Background and Objectives: Date syrup is a nutritious crop of date that its production has a growing trend. Microbial spoilage is one of the problems in production of data syrup. The goal of this study is to investigate the influence of ethanol and methanol extracts of walnut leaf and hull on Saccharomyces cerevisiae, Bacillus Licheniformis and Aspergillus niger in date syrup.

Materials and Methods: Methanol and ethanol extracts of walnut leaf and hull were prepared, and their antimicrobial effects on S. cerevisiae, B. Licheniformis and A. niger were assessed by ager-diffusion. Moreover, MIC and MBC/MFC of the extracts against the mentioned microorganisms were determined by macro-dilution. The influence of extracts on microorganism growth in date syrup was investigated during 14 days.

Results: The diameter of the inhibition zones was proportional to the extract concentration. MIC (MBC) of ethanol and methanol extracts of leaf and hull against S. cerevisiae was 15.625 (31.5) μg/ml. The MIC (MBC) obtained for the ethanol and methanol extracts of leaf and hull against B. Licheniformis was 31.25 (62.5), 15.625 (31.25), 15.625 (31.25) and 31.25 (62.5) μg/ml, respectively. MIC (MBC) of the ethanol extract of the leaf and the ethanol and methanol extracts of hull against A. niger was 250 (500) μg/ml. In date syrup, extracts of walnut leaf and hull inhibited the growth of S. and Bacillus after 24 h while they were only able to decrease the growth of Aspergillus.

Conclusion: Methanol and ethanol extracts of walnut leaf and hull against S. cerevisiae, B. Licheniformis and A. niger in date syrup were effective, and can be used for the spoilage control and shelf-life increasing of the product.

Keywords: Walnut leaf, Walnut hull, Date syrup, Saccharomyces cerevisiae, Bacillus Licheniformis, Aspergillus niger