Antioxidant properties of desferrioxamine E, a new hydroxamate antioxidant

Antioxidant properties of desferrioxamine E, a cyclic trihydroxamate produced by microorganisms, were tested and compared to those of desferrioxamine B and butylated hydroxyanisole (BHA). Desferrioxamine E exhibited significant antioxidant effects in linoleic acid emulsions as well as in emulsions of linoleic acid and β-carotene. In concentrations of 100 ppm, the effect of both desferrioxamines in linoleic acid emulsion was equal to that of BHA. The antioxidant activity of the desferrioxamines in emulsions of β-carotene and linoleic acid was significantly higher than that of BHA. In addition, the initial rate of β-carotene destruction was significantly lower when desferrioxamines were added to the emulsion.     

Antioxidant properties of myricetin and quercetin in oil and emulsions

The effect of quercetin and myricetin on the stability of sunflower oil and oil-in-water emulsions was studied by storage experiments monitored by measurement of peroxide values, conjugated dienes, and headspace volatile analysis. Myricetin showed strong antioxidant activity in oils stored at 60 or 30°C and in oil-in-water emulsions stored at 30°C, whether tocopherols or citric acid were present or not; however, quercetin showed similar antioxidant activity in stripped sunflower oil but no activity in oils that contained tocopherols and citric acid. This showed that myricetin is effective owing to strong radical scavenging and metal-chelating properties, whereas quercetin has weaker radical scavenging activity, although it is also active by metal-chelation. The effects of copper and iron salts on the antioxidant activity of myricetin and quercetin were studied in sunflower oil and oil-in-water emulsions. Quercetin and myricetin enhanced the prooxidant effect of cupric chloride in oil-in-water emulsions (pH 7.4), but this effect was not observed with cupric stearate. The addition of myricetin to emulsions that contained ferric chloride at pH 5.4 also produced a strong prooxidant effect, and small prooxidant effects of flavonols were also detected in the presence of cupric chloride under these conditions. However, myricetin and quercetin reduced the prooxidant effect of ferric palmitate in oils. Myricetin also showed a strong antioxidant effect in oil that contained cupric stearate, although quercetin had no significant effect on the oxidative stability of this system. It therefore appears that flavonols may exert a prooxidant effect in the presence of metal salts, but the nature of the metal salt is important in determining whether a prooxidant effect occurs.     

Synthesis, Molecular Characterization and Preliminary Antioxidant Activity Evaluation of Quercetin Fatty Esters

Quercetin shows interesting pharmacological effects, but its use in topical applications is limited by its low skin permeability and solubility. In this work, the synthesis of highly lipophilic quercetin esters with oleic, linoleic and linolenic acid useful as topical quercetin prodrugs is reported. Partial OH esterification is advisable to maintain the antioxidant activity of these compounds; tetraesters and triesters can be achieved by modulating the reaction conditions utilized for the total esterification of quercetin. The chemical structures of the esters were proven by spectroscopic techniques; quantum chemical NMR calculation were mandatory to unequivocally assign the free position in triesters. Finally, the antioxidant activity of all the synthesized compounds was determined by the 2,2-diphenyl-1-picryl-hydrazyl method and by 2,2-azinobis(3-ethyl-benzothiazoline-6-sulfonic acid) assay.     

Cucumber cotyledon lipoxygenase oxygenizes trilinolein at the lipid/water interface

The reactivity of cucumber cotyledon lipoxygenase with trilinolein was examined. The activity of the enzyme against linoleic acid rapidly decreased with increasing pH of the assay solution, and essentially no activity could be detected above pH 8.5. The rapid decrease in activity was not the result of an inactiveness of the enzyme at alkaline pH, because with trilinolein, the enzyme showed a broad pH-activity profile, and substantial activity could be detected even at pH 9.0. Rather, the decrease in activity was due to the dissociation of the linoleic acid emulsion into acid-soap aggregates and/or the monomeric form, depending on the ionization of the terminal carboxylic group. This suggests that cucumber cotyledon lipoxygenase acts only on an insoluble substrate at the lipid/water interface but not on a soluble one. High-performance liquid chromatography analyses of the products formed from trilinolein revealed that the enzyme inserted oxygen into the acyl moiety of trilinolein without hydrolysis of the ester bonds. Preincubation of the enzyme with triolein emulsions effectively abolished its activity against trilinolein added afterward. Furthermore, the enzyme was adsorbed on the trilinolein or triolein emulsion droplets in an essentially irreversible manner. A reaction velocity curve of the enzyme with trilinolein showed saturation kinetics. This is thought to be due to a regional substrate deficiency as the reaction proceeds. These lines of evidence indicate that the enzyme, once bound to the lipid/water interface, is unable to break free and bind to other emulsions.     

