Ioannis G. Roussis

Reduction of sodium content in Feta cheese by partial substitution of NaCl by KCl

Abstract Feta cheese (five trials) of different sodium content was made from split lots of curd by varying the salting procedure i.e., dry salting with NaCl (control) or mixtures of NaCl/KCl (3:1 or 1:1, w/w basis) and filling the cans with brine made with NaCl or the above NaCl/KCl mixtures, respectively. It was found that up to a 50% reduction of sodium content in Feta cheese is feasible, with partial replacement of NaCl by KCl, without an adverse effect on its quality. The results also indicated that the cheeses made with mixtures of NaCl/KCl exhibited no significant (P > 0.05) differences in compositional (moisture, fat, protein, salt), physicochemical (pH, aw), sensory (appearance, body and texture, flavour, overall quality) and textural (force and compression to fracture, hardness) properties in comparison with the control cheese. The Na:K ratio (molecular basis) decreased from 31.5 in the control cheese to 4.0 and 1.4 in the cheeses salted with 3:1 or 1:1 mixture of NaCl/KCl, respectively. Thus, the use of the 1:1 NaCl/KCl mixture in the salting of Feta cheese effectively brought its Na:K ratio near the desired 1.0, while also greatly reducing the sodium content by about 50%.

Manufacture of Kefalograviera cheese with less sodium by partial replacement of NaCl with KCl

Kefalograviera cheeses (five trials) of different sodium content were made from split lots of curd by varying the salting processes, i.e. brine—and dry—salting with NaCl (control) or a mixture of NaCl/KCl (3:1 or 1:1, w/w basis). The results indicated that up to 50% reduction of sodium content in Kefalograviera cheese is feasible, with partial replacement of NaCl by KCl, without an adverse effect on its quality. It was also found that the cheeses made with the mixtures of NaCl/KCl did not exhibit any significant (p>0.05) difference in compositional (moisture, fat, protein, salt), physico-chemical (pH, aw), or textural (force and compression to fracture, hardness, cohesiveness, springiness, gumminess, chewiness) properties in comparison with the control cheese. Kefalograviera cheese of highly acceptable quality, which did not differ (p>0.05) in sensory characteristics (appearance, body and texture, flavour, total score) from the control cheese, can be produced using a mixture of NaCl and KCl instead of NaCl alone. The Na:K ratio (molecular basis) decreased from 35.3 in the control cheese to 4.2 and 1.4 in the cheeses salted with 3:1 or 1:1 mixture of NaCl/KCl, respectively. The use of the 1:1 NaCl/KCl mixture in the salting of Kefalograviera cheese effectively brought its Na:K ratio close to the desired 1.0, while also greatly reducing the sodium content by about 50%.

Impedimetric biosensor for the assessment of the clotting activity of rennet.

Cheese production is relied upon the action of rennet (a mixture of chymosin and pepsin) onto casein micelles of milk. For the first time, the monitoring of this interaction with electrochemical impedance spectroscopy (EIS) was used to develop a faradic impedimetric biosensor for the assessment of the clotting activity of rennet, using hexacyanoferrate(II)/(III) couple as a redox probe. Gold electrodes were modified with self-assembled monolayers of different thiols (thioctic acid, dithiobis-N-succinimidyl propionate, and cysteamine), and (artificial) casein micelles were immobilized on the modified gold surfaces. The proposed method is based on the measurement of charge-transfer resistance (R(ct)) changes attributed to the degradation of the negatively charged immobilized casein micelles by rennet to neutral biostructures. This action results in the increase of the flux of the redox probe, which exists in the bulk solution, to the surface of the electrode and, consequently, in the decrease of R(ct). Experimental parameters such as the micelle loading, the reaction time, the concentration of rennet, and the working pH, were optimized. Besides EIS measurements, cyclic voltammetry, FT-IR, and atomic force microscopy (AFM) experiments were also performed before and after the interaction of the immobilized micelles with rennet. Finally, the proposed biosensors were successfully tried for various commercial samples.

