Microbiological Quality Control of Food | Microbiology

The following points highlight the top four traditional approaches for control of microbiological quality at source. The approaches are:- 1. Training 2. Facilities and Operations 3. Equipment 4. Cleaning and Disinfection.

Traditional Approach # 1. Training:

Food handlers should be trained in the basic concepts and requirements of food and personal hygiene as well as those aspects particular to the specific food-processing operation. The level of training will vary depending on the type of operation and the precise job description of the employee, however some form of induction training with regular updating or refresher courses is an absolute minimum.

This has been a matter of course in the best food companies for many years, but is now to be a statutory requirement for all food businesses in the UK under the 1990 Food Safety Act.

Training should give food handlers an understanding of the basic principles of hygiene, why it is necessary, and how to achieve it in practice.

A core curriculum for any such course should emphasize:

(1) Micro-organisms as the main cause of food spoilage and foodborne illness and the characteristics of the common types of food poisoning.

(2) How to prevent food poisoning through the control of microbial growth, survival or contamination.

(3) Standards of personal hygiene required of food handlers. These are principally to avoid contamination of food with bacteria the food handler may harbour as part of the body’s flora, e.g Staph, aureus, Salmonella or that they may bring in with them from the outside world, e.g. Listeria, B. cereus. Some do’s and don’ts associated with good personal hygiene are listed in Table 11.5.

(4) Principles of the handling and storage of foods such as the correct use of refrigerators and freezers, the importance of temperature monitoring, the need for stock rotation and the avoidance of cross-contamination.

(5) Correct cleaning procedures and the importance of the ‘clean-as-you-go’ philosophy.

(6) Knowledge of the common pests found in food premises and methods for their exclusion and control.

(7) An introduction to the requirements of current food legislation.

These topics should be illustrated and supplemented with material relevant to the specific type of food business and the foods being handled.

Traditional Approach # 2. Facilities and Operations:

The environment in which food processing is conducted as an important factor in determining product quality. The premises should be of sufficient size for the intended scale of operation and should be sited in areas which are free from problems such as a particular pest nuisance, objectionable odours, smoke or dust.

The site should be well accessed by metalled roads and have supplies of power and potable water adequate to the intended purpose. Particular attention should also be paid to the provision of facilities for the efficient disposal of processing wastes.

Buildings must be of sound construction and kept in good repair to protect the raw materials, equipment, personnel and products within, and to prevent the ingress of pests. The grounds surrounding the plant should be well maintained with lawns but regularly and a grass-free strip of gravel or tarmac around the buildings.

Well- tended grounds will not only prove aesthetically pleasing but will help in the control of rodent pests. Landscaping features such as ponds are not advisable since they may encourage birds and insects.

It is important that the buildings provide a comfortable and pleasant working environment conducive to good hygienic practices. They should be well lit, well ventilated and of sufficient size to maintain the necessary separation between processes that could give rise to cross-contamination.

Features such as control of temperature and relative humidity and a positive pressure of filtered air may be required in some process areas for the benefit of both personnel and product.

In processing areas, floors should be made of a durable material which is impervious, non-slip, washable, and free from cracks or crevices that may harbour contamination. Where appropriate, floors should be gently sloped to floor drains with trapped outlets. Internal walls should be smooth, impervious, easily cleaned and disinfected, and light coloured.

The angle between floors and walls should be coved to facilitate cleaning. Ceilings should be light-coloured, easy to clean, and constructed to minimize condensation, mould growth and flaking. Pipework, light fittings and other services should be sited to avoid creating difficult-to-clean recesses or overhead condensation.

A false ceiling separating processing areas from overhead services has sometimes been advocated though these are generally used only in particularly sensitive areas. Light fittings should be covered to protect food below in the event of a bulb or fluorescent tube shattering.

Windows should have sills sloped away from the glass and, in some climates, should be covered with well-maintained fly screens. All entrances to the plant must be protected by close fitting, self-closing doors to prevent the ingress of birds and other pests. Air curtains may also be used to protect some work areas.

Toilets and changing facilities should be clean, comfortable, well lit and provide secure storage for employees’ belongings. Toilets should not open directly on to food-processing areas and must be provided with hand-washing facilities supplied with hot water, soap and hand-drying facilities.

Ideally, taps and soap dispensers should be of the non-hand-operated type and single-use disposable towels or an air blower be provided for hand drying. Hand washing facilities should also be available elsewhere in the plant wherever the process demands.

The overall layout of the plant should ensure a smooth flow-through from raw materials reception and storage to product storage and dispatch. Areas may be designated as ‘high risk’ or ‘low risk’ depending on the sensitivity of the materials being handled and the processes used.