Antioxidant activity of phenolic compounds in 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidation: Synergistic and antagonistic effects

Interactions between phenolic antioxidants in binary systems were determined by adding two antioxidants simultaneously in equimolar proportions to an aqueous dispersion of linoleic acid that was then subjected to 2,2′-azobis (2-amidinopropane) dihydrochloride-induced oxidation and by evaluating the protective effect of the antioxidant mixture. The antioxidant power of the mixture was then compared with the expected antioxidant activity calculated by the sum of efficiencies of each compound separately, relative to their proportions in the mixture. If it was higher, a synergy was pointed out whereas a lower value was representative of an antagonism. Thus, synergistic effects were observed between rosmarinic acid and quercetin, or rosmarinic acid and caffeic acid, whereas antagonistic effects were obtained with the following mixtures: α-tocopherol/caffeic acid; α-tocopherol/rosmarinic acid; (+)-catechin/caffeic acid; and caffeic acid/quercetin. These mixture effects are partly explained by regeneration mechanisms between antioxidants, depending on the chemical structure of molecules and on the possible formation of stable intermolecular complexes.     

The Interactions Between Rapeseed Lipoxygenase and Native Polyphenolic Compounds in a Model System

The focus of the present research was to study inhibition of lipoxygenase activity by rapeseed native polyphenols and the interactions between those compounds and the enzyme. The enzyme and polyphenolic compounds (polyphenols, phenolic acids) were extracted from rapeseed (Brassica napus) varieties Aviso and PR45DO3. The total phenolic compounds concentration in tested rapeseed was 1,485–1,691 mg/100 g d.m. (dry matter) and the free phenolic acids content in both rapeseed varieties was about 76 μg/100 g d.m. The isolated proteins showed lipoxygenase activity. Prooxidant properties of phenolic compounds in the presence of lipoxygenase and linoleic acid were observed rather in the case of extracts containing a relatively high concentration of miscellaneous polyphenols. Antioxidant properties were recorded in the case of phenolic acid extracts which contain only 1.4–1.9% of phenolics present in raw phenolic extracts. We propose that the prooxidant effect of phenolic compounds comes from quinone and oxidized polyphenols formation. The observed antioxidant activity of phenolic acid extracts is probably due to their ability to scavenge free radicals formed from linoleic acid. However, reduction of lipoxygenase ferric to ferrous ions, which prevent the activation of the enzyme and inhibited its activity, was also observed.     

Antioxidant properties of polyphenol‐containing extract from soybean fermented with Saccharomyces cerevisiae

The antioxidant properties and total phenolic compounds of soybean extract fermented with Saccharomyces cerevisiae during 24 h were evaluated. Total polyphenolic compounds extracted in ethanol/water (1:1) solution were 789.54 mg/g dry extract, and flavonoids were 169.47 mg quercetin equivalents/g of dry extract. Reducing power (91.18%) and DPPH scavenging (79.30% at 4‐times diluted) were excellent, and so high as BHA, 92.17% and 73.8% respectively, while superoxide anion scavenging showed poor inhibition (4876 equivalent SOD U/g). Antioxidant activity in linoleic acid/water emulsion system of fermented extract measured as peroxide formation inhibition at 37 °C was the strongest (95.62%), while it exerted a moderate inhibition for conjugated dienes and thiobarbituric acid reactive substances (64.77% and 54.33%). At 80 °C the antioxidant activity assayed at a higher concentration was less effective (29.35% on CD; 74.58% on PV and 35.04% on TBARS).     

