Inactivation kinetics of Escherichia coli in cranberry juice during multistage treatment by electric fields.

The inactivation of Escherichia coli inoculated in cranberry juice by processing with radio frequency electric fields was studied. E. coli ATCC 35218 was chosen among three non-pathogenic strains based on its ability to survive in low pH cranberry juice. Studies were conducted by measuring the survival population when changing the electric field strength between 2.2 and 13.2 kV cm-1, number of treatment stages from 1 to 6 and flow rates between 13 and 25 L h-1 at moderate temperatures of 20, 30 and 40 °C. A minimum inactivation of 5-log reduction, as requested by the Food and Drug Administration (FDA), can be achieved by increasing the number of treatment stages, temperature or both. At 40 °C and 6 treatment stages, 6.57 ±â€¯0.02 log CFU ml-1 reduction in the initial population of E. coli (ATCC 35218) was obtained. At a constant electric field, increasing the temperature produced higher microbial inactivation, consuming lower radio frequency energy input, than increasing the number of treatment stages. Furthermore, a primary model that accounts for the combined effect of time and electric field is proposed. The model represented the sigmoidal curve composed of shoulder, log-linear and tailing sections as observed when changing electric fields. A secondary model that accounts for the effect of temperature and flow rate on the primary model constants is also proposed. The combined primary and secondary models were found to fit the data well with a high coefficient of determination (R2 = 0.965). The proposed model can be extended to kinetic models for pulsed electric fields.

Phenolic compounds of the Australian native herb Prostanthera rotundifolia and their biological activities.

The chemical identity and bioactivities of phenolic components of the Australian native herb Prostanthera rotundifolia were studied. Phenolic compounds were extracted with 80% (v/v) aqueous methanol and purified by liquid chromatography. The antioxidant capacity of the extract and its inhibiting activity against α-glucosidase, pancreatic lipase and hyaluronidase were determined. Phenolic compounds were identified by a combination of HPLC-PDA, LC-high resolution MS (LC-HRMS), LC-tandem MS (LC-MS/MS) and nuclear magnetic resonance (NMR) spectroscopy. Compared to spearmint, mint bush showed comparable antioxidant capacity, stronger inhibitory activity on pancreatic lipase and comparable and lower activity on α-glucosidase and hyaluronidase, respectively. Major compounds identified were verbascoside (48.8%), 4-methoxycinnamic acid (36.4%), p-coumaric acid glucose ester (9.2%) and 1-O-ß-d-glucopyranosyl sinapate (5.6%), while caffeic acid, p-coumaric acid, hesperidin and naringenin were present in trace quantities. 4-Methoxycinnamic acid, p-coumaric acid glucose ester and 1-O-ß-d-glucopyranosyl sinapate were identified for the first time in the genus of Prostanthera.

Identification and quantification of phenolics in Australian native mint (Mentha australis R. Br.).

Australian native mints have traditionally been used by the aboriginal people for natural remedies; however, their bioactive components have not been studied. Antioxidant capacity and composition of phenolic compounds of Mentha australis R. Br., Lamiaceae were investigated for the first time. Phenolic compounds were analyzed by HPLC photodiode array detector, liquid chromatography high resolution mass spectrometry, tandem mass spectrometry and nuclear magnetic resonance spectroscopy. Aqueous methanolic extract of the mint exhibited comparable antioxidant capacity to the common spearmint. Major compounds identified in the extract were rosmarinic acid (160.4 ± 0.85 µg mg(-1)purified extract), neoponcirin (145.0 ± 0.42 µg gallic acid equivalent(GAE) mg(-1)), narirutin (30.3 ± 0.02 µg GAE mg(-1)), chlorogenic acid (15.4 ± 0.05 µg mg(-1)) and biochanin A (9.6 ± 0.06 µg GAE mg(-1)), while minor compounds were caffeic acid, apigenin, hesperetin and naringenin. Neoponcirin and biochanin A were identified for the first time in the Mentha genus.