High- and low-risk areas of a production process should be physically separated, should use different sets of equipment and utensils, and workers should be prevented from passing from one area to the other without changing their protective clothing and washing their hands.

The cipal situation where such a separation would be required is between an area dealing with raw foods, particularly meat, and one handling the cooked or ready-to-eat product. It should hardly need emphasizing that the same rules governing access, behaviour and the wearing of protective clothing also apply to management, visitors and anyone requiring to visit the processing areas.

Traditional Approach # 3. Equipment:

Equipment and its failings can be a source of product contamination and some notable examples are presented in Table 11.6. The main objectives of the design of hygienic food-processing equipment are to produce equipment that performs a prescribed task efficiently and economically while protecting the food under process from contamination.

There is general agreement on the basic principles of hygienic design, as outlined by a number of bodies. Those given below are taken from the Institute of Food Science and Technology (UK) publication, Good Manufacturing Practice: A Guide to its Responsible Management’ with slight modification.

(1) All surfaces in contact with food should be inert to the food under conditions of use and must not yield substances that might migrate to or be absorbed by the food.

(2) All surfaces in contact with the food should be microbiologically cleanable, smooth and non-porous so that particles are not caught in microscopic surface crevices, becoming difficult to dislodge and a potential source of contamination.

(3) All surfaces in contact with food must be visible for inspection, or the equipment must be readily dismantled for inspection, or it must be demonstrated that routine cleaning procedures eliminate the possibility of contamination.

(4) All surfaces in contact with food must be readily accessible for manual cleaning, or if clean-in-place techniques are used, it should be demonstrated that the results achieved without disassembly are equivalent to those obtained with disassembly and manual cleaning.

(5) All interior surfaces in contact with food should be so arranged that the equipment is self-emptying or self-draining. In the design of equipment it is important to avoid dead space or other conditions which trap food and may allow microbial growth to take place (Figure 11.8).

(6) Equipment must be so designed to protect the contents from external contamination and should not contaminate the product from leaking glands, lubricant drips and the like; or through inappropriate modifications or adaptations.

(7) Exterior surfaces of equipment not in contact with food should be so arranged to prevent the harbouring of soils, micro-organisms or pests in and on equipment, floors, walls and supports. For example, equipment should fit either flush with the floor or be raised sufficiently to allow the floor underneath to be readily cleaned.

(8) Where appropriate, equipment should be fitted with devices which monitor and record its performance by measuring factors such as temperature/time, flow, pH, weight.

Traditional Approach # 4. Cleaning and Disinfection:

In the course of its use, food processing equipment will become soiled with food residues. These may impair its performance by, for instance, impeding heat transfer, and can act as a source of microbiological contamination.

Hygienic processing of food therefore requires that both premises and equipment are cleaned frequently and thoroughly to restore them to the desired degree of cleanliness. Cleaning should be treated as an integral part of the production process and not regarded as an end- of-shift chore liable to be hurried or superficial.

What appears to be clean visually can still harbour large numbers of viable micro-organisms which may contaminate the product.

Cleaning operations in food processing have, therefore, two purposes:

(i) physical cleaning to remove ‘soil’ adhering to surfaces which can protect micro-organisms and serve as a source of nutrients; and

(ii) microbiological cleaning, also called sanitizing or disinfection, to reduce to acceptable levels the numbers of adhering micro-organisms which survive physical cleaning.

These are best accomplished as distinct operations in a two-stage cleaning process (Figure 11.9), although combined detergent/sanitizers are sometimes used for simplicity and where soiling is very light.

In a general cleaning/disinfecting procedure, gross debris should first be removed by brushing or scraping, possibly combined with a pre-rinse of clean, potable (drinking quality) water. This should be followed by a more thorough cleaning which requires the application of a detergent solution.

The detailed composition of the detergent will depend on the nature of the soil to be removed, but a main component is likely to be a surfactant; a compound whose molecules contain both polar (hydrophilic) and nonpolar (hydrophobic) portions.

Its purpose in detergent formulations is to reduce the surface tension of the aqueous phase, to improve its penetrating and wetting ability and contribute to other useful detergent properties such as emulsification, dispersion and suspension.

