Amaranth is an excellent source of various bioactive compounds that could be beneficial in the prevention of some human diseases. This study investigated the extraction and characterization of bioactive compounds from amaranth using ultra-sonication and agitation at 30, 50 and 70 °C. Color L* values showed significant (p
< 0.05) differences at 70 °C between ultra-sonication and agitation. Ultra-sonication temperature had significant effect on L* and a* values whereas agitation temperature did not have a significant effect on L*, a* and b* values. No significant (p
< 0.05) differences were found in terms of total phenol, total flavonoid, DPPH•+
scavenging activity, betacyanins, betaxanthin and betanicaicd between ultra-sonication and agitation. However, temperature had a significant (p
< 0.05) effect on total phenol (8.64–10.598 mg/g), DPPH+
scavenging activity (84.36–94.44%), betacyanins (4585.95–5325.32 mg/100 g), betaxanthin (1312.56–1524.06 mg/100 g) and betalamic acid (1408.15–1790.22 mg/100 g) in ultra-sonication. Higher temperature (70 °C) showed greater amount of arbutin and hydroxybenzoic acid than those of lower temperature (30 °C) for both extraction methods. Meanwhile, temperature did not affect vanillic acid, p
-coumaric acid and ferulic acid for both samples. Fourier-transformed infrared (FTIR) spectrometry showed that ultra-sonication and agitation resulted in similar effect on the structure of amaranth extracts. Higher temperature was correlated with bioactive compounds, which were observed by principal component analysis (PCA). Therefore, agitation at 70 °C could be used as an alternative for ultra-sonication to improve the bioactive compounds and antioxidant activities of amaranth. In addition, agitation and ultra-sonication techniques might be served as an alternative of conventional technique.
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