A group of researchers from Hawaii analyzed probiotic bacteria cultured in extracts from local food byproducts and investigated their antimicrobial properties. To achieve this objective, dried pineapple peel, pineapple core, and taro peel were ground into powder. The chemical analysis showed significant differences in protein content, with taro peel having the highest value (10.7%). The three materials had similar crude fat and moisture contents. Regarding ash content, taro peel (7.5%) was significantly higher than the other two materials. For carbohydrates, pineapple core had the highest content (90.24%), and significant differences were observed among the three materials. Lastly, pineapple peel and taro peel had significantly higher crude fiber content than pineapple core.
Broth media with different concentrations of pineapple peel, pineapple core, or taro peel powder were evaluated for their potential to support the growth of the probiotic bacteria Lactococcus lactis. Lactobacillus deMan, Rogosa, and Sharpe (MRS) medium broth was used as a reference. Growth performance in 10% pineapple core and 10% pineapple peel was significantly higher than in 5% and 20%. For taro peel, the 20% extract was too viscous to filter through a membrane. The bacterial number was higher in the 10% taro peel broth than in the 5% medium. MRS showed similar performance to the three materials in supporting probiotic growth. Therefore, 10% of pineapple peel, 10% taro peel, and MRS were further evaluated with four additional probiotic strains: Lactobacillus plantarum, Pediococcus acidilactici, Bacillus sp., and Enterococcus sp. Statistical analysis showed no significant differences in bacterial counts at 48 hours between the three tested media for any of the probiotic strains, indicating that all three media supported probiotic growth.
In addition, the antimicrobial activity of probiotic cultures in MRS, 10% of pineapple peel, and 10% taro peel was assessed against the fish pathogens Streptococcus agalactiae and Francisella orientalis (Fo). Interestingly, both pineapple peel and taro peel exerted significant inhibitory and even bactericidal effects on Streptococcus agalactiae, as evidenced by the complete elimination of viable cells after 24 h of incubation, whereas MRS retained bacterial viability. This highlights the potential of these food byproducts as natural antimicrobial agents against Streptococcus agalactiae.
Against Fo, Lactobacillus plantarum-inoculated pineapple peel and MRS broth supernatants demonstrated the strongest antimicrobial activity at 48 hours, with Fo counts dropping to undetectable. For Lactococcus lactis, pineapple peel medium supernatant exhibited a bactericidal effect. Taro peel and MRS broth supernatants held back the growth of Fo. For Pediococcus acidilactici, pineapple peel and MRS supernatants showed no significant differences at 48 hours. However, both exhibited stronger bactericidal effects on Fo than the taro peel supernatant. These results suggest pineapple peel is an effective substrate for producing inhibitory compounds by probiotics against Fo, performing comparably to MRS. Also, this knowledge gained will help researchers to understand the potential of these byproducts as sustainable substrates for probiotic culture and natural disease control in aquaculture.
This study was developed by Dr. Yong Li (UH), who led the probiotics portion of the recently completed project, “Assessment of Hawaiian aquaculture for disease mitigation and control,” which achieved its objectives across multiple health-related areas.
