|WU, BIYU - University Of Hawaii|
|LIU, XIAOHAN - University Of Hawaii|
|NAKAMOTO, STUART - University Of Hawaii|
|LI, YONG - University Of Hawaii|
Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2022
Publication Date: 3/14/2022
Citation: Wu, B., Liu, X., Nakamoto, S., Wall, M.M., Li, Y. 2022. Antimicrobial activity of ohelo berry (Vaccinium calycinum) juice against Listeria monocytogenes and its potential for milk preservation. Microorganisms. 10(3). Article 548. https://doi.org/10.3390/microorganisms10030548.
Interpretive Summary: This study showed the antimicrobial effect of ohelo berry juice on Listeria monocytogenes in culture media and milk products. The minimum inhibitory concentration was 12.5% for ohelo juice. The expressions of motility-, biofilm formation-, and virulence-related genes in L. monocytogenes were down-regulated by the juice treatments. L. monocytogenes was significantly inhibited in whole and skim milk supplemented with 50% ohelo berry juice, regardless of fat content. Due to its antimicrobial properties, ohelo berry may be used as a natural preservative and a functional food.
Technical Abstract: Listeria monocytogenes is a foodborne pathogen and causes illnesses with a high mortality rate in susceptible populations. Several dairy-related outbreaks have been attributed to contamination by L. monocytogenes, which requires antimicrobial interventions for enhancing the safety of these products. Ohelo berry (Vaccinium calycinum) is a Hawaiian wild relative of cranberry (Vaccinium macrocarpon). Previous research indicates that ohelo berry is a rich source of polyphenolic compounds and might act against microorganisms. This study aimed to determine the antimicrobial activity of ohelo berry against L. monocytogenes in culture media and milk products. The effect of ohelo berry juice at its sub-inhibitory concentration on the physicochemical properties and biofilm formation capability of L. monocytogenes was also investigated. Chemical analysis of ohelo berry juice revealed that the concentrations of sugar and organic acids, total phenolics, and anthocyanins were 7.6/1.42 oBrix/acid, 4.2 mg/mL GAE, and 55.11 mg/L cyd-3-glu, respectively. The minimum inhibitory concentration of ohelo berry juice against L. monocytogenes was 12.5%. The sub-inhibitory concentration of ohelo berry juice (6.25%) significantly increased the auto-aggregation and decreased the hydrophobicity, swimming motility, swarming motility, and biofilm formation capability of L. monocytogenes. The relative expression of genes for motility (flaA), biofilm formation and disinfectant resistance (sigB), invasion (iap), listeriolysin (hly), and phospholipase (plcA) was significantly downregulated in L. monocytogenes treated by the 6.25% juice. L. monocytogenes was significantly inhibited in whole and skim milk supplemented with 50% ohelo berry juice, regardless of the fat content. These findings highlight the potential of ohelo berry as a natural preservative and a functional food to prevent L. monocytogenes infection.