Must oxygenation together with glutathione addition in the oxidation of white wine

Abstract White wines were made from oxygenated musts with or without glutathione addition and without SO 2 . Must oxygenation led to wines with lower phenolic contents and browning capacity, and lower non-polymeric and polymeric phenolics in relation to control (made with SO 2 addition) wines. These wines were of good colour but their flavour was not typical of the grape variety used. The wines that were produced from oxygenated musts, together with glutathione addition, appeared to have somewhat higher total phenolics and browning capacity and non-polymeric and polymeric phenolics than those produced from oxygenated musts alone. Glutathione addition and must oxygenation led to wines of acceptable and stable colour with good flavour typical of the grape variety used.

Protective Effect of Thiols on Wine Aroma Volatiles

The ability of glutathione, oxidized glutathione, N-acetyl-cysteine, and N-acetyl-serine to protect wine aroma volatiles was examined. Muscat-white and Xinomavro-red wine were stored in open bottles at 20 o C and aroma volatiles were determined using solid phase microextraction along with GC-MS. Glutathione and N-acetyl-cysteine inhibited the decrease of several ace- tate esters, ethyl esters and terpenols, while oxidized glutathione and N-acetyl-serine did not. Present results show that the free -SH is responsible for the ability of glutathione and N-acetyl-cysteine to protect white and red wine aroma volatiles. Consequently, the protective action of any thiol in any wine may be taken into account.

Comparative Antioxidant Effectiveness of White and Red Wine and Their Phenolic Extracts Towards Low-Density Lipoprotein Oxidation

The ability of six white and four red Greek wines to inhibit the Cu2+-induced oxidation of LDL was evaluated. All red wines exhibited much higher antioxidant activity and total phenolics than white wines. Moreover, all red wines exhibited lower concentration of total phenolics that induces a 50% prolongation of the lag time of LDL oxidation (IC50value) than white ones. Two out of four red wines exhibited lower IC50values than the others. One white and one red wine—young and aged—were fractionated by extraction, and several fractions were sub-fractionated by column chromatography. All white and red wine fractions and sub-fractions appeared to be effective in inhibiting LDL oxidation indicating that many wine phenolics may be active. Some young red wine sub-fractions exhibited IC50 values different from the respective components of aged wine, indicating that the oxidative aging in barrels may have an effect on the antioxidant potency of wine phenolics towards LDL oxidation. One white wine phenolic sub-fraction exhibited IC50 values similar to the two most active red wine sub-fractions, indicating that, besides red, white wine may also be considered as a pool of very active phenolics in inhibiting LDL oxidation. These three most active sub-fractions were rich in phenolic acids and flavonols. Some biotechnological strategies may serve to enrich wines with active phenolic components and improve their potency towards LDL oxidation.

Kappa-casein based electrochemical and surface plasmon resonance biosensors for the assessment of the clotting activity of rennet.

We report for the first time the development of kappa-casein (κ-CN)-based electrochemical and surface plasmon resonance (SPR) biosensors for the assessment of the clotting activity of rennet. Electrochemical biosensors were developed over gold electrodes modified with a self-assembled monolayer of dithiobis-N-succinimidyl propionate, while SPR measurements were performed on regenerated carboxymethylated dextran gold surfaces. In both types of biosensor, κ-CN molecules were immobilized onto modified gold surfaces through covalent bonding. In electrochemical biosensors, interactions between the immobilized κ-CN molecules and chymosin (the active component of rennet) were studied by performing cyclic voltammetry, differential pulsed voltammetry, and electrochemical impedance spectroscopy (EIS) measurements, using hexacyanoferrate(II)/(III) couple as a redox probe. κ-CN is cleaved by rennet at the Phe105-Met106 bond, producing a soluble glycomacropeptide, which is released to the electrolyte, and the positively charged insoluble para-κ-casein molecule, which remains attached to the surface of the electrode. This induced reduction of the net negative charge of the sensing surface, along with the partial degradation of the sensing layer, results in an increase of the flux of the redox probe, which exists in the solution, and consequently, to signal variations, which are associated with the increased electrocatalysis of the hexacyanoferrate(II)/(III) couple on the gold surface. SPR experiments were performed in the absence of the redox probe and the observed SPR angle alterations were solely attributed to the cleavage of the immobilized κ-CN molecules. Various experimental variables were investigated and under the selected conditions the proposed biosensors were successfully tried to real samples. The ratios of the clotting power units in various commercial solid or liquid samples, as they are calculated by the EIS-based data, were almost identical to those obtained with a reference method. In addition, EIS measurements showed an excellent reproducibility, lower than 5%.

