Effect of food components on the antimicrobial activity of phenolic antioxidants

This study was conducted to elucidate exactly what effects various food components, such as lipids and proteins, have on the antimicrobial activity of butylated hydroxyanisole (BHA) and tertiary butylhydroquinone (TBHQ).

Five microorganisms were used in this study: the molds, Penicillum citrinum NRRL 5727 and Aspergillus niger; a yeast, Saccharomyces cerevisiae; and the bacteria. Pseudomonas fluorescens ATTCC 15456 and Staphylococcus aureus ATCC 12600. All cultures were incubated under optimum conditions. Inhibition studies were conducted as follows: (1) bacteria and yeast — samples were removed from each flask at selected time intervals and enumerated by the pour plate technique and (2) molds — the mycelial mat weight was used as an indication of growth.

Concentrations of BHA and TBHQ used in this experiment were as follows: P. citrinum, 200 ppm BHA, 400 ppm TBHQ; A. niger. 200 ppm BHA, 600 ppm TBHQ; S. cerevisiae, 200 ppm BHA, 400 ppm TBHQ; S. aureus, 300 ppm BHA, 50 ppm TBHQ; P. fluorescens. 200 ppm BHA, 300 ppm TBHQ. The antimicrobial effectiveness of these compounds was tested in the presence of 0, 1.5, 3.0 and 4.5%(v/v) of a lipid (corn oil) or 0, 3, 6 and 9%(w/v) of a protein (casein).

In every case, the presence of casein in the growth media diminished the antimicrobial activity of BHA and TBHQ. The overall effects were dependent upon species of microorganism tested as well as the type of antioxidant. BHA was affected more by casein than TBHQ. Decreased antimicrobial activity was probably due to binding of the antioxidants by the casein.

As with casein, corn oil also depressed the antimicrobial activity of both antioxidants. BHA was more affected in all cases by the lipid than by the protein. In most cases, even the presence of the emulsifier, Tween 80, eliminated much of the effectiveness of BHA. In contrast, TBHQ was less affected by the lipid than BHA, except in the case of S. aureus where only 50 ppm TBHQ were used.

In summary, the antimicrobial effectiveness of BHA and TBHQ against a variety of microorganisms was significantly diminished by both casein and corn oil. However, in most cases, TBHQ was affected less by the food components than BHA. The reason for this was most likely a combination of the higher concentrations used and polarity differences of the compound. Finally, the primary cause for the loss in activity of the antioxidants in the presence of the lipid was due to their solubilization into the lipid phase.