Fruit and vegetable processing industries produce very large quantities of
products which are intended for consumption, often on a daily basis, by the
population at large. Such industries therefore have a special responsibility
to ensure that their products are both wholesome and safe, as well as
successful in the marketplace.
Fundamentals of Agriculture Vol.-1&2
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This manual is intended for use by processors of fruit and vegetable
products as a guide to the establishment and operation of soundly based and
effective quality control systems. The manual deals with quality control in
the following types of fruit and vegetable processing:
- pickling, syruping, crystallizing and chemical preservation.
In preparing the manual it was accepted that only limited resources can be
made available in any commercial enterprise for quality control. It was also
recognized that at least a minimum level of quality control is essential
because the products of the fruit and vegetable processing industry are
intended for human consumption.
The amount of a company’s resources that should be given to quality control operations will vary according to the nature of the product and process, the possible hazards associated with defective products being produced and consumed, and other factors. It was also recognized that the way quality control systems are structured and manned varies according to the nature of the product and process and the size of the manufacturing operation. In some factories employing only a few people, quality control may be only one of several responsibilities of a particular member of staff but even in that situation it is essential that an appropriate level of quality control be maintained.
Containers, labels and packaging materials
Quality control staff should inspect each consignment of containers, labels
and packaging materials to ensure that they are delivered in good conditions
and that the items comply with the purchasing specification. In addition,
samples of primary containers (cans, drums, glass jars, flexible pouches and
bags and semi-rigid aluminium tray packs) should be examined to determine
that the properties of these items that are critical to the safety and
storage stability of the product are satisfactory.
Cans: Samples of cans should be examined to determine that the following
features are within specifications:
. the double seam;
. the side seam and flange of the open end;
. the type and coating mass of internal lacquers, and their coverage
and degree of adhesion;
. the tin coating mass;
. the structure of the loose ends and the placement and amount of
Some cans should also be filled with water and closed so that the canner’s double seam may be assessed. If the seams are of doubtful quality the cans should also be leak tested.
Glass containers. Samples of glass containers should be examined for defects in construction and for variations in dimensions that may affect their ability to be properly closed and to withstand impacts and other abuses which are encountered during filling, closing, processing, distribution and storage. Quality control staff should give special attention to the sealing surface of glass containers; this surface should be horizontal and smooth and it should make a cleanly-defined and continuous contact with the gasket when the closure is applied under usual processing conditions.
Many types of closures are applied to glass containers so quality
control staff should obtain information on the structure and application of
the closures from the container manufacturer to plan realistic inspection
procedures. The critical factors influencing the quality of the seal on
glass containers include the dimensions of the closure and the type, quantity
and distribution of the gasket material.
The storage performance of glass containers closed with metal closures often depends on the resistance of the closure to corrosion by the product, especially an acidic product containing salt and sulphur dioxide. Metal closures are usually protected by an internal lacquer which must have excellent barrier properties. Sample closures should therefore be examined to determine that the lacquer is
essentially continuous, applied at the specified coating mass and adheres strongly to the surface of the metal.
Plastic pouches and semi-rigid aluminium tray packs. Semi-rigid aluminium
tray packs have some technical features in common with plastic pouches in
that they are closed by heat sealing and they have some flexibility. Quality control staff should confirm the identity and thickness of plastic packaging
materials since these properties mainly determine the barrier properties of
the package (British Cellophane, 1970). If the shelf life of the product is
critically dependent on the barrier properties of the package, the oxygen
permeability and/or the water vapour permeability and the integrity of sample
packages should be determined before they are used in production.
Labels, cartons and other ultimate containers. Quality control staff should
inspect and measure these items to determine that they conform to the
purchasing specifications. The information displayed on labels and on
ultimate containers should be checked for accuracy, and the registration and
quality of the printing and art work should be assessed by quality control
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Detergents, sanitizers and similar materials
Quality control staff should inspect these items on receival using the same
approach as that described for food ingredients”Sugar, salt, spices,
food acids and other minor ingredients”.
Production staff have primary responsibility for carrying out such treatments
as sorting, grading, washing, blanching and mixing. However, because quality
control of these operations is mainly based on visual inspection production
staff should be encouraged to assist quality control staff to ensure, for
- sorting and trimming is properly done;
- foreign material is removed;
- the product is thoroughly washed;
- the product is sub-divided as required for the style of the pack;
- the product moves continuously and with minimum delay through the
Quality control staff should monitor the concentration of chemicals in
chemical peeling baths; usually the active material is caustic soda (sodium
hydroxide) so acid titrations should be done often enough to ensure that the
required concentration can be maintained.
Quality control staff should also check the composition of brines and
syrups used as packing media and in the manufacture of pickled, syruped and
crystallized products. The concentration of salt in simple brines may be
estimated by hydrometry, and indicated by a simple test of
electrical conductivity, or even by tasting. In brines containing other
substances chemical methods are used t o determine the concentration of salt.
The concentration of sugar in simple syrups is most readily determined by refractometry but hydrometry may also be used. Again tasting gives an estimate of the strength of a syrup.