Soybean lipoxygenase-promoted oxidation of free and esterified linoleic acid in the presence of deoxycholate

Lipoxygenase (EC 1.13.11.12) catalyzes the reaction between oxygen and polyunsaturated fatty acids to give fatty acid hydroperoxides. Recent work showed that soybean lipoxygenase 1 can oxidize diacylglycerols when deoxycholate is present in the reaction medium. Conditions were sought to maximize 1,3-dilinolein oxidation with a commercial soybean lipoxygenase preparation. It was found that dilinolein was oxidized most rapidly in a multicomponent buffer medium that contained 10 mM deoxycholate between pH 8 and 9. When dilinolein oxidation was conducted in the individual components of the multicomponent buffer, the oxidation rate decreased two- to threefold. Addition of 0.2 M NaCl to one of the components, Tricine buffer, caused a twofold increase in the oxidation rate, demonstrating that high ionic strength is a major factor promoting rapid oxidation in the multicomponent buffer. In the deoxycholate multicomponent buffer, the order of reactivity toward oxidation was monolinolein>methyl linoleate≈ linoleic acid>dilinolein. Competition experiments in which mixtures of the substrates were presented simultaneously to lipoxygenase in the presence of deoxycholate showed that linoleic acid was the most reactive substrate. When no surfactant was present or when the surfactant was Tween 20, linoleic acid was the most rapidly oxidized substrate. Overall, the results demonstrate that monolinolein and methyl linoleate are just as reactive, or more so, as linoleic acid to oxidation by lipoxygenase under specified reaction conditions. In competition experiments, linoleic acid oxidation predominates, probably because its free carboxyl functionality allows it to be preferentially bound to the active site of lipoxygenase.     

Lipoxygenase activity in olive (Olea europaea) fruit

The present work was designed to characterize lipoxygenase activity in olive fruit pulp, in order to determine its significance in the biosynthesis of virgin olive oil aroma. Lipoxygenase activity has been detected in particulate fractions of enzyme extracts from olive pulp subjected to differential centrifugation. The activity in different membrane fractions showed similar properties, with optimal pH in the range of 5.0–5.5 and a clear specificity for linolenic acid, which was oxidized at a rate double that of linoleic acid under the same reaction conditions. The enzyme preparations displayed very low activity with dilinoleoyl phosphatidylcholine, suggesting that olive lipoxygenase acts on nonesterified fatty acids. The enzyme showed regiospecificity for the Δ-13-position of both linoleic and linolenic acid, yielding 75–90% of Δ-13-fatty acid hydroperoxides. Olives showed the highest lipoxygenase activity about 15 wk after anthesis, with a steady decrease during the developmental and ripening periods. Olive lipoxygenase displayed properties that support its involvement in the biogenesis of six-carbon volatile aldehydes, which are major constituents of the aroma of virgin olive oil, during the process of oil extraction.     

A kinetic study of the autoxidation of methyl linoleate and linoleic acid emulsions in the presence of sodium chloride

Autoxidation of linoleic acid and methyl linoleate emulsions in aqueous buffer solutions was studied by the rate of oxygen uptake. The oxidation rates of methyl linoleate emulsions increased with an inerease in the pH of the buffer solution. With linoleic acid, oxidation rates rose until the increase reached its peak at pH 5.50 and then decreased gradually to a minimum at pH 8.00. Oxidation rates of methyl linolente and linoleic acid emulsious decreased with increased concentration of NaCl in the system. The effect of variation of pH of the emulsion in the range investigated was similar to that in emulsions without NaCl. There was no evidence that NaCl accelerated the oxidation rates in the system. The observed inhibitory effect of NaCl may result from the decreased solubility of oxygen in the emulsion with the increased concentration of NaCl. Consequently the availability of oxygen would be a limiting factor in oxidation rates. The activation energy for the monomolecular and bimolecular reactions of methyl linoleate and linoleic acid autoxidation was found to be independent of the pH value and sodium chloride concentration of the system. The energy of activations for the monomolecular and bimolecular reactions of methyl linoleate and of linoleic acid are 22,000, 18,200, 19,600, and 16,400 cal./mol., respectively. Spectrophotometric studies of the autoxidized emulsions of linoleic acid and its methyl ester indicate that the magnitude of the absorption at 2325 Å is the same at different pH values. On the contrary, the secondary products showing absorption at 2775 Å are to some extent dependent on the pH value of the emulsion.     

