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Interactions between the different compounds present in foods are common and have influence on the nutritional and functional properties of food products. Among a wide range of these interactions, the formation of complexes between proteins and phenolic compounds seems to be the most important issue. Complexation of the phenolic compounds with proteins can be analysed considering several aspects. These complexes might strongly affect nutritional potential of polyphenols by masking their antioxidant capacity, and on the other hand might have influence on the structure of proteins which may cause their precipitation or decrease susceptibility to digestion. The complexity of protein–phenolic compound interactions is a challenge for food analysts and forced researchers to establish a wide range of analytical methods, allowing determination of complexes formation. The main aim of this review is to give researchers an overview of the currently used methods that can be applied to study the interactions between proteins and phenolic compounds.

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50 % (on average over 36 and 45 % in green and roasted coffee extracts, respectively). Significant differences between the AC values determined for CB and PA samples were noticed only for the MCA and DPPH methods which reflect the different molecular mechanisms underlying each of the assays. Additionally, the statistical methods, including principal component analysis, applied to results of antioxidant capacity obtained with different analytical techniques confirmed their feasibility to distinguish between coffee brews with different degrees of roasting, regardless of coffee origin. Abstract The antioxidant capacity (AC) of boiled-type coffee brews (CB) and phenolic acids (PA) isolated from them, obtained from the caffeinated and decaffeinated beans of different geographical origins and species and with different roasting degrees, was examined. The AC of PA and CB samples was tested in five antioxidant assays: a total antioxidants reducing capacity assay using a Folin-Ciocalteu reagent (FCR), a ferric ion reducing antioxidant power (FRAP) assay, a DPPH · radical-scavenging activity (DPPH) assay, a metal chelating activity (MCA) assay and a total radical trapping antioxidant parameter (TRAP) assay. In most samples, the total amount of phenolic acids, determined by HPLC, decreased with the increasing degree of roasting the coffee beans, leading to reduced AC. All used methods showed that CB exhibits higher AC compared with the PA samples. Phenolic acids isolated from CB samples have the main contribution (on average over 95 and 84 % in green and roasted coffee extracts, respectively) in AC of the CB samples in FCR, FRAP and TRAP assays, whereas in DPPH and MCA tests, the phenolic acid contribution in AC of CB samples was below Keywords

Lupin seed globulin proteins form complexes with flavonoids, predominantly apigenin C-glycosides. Enzymes typical for the gastrointestinal tract were used to hydrolyze lupin seed globulins. Release of native flavonoids as a result of the proteolysis reaction was observed. Different analytical methods such as size exclusion chromatography, HPLC-MS, and fluorescence spectroscopy (steady-state fluorescence, fluorescence anisotropy, fluorescence lifetimes) were used for a detailed characterization of this phenomenon. Flavonoids liberated from lupin globulin proteins as a result of pancreatin-catalyzed digestion were bound by γ-conglutin resistant to this enzyme. Two possible mechanisms of this interaction may be suggested: hydrogen bonding between oligosaccharide chains of glycoproteins and the sugar moieties of the flavonoid glycosides or electrostatic attraction between positively charged γ-conglutin and flavonoids partially ionized at pH 7.5.

Sinapic acid and its derivatives are main phenolic compounds present in rapeseed. Identification and quantitative determination of those compounds were carried out in crude extracts as well as extracts after basic and acidic hydrolysis. The total phenolic content in the crude extracts, expressed as sinapic acid equivalent, ranged from 1577 to 1705 mg/100 g for cv. Visby and Bellevue, respectively. An increase in total phenolics contents was observed in extracts after hydrolysis in comparison to crude extracts. The predominant phenolic acids in rapeseed samples were trans‐sinapic and cis‐sinapic acids. The highest concentration of sinapic acid methyl ester (2533–2702 mg/100 g) was detected in the extract after basic hydrolysis. In turn, two sinapic acid derivatives, i.e., kaempferol 3‐dihexoside‐7‐sinapoyl‐hexoside and 3‐hexoside‐7‐sinapoyl‐hexoside, were detected in the hydrolysed extracts. Total peroxyl radical‐trapping potential (TRAP) of the investigated crude extracts amounted to 20.21 and 27.05 μM Trolox Eq/g in the case of cv. Visby and Bellevue, respectively. The increase in antioxidant activity of the analyzed extracts after basic and acidic hydrolysis was probably a result of the release of free phenolic compounds from their conjugates (esters, glycosides). Practical applications: The content and qualitative composition of the phenolic compounds in rapeseed have much influence on the stability, sensory, and nutritional characteristics of the products. During oil production process phenolic compounds may be transferred into final products and inhibit lipid oxidation. Rapeseed oil, among all commercially available oils, has the highest content of phenolic compounds, especially sinapic acid and their derivatives. That is why the antioxidant activity of phenolic compounds was investigated in the presented study. Determination of polar phenolics before and after hydrolysis indicates which compounds are responsible for antioxidant effect in oils and which are available for the human organism after digestion in the digestive tract.

