Transformation of substituted cinnamic acids using l-cysteine metal complexes in aqueous media

4-Hydroxycinnamic, 4-methoxycinnamic, ferulic and cinnamic acids were both non-oxidatively and oxidatively decarboxylated in alkaline aqueous media in the presence of l-cysteine–Fe(II) and l-cysteine–Co(II) heterogeneous catalysts using hydrogen peroxide or molecular oxygen. GC/MS analysis of diethylether extracts of reaction mixtures confirmed that the addition of hydrogen peroxide resulted predominantly in oxidative decarboxylation of substituted cinnamic acids, producing the corresponding carbonyl compounds (4-hydroxybenzaldehyde, 4-methoxybenzaldehyde, vanillin, benzaldehyde). On the other hand, saturation of this heterogeneous reaction system with molecular oxygen led to the formation of a variety of products, probably via peroxoacid anions or peroxoradical intermediates, e.g., ferulic acid was transformed to vinylguaiacol and vanillin with yields of 22% and 0.7%, respectively.     

Enzymatic formation of styrene during wheat beer fermentation is dependent on pitching rate and cinnamic acid content

Styrene is formed by the thermal decarboxylation of cinnamic acid during wort boiling or by enzymatic decarboxylation during fermentation. The enzymatic reaction processes simultaneously to the decarboxylation of ferulic‐ and p‐cumaric acid to clove‐like 4‐vinylguaiacol and phenolic 4‐vinylphenol by the same PAD1 and FDC1 decarboxylase enzymes. However, the formation of styrene occurs much faster within the first hours of fermentation. In addition, the conversion of cinnamic acid starts immediately after pitching without an adaption of yeast on the new medium. Only after 120 min does the level of transposition decrease. Moreover, high cinnamic acid content in pitching wort, in combination with an open fermentation management, causes faster and higher styrene formation during this period. In contrast to the formation of 4‐vinylguaiacol, a correlation between pitching rate and styrene formation during open fermentation could be shown. The resulting time interval between styrene and 4‐vinylguaiacol formation provides scope for minimization strategies for styrene, while maintaining the typical wheat beer flavours. Copyright © 2012 The Institute of Brewing & Distilling     

CONTROL OF FERULIC ACID AND 4-VINYL GUAIACOL IN BREWING

Phenolic acids in beer are important because they can be decarboxylated to phenols, which usually impart off-flavours. An improved high performance liquid chromatographic system was used to monitor phenolic acids and phenols during the brewing process. Ferulic acid was the most significant phenolic acid found in beers prepared from malted barley. Extraction of ferulic acid from malt involved an enzymatic release mechanism with an optimum temperature about 45°C. Mashing-in at 65°C significantly decreased the release of free ferulic acid into the wort. Wort boiling produced 4-vinyl guaiacol by thermal decarboxylation, in amounts (0.3 mg/L) close to its taste threshold, from worts that contained high contents of free ferulic acid (> 6 mg/L). The capacity of yeasts to decarboxylate phenolic acids (Pof⁺ phenotype) was strong in wild strains of Saccharomyces and absent in all lager brewing yeast and most ale brewing yeasts. Some top-fermenting strains, especially those used in wheat beer production, possessed a weak decarboxylating activity (i.e. Pof^δ). During storage of beers there were appreciable temperature-dependent losses of 4-vinyl guaiacol. These results indicated that the production of 4-vinyl guaiacol is amenable to close technological control.     

Effect of thermal sterilization on ferulic, coumaric and cinnamic acids: dimerization and antioxidant activity

BACKGROUND: Some phenolic compounds, such as ferulic acid and p‐coumaric acid, exist in the form of free acids, in fruits, rice, corn and other grains. Thermal treatment (121 °C at 15–17 psi) for different times on ferulic, p‐coumaric and cinnamic acids as well as equimolar mixtures of these acids was investigated. RESULTS: Ferulic and p‐coumaric acids underwent decarboxylation, yielding dimeric products formed through their corresponding radical intermediates, while cinnamic acid was recovered unreacted. High‐performance liquid chromatography analysis showed no cross‐dimerization when equimolar mixtures of pairs of hydroxycinnamic acids were treated under the same conditions. Dimers were characterized as (E)‐4′,4″‐(but‐1‐ene‐1,3‐diyl)bis(2′‐methoxyphenol)) (dimer of 4‐vinylguaiacol) and (E)‐4,4′‐(but‐1‐ene‐1,3‐diyl)diphenol) (dimer of 4‐vinylphenol) by nuclear magnetic resonance and mass spectrometry. CONCLUSION: Sterilization by thermal processing produced dimers of ferulic and coumaric acid. The antioxidant activity of these dimers was greater than that of the respective hydroxycinnamic acids. These results may be relevant for fruits and grains that contain hydroxycinnamic acids and undergo sterilization processes such as canning. Copyright © 2012 Society of Chemical Industry     

