Growth Kinetics of Bacteria Isolated from Laboratory Prepared Cheese Made From Different Milk Sources

Abstract

Background: Dairy food products constitute a major part of our routine diets and it is fundamental to the food industry globally. However, the need for quality control cannot be over-emphasized. A microbiological guideline must be used to define the differences between unacceptable and acceptable food products as food-borne related diseases have been associated with milk and dairy products. Aim of Study: The study aims to evaluate the growth kinetics of cheese prepared in the laboratory from different milk types over a 96 hour period in order to determine its bacteriological quality and assess the effect of storage time on the pH of the various cheeses. Methods: The laboratory cheese was prepared from fresh Goat, cow, sheep and soybeans using the traditional method. Thereafter, 10g of the cheese samples were stored in sterile 250 ml conical flasks at temperature of 28±2 oC for duration of 96 h. The samples were analyzed every 12-24 h interval using Nutrient Agar, MacConkey Agar, Mannitol Salt Agar and De Mann Rogosa and Sharpe Agar for their bacterial, coliform, staphylococcal and lactobacilli load respectively. Results: At 96 h the highest heterotrophic bacterial load, coliform, staphylococcal and lactic acid bacteria counts were observed in sheep milk cheese (8.27 ± 0.02 Log10cfu/g), (7.10 ± 0.33 Log10cfu/g), (7.40 ± 0.34 Log10cfu/g) and cow milk cheese (8.19 ± 0.05 Log10cfu/g) respectively. At 0 h the highest pH was recorded in Soybean milk cheese (5.76±0.01) while the least was cow milk cheese (4.97±0.11). The highest pH at 96 h was Soybean milk cheese (6.96±0.01) while the least pH was recorded in sheep milk cheese (6.12±0.00). Comparing results of this present study with that of the European Union microbiological regulations (EUMR) and the Gulf Standards Organization (GSO) for foods, the bacteria load of all cheese samples at 12 h was within the acceptable or permissible limit. Conclusion: The present study indicates that laboratory prepared cheese contains a repertoire of significant public health microorganisms in numbers above the permissible limit. It is recommended that appropriate aseptic procedures should be strictly upheld by dairy handlers across the entire chess production value chain.