What is the difference between true/crude/total protein?
Crude protein, also referred to as total protein, is the protein content based on the total amount of nitrogen (N) in a sample. This means that non-protein nitrogen (NPN) compounds will also be included in this value. True protein on the other hand represents only the content of actual protein (based on only protein N), hence the denotation true. Human milk contains a large proportion of NPN, about 20-25 % of the total N. This is necessary to keep in mind when comparing results and reference samples analysed by different methods – does it give crude or true protein. The Miris HMA presents both crude and true to avoid misunderstandings. Miris applies the factor 6.38 to convert N content to protein content.
What is the effect of storage on components? Which one is most critical?
Longer storage time increases the risk of protein aggregation, which may result in the HMA giving low protein values or zero/negative protein values. Long storage time also gives an increased risk of “oiling off” (oil droplets on the surface of the milk). When analysing such milk there is a risk to get unstable and inaccurate fat values.
What is the cuvette volume? What is the minimum amount of milk we can inject?
The cuvette volume is very small, about 3 µl. However, you have to keep in mind that there is milk in the syringe, inlet, tubes, and outlet, so the actual minimum volume is 1 ml for a sample. The reason that we recommend 3 ml is that we can't guarantee a small carry-over effect from previous sample if you use smaller volumes.
How do I prepare frozen milk before analysis?
In the following order:
- thaw the sample in refrigerator (4°C)
- heat the sample to 40 ºC in a water bath (or similar)
- homogenize the sample with Miris Ultrasonic Processor (or Miris Sonicator, or equivalent instrument approved by Miris)
- Analyse imidiately or keep the sampel in the water bath until analysis, maximum 15-20 minutes
Is there a standard operating procedure when using the Miris HMA™?
Yes, there is. The standard operation procedure can be found in the user manual.
Is it possible to analyses pasteurized human milk using the calibration 1 for homogenized milk?
Pasteurized milk is not a problem when you use Calibration 1 in the Miris HMATM.
What are ”typical” breast milk values?
The composition of human milk is highly variable, with factors such as diurnal variation, longitudinal changes associated with postpartum duration, time since last feed, volume of milk consumed at the prior feed, time during feed, and maternal physiological let down to consider. The internal calibration of the Miris HMATM can handle samples within the following measuring range:
Fat 0.6 – 5.9 g/100 ml, Crude Protein 0.8 – 3 g/100 ml, True Protein 0.6 – 2.4 g/100 ml, Carbohydrate 4 – 8 g/100 ml
Why do I have to warm the milk to 40 degrees?
In order to get a more homogeneous sample, which gives more reliable results. The analysis time will be shorter and to avoid damaging the instrument’s sample cell.
How much milk is required for each analysis?
Can I use the milk after it has been flushed through the instrument?
How do I get a representative sample if I can’t warm the whole bottle of milk?
Try mixing gently by turning the bottle back and forth. Keep in mind that this might be a non-representative sample when performing the analysis – the instrument measures only the milk you inject.
How do I know when the milk is of ”bad quality”?
If the milk has started to curdle and separate, if there are visible white spots, or if there are oil droplets on the surface (oiling-off) then it should not be analysed.
Can I analyse preserved milk?
Yes, if you have used the preservative ”Bronopol” 2-bromo-2-nitropropane-1,3-diol.
Is it possible to analyse anything based on milk?
Contact Miris with your specific question.
Which range of concentration is the HMA able to analyse protein in human milk?
You can analyse protein in the range of 0.8 - 3 g/100ml.
Does the Miris HMA report lactose in human milk, or the total carbohydrate content?
In human milk the proportion of carbohydrates is about 70 % lactose and 30 % oligosaccharides. In the HMA the determination is based on hydroxyl groups (waveband 9.6 µm in the infrared spectra), which means it measures the total carbohydrate content.