Depression of cellulose digestion by esterified cinnamic acids

Cinnamic acids commonly found in forages were esterified to cellulose and tested for their inhibition of cellulose degradation by mixed cultures of rumen microorganisms in vitro. Concentrations of cinnamic acids used in the cellulose esterification procedure were 20–100 g kg^?1, but measurement of actual ester concentrations by alkaline extraction were not possible for solka floc cellulose and ranged from 0–9.1 g kg^?1 for Whatman No. 54 filter paper. Cinnamic acid esters significantly depressed cellulose digestion. For both cellulose sources, caffeic acid was the most inhibitory compound. Solka floc cellulose digestion was also inhibited by sinapic acid, whereas p-coumaric and ferulic acids also depressed digestion of filter paper cellulose. The proportions of volatile fatty acids produced by fermentation of filter paper were not altered by cinnamic acid esters. Esterified cinnamic acids depressed cellulose digestion to a significantly greater extent than did free cinnamic acids. The data suggest that the natural form of cinnamic acids (ester-linked to cell wall fibre) are inhibitors of microbial digestion at concentrations reported to occur in forages.     

Metabolism of food phenolic acids by Lactobacillus plantarum CECT 748

Phenolic acids account for almost one third of the dietary phenols and are associated with organoleptic, nutritional and antioxidant properties of foods. This study was undertaken to assess the ability of Lactobacillus plantarum CECT 748^T to metabolize 19 food phenolic acids. Among the hydroxycinnamic acids studied, only p-coumaric, caffeic, ferulic and m-coumaric acids were metabolized by L. plantarum. Cultures of L. plantarum produced ethyl and vinyl derivatives from p-coumaric and caffeic acids, 4-vinyl guaiacol from ferulic acid, and 3-(3-hydroxyphenyl) propionic acid from m-coumaric acid. Among the hydroxybenzoic acids analysed, gallic acid and protocatechuic acid were decarboxylated to pyrogallol and catechol, respectively. Inducible enzymes seem to be involved, at least in m-coumaric and ferulic acid metabolism, since cell-free extracts from cultures grown in the absence of these phenolic acids were unable to metabolize them. Further work is needed for the identification of the enzymes involved, since the knowledge of the metabolism of phenolic compounds is an important issue for the food industry.     

Phenolic acids from malt are efficient acetylcholinesterase and butyrylcholinesterase inhibitors

Anticholinesterase activities of mashes produced using wheat (‘Wheat Pale’) or barley malts (‘Pilsner’, ‘Pale Ale’, ‘Munich Light’, ‘Carahell’ or ‘Carared’) were studied by spectrophotometric method. The highest inhibition of acetylcholinesterase and butyrylcholinesterase was observed at 52 °C and/or 64 °C, followed by a decrease or stabilization of the activity at 72 °C. Changes in the total phenolics content in the test mashes were correlated with changes in the acetylcholinesterase and/or butyrylcholinesterase activities. Phenolic acids were singled out from phenolic compounds for more detailed studies owing to their simplicity and structural similarity to well‐known cholinesterase inhibitors. The main phenolic acids in the test malts were ferulic, gallic, p‐coumaric and vanillic acids followed by chlorogenic, caffeic, syringic, p‐OH‐benzoic, sinapic and protocatechuic acids. The anticholinesterase activities of the phenolic acids were studied using model standard solutions at concentrations similar to the maximal content of these compounds in the test mashes. Among the phenolic acids, p‐coumaric acid had the largest share in the anticholinesterase activity, even though it was present in the test mashes at a significantly lower concentration (~0.38 mm L^?1) than ferulic acid (~1.00 mm L^?1). Sinapic acid and p‐OH‐benzoic acid (0.03 and 0.01 mm L^?1, respectively) were equally efficient inhibitors as ferulic acid at ~1.00 mm L^?1. This preliminary study should be extended to other phenolic compounds from malt (wort) in the near future. Copyright © 2012 The Institute of Brewing & Distilling     

Determination of oil palm fruit phenolic compounds and their antioxidant activities using spectrophotometric methods

