Carmen Gómez-Cordovés

Food phenolics and lactic acid bacteria.

Phenolic compounds are important constituents of food products of plant origin. These compounds are directly related to sensory characteristics of foods such as flavour, astringency, and colour. In addition, the presence of phenolic compounds on the diet is beneficial to health due to their chemopreventive activities against carcinogenesis and mutagenesis, mainly due to their antioxidant activities. Lactic acid bacteria (LAB) are autochthonous microbiota of raw vegetables. To get desirable properties on fermented plant-derived food products, LAB has to be adapted to the characteristics of the plant raw materials where phenolic compounds are abundant. Lactobacillus plantarum is the commercial starter most frequently used in the fermentation of food products of plant origin. However, scarce information is still available on the influence of phenolic compounds on the growth and viability of L. plantarum and other LAB species. Moreover, metabolic pathways of biosynthesis or degradation of phenolic compounds in LAB have not been completely described. Results obtained in L. plantarum showed that L. plantarum was able to degrade some food phenolic compounds giving compounds influencing food aroma as well as compounds presenting increased antioxidant activity. Recently, several L. plantarum proteins involved in the metabolism of phenolic compounds have been genetically and biochemically characterized. The aim of this review is to give a complete and updated overview of the current knowledge among LAB and food phenolics interaction, which could facilitate the possible application of selected bacteria or their enzymes in the elaboration of food products with improved characteristics.

Updated Knowledge About the Presence of Phenolic Compounds in Wine

Phenolic compounds are partly responsible for the color, astringency, and bitterness of wine, as well as for numerous physiological properties associated with wine consumption. Mass spectrometry has allowed for great progress in the identification and characterization of wine polyphenols. The aim of the present article is to summarize the numerous advances recently achieved in this field. The main type of phenolic compounds found in wine, including hydroxybenzoic and hydroxycinnamic acids, stilbenes, flavones, flavonols, flavanonols, flavanols, and anthocyanins, are firstly described. Chemical reactions and mechanisms involving phenolic compounds during winemaking are also extensively discussed, including enzymatic and chemical oxidation reactions, direct and acetaldehyde-mediated anthocyanin-tannin condensation reactions, acetaldehyde-mediated and glyoxylic acid-mediated tannin-tannin condensation reactions and, C-4/C-5 anthocyanin cycloaddition reactions with 4-vinylphenols, vinylflavanols and pyruvic acid, among others, leading to the formation of pyranoanthocyanins. Useful mass spectral data of well-known and novel phenolic compounds recently identified in wine, and details related to their fragmentation pathway according to different ionization techniques, are given.

MALDI-TOF MS analysis of plant proanthocyanidins.

Proanthocyanidins or condensed tannins are among the most abundant polyphenols compounds in our diet and may play a key role in the prevention of cardiovascular and neurodegenerative diseases and cancer. These antioxidants are widely distributed in the plant kingdom both in food plants and in non-food plants. The biological activity of plant proanthocyanidins depends on their chemical structure and concentration. However, due to their structural diversity and complexity, the qualitative and quantitative analysis of proanthocyanidins is a difficult task. Mass spectrometry has enabled great advances in the characterization of plant proanthocyanidins. Among these techniques, MALDI-TOF MS has proved to be highly suited for the analysis of highly polydisperse and heterogeneous proanthocyanidins. The objective of the present paper was to assess the potential, limitations and future challenges of the analysis of plant proanthocyanidins by MALDI-TOF MS techniques. Firstly, the fundamental of this technique, including modes of operation, advantages and limitations, as well as quantitative and qualitative operations, have been summarized. Applications of MALDI-TOF analysis to plant proanthocyanidins reported in the last decade (1997-2008) have been extensively covered, including the sample preparation protocols and conditions used for proanthocyanidin analysis, as well as the main findings regarding the determination of the structural features of different plant proanthocyanidin types (procyanidins, propelargonidins, prodelphinidins, profisetinidins and prorobinetinidins). Finally, attempts in the assessment of the molecular weight distribution of proanthocyanidins by MALDI-TOF are described.

