• Journal of Sensor Science and Technology
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• v.20 no.4
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• pp.234-237
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• 2011

This paper presents a study into pH Indicator-Embedded hydrogel micro-particles which are encoded various shapes according to the captured indicator. We incorporate various pH indicators into a photo-curable hydrogel, PEG-DA(Poly(ethylene glycol) diacrylate). Using the latest fluidic lithography techniques, we can easily fabricate variously patterned hydrogel particles based on in-situ photopolymerization of the PEG-DA in a micro-fluidic channel. The shape of the particle is related to the pH indicator inside the particle. We demonstrate that the micro pH sensors change their colors according to the pH levels. The micro pH sensors have various characteristics that are related to the curing time, particle size, etc. By changing these conditions, we can adjust the long term stability and reaction time of the hybrid micro pH sensors.

• Clinical Nutrition Research
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• v.5 no.3
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• pp.172-179
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• 2016

Acid food indicators can be used as pH indicators for evaluating the quality and freshness of fermented products during the full course of distribution. Iron oxide particles are hardly suspended in water, but partially or completely agglomerated. The agglomeration degree of the iron oxide particles depends on the pH. The pH-dependent particle agglomeration or dispersion can be useful for monitoring the acidity of food. The zeta potential of iron oxide showed a decreasing trend as the pH increased from 2 to 8, while the point of zero charge (PZC) was observed around at pH 6.0-7.0. These results suggested that the size of the iron oxide particles was affected by the change in pH levels. As a result, the particle sizes of iron oxide were smaller at lower pH than at neutral pH. In addition, agglomeration of the iron oxide particles increased as the pH increased from 2 to 7. In the time-dependent aggregation test, the average particle size was 730.4 nm and 1,340.3 nm at pH 2 and 7, respectively. These properties of iron oxide particles can be used to develop an ideal acid indicator for food pH and to monitor food quality, besides a colorant or nutrient for nutrition enhancement and sensory promotion in food industry.

• Journal of the Korean Chemical Society
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• v.33 no.2
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• pp.203-207
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• 1989

The methyl red stock solution was added to sample solution and the absorbance values of this solution were measured at the maximum absorption wavelengths of the acidic form, the basic form, and the isosbestic point of the indicator. From the measurements of absorbance, the pH of this solution was calculated. The range of absorbance at the isosbestic point was maintained within 0.1 ${\sim}$ 0.3. The error of pH measurement was within ${\pm}0.08$ pH unit in the pH range of sample solution of $pK_I{\pm}1$.

• Journal of Sensor Science and Technology
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• v.26 no.6
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• pp.414-419
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• 2017

The optical characteristics of cresol red, phenol red, and neutral red immobilized in the thin film were investigated with absorbance measurement in order to find a sensing part of a fiber-optic pH sensor. Sol-Gel method with tetramethyl orthosilicate as a precursor was used to immobilize the pH indicators in the thin film. The absorbance spectra were measured when pH indicators were immobilized in the film and were dissolved in the buffer solution. Experimental results showed that the absorbance spectra could be changed when the pH indicator is immobilized in the thin film. As compared with other pH indicators, the neutral red exhibited similar absorbance spectra regardless of physical conditions and was sensitive over whole pH range between 4 and 11. In addition, the absorbance ratio of base peak to acid peak tended to increase in proportion to the increase in pH. Experimental results indicate that the neutral red is a good pH indicator for fabrication of a sensing part of the fiber-optic pH sensor.

• Applied Biological Chemistry
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• v.49 no.2
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• pp.158-162
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• 2006

To determine freshness and quality change of tofu during storage, we manufactured a freshness indicator and monitored the surface pH, volatile basic nitrogen (VBN), thiobarbituric acid reacted substance (TBARS), total bacterial counts, and sensory evaluation. Tofu had a change in color of the freshness indicator after storage of 8 days at $4^{\circ}C$, and its pH and total bacterial counts reached 5.6 and 7.63 log CFU/g, respectively. VBN and TBARS values increased and reached the decay point at the time of color change of the freshness indicator. Sensory evaluation also indicated that samples were unacceptable by off-odor and decrease of firmness at day 8 of storage. These results suggest that a freshness indicator should be useful in determining expiration date of tofu products during marketing by indicating the microbial safety as well as sensory change.

