Allen J. St. Angelo

Lipid oxidation in foods

This review discusses the basic chemical reactions that affect food flavor quality. Although there are many reactions that can lead to the deterioration of quality in foods, this review focuses on lipid oxidation and how it adversely affects flavor principles. It also presents technological advances for studying the basic mechanism of lipid oxidation, for measuring its intensity, and for retaining food quality. The food commodities that provide the subject matter for this review include vegetable oils, legumes, cereal grains, eggs, beef, lamb, poultry, seafoods, and catfish. The methodologies for assessing food quality form a multidisciplinary approach that includes primarily instrumental analysis by direct gas chromatography, chemical analysis by the TBA test, and sensory analysis by quantitative descriptive determinations. The author hopes that the information presented in this review is applicable to food commodities not discussed.

Comparison of methods for determining peroxidation in processed whole peanut products

Oxidation of fatty acids in peanut butter produces peroxides and changes in the conjugated diene contents. Two of the most widely used methods for measuring these oxidative effects, peroxide value and the spectrophotometric assay of conjugated diene hydroperoxides, were compared in determinations of shelf-life stability of peanut butters during short and long term storage. Results by the conjugated diene hydroperoxides method correlated with those by the peroxide value method over 4 and 12 week storage periods. The conjugated diene hydroperoxides method requires smaller samples and is quicker, more accurate, and simpler than the peroxide value method, nor does it require additional reagents nor depend upon a chemical reaction or color development.

Isolation of edestin from aleurone grains of Cannabis sativa.

Abstract Aleurone grains, protein bodies, have been isolated from a homogenate of viable hempseeds by employing a density gradient of carbon tetrachloride and refined cottonseed oil. Electron microscopic monitoring of a cross-section of aleurone grains showed them to be composed of at least three different components: large crystalloid substructures, globoids, and some other minor constituents. All are enveloped by a membrane. The crystalloids were extracted from the isolated aleurone grains by repeated washings with solutions of sodium chloride and sodium dodecyl sulfate. Sedimentation coefficients and electrophoretic analysis of solutions of crystalloids indicated that the crystalloids were comprised of pure edestin, and therefore established edestin as an aleurin. Further monitoring of the crystalloids by electron microscopy suggested that they have a pebbly surface and are composed of repeating polygonal-shaped units even down to the 80 A level.

Localization of an acid proteinase in hempseed

Abstract An acid proteinase was detected in a solubilized preparation of dormant hempseed. It has an optimum pH of 3·2 with hemoglobin as substrate, and 4·3 with its natural substrate, edestin. The enzyme is temperature sensitive, the optimal temperature being 53°. Aleurone grains (protein bodies) are the principal subcellular site for the acid proteinase.

Analysis of lipids from cooked beef by thin-layer chromatography with flame-ionization detection

Lipids were extracted from cooked ground beef with methylene chloride/methanol (2:1). The lipids were separated on a silicic acid column, into neutral and polar fractions by elution with methylene chloride, followed by methanol. These fractions were analyzed by Iatroscan thin-layer chromatography with flame-ionization detection instrumentation on Chromarods S-III (silica gelcoated quartz rods). Comparison of cooked beef stored for 0, 4 and 7 d at 4°C indicated that storage caused a decrease in total lipids, an increase in neutral lipids and a decrease in polar lipids, specifically in phosphatidylcholine. These changes in the lipid fraction were associated with meat flavor deterioration and an increase in lipid oxidation.

Properties of a purified proteinase from hempseed.

Abstract A proteolytic enzyme, edestinase, was isolated from resting seeds of Cannabis sativa . It exhibits an optimal pH of 3·4 when denatured hemoglobin was used as substrate. The enzyme is active over a broad range of temperature and has a sharp temperature-dependence at 50°. The apparent Michaelis-Menton constant is 0·44 × 10 −4 M by both the Lineweaver-Burk plot and by the Woolf method. V max is 0·742. Substrate concentrations greater than 0·25 mM cause inhibition. Numerous compounds that inhibit proteolytic enzymes are ineffective when tested on edestinase. Neither cysteine nor ethylenediamine tetra-acetic acid causes stimulation, i.e. it is not a sulfhydryl-enzyme nor a serine-enzyme. Because of these characteristics and its localization, edestinase of hempseed resembles Cathepsin D, an enzyme found in lysosomes of mammalian tissue.

A simplified gas chromatographic procedure for analysis of lipoxygenase reaction products

A simple and very sensitive technique was devised to analyze lipoxygenase reaction products by direct gas chromatography. Results showed that peanut lipoxygenase oxidizes linoleic acid at the C-13 position exclusively.

Localization of allantoinase in glyoxysomes of germinating castor beans

Abstract Intracellular localization of allantoinase was studied in germinating castor bean endosperm. Glyoxysomes and mitochondria were separated by density gradient centrifugation. Using isocitrate lyase and fumarase as the respective marker enzymes for the separated organelles, allantoinase was found in glyoxysomes but was absent in mitochondria.

Effect of minor constituents and additives upon peroxidation of oil in peanut butter

Metalloproteins and ionic iron and copper salts are major catalysts of fatty acid peroxidation, but chelating agents, such as ethylenediaminetetraacetic acid and citric acid in water, can retard or reduce this catalytic effect. To extend shelf-life and retain the high quality of peanut butter, methods to prevent or decrease the catalytic effect of these metalloproteins and salts were conducted. Chelating agents suspended in inert solvents (mineral oil) were not as effective as when they were added in water. Depending upon the concentration, water can act as a prooxidant or an antioxidant in peanut butter.

Rapid Instrumental Analysis of Lipid Oxidation Products

The oxidation of unsaturated fatty acids initially involves the formation of their hydroperoxides. Once these products are formed, they can be decomposed or further oxidized to secondary products such as alcohols, acids, ketones, and aldehydes that are capable of reacting with other constituents of food such as amino acids, proteins, enzymes, and vitamins. These reactions can have an adverse affect on the nutritive value and quality of their respective foods. Additionally, as witnessed in other chapters of this book, the free radicals generated by the oxidative mechanisms have been implicated in reactions that can lead to pathological changes in animal and human tissue.