Polyphenols and Antioxidant Properties of Almond Skins: Influence of Industrial Processing

Almond (Prunus dulcis[Mill.] D.A. Webb) skins have been proposed as a source of bioactive polyphenols. In this article, the phenolic composition and antioxidant activity of almond skins obtained from different processes (blanching [freeze-drying], blanching + drying, and roasting) were studied. A total of 31 phenolic compounds corresponding to flavan-3-ols (33% to 56% of the total of phenolic compounds identified), flavonol glycosides (9% to 36%), hydroxybenzoic acids and aldehydes (6% to 26%), flavonol aglycones (1.7% to 18%), flavanone glycosides (3% to 7.7%), flavanone aglycones (0.69% to 5.4%), hydroxycinnamic acids (0.65% to 2.6%), and dihydroflavonol aglycones (0% to 2.8%) were determined in the skins from 3 different varieties of almonds. The total contents of phenolic compounds identified were significantly (P < 0.05) higher (around 2-fold) in the roasted samples than in the blanched almonds (freeze-dried). Industrial drying (oven drying) of the blanched almond skins produced an increase (< 2-fold) in the contents of phenolic compounds, although the results were only statistically significant (P < 0.05) for some samples. The antioxidant activity (ORAC values) was higher for the roasted samples (0.803 to 1.08 mmol Trolox/g), followed by the samples subjected to blanching + drying (0.398 to 0.575 mmol Trolox/g) and then the blanched (freeze-dried) samples (0.331 to 0.451 mmol Trolox/g). Roasting is the most suitable type of industrial processing of almonds to obtain almond skin extracts with the greatest antioxidant capacity.

Barley spent grain: release of hydroxycinnamic acids (ferulic and p‐coumaric acids) by commercial enzyme preparations

Barley spent grain is a residue from the brewing process. In this paper, four different commercial enzyme preparations (Viscozyme L, Ultraflo L, Termamyl and Lallzyme) were tested for their ability to release hydroxycinnamic acids, ferulic acid (FA) and p-coumaric acid (PCA), from barley spent grain. The cinnamic acid esterase activities of the enzyme preparations were measured against the model substrate methyl ferulate. Termamyl was the only enzyme preparation that showed no esterase activity. Incubation of Ultraflo L (1.3 U g - 1 substrate, 24 h) with barley spent grain released 70% of the total alkali-extractable FA and 8% of the total alkali-extractable PCA. Under the same conditions, Viscozyme L and Lallzyme released, respectively, 33 and 55% of the total alkali-extractable FA, and 0.8 and 1.6% of the total alkali-extractable PCA. For FA release, enzyme concentrations higher than 1.3U g -1 were saturating. However, for the release of PCA, a continuos increase was observed until 13 U g -1 . The percentages of the FA released by Viscozyme L, Ultraflo L and Lallzyme were higher than those obtained by pure ferulic acid esterases. These three enzyme preparations could be employed for the effective release of hydroxycinnamic acids from barley spent grain.

Determination of some structural features of procyanidins and related compounds by photodiode-array detection

Abstract In this work we have examined the use of a photodiode-array detector to identify unknown peaks correspoding to procyanidins and related compounds. The type of flavan-3-ol unit can be recognised from the absorption maximum (278.9) nm for catechin and epicatechin, and 270.6 nm for epigallocatechin), whereas the number of flavan-3-ol units does not affect this parameter. The min-max distance (distance between the minimum and the maximum in the original spectrum) decreases by 1.3 nm for each catechin or epicatechin unit. Gallates of flavan-3-ol can be detected by reference to the value of the convexity interval (distance between the inflection points before and after the maximum in the original spectrum).

HPLC study of the efficiency of extraction of phenolic compounds

SummaryThe rate of extraction of phenolic compounds in two different solvents has been studied by liquid chromatography (HPLC) under reverse phase, gradient elution conditions. The solvents were diethyl ether and ethyl acetate. The method has been applied to two natural samples, a white wine and apple pulp.