There are three main types of surfactant, classified according to the nature of the hydrophilic portion of the molecule:

(i) anionic – in these, which, include soaps, alkyl sulfonates and alcohol sulfates, the hydrophilic portion is a negatively charged ion produced in solution. They are incompatible with the use of quaternary ammonium compounds (QUATs) which art positively charged;

(ii) non-ionic – made by condensing ethylene oxide on to the polar end of a fatty acid, fatty alcohol or alkyl phenol;

(iii) cationic – quaternary ammonium compounds (QUATs) which have a positive charge in solution and are used mainly for their bacteriostatic and bacteriocidal activity rather than their cleaning properties.

Detergent preparations also often include alkalis such as sodium hydroxide, sodium silicates, or sodium carbonate which assist in solubilizing organic material such as fats and proteins. Acids are used in other formulations designed to remove the tenacious mineral scales such as milkstone which build up on surfaces, particularly heated ones, after repeated use.

Phosphates have a number of useful functions in detergents though their subsequent environmental impact can pose problems. Detergent performance is improved by sequestering agents which chelate calcium and magnesium ions and prevent the formation of precipitates.

Polyphosphates are often used for this purpose, although ethylenediamine tetra acetic acid (EDTA) and gluconic acid are alternatives which have the advantages of heat stability and compatibility with QUATs. Polyphosphates also inhibit the re-deposition of soil; a role for which sodium carboxymethyl cellulose is sometimes included.

Several other factors contribute to an effective cleaning procedure in addition to the chemical activity of the detergent solution. Heat generally improves the efficiency of cleaning, particularly with fat-containing soils, although the tempera­ture used must be compatible with the detergent, the soil type, and the processing surface being cleaned.

Mechanical energy in the form of shear forces created by turbulence, scrubbing or some other form of agitation considerably assists in the cleaning process. For smaller items of equipment this can be done manually but for larger areas and pieces of equipment some form of power cleaning is necessary.

This may involve the use of a high pressure low volume (HPLV) jet of water or detergent solution. HPLV systems operate at pressures in the range 40-100 bar (\ j with flow rates between 5 and 90 1 min^-1 and are best suited for cleaning equipment where it is necessary to direct a powerful jet into relatively inaccessible areas (though hygienic design should minimize these).

They are also used to rinse off detergents applied to equipment in the form of gels or foams; systems which give longer contact times between detergent and soil than would be obtained simply by spraying with an aqueous detergent solution. Gel or foam cleaning is particularly suited to use with more recalcitrant soils and on non-horizontal equipment surfaces where conventional detergent solutions would quickly run off.

Low pressure/high volume (LPHV) cleaning (≈ 5 bar; ≈ 500 1 min^-1) is suitable for areas with a low level of soiling with water soluble residues or washing light debris to a floor drain.

It is desirable that equipment is not left wet after cleaning since micro-organisms will be able to grow in any residual water film. This is best achieved by provision of sufficient drainage points and natural air drying, although drying with single-use tissues may be required in some circumstances.

Many micro-organisms will be removed along with the soil in the course of cleaning, but many may remain on an apparently clean surface. It is therefore necessary to disinfect equipment after cleaning. A most efficient means of doing this is through the application of moist heat, which has a distinct advantage over chemical disinfectants in that its efficacy is not impaired by residual organic matter.

It does however require careful control to ensure that the required temperature is maintained long enough for it to be effective. This is most appropriate in enclosed systems and is not always practicable in other areas for which chemical disinfectants are the method of choice.

Six types of chemical disinfectant are most commonly used in food processing:

(1) chlorine and chlorine compounds

(2) iodophors

(3) quaternary ammonium compounds (QUATs)

(4) biguanides

(5) acid anionic surfactants

(6) amphoteric surfactants

Hydrogen peroxide and per-acetic acid are also used in some applications such as the disinfection of packing materials. Chemical disinfectants do not act specifically on a single aspect of a microbial cell’s metabolism but have a more broadly based inhibitory effect.

In the case of chlorine, iodophors and per-acetic acid, they act as non-specific oxidizing agents oxidizing proteins and other key molecules within the cell, while others such as QUATs and amphoterics act as surfactants, disrupting the cell membrane’s integrity.

For this reason, development of microbial resistance requires quite complex cellular changes. This’ has been noted in capsulated Gram-negative bacteria where changes in the composition of the cell membrane have resulted in resistance to QUATs and amphoterics.

Development of resistance by some pseudomonads to these agents can, however, be prevented by addition of a sequestering agent which is believed to interfere with calcium and magnesium binding in the outer membrane and capsule, making the cell more vulnerable. Acquisition of resistance to oxidizing disinfectants has not been observed.

The main considerations in choosing a chemical disinfectant for use in the food industry are:

(1) Its microbiological performance – the numbers and types of organisms to be killed.

(2) How toxic is it and what is its effect on the food?

