Ultra high temperature milk: microbiological quality, age gelation and a proposal of an alternative method for microbial detection
Authors:   , Moreira Isabella Maria Fernandes Botelho 
Published: August 2024

The UHT (Ultra High Temperature) milk is a food that has stood out in the market due to its ease of transport, storage conditions and long shelf life. Due to this, it is becoming increasingly important to study this product in order to guarantee the quality and food safety of the consumer. The objective of this study was to evaluate three different lines within the “UHT milk universe”: the microbiological quality of the product, the action of stabilizing salts on the gelation process caused by bacterial proteases and an alternative and faster methodology for microbial detection. Microbiological quality was determined through the evaluation of 184 samples of Brazilian UHT milk for the presence of vegetative cells of aerobic mesophilic bacteria and spores. The 335 isolates obtained were purified, phenotypically characterized and subjected to molecular analyzes in order to determine the biodiversity between them. By constructing a phylogenetic tree, it was possible to identify bacteria belonging to the genus Bacillus sp. that in addition to being capable of forming spores, some strains in the group also secrete proteolytic and lipolytic enzymes that compromise the quality of the product throughout its shelf life. Based on this, the second project aimed to evaluate the action of phosphate and citrate salts on the gelation process in UHT milk samples intentionally inoculated with strains of Pseudomonas fluorescens 07A, a strain that produces the AprX protease, for a period of 18 h at 20 °C. In this project, five stabilizing salts (polyphosphate (T1), pyrophosphate (T2), citrate (T3), tripolyphosphate (T4) and monophosphate (T5)) were evaluated for 30 days in three repetitions in samples of UHT milk produced through reconstitution of skimmed milk powder. Through physical-chemical analyzes (pH, thermal stability in the oil bath, azocasein assay, SDS-page, protein content) and visual evaluation of the gel formed at the bottom of the sample bottles, it was possible to determine that the treatment added with tripolyphosphate (T4) was that showed greater efficiency in reducing the speed gelation of samples. Finally, the last project came from the demand for less laborious and faster methods for detecting microbial contamination in food. The BD BACTEC™ FX is currently used for the rapid detection of microbial growth in blood samples. The project was divided into two stages in which, in the first, samples of UHT milk intentionally inoculated with strains of Bacillus spizizenii ATCC19659 were evaluated, and in the second, industrial samples of UHT milk were evaluated. Through the results obtained, it was verified that the equipment was very promising due to its ease of use, shorter contamination detection time and greater sensitivity when compared to conventional methodologies. The results obtained in all three projects were very satisfactory, but they are just the beginning of a range of possibilities for advances and discoveries that permeate the main object of the study, UHT milk. Keywords: UHT milk; Quality; Age Gelation; Stabilizing Salts; Alternative Analysis Methods.