Effects of Ocimum gratissimum Extracts on Spoilage Organisms Obtained from Yoghurt Samples

Abstract

Ocimum gratissimum (OG) is recognised for its nutritional, antioxidant, and antimicrobial properties, making it a strong candidate for natural food preservation. However, its specific application in yoghurt preservation has been underexplored, particularly in North-Central Nigeria. This study evaluated the effects of ethanolic and aqueous OG leaf extracts against spoilage organisms isolated from laboratory-prepared yoghurt samples stored at room temperature for ten days. The agar well diffusion technique was employed for antimicrobial screening, while the broth microdilution method was used to determine both minimum inhibitory concentration (MIC) and minimum cidal concentration (MCC). The isolated organisms included Bacillus subtilis, Bacillus spp., Saccharomyces cerevisiae, Saccharomyces bulderi, Pichia kudriavzevii, Aspergillus niger, and Aspergillus flavus. The aqueous extract at 62.50 mg/mL inhibited Bacillus subtilis, Saccharomyces bulderi, Pichia kudriavzevii, and Saccharomyces cerevisiae, with inhibition zones ranging from 5.00 to 6.20 mm. The ethanolic extract exhibited antimicrobial effects against Bacillus subtilis, Bacillus spp., Saccharomyces bulderi, Pichia kudriavzevii, and Saccharomyces cerevisiae at the same concentration (62.50 mg/mL), but with larger inhibition zones ranging from 5.30 to 11.35 mm. The aqueous extract showed substantial inhibition of Bacillus subtilis, Saccharomyces bulderi, and Pichia kudriavzevii, with an MIC of 62.50 mg/mL. In contrast, the ethanolic extract demonstrated an MIC of 31. 25 mg/mL for Bacillus subtilis, Bacillus spp., and Aspergillus niger. The MCC of the aqueous extract was 250 mg/mL for Bacillus subtilis, Saccharomyces bulderi, Pichia kudriavzevii, Aspergillus flavus, and Saccharomyces cerevisiae, while the MCC of the ethanolic extract was 125 mg/mL for Bacillus subtilis and Bacillus spp. Overall, the OG extracts exhibited substantial antimicrobial effects, effectively inhibiting the growth of spoilage organisms isolated from stored yoghurt samples. Harnessing the potential of OG can lead to an extended shelf life for yoghurt, positioning OG as a promising natural preservative.