Session 1: The food chain approach from an international perspective
1. INTRODUCTION
Iran with a total area of 1,648 million square km and a population of more than 66 million in 2002, produces more than 6 million tons of milk. More than 40% of this amount is processed in small, medium size and large dairy plants and reaches the market as processed and packaged products while the remaining part is transformed into different products especially cheese, butter oil, yogurt and traditional dairy products by the traditional sector. In fact, the Iranian dairy sector is a combination of large, sophisticated dairy farms, a large number of medium size modern farms and a larger number of small holder farmers with 4-5 cows each. This diversity creates a wide range of milk harversting and handling systems which needs to be integrated into an overall industry approach to ensure highest milk quality and safe dairy products. Large and medium sized producers use milking machines as well as efficient cooling systems and CIP processes to clean the equipments in contact with milk. The small producers have native breed cows and milk them by hand.As far as processing is concerned, the major part of dairyproducts produced by traditional units is not under efficientcontrol of the institutions in charge of food quality and safety.
2. LIVESTOCK AND MILK PRODUCTION IN IRAN
The data of Table 1 show the population and the produced milk of different types of milking animals in Iran (1). Sheep and goat milk is produced in rural and nomadic areas and is also processed by using traditional methods. During the last 60 years and especially the last two decades, the development of cow’s milk, in particular from high efficient pure breed and cross bred animals in urban areas has been remarkable. The establishment of large and medium size farms caused considerable improvements in the quality and quantity of milk production. Since few years ago, the increase of the number of pure breeds namely Holstein and hybrid cows in rural areas has been in full development. According to the latest survey, the production per head of a Holstein milking cow in large farms exceeds 7 tons a year while, this figure is 2.8 tons for a crossbred cow and less than 1 tone for a and native cow ( 2 ).
3. MILK PRODUCTION PER CAPITA IN IRAN
Milk production and milk production per capita have been in constant
increase over the past 2 decades despite population growth rate and social events. Figure 1 shows this trend from 1979 to 2003.
TABLE 1
Livestock population and milk production in Iran (2003)
| Type of livestock |
Sheep |
Goat |
|
Cow |
|
Buffalo |
|
|
|
PB |
CB |
NR |
|
| Livestock Population ( x 000 ) |
52000 |
25700 |
720 |
2600 |
4200 |
400 |
| Milk production ( x 000 tons ) |
300 |
370 |
1850 |
1820 |
1600 |
220 |
| Percentage of national production |
4.9 |
6 |
30 |
29.5 |
26 |
3.6 |
PB: Pure bred
CB: Cross bred
NR: Native race
4. MILK COLLECTION AND PROCESSING
4.1 Milk collection centers ( M.C.Cs )
The rapid growth of the industry resulted in shortage of raw milk for many plants. In order to respond the demand of industry, the raw material was supplied originally through imported skim milk powder and butter. This trend continued during the 70 and 80 s and originated the establishment of M.C.Cs in rural areas to collect and supply the needed milk of newly created dairy plants. As a first step, 98 centres were established from 1985 to 1988. In 1996, 1999 and 2002, more than 800 centres were operational. At present, the quantity of collected milk by these centres is more than 1 million tone a year.
The average number of milk producers for each M.C.C is about 200 to supply 4.5 tons of milk per day. Milks of different producers are mixed and this process causes quality problems that will be discussed later.
4.2 Milk processing
Following the start up of the Tehran pasteurized milk plant in 1957, there has been a trend in establishment of dairy plants reaching 25 in 1985 with an annual nominal capacity of 950.000 tons and 61 large plants and more than 260 small and medium size plants in term of capacities in 2002 with a total nominal capacity of 4 million tons. Out of 61 large plants, 14 belong to IDIC that has more than half of the practical capacity of the large dairy plants.
The development of small dairy plants in rural areas started in 1989. These units are mainly cheese manufacturers that standardize and pasteurize the milk and carry out some tests to evaluate the quality and safety of their products. Economically, the small plants are not competitive and the majority of them can not continue their production activities without subsidies. In term of hygienic quality and safety their products are better than traditional products although their laboratories are not well equipped(3).
