Whole polished rice grains were ground using cryogenic and hammer milling to understand the mechanisms of degradation of starch granule structure, whole (branched) molecular structure, and individual branches of the molecules during particle size reduction (grinding). Hammer milling caused greater degradation to starch granules than cryogenic milling when the grains were ground to a similar volume-median diameter. Molecular degradation of starch was not evident in the cryogenically milled flours, but it was observed in the hammer-milled flours with preferential cleavage of longer (amylose) branches. This can be attributed to the increased grain brittleness and fracturability at cryogenic temperatures, reducing the mechanical energy required to diminish the grain size and thus reducing the probability of chain scission. The results indicate, for the first time, that branching, whole molecule, and granule structures of starch can be independently altered by varying grinding conditions, such as grinding force and temperature.
This study applied Illumina high-throughput sequencing to explore the microbial communities and functions in anaerobic digestion sludge (ADS) from two wastewater treatment plants based on a metagenomic view. Taxonomic analysis using SILVA SSU database indicated that Proteobacteria (9.52-13.50 %), Bacteroidetes (7.18 %-10.65 %) and Firmicutes (7.53 %-9.46 %) were the most abundant phyla in the ADS. Differences of microbial communities between the two types of ADS were identified. Genera of Methanosaeta and Methanosarcina were the major methanogens. Functional analysis by SEED subsystems showed that the basic metabolic functions of metagenomes in the four ADS samples had no significant difference among them, but they were different from other microbial communities from activated sludge, human faeces, ocean and soil. Abundances of genes in methanogenesis pathway were also quantified using a methanogenesis genes database extracted from KEGG. Results showed that acetotrophic was the major methanogenic pathway in the anaerobic sludge digestion.
A novel, fast, and straightforward procedure is presented for the characterization of starch (the largest energy component in food) and modified starches (such as octenyl succinic anhydride (OSA)-modified starches used as a dispersing agent in the food industry). The method uses (1)H NMR to measure the degree of branching and also, for modified starches, the degree of chemical substitution. The substrate is dissolved in dimethyl-d(6) sulfoxide; addition of a very low amount of deuterated trifluoroacetic acid (d(1)-TFA) to the medium gives rise to a shift to high frequency of the exchangeable protons of the starch hydroxyl groups, leading to a clear and well-defined (1)H NMR spectrum, which provides an improved way to determine the degrees of both branching and chemical substitution. Measurements of the size and molecular weight distributions by multiple-detector size exclusion chromatography show that degradation by TFA does not affect the accuracy of the method.
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