Carbohydrates in hot water extracts of soil aggregates as affected by long-term management

Microbial carbohydrates are immediate by-products of microbial metabolism and play an important role in the formation and stabilization of soil structure. The effect of long-term management on soil carbohydrate content and monosaccharide composition was investigated in five. Danish sandy loams under organic and conventional management with animal manure and mineral fertilizers. Hot-water (80°C)extraction was used to measure the distribution and composition of carbohydrates in aggregate size. Carbohydrates released to hot water were determined after hydrolysis as reducing sugars equivalent to glucose. The monosaccharide composition in hot-water extracts was analyzed as the corresponding alditol acetates. Sites with a history of long-term continuos management practices were used. Three treatments from the >100 year Askov long-term field experiment were used to show results of contrasting fertilization on soil carbohydrate content. These were all grown to a four-course crop rotation. Total carbohydrate content was signifcantly infuenced by long-term management practices, with a signifcantly higher carbohydrate content in soils fertilized with either mineral fertilizers or animal manure (1200 to 800 mg C kg-1 DM aggregate)than in an unfertilized soil (600 to 500 mg C kg-1 DM aggregate). These results were as true for micro-aggregates (,0.25 mm)as for the 0.5–1. 0mmand 4.0–8.0 mm fractions. The organically managed soil (>40years) was sited at a commercial farm with forage crop rotations, organic manure and nouse of crop protection chemicals. These results showed signifcantly higher levels of carbohydrate both in micro-aggregate and macro-aggregates (1200 to 900 mg C kg-1 DM aggregate) than an adjacent conventionally managed soil with annual cash crop, mineral fertilizers and use of cropprotection chemicals (960 to 760 mg C kg-1 DM aggregate). Carbohydrate Ccontent generally increased as aggregate size decreased in both soils. Monosaccharide distribution was generally similar among three aggregate size classes studied. In all soils the content of monosaccharide was highest in micro-aggregates and lowest in macro-aggregates. Mannose and galactose were normally the most common monosaccharides in the hot-water extracts of aggregate fractions, indicating a predominantly microbial origin

Light-induced protein and lipid oxidation in cheese: Dependence on fat content and packaging conditions

Photo-oxidation of cheese products has become an issue due to the fact that packaging of cheeses in transparent materials is very frequently used. The present study aimed to investigate the effect of fat content and availability of oxygen on light-induced oxidation in cheese, as we expected that the fat content would affect the oxidation pathways. Two different model cheeses with 5.4% and 18% fat were packed in air and in vacuum, respectively. The contents of protein (dityrosine and dimethyl disulphide (DMDS)) and lipid (lipid hydroperoxides, pentanal, hexanal and heptanal) oxidation products were significantly reduced in vacuum-packed cheeses compared to cheeses packed in air. Protein oxidation correlated to the concentration of lipids in the cheeses, and interactions between the lipid radicals and proteins seemed to be decisive for the generation of dityrosine, whereas the influence of lipid radicals on the generation of the DMDS seemed more ambiguous. The higher levels of dityrosine and DMDS in the cheese with a high fat content indicated that transfer of radicals from the lipids to the proteins occurred. Even though the generation of DMDS was reduced in vacuum-packed cheese when compared to cheese packed in air, DMDS was formed in vacuum-packed cheese