The pH of the medium is the key environmental parameter of chemical selectivity of oxalic acid biosynthesis by Aspergillus niger. The activity of the enzyme oxaloacetate hydrolase, which is responsible for decomposition of oxaloacetate to oxalate and acetate inside the cell of the fungus, is highest at pH 6. In the present study, the influence of pH in the range of 3–7 on oxalic acid secretion by A. niger W78C from sucrose was investigated. The highest oxalic acid concentration, 64.3 g dm−3, was reached in the medium with pH 6. The chemical selectivity of the process was 58.6% because of the presence of citric and gluconic acids in the cultivation broth in the amount of 15.3 and 30.2 g dm−3, respectively. Both an increase and a decrease of medium pH caused a decrease of oxalic acid concentration. The obtained results confirm that pH 6 of the carbohydrate medium is appropriate for oxalic acid synthesis by A. niger, but the chemical selectivity of the process described in this paper was high in comparison to values reported previously in the literature.

JEL Classification: I120Streszczenie: Woda jest niezbędnym składnikiem pokarmowym i dlatego musi być stale dostarczana do organizmu w celu zapewnienia jego prawidłowego funkcjonowania. Niedostateczne spożycie wody w stosunku do zapotrzebowania może doprowadzić do zachwiania homeostazy, a w konsekwencji do zaburzeń stanu zdrowia. Odwodnienie obniża wydolność fizyczną, a także powoduje zaburzenia funkcji poznawczych i nastroju. Zwiększone ryzyko odwodnienia występuje m.in. u osób starszych, czego przyczyną jest zmniejszone odczucie pragnienia, zmniejszone spożycie wody oraz mniejsza sprawność resorpcji wody i niektórych składników mineralnych. Odwodnienie jest problemem zdrowia publicznego i zasługuje na większą uwagę nie tylko ze strony wykwalifikowanego personelu medycznego. Dbałość osób starszych oraz ich opiekunów o odpowiednie spożycie wody przyczyni się do obniżenia chorobowości i śmiertelności w tej grupie wiekowej. Celem niniejszej pracy było zebranie i przedstawienie informacji dotyczących zapotrzebowania na wodę, czynników ryzyka odwodnienia u osób po 65 roku życia oraz strategii diagnostycznych i terapeutycznych. Realizację celu oparto na analizie piśmiennictwa dotyczącego nawodnienia i żywienia osób starszych.Słowa kluczowe: woda, gospodarka wodno-elektrolitowa, homeostaza, osoby w wieku podeszłym. Summary:Water is an essential nutrient and therefore has to be constantly supplied to ensure the proper function of the organism. Inadequate intake of water could cause disruption of human body homeostasis and consequently lead to health disorders. Dehydration reduces physical capacity, and causes cognitive and mood disorders. Increased risk of dehydration occurs in the elderly, which is caused by reduced sensation of thirst leading to the reduced water consumption. Dehydration is a public health problem and deserves attention not only from qualified medical personnel but also from the older people care taking into account that adequate water intake will help to reduce morbidity and mortality in this group. The aim of this study was to collect and provide information regarding water requirements and the risk factors of dehydration in people over 65 years old and to propose diagnostic and therapeutic 56Ewelina Dymarska, Małgorzata Janczar-Smuga strategies. The objective of this study was accomplished based on a thorough analysis of the literature concerning hydration and nutrition of elderly people.

Citric acid is currently produced by submerged fermentation of sucrose with the aid of Aspergillus niger mold. Its strains are characterized by a high yield of citric acid biosynthesis and no toxic by-products. Currently, new substrates are sought for production of citric acid by submerged fermentation. Waste materials such as glycerol or pomace could be used as carbon sources in the biosynthesis of citric acid. Due to the complexity of the metabolic state in fungus, there is an obvious need to optimize the important medium constituents to enhance the accumulation of desired product. Potential optimization approach is a statistical method, such as the central composite rotatable design (CCRD). The aim of this study was to increase the yield of citric acid biosynthesis by Aspergillus niger PD-66 in media with waste glycerol as the carbon source. A mathematical method was used to optimize the culture medium composition for the biosynthesis of citric acid. In order to maximize the efficiency of the biosynthesis of citric acid the central composite, rotatable design was used. Waste glycerol and ammonium nitrate were identified as significant variables which highly influenced the final concentration of citric acid (Y1), volumetric rate of citric acid biosynthesis (Y2), and yield of citric acid biosynthesis (Y3). These variables were subsequently optimized using a central composite rotatable design. Optimal values of input variables were determined using the method of the utility function. The highest utility value of 0.88 was obtained by the following optimal set of conditions: waste glycerol—114.14 g∙L−1and NH4NO3—2.85 g∙L−1.

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