Effect of environmental water activity on microbial inactivation by intense pulsed light (IPL).

In this study, the effect of environmental aw on microbial inactivation by intense pulsed light (IPL) was investigated. Three different microorganisms (Gram-positive bacteria, Gram-negative bacteria, and yeast) were used as test organisms. The effect of environmental aw was assessed by irradiating each microbial suspension in sodium chloride solutions with different environmental aw levels (0.99-0.80). As the aw decreased, the aggregation of intracellular material of cell interior was changed and the cell number was increased. However, there was no significant difference in microbial reduction according to the aw after the 0.23-3.05 J/cm2 of IPL treatment. It was confirmed that yeast had the highest resistance to IPL because of the differences in cell structure and cell wall components between yeast and bacteria. Additional research is needed to clearly understand the inactivation mechanism according to the type of microorganism by controlling aw using various solutes.

Thermal conversion kinetics and solubility of soy isoflavones in subcritical water extraction.

The conversion of isoflavones during subcritical water extraction were studied using first-order reaction kinetics modeling. Isoflavones were extracted from soybean using temperatures from 100℃ to 180℃ for 3 to 30 min. It was found that malonylgenistin was the most thermally unstable, with little being detected above 100℃. The optimal extraction temperatures for acetylgenistin (AG), genistin (G), and genistein (GE) were 120℃, 150℃, and 180℃, respectively. A larger sum of the numbers of both hydroxyl groups and oxygen molecules was associated with a lower melting point and optimal extraction temperature. Kinetics modeling of reaction rate constant k and activation energy Ea showed that all of the reaction rates tended to increase with temperature, with the relationship fitted well by a first-order model in nonlinear regression. For temperatures between 100℃ and 150℃, AG â†’ G and AG â†’ GE conversions showed the highest rate constants, but G â†’ GE and G â†’ D3 (degraded G) conversions became dominant at 180℃. Chemical compounds studied in this article: genistein (PubChem CID: 5280961), genistin (PubChem CID: 5281377), 6″-O-malonylgenistin (PubChem CID: 15934091), 6″-O-acetylgenistin (PubChem CID: 5315831).

Comparison of microbial reduction effect of intense pulsed light according to growth stage and population density of Escherichia coli ATCC 25922 using a double Weibull model.

This study evaluated how the efficacy of intense pulsed light (IPL) was influenced by biological factors such as the incubation time and the population of Escherichia coli. According to the 4D value, the microorganisms in the exponential phase were more susceptible to IPL (0.51 J/cm2), while those in the stationary phase were the most resistant (0.67 J/cm2). The microorganisms in the exponential phase could have more critical DNA damage. In addition, the degree of inactivation was affected by the microbial population. When the population was 109 CFU/ml, a maximum 3.4-log reduction was observed after applying IPL at 12.5 J/cm2. In contrast, a population with a density of 1010 CFU/ml showed maximally 0.13-log reduction when IPL was applied at 18.7 J/cm2. This large difference might have been due to cell distribution and aggregation. The study is expected to contribute to the analytical confirmation of the microbial reduction mechanism through non-thermal technologies.

Application of Pulsed Electric Field as a Pre-Treatment for Subcritical Water Extraction of Quercetin from Onion Skin.

Pulsed electric field (PEF) treatment promotes the electroporation of biological membranes, and if included as a pre-treatment, could improve the extraction of certain constituents therefrom. The aim of this study was to determine the optimal extraction conditions for extracting the flavonoid quercetin from dried onion skin and to establish whether the yield could be enhanced by combining PEF pre-treatment with an eco-friendly extraction method that uses subcritical water extraction (SWE). Samples of onion skin were treated with PEF under conditions of varying electric field strength (0.5-2.5 kV/cm) and duration (5-120 s). SWE was then performed with an extraction time of 15 min and at temperatures ranging from 105 °C to 185 °C. Among the conditions tested, the yield of total quercetin was the highest after pretreatment with PEF at 2.5 kV/cm for 15 s, followed by SWE at 145 °C for 15 min (yield 19.25 ± 0.77 mg/g dried onion skin, mean ± standard deviation). Pretreatment with PEF improved the yield of total quercetin extracted by 33.22% compared with the PEF-untreated samples. These findings demonstrate that pretreatment of onion skin with PEF has the potential to improve flavonoid extraction.

