ULTRASOUND ASSISTED EXTRACTION OF SORGHUM ANTHOCYANINS

Sorghum is an important food crop in Africa and its use in research and as gluten free food ingredient in commercial products is increasing in many countries such as United States of America and Brazil. This growth in popularity is mainly due to its agronomic advantages and potential health benefits. Special sorghum varieties are good sources of phenolic compounds such as anthocyanins. Sorghum anthocyanins, the unique 3-deoxyanthocyanins, are more stable relative to the anthocyanins found in fruits and vegetables, which shows their potential to be used in the food industry as natural food colorant and health promoting component due to their antioxidant activity. However, overall, the extraction rate of phenolic compounds from cereals is low due to strong interactions of these compounds with cell wall polymers. Thus, new extraction methods are necessary to be studied in order to optimize the extraction of sorghum anthocyanins. The objective of this work was to evaluate the ultrasound assisted extraction of total anthocyanins from black sorghum flour. In the conventional method (control), phenolic extract was obtained by extraction of black sorghum flour with acidified methanol (1% HCL/methanol) with stirring for 2 h. The ultrasound extraction was performed with the same solvent in an ultrasonic bath and the parameters time, temperature, sonication power and frequency were evaluated. Phenolic extracts from both extractions were centrifuged at 1500 x g for 10 min and filtered through a filter paper. The content of total anthocyanins (mg luteolinidin equivalents/100 g of sorghum flour) of the obtained supernatants was determined (Awika et al. 2004). The study was done in three repetitions and the statistical analysis was performed using SAS software (version 9.4). Overall, the best results found for total anthocyanin content (from 97.3 to 102.6 mg/100 g) were obtained when the ultrasonic bath was set to the following parameters: temperature (40 or 70oC), sonication power (50 or 90%), frequency (45 kHz) and time (40 or 75 min). A total anthocyanin content of 102.6 ± 6.08 mg/100 g was obtained when the ultrasonic bath was set to temperature of 70oC, sonication power of 90%, frequency of 45 kHz and time of 40 min. This amount was almost twice higher than the total anthocyanin content obtained by the conventional method (54.2 ± 1.91 mg/100 g), which takes 2 hours of extraction. Therefore, this study demonstrated that the ultrasound assisted extraction is a promising method to extract higher levels of sorghum 3-deoxyanthocyanins in shorter times. This is important due to the health benefits and potential as natural food colorants of the anthocyanins.

Reference:

Awika, J.M., Rooney, L.W., Waniska, R.D. 2004. Properties of 3-Deoxyanthocyanins from Sorghum. J. Agric. Food Chem. 52, 4388−4394.