• Food Science and Preservation
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• v.15 no.4
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• pp.491-496
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• 2008

To develop a freshness indicator of Chonggak-kimchi for marketing purposes, Chonggak-kimchi was prepared and pH, total acidity, total aerobic bacterial load, lactic acid bacterial levels, and reducing sugar content were measured. Sensory evaluation tests on product stored at $4^{\circ}C,\;10^{\circ}C,\;and\;20^{\circ}C$, were performed. The pH increased slightly early in storage, and then decreased to pH 4.2-4.3 for all samples. The rate of decrease of pH rose with increasing storage temperature. Total acidity values rapidly increased after 1, 5, and 7 days of storage at $20^{\circ}C,\;10^{\circ}C,\;and\;4^{\circ}C$, respectively. Populations of total aerobic bacteria and lactic acid bacteria increased slightly until 4 days, 10 days, and 30 days of storage at $20^{\circ}C,\;10^{\circ}C,\;and\;4^{\circ}C$, respectively, and then decreased drastically. Sensory evaluation data showed that Chonggak-kimchi was edible until 4 days(pH 4.5), 10 days(pH 4.4), and 30 days(pH 4.3) of storage at $20^{\circ}C,\;10^{\circ}C,\;and\;4^{\circ}C$, respectively. These results clearly suggest that the shelf-life of Chonggak-kimchi depends on storage temperature, and the pH limit for marketing is 4.3; this is a freshness indicator for Chonggak-kimchi.

• Journal of the Korean Chemical Society
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• v.50 no.2
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• pp.99-106
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• 2006

The electronic absorption spectra of [3-(2-thenoyl) 3-(p-NO2-phenylhydrazone) ethyl pyruvate] (I), p-Br (II) and p-CH3 (III) were studied in ethanol and the spectra comprise four absorption bands which assigned to the corresponding electronic transition. The pK values of these compounds have been determined spectrophotometrically and pH-metrically, the results shown that the interval range for color change of compound (I) is (8-10) similar to that of phenolphethalin indicator, indicating that this compound can be used as acid-base indicator. The successive stability constants of the compounds under study with some transition elements (Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), UO2(II), La(III) and Zr(IV) have been determined pH- metrically. Stoichiometric complexes with ratios 1:1 and 1:2 (M: L) were formed for all metals. The pK of the three derivatives and the values of the stability constant (logK) of the complexes have the order; III > II > I. Also conductometric titrations have been carried out and the results show that this titration can be used for determination of both the metal ion and the ligand concentrations by each others.

• Korean Journal of Environment and Ecology
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• v.21 no.1
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• pp.22-29
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• 2007

Investigation of carabid beetles as on ecological indicator species for wetland characterization and monitoring was conducted in three types of wetlands such as emergent wetland, forested wetland, and estuary, During the investigation period, twenty-eight species belonging to twenty-two genera and three families(Carabidae, Harpalidae, Brachinidae) were identified. The diversity of carabid beetles at riverine wetland such as Woopo (H'=1.18) and Hwapo-neup (H'=1.08) were higher than in the forested wetland (H'=1.03) and estuarine (H'=0.91). Species compositions in each wetland were significantly different(${\chi}^2=1716.8$, P<0.01). Riverine wetlands differed significantly from the forested wetland. Indicator species for the wetland chose with indicator species analysis were reacted sensitively on the parameter such as soil composition, moisture of soil, and environmental change. Thus, it was consequently suggested that these indicator species may be applied for wetland characterization and monitoring of the wetland ecosystem.

• Food Science of Animal Resources
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• v.29 no.3
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• pp.325-333
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• 2009

Beef quality indicators of off-flavor development during storage were investigated in terms of temperature dependence. The off-flavor development time (ODT) was detected using the R-index sensory test. During varying storage conditions at $25^{\circ}C$, $15^{\circ}C$, and $5^{\circ}C$, elements of beef quality were measured, such as volatile basic nitrogen (VBN), pH, color (CIE $L^*$, $a^*$, $b^*$), Warner-Bratzler shear force (WBSF), Pseudomonas spp. CFU, and lactic acid bacteria (LAB) CFU. A model with temperature dependence of ODT during storage was developed using Arrhenius-like equation, and a requirement with quality indicators was mathematically derived, resulting in similar temperature dependence. The temperature dependence of beef quality indicators was represented by the Arrhenius activation energy (Ea). Upon comparing the Ea of beef quality indicators and ODT, the temperature dependence similarity was found to be higher in the order of three groups: VBN, pH, $a^*$ value; LAB, Pseudomonas spp.; and WBSF, $L^*$ value, $b^*$ value. Therefore, VBN were determined as the most effective indicator of beef quality during off-flavor development.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.51 no.5
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• pp.590-594
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• 2018

We developed a time-temperature indicator (TTI) that rapidly determines whether frozen mackerel Scomber japonicus has thawed during its distribution. Our TTI was made from filter paper capable of absorbing mackerel exudate that was soaked in a 20% citric acid solution at pH 4.0 and then dried. The dried absorbent paper was cut and attached to blue litmus paper with a 2 mm overhang. The fixed litmus paper was covered with a polypropylene film and sealed. The indicator was placed inside a polyvinyl vacuum package containing the mackerel sample. The vacuum-sealed packaged was frozen at $-20^{\circ}C$ for 24 h. After freezing, the color change and time dependence of the indicator were observed at room temperature ($25^{\circ}C$) and demonstrated the utility of this TTI for rapidly determining whether frozen mackerel underwent thawing during distribution.