Effect ofd-α-tocopherol analogues on lipoxygenase-dependent peroxidation of phospholipid-bile salt micelles

In order to know whether or not vitamin E acts as an effective antioxidant in lipoxygenase-dependent peroxidation of phospholipids, the effect of vitamin E and vitamin E analogues, 2,2,5,7,8-pentamethyl-6-hydrohychroman (PMC) and 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox C), was investigated in enzymatic lipid peroxidation of bile salt micelles of pig liver phosphatidylcholine (PC) using soybean lipoxygenase. 15-Hydroperoxy-5,8,11,13-eicosatetraenoic acid was exlusively produced by the reaction with the PC molecular species containing arachidonic acid moiety, indicating that the hydroperoxidation of pig liver PC entirely progresses through the enzymatic reaction. PMC suppressed the accumulation of PC-hydroperoxides (PC-OOH) more efficiently than eitherd-α-tocopherol (α-Toc) or Trolox C, and 50% inhibition concentration by PMC was close to that of quercetin, a known lipoxygenase inhibitor from natural origin. The antioxidant activity of PMC was also superior to that of either α-Toc or Trolox C in ferrous ion-induced nonenzymatic oxidation of PC micelles in the presence of a trace amount of PC-OOH, although the radical-scavenging activities of these compounds in solution were similar or comparable to one another. In conclusion, PMC is more effective than α-Toc as an inhibitor of lipoxygenase reaction with phospholipids and of autoxidation in phospholipids. The phytyl chain of α-Toc seems to be unfavorable for exerting an inhibitory effect on lipoxygenase reaction with phospholipid-bile salt micelles.     

Effect of substrate polarity on the activity of soybean lipoxygenase isoenzymes

In order to characterize the several isoenzymes of soybeans, they were examined with respect to the effect of the polar nature of the substrate. In general, lipoxygenase-1 was most active when presented with charged substrates such as the anionic form of linoleic acid or of potassium linoleyl sulfate, whereas lipoxygenase-2 and-3 preferred nonpolar substrates such as unionized linoleic acid, methyl linoleate, linoleyl methane sulfonate, 10,13-nonadecadieneamine, or linoleyl acetate. Linoleyl sulfate, which has been advanced as an excellent readily soluble substrate for lipoxygenase, was indeed the best substrate found for lipoxygenase-1. Lipoxygenase-2 and-3 were, by contrast, totally inactive against this substrate. The favorable response of linnoleic acid to lipoxygenase-2 and-3 at pH 6.8 was ascribed to the anomalously high pK_a value of linoleic acid compared to that of short chain carboxylic acids. The pH-activity profile obtained with lipoxygenase acting on linoleyl sulfate (which was charged at all pH values examined) was shifted to lower pH values compared to the linoleic acid activity profile. The effect of changing from the charged to the uncharged substrate, when tested against lipoxygenase-1, was to increase the K_m by an order of magnitude.     

毛尖茶叶中的黄酮类化合物对脂氧合酶的抑制性

采用紫外可见光分光光度法,以亚油酸钠为底物,研究了都匀毛尖茶叶中的黄酮类化合物对大豆脂氧合酶活性的抑制作用。结果表明,毛尖茶叶中的黄酮类化合物的提取率为5.227%,毛尖茶叶中的黄酮类化合物对大豆脂氧合酶有一定的抑制效果,并且随着黄酮类化合物的浓度的增加抑制效果增强。     

Lipophilization of dihydrocaffeic acid affects its antioxidative properties in fish‐oil‐enriched emulsions

The aim of the present study was to evaluate the antioxidative effect of lipophilized dihydrocaffeic acid, i.e., octyl dihydrocaffeate and oleyl dihydrocaffeate. Furthermore, the relationship between the measured efficacy of the antioxidants in emulsions, their partitioning into different phases of an emulsion system and their in vitro antioxidant properties was also evaluated. Lipid oxidation in the emulsions was affected by the antioxidants applied. Thus, despite a reduced antioxidant activity of lipophilized dihydrocaffeic acid in the antioxidant assays, lipophilized dihydrocaffeic acid was more efficient than caffeic and dihydrocaffeic acids. Octyl dihydrocaffeate had a significantly higher antioxidative effect than oleyl dihydrocaffeate in emulsions. The results partly supported the polar paradox hypothesis, since lipophilized compounds resulted in increased oxidative stability. However, the decreased antioxidative efficacy with increasing alkyl chain length esterified to dihydrocaffeic acid supported a newly suggested cut‐off effect hypothesis. This hypothesis suggests that when a certain level of hydrophobicity is obtained for lipophilized phenolic acids, the ester forms micelles in the aqueous phase rather than being located at the interface or oil phase. This phenomenon is suggested to explain the reduced antioxidant activity of oleyl dihydrocaffeate compared with octyl dihydrocaffeate. Practical application: The finding that lipophilization of phenolic compounds increase their efficacy opens up new possibilities for producing new and more efficient antioxidants for food systems. However, the results also show that optimization of the chain length for each type of phenolic compound may be necessary. Since these compounds may have a much higher efficacy against lipid oxidation a lower amount of antioxidant will be necessary to obtain the same effect. This would decrease the costs. In addition, the use of synthetic antioxidants, that might have toxic effect in vivo, can be avoided. The raw materials used for the lipophilized compounds are natural compounds, however the fate of the lipophilized compounds in vivo should eventually be evaluated.     