Brines and syrups are sometimes acidified and in some instances the level of acidification is critically important in determining the safety of the final product. Quality control staff should check the acidity of each batch of acidified brine or syrup by alkaline titration; pH measurements or tasting are not appropriate in this situation.
Quality control staff should monitor the filling operation to ensure that each container receives at least the nominated amount of the product and that the container is not excessively filled. Excessive fills are commercially wasteful and in some instances they may be hazardous. For example, the double seams of canned foods may be damaged if the can is overfilled because the product expands more than the metal of the can during the heat sterilization process. The fill may be checked by weighing or by measuring the volume of the product. The headspace, i.e. the distance between the top of the open can and the surface of the product, may also be measured. It should be remembered that the mass and volume of a product will vary with its density, and density will vary according to the composition of the product and its temperature.
Quality control staff, with support from production staff, should inspect the filling operation to ensure that the sealing surfaces of the containers are not contaminated with spilt products which may cause the seal to be substandard. Fibrous vegetable tissue may cause leaky seals if the tissue is incorporated in double seams of cans or between the gasket and finish of glass containers. The heat-seal surfaces of flexible pouches and semi-rigid aluminium tray packs should also be free of the product and moisture if sound heat seals are to be produced.
In some processes, e.g. the hot-fill, close, hold and cool procedure which is sometimes used in canning acid foods, the temperature of filling is a critical factor in ensuring the product is shelf-stable.
This temperature should be monitored continually using a temperature recorder, or it should be under frequent observation of quality control staff with the support of production staff. The temperature of filling may also be an important factor
in producing the required vacuum in canned products and again thisntemperature should be monitored as described above.
CLOSING AND SEALING OPERATIONS
Many processed fruit and vegetable products must be hermetically sealed in
their primary package if they are to be safe and shelf-stable. Quality
control staff, preferably with assistance from production staff, should
inspect filled containers, loose ends and caps as they arrive at the closing
machines or heat-sealers, and some of the closed containers as they leave the
Operators of can closers should inspect the finished double seams for
defects such as droops, spurs, cut-overs and false seams. At regular
intervals, depending on the rate of production, detailed examinations should
be made of the closures on sample containers taken from each head of the
closing machines. Samples should also be examined after the machine is
adjusted and after accidents that may have altered the settings of the
closing machines and the quality of the seals. The assessment of heat seals should be mainly based on visual examinations during production but the seals should be pressure tested when the sealing machines are being adjusted before processing starts or after accidents that may alter their performance.
Quality control staff should also check that the correct date, product
name and manufacturer’s codes are being applied in legible form to the
primary containers, and that the appropriate codes are changed frequently
enough to allow production batches to be identified and isolated if there is
evidence that they are defective.
In addition to packaging processed fruits and vegetables in properly sealed containers, the products must be given other treatments to ensure that they
are stable during storage. Some preservation treatments such as dehydration
and crystallizing are usually done before packaging while other treatments
are usually applied after packaging, e.g. the heat sterilization process in
canning. The preservation treatments involve different physical and chemical
processes and they require different actions by quality control staff to
ensure that safe, stable products are produced.
The safety and s torage stability of canned foods, including heat-processed
foods in drums, glass containers, flexible and semi-rigid containers, depend
on the product being heated at a specified temperature for a specified time.
The most commonly used heating media are hot water, sometimes under a
superimposed pressure, and air-free saturated steam.
Quality control staff should ensure that the primary control
instruments for heat-sterilization processes, the thermometer and clock, are
accurate and maintained in good condition. Mercury-in-glass thermometers, or
temperature-measuring instruments of at least the same accuracy and
reliability, should be calibrated at least twice a year or more frequently if
their settings appear to have been disturbed.
Most heat-sterilizing equipment should also be fitted with chart
recorders which give a permanent graphical record of the temperature of the
heating medium and, with batch processes, a record of the duration of
heating. This record should be used by quality control staff at the end of
each shift to check that the specified processes were applied and to confirm
the processing details recorded in the log book maintained by the operators
of the heat-processing systems.
At regular intervals, perhaps weekly, quality control staff should
inspect the heat-sterilizing equipment to ensure that it is operating in the
required way. Special attention should be given to the valves on the
compressed air and water lines that are connected to steam-heated sterilizing
equipment. The traps on steam-heated retorts should also be inspected to
ensure that condensate is quickly removed from retorts. The steam, water and
air distribution pipes should be inspected for blockages and rust deposits
and the systems used to circulate water in water-heated equipment should be
checked to determine that the equipment is operating satisfactorily.
The safety and storage stability of dehydrated foods, including some syruped
and crystallized foods, depend on the moisture content of the product being
reduced to a value at which potential spoilage organisms cannot grow. Although equilibrium relative humidity. is the best index of the amount of water available
for microbial growth, quality control of dehydration processes is usually
based on the measurement of moisture content. The relationship between moisture content and equilibrium relative humidity varies according to the composition of the food so the moisture content required to give a shelf-stable product should be determined for each food.
