The aim of this study was to investigate the quality changes of raw ground pork with the addition of allspice, bay leaf, black seed, caraway, cardamom, cloves or nutmeg extract and stored at 4°C. Lipid oxidation was evaluated by the peroxide value (POV), conjugated diene (CD) content, oxidation induction period (IP) by differential scanning calorimetry (DSC), thiobarbituric acid reactive substances (TBARS), and hexanal content; whereas protein oxidation by the thiol group content. Moreover, total viable aerobic bacteria count (TVC), Pseudomonas, Enterobacteriaceae, and lactic acid bacteria growths, pH and finally color of all samples were determined. POV, CD, TBARS and thiol group content were found to be highly correlated. Clove extract showed the highest antioxidant activity (1443 μM/g) and total phenolic content (TPC = 167 mg/g) and was the most effective antioxidant and antimicrobial agent in raw ground pork (TBARS = 0.31 mg/kg, POV = 5.1 meq O 2 /kg, thiol group content = 49 nmol/mg, IP = 68 min, TVC = 6.74). Cardamom and caraway also increased the oxidative stability of raw pork significantly (TBARS were equal to 0.3 and 0.28 mg/kg, POVs to 4.9 and 4.5 and thiol group content to 48 and 49 nmol/mg, respectively), despite their low antioxidant activities (72 and 300-fold lower than for cloves, respectively) and TPCs (1.2 and 2.4 mg/g). The results suggested that the application of natural antioxidants like spice extracts could enhance the stability and safety of raw ground pork, thus increasing its shelf-life. ARTICLE HISTORY

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In the present study, the ability of green tea catechins to induce electrophile-responsive element (EpRE)mediated gene expression and the role of their quinones in the mechanism of this induction were investigated. To this end, Hepa1c1c7 mouse hepatoma cells were used, stably transfected with a luciferase reporter gene under the expression regulation of an EpRE from the human NAD(P)H:quinone oxidoreductase 1 (NQO1) gene. The results obtained show that several, but not all, catechins tested are able to induce EpRE-mediated gene transcription, with epigallocatechin gallate (EGCG) and gallocatechin gallate (GCG), both containing a pyrogallol and a galloyl moiety, being the most powerful inducers. Moreover, it was demonstrated that the EpRE-mediated response to catechins was increased in cells with reduced cellular glutathione (GSH) levels and decreased in cells with increased levels of GSH, corroborating a role for catechin quinones. The intrinsic capacity of catechins to form quinone type metabolites upon their oxidation was demonstrated using incubations of epigallocatechin (EGC) and EGCG with tyrosinase and the GSH-trapping method. Glutathione conjugates formed in these incubations were identified as 2′-glutathionyl-EGC, 2′,6′-diglutathionyl-EGC, 2′-glutathionyl-EGCG, and 2′,6′diglutathionyl-EGCG, supporting the formation of quinone type metabolites involving especially the pyrogallol moiety of these catechins. Formation of the EGCG-quinone-glutathionyl adducts was also observed in the EpRE-LUX cellular system. This further supports the importance of the pyrogallol moiety for the quinone chemistry of the catechins. Finally, the presence of the pyrogallol moiety in the catechins also results in a relatively lower half-wave oxidation potential (E 1/2 ) and calculated heat of formation (DHF) for conversion of the catechins to their corresponding quinones, pointing at an increased ability to become oxidized. Altogether, our studies reveal that catechins, especially those containing a pyrogallol moiety, induce EpRE-mediated detoxifying gene expression and that this induction is likely to be the result of their quinone chemistry.

The effects of black seed (Nigella sativa), allspice, bay leaf, caraway, cardamom, clove, and nutmeg extracts on the quality of raw ground chicken legs stored at 4 °C were investigated. During 12 days of storage, conjugated diene (CD) content, thiobarbituric acid reactive substances (TBARS), oxidation induction time (IP) by DSC (differential scanning calorimetry), hexanal content by GC-SPME-MS, thiol group (SH) content were determined. Moreover, microbial growth, pH and color of the samples were investigated. Sensory analysis was also realized. All extracts increased oxidative stability and safety of meat, significantly changed the color of the samples, stabilized the pH and increased their sensory scores (except color of samples with bay leaf and black seed) when comparing to control. Black seed, allspice and clove extracts showed high antioxidant capacity in lipid (CD = 0.23%, 0.28%, and 0.37%, respectively; TBARS = 0.55, 0.50, and 0.48 mg/kg, respectively) and protein fraction (SH content = 47.9, 52.1 and 52.7 nmol/g, respectively), although the ABTS•+ radical scavenging activity of black seed (33.1 µM/g) was significantly lower than the cloves (2496 µM/g) and allspice (815 µM/g). In the sensory analysis the highest scores were ascribed to the sample with cardamom followed by cloves. Principal component analysis (PCA) indicated complex and inseparable interrelationship among lipid and protein oxidation processes and the relationship of the protein oxidation on the lightness of meat. The results enabled to discriminate the meat samples, showing a great impact of the extracts on the final quality of raw chicken meat with black seed being potent antioxidant active additive.

The influence of stereochemistry on the radical scavenging activity of catechins was investigated by studying the effect of pH on the antioxidant properties of catechin epimers. The difference in the pH-dependent Trolox equivalent antioxidant capacity (TEAC) profiles was observed only in case of gallocatechin gallate (GCG) and epigallocatechin gallate (EGCG), indicating the influence of steric structure on the TEAC antioxidant activity of these galloyl moiety-containing catechins. Based on comparison of the pH-dependent TEAC values to theoretically calculated parameters, including homolytic OH bond dissociation energy and ionization potential (IP) as well as theoretically predicted structures of the most stable monoanions of GCG and EGCG, it was concluded that due to steric hindrance in GCG molecule, the IP value of GCG monoanion increases reflecting lower radical scavenging capacity of GCG in comparison with EGCG. It results in the difference in the pH-dependent TEAC profiles of these two catechin epimers at pH above 3.5. This effect does not occur for other pairs of catechin epimers of this study.