There is scarce information on the phenolics of oil palm fruits (Elaeis guineensis). In this study, phenolics were extracted from oil palm fruits and analysed using spectrophotometry for information on the different types of palm phenolics and their antioxidative activities. Analyses of the total phenolic content (TPC), total flavonoid content (TFC), o‐diphenols index, hydroxycinnamic acid index, flavonols index and phenol index showed ranges between 5.64 and 83.97 g L^?1 gallic acid equivalent (GAE), 0.31–7.53 g L^?1 catechin equivalent, 4.90–93.20 g L^?1 GAE, 23.74–77.46 g L^?1 ferulic acid equivalent, 3.62–95.33 g L^?1 rutin equivalent and 15.90–247.22 g L^?1 GAE, respectively. The antioxidant assay, 2,2‐diphenyl‐2‐picrylhydrazyl radical scavenging assay, showed antioxidative activities in all the extracts with results ranging from 4.41 to 61.98 g L^?1 trolox equivalent. The high antioxidant activities of the oil palm fruit phenolics were also found to increase with increasing TPC and TFC.     

Ability of Lactobacillus brevis strains to degrade food phenolic acids

The potential to degrade 15 food phenolic acids was investigated for several Lactobacillus brevis strains isolated from different sources. All the strains analysed in this study showed a similar metabolism on phenolic acids. Among the cinnamic acids assayed, only p-coumaric, ferulic and caffeic acids were metabolized by the L. brevis strains. These acids were decarboxylated to produce their corresponding vinyl derivatives. Contrarily to the results previously reported on Lactobacillus plantarum, the L. brevis strains analysed in this study were unable to subsequently reduce or metabolize these vinyl derivatives. In L. brevis, vinyl phenol, vinyl catechol, and vinyl guaiacol were the final metabolic products from p-coumaric, caffeic or ferulic acids, respectively. From the benzoic acids analysed, and similarly to L. plantarum strains, only gallic and protocatechuic acids were modified by L. brevis strains. Both acids were decarboxylated to pyrogallol and catechol, respectively. Currently, the enzymes involved in the metabolism of phenolic acids in L. brevis remain uncharacterized.     

Cell wall phenolics of white and green asparagus

Cinnamic acids influence physical and textural attributes of plant foods as they play an important role in lignification and cross‐linking of cell‐wall polymers. Several trans‐cinnamic acids have been detected in asparagus cell wall (CW), and, of these, amounts of ferulic acid (FA) and its dehydrodimers have been found to increase significantly during post‐harvest storage. The distribution of these compounds along the different sections of white and green spears, as well as their modifications during postharvest storage, has been investigated. It has been observed that the cell walls from the apical, middle and lower sections of the green spears contain equivalent amounts of FA derivatives (about 400 µg g^?1 CW), while these compounds are mainly located in the middle (681 µg g^?1 CW) and lower section (975 µg g^?1 CW) of the white ones. During asparagus post‐harvest storage a general increase of FA monomers and dimers took place that affected every section of both green and white spears. Major changes occurred in the middle and lower sections of the white asparagus, where the amounts of ferulic derivatives increased to 1700 and 1678 µg g^?1 CW after storage. A similar but less pronounced trend was observed for the green spears. Copyright © 2005 Society of Chemical Industry     

Use of microfungi in the treatment of oak chips: possible effects on wine

BACKGROUND: Oak barrels are commonly used in the aging of wines and spirits because of their positive effects on the product. In recent years the addition of oak chips has been used to introduce desirable wood aromas and flavours into wines. In this study, oak chips in saline solution or laboratory medium were inoculated with Penicillium purpurogenum, Aureobasidium pullulans, Phialemonium obovatum, Phanerochaete chrysosporium and a combination of Ph. chrysosporium and A. pullulans. After 12 weeks of incubation, oak chips (2 g L^?1) were macerated in a red wine for 17 days. Gas chromatography/mass spectrometry and high‐performance liquid chromatography were used to evaluate 14 compounds, namely furfural, furfuryl alcohol, guaiacol, syringol, cis‐β‐methyl‐γ‐octalactone, 2‐phenylethanol, 4‐vinylguaiacol, benzyl alcohol, 2,3‐butanediol, γ‐butyrolactone, benzaldehyde, 4‐ethylguaiacol, gallic acid and ellagic acid. RESULTS: The microfungal treatments increased the concentration of some components. In particular, P. purpurogenum resulted in a significant improvement in the levels of guaiacol, furfural, syringol, furfuryl alcohol and 2‐phenylethanol. CONCLUSION: Penicillium purpurogenum and Ph. chrysosporium showed a constant trend (enrichment of furfural and benzaldehyde) independent to some extent of the medium used for chip treatment. Copyright © 2010 Society of Chemical Industry     

Effect of phenolic acids on the rheological properties and proteins of hard wheat flour dough and bread