Growth and release of hydroxycinnamic acids from Brewer's spent grain by Streptomyces avermitilis CECT 3339

Streptomyces avermitilis CECT 3339 is grown on Brewer’s spent grain (BSG) and the production of feruloyl esterase (FAE) and (1→4)-β-d-xylan xilanohydrolase (xylanase) activities is studied over 5 days. Maximum level of xylanases was found at day 1. FAE activity on methyl ferulate reached a maximum level at day 2, whereas FAE activity on feruloylated oligosaccharides, either from wheat bran or sugar-beet pulp, was maximal at day 1. The cultures (1–5 days) from S. avermilitis CECT 3339 grown on BSG and on other two agro-industrial residues such as de-starched wheat bran and sugar-beet pulp were tested for the release of hydroxycinnamic acids (ferulic and p-coumaric acids) from BSG. Most ferulic acid (FA) was released when culture supernatants from day 1 and BSG as carbon source (43% of total alkali-extractable ferulic acid) and from day 2 and de-starched wheat bran as carbon source (41.2%) were used. The level of p-coumaric released in all cases was lower (<9% of total alkali-extractable p-coumaric acid; pCA). The importance of the time of growth for the enzyme production involved in the hydrolysis of BSG is discussed.

Fast determination of procyanidins and other phenolic compounds in food samples by micellar electrokinetic chromatography using acidic buffers.

Procyanidins are phenolic oligomers, mainly composed of (+)‐catechin and (–)‐epicatechin units that exhibit certain sensorial and physiological properties of interest (e.g., astringency and bitterness of food, antioxidant activity, etc.). This paper shows the development of a micellar electrokinetic chromatography (MEKC) method for the separation of three procyanidin dimers (B1, B2, and B3), their monomers ((+)‐catechin and (–)‐epicatechin), and the cis‐ and trans‐forms of p‐coumaric acid. Separation conditions are optimized in terms of buffer pH, SDS concentration, and washing routine between injections. The best results in terms of peak resolution and reproducibility between separations were obtained with a MEKC running buffer at pH 5 with 100 mM SDS and a washing routine that includes a rinse step with 0.1 M sodium hydroxide. Using this new MEKC method it is possible to separate in less than 5 min the seven substances. More interestingly, it is demonstrated that the low pH used in this MEKC method allows one to obtain clean electropherograms when samples are injected. The method is shown to be reproducible between different days with relative standard deviation (RSD) values lower than 1% for migration times and lower than 7% for peak areas (3 days, 24 injections). The usefulness of this procedure to determine these compounds in effluents from food processing (i.e., soaking water from lentils, white beans and black beans) and in food by‐products (i.e., almond peels) considered as potential procyanidin sources is demonstrated. To our knowledge, this is the first report of separation and determination of procyanidins in food samples done by capillary electrophoresis.

Phenolic characterisation of red wines from different grape varieties cultivated in Mendoza province (Argentina)

BACKGROUND Knowledge of the chemical composition of wine and its association with the grape variety/cultivar is of paramount importance in oenology and a necessary tool for marketing. Phenolic compounds are very important quality parameters of wines because of their impact on colour, taste and health properties. The aim of the present work was to study and describe the non-flavonoid and flavonoid composition of wines from the principal red grape varieties cultivated in Mendoza (Argentina). RESULTS Sixty phenolic compounds, including phenolic acids/derivatives, stilbenes, anthocyanins, flavanols, flavonols and dihydroflavonols, were identified and quantified using high-performance liquid chromatography with diode array detection coupled with electrospray ionisation mass spectrometry (HPLC-DAD/ESI-MS). Marked quantitative differences could be seen in the phenolic profile among varieties, especially in stilbenes, acylated anthocyanins and other flavonoids. CONCLUSION The polyphenolic content of Malbec wines was higher compared with the other red varieties. Dihydroflavonols represent a significant finding from the chemotaxonomic point of view, especially for Malbec variety. This is the first report on the individual phenolic composition of red wines from Mendoza (Argentina) and suggests that anthocyanins, flavanols and phenolic acids exert a great influence on cultivar-based differentiation.