Pizza is a dish that was invented in Naples, Italy, and is made with a flattened disk of bread dough and then topped with ingredients of choice, normally a combination. Some popular toppings are; oregano, tomato, olives, cheese, pepperoni, minced beef, sliced chicken, and many other ingredients. It is usually baked in a commercial setting, using a wood-fired oven heated at a specific temperature, and is usually served hot.
Freezing is lethal to the cells of many microbes – 90% or more of the microbial population can die during low-temperature preservation of foods such as; freezing (Erkmen and Bozoglu, 2016). The shelf-life of many foods can be increased when they are frozen at low temperatures. As the storage temperature decreases, the growth of microorganisms slows down and likewise, metabolic activity increases with a rise in temperature.
The same study by (Erkmen and Bozoglu, 2016) reports that for each 10 °C decrease in temperature from minimum, there is a twofold decrease in the rate of catalytic activity of enzymes, within the food. That means that the lower the freezing temperature of a food or food product, the better the maintenance of its quality and hence the longer its shelf-life.
There are several factors that can affect the shelf-life of frozen pizza such as; the freezing temperature, the time of freezing, power fluctuations and thawing, the processing methods of the ingredients used, the storage packaging material and light exposure, and even the choice of pizza toppings used.
Interestingly, the shelf-life of pizza is influenced by the type of storage packaging material as was reported in an early study by (Komolprasert, Stine and Harte, 1988). When pizza was packaged in a good barrier material, a 75m thick nylon/polyethylene laminate, it resulted in maintenance of a good quality of the pizza samples, even after five months in the freezer whiles exposed to light.
The quality of the pizza in these films was better than after one month exposure with no oxygen barrier. However, this was only when the head space oxygen was removed by vacuum sealing.
In freezing a food product with the aim of extending its shelf-life, the freezing temperature is very important, since freezing at temperatures that are not low enough may facilitate microbial growth and may not be able to Inhibit certain chemical reactions.
In the study by (Komolprasert, Stine and Harte, 1988), the pizza samples were stored at –18 °C ± 3 °C or –7 °C ± 3 °C. The samples were then removed from storage at –18 °C to a temperature of 5 °C, and thermometer was inserted through the pizza packages into the crusts to record their temperature profiles. At monthly intervals for 5 months, the samples were analyzed. The study reported that some toppings of the pizza such as pepperoni and pork sausage underwent lipid oxidation, and in comparison, those stored at –7 °C ± 3 °C were more oxidized as compared to those stored at –18 °C ± 3°C.
Also in comparing pepperoni toppings and pork sausage toppings, the pepperoni toppings underwent less oxidation than the pork sausage toppings, which could be due to the influence of the nitrites and antioxidants. This showed that the choice of pizza toppings has an influence on the shelf-life of pizza.
Power fluctuations are one of the major challenges in low temperature storage of food products such as; pizza. Power fluctuations when they happen, especially for a long period, causes the foods being frozen to thaw, which is not ideal for long-term storage of pizza by freezing, considering how delicate it can be due to the risk of the crust becoming moist, and the toppings absorbing water. The more water is absorbed as the rapid ice crystals that were formed when the pizza was undergoing freezing initially break down and melt, the higher the water activity (aw), and the higher the risk of microbial growth and activity, which may cause the release of spoilage toxins, leading to a reduction in the pizza quality and the initial shelf-life of the pizza.
Another early study done by (Childers and Kayfus, 1982) aimed at determining the shelf-life of pizza and also studied the effect of the time of freezing on the quality of the pizza and ultimately the shelf-life of the pizza. In the study, it was reported that the time-temperature relationship during the freezing of pizza influences its shelf-life. The frozen pizza samples were analyzed, and it took a duration of more than 200 days before the quality of the pizza samples fully down to a 0% quality. The quality deteriorated down by 50% when the frozen pizza samples were stored for a period of 120 days.
When vegetables and fruits that are added as toppings on pizza undergo processing and/or pre-treatment methods such as; blanching, they deactivate the enzymes that are naturally present.
This in effect extends the shelf-life of pizza as oxidation is prevented and/or minimized, due to the inactivation the of enzymes. This makes the processing and pre-treatment methods of pizza toppings one of the ways of maintaining the quality of pizza and extending its shelf-life, among other functionalities.
The freezing temperature, the time of freezing, power fluctuations and thawing, the processing methods of the ingredients used, the storage packaging material and light exposure, and the choice of pizza toppings used are all factors that influence the shelf-life of frozen pizza.
References
1. Childers, A. B. and Kayfus, T. J. (1982) ‘Determining the Shelf–Life of Frozen Pizza’, Journal of Food Quality, 5(1), pp. 7–16. doi: 10.1111/j.1745-4557.1982.tb00952.x.
2. Erkmen, O. and Bozoglu, T. F. (2016) Food Preservation by Low Temperatures.
3. Komolprasert, V., Stine, C. M. and Harte, B. R. (1988) ‘PACKAGE MATERIAL ON THE FLAVOR’, JOURNAL OF PLASTIC FILM & SHEETING, 4(JuLY 1988), pp. 227–240.
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