Selective extraction of oxygenated terpene in caraway (Carum carvi L.) using subcritical water extraction (SWE) technique.

Caraway contains terpenes such as carvone, limonene and carveol, that have antibacterial and antifungal properties. Subcritical-water extraction (SWE) can be used to extract terpenes by changing temperature under high pressure. This study evaluated the SWE of terpenes from caraway when varying the extraction conditions of temperature (110 °C-190 °C), time (5-15 min), and particle size (>1000, 850-1000, 425-850, and < 425 µm). The optimal conditions for the extraction of carvone, which determines the quality of caraway, were found to be 170 °C, 15 min, and a particle size of < 425 µm. Also, the carvone yield was much higher when using SWE (28.5 mg/g caraway) than for solvent extraction (20.2 mg/g caraway) and hydrodistillation (19.8 mg/g caraway). The overall results showed that oxygenated terpene like carvone has a high solubility in subcritical water, and nonoxygenated terpene like limonene can partially be converted to carvone via a process of SWE.

Improving the Extraction of Catechins of Green Tea (Camellia sinensis) by Subcritical Water Extraction (SWE) Combined with Pulsed Electric Field (PEF) or Intense Pulsed Light (IPL) Pretreatment.

The aim of this study was to find the optimum condition of pulsed electric field (PEF) and intense pulsed light (IPL) for the enhancement of subcritical water extraction (SWE), which is an eco-friendly extraction method, for extracting tea catechins from green tea leaves (Camellia sinensis). The leaves were treated with PEF under conditions of electric field strength (1, 2 and 3 kV/cm) during 60 s. Moreover, IPL was applied at various voltages (800, 1000, and 1200 V) for 60 s. The SWE was performed for 5 min at varying temperatures (110, 130, 150, 170, and 190 °C). The maximum yield of total catechin was 44.35 ± 2.00 mg/g dry green tea leaves at PEF treatment conditions of 2 kV/cm during 60 s, as well as the SWE temperature of 130 °C. In the case of IPL treatment, the largest amount of total catechin was 48.06 ± 5.03 mg/g dry green tea leaves at 800 V during 60 s when the extraction temperature was 130 °C. The total catechin content was increased by 15.43% for PEF and 25.09% for IPL compared to the value of untreated leaves. This study verified that PEF and IPL had a positive effect on the enhancement of tea catechins extraction from green tea leaves using SWE.

Impact of factors affecting the efficacy of intense pulsed light for reducing Bacillus subtilis spores.

This study investigated how the following four intense pulsed light (IPL) treatment factors affect the inactivation of Bacillus subtilis (KCCM 11,315) spores: distance between the sample and IPL lamp (8, 13, and 18 cm), pulse width (0.5, 1.3, and 2.1 ms), charging voltage (1000, 1200, and 1400 V), and processing time (10, 20, and 30 s). The results showed that all four factors considerably influenced the spore inactivation rate in different ways. Excluding processing time, which does not affect the pulse itself, the effect was largest for pulse width, followed by distance, and charging voltage. The optimal treatment condition that maximized the inactivation rate was a distance of 8 cm, a pulse width of 2.1 ms, a charging voltage of 1000 V, and a processing time of 30 s, which together produced a 6 log reduction. It revealed that individual factors need to be investigated together for achieving the optimal condition of IPL.

Microbial inactivation in fresh and minimally processed foods by intense pulsed light (IPL) treatment.

The purposes of this study were to evaluate the inactivation effects of intense pulsed light (IPL) on indigenous and inoculated microorganisms in fresh and minimally processed foods and the industrial applicability of this nonthermal sterilization method. The samples were treated with IPL by varying the treatment time and voltage. The inactivation effect tended to increase as the treatment conditions increased. Further, indigenous microorganisms showed a lower inactivation level than inoculated microorganisms, E. coli ATCC 25922, due to the variability of indigenous microorganisms and their properties. Chopped garlic showed a higher E. coli inactivation effect (2.65 log reduction after 0.185 J/cm2 of IPL) than peeled garlic (1.21 log reduction) due to its larger surface area. The manila clam showed a lower E. coli inactivation (0.93 log reduction) effect than squid (1.84 log reduction) due to its rougher surface. After the IPL treatment, there was no significant difference in temperature, moisture content, and color.

