Eggplant lipoxygenase (Solanum melongena): product characterization and effect of physicochemical properties of linoleic acid on the enzymatic activity

The influence mechanism of phospholipids structure and composition changes caused by oxidation on the formation of flavor substances in sturgeon caviar

The oxidation-induced phospholipids (PLs) underwent structural and compositional analysis, alongside the establishment of a simulation system to verify the link between phospholipid oxidation and flavor substances formation in sturgeon caviar. Structural alterations of PLs were tracked using 31P and 1H nuclear magnetic resonance (NMR), electron spin resonance spectroscopy (ESR), and Raman spectroscopy. The findings revealed a reduction in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) from 82.3% and 10.4% to 58.2% and 5.8% respectively. Free radical signals exhibited an initial increase followed by a decrease. The diminished intensity in Raman spectra at 970 and 1080 cm-1 indicated reduced fat unsaturation attributable to PLs oxidation. Correlation analysis highlighted a significant association between PC and PE containing C22:6, C20:5, C20:4, and C18:2 with flavor substances, suggesting their role as key precursors for flavor development. This study established a theoretical basis for understanding the change of flavor quality in sturgeon caviar during storage.

Formation of Lipid-Derived Flavors in Dry-Cured Mackerel (Scomberomorus niphonius) via Simulation of Autoxidation and Lipoxygenase-Induced Fatty Acid Oxidation

In this study, lipoxygenase (LOX) extracted from dry-cured mackerel was purified, resulting in a 4.1-fold purification factor with a specific activity of 493.60 U/min·g. LOX enzymatic properties were assessed, referring to its optimal storage time (1-2 days), temperature (30 °C), and pH value (7.0). The autoxidation and LOX-induced oxidation of palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:2n9c), linoleic acid (C18:2n6c), arachidonic acid (C20:4), EPA (C20:5), and DHA (C22:6n3) were simulated to explore the main metabolic pathways of key flavors in dry-cured mackerel. The results showed that the highest LOX activity was observed when arachidonic acid was used as a substrate. Aldehydes obtained from LOX-treated C18:1n9c and C18:2n6c oxidation, which are important precursors of flavors, were the most abundant. The key flavors in dry-cured mackerel were found in the oxidative products of C16:0, C18:0, C18:1n9c, C18:2n6c, and C20:4. Heptanaldehyde could be produced from autoxidation or LOX-induced oxidation of C18:0 and C18:1n9c, while nonal could be produced from C18:1n9c and C18:2n6c oxidation. Metabolic pathway analysis revealed that C18:1n9c, C18:2n6c, EPA, and DHA made great contributions to the overall flavor of dry-cured mackerel. This study may provide a relevant theoretical basis for the scientific control of the overall taste and flavor of dry-cured mackerel and further standardize its production.

HPLC Analysis and Biochemical Characterization of LOX from Eschscholtzia californica Cham

BACKGROUND

Plant lipoxygenases (LOXs, EC 1.13.11.12) are involved in lipid degradation, regulation of growth and development, senescence, and defence reactions. LOX represents the starting enzyme of the octadecanoid pathway. The aim of the work was to purify LOX from California poppy (Eschscholtzia californica Cham.), to determine its biochemical properties and to identify and quantify the products of LOX reaction with unsaturated fatty acids.

METHODS

LOX from California poppy seedlings was purified by hydrophobic chromatography (Phenyl-Sepharose CL-4B) and by ion-exchange chromatography (Q-Sepharose). The isolated LOX was incubated with linoleic acid used as a substrate. The HPLC experiments were performed with the Agilent Technologies 1050 series HPLC system. For the preparative separation of a mixture of hydroxy fatty acids from the sample matrix, the RP-HPLC method was used (column 120-5 Nucleosil C18). Then, the NP-HPLC analysis (separation, identification, and determination) of hydroxy fatty acid isomers was carried out on a Zorbax Rx-SIL column.

RESULTS

The purified LOX indicates the presence of a nontraditional plant enzyme with dual positional specificity (a ratio of 9- and 13-hydroperoxide products 1:1), a relative molecular mass of 85 kDa, a pH optimum of 6.5, an increasing activity stimulation by CaCl₂ till 2 mM, and a high substrate reactivity to linoleic acid with kinetic values of KM 2.6 mM and Vmax 3.14 μM/min/mg.

CONCLUSIONS

For the first time, the LOX from California poppy seedlings was partially purified and the biochemical properties of the enzyme were analyzed. A dual positional specificity of the LOX found from California poppy seedlings is in agreement with the results obtained for LOXs isolated from other Papaveraceaes. A 1:1 ratio of 9-/13-HODE is attractive for the simultaneous investigation of both biotic stress responses (indicated by the 9-HODE marker) and the biosynthesis of jasmonic acid and jasmonates (indicated by the 13-HODE marker).

