Comparative Antibacterial Efficacy of Olea Africana and Acacia Etbaica Wood Smoke in Raw Milk from Southern Ethiopia

Abstract

Background: The rapid spoilage of milk can lead to foodborne illness, making effective preservation methods essential for ensuring food safety and extending shelf life. This study examined the antibacterial effects of wood smoke from Olea africana and Acacia etbaica on raw milk samples from Wondo Genet, Southern Ethiopia.

Methods: Raw milk samples were collected in February and April 2018, comprising 20 from a dairy farm and 20 from randomly selected smallholder farmers. The microbial loads of raw milk samples stored in smoked and non-smoked containers at 25 °C were compared. Microbial analysis included aerobic mesophilic bacterial count (AMBC), Staphylococcus aureus count (SC), total coliform count (TCC), and yeast and mold count (YAMC) over a 36-hour period. Pathogen screening targeted Salmonella spp. and Shigella spp. Statistical analysis was performed using one-way ANOVA followed by Tukey’s post-hoc test to determine significant differences (p < 0.05). Analyses were conducted with SPSS Statistics software, version 26.0 (IBM Corp., Armonk, NY, USA).

Results: At 0 h, the dairy farm milk samples in non-smoked containers exhibited lower microbial loads than those from smallholder farmers, with significant differences (p < 0.05) in AMBC (5.74 vs. 6.04 log₁₀ CFU/mL), SC (3.4 vs. 3.8 log₁₀ CFU/mL), and TCC (2.71 vs. 3.51 log₁₀ CFU/mL). Both wood smoke types effectively reduced microbial counts, with Olea africana showing greater efficacy. After 24 h, AMBC decreased by 0.9 log units for Olea africana compared with 0.47 for Acacia; SC decreased by 2.09 log units versus 1.14; and YAMC decreased by 1.51 log units compared with 0.76 log units. Significant reductions in TCC were observed only at 24 h. Pathogens such as Salmonella (30%) and Shigella (32.5%) were more prevalent in samples stored in non-smoked containers.

Conclusion: These results underscore the antimicrobial potential of traditional wood-smoking practices, especially those using Olea africana, in reducing microbial contamination in milk.