Optimization and comparison of microwave and ultrasound assisted extraction of clove bud oleoresins in terms of chemical composition and biological potential

The present investigation deals with the optimization of various parameters for extraction of oleoresins from Syzygium aromaticum (L.) Merr. and L.M. Perry buds (clove) using microwave assisted extraction (MAE) and ultrasound assisted extraction (UAE) by response surface methodology comparing the results with Soxhlet extraction (SE). The chemical composition of oleoresins was studied by GC-MS analysis. This was followed by testing their antibacterial potential against Escherichia coli, Yersinia enterocolitica, Staphylococcus aureus and Bacillus sp. and antioxidant potential. The maximum yield of clove oleoresin (COR) was obtained by UAE (42.00%) at 1:35 (solid to liquid ratio), 70^°C for 12.50 min followed by SE (41.38%) and MAE (41.07%, 1:31 (solid to liquid ratio), 625 W for 60 s). The COR extracted by MAE showed the maximum percentage of various oxygenated terpenes (76.96%), followed by UAE (74.98%) and SE (44.92%). The major compound found in CORs extracted by MAE and UAE was eugenol acetate and for SE was 4,8,13-duvatriene-1,3-diol. The CORs extracted by MAE exhibited maximum antibacterial potential with minimum inhibitory concentration (MIC) which is the lowest COR concentration that inhibited the detectable growth of the test microorganisms in the range of 2.80–4.20 mg/ml followed by UAE (3.20–4.45 mg/ml) and SE (3.75–4.56 mg/ml). The COR extracted by MAE also exhibited maximum antioxidant activity against mustard oil degradation having the least increase in peroxide value, anisidine value, thiobarbituric acid value and total oxidation value after 28 days of storage. Hence, the maximum yield of COR was obtained by UAE but the maximum antibacterial and antioxidant potential was shown by COR extracted by MAE. Hence, COR extracted by MAE can be used as a natural food preservative as an alternative to synthetic food preservatives.