The study describes isolation and semi-preparative HPLC scale purification of plastochromanol-8 (PC-8). The PC-8 standard was obtained from flaxseed oil. The purity of the obtained PC-8 standard was 93.06% determined by UV-Vis detection. The HPLC/MS n fragmentation pattern of PC-8 side chain resulted in the successive release of eight isoprene fragments which confirmed the correct structure identification. The established PC-8 molar absorption coefficient (3616.5 M À1 cm À1 ) will allow the precise quantitative analysis of this compound in real samples without the use of a standard. Usefulness of the obtained PC-8 standard was verified by HPLC determination of PC-8, tocopherols, and tocotrienols at the same time. The PC-8 recovery was 107.08%, and limit of detection (LOD) and limit of quantitation (LOQ) were 0.75 and 2.27 mg/mL, respectively.Practical applications: There are no commercially available standards of plastochromanol-8 (PC-8), and therefore effective ways of isolation of this compound are needed. A semi-preparative HPLC is one of the available options allowing obtaining pure PC-8.

Eight tocochromanols (a, b, g, and d homologues of tocopherol and tocotrienol) naturally occurring in foods were successfully separated within a 13-min run in the RP-HPLC mode. Analytes were separated on the Phenomenex Luna PFP column filled with the pentafluorophenyl stationary phase (3 mm, 150 mm  4.6 mm) using the mobile phase containing methanol:water (93:7 v/v) with an elution flow rate of 1 ml/min and column oven temperature of 40°C. The method was rapid, linear, accurate, and precise with detection limits in the range of 0.000184-0.000605 mg, preventing analyte losses due direct dissolution in 2-propanol. The developed RP-HPLC method in comparison with the NP-HPLC mode had a significantly higher sensitivity, speed, and repeatability, but primarily it protected against the loss of analytes and thus reduced the risk of possible error measurements. It was found that tocopherol contents in the tested butter samples amounted to 2.00-16.92 mg/100 g for samples coming from Poland and 2.61-2.98 mg/100 g for samples from Latvia, respectively. The method is characterized by simplicity of implementation and it was successfully applied in the determination of tocochromanols in butter to verify product authenticity.Practical applications: To ensure consumers' protection, food products should be subject to continuous quality and authenticity control. One way to determine butter authenticity is to analyze native tocochromanol contents. This paper describes a simple and fast method determine plant oils added to milk fat with the use of RP-HPLC techniques.à Details of separation conditions: column oven temperature 40°C and ambient temperature 21°C; flow rate 1 ml/min. Eur. J. Lipid Sci. Technol. 2014, 116, 895-903 Tocopherolsauthenticity markers of butter à Details of separation conditions: flow rate 1 ml/min; ambient temperature 21°C; mobile-phase MeOH/H 2 O, 93:7 v/v. Eur. J. Lipid Sci. Technol. 2014, 116, 895-903 Tocopherolsauthenticity markers of butter à Details of separation conditions: flow rate 1 ml/min; column over temperature 40°C and ambient temperature 21°C; mobile-phase MeOH/ H 2 O, 93:7 v/v. Eur. J. Lipid Sci. Technol. 2014, 116, 895-903 Tocopherolsauthenticity markers of butter