Emulsions stabilised with pectin-based microgels: investigations into the effect of pH and ionic strength on emulsion stability.

Pectin-based microgel particles (MGPs) are encouraging sustainable emulsifying agents for food-applications. Based on polyelectrolytes, pectin-based MGPs are assumed to be pH and ionic strength sensitive, in a similar manner to MGPs of synthetic polymers. Besides building a barrier around oil droplets, charged MGPs repulse each other. Thus the stabilisation mechanisms of pectin-based MGPs should be both steric and electrostatic. To investigate this, emulsions were homogenised with MGP concentrations ranging from 0.5 to 2 wt% MGPs. After emulsification, the pH of the emulsions was adjusted to 4, 3, or 2; and the resulting droplet sizes were measured. We found out that the droplet size and the appearance of agglomerates increased with decreasing pH values. This was caused by the loss of the MGP surface charge, as stated by their ζ-potential, showing an increase from -33.71 ± 4.1 mV for samples with pH 4 to -17 ± 0.6 mV, and -3.4 ± 0.6 mV for pH 3 and 2, respectively. However, the degree of coalescence was dependent on the MGP concentration, as samples with 0.5 wt% coalesced more readily than samples with 2 wt% MGP. These results help understand the emulsion stabilisation mechanisms of pectin-based MGPs and what effect formulation parameters have on the long-term stability of MGP-stabilised emulsions.

Determination and evaluation of the phosphorus load of an artificial shallow lake.

Enhanced eutrophication of lakes due to high nutrient loads from anthropogenic sources has become a worldwide problem. Dying ecosystems and limitation of uses are the consequences. In Bochum, Germany, Lake Umminger is an integral part of a recreation area, but also receives high nutrient loads from the local sewer system, as could be shown with the help of water and nutrient balances. Mass algae growth, the dying of fish and production of digestion gas implied a demand to rehabilitate the lake. Primarily, the urgency and sanitation potential as well as the applicability of external and internal enhancement measures had to be evaluated. The trophic classification needed was based upon the German guideline for the classification of the water quality of natural lakes according to trophic criteria, mainly using Vollenweider's eutrophication model. This paper focuses on a description and analysis of the problems that arose during the application of this model to Lake Umminger, stating that shallow, artificial lakes cannot be evaluated correctly with the existing methods. Although some suggestions for further improvement are given, the development of new evaluation criteria was not in the scope of the study presented.