Effect of citric acid addition on functional properties of pasteurized liquid whole eggs

Application of New Yarrowia lipolytica Transformants in Production of Citrates and Erythritol from Glycerol

Citric acid and erythritol are obtained on an industrial scale using biotechnological methods. Due to the growing market demand for these products, research is underway to improve the process economics by introducing new microorganisms, in particular of the species Yarrowia lipolytica. The aim of this study was to evaluate transformants of Y. lipolytica for growth and ability to overproduce citric acids and erythritol from glycerol. The transformants were constructed by overexpressing glycerol kinase, methylcitrate synthase and mitochondrial succinate-fumarate transporter in the mutant Wratislavia 1.31. Next, strains were assessed for biosynthesis of citrate (pH 5.5; nitrogen limitation) and erythritol (pH 3.0; high osmotic pressure) from glycerol. Regardless of culture conditions strains, 1.31.GUT1/6 and 1.31.GUT1/6.CIT1/3 exhibited high rates of substrate utilization. Under conditions favoring citrate biosynthesis, both strains produced several percent more citrates, accompanied by higher erythritol production compared to the parental strain. During erythritol biosynthesis, the strain 1.31.GUT1/6.CIT1/3.E34672g obtained as a result of co-expression of all three genes stood out, producing 84.0 g/L of erythritol with yield and productivity of 0.54 g/g and 0.72 g/Lh, respectively, which places it in the group of the highest-ranked producers of erythritol among Y. lipolytica species.

Effect of nisin, EDTA, and abuse temperature on the growth of Salmonella Typhimurium in liquid whole egg during refrigerated storage

Salmonella spp. can be present in pasteurized liquid egg products because of its heat resistance or post-processing contamination, thereby representing a food safety risk. The effect of 1000 IU nisin/ml plus 20 mM disodium ethylenediaminetetraacetic acid (EDTA), two refrigerated temperatures (7 °C and 10 °C), and two inoculation levels (103 and 105 cfu/ml) were studied in the growth of S. Typhimurium in pasteurized liquid whole egg (LWE). Two mathematical models were used to fit the microbial curves. Physicochemical characteristics of LWE, such as pH and color, were assessed for 31 days at the two storage temperatures, and no significant changes (p < 0.05) were observed for most of the samples. Results showed the significant impact of temperature on microbial growth. Samples kept at 7 °C showed the decay of microbial cells during storage; meanwhile, the effect at 10 °C was shown as fast growth. The combination of nisin plus EDTA and 7 °C accelerated the decay of microbial cells during the storage showing a synergistic effect. The Weibull model described the decline of cells during the shelf-life. Meanwhile, the logistic model fitted the growth of Salmonella in LWE at 10 °C. Adding these additives to LWE, combined with the correct temperature during pasteurization and adequate conditions during the cold chain, can minimize the food safety risk related to Salmonella.