Antioxidant activity of amino acids bound to trolox-C

Various amino acids, selected for their potential antioxidant activity, were, covalently attached to 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox-C), a lower homolog of vitamin E that has great antioxidant effectiveness. The resulting Troloxylamino acids (T-AA) had greater antioxidant effectiveness than Trolox-C in a linoleate emulsion system oxidized by hemoglobin. Troloxyl-tryptophan-methyl ester and Troloxyl-methionine-methyl ester were the most effective T-AA evaluated in the linoleate emulsion. However, butylated hydroxyanisole (BHA), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT) and α-tocopherol were more antioxidant than any T-AA in the emulsion system. In a Schaal oven test at 45 C. Trolox-C was by by far the most effective antioxidant evaluated in corn oil. BHT and Troloxylcysteine had significant antioxidant activity in corn oil, but no other T-AA was antioxidant in corn oil. In butter oil, Trolox-C again had the highest antioxidant activity, and BHA and BHT were also highly antioxidant. All t-AA had antioxidant activity in butter oil, with Troloxyl-methioninc and Troloxyl-cysteine having the grcatest antioxidant effectiveness. The T-AA of highest antioxidant activity were hydrolyzed by chymotrypsin and/or trypsin, in vitro.     

Enzymatic oxidations of linoleic acid and glycerol-1-monolinoleate in doughs and flour-water suspensions

Enzymatic oxidations of linoleic acid and glycerol-1-monolinoleate, and the products formed by these oxidations in flour-water suspensions and doughs were studied. Oxidation of linoleic acid leads through simultaneous reactions to two isomeric hydroperoxy-octadecadienoic acids and two isomeric hydroxy-epoxy-octadecenoic acids. Reduction of the former leads to hydroxyoctadecadienoic acid, while hydrolysis of the latter yields trihydroxy-octadecenoic acids. The hydroperoxy acids are formed by the enzyme lipoxygenase (E.C. 1.13.1.13), whereas the hydroxy-epoxy acids are formed by combined action of lipoxygenase and an unknown factor Y. This factor Y is localized in the gluten fraction. Oxidation of glycerol-1-monolinoleate gives a product having a hydroperoxy group and acis,trans conjugated diene bond. The oxidation of glycerol-1-monolinoleate is probably a lipoxygenase reaction.     

Behavior of alpha,gamma, and delta tocopherols with linoleic acid in aqueous media

Tocopherols can exhibit opposite effects in aqueous media on linoleic acid autoxidation rate. The effect which was observed depended on tocopherol concentration and on the tocopherol itself. At 0.05 mole of tocopherol per mole of linoleic acid, α-tocopherol was prooxidant while in similar conditions, δ-tocopherol was anti-oxidant as well as γ-tocopherol. However, this latter one exhibited a slight antioxidant activity. When tocopherol concentration decreased (twice as weak), α-tocopherol still exhibited the same pro-oxidant activity, while the antioxidant effect of γ and δ tocopherols was increased. The study of tocopherol stability by HPLC has shown that tocopherol oxidation increased in order δ < γ < α. There was a relationship between the ability for a tocopherol to be easily oxidized by air and its prooxidant activity. Tocopherol oxidation would enhance the formation of a perhydroxyl radical ([·OOH] or one of this type [O₂0=, ·OH]) which was responsible for the prooxidant effect.     

