Modelling the stability of red pigments produced by Penicillium purpurogenum GH2 under sonication treatment
In the past years consumer trends are pointing towards more healthy food consumption and therefore the consumption of natural products has been increasing. The preoccupation over the safety of synthetic pigments has managed to the controlled implementation of synthetic pigments as food additives. Research opportunities for the production of natural colorants by microorganism are emerging owing to the extensive spectrum of colors that microorganism are able to produce. Moreover the production of pigments by microorganism can be managed in controlled conditions (bioreactor) and thus ensuring consistency in production yields. The application of any natural pigment in food manufacturing processes requires an accurate understanding of how food processes conditions of pasteurization, stabilization, packing and storage may affect the stability of natural pigments and thus the final color of the colored products. Thermal treatment is the most common technology used for food processing and preservation for the inactivation of enzymes and microbial decontamination at the expense of the final product quality. Growing consumer demand for fresh and healthier foods than thermally processed foods has led to the search for processes of pasteurization/sterilization alternatives that do not involve the application of heat to maintain quality by minimizing changes in nutritional and organoleptic properties but still ensure safety and stability of foods during storage. To ensure safety and stability of food is extremely important the presence of a process that has the objective of microbial destruction. Ultrasonic processing has proven to be useful in microbial inactivation, which is an alternative treatment to those materials sensitive to high temperatures. Power ultrasound has shown to be an effective technology to meet the requirements of the US Food and Drug Administration for a 5-log reduction in microorganisms present in fruit juices. Microbial inactivation by ultrasound depends on many factors so that the process could be carried out successfully. These factors range from the application of ultrasound as wave amplitude, power, temperature, and sample volume to the physical and chemical properties of the product as well as the characteristics of the microorganism. The present work aims to define the optimum conditions of ultrasonic pasteurization to obtain a minimal impact on color intensity provided by the pigments produced by Penicillium purpurogenum GH2 while ensuring the requirements for a 5 log reduction in pertinent microorganism found in food reported in previous studies which have asses the microbial inactivation effect of sonication. Czapex-dox modified medium was used for pigment production (pH 5-6). A mycelial suspension of Penicillium purpurogenum GH2 was used as inoculum. The inoculated flasks were incubated at 30±2°C on an orbital shaker (Inova 94, New Brunswick Scientific, USA) at 200 rpm for 8 days. For pigment extraction, each sample was centrifuged at 8000 rpm for 20 min at 4oC (Sorball, Primo R Biofuge Centrifugation Thermo, USA). The supernatant was then filtered through a 0.45 μm cellulose filter (Millipore, USA). The concentration of red pigments was quantified indirectly measuring the optical density at 500 nm using a spectrophotometer (Cary 50, UV-Visible Varian, USA). Red pigment extract was treated at different time-acoustic energy density (AED) combinations in the range of 0-10 min and AED 0.6 to 2.6 W/mL. Degradation of pigments was well described by a first order model (R2=0.99) with a non-zero equilibrium value and D-values for ultrasound degradation ranged from 114.43 to 14.88 min. Red pigments presented moderate stability (76.66-99.24%) compared with pasteurization processes of typical microorganisms however this degradation can be minimized in high acoustic energy density levels and short time conditions. D-values for a specific microorganism are influenced by a number of factors therefore more studies need to be done for a full knowledge of the pigment stability during ultrasound processing.
Keywords: Fungal pigments, modelling, stability, ultrasound.