N.A. Michael Eskin

Biochemistry of lipoxygenase in relation to food quality

A renewed interest in lipoxygenase has led to detailed studies of its isoenzymes, substrate specificity, and the nature of its reaction products. Lipoxygenase is highly specific for cis,cis-1,4-pentadiene systems such as linoleic, linolenic, and arachidonic acid (or ester) and catalyzes the formation of the corresponding hydroperoxides with a cis,-trans-conjugated diene system. The hydroperoxides can then undergo enzymic or spontaneous degradation, producing a range of carbonyl compounds. This review will discuss the biochemical properties of this enzyme and its contribution to the quality of raw and processed food products. An attempt has been made to discuss both the desirable and undesirable effects associated with the action of lipoxygenase, citing specific food examples where appropriate.

Interaction of wheat and rice starches with yellow mustard mucilage

The effect of yellow mustard mucilage (YMM) on gelatinization and retrogradation of wheat and rice starches were studied. Considerable interactions were observed between YMM and wheat and rice starches which were accompanied by a marked increase in viscosity. DSC studies showed that the presence of YMM did not affect peak gelatinization temperature (Tp) of wheat and rice starches, but slightly increased melting enthalpy (ΔH) and the phase transition temperature range (Tc−T0). Addition of YMM markedly changed wheat and rice starch gel textures by increasing hardness, adhesiveness, chewiness and springiness. The addition of YMM–locust bean gum (LBG) mixture (9:1) similarly increased the viscosity of wheat and rice starches but decreased gel hardness. The swelling power as well as solubilized starch and amylose were decreased for both starches in the presence of YMM. Syneresis in wheat and rice starches was also decreased by the presence of YMM.

Interactions of native and acetylated pea starch with yellow mustard mucilage, locust bean gum and gelatin

The interactions of yellow mustard mucilage, locust bean gum and gelatin with native and acetylated pea starch were studied by a Brabender viscograph, a Bohlin rheometer and differential scanning calorimetry (DSC). In the presence of mustard mucilage or locust bean gum, the onset temperature of the viscogram shifted to lower temperatures, whereas the final viscosities of the pastes increased markedly for both native and modified pea starch. Gelatin produced only a slight increase in the viscosity of native pea starch, whereas the viscosity of modified pea starch in the presence of gelatin decreased. DSC studies demonstrated that the presence of a hydrocolloid did not change the gelatinization temperature of pea starch. The variation in the viscosity onset temperature, as observed with Brabender, was attributed to an increase in the medium viscosity of a starch/hydrocolloid dispersion. The increase in starch paste viscosity was due to synergistic interactions of starch and gums. Pea starch pastes exhibited the typical shear thinning behaviour and the addition of a hydrocolloid altered the degree of pseudoplasticity of a starch paste. Mustard mucilage, for example, increased the pseudoplasticity of pea starch pastes, and exhibited higher paste viscosities at low shear rates.

Browning Reactions in Foods

This chapter provides the latest information on browning reactions in foods, including mechanisms and methods of control. Since the second edition, the Maillard reaction or glycation has been shown to play an important role in aging and chronic diseases in humans. This chapter has incorporated the latest information on the structure and formation of melanoidins as well as the effect of polyphenols on these polymers. Also included is a discussion of the role that Strecker degradation plays in the conversion of asparagines to acrylamide. Besides the Maillard reaction, this chapter provides an in-depth review of both caramelization and ascorbic acid oxidation.

Lipase from Vicia faba minor

Abstract Lipase was partially purified from small faba beans by ethanol precipitation and Sephadex gel filtration and characterised by disc gel electrophoresis, isoelectric focusing and molecular weight determination in the presence of sodium dodecyl sulphate. Kinetic studies demonstrated that the properties of the enzyme conformed generally to those of lipases from other sources. The isoelectric point was pH 4·8, and electrophoresis at pH 9·3 revealed one lipase band in the Rf0·25–0·31 region. The molecular weight was 210,000 ± 20,000. The possible importance of lipase is discussed with respect to the degradation of small faba bean lipids and to chemical changes occurring during storage of processed faba beans.

Turbidimetric measurement of haze in canola oil by acetone precipitation

Formation of turbidity in canola oil was facilitated with addition of acetone, and a method to measure the sediment content based on the oil turbidity has been developed. Canola oil was mixed with acetone at the ratio of 60:40, and the turbid solution developed in an ice bath for 20 min. The turbidity of the oil solution was determined by a turbidimeter. The relation between turbidity of the oil solution and sediment content was nonlinear and could be correlated by a second-order polynomial. There was no difficulty in the development of turbidity in canola oil solutions in the presence of added lecithin (2%, w/w). However, with added lecithin, turbidity was 23% higher at the same sediment content.

Cereals and Legumes

Cereal grains and legumes are complex biological structures with incredible importance as human dietary staples worldwide. Postharvest conditions and treatments, including storage, germination, and fermentation, are capable of causing significant biochemical changes that affect the nutritive value of these foods. In this chapter, mature grain and seed structure, as well as macronutrient synthesis, classifications, and storage forms within the seeds are discussed. The effects of storage conditions, and germination and fermentation processes are examined with regard to proximate and micronutrient composition, phytonutrient contents, the presence of anti-nutritional factors, and overall food quality.

Buckwheat lipoxygenase: Inactivation by gamma-irradiation

Abstract Lipoxygenase (LOX) activity was detected in buckwheat extracts, and was shown to have a pH optimum of 6·5. LOX activity was not affected during 6 days of germination. The specific activity increased when ground buckwheat seeds were extracted with 0·01% or 0·1% solutions of calcium chloride or magnesium chloride, compared to extractions with distilled water or 1·0% solutions of either of these salts. Increase in specific activity was greater in the presence of calcium ions compared to magnesium ions. Gamma-irradiation of buckwheat seeds up to 4 kGy resulted in a decrease in LOX activity to a level of approximately 22% of the untreated control, but increased to approximately 43% of the control at a dose of 6 kGy. These results suggest that gamma-irradiation reduces LOX activity, but is not likely to completely prevent lipid oxidation in buckwheat.

Fruits and Vegetables

This chapter reviews those biochemical changes occurring in postharvest fruits and vegetables which affect quality. New developments in plant physiology have been incorporated including regulation of ethylene and genes encoding the enzymes involved in chlorophyll biosynthesis. The latest information on plant cell walls and textural changes during ripening is also included. A new section on flavor, including aroma and taste, has been added, as well as new developments in postharvest storage.

Solvent effects on phase transition behavior of canola oil sediment

Differential scanning calorimetry (DSC) was used to study the melting and crystallization behavior of waxy sediment in canola oil and in mixtures (1:1, w/w) of oil and acetone or hexane under dynamic heating/cooling regimes. In the presence of a solvent, the DSC melting peak of sediment shifted to lower temperatures, suggesting that sediment was more soluble in the solvent/oil systems than in oil alone. This effect was greater with hexane than with acetone. The influence of a solvent on crystallization was more complex. With inclusion of hexane, the crystallization temperature of sediment was always lower than that in oil. With acetone, however, the crystallization temperature of sediment was slightly lower at high sediment content, but higher at low sediment content than in oil alone. The differences in melting and crystallization behavior of sediment in canola oil and the solvent/oil systems were attributed to solubility and viscosity effects. Variation in the crystalline solid structures of sediment was not evident from the melting enthalpies associated with the phase transformation.