This study investigates bioactivities and active phytochemicals of the extracts of twigs and branches from the indigenous Taiwanese tree Acacia confusa Merr. The bioassay-guided fractionation yielded 8 potent antioxidative phytochemicals. Catechins are the major components in the extract of 5 cm branch bark, including catechin, catechin-3-O-rhamnopyranoside, epi-catechin, and quercetin-3-O-rhamnopyranoside, while flavonol glycosides are the major components in twig extract, namely, myricetin-3-O-glucopyranoside, myricetin-3-O-rhamnopyranoside, quercetin-3-O-rhamnopyranoside, myricetin-3-O-(2''-O-galloyl)-alpha-rhamnopyranoside, and luteolin. Of the test compounds, myricetin-3-O-(2''-O-galloyl)-alpha-rhamnopyranoside exhibited the highest antioxidant activity against DPPH radicals, showing a 2.8-fold lower IC(50) value of 5.3 microM related to that of quercetin. On the other hand, catechins apparently had no XOD inhibitory effect apart from their good antioxidant activities, while luteolin exhibited excellent activity against XOD with an IC(50) value of 11.6 microM. These results may provide useful information for future studies on the applications of A. confusa to be used as a source for natural health products.
The effects of high hydrostatic pressure (HHP) treatments on histamine-forming bacteria (HFB) Morganella morganii and Photobacterium phosphoreum in phosphate buffer and tuna meat slurry were investigated using viability counting and scanning electron microscopy. The first-order model fits the destruction kinetics of high pressure on M. morganii and P. phosphoreum during the pressure hold period. The D-values of M. morganii (200 to 600 MPa) and P. phosphoreum (100 to 400 MPa) in phosphate buffer ranged from 16.4 to 0.08 min and 26.4 to 0.19 min, respectively, whereas those in tuna meat slurry ranged from 51.0 to 0.09 min and 71.6 to 0.19 min, respectively. M. morganii had higher D-values than P. phosphoreum at the same pressure, indicating it was more resistant to HHP treatment. HFB had a higher D-value in tuna meat slurry compared with that in phosphate buffer, indicating that the HFB were more resistant to pressure in tuna meat slurry. The Zp values (pressure range that results in a 10-fold change in D-value) of M. morganii and P. phosphoreum were 162 and 140 MPa in phosphate buffer and 153 and 105 MPa in tuna meat slurry, respectively. Damage to the cell wall and cell membrane by HHP treatments can be observed by scanning electron microscopy. To our knowledge, this is the first report to demonstrate that HHP can be applied to inactivate the HFB M. morganii and P. phosphoreum by inducing morphological changes in the cells.
HIGHLIGHTS
The inactivation and damage of histamine‐forming bacterium,
Morganella morganii
, in phosphate buffer and tuna meat slurry by high hydrostatic pressure (HHP) alone or in combination with 0.2% lemon essential oil (LEO) treatments were studied using viability measurement and scanning electron microscopy (
SEM
). HHP alone or in combination with LEO treatments showed first‐order destruction kinetics to
M. morganii
during pressure holding period. The D values of
M. morganii
(200 to 600 MPa) in phosphate buffer ranged from 16.4 to 0.08 min, whereas those in tuna meat slurry ranged from 51.0 to 0.10 min, respectively.
M. morganii
in tuna meat slurry had higher D values and were more resistant to HHP treatments than in phosphate buffer. In addition, the D values of HHP in combination with LEO treatment were lower than those of HHP treatment alone at <400 MPa of pressure, indicating that it is more effective to inactivate
M. morganii
under the same pressure. The results showed the
M. morganii
at HHP in combination with LEO treatment was more susceptible to pressure treatment alone. HHP with or without LEO treatments can be used to inactivate
M. morganii
by causing disruption to bacterial cell membrane and cell wall as demonstrated by
SEM
micrographs.
In the research, we evaluated the effects of high-pressure processing (HPP) on the growth and histamine formation of histamine-forming bacteria (HFB) in yellowfin tuna meat during storage. Tuna meat samples inoculated with the individual HFB species Morganella morganii and Photobacterium phosphoreum were subjected to HPP treatment at 250, 350, 450, and 550 MPa for 5 min, and the changes in bacterial count, total volatile basic nitrogen (TVBN) content, pH, and histamine content during storage at 4 and 15 °C were analyzed. The results indicate that the bacterial counts of the HFB species decreased significantly with increasing pressure, and HFB became undetectable in the samples treated at 450 and 550 MPa. At a storage temperature of 15 °C, the bacterial counts of both HFB species in the control group and samples subjected to HPP treatment at 250 and 350 MPa increased significantly with storage time. The bacterial counts of M. morganii in the samples stored at 4 °C decreased, whereas those of P. phosphoreum increased gradually owing to its psychrophilic nature. HPP treatment (>250 MPa) inhibited the increases in pH and TVBN content of the samples stored at 15 °C and delayed histamine formation in the samples during storage; these effects were more significant as the pressure during HPP treatment was increased.
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