Selective 1D TOCSY NMR method for the determination of glutathione in white wine

Glutathione, a naturally occurring tripeptide, is the main thiol in must and wine which inhibits must oxidative browning and prevents the loss of wine aroma. In the present work a direct quantification of glutathione in fresh white wine with the use of selective 1D TOCSY NMR experiments is demonstrated. The method is based on the selective excitation of the βCH2SH protons of the Cys residue resulting in the magnetization transfer to the αCH proton followed by its quantification with the use of the standard addition method. The method: (i) does not involve any derivatization and/or extensive sample preparation procedures; (ii) it allows the spin-coupling network of the L-cysteine residue to be elucidated even in the presence of strongly overlapped abundant analytes; (iii) has good NMR analytical performance characteristics and (iv) allows the simultaneous identification and quantification of both reduced and oxidized glutathione.

Inhibition of the oxidation of corn oil stripped of tocopherols and refined olive oil by thiols.

The ability of N-acetyl-cysteine and glutathione to inhibit the oxidation of corn oil stripped of tocopherols and refined olive oil was examined. The oxidative stability of corn oil stripped of tocopherols at 50 o C, 120 o C and 180 o C was evaluated. The absorbances at 234 nm and 270 nm, and p-anisidine value were monitored. N-acetyl-cysteine and glutathione inhibited the oxidation of oil, N-acetyl-cysteine at a higher degree. In comparison to BHA at 200 mg/L, both thiols at 20-40 mg/L exhibited lower (50 o C and 120 o C) or similar (180 o C) antioxidant activities. Compounds similar to the two thiols but not containing –SH group, N-acetyl-serine and oxidized glutathione, exhibited very low or no antioxidant activities. The oxidative stability of refined olive oil at 20 o C was determined by monitoring the peroxide value. N-acetyl-cysteine and glutathione at 20 mg/L exhibited antioxidant activities comparable to that of BHA at 200 mg/L. Present results show the ability of N-acetyl-cysteine and glutathione to inhibit the oxidation of corn oil stripped of tocopherols and refined olive oil indicating that thiols can inhibit the oxidation of any oil.

Casein and Cheese Peptide Degradation by Enterococcus durans FC12 Isolated from Feta Cheese

The growth of Enterococcus durans FC12 isolated from Feta cheese in broths containing casein, casein hydrolysate or cheese water-soluble extract as sole nitrogen source was studied. FC12 assimilated casein hydrolysate and casein, the former at a higher extent, while it also grew in the presence of 4% NaCl. It assimilated at a similar extent cow, ewe or goat casein, and it grew rapidly using cheese soluble nitrogenous materials. The cell-envelope enzyme preparation of E. durans FC12 hydrolysed both α-casein and β-caseins, the latter more rapidly, producing three main peptides. It also hydrolysed two peptides analog to the cheese peptide αs1-CNf1-23 that is a key peptide in the first steps of cheese proteolysis. FC12 cell-envelope enzyme preparation degraded the above caseins and peptides in the presence of 4% NaCl. The ability of E. durans FC12 to assimilate casein and cheese soluble nitrogenous materials along with the ability of its cell-envelope enzyme preparation to hydrolyse caseins and peptides analog to the αs1-CNf1-23 indicates that the FC12 strain may be useful in cheese proteolysis as an adjunct culture.