Effects of heating and recovery media pH on the heat resistance of Alicyclobacillus acidoterrestris Ad 746 spores.

AIMS: Alicyclobacillus acidoterrestris is a sporulating, acidophilic bacterial species which spoils acidic beverages such as fruit juices. This work aims to quantify the heat resistance of A. acidoterrestris spores and their recovery potential as a function of heating and recovery media pH. METHODS AND RESULTS: The heat treatments were carried out with the strain of A. acidoterrestris Ad 746 in Bacillus acidoterrestris thermophilic medium. The pH of the heating medium from pH 7 to pH 2 nonsignificantly reduced the heat resistance. However, the pH levels of the recovery media strongly affected the apparent heat resistance of this strain. The maximum heat resistance was found when the pH was 4·70 and decreased when the pH decreased to pH 2·8, close to the minimum growth pH and when the recovery medium pH increased to pH 5·3. CONCLUSION: The heating medium pH has a slight effect on the spore heat resistances of this acidophilic species. However, the pH of the recovery media strongly affected the apparent heat resistance of this strain. SIGNIFICANCE AND IMPACT OF THE STUDY: The obtained parameters quantifying the heat resistance of A. acidoterrestris spores are tools to optimize the heat treatments and to control its development.

Assessing the individual microbial inhibitory capacity of different sugars against pathogens commonly found in food systems.

Highly concentrated sugar solutions are known to be effective antimicrobial agents. However, it is unknown whether this effect is solely the result of the collective osmotic effect imparted by a mixture of sugars or whether the type of carbohydrate used also has an individual chemical effect on bacterial responses, that is, inhibition/growth. In view of this, in this work, the antimicrobial properties of four sugars, namely, glucose, fructose, sucrose and maltose against three common food pathogens; Staphylococcus aureus, Escherichia coli and Salmonella enterica, were investigated using a turbidimetric approach. The results obtained indicate that the type of sugar used has a significant effect on the extent of bacterial inhibition which is not solely dependent on the water activity of the individual sugar solution. In addition, while it was shown that high sugar concentrations inhibit bacterial growth, very low concentrations show the opposite effect, that is, they stimulate bacterial growth, indicating that there is a threshold concentration upon which sugars cease to act as antimicrobial agents and become media instead. SIGNIFICANCE AND IMPACT OF THE STUDY: In this work, an analysis on the antimicrobial properties of glucose, fructose, sucrose and maltose in solution was conducted using a turbidimetric approach. Our findings indicate that while, as expected, all of these sugars exhibit significant antimicrobial effects at high concentrations, at low concentrations they appear to act as substrates for the bacteria which results in enhanced microbial growth instead of inhibition. In addition, the results obtained also suggest that the resultant osmotic stress imparted by the sugar solutions is not the only factor which determines their antimicrobial activity and that other chemical factors may be playing a significant role.