Use of natural plant extracts as a novel microbiological quality indicator in raw milk: An alternative for resazurin dye reduction method

• Published in: Food science & technology 2021-06, Vol.144, p.111221, Article 111221
• Main Authors: Madushan, Ranga, Vidanarachchi, Janak K., Prasanna, P.H.P., Werellagama, Shanika, Priyashantha, Hasitha
• Format: Article
• Language: English
• Subjects: Animal and Dairy Science; Anthocyanin; Food Science; Husdjursvetenskap; Livsmedelsvetenskap; Microbiological safety; Milk keeping quality; Plant aqueous extracts; Platform test
• ISSN: 0023-6438; 1096-1127; 1096-1127
• DOI: 10.1016/j.lwt.2021.111221

In the present study, we propose a novel field-scale analytical tool for rapid screening of microbiological quality in raw milk using aqueous extracts of plant materials, i.e. flowers (e.g. Hibiscus rosa-sinensis L. and Clitoria ternatea), taproots (e.g. Beta vulgaris) and pricklypears (e.g. Opuntia dillenii). For each plant extract, the colour changes in raw milk were evaluated between 4.5 and 6.5 pH against the resazurin dye as a control. The plant anthocyanin content in each extract was analyzed by the differential pH method using a spectrophotometer. The Hibiscus rosa-sinensis flower extract was opted to further test since it had a pH-sensitive colour change (6.5; maroon to 6.2; light-pink) compared to other plant extracts, which did not indicate a noticeable colour variation with pH. Anthocyanin content of the Hibiscus extract was 0.59 g/mL. The novel method showed high linearity (R2 = 0.95), 100% accuracy and greater repeatability with an intermediate level of precision. The limit of quantification and detection was 0.46 and 0.15 g/mL, respectively. In conclusion, we demonstrated the potential in using water extract of Hibiscus rosa-sinensis L. flowers as an alternative to the resazurin dye reduction method for rapid and accurate microbiological quality control for raw milk procurement in remote areas. [Display omitted] •pH-sensitive colour changes in plant extracts were evaluated to screen microbiological quality of milk.•A valid method was developed from Hibiscus rosa-sinensis flowers' anthocyanin extract.•Anthocyanin concentration of the Hibiscus rosa-sinensis flowers' water extract was 0.59 g/mL.•The extract showed visible colour changes in milk samples with varying pH levels.•The novel method was validated and can be useful in field-scale milk quality determinations.