4.3 Raw milk quality
4.3.1 Biological quality
In 1996, an investigation was done on the quality of M.C.Cs milk. 288 M.C.Cs were studied by using questionnaires and some analyses. The microbiological tests were carried out according to ISO’s methods. Also, several samples from large farms were tested. Total Count, coliforms and psychrotrophic bacteria were counted during 9 months including hot season. Hygien conditions and practices for milking in most small farms were poor. Milking is done in dark and poorly ventilated buildings and just a few producers used detergents to clean their vessels. In large farms, milking is done properly by machine and the equipment and storage tanks are cleaned using caustic soda and hot water. While the vast majority of small farms have no cooling facilities, the use of cooling machines in large farms is regularly at work. Since 1996, the temperature of raw milk at reception points of dairy plants is a factor determining the milk price. This temperature should be below 10 ºC. One of the problems in ensuring the quality of raw milk is that until now, the M.C.Cs have not been able to control the temperature of the received milk.
The cooling of milk is done in M.C.Cs and the milk is not cooled before reception. If the time between milking and reception at MCC is long, the organisms grow in the milk and deteriorate the milk quality. Sine 1996, IDIC helps the small producers to replace their plastic cans with aluminium ones and at the same time, the M.C.Cs replace their slow cooling systems by plate coolers that use chilled water to reduce milk temperature in few minutes. By carrying out the new measures, the microbial characteristics of raw milk have dramatically improved. Figure 2 indicates the effects of the application of the new measures in improving milk quality in 2003 compared with 1996. When the milk quality deteriorates, the major constituents of microbial population are coliforms and psychrotrophic bacteria. Other results showed that if the milk of small producers has been delivered directly to the plants, the quality remains higher compared to milk delivered by M.C.Cs. In 2003, the microbial qualities of industrial farms and M.C.Cs milks received in dairy plants belonging to IDIC were studied. Figure 3 shows the quality classifications of different kinds of the milks according to the number of bacteria found in one ml (4). The improvement of the quality of raw milk was important between 2002 - 2003. In this period a prize and fine system was applied to the milk treated in IDIC plants. The decreases of the number of organisms in 1 ml of the milk of large farms and M.C.Cs were respectively 25 and 23 percent. The number of coliform bacteria in M.C.Cs milk increased from 3x105 to 2x106 in 1 ml in 2003. For a quality milk it should be less than 100 ml.
4.3.2 Risk assessment
4.3.2.1 Antibiotic in milk
According to the Iranian standard, raw milk should be free from antibiotic residues because antibiotics inhibit the growth and activity of microorganisms used to produce cultured products such as yogurt and cheese on one hand and indicate the lack of good farming practice on the other. Furthermore, these residues may cause human health problems such as allergy or the development of antibiotic resistant pathogens. So, in many countries, severe penalties are applied where the antibiotic test in raw milk is positive. An investigation aimed to test the quantities of antibiotics in raw milk received in 6 dairy plants belonging to IDIC was done from April 2002 to March 2003 (5). 92 samples were tested, of which 261 were positive while 732 samples were free from antibiotics. The amount of penicillin G in positive samples was 1.2 ppb which was more than the upper limit accepted by legislations (5). These results indicate that the antibiotic residues tests should be applied to the milk processed by dairy plants. IDIC plants have already applied the test according to the Iranian standard.
4.3.2.2 Aflatoxin M1 in milk of some Iranian regions
Mycotoxins are produced by moulds. The major mycotoxin of importance to milk is aflatoxin M1 (AFM1) which derives from aflatoxin B (AFB) found in forage (6). In the five Iranian provinces, a study has been done on the raw milk received by IDIC plants concerning the amount of aflatoxin M1. The quantities of aflatoxin M1 in raw milk samples was between 0.031 to 0.049 ppb. According to these results, the upper level of toxin is less than 0.05 ppb. The minimum amount was found in the milk of the western part of Iran and the maximum level in the north of the country (7). According to these data, the level of AFM1 was less than the upper limit stated by Codex Alimentarius.
4.4 Effect of raw milk quality on the shelf life of related pasteurized milk
The definition of shelf life:This is “time between the production and packaging of the product and the point at which it becomes unacceptable under defined environmental conditions“. (3)
In fact, storage and distribution are necessary links in the food chain. The safety considerations dictate the conditions and maximum duration of these links.
The consumers and legislation expect that no quality deterioriation occurs before limiting time.
Factors affecting the shelf life of pasteurized milk are:
- Quality of raw milk
- Heat treatment
- Post processing contamination (PPC)
- Packaging system
- Storage temperature
When total count of raw milk is under 30000 ml in one, and the other conditions are suitable, the shelf life of pasteurized milk at 6ºC or less could be about 30 days.