BACKGROUND: The effects of different phenolic acids on the rheological properties and gluten proteins of hard wheat flour dough and bread were investigated. Caffeic, ferulic, syringic and gallic acids were each blended with hard wheat flour at a concentration of 4.44 µmol L^?1 g^?1 flour. RESULTS: Mixing time and tolerance were reduced with the addition of phenolic acids. The phenolic acids reduced the maximum resistance to extension (R_max) and increased the extensibility of dough, with effects in the following order: gallic < syringic < ferulic < caffeic acid. The effect on R_max was more pronounced in overmixed dough. Loaf volume was most significantly decreased with the addition of caffeic acid. Extraction of sodium dodecyl sulfate‐soluble high‐molecular‐weight proteins was increased in both mixed and fermented doughs by the addition of ferulic and caffeic acids. The order of influence of the phenolic acids on the rheological properties and protein structure of dough and bread was consistent with that of their antioxidant activity. CONCLUSION: The addition of caffeic and ferulic acids reduced R_max and increased the extensibility of hard wheat flour dough by modifying the high‐molecular‐weight gluten, which resulted in decreased bread volume. Copyright © 2011 Society of Chemical Industry     

Synthesis of volatile phenols by Saccharomyces cerevisiae in wines

Vinylphenols (4-vinylphenol and 4-vinylguaiacol) are natural constituents of wine and can play a role in wine aroma. However, only white wines contain important quantities of these volatile substances which, beyond a certain concentration (limit threshold = 725 μg litre^?1 of 4-vinylguaiacol+4-vinylphenol (1:1)), can be responsible for a depreciating ‘phenolic’ or ‘pharmaceutic’ characteristic, Saccharomyces cerevisiae possesses a type-(E) enzymic activity, substituted cinnamate carboxy-lyase (SCD), which is capable of transforming, by non-oxidative decarboxylation, the phenolic acids in the must, (E) p-coumaric and (E) ferulic acids, into corresponding vinylphenols. This endocellular activity is constitutive, it is only expressed during alcoholic fermentation and with a variable intensity depending on the yeast strain. Furthermore, the enzyme is rapidly inhibited by catechic tannins, which explains why, in comparison with white wines, red and rosé wines contain low levels of vinylphenols despite having more precursors. A yeast strain with a weak SCD activity has been selected and its use in vinification should eliminate the appearance of the phenolic taint in white wines coming from grapes rich in decarboxylable hydroxycinnamic acids.     

Phenolic compounds in peanut seeds: Enhanced elicitation by chitosan and effects on growth and aflatoxin B1 production by Aspergillus flavus

Effects of chitosan and Aspergillus flavus to enhance elicitation of phenolic compounds in viable peanut seeds were conducted at two water activity levels. In vitro effects of phenolic acids on A. flavus growth and aflatoxin B₁ production were also studied. Chitosan enhanced elicitation of free phenolic compounds (FPC) at Aw .85 and .95 levels. A. flavus initially decreased and subsequently increased FPC content, but bound phenolic compounds (BPC) decreased during incubation. Chitosan + A. flavus treatment caused an increase in FPC reaching a plateau between 24–48 h at Aw .85 while BPC levels increased over the same period at both Aw levels. Major free and bound phenolic acids detected were p‐coumaric, ferulic and an unknown phenolic acid eluting at a retention time of 22 min. Generally, chitosan significantly enhanced elicitation of free ferulic and p‐coumaric acids and bound p‐coumaric acid at Aw .95. Free unknown phenolic and bound ferulic acids at Aw .85 were enhanced by chitosan. A. flavus caused significant induction of bound p‐coumaric and ferulic acids and free unknown phenol at Aw .85. Chitosan + A. flavus enhanced free p‐coumaric (3 h) and unknown phenolic acids and bound p‐coumaric acid at Aw .95 while bound ferulic acid was enhanced at Aw .85. Chitosan limited A. flavus growth and subsequent aflatoxin production by inducing susceptible tissues to produce more preformed phenolic compounds.

Analysis of liquid cultures of A. flavus revealed that p‐coumaric, ferulic, and vanillic acids and a mixture of these phenolic acids slightly inhibited mycelial growth. Production of aflatoxin B₁ by A. flavus was completely inhibited at 1 mM and 10 mM concentrations of the phenolic acids and their mixture on four days of incubation. Mode of action of phenolic acids is likely on the secondary pathway for aflatoxin B₁ production and not on the primary metabolism for fungal growth.     

