Lidija Jakobek

Interactions of polyphenols with carbohydrates, lipids and proteins

Polyphenols are secondary metabolites in plants, investigated intensively because of their potential positive effects on human health. Their bioavailability and mechanism of positive effects have been studied, in vitro and in vivo. Lately, a high number of studies takes into account the interactions of polyphenols with compounds present in foods, like carbohydrates, proteins or lipids, because these food constituents can have significant effects on the activity of phenolic compounds. This paper reviews the interactions between phenolic compounds and lipids, carbohydrates and proteins and their impact on polyphenol activity.

The influence of interactions among phenolic compounds on the antiradical activity of chokeberries (Aronia melanocarpa)

In the present work, interactions between phenolic compounds from chokeberries and their influence on the antiradical activity was studied. Three fractions were isolated from chokeberries containing different classes of phenolic compounds. The first fraction contained a major part of phenolic acids and flavonols, the second anthocyanins, and the third insoluble phenols and proanthocyanidins. The phenolic compound content was determined using high-performance liquid chromatography, and the antiradical activity using the DPPH test. In order to evaluate the effects of interactions between phenolic compounds on the antiradical activity, the antiradical activity of individual phenolic fractions was compared with that obtained by mixing phenolic fractions. Phenolic mixtures showed the decrease in the antiradical activity in comparison with the individual phenolic fractions. These results suggest the existence of complex interactions among phenolic compounds that caused the decrease of the antiradical activity. Interactions among chokeberry phenols promoted a negative synergism.

Influence of Anthocyanins, Flavonols and Phenolic Acids on the Antiradical Activity of Berries and Small Fruits

One fraction enriched with flavonols and phenolic acids; and the fraction enriched with anthocyanins, were isolated from red raspberry, blackberry, sour cherry, strawberry, chokeberry, elderberry, and blueberry to study their antiradical activity using the free radical, 2,2-diphenyl-1-picrylhydrazyl, test. The phenol content was determined using high-performance liquid chromatography. The antiradical activity of anthocyanins was 7 to 25 times higher than the antiradical activity of flavonols and phenolic acids. High correlations were found between the content of anthocyanins, flavonols, phenolic acids, quercetin derivatives, caffeic acid derivatives, and the antiradical activity (r = 0.99, 0.93, 0.83, 0.93, 0.94, respectively). Among the phenols studied in this work, anthocyanins showed the highest influence on the antiradical activity in all fruits. Other phenolics with relatively strong influence on the antiradical activity of fruits were quercetin derivatives and caffeic acid derivatives (chlorogenic acid) in chokeberries and blueberries, quercetin derivatives in blackberries, quercetin derivatives and caffeic acid derivatives (chlorogenic acid) in elderberries, and hydroxycinnamic acids in sour cherries.

Variation in the Bioactive Compound Content at Three Ripening Stages of Strawberry Fruit

During the harvest season of two consecutive years, five strawberry cultivars (‘Arosa’, ‘Elsanta’, ‘Marmolada’, ‘Miss’ and ‘Raurica’), grown in the continental part of the Republic of Croatia, were examined. Strawberry fruits quality was evaluated by individual phenol compounds, individual anthocyanins and fruit color. Fruits were harvested in three different periods. Analyzed strawberry cultivars show very good average values of the studied phenolic acids and flavonoids with predominant caffeic acid and epicatechin content in all researched strawberry cultivars. Considering the content of individual anthocyanins, pelargonidin 3-glucoside is predominant in strawberry extract followed by cyanidin-3-glucoside and pelargonidin 3-rutinoside. The correlation between individual anthocyanin content and chromaticity parameters was detected in all strawberry cultivars, additionally correlation coefficients and statistical significance were much lower. The results show a positive association between cultivar and harvest time on strawberry pulp color, with each of the color variables, a, b, a/b ratio, C, L and h° values.

Quality of strawberries produced applying two different growing systems

The quality of strawberry fruits (cv. “Clery” and cv. “Asia”) was studied and compared under the conditions of two different growing systems (under a high plastic tunnel and in the open field). Several chemical parameters were determined in the harvested fruits: dry matter, soluble solids, total acidity, ratio between sugars and acids, vitamin C, total phenols, non-flavonoid phenolic compounds, total anthocyanins, reducing sugars, sucrose, colour of fruits, and HPLC analysis of flavonols, flavanols, and phenolic acids content. The fruits of cultivar “Clery” had more antioxidant compounds than the fruits of cultivar “Asia” when grown in the open field. The fruits of both cultivars grown under a tunnel generally had good properties; however, the total phenol content and the non-flavonoid fraction were somewhat lower. Among the phenolic compounds, (+)-catehin, (−)-epicatehin, ellagic, p-coumaric acid, quercetin, and kaempferol were identified and quantified using HPLC equipped with Photo Diode Array detection. The highest content of phenolic compounds was found in cv. “Clery” from the open field production. Analysis of antioxidant compounds has not shown statistically significant differences as a result of growing system or grown cultivar. Samples of strawberries grown under a high plastic tunnel, regardless of examined cultivar, had better basic chemical parameters. The mash colour also depends on cultivar and growing system.