Anthocyanin Structure and pH Dependent Extraction Characteristics from Blueberries (Vaccinium corymbosum) and Chokeberries (Aronia melanocarpa) in Subcritical Water State.

This study determines the optimal extraction conditions for the subcritical-water extraction (SWE) of anthocyanin from blueberries and chokeberries and compares the performance using conventional extraction methods. SWE is carried out under different conditions of extraction temperature (110 °C, 130 °C, 150 °C, 170 °C, 190 °C, and 200 °C), extraction time (1, 3, 5, and 10 min), and solvent pH (water and 1% citric acid). The solubility and stability of anthocyanin from blueberries and chokeberries influences the optimal condition for SWE. The presence of more methoxy and hydroxyl functional groups in the basic skeleton of anthocyanin will result in a lower solubility at a high temperature. Water at a higher temperature exhibits a better dissociation reaction, and a solvent has a lower pH at a higher temperature. One percent citric acid is used to reduce the pH of the solvent, which increases the extraction efficiency of anthocyanin in a subcritical water state.

Recovery of hesperidin and narirutin from waste Citrus unshiu peel using subcritical water extraction aided by pulsed electric field treatment.

The objective of this study was to identify whether the efficacy of extracting hesperidin and narirutin from Citrus unshiu peel by-products can be increased by combining pulsed electric field (PEF) and subcritical water extraction (SWE). The samples were treated with a PEF at a strength of 3 kV/cm for 60 and 120 s. Subsequent SWE was conducted at extraction temperatures of 110-190 °C for 3-15 min. The concentration of hesperidin was highest at 46.96 ± 3.37 mg/g peel (dry basis) after PEF treatment at 120 s, combined with SWE at 150 °C for 15 min, while that of narirutin peaked at 8.76 ± 0.83 mg/g after PEF treatment at 120 s, integrated with SWE at 190 °C for 5 min. The concentrations of both hesperidin and narirutin increased with PEF treatment time. The PEF increased the amounts of hesperidin and narirutin extracted by 22.1% and 33.6%, respectively. This study demonstrate the potential of PEF pretreatment for enhancing the SWE of flavonoids from C. unshiu peel.

Bacillus spores: a review of their properties and inactivation processing technologies.

Many factors determine the resistance properties of a Bacillus spore to heat, chemical and physical processing, including thick proteinaceous coats, peptidoglycan cortex and low water content, high levels of dipicolinic acid (DPA), and divalent cations in the spore core. Recently, attention has been focused on non-thermal inactivation methods based on high pressure, ultrasonic, high voltage electric fields and cold plasmas for inactivating Bacillus spores associated with deterioration in quality and safety. The important chemical sporicides are glutaraldehyde, chorine-releasing agents, peroxygens, and ethylene oxide. Some food-grade antimicrobial agents exhibit sporostatic and sporicidal activities, such as protamine, polylysine, sodium lactate, essential oils. Surfactants with hydrophilic and hydrophobic properties have been reported to have inactivation activity against spores. The combined treatment of physical and chemical treatment such as heating, UHP (ultra high pressure), PEF (pulsed electric field), UV (ultraviolet), IPL (intense pulsed light) and natural antimicrobial agents can act synergistically and effectively to kill Bacillus spores in the food industry.

Subcritical water extraction of bioactive compounds from Orostachys japonicus A. Berger (Crassulaceae).

Subcritical-water extraction is an ecofriendly method for extracting antioxidant compounds only using water. The Subcritical-water extraction was employed for the extraction of bioactive compounds from Orostachys japonicus known as rock pine by investigating the use of various temperatures (110-260 °C) and extraction times (5-20 min). The Subcritical-water extraction condition at 220 °C for 15 min; the total phenolics content (39.9 ± 4.1 mg/g), flavonoids content (11.4 ± 0.6 mg/g), and antioxidant activities (90.3 ± 2.2%, 96.0 ± 2.9%, and 662.4 ± 17.2 mg/g) of Subcritical-water extract were higher under this condition than for extraction with either methanol or ethanol. Triterpene saponins were observed only in subcritical-water extraction condition at 220 °C for 15 min. Further, some of its phenolic constituents; gallic acid, quercetin, and kaempferol were quantified by high performance liquid chromatography. Subcritical-water extraction is an effective method for extracting valuable bioactive compounds from Orostachys japonicus.

