Clin Nutr Res.  2016 Jul;5(3):172-179. 10.7762/cnr.2016.5.3.172.

Application of Iron Oxide as a pH-dependent Indicator for Improving the Nutritional Quality

• Meng X
• Ryu J
• Kim B
• Ko S

• KMID: 2344889
• DOI: http://doi.org/10.7762/cnr.2016.5.3.172

Abstract

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.

Keyword

Iron oxide; Particle; pH; Acid food indicator

MeSH Terms

Food Industry
Food Quality
Hydrogen-Ion Concentration
Iron*
Nutritive Value*
Particle Size
Water
Iron
Water

Figure

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  Figure 1 Illustration of the indication process of iron nanoparticles as CO2 indicator at pH 2 and pH 7 condition.

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  Figure 2 Picture of iron oxide particles. (A) Normal graph of iron oxide powder by naked eye, (B) Micrographs of iron oxide particles by SEM (scale bars, from left to right: 500 nm).

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  Figure 3 Size distribution of iron oxide particles.

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  Figure 4 Zeta-potential of iron oxide particles at different pH levels.

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  Figure 5 Time-resolved DLS of iron oxide particle suspensions at different pH: (A) pH 2.0 and (B) pH 7.0.

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