Surfactant Concentration,Antioxidants, and Chelators Influencing Oxidative Stability of Water‐in‐Walnut Oil Emulsions

Effects of surfactant concentration, antioxidants with different polarities, and chelator type on the oxidative stability of water‐in‐stripped walnut oil (W/O) emulsions stabilized by polyglycerol polyricinoleate (PGPR) were evaluated. The formation of primary oxidation products (lipid hydroperoxides) and secondary oxidation products (hexanal) decreased with increasing PGPR concentrations (0.3–1.0 wt% of emulsions). Excess surfactant might solubilize lipid hydroperoxides out of the oil–water interface, resulting in the decreased lipid oxidation rates in W/O emulsions. At concentrations of 10–1000 μM, the polar Trolox demonstrated concentration‐dependent antioxidant activity according to both hydroperoxide and hexanal formation. The antioxidant efficiency of the non‐polar α‐tocopherol was slightly reduced at the higher range of 500–1000 μM based on hydroperoxide formation. Both ethylenediaminetetraacetic acid (EDTA) and deferoxamine (DFO) at concentrations of 5–100 μM reduced the rates of lipid oxidation at varying degrees, indicating that endogenous transition metals may promote lipid oxidation in W/O emulsions. EDTA was a stronger inhibitor of lipid oxidation than DFO. These results suggest that the oxidative stability of W/O emulsions could be improved by the appropriate choice of surfactant concentration, antioxidants, and chelators.     

The Efficacy of Compounds with Different Polarities as Antioxidants in Emulsions with Omega-3 Lipids

According to the so-called polar paradox hypothesis, the efficacy of an antioxidant in emulsions is highly affected by its polarity and thereby location in the different phases. However, other factors also affect the efficacy of antioxidants in multiphase systems. The aim of this study was to evaluate the efficacy of antioxidants [ascorbic acid, ascorbyl palmitate, ascorbyl CLA and CLA (conjugated linoleic acid)] with different polarities in two different emulsion systems: o/w emulsion (5% oil) and w/o emulsion (98% oil) stabilized with citrem and PGPR, respectively. The efficacy of the antioxidants was compared to their partitioning in an o/w emulsion system and to results obtained from different antioxidant assays: iron reducing power, chelating activity and radical scavenging activity. For the w/o emulsions the efficacy of the antioxidants followed the polar paradox hypothesis: ascorbyl palmitate = ascorbyl CLA > ascorbic acid ≥ CLA > reference. For the o/w emulsion the antioxidative effects were not in accordance with the polar paradox. In the beginning of the storage, ascorbyl palmitate and ascorbic acid were most efficient, however in the end they acted as prooxidants. Ascorbyl CLA was located at the interface but was inactive as an antioxidant. This may be due to impurities or interaction with citrem.     

Soybean lipoxygenase is active on nonaqueous media at low moisture: a constraint to xerophilic fungi and aflatoxins?

Previous workers have reported that certain products of the lipoxygenase pathway are detrimental either to the development and growth of Aspergillus species or to aflatoxin production by these organisms. Since Aspergillus often thrives on “dry” stored grains, depending on the level of the relative humidity, we sought to determine if lipoxygenase could catalyze the oxidation of linoleic acid on these “dry” substrates equilibrated at various relative humidities. A desiccated model system, previously adjusted to pH 7.5, was composed of soybean extract, linoleic acid, and cellulose carrier. The model system was incubated for up to 24 h at four relative humidities ranging between 52 and 95% to determine the extent of oxidation catalyzed by lipoxygenase, compared with heat-inactivated controls. Oxidation in the active samples was much greater than in the controls at all relative humidities, and oxidation was principally enzymatic as demonstrated by chiral analysis of the linoleate hydroperoxides formed. The main product was 13S-hydroperoxy-9Z,11E-octadecadienoic acid, accompanied by a significant percentage of 9S-hydroperoxy-10E,12Z-octadecadienoic acid. Since the products became more racemic with time of incubation, autoxidation appeared to be initiated by the lipoxygenase reaction in dry media. Additionally, the biological relevance of lipoxygenase activity was tested under these xerophilic conditions. Thus, enzyme-active and heat-inactivated defatted soy flour amended either with or without 3.5% by weight linoleic acid was inoculated with fungal spores and incubated at 95% relative humidity. Although fungal growth occurred on all treatments, samples inoculated with Aspergillus parasiticus showed significantly less aflatoxin in the enzyme-active samples, compared to inactivated flour. Addition of linoleic acid had little effect, possibly because the defatted soy flour was found to contain 1.7% residual linoleic acid as glyceride lipid.