Pilot-scale subcritical-water extraction of nodakenin and decursin from Angelica gigas Nakai.

Active components were extracted from Angelica gigas Nakai by subcritical-water extraction (SWE) with the purpose of determining how the extraction conditions affect the SWE of antioxidant properties and active components (nodakenin and decursin), and to compare pilot-scale SWE (8 L) and conventional extraction methods. The extraction yields of nodakenin and decursin in the pilot-scale system were highest at 150 °C for 10 min and 190 °C for 15 min, respectively. The extraction yield of decursin increased as the stirring speed was increased to 200-250 rpm. Pearson's correlation indicated that the radical-scavenging activities using DPPH and ABTS assays were more sensitive to the Maillard reaction (R2 = 0.822 and 0.933, respectively) than to the total phenolic contents (R2 = 0.486 and 0.724, respectively). The extraction yield of decursin was higher when using conventional extraction methods than for SWE.

Improving the quality of vegetable foodstuffs by microwave inactivation.

With the aim of improving the loss of quality in retorted vegetables, experiments on pretreatment inactivation using microwaves were carried out to allow the heating intensity to be reduced during retorting. Microwave heating reduced the bacteria level by 103 CFU/g, and was a more effective method considering the short processing time of 3 min and the required energy being 70-80% of that when using steam. The inactivation effect was due to dielectric heat generation by the high-frequency microwaves. The inactivation effect for heat-resistant Bacillus amyloliquefaciens was indicated by a reduction of 102 CFU/g after 3 min of microwave heating. The total bacteria counts for peeled potato and spicy sauce with vegetables decreased by 3-4 log CFU/g after 3 min using microwaves, and heat-resistant microorganisms were reduced by 2 log CFU/g. Combining microwave heating and mild retorting is expected to produce higher quality vegetable foodstuffs compared to conventional retorting.

Hydrolysis of beta-glucan in oat flour during subcritical-water extraction.

Oat (Avena sativa L.) ß-glucan is bound tightly to other components of the endosperm cell wall, which means that ß-glucan extraction processes are complex and involve many different stages. Subcritical-water extraction (SWE) has emerged as a promising method for extracting ß-glucan under high temperature and pressure conditions. This study investigated the efficiency of the SWE of ß-glucan from oat flour. The yield of ß-glucan was optimized under the following conditions: extraction temperature of 200 °C, solvent pH of 4.0, extraction time of 10 min, and particle size of 425-850 µm. The extraction yield under the optimal condition was 6.98 ±â€¯1.17 g/100 g oat flour, which was more than twofold higher than when using hot-water extraction at 60 °C for 3 h. ß-glucan degradation to 5-hydroxymethyl-2-furaldehyde was increased under high-temperature conditions. SWE is a feasible alternative for extracting ß-glucan in a single-step process, and could be developed into an effective industrial process.

Inactivation of Bacillus subtilis spores at various germination and outgrowth stages using intense pulsed light.

It is important to inactivate spore-forming bacteria in foods because their spores are highly resistant to various stresses. Although thermal treatment is an effective inactivation method, the associated high temperatures can cause changes in food quality. Intense pulsed light (IPL) is a nonthermal technique that can effectively improve food safety. This study evaluated the inactivation effects of IPL at various fluences on Bacillus subtilis spores. IPL treatment at a total fluence of 7.40 J/cm2 resulted in a 7 log reduction, indicating the potential of IPL to effectively inactivate bacterial spores. The sensitivity of B. subtilis spores to IPL during germination and outgrowth was also measured. The resistance to the IPL increased temporarily until 1 h after the start of incubation, and then gradually decreased for longer incubation periods. This temporary increase in resistance at the early stage of incubation was attributed to the leakage of dipicolinic acid from the spores. The results also showed that the inactivation efficiency increases after 1 h pre-incubation because the numbers of vegetative cells increased with the incubation time.

