الفهرس 
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Abstract
This study was carried out to evaluate the physical, mechanical and functional properties of the oriented polypropylene films (BOPP) as well as chemical and microbiological characteristics of potato chips and puffed corn packed in the studied films.
The BOPP films were obtained from three different companies of production in Egypt. Two types of BOPP films were obtained i.e. plain transparent films, and laminated films with a thin aluminum layer.
The mechanical and thermal properties included thickness, tensile characteristic, heat seal temperature, strength, water vapor permeability and oxygen transmission rate.
The application of metallized laminated BOPP films for potato chips and puffed corn packaging was evaluated under different conditions of storage up to 44 week.
The obtained results of our study are summarized in the following points:
Part 1: Mechanical, physical and functional properties of BOPP films:
A. Thickness
1- As for thickness and surface characteristics, the obtained results proved that thickness values were in the range of 23 to 24 micron with no significant differences within or between the sheets obtained from different sources.
2- The thickness values were increased by about three microns through the addition of aluminum layer.
3- Thickness of the printed and laminated sheet, was increased to the level of 45-46 micron for the printed transparent sheet. On the other side, printing of metallized (laminated sheet) raised the thickness to the level of 47 micron.
4- The homogeneity in the thickness of BOPP films from the different three sources (companies) means the stability in the thickness of the produced films as well as compatibility of the obtained sheets.
5- Thickness is important parameter for preserving the packed food, production costs of packaging, printing quality and stability and quality of the enclose food product.
B. Tensile characteristics:
1- Tensile values limit the machinability of the BOPP films.
2- The tensile strength values in the transfer direction were higher than those obtained for the machine direction; it ranged from 2218 to 2234 kg/cm2 for the former, while it ranged from 1106 to 1128 kg/cm2.
3- The differences in the tensile strength values during production period were negligible and insignificant, which indicate the stability in thickness and tensile strength values of the produced sheets.
4- Metallization of BOPP films with a thin layer of aluminum did not significantly increase the tensile strength values of sheets.
A. Sealing temperature and sealing strength:
1- The average of heat seal temperature for the transparent BOPP sheet obtained the different sources under investigation ranged between 132.8 °C and 129 °C.
2- The variation in sealing temperature during production period was non- significant indicating the relatively stable production parameters over the time.
3- Relation between sealing temperature and thickness was observed.
4- The average value of sealing strength for produced sheets ranged between 178 and 181.4 gm/cm.
5- Metallization of the transparent sheet with an aluminum layer did not significantly change the heat sealing temperature.
A. Water vapor permeability:
1- The average of water vapor permeability values ranged from 8.08 to 9.24 gm H2O/m2. day according to the production source.
2- Metallization of the transparent films with a thin layer of aluminum drastically reduced the water vapor permeability to one tenth that of transparent film. The level of obtained values was in the range of 0.846-1.34 gm H2O/m2. day.
3- The values of water vapor permeability for the metallized films comply with the thickness and weight of aluminum layer.
4- lamination of transparent films recorded water permeability to 50% that of single transparent film.
D. Oxygen permeability:
1- The average values for oxygen transportation ratio were in the range of 1864-1880.6
2- Metallization of the transparent BOPP sheet reduced the permeability level of oxygen to the range of 144-169.6 cm3 O2/m2.day.bar.
3- Metallization prevents light from entering because light is a catalyst for the fat oxidation.
4- Lamination improved the barrier characteristics of the obtained BOPP films.
Part 2. Application of metalized laminated BOPP films in packaging of potato chips and puffed corn
1- In summer period, the atmospheric composition of gas atmosphere inside the bags reached equilibrium with the surrounding atmosphere after 8 weeks of storage.
2- During winter season, the chips bags reached the level of 80% nitrogen, 19% oxygen and 0.1% carbon dioxide after 14 week of storage.
3- Chips bags samples stored on the roof reached equilibrium after only 6 weeks.
4- As for the migration of moisture to inside the bags the initial moisture content of chips was 1% and it was increased during storage up to 32 week for chips bags filled in nitrogen atmosphere and stored under the different storage conditions.
5- The aluminum layer has the capacity level to withstand and prevent oxygen from penetration through the BOPP bags and reduce the rancidity stage of the stored potato chips.
6- The induction period for fat oxidation in potato chips stored in metallized laminated BOPP was extended up to 12 week for samples stored under nitrogen gas atmosphere in winter and summer season.
7- Peroxide value was slowly increased to the level of 0.21 mEq/kg.oil after 36 week. The opposite trend was observed for samples stored under outside and light conditions.
Part 3. Microbiological quality of potato chips under different packaging and storage conditions.
1- The safety of potato chips packed in transparent BOPP films and stored for 8 weeks was agree with the level of oxygen penetration and moisture content which did not exceeded 12% and 1.8%, respectively.
2- The bacterial and fungi counts started to grow on the surface of studied samples after 20 week of storage.
3- The obtained results of microbiological tests showed that no pathogenic hazards existing in the product until 16 week of storage.
4- Metalized BOPP bags showed sterility of the product until 16 week of storage and there was no CFU values were found for total bacteria, yeast and mold counts.
Conclusion
The most important factor in determining the functionality of BOPP sheets is not the thickness, but the quality and integrity of the aluminum layer. In transparent BOPP-bags, the protecting effect of nitrogen gas lasts for only 12 weeks during storage, because the inside atmosphere is approaching outside atmosphere after this period of storage. Rancidity values of potato chips packed in metalized BOPP-bags stored under nitrogen atmosphere was still under the limits allowed in the Egyptian Standard, so that the quality of the chips was maintained up to 36 week (252 day). Use of palm olein oil in frying potato chips delayed the incidence of remarkable rancidity during the 6 months storage of chips bags under nitrogen atmosphere due to the stability of palm olein oil, in spite of health hazards associated with its consumption. If the potato chips industry plan to change the use of palm olein oil with other oil in frying potato chips, efforts should be addressed to improve the alumination and lamination process of BOPP films to meet the requirements for preventing oxygen from penetration the bags and deteriorate their content. The moisture content of the packaged puffed corn did not exceeded 4% under nitrogen atmosphere after 36 weeks storage in metallized BOPP, which agree with the value mentioned in the corresponding Egyptian standard. Both chips and puffed corn were free from pathogenic contamination as well as yeast and molds during the first 24 weeks of storage. It is recommended to use BOPP sheets (metallized and laminated) for the safe packaging of potato chips and puffed corn under the conditions that the aluminum layer not under 165 mg/m2 to assist the functional properties of the used sheets. Specifications of a good packaging that preserves the quality of the food during the shelf life are as follows: the weight of the aluminum layer varies between 200 – 250 mg/m2. Transparency value should be between 1.1 to 1.8 OD, a heat seal temperature is 136°C, water vapor permeability is the range of 0.16 - 0.2 gH2o/m2.d and oxygen transmission rate lower than 45 cm3 O2/m2.d.bar.