[Identification of thermal protective effect of food proteins in relation to phycocyanin]

One of the promising sources for creating specialized foods is the biomass of Arthrospira platensis food microalgae. Biomass of A. platensis and its aqueous extracts are used as a source of bioactive compounds, primarily phycocyanins which are protein macromolecules that largely determine the antioxidant, immunomodulatory and anti-inflammatory properties of this cyanobacterium. The chromophore part of phycocyanin is photo- and thermolabile and can undergo restructuring, as a result of which phycocyanin loses its biological value. Various food proteins can be used to protect chromophoric compounds. In this work, two types of proteins (whey and egg proteins) were studied in the complex with phycocyanin. The aim of the study was to identify the heat-protective effect of egg and milk proteins in relation to phycocyanin by using colorimetric method and differential scanning calorimetry. Material and methods. Food sodium caseinate, whey protein concentrate, unfractionated edible egg white and phycocyanin concentrate were used as research objects. Combinations of phycocyanin with proteins were prepared by mixing equal volumes of 1% aqueous solutions, followed by thermostatting the mixtures at a temperature of (28±0.5) °C for 60 minutes in an incubator shaker at a stirring speed of 100 rpm. Studies of the thermodynamic characteristics of the samples separately and in combination with phycocyanin were carried out using differential scanning calorimetry by heating of the samples from 25 to 200 °C at a rate of 5 °C/min. The color change of phycocyanin solutions during storage for 20 min at a temperature of 50 °C was assessed by spectrocolorimetry. Results. The most pronounced low-temperature endothermic effect (peak at 60 °C) was detected in the whey protein concentrate. The ovalbumin had a small thermal effect at 70 and 100 °C, while the sodium caseinate had a small thermal effect at 132 °C. The dry phycocyanin sample had two peaks at 80 and 121 °C and the onset of thermal degradation at 65 °C. The destruction temperature of the sodium caseinate solution was 100.8±1.3 °C, for the whey protein concentrate solution - 113.7±0.8 °C. The aqueous solution of phycocyanin had a thermal effect peak at 103.3±1.7 °C. Mixing phycocyanin with the studied edible proteins resulted in changes in the peak degradation temperatures. The most noticeable decrease was observed for ovalbumin in complex with phycocyanin (at 101.9±1.9 °C), indicating a decrease in the thermal stability of phycocyanin in the presence of this protein. The combination of phycocyanin with whey protein concentrate led to a significant increase in the destruction temperature (at 112.0±2.1 °C). In terms of color index, solutions of phycocyanin complexes with proteins differed significantly from an aqueous solution of phycocyanin. The samples had threshold values for color tolerance (ΔE) in the range of 2 units, that is they were visually distinguishable immediately after preparation. All samples tended to darken when heated to 50 °C. Conclusion. Increasing the thermal stability of phycocyanin is possible when it is combined with whey protein concentrate. The observed effect significantly exceeds the effect of combining phycocyanin with sodium caseinate and egg protein. The change in color of solutions of the studied complexes when heated to 50 °C occurred to a lesser extent in the presence of whey protein concentrate, which may indicate greater preservation of the chromophoric groups of phycocyanin. The results obtained indicate the prospects of using whey protein concentrates for the development of new forms of functional food ingredients containing phycocyanin.