Sampling of milk and milk products

Sampling is the extraction of a large, approximate quantity of material representative of the whole.

Table of Contents

Aims /objectives:

To become familiar with the different procedures to be followed in collecting samples of milk and milk products for analysis.
To arrive at correct conclusions about the quality of the sample and avoid misinterpretations.

Principle:

The result obtained from analysis of any sample depends on the sampling procedures and they are only as good as the quality of the sample. The proper collection and handling the sample, therefore, assumes a remarkable significance.

General Requirements:

Samples should be drawn by an experienced person in a protected place not exposed to damp air, bright , light, dust, root or smoke particles rain etc.
The sample temperature while sampling should be between 0 to 15 ^oC, and while transporation 0-7⁰ C (for ice-cream – 15⁰ C)
Care must be exercised to avoid adventitious contaminations of the sample adulteration sampling instruments and containers etc.
The sampling instruments and containers should be clean, dry and should not impart any foreign odour or flavor.
The sampling appliance should be made of approved material (SS), light in weight and easily operable.
The sample containers should be of adequate dimesions to allow for expansion at the top yet preventing air from exerting any detrimental effect
Each sample should be properly sealed after filling and marked with full details of sampling e.g. identifications of the sample, date, temperature at sampling .Name of the samples etc.
The sample should immediately be dispatched to the analytical laboratories , alternatively , there are required to be stored under approved conditions of storage

Refrigeration (0- 5⁰ C)
Preservatives –formalin (0.1ml /25 aulorg); pot. dichromate instrumental analysis (0.06g/100ml); Chloride 0.5g / 250ml – cryoscopie LPFA- declaration the label

While sampling for microbiology analysis all instruments and containers should be sterile and all aseptic precautions should be observed .

For chemical analysis container must be – clean & dry must be clean , dry sterile free from odorous compounds.

Sampling of Liquid Products:

The milk to be sampled must be thoroughly mixed by:

i ) Pouring milk in small containers from one to another several times.

ii) By plunging bulk samples several times.

iii) Moving a submerged plunger from place (especially true for cream)

iv) By agitation of bulk samples with a mechanical stirrer.

Care must be taken to avoid mixing too long or violently as this could lead to churning homogenization or foaming which will after finial result

The preferable method of sampling is to use individually wrapped, sterile or pasteurize.
Plastic single – service sampling tubes which may be dipped directly in to the milk. The portion of the container that wile contact the milk should be carefully handled .
Other method include the use of sanitized tubes or SS metal dippers for transfer of the sample into the sanitized or sterile containers .
Direct- line sampling- for this lives are required to be equipped with sanitized gaskets that will permit such sampling. The needle of a disposable, plastic, sterile hypodermic syringe can be inserted through the gasket. Care must, however, be taken during sampling not to introduce contamination .

Sampling for microbiology analysis must be kept between 0 and 5 C and analyzed within 24 hours of sampling . Samples for sensory analysis should likewise be kept between 0-50 C and analyzed as soon as possible . Its chemical analysis is to be done on the same set of samples; the portion needed for microbiology and sensory testing should be removed aseptically first. For chemical analysis alone, suitable preservatives many be used and such sample may than be transported at ambient temperature. Preserved sample should never be analyzed for microbiology or sensory properties.

Sampling of Dry Products:

A dry sampling may be representative of many bags in a shipment or it may be one sample container as small as a retail consumer pack or as a large as a rail or rood ear. Statistically sound plans should be developed and applied before actual sampling. Dry dairy products are very hygroscopic ; they should be exposed to the atmosphere for a minimal period to avoid moisture adsorption . Generally, a composite sample of several bags or areas within a bulk quantity is preferred. Dry sample are particularly susceptible to oxidation and should be protected from air oxygen and light after compositing . When the final sample is extracted for analysis, the composite sample should be mixed by shaking prior to taking the sub sample.

Sampling of Butter:

Butter may be sampled directly from the churn from bulk quantities, or form consumer size packs. Butter samples should be cooled between 0 and 5⁰ C immediately after sampling. samples should be placed into sterilized (or sanitized, if for chemical or sensory analysis only ) containers. Butter is sampled with a stainless steel trier. The trier can be sterilized between sample by wiping with a clean disposable towel or tissue, dipping in 70% alcohol flaming to remove excess alcohol and temperature by twice inserting into butter to be sampled . If samples are taken only for chemical or sensory examination, the trier can be cleaned and dried between each samples without sterilization in alcohol sampling should be accomplished from several different points to ensure a representatives mixture. The trier should pass diagonally through the butter from top to bottom though the centre to obtain a representative samples

Sampling of Cheese:

Cheese sampling is done with a cheese trier and the sample quantity is >50g. After the sample is extracted, care must be taken to close the hole. Sealing compounds such as a mixture of molten paraffin, beeswax, and white petroleum (1:1:2) or a mixture of white petroleum and paraffin (1:1 ) can be used to close the hole to prevent mold growth in the rest of the cheese. Cheese can be resealed in a vacuum – heat – sealable plastic pouch sub sample are taken following passage of cheese through a food chopper three times. Alternatively , The cheese may be cut or shred very finely and mixed .