Influence of processing parameters on permeate flow and retention of aroma and phenolic compounds in chokeberry juice concentrated by reverse osmosis

ABSTRACT Reverse osmosis (RO) concentration of chokeberry juice, a rich source of polyphenols, at three different pressures (45, 50 and 55 bar) and two temperature regimes (with cooling and without cooling of the retentate) was studied. Concentration was carried out on a laboratory membrane unit with plates and frames on composite Alfa Laval membranes RO98pHt. Juice was concentrated till 24.9% of total soluble solids content (TSSC) . The permeate flow highly depended on processing parameters and varied from 15.19 ± 3.22 L/m2h at the beginning to 8.00 ± 2.21 L/m2h at the end of processes. Total phenolic compounds (4 anthocyanins, 2 flavonols and 2 phenolic acids) were determined by high performance liquid chromatography (HPLC). Twenty four volatile compounds were identified by gas chromatography with mass spectrometry (GC-MS) in chokeberry juice and concentrates. Processes at 50 and 55 bar with cooling proved to be the best in terms of chokeberry aroma, antioxidant activity and total phenolic compounds retention.

Validation of spectrophotometric methods for the determination of total polyphenol and total flavonoid content

The aim of this study was to validate spectrophotometric methods for the measurement of total polyphenol (TP; via the Folin-Ciocalteu method) and total flavonoid (TF) content [via the aluminum chloride (AlCl3) method]. Validation parameters of these methods were determined, including linearity, sensitivity, precision (intra-assay and intermediate), accuracy, LOD, and LOQ. For the validation process, groups of polyphenol standards were used, including phenolic acids (gallic, p-coumaric, caffeic, and chlorogenic acids), flavan-3-ols [(+)-catechin and procyanidins B1 and B2], flavonols (quercetin and quercetin-3-rutinoside), and dihydrochalcones (phloretin and phloretin-2-glucoside). Obtained validation parameters were within acceptable ranges with high determination coefficients, reasonably low LODs and LOQs, and high slopes in the calibration curves for both methods, except for phloretin and phloretin-2-glucoside, for which there were low slopes in the calibration curves for the AlCl3 method. To evaluate differences in polyphenol content, the validated spectrophotometric methods were used to determine TP and TF content in wines (Plavac, Graševina, and Vranac) and juices (blueberry, strawberry, and blackcurrant juice) according to the polyphenol calibration curves. Polyphenol contents were different for both methods in all wines and juices.

Adsorption of apple polyphenols onto beta-glucan

The adsorption of polyphenols from apples, a good source of polyphenols in the human diet, onto β-glucan, a soluble dietary fibre were studied. Polyphenols were extracted from the flesh and peel of two apple varieties (wild apple and Slavonska srcika) and adsorbed onto β-glucan for 16 hours. The adsorption capacities (mg/g) and equilibrium polyphenol concentrations (mg/l) were modelled with Freundlich and Langmuir isotherms. Polyphenols from the flesh and peel showed different behaviours – flesh polyphenols exhibited greater affinity and peel polyphenols greater theoretical adsorption capacity. The analysis of individual polyphenols with high-performance liquid chromatography revealed that the composition of the flesh and peel differed (flesh was rich in phenolic acids, peel in flavonols) which could explain the contrasting adsorption behaviour. This study shows that polyphenols from apples can be adsorbed onto β- glucan, that the flesh and peel exhibit distinct adsorption behaviours and that the polyphenol composition can affect the adsorption mechanism.

Polyphenols and β-glucan interactions through linear adsorption models

The aim of this work was to obtain information about interactions between polyphenols and β- glucan through linear adsorption equilibrium models. Polyphenolic compounds can interact with various food ingredients such as carbohydrates, proteins and lipids and this interactions can affect polyphenol bioactivities. Interactions can be studied through adsorption process at constant temperature and adsorption isotherms can be obtained. In this work the interactions between polyphenols like gallic acid, cyanidin-3- galactoside and cyanidin-3-glucoside and β- glucan as natural dietary fiber were studied through Freundlichs, Langmuirs, Dubinin- Radushkevichs, Tempkins and Hills models. Adsorption was carried out through model solutions of different concentrations of polyphenols and β-glucan in 16 hours at 25°C. After the adsorption, unadsorbed polyphenols were separated from adsorbed polyphenols by ultrafiltration. Concentration of unadsorbed polyphenols were determined by spectrophotometric Folin-Ciocalteu method for gallic acid and pH differential method for cyanidin-3-galactoside and cyanidin-3- glucoside. The results of adsorption isotherm parameters showed that adsorption between all polyphenols and β-glucan were physical and all interactions were favorized. Gallic acid showed the highest maximum adsorption capacity onto β- glucan. This study showed that information about interactions between polyphenols and dietary fibers can be obtained through the linear adsorption equilibrium isotherms.