat, and corn, coconut, rapeseed, and soybean oils were exposed to 500 ft-c of fluorescent light at varying time-temperature conditions. Oxidation rates were measured by the peroxide values. Vitamin A and β-carotene content of butterfat were estimated. The effect of wavelength on the relative rates of oxidation was determined. The light transmitting properties of the samples at 15 and 30 C over a spectral range of 380–750 nm were measured. It was observed that there was no increase in oxidation rate when the light was switched off. The stability of the oils as shown by the oxidation rates did not correlate well with the ratios of C18:2 to C18:1 or C18:3 to C18:2 nor with the degree of unsaturation. Increase in temperature alone had minimal effect; however, in the presence of light the rate of oxidation increased considerably with a corresponding decrease in the content of Vitamin A and β-carotene. β-Carotene provided strong protective properties. After the photobleaching of β-carotene in butterfat, there was a rapid increase in peroxide values. With coconut oil, the oxidation rate was greater at 15 C than at 30 C due to greater light absorption at 15 C over the entire spectrum. The rate of oxidation decreased at higher wavelengths, and this effect was more pronounced in the vegetable oils than in butterfat, where the β-carotene was considered to serve as a filter for light of low wavelength.