Sampling dairy products facilitates comprehensive analysis of any given product for quality assurance. A sample represents the quality of the entire volume of the product under consideration.
Sampling is necessary because it is practically impossible to test the whole volume of milk.
There is need to examine milk for the following reasons:
- Examination will reveal the chemical composition of milk such as fat, protein, lactose contents and vitamins
- Analysis will help determine the quantity of developed acidity in the milk
- To determine the presence of adulterants or preservatives in the milk
- Examination will help estimate bacterial content and the amount of sediments in the milk
It is important to carry out a proper sampling to obtain accurate results.
Some common definitions you should know when sampling dairy products
Sampling: – drawing out of a portion of substance/material from the total population
Population: – total quantity of material whose characteristics you are seeking through sampling
Sample: – a small portion of the population which you obtain in such a way as to represent the characteristics of that particular population as closely as possible. Only a representative sample will produce consistent results.
You can have a single sample different sub-samples, which you collect from different parts of the population. You get a representative sample by randomly drawing from the population.
Random sample: – a random sample occurs when every object in the population has an equal chance of selection
Biased sample: – a sample where some objects in the population have unlikely chance of selection
Laboratory sample: – when a sample is too large for a normal lab examination procedure, you take its fraction. This fraction is the lab sample.
The primary objective of sample selection is to ensure that the features of the lab sample represent the population.
It is necessary to limit sample size to cut down on time, cost, and personnel required for that analytical work. Limited samples exhibit limited estimates of the whole population.
Equipment for sampling dairy products
This equipment is useful for attaining consistency in the milk/cream for a representative sampling of these dairy products. It is made of stainless steel, aluminium or any other metal that does not adversely affect the milk.
It consists of a perforated disk with a long handle fixed at its center to help in moving the equipment through the milk to achieve effective mixing.
Consists of a small cup fixed to one end of a long handle. It is mainly used to collect sample from the container. They vary in capacity.
Consists of an open ended tube with provision for closing one of the ends. It has the following advantages:
- You can obtain a representative sample regardless of how long the milk has stood before sampling
- You can collect a sample from a column of milk representative of the batch (from the top to the bottom of the container).
Sampling of milk and milk products differs in terms of materials you use and the purpose of the sample.
Things to remember when sampling dairy products
- If you have to transport the milk over long distances, chill and transport it using insulated containers/refrigerated trucks.
- Ensure that you examine the samples as soon as you draw them since chemical and microbiological changes may affect the results obtained
- Avoid violent mixing of the milk since the viscosity of milk will not allow air bubbles to rise to the top. Churning of the fat globules will also take place
- Unfreeze (thaw) milk (in case of frozen milk) before sampling begins
- Ensure you have a uniform mix of the milk from which you intend to draw the sample
- Fat is the most variable constituent of a standing milk sample
- You should onlu used chemically preserved milk for a chemical analysis.
Sample selection and sampling plans used for sampling dairy products
Sample selection is necessary because the destruction of the population occurs over time. The process is also tedious and time consuming.
A sampling plan is necessary because it ensures that the lab sample is truly representative of the entire population.
You should clearly write down your sampling plan in a document that contains the details the analyst will use. Such details may include the sample size, the population, method of collection, and preservation methods.
The sampling plan should also stipulate the required documentation of the sampling procedures. The choice of sampling plan will depend on:
- Purpose of the analysis
- Property to be analyzed
- Nature of the total population and individual samples
- Type of analytical technique to be used in characterizing the sample
Purpose of Analysis
Analysis is done for various reasons, which will affect the sampling plan. They include:
Necessary for legal requirements by government labs. This ensures that the suppliers/producers/manufacturers produce safe products that meet legal and labeling requirements e.g. whole milk sampling for butterfat content determination.
Necessary to ascertain the quality of materials a factory uses for processing are compliant. This ensures that the material will withstand the manufacturing processes.
High quality products
Quality of the products depends on the quality of the raw materials used for making themQuality of the products depends on the quality of the raw materials they're made from #qualityassurance Click To Tweet
Process control samples
Samples analyzed during processing to ensure that the process is operating in an effective manner. It aims at detecting problems and adjusting accordingly to end up with good quality products.
Techniques used in process controls should produce process results within a short time. This can be done in the following two ways:
- Measure the quality of the food online e.g. flow diversion valve
- Select/remove samples and test them in a quality assurance laboratory e.g. standardization
The finished product sampling
Aims at ensuring that the finished products are safe and they meet legal requirements
Property you intend to measure
Specify the particular property you want to analyze e.g. fat content, microbial load, developed acidity, etc. You can classify these properties as either attributes or variables.
Attributes: – properties that a product should either have or not.
Variables: – properties that you can measure on a continuous scale such as the butter fat content, weight, moisture content of milk powder, etc.
Variable sampling requires less samples than attribute samples. The type of property measured should determine the seriousness of the outcome (such as when measuring for harmful microorganisms, there is need for high precision due to the danger it poses than when measuring for fat content).
Nature of the population from which you draw the sample
A population can either be finite or infinite.
Finite population: – has a defined size e.g. tanker full of milk.
Infinite population: – has no defined size e.g. sampling from a conveyor belt which continuously supply the product e.g. packaging machine.
Analysis of finite population provides properties about that population. Analysis from an infinite population gives information about the processes.
Therefore, to facilitate sampling population, it is convenient to divide the infinite population into a number of finite populations e.g. all products produced in one shift forms one finite population.
This will help to trace the source of problems in the process.
A population can also be continuous or compartmentalized, homogeneous or heterogeneous
Continuous population: – no physical separation between the different parts of the sample e.g. well stirred milk in a tanker
Compartmentalized: – split into a number of separate sub-units
Homogeneous: – properties of an individual sample is the same as those of the other samples in different regions of the population
Heterogeneous: – characteristics of one sample vary within different locations of the population e.g. raw milk and its butterfat content; a well stirred milk is homogeneous while standing milk is heterogeneous.
Practically, most samples are heterogeneous hence the importance of selecting samples from different locations. You will then mix the parts well to obtain a representative sample.
Nature of the test procedure
Test procedure usually takes into account:
- Accuracy and precision
- The speed of measurement
- Cost per analysis
- Whether the technique is destructive/non-destructive
When you realize that the procedure is cheap, rapid and non-destructive, take more samples. More samples increases accuracy of the results you intend to achieve by sampling dairy products for analysis.