Effect of nanogrinding on the pigment and bioactivity of Djulis ( Chenopodium formosanum Koidz.).

Betanin is an antioxidant pigment found in djulis, a grain native to Taiwan, and is a natural source food coloring, but the bright red color degrades rapidly if submitted to light, heat, or oxygen. The effects of nanogrinding on the stability of pigments and bioactive components are unknown. In this study, the color characteristics and bioactivity (antioxidant capacity and enzyme activity) of nanoparticle (NP) djulis was compared with those of intact granules (IG) and microparticles (MP). Results showed that the NP samples exhibited the highest betanin content (2.04 mg/g), which was almost twice that of IG. It was observed that nanogrinding resulted in higher pigment extraction efficiency. However, during storage (5-35 °C for 56 days), NP samples showed the most serious pigment degradation, and this color degradation, as expected, had the lowest activation energy. This was more evident when the storage temperature was high. Antioxidant capacities showed the same trends. MP and NP exhibited significantly higher activity of superoxide dismutaste-like activity, lactoperoxidase (LPO), and lysozyme than IG. Gel permeation chromatography confirmed the degradation of larger particles during nanogrinding, which might favor enzyme extraction and their activities. Statistical analysis revealed a close relationship between betanin and antioxidant capacity.

Thermal and pH stability of betacyanin pigment of Djulis (Chenopodium formosanum) in Taiwan and their relation to antioxidant activity.

The betacyanin pattern of Djulis (Chenopodium fromosanum), a native cereal plant in Taiwan, was reported for the first time. The determination of characteristics of the pigment, including pH and thermal stability and their relation to antioxidant activities, indicated that betacyanin of Djulis exhibited the maximum absorbance at 530 nm and their thermal stability was dependent on the pH. Antioxidant capacities as well as red color of that pigment were significantly positively related with A(530). Therefore, A(530) can be used as a simple index of the antioxidant capacity of that pigment. Four peaks including betanin (47.8%), isobetanin (30.0%) with m/z 551.0, and armaranthin (13.6%), isoamaranthinee (8.6%) with m/z 727.0 were purified from the pigment extract by HPLC and identified through LC/MS. Among them, betanin and isobetanin totally accounted for more than 70% of FRAP reducing power or DPPH scavenging capacity and were a major source of the antioxidant capacities. Our findings of this pigment confirmed that Djulis can be used as a novel source of betanin antioxidants and may provide a basis for its sustainable utilization in the food industry.