Antimicrobial evaluation of red, phytoalexin-rich sorghum food biocolorant

Abstract

Sorghum (Sorghum bicolor) extract is traditionally used as red biocolorant in West Africa to colour foods, among which wagashi, a soft cheese. This biocolorant is a source of the phytoalexin apigeninidin and phenolic acids, and users claim that it has preservative effects next to its colouring properties. If such a claim can be scientifically substantiated, it adds a valuable functional property to this natural red colorant, thereby increasing its potential applications in the food industry. Hence, the present study evaluated the antimicrobial properties of dye sorghum extracts using challenge tests in broth and wagashi as a model of a popular food application. The alkaline extract and hot aqueous extract were used for dyeing wagashi by 87.7% and 12.3% of the traders, respectively. The dyeing procedure is perceived as a preservation strategy, and is also a means to maximise the revenues. However, results demonstrated that the application of sorghum biocolorant on wagashi had no inhibitory effect on the growth of fungi (Penicillium chrysogenum, Cladosporium macrocarpum) and Escherichia coli O157:H7. Furthermore, sorghum biocolorant in broth had no effect on growth of Listeria monocytogenes and Escherichia coli O157:H7. Consequently, the commonly used extracts for colouring soft West-African cheese did not show a preservative effect. In addition, dyeing did not affect the physico-chemical properties of wagashi. Still, the red colour hampered visual detection of microbial growth, thus clarifying the preservative effect reported by users.

Antimicrobial Activity of Sorghum Phenolic Extract on Bovine Foodborne and Mastitis-Causing Pathogens

“…Questions of which specific compound(s) in sorghums has efficacy, and the representation of those compound(s) in the diversity of sorghum was not in the scope of this project. Furthermore, a second limitation was that only two species of Gram-positive bacteria were tested, but the findings are similar to other researchers [ 32 , 44 ]. Akogou et al [ 44 ] demonstrated no antimicrobial activity of red, phytoalexin-rich sorghum extract against E. coli O157.…”

Sorghum Grain: From Genotype, Nutrition, and Phenolic Profile to Its Health Benefits and Food Applications

“…3-Deoxyanthocyanidins are also plant phytoalexins with antimicrobial activity. Studies have demonstrated that 3deoxyanthocyanidins are effective against a range of fungi and bacteria in vitro (Aida, Tamogami, Kodama, & Tsukiboshi, 1996;Stonecipher, Hurley, & Netzly, 1993), although a recent study showed no significant antimicrobial effect on an African food Wagashi (Akogou, Besten, Kayode, Fogliano, & Linnemann, 2018). Nevertheless, 3-deoxyanthocyanidins could play a role in food preservation, reducing and possibly replacing the synthetic antimicrobial additives in foods.…”

Phytochemical screening and antibacterial activities of Sorghum bicolor leaves derived from in vitro culture

“…In contrast, sorghum crude stem extract showed high inhibition against P. aeruginosa (gram-negative) compared to B. subtilis (gram-positive) [3]. On the other hand, extracts of dye sorghum leaf sheaths found have no anti-bacterial properties on E. coli tested in a nutrient-rich traditional West African cheese [5]. However, similar trends of exerting higher activity against gram-positive bacteria compared to gram-negative strains have been also reported on seed extracts of sorghum.…”

“…Other important uses, especially from leaves, sheath, stalks, glumes, and root were also available including food additives and folk pharmaceuticals. Red or purple pigments are largely extracted from the sheath and used as food colourants such as cheese and porridges, and dyes for leather, textile, and wood in numerous countries of Africa and Asia [3][4][5]. Sorghum extracts is reported to have antiabortion, cyanogenic, demulcent, diuretic, emollient, intoxicant, and toxic properties [6].…”