CONCORDANCE OF METHYLENE BLUE REDUCTION AND MICROBIOLOGICAL TECHNIQUES IN THE ANALYSIS OF RAW AND PROCESSED MILK QUALITY: A COMPARATIVE STUDY

Abstract

Raw milk is a milk that has not undergone pasteurization for an effective pathogen elimination, thus having a reduced shelf life due to microbial activities. Microorganisms such as bacteria can affect the quality of diary products, hence the need to assess the microbial quality of natural cow milk, pasteurized milk and processed tin-milk which are consumed on daily basis in Nigeria, Africa and the world at large. In this study, raw (unpasteurized) and processed milk samples from two locations (Bogobiri and Watt market) in Calabar municipal were analyzed using methylene blue reduction test (MBRT), total heterotrophic bacterial count (THBC) and total coliform count (TCC). The total Heterotrophic bacterial count ranged from too numerous to count (TNTC) to 3.86 x 106 colony forming unit (CFU)/milliliter (ml) in samples MA (Unpasteurized/Raw cow milk) and MB (Pasteurized cow milk) respectively. There was no fungal growth in five of the samples except MA that had a fungal count that was TNTC. The highest TCC was obtained from sample MA, with a value of 2.96 x 106 CFU/mL while sample MD had the lowest count of one colony. The total microbial count from sample MA was extremely high and above the standard signifying that it is unfit for human consumption. The MBRT result revealed that MD (Processed liquid tin-milk) and MC (Processed liquid tin-milk) gave no methylene blue reduction (excellent quality) while MB (Pasteurized cow milk), ME (Processed liquid tin-milk) and MF (Processed liquid tin-milk) were of fair quality. However, MA gave a poor quality based on the MBR time of between 30 m to 2 h corroborating with the high value of its THBC which was above the standard. Milk being a vital protein source and an excellent medium for microbial growth should be thoroughly treated by sterilization in a bottle as the study revealed that the milk microbial load can be greatly reduced by pasteurization, with sterilization in bottle having a greater bactericidal effect than pasteurization.