Antimicrobial Efficacy of Industrial Sweet Orange Waste Extracts against S. mutans & L. casei

Objectives: This study aims to investigate the antimicrobial efficacy of industrial sweet orange waste (SOW) extracts against planktonic cultures of the cariogenic pathogens Streptococcus mutans and Lactobacillus casei.
Methods: The bioactive compounds from SOW were extracted by microwaving at 70 and 90 ⁰C for 5(A), 10(B), and 15(C) minutes. The extracts were analysed for detection and quantification of flavonoid compounds using LC-MS and HPLC respectively. The antimicrobial properties including the minimum inhibitory and bactericidal concentrations (MIC and MBC respectively), and the incubation time required to achieve bacterial death, of the SOW extract and pure flavonoid compounds have been explored against two model dental cariogenic bacteria. Chlorhexidine (CHX) was used as a positive control for the antimicrobial assays.
Results: The identified flavonoids in the SOW included flavanones, flavonols, and flavones. Among the pure flavonoids, flavones were found to be the most effective antimicrobial compounds against these two pathogens. However, this was not as effective as SOW. The lowest MIC and MBC of the SOW extract against S. mutans were obtained using extraction protocols performed at ‘70_B’ (13±2; 37.66±1.53 mg/ml respectively), and ‘90_A’ (11±1.73; 35 ±353 mg/ml respectively). A similar trend was found against L. casei but at a higher dose compared to S. mutans. The time required to achieve inhibition of S. mutans, and L. casei using SOW extracts obtained with the ‘70_B’ method were 18.43±0.51 and 20.77±0.4 hours respectively, and with the ‘90_A’ method 17.67±0.58 and 20.87±0.51 hours respectively. The time was significantly reduced when extracts were combined with bacteria specific MBC dose of CHX.
Conclusions: Industrial sweet orange waste products have the potential to be used as antimicrobials against cariogenic bacteria. The adaptation of these waste products will help the development of alternative therapies and ease industrial waste management which is a financial liability to juice processing industries.