Sulphur dioxide is added to some foods before, during or after the
drying process, sometimes as an anti-microbial agent, but more often to block
non-enzymic browning of the product during storage. Quality control staff
should therefore monitor the sulphuring processes and the concentration of
sulphur dioxide in the finished product to ensure that enough is present
to meet the technological needs but the amount does not exceed the limits set
by regulatory authorities.
The critical factor in ensuring that frozen foods are safe and store satisfactorily is the temperature of storage which should be maintained at an essentially constant value at or below – 18°C. Quality control staff should measure the temperature of the product as it leaves the production line to ensure that freezing is complete and to determine whether the product should be close- or open-stacked in the cold storage room. The temperature of the cold storage room should be monitored at least twice daily or preferably by using a chart recorder.
Quality control staff should also inspect the cold storage space to determine that it is clean and that stock is properly handled and rotated.
Pickled and chemically preserved foods
Spoilage of these foods is prevented by establishing a defined chemical environment throughout the product and by processing the raw materials so that the product is contaminated only by low numbers of micro-organisms. The materials used to make these products shelf-stable include some of those described in section 4.2: acetic and other food acids; benzoic acid; salt; sugar; sorbic acid and sorbates; and sulphur dioxide. In many cases the pH of the food must also be controlled to obtain shelf-stable products.
Quality control staff should ensure that the manufacturing process is carried out so that the level of microbial contamination is minimized. Quality control staff should also monitor the pH and the concentration of the critical preserving agents in each product batch often enough to ensure that the end product will comply with its specifications. Usually samples for analysis should be taken from different parts of pickling or syruping tanks to determine that the critical materials are properly distributed and present at concentrations within the limits set for the process.
LABELLING, PACKAGING AND WAREHOUSING
Quality control of these operations involves inspection of the labelling and packing process to determine that the correct materials are being used, that
the products are being properly packed and the ultimate containers are securely stacked ready for distribution.
Quality control staff should inspect warehouse stocks at approximately
weekly intervals for evidence of spoilage and other forms of deterioration,
and to ensure the warehouse is clean, orderly and free of foreign materials
and infestation. A short time before stored stocks are to be shipped quality control
staff should select one ultimate container from five widely distributed
points in each batch in the consignment. Each primary container in these
samples should be inspected for evidence of spoilage and other forms of
deterioration. One primary container from each ultimate container should
then be taken for more detailed examinations. The product from each primary
container should be tasted to determine that it has acceptable organoleptic
Cans should be examined for vacuum, excessive internal corrosion,
staining and loss of adhesion by the lacquer. If the microbiological stability of the product depends on its pH, e.g., in acidified low-acid foods, the pH should be measured. If the intended market requires particular characteristics in the
product, e.g., more than a minimum drained weight or syrup strength,
appropriate measurements should be made. Dried foods should be inspected for integrity of the package, insect infestation and microbial spoilage, especially by moulds. The moisture content and, when appropriate, the concentration of sulphur dioxide or other materials specified by the purchasing and regulatory authorities should be determined. With frozen foods the final examination usually involves inspection of the primary package and organoleptic testing of the product. The temperature of the product should also be measured to confirm that it is at or below the recommended value.
The concentration of salt, acid and preservatives and the pH should be
determined as appropriate in pickled and preserved products before they are
dispatched. Attention should be given to the condition of
metal containers and to the metal closures on glass jars especially as these
products are often particularly corrosive.
CLEANING, SANITATION AND WASTE DISPOSAL
Quality control staff should monitor all operations that contribute to the
manufacturing process being carried out under satisfactory hygienic
conditions. The food processing equipment that handles the product during
and after the last steps of the preparative operations should be kept at
least as clean as the kitchens of a well-run hotel. Quality control staff
should inspect the processing lines before manufacturing starts to determine
that they are clean and free of waste food, foreign materials and insect
infestation. The lines should also be inspected after they are cleaned at
the end of the shift. During production quality control staff should inspect
the line for evidence of accumulated dirt and waste material, and for any
product which has been delayed or by-passed on the line.
Special attention should be given to canned foods immediately after the heat sterilization process; the outside surface of the containers must be kept as free of
microbial contamination as possible reduce the risk of organisms gaining
entry to the product through the wet closures which at that stage may not
have formed an hermetic seal. Wet containers should not be manually handled
or contaminated by contact with wet and dirty mechanical equipment. Quality
control staff should require can handling equipment to be dry, or if it must
be wet it should be regularly sanitized.
There is little value in taking microbiological swabs of fruit and vegetable processing equipment to assess the effectiveness of cleaning operations; it is usually sufficient to inspect the equipment, to search for off-odours, to feel metal surfaces for sliminess and to wipe the surfaces with a clean tissue to detect residual dirt.
Quality control staff should also inspect all other areas of the
processing plant and the immediate outside areas for evidence of waste,
insects, rodents and other animals, birds and other materials that may
present a risk to the production of safe, wholesome processed fruit and