An introduction to commercial sterility
16Pages

An introduction to commercial sterility

Introduction History Single-cell friends and enemies The logarithmic order Approaching absolute sterility A weak link breaks the chain Meeting market requirements How many samples? Increasing sterilization efficiency A mixture of remedies UHT treatment Microfiltration Summary

Introduction The purpose of this booklet is to provide a basic understanding of the microbiological aspects of aseptic technology with the focus on the processing part. We do not aim to cover everything in detail, but instead try to give you a good overview of the importance of commercial sterility and how to achieve it. If you need more detailed information, do not hesitate to contact us at Tetra Pak. We are happy to assist you with our competence and experience. All quality is based on competence.

History The destruction of microorganisms Even before Louis Pasteur proved over a century ago that microorganisms caused fermentation and disease, Nicolas Appert, a Parisian confectioner, first succeeded in preserving certain foods in glass bottles that had been kept in boiling water for varying lengths of time. This happened in the first decade of the 1800’s and by 1839, tin-coated steel containers were widely in use. Thus began the birth of high heat treatment and canning as a means of preserving food. Today, a combination of continuous heat-treatment and aseptic packaging produces high...

The logarithmic order A never-ending story Aseptic processing involves one or more separate sterilization steps aimed at killing all microorganisms. When applying a sterilization procedure, e.g. using heat, not all bacterial spores are killed at the same time. A certain number will be killed within a given unit of time as shown in the table here. The principle behind the killing process is independent of the sterilization temperature. When the number of surviving spores is plotted against their logarithmic reduction, we obtain a straight line as shown in Figure 1. This straight line is...

Approaching absolute sterility As a logarithmic function never can reach zero but only approach it, absolute sterility never can be reached or guaranteed. The efficiency of a sterilization process is expressed by the number of decimal reductions in the count of resistant spores. The D-value (decimal reduction time) is normally used to indicate the killing rate, i.e. the time required at a certain temperature to kill 90% of the spores, which is the same as reducing their number by one logarithm unit. Measured under the same conditions, the D-value will be affected by the species of bacteria....

A weak link breaks the chain Aseptic processing and packaging is rather complex because a minimum of three different sterilization steps are required to achieve aseptic filling of the liquid food product. Sterilization is carried out: • on the equipment prior to production; • on the liquid food product; • on the packaging material surface. Each link in the processing and packaging chain must be equally strong. Packaging material The performance level of an aseptic plant must be regarded as the performance level of the entire process rather than that of a single component of the production...

Meeting market requirements The processing result is not determined by the processing factors alone but also by the quality of raw material, pre-processing procedures, environmental and operative parameters as well as maintenance. Absolute sterility – defined as the total absence of microorganisms – is not possible for the reason mentioned earlier and thus cannot be guaranteed. Commercial sterility According to the WHO/FAO, commercial sterility of low-acid food is defined as follows: “Commercial sterility means the absence of microorganisms capable of growing in the food at normal...

How many samples? More samples will improve the detection level To determine how many samples we need to take to detect a defective product, let’s look at a typical example. How many samples are required to detect a defect rate of 1 per 1 000 with 90% probability? This problem is solved with the help of the random sampling curve for 90% probability shown in Figure 3. If we follow the 1% figure up to where the curve intersects the y-axis we get the result 240. For 0.1% (1 per 1 000) the answer to the question is 2 400. The statistical results are affected only by the sampling size and not by...

Increasing sterilization efficiency The efficiency of a sterilization process can be expressed as the number of decimal reductions in microbial population achieved by the process. This is mainly determined by two factors: 1. The temperature and the length of time it is applied. 2. The heat-resistance of bacterial spores present, D-value. Some other factors, e.g. the composition, viscosity, uniformity and pH of the liquid food product, will also affect the sterilization efficiency. For typical UHT processing equipment it can be assumed that an average of 9 – 10 decimal reductions can be...

A mixture of remedies The importance of initial spore load on sterilization efficiency, and hence end-product quality, is obvious. But what can be done to improve the situation? The most important methods of achieving this are given below and summarized in the table. Improved hygiene A high concentration of spores may already be present in milk at the farm, or be introduced into raw materials as a result of poor preprocessing routines. The answer here is to improve the level of hygiene both at the farm and the processing plant. However, it is difficult to control what happens on a farm and...

UHT treatment Two principles There are two different UHT methods used in the liquid food industry – direct and indirect heating. Which one to use depends on a number of factors such as desired end product quality level and production economy. Direct heating When using direct heating, the product is brought into direct contact with hot steam under strictly controlled conditions. The sterilization temperature (140°C for 4 sec) is rapidly reached and after holding, the temperature is lowered by flash cooling in a vacuum vessel. The rapid heating and cooling gives minimal heat-load on the...