No abstract

Different strains of the saprophytic yeast-like fungus Aureobasidium pullulans (Ascomycota: Dothideales) exhibit different biochemical characteristics, while their ubiquitous occurrence across diverse habitats and environmental conditions makes them an easily accessible source for biotechnological exploitation. They are useful in agricultural and industrial applications. Their antagonistic activities against postharvest pathogens make them suitable bioagents for the postharvest preservation of fruits and vegetables, while they possess antimicrobial activities against bacteria and fungi. Additionally, A. pullulans appears to be a potent source of single-cell protein. Many strains of A. pullulans harbor a wide range of industrially important enzymes, while the trademark exopolysaccharide pullulan that they produce has been extensively studied and is currently used in many applications. They also produce poly (β-L-malic acid), heavy oil liamocins, siderophore, and aubasidan-like β-glucan which are of interest for future applications. Ongoing studies suggest that A. pullulans holds many more interesting properties capable of further potential biotechnological applications.

Surfactants are used to stabilize nanoemulsions by protecting their physical stability and preventing deterioration of the entrapped bioactive during processing and storage. The effect of surfactant concentration on physical-chemical properties of nanoemulsions with entrapped curcumin, relevant to commercial applications, was addressed in this research. Furthermore, the functionality of nanoemulsified curcumin in terms of lipid oxidation inhibition was determined. Protection against varying pH and thermal treatments was more significant in the nanoemulsions at the elevated surfactant level, but at these high concentrations, the surface charges of the emulsions dramatically decreased under sodium salt addition, which may result in instability over time. Nanoemulsions showed the potential to inhibit malondialdehyde (MDA) formulation by protecting the entrapped curcumin and enhance its antioxidant activity when added to milk. The fortified milk with added curcumin systems had a yellow color compared to the control. The results of the study are critical in choosing the surfactant concentration needed to stabilize emulsified curcumin, and to protect the entrapped curcumin under specific conditions of use to support the utilization of curcumin nanoemulsions as a food additive in different commercial products.

An obligate halophilic Aspergillus gracilis which was isolated from a hypersaline man-made saltern from Thailand was screened for its potential of producing extracellular α-amylase in the previous studies. In this study the α-amylase was extracted and purified by the help of column chromatography using Sephadex G-100 column. Presence of amylase was verified by SDS-PAGE analysis, showing a single band of approximately 35 kDa. The specific activity of the enzyme was found to be 131.02 U/mg. The Lineweaver-Burk plot showed the V max and K m values of 8.36 U/mg and 6.33 mg/mL, respectively. The enzyme was found to have the best activity at 5 pH, 60°C, and 30% of NaCl concentration, showing its polyextremophilic nature. The use of various additives did not show much variation in the activity of enzyme, showing its resilience against inhibitors. The enzyme, when tested for its use for synthetic waste water remediation by comparing its activity with commercial amylase in different salt concentrations showed that the α-amylase from A. gracilis was having better performance at increasing salt concentrations than the commercial one. This shows its potential to be applied in saline waste water and other low water activity effluents for bioremediation.

Tropical isolates of Aureobasidium pullulans previously isolated from distinct habitats in Thailand were characterized for their capacities to produce the valuable polysaccharide, pullulan. A. pullulans strain NRM2, the so-called "color variant" strain, was the best producer, yielding 25.1 g pullulan l(-1) after 7 days in sucrose medium with peptone as the nitrogen source. Pullulan from strain NRM2 was less pigmented than those from the other strains and was remarkably pure after a simple ethanol precipitation. The molecular weight of pullulan from all cultures dramatically decreased after 3 days growth, as analyzed by high performance size exclusion chromatography. Alpha-amylase with apparent activity against pullulan was expressed constitutively in sucrose-grown cultures and induced in starch-grown cultures. When the alpha-amylase inhibitor acarbose was added to the culture medium, pullulan of slightly higher molecular weight was obtained from late cultures, supporting the notion that alpha-amylase plays a role in the reduction of the molecular weight of pullulan during the production phase.