BS ISO 19344:2015 pdf free

BS ISO 19344:2015 pdf free.Milk and milk products一Starter cultures, probiotics and fermented products
Flow cytometry is a technique for rapid quantification of cells combining light source, optics, flow chamber, liquid sample delivery system, light detectors, electronics and software. The flow cytometer provides a constant f low of sheath fluid through a cuvette, singularizing and preparing the cells for analysis. The cuvette is traversed by a beam of light to illuminate f lowing cells. Around the cuvette,detectors collect scattered light in two angles [forward scatter channel (FSC) and side scatter channel (SSC)] and f luorescence in different colours (e.g. green, yellow, red). When a cell reaches the flow cuvette, a proportion of the light beam is scattered and cellular f luorescence markers are excited to emit f luorescence. The detection of the scattered light and the concomitant emission of f luorescence are referred to as an event, i.e. each cell passing through gives rise to one event, each of which shows the state of the cell.
Whereas the detected fluorescence is linked to the state of the cell, i.e. enzyme activity, membrane integrity and/or membrane potential, the FSC provides information on cell size and optical density. The SSC provides information on cell morphology, reflectivity and granularity.The recorded events per microlitre sample indicate how many cells are counted and at the same time differentiate, based on f luorescence parameters, the cells into two categories: active f luorescent and non-active fluorescent.
Flow cytometer configuration settings for the optimal functioning of the three protocols are given in Table 3. Some of the parameters, e.g. excitation source and filters for the detectors, are important for the proper performance of the individual protocols, whereas some are less important, e.g. event rate is equipment dependent and varies significantly from instrument to instrument.
The flow cytometer shall be properly calibrated in accordance with manufacturer instructions. Most flow cytometers are calibrated for accurate volumetric determination of the analysed sample for easy calculation of the cell concentration. For instruments without calibrated volumetric determination, the number of AFUs or TFUs in the sample is calibrated against standardized fluorescent beads, added to the sample as an internal standard, with a known concentration.BS ISO 19344 pdf download.