Bakery products are very sensitive substrate of organic origin in which physical and chemical processes occur during storage which for a consequence has a change of quality, organoleptic, chemical and nutritional value. Product diversity and complex composition represents a special problem when it comes to their protection. In addition, it is important to produce them in an adequate manner, it is essential to preserve product quality. To achieve this it is necessary to put products into suitable container that will provide protection against mechanical damage and from chemical and biochemical changes caused by external factors (Vlahovic, 1999). Big problem of bakery industry is the shelf-life of bakery products. Regardless of different types of additives that are added to products to extend their shelf-life, bakery products’ shelf-life is short. Spoilage of these products is influenced by many factors, some of them are: high water content (high aw), very high nutritional value, abundance of minerals, vitamins, proteins, fats and carbohydrates which actually make them an ideal nutrient medium for all kinds of microorganisms.

Strudel filled with poppy seeds is produced according to traditional recipes from raw materials obtained in domestic production by a special technological process. The raw materials used in technological process of production are classified as basic and additional materials. Basic raw materials are wheat flour, water, fresh baker's yeast and salt. Other ingredients include: poppy seeds, sugar, vegetable fat, fresh eggs, vanilla sugar and lemon peel.

To achieve microbiological proper and sustainable products, it is essential that all materials are microbiologically correct.

To obtain the original strudel from Vojvodina, high quality wheat flour T-500 should be used in production, which should, in addition to the parameters of quality, satisfy microbiological parameters as well. Due to its chemical composition, flour is a very convenient base for the development of different populations of microorganisms. The usual micro flora in flour is comprised of bacteria, yeasts and moulds (Stojanovic, Psodorov, 2007). The majority of microorganisms in the flour come from the wheat itself. Wheat grains are suitable environment for microbial growth. Therefore, the grain surface treatment is a necessary condition to obtain products of proper hygiene, especially flour, irrespective of the proportion of peripheral parts of the grain (Plavsic et al., 2007).

Water used in the production of strudel with poppy seeds should fulfil certain quality requirements, which means that it is micro-biologicaly and chemically proper, without foreign tastes and odours, colourless and transparent, in other words it should fulfil all the conditions required by the Regulations on the hygienic quality of drinking water (Pravilnik o higijenskoj ispravnosti vode za piće “Sl. list SRJ”, br. 42/1998 i 44/1999). Fresh baker's yeast (Saccharomyces cerevisiae), salt and other additional raw materials listed above, should primarily meet the requirements of microbiological safety, according to the Regulation on microbiological safety of food in trade (Pravilnik o mikrobiološkoj ispravnosti namirnica u prometu, “Sl.list SRJ”, br. 26/1993,53/1995 i 46/2002).

According to the traditional recipe for the production of strudel with poppy seeds, poppy seeds are first milled and added to the strudel in form of filling in the quantity of at least 60% dough basis. In nutritional purposes poppy seeds (Papaver somniferum L.) are used as raw material for production of edible oils and for making various types of cakes, usually with grinded poppy. Poppy comes from Asia Minor. From there it spread to the Far East and Europe. Poppy seeds can be red, gray, yellow, blue or black. The chemical composition of poppy seed is very rich: 5.8% water, 22% crude proteins, 47.5% oils, 10.2% carbo-hydrates, 7.8% crude fibres and about 6.2% mineral materials. Oils make the highest percentage, and content may vary depending on the subspecies from 39.67% to 48.92% (Sabados et al., 2010), while the percentage of oils in poppy seeds originating from Macedonia is between 52% and 61%. Preservation of poppy seeds is very important. When stored, it should not contain more than 10% water, or poppy seeds will quickly turn mouldy and rancid. Fine granulation makes a great contact surface for microorganisms. By grinding the seeds, the surface area is additionally increased. Because of their small size, poppy seeds, like spices, are subject to microbiological contamination, in terms of increased numbers of bacteria and fungi. Therefore, poppy seeds can be a source of microbiological spoilage of products in which they are included (Banerjee & Sarkar, 2003). Due to the large percentage of oil, poppy seeds are susceptible to oxidative changes, and as such may affect the safety of the final product in which they were used.

Oxidative processes are often the cause of changes in composition and organoleptic characteristics of packaged foods, especially baked goods. The effect of oxygen often causes undesirable changes in colour, taste and flavour, reduces the nutritional value of food and, in certain cases, can be toxic to humans (Vereš, 1991). Given the easy spoiling and great sensitivity of food products, containers intended for food packaging act like barriers. Selected packaging materials must be acceptable for human health and must meet the conditions foreseen by the Law on Health Safety of Food and Items of General Use (Vujković, 1992; Vujković, 1983).

In terms of food production different packaging operations are used. They are dependent on: the type of food product, selected packaging and subsequent operations with packed content. The quality of the selected package is an important prerequisite for ensuring the shelf-life of packaged products.

To maintain product quality in the desired period, the containers must have defined quality characteristics and proper packaging operations must be applied.

For packaging sensitive bakery products packaging materials must be impermeable or slightly permeable to oxygen and water vapour, suitable for packing in protective atmosphere or vacuum. Since not all polymers have good barrier properties, multi-layer and combined materials manufactured with most advanced methods of laminating, extrusion coating and co-extrusion are used for food packaging (Lazic et al., 2000), (Lazic et al., 2008).