State of polyphenols in the drying process of fruits and vegetables

This review presents an overview of drying technologies and its impact on the polyphenol content of vegetables and fruits. Polyphenols contribute to many health benefits and can act as antioxidants. Specifically an increased intake of polyphenols has been shown to decrease the incidence of cardiovascular disease; furthermore, it has been shown to help reduce the risk of neurodegenerative diseases in humans. Many researchers have reported on the effect of different drying techniques on the polyphenol content in fruits and vegetables. Polyphenol degradation mechanisms proposed in literature and pretreatments that potentially lead to higher retention of polyphenols during drying are also discussed.

Effect of phenolic compounds on the oxidative stability of ground walnuts and almonds

This study reports the shift of phenolic compound role from antioxidant to prooxidant in the thermal oxidation of ground walnuts and almonds.

Effect of protonation and aggregation state of (E)-resveratrol on its hydroperoxidation by lipoxygenase

The protonation and aggregation states of (E)-resveratrol were used as tools to investigate the kinetic properties of lipoxygenase (LOX). It was found that the deprotonation of the 4'-hydroxyl group at pH values higher than the pK(a1) of (E)-resveratrol produced an increase in the LOX activity, with an optimum pH of 8.5. Moreover, the results show how LOX activity is strongly affected by the aggregation state of (E)-resveratrol. When the enzyme uses monomers of (E)-resveratrol as substrate, LOX shows a Michaelian behavior and the K(m) value can be determined (44.39 microM). However, when (E)-resveratrol concentration is increased to values higher than the critical concentration determined by fluorescence methods (35 microM at pH 8.5), LOX shows strong inhibition. These results can be interpreted as a previously unreported aggregate-induced enzyme inhibition, which can be modified by the use of different modulators of the aggregation state of (E)-resveratrol, such as cyclodextrins or ethanol. Finally, when the reaction was kinetically characterized in the optimum conditions of both aggregation and protonation state, a typical induction period was observed, along with a dependence of the hydroperoxidation rate with the hydrogen peroxide concentration.

Mung bean lipoxygenase in the production of a C6-aldehyde. Natural green-note flavor generation via biotransformation

Mung bean was investigated as a novel source of lipoxygenase in the natural production of the green-note aroma compound hexanal. Lipoxygenase extracted from mung bean catalyzed the oxidative reaction of linoleic acid, after which the intermediate hydroperoxide compound was split via green bell pepper hydroperoxide lyase to produce hexanal. In comparison to soybean lipoxygenase, mung bean lipoxygenase was found to be a good substitute as it produced 15.4 mM (76% yield) hexanal while soybean gave 60% yield. The mung bean pH profile comprised a wide peak (optimum pH 6.5) representing lipoxygenase-2 and lipoxygenase-3 isozymes, whereas two narrower peaks representing lipoxygenase-1 and lipoxygenase-2/3 isozymes were observed for soybean (optimum pH 10). Extraction at pH 4.5 was preferred, at which specific lipoxygenase activity was also the highest.

Enhanced production of hydroperoxides by immobilized lipoxygenase in the presence of cyclodextrins

The advantages of the presence of cyclodextrins in a reaction catalyzed by immobilized lipoxygenase at neutral pH are reported for the first time. The steady-state rate in the presence of beta-cyclodextrins was seven times higher than in control experiments using the same concentration of linoleic acid; furthermore the percentage of substrate conversion (and product accumulation) obtained in the presence of beta-cyclodextrins was higher than in the control assays. The optimum concentration of free linoleic acid coincided with the critical micellar concentration for linoleic acid at neutral pH. The operational stability of the immobilized enzyme increased in the presence of beta-cyclodextins, while an increase in the percentage of 13-HPOD was also observed.

Lipase-catalyzed preparation of S-propranolol in presence of hydroxypropyl β-cyclodextrins

A simple method for the preparation of S-propranolol catalyzed by a Rhizopus niveus lipase in an aqueous medium is described. Hydroxypropyl-beta-cyclodextrin was used for the first time to increase the solubility of (R,S)-O-butyryl propranolol thus permitting the reaction to be carried out in water. The formation of an inclusion complex between (R,S)-O-butyryl propranolol and hydroxypropyl-beta-cyclodextrin was studied and a stoichiometry of 1:1 was determined. The influences of the hydroxypropyl-beta-cyclodextrin concentration, pH and percentage of ethanol on the enzymatic activity were also investigated. Under the conditions presented in this paper, values of ee(s) of 90% and E=48 were obtained.

Purification of a novel lipoxygenase from eggplant (Solanum melongena) fruit chloroplasts

A novel membrane lipoxygenase (LOX; EC 1.13.11.12) from eggplant (Solanum melongena L. cv. Belleza negra) fruit chloroplasts has been purified 20-fold to a specific activity of 207 enzymatic units per mg of protein with a yield of 72%. The purification was carried out by sonicating the chloroplastic membranes in the presence of Triton X-114 followed by phase partitioning and anion exchange chromatography. The purified membrane LOX preparation consisted of a single major band with an apparent molecular mass of 97 kDa after sodium dodecyl sulfate polyacrylamide gel electrophoresis. The results obtained using intact chloroplasts indicate that the enzyme is not localized in the stroma. When the enzyme reacts with linoleic acid, it produces a single peak, which comigrates with standard 9-hydroperoxy-octadecadienoic acid. A physiological role for this chloroplastic LOX is proposed.