Sorghum bio-colorants for food dyeing

Bioactive properties of red sorghum bio-colorants and their derivatives

Several sorghum (Sorghum bicolor) varieties are cultivated for the red dye present in the leaf sheaths. In Benin, this dye is used particularly for food preservation (namely local cheese) and for food colouring (e.g. of porridge). Fulani cheese, locally known as Warangashi, is a popular, protein-rich food product made from the milk of cows and goats in Benin and neighboring countries (Aïssi, et al., 2009). Kayodé et al. (2012) reported that bio-colorants extracted from the leaf sheaths of sorghum (Sorghum bicolor) are generally used to give Warangashi a red color ( The red pigment from the dye sorghum is said to have antimicrobial and antifungal properties (Balole & Legwaila, 2005). The high amount of benzoic acid found in sorghum leaf sheaths (801.4 μg/g) (Kayodé et al., 2011) is likely to play an important role in the antimicrobial activity of the extracts. Little is known about their bio-functionality and their impact on the sensory quality of the foods dyed ( Warangashi and porridge) with them.

This project aims (a) to assess the food uses of sorghum bio-colorants in Benin, (b) to study the preservative effects of sorghum bio-colorants on Warangashi and (c) to study the accessibility of nutrients (proteins and minerals) in dyed foods (namely porridge).

During a survey, we will identify (a) the way in which the sorghum dyes are prepared and applied to colour foods, (b) the perception that users have about the preservative effect of the sorghum dye on Warangashi and (c) the sensory characteristics of dyed foods that consumers distinguish and appreciate.

The antimicrobial properties of sorghum bio-colorants against spoilers and pathogens found in Warangashi will be assessed with disc diffusion method (Murray et al., 1995) and Microwell Dilution Assay (Güllüce et al. 2003). The effect of the sorghum bio-colorants on the microbial flora of Warangashi in relation to (a) the extraction method (sheath grades and extraction aids), (b) the bio-colorant concentration in the dyeing liquid and (c) the size of cheese will be measured and used to describe the reaction kinetics (van Boekel, 2009).
The accessibility of proteins and minerals (iron and zinc) of dyed porridge will be evaluated using respectively the couple pancreatin and pepsin (Akeson et al., 1964) and the in vitro digestion method (Kiers et al., 2000).

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