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. 2018 Mar 21;13(3):e0194657.
doi: 10.1371/journal.pone.0194657. eCollection 2018.

Antimicrobial evaluation of red, phytoalexin-rich sorghum food biocolorant

Folachodé U G Akogou  1   2   3 , Heidy M W den Besten  3 , A P Polycarpe Kayodé  1 , Vincenzo Fogliano  2 , Anita R Linnemann  2
Affiliations

Antimicrobial evaluation of red, phytoalexin-rich sorghum food biocolorant

Folachodé U G Akogou et al. PLoS One. .

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.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1
Flow chart of the coagulant extraction (A), the pre-treatment of the milk (B) and the clotting (C) in wagashi processing.
Fig 2
Fig 2
Growth of Listeria monocytogenes (a) and Escherichia coli O157:H7 (b) in dyed (■) and non-dyed (□) broth. Error bars represent standard deviations.
Fig 3
Fig 3. Growth of Listeria monocytogenes (■) in broth with increasing apigeninidin concentration after incubation for 24 h at 37°C (starting concentration 6.5 log CFU/mL).
Error bars represent standard deviations.
Fig 4
Fig 4
Analysis of the spreading area of fungi after growth on dyed (a) and control (b) wagashi with ImageJ 1.46r (c and d).
Fig 5
Fig 5. Percentage of traders willing to sell their wagashi when it is dyed (■) and non-dyed (□).
See this image and copyright information in PMC

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