A procedure for packaging in controlled atmosphere(CAP), i.e. modified atmosphere (MAP) has been developed more recently (Smith et al., 1996). Packaging in protective atmosphere is a technique during which the proportion of oxygen in the area around the food is changed, usually decreased, and an inert gas or mixture of gases is flushed instead. In practice, firstly, a partial vacuuming of space around the product is performed (special attention is paid to the consistency of the product - the appearance and structure of the product must not be impaired), then inert gas is injected. In that way the oxygen content around the product is decreased. The choice of gas is dependant on the micro flora present in or on the product, the product’s sensitivity to O2 and CO2, the stability of colour, odour and taste (Philips, 1996).

Oxygen can affect food in different ways – it can favour the growth of aerobic micro-organisms and inhibit the growth of anaerobic microorganisms. Higher concentrations of O2 can cause spoilage, especially in food with high content of fat, vitamin degradation and undesirable colour changes. Oxygen is res-ponsible for the oxidation of food constituents and development and reproduction of micro-organisms and insects. Modified atmosphere packaging and vacuum packaging are widely accepted in order to exclude oxygen from the free space in packagings. However, these physical methods of packaging usually do not s remove all the oxygen (Psodorov, 1999).

Nitrogen is used for packaging products with a large proportion of fat (strudel filled with poppy seeds contain about 8% fat) and exclusion of oxygen in order to prevent undesirable oxidative changes, to inhibit the growth of aerobic organisms and as a filling gas for packaging in high concentrations of CO2, when absorption of CO2 in the content over time occurs. Nitrogen behaves as an inert gas and has no microbiotic activity (Philips, 1996).
Carbon dioxide is the major microbiotic factor in the packaging technique by using protective atmosphere. It inhibits the growth of moulds and bacteria that cause spoilage. In order to have any effect, CO2 must be added in relatively high concentrations (20% or more). Carbon dioxide reacts with water in the product and creates carbonic acid that lowers the pH value which inhibits the development and proliferation of most types of microorganisms. Influence of CO2 is not universal and depends on the type of micro flora present in a food product (Kotsianis et al., 2002).

Because of the effects of gases like nitrogen and carbon dioxide, it is necessary to select a packaging material that will enable the preventive action of gases in the package against the development of micro flora, while, at the same time, they should not react with the content or external environment.
The selected packaging material must have adequate permeability, good appearance, good mechanical properties and a reasonable price. It must be suitable for packaging machines that use MAP technique.

Microbiological safety of basic and additional raw materials used in the production of strudel with poppy seed filling was examined in the first phase of this study. Then, selection of packaging materials was performed.

Packaging was performed on a semi-automatic packaging machine (Multivac, Germany). Modified atmosphere was made by an automatic mixer of gases from mixture of CO2 and N2 in proportion 20:80. Manufacturing and packaging of strudel filled with poppy seeds was carried out in industrial conditions in “Kikinda AD” Bakery according to traditional recipe.

The packaged strudels with poppy seed filling were stored under ambiental conditions (23 °C to 25 °C). The tests were performed on the day of production and successively after every 7 days following the dynamics 0, 7, 14, 21, 28, 35 days.

The samples were tested in accordance to the Regulation on the Microbiological Safety of Food in Trade (Pravilnik o mikrobiološkoj ispravnosti namirnica u prometu,“Sl.list SRJ“, br. 26/1993,53/1995 i 46/2002)., Regulation on the Hygiene of Drinking Water (Pravilnik o higijenskoj ispravnosti vode za piće “Sl. list SRJ”, br. 42/1998 i 44/1999) and Law on health safety of food and items of general use (Zakon o zdravstvenoj ispravnosti životnih namirnica i predmeta opšte upotrebe "Sl. list SFRJ", br. 53/91 i "Sl. list SRJ", br. 24/94, 28/96 i 37/2002 i "Sl. glasnik RS", br. 101/2005 - dr. zakon i 79/2005 - dr. zakon).

Determination of microbiological parameters was done according to the Methods of Carrying Out Microbiological Analysis and Super-Analysis (Pravilnik o metodama vršenja mikrobioloških analiza i superanaliza, “Sl. list SFRJ“, br. 25/1980), according to official methods (method 1, method 3, method 4, method 7, method 8, method 9, method 10, method 11, method 12) and according to the Regulation on sampling method and methods for laboratory analysis of drinking water (Pravilnik o načinu uzimanja i metodama za laboratorijsku analizu vode za piće, “Sl. list SFRJ“, br. 33/1987-Prilog III), (method 1, method 3, method 4, method 5, method 6, method 7).

In order to achieve microbiologically safe and sustainable product, it is essential that all raw materials are microbiologically correct.

Tables 1 and 2 show the results of microbiological safety of basic and additional raw materials.

According to the Regulation on microbiological safety of food in trade (Pravilnik o mikrobiološkoj ispravnosti namirnica u prometu, “Sl. list SRJ”, br. 26/1993, 53/1995 i 46/2002), the products are microbiologically valid if the sample does not contain the following pathogenic microorganisms: coagulase positive Staphylococcus, sulphitereducing clostridia, Proteus sp. and Escherichia coli.

Based on the results shown in Tables 1 and 2 above, no pathogenic microorganisms were isolated. The count of microorganisms  and yeasts and moulds was in the acceptable limits according to the Regulation (Pravilnik o mikrobiološkoj ispravnosti namirnica u prometu,“Sl. list SRJ”, br. 26/1993, 53/1995 i 46/2002). Lipolytic microorganisms were not isolated.