SOP: Milk Powder — Preparation of Sample and Determination of Moisture
GIFSQ — Global Institute for Food Safety & Quality
Scope
Whole milk powder, skimmed milk powder, partially skimmed milk powder, infant milk food, infant formula, milk cereal weaning food and processed cereal based weaning food fall under this category.
1. Preparation of sample of milk powder
Make the sample homogeneous either by mixing or shaking, or alternately rolling and inverting the container. Avoid excessive temperature and humidity when opening the sample container, to prevent absorption of moisture.
2. Determination of moisture in milk powder
Scope
This can be applied to all milk powder, infant foods, etc.
Principle
The sample is dried to constant weight at 102 ± 2°C and the loss in weight reported as moisture.
Apparatus
a. Flat-bottom moisture dishes with cover: of stainless steel, nickel or aluminium, having approximately 50 mm diameter and 25 mm depth. The dishes shall have lids which fit well and can readily be removed.
b. Hot air oven: maintained at 102 ± 2°C.
c. Desiccator: containing an efficient desiccant.
Procedure
Uncover a dish and place the dish and its lid in a hot air oven at 102 ± 2°C for 1 hour
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Place the lid on the dish, transfer the covered dish from the hot air oven to the desiccator, allow it to cool to room temperature and weigh it
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Put approximately 1 g of the dried milk sample in the dish, cover the dish with the lid and weigh the covered dish accurately and quickly
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Uncover the dish and put it with its lid in the hot air oven maintained at 102 ± 2°C for 2 hours
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Replace the lid, transfer the covered dish to the desiccator, allow it to cool to room temperature (for approximately 30–45 minutes) and weigh it accurately and quickly
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Heat the uncovered dish and lid in the hot air oven at 102 ± 2°C for a further 1 hour, replace the lid, allow the covered dish to cool to room temperature in the desiccator and weigh it
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Repeat the process of drying, cooling and weighing until the successive weighings do not differ by more than 0.5 mg. (It is usually found that drying is complete after the first 2 hours.)
Calculation
Moisture % by mass = 100 × (M₁ − M₂) ÷ (M₁ − M)
Where,
– M = mass in g of the empty dish (with lid)
– M₁ = initial mass in g of the dish and lid with the material taken for analysis
– M₂ = final mass in g of the dish and lid with the material after drying
The maximum deviation between duplicate determinations should not exceed 0.06% by mass of moisture.
Caution
These products are hygroscopic in nature and they can easily absorb environmental moisture. Care should be taken during handling of sample.
Note
This method gives free moisture content in powder, i.e. it does not include water of crystallization of alpha lactose monohydrate.
References
Manual of Methods of Analysis of Foods, Milk and Milk Products, FSSAI, 2016, Method 10.2.