Bactericidal effect of intense pulsed light on seeds without loss of viability.

This study investigated the microbial inactivation effects of intense pulsed light (IPL) treatment as an alternative to chemical treatment for decontaminating the radish and pak choi seeds. The f R values (which indicate the resistance to IPL treatment) for radish and pak choi seeds were 24.50, 20.81 J/cm2, respectively. This resistance exhibited by seeds to IPL treatment is related to their surface roughness. Their Rq (the root-mean-square roughness), average surface roughness (Ra), and 10-point height roughness (Rz) values indicate that each crevice on a rough surface could shelter microorganisms from IPL. Viability tests of seeds exposed to IPL treatment indicated that the average germination rates of treated seeds exceeded 85% on day 3 of germination, which is considered as an acceptable criterion for germination. Also, on day 5 of germination the average shoot lengths of sprouts exposed to IPL did not differ significantly from those of untreated seeds.

Conversion of 6-gingerol to 6-shogaol in ginger (Zingiber officinale) pulp and peel during subcritical water extraction.

Subcritical water extraction is an eco-friendly method for the extraction of less polar compounds without the use of organic solvents. This study determined the extraction conditions that maximize the contents of 6-gingerol and 6-shogaol obtained from ginger pulp and peel. The highest yields of 6-gingerol (0.68 ±â€¯0.08 mg/g), and 6-shogaol (0.39 ±â€¯0.03 mg/g) were obtained from ginger pulp at the extraction conditions of 130 °C/25 min, and 190 °C/15 min. 6-Shogaol content increased with the increasing extraction temperature and extraction time due to the conversion of 6-gingerol to 6-shogaol by thermal cracking. The antioxidant activity of ginger extracts were increased depending on the increasing of 6-shogaol content.

Effects of approved dose of e-beam irradiation on microbiological and physicochemical qualities of dried laver products and detection of their irradiation status.

Most commercial dried laver products show higher microbial contamination. This work evaluated effects of approved dose (7 kGy)-recommended in the Korean Food Code for algal food-of electron beam (E-beam) irradiation on microbiological, physicochemical and luminescence properties of dried laver products. E-beam irradiation caused dose-dependent microbial reductions. For example, a 4 kGy irradiation dose reduced coliform (<2.5 log CFU/g) to undetectable levels (<10 CFU/g), while a 7 kGy irradiation dose reduced total aerobic bacteria count (6.6 log CFU/g) by approximately 2 log cycles. Physicochemical attributes of dried lavers were not significantly (p > 0.05) affected before and after 7 kGy irradiation, but carotenoid content was significantly (p < 0.05) reduced at 10 kGy irradiation. Irradiated samples (>4 kGy) could be detected from non-irradiated ones by luminescence techniques. Overall, results indicated that <7 kGy irradiation is recommended along with other heat treatment for improving microbiological contamination by at most 4 log CFU/g in dried lavers.

Manufacture of low-benzo(a)pyrene sesame seed (Sesamum indicum L.) oil using a self-designed apparatus.

The aim of this study was to lower benzo(a)pyrene (BaP) contents in sesame seed oil (SSO) during manufacture by using a self-designed apparatus, to determine its optimal conditions, and to analyze antioxidants in SSO which might be related to BaP content reduction. Washing and spin-drying steps reduce exogenous BaP contamination, and the reduced moisture in seeds lowered BaP content in final SSO. A ventilation system in the roasting step inhibits BaP formation and reabsorption, followed by a controlled compression step. The optimal condition, a single washing cycle with 2-min spin-drying, 1350-rpm ventilation, and a single compression cycle, reduced the BaP content in SSO to 2.93 µg/kg, where the raw seeds had been spiked with 10-µg/kg BaP. Total phenolic contents showed a reversal pattern to the distribution of BaP contents. Sesamol and sesamolin were quantified by a high performance liquid chromatography-ultraviolet detector, and it was suggested that sesamol which is a strong antioxidant might have prevented BaP formation during the roasting step. This study enabled the commercial production of low-BaP SSO, and the data could be used in further investigations of the BaP content reduction mechanism with quantitative chemical analysis of the SSO composition.