Back to top

Shelf-life evaluation of natural antimicrobials for Concord and Niagara Grape Juices

Research in Plain English

Research In Plain English provides brief, non-technical summaries of journal articles by Cornell faculty, students, and staff.
(2013) Journal of Food Protection 76: 72-78

Authors: Passaporn Siricururatana, Meera M. Iyer, David C. Manns, John J. Churey, Randy W. Worobo, and Olga I. Padilla-Zakour
Summary by Amanda Garris

Why?

Preservatives are required to prevent spoilage in juices, particularly in cold-filled or carbonated juices which do not receive a final heat treatment during bottling and may therefore be vulnerable to wild and preservative-resistant yeasts. Traditional preservatives include systems based on sorbate and benzoate, however growing consumer concerns about chemical preservatives is driving interest in natural preservatives. Rigorous testing is needed to evaluate the effectiveness of natural preservatives for maintaining food safety and product quality.

How?

We evaluated three natural antimicrobials: Dimethyldicarbonate (DMDC), an approved food additive also approved for use in wine; natamycin, a naturally occurring antifungal compound produced by the bacteria Streptomyces natalensis; and Microgard200, also known as cultured dextrose, a composite of many antifungal and antibacterial compounds produced by bacteria. Not-from-concentrate commercial Concord and Niagara juices were inoculated with a cocktail of spoilage microbes, including Zygosaccharomyces, Kluveromyces, Dekkera, and Brettanomyces, at low and high levels.  Using the traditional potassium sorbate/sodium benzoate combination as a control, the following treatments were tested in still juice: 0.1% and 0.2% weight/volume cultured dextrose, 250 ppm DMDC, and 10 and 20 ppm natamycin. In addition, the combination of 250 ppm of DMDC with 5 or 10 ppm of natamycin was tested. In carbonated juice, a combination of 250 ppm DMDC with 10 ppm of natamycin was tested. Samples were store at 21°C (70°F) for six months and were tested every two weeks for pH, °Brix, turbidity, and microbial counts for indications for spoilage.

What we learned:

  • In Concord juice, none of the natural antimicrobials at the concentrations tested performed as well as the traditional preservatives. The combination of DMDC and natamycin in samples with the lower level of microbial inoculation inhibited yeast during the early storage period (up to 49 days), with the higher level of natamycin (20 ppm) providing longer shelf life.
  • In Niagara still juice, DMDC alone, 20 ppm natamycin, and DMDC used in combination with natamycin were as effective as the traditional preservatives and prevented spoilage for up to six months. The greater efficacy of the treatment in Niagara compared to Concord may be due to the additional antimicrobial effect of low levels of residual SO2 present in the Niagara juice (7.8 ppm), as sulfites may have been added during harvest to prevent browning.
  • Carbonated juices had lower pH and longer shelf-life due to the dissolved carbon dioxide content, which contributed to the efficacy of DMDC plus natamycin in both Concord and Niagara carbonated juices. They were as effective as the traditional preservative.

The bottom line

In still Niagara juice and carbonated Concord and Niagara juices, the combination of natural preservatives DMDC with natamycin provided comparable shelf-life extension to traditional preservatives.

Amanda Garris is a freelance writer based in Geneva, NY.