Bacterial spoilage profiles in the gills of Pacific oysters (Crassostrea gigas) and Eastern oysters (C. virginica) during refrigerated storage.

Microorganisms harbored in oyster gills are potentially related to the spoilage and safety of oyster during storage. In this study, the microbial activities and pH changes of the gills of the two species, Crassostrea gigas and C. virginica, harvested from three different sites were determined and sensory evaluation was conducted during refrigerated storage. The bacteria in gills with an initial aerobic plate count (APC) of 3.1-4.5 log CFU/g rose remarkably to 7.8-8.8 log CFU/g after 8-days of storage. The APC of Enterobacteriaceae increased from 2.5 to 3.6 log CFU/g to 4.5-4.8 log CFU/g, and that of lactic acid bacteria (LAB) fluctuated in the range of 1.4-3.0 log CFU/g during the whole storage period. The results of sensory analysis indicated that the oysters had 8-days of shelf-life and that the gill presented the fastest deterioration rate. The pH of all samples showed a decrease in the early stages followed by an increased after 4-days of storage. The dynamic changes in microbial profiles were depicted to characterize gill spoilage by Illumina Miseq sequencing to characterize gill spoilage. The results revealed that oysters harvested at different sites showed common bacterial profiles containing Arcobacter, Spirochaeta, Pseudoalteromonas, Marinomonas, Fusobacterium, Psychrobacter, Psychromonas, and Oceanisphaera when spoiled, especially, among which Psychrobacter and Psychromonas (psychrotrophic genus) were represented as the most important gill spoiled bacteria during refrigerated storage, and Arcobacter with pathogenic potential was the dominated bacteria in all spoiled oysters. The consumption quality and safety of refrigerated oysters could be greatly improved by targeted control of bacteria in oyster gills according to the results the present study provided.

Conformational Properties of Flaxseed Rhamnogalacturonan-I and Correlation between Primary Structure and Conformation.

The pectic polysaccharides extracted from flaxseed (Linum usitatissiumum L.) mucilage and kernel were characterized as rhamnogalacturonan-I (RG-I). In this study, the conformational characteristics of RG-I fractions from flaxseed mucilage and kernel were investigated, using a Brookhaven multi-angle light scattering instrument (batch mode) and a high-performance size exclusion chromatography (HPSEC) system coupled with Viscotek tetra-detectors (flow mode). The Mw of flaxseed mucilage RG-I (FM-R) was 285 kDa, and the structure-sensitive parameter (ρ) value of FM-R was calculated as 1.3, suggesting that the FM-R molecule had a star-like conformation. The Mw of flaxseed kernel RG-I (FK-R) was 550 kDa, and the structure-sensitive parameter (ρ) values ranged from 0.90 to 1.21, suggesting a sphere to star-like conformation with relatively higher segment density. The correlation between the primary structure and conformation of RG-I was further discussed to better understand the structure-function relationship, which helps the scale-up applications of pectins in food, pharmaceutical, or cosmetic industries.

Structural and conformational characterization of arabinoxylans from flaxseed mucilage.

The structure of neutral fraction gum from flaxseed mucilage (FM-NFG) was studied for better understanding of the relationship between primary structure and conformation. Based on methylation/GC-MS, nuclear magnetic resonance (NMR) spectroscopy, the structure of FM-NFG was proposed as arabinoxylans. Flaxseed mucilage arabinoxylans contained ß-1,4-linked xylose backbones, which were mainly substituted at O-2 and/or O-3 positions by 1-3 sugar residues. The possible branches included → 5)-α-l-Araf-(1 → (17.3 mol%), → 3)-α-l-Araf-(1 → (4.9 mol%), and → 4)-α-d-Glcp-(1 → (3.5 mol%), which were ended with three terminal sugar units: T-ß-d-Xylp-(1 → (15.5 mol%), T-α-d-Glap-(1 → (4.5 mol%), and T-α-l-Araf-(1 → (2.6 mol%). The weight average molecular weight (Mw) of flaxseed mucilage arabinoxylans was calculated to be 1747 kDa by static light scattering (SLS), and it exhibited random coil conformation. The proposed structure and conformational models confirmed that different backbone sugar units especially substitution positions directly contributed to the conformational diversity and rigidity of polysaccharide molecules.

Biological hydrolysis pretreatment on secondary sludge: Enhancement of anaerobic digestion and mechanism study.

The performance of biological hydrolysis (BH) pretreatment on municipal secondary sludge was evaluated in this study. During 6-day BH at 42°C (BH42), soluble chemical oxygen demand (sCOD) increased from 175.2±38.2mg/L to 3314.5±683.4mg/L; the dominant volatile fatty acid (VFA) was acetic acid, and its concentration increased from 41.5±2.1mg/L to 786.0±133.2mg/L. The extracted extracellular polymeric substances (EPS) from untreated secondary sludge contained three main fractions, and Fraction I gradually decreased from 133.9kDa to 24.9kDa during 6-day BH42. The BH pre-treatment at 42°C and 55°C both achieved more than 4-log reduction of total coliforms and 3-log reduction of E. coli. The BH pretreated secondary sludge at 15-day biochemical methane potential (BMP) test was comparable with the untreated secondary sludge after 30-day BMP, showing a significant enhancement on the acceleration of biogas production by BH pretreatment.

Xyloglucans from flaxseed kernel cell wall: Structural and conformational characterisation.

The structure of ethanol precipitated fraction from 1M KOH extracted flaxseed kernel polysaccharides (KPI-EPF) was studied for better understanding the molecular structures of flaxseed kernel cell wall polysaccharides. Based on methylation/GC-MS, NMR spectroscopy, and MALDI-TOF-MS analysis, the dominate sugar residues of KPI-EPF fraction comprised of (1,4,6)-linked-ß-d-glucopyranose (24.1mol%), terminal α-d-xylopyranose (16.2mol%), (1,2)-α-d-linked-xylopyranose (10.7mol%), (1,4)-ß-d-linked-glucopyranose (10.7mol%), and terminal ß-d-galactopyranose (8.5mol%). KPI-EPF was proposed as xyloglucans: The substitution rate of the backbone is 69.3%; R1 could be T-α-d-Xylp-(1→, or none; R2 could be T-α-d-Xylp-(1→, T-ß-d-Galp-(1→2)-α-d-Xylp-(1→, or T-α-l-Araf-(1→2)-α-d-Xylp-(1→; R3 could be T-α-d-Xylp-(1→, T-ß-d-Galp-(1→2)-α-d-Xylp-(1→, T-α-l-Fucp-(1→2)-ß-d-Galp-(1→2)-α-d-Xylp-(1→, or none. The Mw of KPI-EPF was calculated to be 1506kDa by static light scattering (SLS). The structure-sensitive parameter (ρ) of KPI-EPF was calculated as 1.44, which confirmed the highly branched structure of extracted xyloglucans. This new findings on flaxseed kernel xyloglucans will be helpful for understanding its fermentation properties and potential applications.