Effects of processing and storage on the stability of the red biocolorant apigeninidin from sorghum

A major drawback to the industrial application of many biocolorants is their instability to processing conditions, thereby limiting their use to replace artificial colorants. 3-Deoxyanthocyanidins have promising features to ensure colour stability in food processing conditions. This study evaluated the stability of apigeninidin, the main 3-deoxyanthocyanidin from sorghum leaf sheaths, to food processing conditions in watery extracts and in a maize porridge. Apigeninidin was not soluble at pH 5.04 ± 0.02. However, apigeninidin was soluble and stable at pH 6–10 with increased colour density and resistance to bleaching at alkaline pH. A heat treatment of 121 °C/30 min degraded 61% of the anthocyanins. At 65 °C, degradation rate of apigeninidin was four times lower at pH 9.03 ± 0.04 than 6.08 ± 0.02. Storage at room temperature promoted endothermic degradation reactions. Nevertheless, photodegradation of apigeninidin was not observed during storage. In the maize porridge, thermal stability of apigeninidin and redness were similar at pH 4–6 whereas they were higher at pH 9.03 ± 0.04. In summary, the watery extract of apigeninidin from sorghum leaf sheaths showed good stability regarding common industrial processes. Nevertheless, the biocolorant's precipitation at pH 5.04 ± 0.02 and degradation at pH 6.08 ± 0.02 and 9.03 ± 0.04 need further investigation to optimise its industrial applications.