Distribution of bound and free phenolic acids in oranges (Citrus sinensis) and Grapefruits (Citrus paradisi)

Free phenolic acids may be the precursors for vinyl phenols and off-flavours formed in citrus products during storage. Quantitative determination of free and bound phenolic acids in fruit parts of grapefruit (Citrus paradisi Macfadyen) and oranges (Citrus sinensis (L) Osbeck) was performed by extraction with ethyl acetate, silica gel column chromatography and HPLC analyses of samples before and after alkaline hydrolysis. The content of free and bound phenolic acids was further determined in juice derived from fruit harvested early, mid and late in season. As found previously for ferulic acid, phenolic acids occur mainly in bound forms in grapefruits and oranges. In both fruits the peels contained the major portion of cinnamic acids compared with the endocarp, and the flavedo was richer in hydroxycinnamic acids than the albedo. In most cases, hydroxycinnamic acid content was in the following order: ferulic acid>sinapic acid>coumaric acid>caffeic acid. Results showed that the content of bound cinnamic acids was unchanged or slightly elevated from early to late season. However, the content of free acids was reduced during that period.     

Potentiall of Ferulic Acid as a Precursor to Off-Flavors in Stored Orange Juice

The hypothesis that free ferulic acid in stored orange juice contributes to the objectional aroma of p-vinyl guaiacol (PVG) was tested. Single-strength orange juice (SSOJ) contained 185 μg/L free ferulic acid which increased to 316 μg/L after pasteurization. Commercial samples of SSOJ contained 3.7mg/L free ferulic when incubated at 35°C for 28 days; incubation at 50°C, resulted in 9.5 mg/L, while samples kept at 4°C contained 2.9 mg/L. Simultaneously, PVG content in SSOJ increased by 2-(35°C) to 3-(50°C) fold, while addition of ferulic acid accelerated formation of PVG. Inclusion of orange juice with added ferulic acid, produced a less acceptable aroma (laboratory taste panel) than juice incubated without added ferulic acid.     

Application of the Weibull model to describe inactivation of Listeria monocytogenes and Escherichia coli by citric and lactic acid at different temperatures

Inactivation of Listeria monocytogenes and Escherichia coli by citric (10‐150 g L^?1) and lactic (1‐60 mL L^?1) acids at different temperatures (4, 20, 40 °C) has been investigated. Bactericidal effect of both acids was dependent on time and temperature of exposure and acid concentration. Survival curves of L. monocytogenes treated by lactic acid were concave downward and those treated by citric acid were linear. On the other hand, survival curves of E. coli treated by both organic acids were concave upward. Shape of survival curves depended on the type of acid but not on the treatment temperature. A mathematical model based on the Weibull distribution accurately described the kinetics of inactivation of both microorganisms by both acids. This model allowed quantification and comparison of the acid resistance of L. monocytogenes and E. coli. Lactic acid was more effective than citric acid and E. coli was more sensitive to both acids than L. monocytogenes. Copyright © 2006 Society of Chemical Industry     

Nitrogen concentration and nitrate/ammonium ratio affect yield and change the oxalic acid concentration and fatty acid profile of purslane (Portulaca oleracea L.) grown in a soilless culture system

Purslane is an excellent source of omega‐3 fatty acids, amino acids and vitamins. The aim of this research was to study the effect of different nitrogen levels and NO₃⁻‐N/NH₄⁺‐N ratios in the nutrient solution on the yield and on the oxalic acid content and fatty acid profile in purslane grown in a soilless culture system. Two experiments were carried out to test different levels of nitrogen: (1) 8–12–16 mmol L⁻¹ and (2) 0–12–24–36 mmol L⁻¹. A third experiment was carried out maintaining the N level fixed (12 mmol L⁻¹) but varying the NO₃⁻‐N/NH₄⁺‐N ratio: 60:40, 40:60, 0:100. The results indicated that plants grew with increasing nitrogen level up to 36 mmol L⁻¹. Nitrogen supplied in both NO₃⁻ and NH₄⁺ forms produced bigger plants than N supplied in NH₄⁺ form only. Nitrogen did not significantly influence the polyunsaturated fatty acid content in the canopy. Significant trends were found for α‐linolenic acid (LNA; 18:3 n‐3) and linoleic acid (LA; 18:2 n‐6), indicating a favorable accumulation of omega‐3 fatty acids with increasing N; palmitic acid decreased by increasing N and by switching the NO₃⁻/NH₄⁺ ratio towards the NH₄⁺ level in the nutrient solution, but using 0:100 NO₃⁻/NH₄⁺, decreased plant quality. Increasing N lowered oxalic acid production and palmitic acid content, enhancing purslane nutritional quality. Keeping a high N level in the nutrient solution with a 40:60 NO₃⁻/NH₄⁺ ratio would give the best results in terms of yield, oxalic acid concentration and fatty acid profile. Copyright © 2006 Society of Chemical Industry