OKSİDASYON-REDÜKSİYON POTANSİYELİNİN ULTRAFİLTRE BEYAZ PEYNİRİN OLGUNLAŞMA SÜRECİ ÜZERİNE ETKİSİ

Abstract

Oxidation–reduction (redox) potential is a fundamental physicochemical parameter that determines the ability of chemical or biochemical systems to oxidize or reduce. Altering intracellular and extracellular redox potentials can significantly affect the biochemical reactions and the quality of fermented products. The aim of the study was to determine the effect of redox potential on the ripening characteristics of ultrafiltered (UF) white cheese. In the first step, it was determined that the reducing activities and the acidification rates of the starter lactococcal strains were different from each other. In the second step, in order to determine the effect of redox potential on amino acid catabolism, the volatile compounds produced by the catabolisms of phenylalanine, methionine, tryptophan and leucine in the control, reduced and oxidized model systems by these strains were detected. It was determined that the species and concentration of the volatile compounds varied depending on the amino acid, the Lactococcus strain and the redox potential of the medium. In the third step, the effects of various redox agents on the redox potential and pH of the fermented milk were determined. As reducing agent, sodium hydrosulfite, dithiothreitol, cysteine, ascorbic acid, and hexose oxidase were used. Potassium iodate and potassium ferricyanide were used as oxidizing agent. It was decided to use sodium hydrosulfite (Na2H2O4) as the reducing agent and potassium iodate (KIO3) as the oxidizing agent in the cheese production, considering the initial pH of the milk, the pH at the end of fermentation, the rate of drop of pH, the initial redox potential, and the redox potential at the end of fermentation. Optimization studies were carried out to determine the concentrations of sodium hydrosulfite and potassium iodate to be used in the cheese production by using reduced fat ultrafiltered (UF) milk. The increase in the concentration of these redox agents negatively affects the pH drop, as well as the viability of the starter cultures used. For this reason, it was decided to addition of 0.01% (w/w) of sodium hydrosulfite as the reducing agent to the full fat UF milk in the cheese production. As the oxidizing agent potassium iodate was added to the full fat UF milk (0.05% (w/w) in total) at a ratio of 0.025% (w/w) at the beginning and then added to the cheese at the ratio of 0.025% (w/w) with salt after the sufficient pH drop was achieved. It has been determined that the redox potential of the reduced fat UF milk was 125.2 ± 4.8 mV (Eh, 332.2 mV) and the redox potential of the full fat UF milk was 146.9 ± 8.3 mV (Eh, 353.9 mV). In the fourth step, the single strains of Lactococcus lactis subsp. lactis CM41 and Lactococcus lactis subsp. cremoris UD459 were selected as the starter culture for UF cheese production, considering the data up to this part of the study. For each culture, three different cheeses were produced: control, reduced and oxidized. Control l (K1), reduced 1 (I1) and oxidized 1 (Y1) cheeses were produced with Lactococcus lactis subsp. lactis CM41 strain and, control 2 (K2), reduced 2 (I2) and oxidized 2 (Y2) were produced with Lactococcus lactis subsp. cremoris UD459 strain. The produced cheeses were ripened for 90 days. On the 7th, 30th, 60th, and 90th days of ripening, microbiological analyses, composition analyses, analyses to determine ripening characteristics (pH 4.6 soluble nitrogen, 12% TCA soluble nitrogen, peptide profile by RP-HPLC, total free amino acid content, urea-PAGE, SDS-PAGE, free fatty acid content, organic acids, volatile compounds), textural and sensory analyses were performed. On the 7th day of ripening, the redox potentials (as ORP value) of K1, I1, Y1, K2, I2 and Y2 cheeses were found to be -311.2, -337.4, 164.0, -329.5, -348.4 and 185.1 mV, respectively. According to the results of the composition analysis, it was determined that the moisture content was high in the oxidized cheeses (Y1 and Y2) and the reduced cheese (İ2) because the pH did not decrease below 4.9, consequently the whey separation was high in these cheeses and the titratable acidity was low. On the 1st day of ripening, the K1, I1, Y1, K2, I2 and Y2 cheeses were found to contain 9.14, 9.20, 8.30, 8.46, 7.89 and 7.95 log CFU/mL viable lactococci, respectively. On the 90th day of ripening, the number of viable lactococci in K1, I1, K2 and I2 cheeses were 7.34, 5.78, 6.51 and 7.55 log CFU/mL, respectively. However, it was determined that the starter lactococci in the oxidized cheeses have lost their viability from the 60th day of the ripening. It was determined that the redox potential affected the proteolysis by lactococcal strains. It was found that there was a positive correlation between the reduced redox potential and the peptidolytic activity of lactococci. The redox potential of the cheeses was found to have no effect on the lipolysis. When the organic acid results were examined, it was found that particularly the production of lactic acid and some other organic acids were influenced by the redox potential of the cheese. It was determined that the redox potential of the medium significantly affected the variety and concentration of the volatile flavour compounds present in the cheese. Especially in the cheeses with oxidized redox potential (Y1 and Y2), benzaldehyde, 4-methyl benzaldehyde and benzonitrile with almond aroma were found to be in high concentration. In addition, the control and reduced cheeses were rated higher by the panelists than the oxidized cheeses in terms of their sensory properties. As a result, it has been determined that low redox potential was required during cheese ripening to obtain a quality UF white cheese.