(3) What is its effect on plant – does it stain or corrode equipment?

(4) Does it pose any hazard to staff using it?

(5) Is it adversely affected by residual soil?

(6) What are the optimal conditions for its use, i.e. temperature, contact time, pH, water hardness?

(7) How expensive is it?

Some of these characteristics are summarized in Table 11.7.

All disinfectants are deactivated to some extent by organic matter. This is why they are best used after thorough cleaning has removed most of the soil. Chlorine in the form of hypochlorite solution is the cheapest effective disinfectant with a broad range of antimicrobial activity which includes spores. The active species is hypochlorous acid (HOCl) which is present in aqueous solutions at pH 5-8.

It is corrosive to many metals including stainless steel although this can be minimized by using it at low concentrations, at alkaline pH, at low temperature and with short contact times. For most purposes an exposure of 15 minutes to a solution containing 100 mg l^-1 available chlorine at room temperature is sufficient.

In iodophors, iodine is dissolved in water by complexing it with a non-ionic surfactant. Phosphoric acid is often included since the best bactericidal activity is observed under acidic conditions. To disinfect clean surfaces a solution containing 50 mg l^-1 available iodine at a pH < 4 is usually required.

The amber colour of iodophors in solution has two useful functions: it provides a crude visual indication of the strength of the solution and it will stain organic and mineral soils yellow indicating where equipment has been inadequately cleaned. However, they can also stain plastics and can taint some foods.

QUATs are highly stable with a long shelf-life in concentrated form. They are non-corrosive and can therefore be used at higher temperatures and with longer contact times than other disinfectants. However at low concentrations (< 50mg l^-1) and low temperatures they are less effective against Gram-negative bacteria.

This is not usually a problem under normal conditions of use (150-250 mg l^-1; >40 °C; contact time > 2 min), although incorrect usage could result in a build up of QUAT-resistant bacteria on equipment.

Because of their surfactant properties, QUATs (and amphoterics) adhere to food-processing surfaces even after rinsing. This can be an advantage; in one study in a poultry plant, levels of bacteria on plant were shown to continue decreasing for nine hours after disinfection as a result of the effect of residual QUAT.

In some areas though, it can be a problem; residual QUAT or amphoteric may inhibit starter culture activity in cheese and yoghurt production and can also affect head retention on beer. Biguanides are similar to QUATs but have greater activity against Gram negatives, although development of resistance has been noted here too.

Amphoterics are surfactants with a mixed anionic and cationic character which are far less affected by changes in pH than other disinfectants. Their high foaming characteristics make them unsuitable for some uses.

In modern food processing much equipment cleaning is automated in the form of cleaning-in-place (CIP) systems. These are most readily applied to cleaning and disinfecting plant which handles liquid foods and have therefore found widest application in the brewing and dairy industries, although they are now appearing in meat processing plants.

A CIP system is a closed section of plant which can be cleaned by draining the product followed by circulation of a sequence of solutions and water rinses that clean and then disinfect the plant leaving it ready for resumed production.

Though the initial capital investment is high, CIP offers a number of advantages. Its running costs are lower than traditional cleaning procedures since labour costs are low and it gives optimal use of detergents, disinfectants, water and steam.

As it does not involve the dismantling of plant prior to cleaning, CIP minimizes unproductive ‘down time’ and the risk of equipment damage during disassembly. It is also safer since personnel are no longer required to perform the sometimes hazardous operations of climbing up on to, or into, equipment and, provided the system is correctly formulated, it gives a consistent result with little chance of human error.

To ensure cleaning and disinfecting procedures are achieving the desired result some form of assessment is necessary. The inadequacy of visual inspection of equipment to determine its microbiological status has already been alluded to. It is however worth noting that, with few exceptions, if a surface is visually dirty it is also likely to be microbiologically dirty.

Culturing micro-organisms removed from a cleaned surface by swabbing, rinsing or a contact-transfer technique will give an indication of the level of contamination, but only after sufficient time has elapsed for the organisms to produce visible growth. Recently the use of ATP bioluminescence has found increasing use in this area.

It provides a rapid measure of the hygienic status of a surface without having to distinguish between microbial and non-microbial ATP since high levels of ATP, whatever the origin, will indicate inadequate cleaning and disinfection.

Cleaning dry process areas presents an entirely different problem from that discussed above. By their very nature these areas are inimical to microbial growth due to the absence of water. To introduce moisture in the name of hygiene could have exactly the opposite effect and give rise to microbiological problems. Cleaning in dry process areas should therefore be mechanical, using vacuum cleaners, wipes and brooms.