Shelf life ends when the following changes appear in the product:
- The standard plate count exceeds 106 / ml
- The chemical reaction leading to undesirable changes such as oldness, fruit taste, bitterness and metallic taste take place.
The temperature - time of milk pasteurization in our experience was 76ºC at 16 seconds. Under these conditions, the coliforms and psychrotrophic bacteria are destroyed but the thermoduric and spore forming bacteria resist.
It should be noted that for the low quality milk, heat treatment has to be applied as soon as milk is received at dairy plants and the lactoperoxydase system has no significant effect in this case.
When the microbial population of raw milk is low enough, the pasteurization of milk 3 or 4 days after storage at low temperature leads to a longer shelf life. The results of our work showed that the contamination of milk after pasteurization along with the storage temperature are the most significant factors on product shelf life duration. The most important sources of post pasteurizing, contamination are: cooling section of pasteurizer, leakage and unsufficient cleaning of pasteurizer, packaging materials, enviroment of packaging machine, pasteurized milk storage tanks and transportation conditions.
The results indicated that there was significant relation ship between psychrotrophic bacteria number and product shelf life in winter.
In high quality raw milk, the ratio of psychrotrophic bacteria to total count is less than 10% while this reaches to 70%in low quality raw milk. While the number of this kind of bacteria in raw milk is more than 5 million in one ml, the taste changes occurs.
Figure 4,5 and 6 show the evolution sat PH, acidity and microbial number at 6ºc in pasteurized milk.
Figure 6 shows that the number of thermoduric bacteria remains stable during storage time. The same trends are seen for the spore forming bacteria but it indicates that the growth of psychrotrophic bacteria is much more accelerated under the same conditions.
5. CONCLUSIONS
Good farming practice and improved milking system should be applicable in small and large farms. We need a clear safety policy and an action plan to reduce the risk of microbial contamination of raw and pasteurized milk. In small farms, the plastic cans should be replaced by metallic ones. Milk cooling has to be done as soon as milking is done by using the simple ways such as utilization of stream water in villages.
The transportation of milk from farm to MCCs using cleaned, insulated containers should take place rapidly and in MCCs, application of quick cooling system by using a plate cooler is an efficient method to stop milk deterioration. In MCCs, by using a CIP system, all the tanks, pipes and containers in contact with milk have to be washed and disinfected. The MCCs that supply high quality milk should be rewarded consistently. The application of HACCP in large farms is efficient and this system should apply generally to all the farms.
At dairy plants, along with the tests measuring the chemical and biological tests, the antibiotic tests should be done for all the received milks.
As soon as raw milk is delivered to dairy plants, thermization at 63ºc, 15s should be applied and then, cooling should take place.
After pasteurization, the cold chain should be maintained until milk distribution. The execution of new methods and tests prevents PPC from pasteurizer to packaging machine.
The most important decision to be made to execute all the necessary policies is to create a single body involving all the private and public institutions representatives with regard to milk production, processing, distribution and consumption. For the implementation of all the policies, in emerging dairy nations, human resource development is the most important priority. The unofficial sector, small scale producers and street side vendors constitute an enormous challenge for institutions in charge of food monitoring. Given the number and diversity of this sector, the only ways at present are to inform consumers and apply subsidies for safe dairy products to ensure the security and safety in this area.
REFERENCES
1. Annual report (2003), Ministry of Agriculture, Tehran, Iran.
2. Technical report (2003), Center of Animal Breeding and Milk Improvement, Karaj, Iran.
3. General dairy studies (2003), Technical report No4, IDIC, Tehran, Iran.
4. Milk quality (2003). Monthly report, IDIC, Tehran, Iran.
5. Ghanavi, Z (2003), Penicillin G in raw milk of five Iranian regions, National Iranian Standard organization, Tehran, Iran.
6. Harding, F (1995), Milk Quality, 1st ed. Chapman and Hall, London, UK.
7. Tajkarimi, M ( 2004 ), Seasonal study on the level of aflatoxin M1 in raw and pasteurized milk in five Iranian provinces, paper submitted at 68th annual national environmental health association, 9-12 May 2004, Alaska, U.S.A.
8. Man, C.M.D ( 1994 ), Shelf life evaluation of foods, P27, 1st ed. chapman and Hall, London, UK
9. Daneshi, M (2003), shelf life of pasteurized milk in Tehran region, First specialized dairy gathering, IDIC, Tehran, Iran.
IDF/FAO international symposium on dairy safety and hygiene Cape Town,
2–5 march 2004,
South Africa |
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