Thermal instability and characteristics of donkey casein micelles.

The thermal stability of donkey milk, which largely depends on the stability of casein and whey proteins, plays a critical role in the manufacture of donkey dairy products. However, the thermal stability of donkey casein micelles is poorly understood. Our study first found that donkey milk exhibited poor thermal stability, with sedimentation observed after heating at 75 °C for 10 min. Moreover, electrophoresis results indicated that donkey casein micelles were more sensitive to heat treatment than whey protein. The characteristics of donkey casein micelles were then studied to determine the thermal instability mechanism. Donkey casein micelles had a larger diameter (295 ±â€¯11 nm) and lower absolute zeta potential (-15.4 ±â€¯0.5 mV) than bovine casein micelles, mainly due to their very low κ-casein levels. The higher proportion (51%) of ß-casein in donkey casein micelles made them less hydrated. Furthermore, <40% of calcium in donkey milk was associated with donkey casein micelles. To eliminate the influence of whey protein, micellar casein was isolated from skim donkey milk by ultracentrifugation and then redispersed in its ultrafiltrate. Transmission electron microscopy and particle size analysis showed the extensive aggregation of isolated casein micelles after thermal treatment, which confirmed the thermal instability of casein micelles observed in donkey milk. Overall, poor colloidal stability and a high­calcium environment largely contributed to the thermal instability of donkey casein micelles.

[Detection of Mycobacterium tuberculosis complex in paraffin-embedded tissues by real-time fluorescent quantitative polymerase chain reaction].

OBJECTIVE: To investigate the feasibility of real-time fluorescent quantitative (qPCR) assay in detecting mycobacterium tuberculosis complex (MTB) in paraffin embedded tissues for diagnostic purpose. METHODS: Using qPCR assay, 1000 consecutive formalin-fixed and paraffin embedded (FFPE) tissues (from 2011 to 2012) suspected of MTB infection were tested by amplifying the MTB specific insertion sequence 6110 (IS6110). The specificity of the PCR product was confirmed by Sanger sequencing as compared with the MTB genomic DNA of the IS6110 sequence. Tissues with Ziehl-Neelsen acid-fast staining were used as control. RESULTS: In the 1000 samples, 513 were positive for mycobacterium by Ziehl-Neelsen acid-fast staining (detection rate 51.3%); whereas 546 were MTB positive by qPCR assay (detection rate 54.6%). Concordance rate for both assays was 73.1%. The diagnosis rate increased by 14.4% by combinination of Ziehl-Neelsen acid-fast staining and qPCR results. More interestingly, by analyzing the Ziehl-Neelsen acid-fast staining and qPCR results three cases of M.leprae infection and four cases of non-tuberculous Mycobacterium (NTM) infection were identified. CONCLUSIONS: qPCR detection of MTB in FFPE tissue is more sensitive than Ziehl-Neelsen acid-fast staining assay. Combination of these two assays can increase the detection rate and also identify some rare cases of NTM infection.