Biodegradation of sucrose poly fatty acid esters in soils

Sucrose polyesters (SPEs) were applied to soil at rates equivalent to 1062 to 1293 kg per hectare and incubated over periods of 100 to 403 days at 20 ± 2°C in darkness and at a soil moisture of 40 % of the maximum water holding capacity. All applied forms of SPEs were aerobically biodegraded to some degree in both American and German soil. However, the mineralization rates varied considerably and were dependent on both SPE and soil type. For example, sucrose octaoleate underwent slow and limited mineralization in the German soils Speyer and Borstel as well as in the American soil Madera, reaching only 6.9 – 18.4 % mineralisation after over 400 days incubation. The same material in the American soils Hollande, Thermal and Uvalde as well as in the German soil Speicherkoog, reached 35–52 % after the same incubation period. Of the SPEs most realistic for use in food products, the more liquid (i.e. with the least saturated fatty acids) underwent the most rapid and extensive mineralization. However, the mineralization rates for these materials were distinctly lower than the corresponding ones for sucrose octaoleate. In all cases the extent of mineralization of the SPEs in soil was significantly lower than that of a control fat (synthetic triglyceride mixture HB307), which typically underwent over 50 % mineralization in 60 days.

As field conditions would be considerably different to those in the laboratory (due to the presence of microbially acclimatised sewage sludge, fluctuations in soil temperature and moisture, and contamination by ecotoxic pollutants) it is difficult to predict accurately, on the basis of laboratory results, the likely rate of mineralization of SPEs in the field. However, this study does suggest that the more solid the SPE, the more likely it is to persist, and possibly accumulate, following application to soil.