Optimized carotenoid production and antioxidant capacity of Gordonia hongkongensis

Abstract

The current emphasis within the cosmetic market on sustainable ingredients has heightened the exploration of new sources for natural, active components. Actinomycetota, recognized for producing pigments with bioactive potential, offer promising functional cosmetic ingredients. This study aimed to optimize pigment and antioxidant metabolite production from the Gordonia hongkongensis strain EUFUS-Z928 by implementing the Plackett-Burman experimental design and response surface methodology. Extracts derived from this strain exhibited no cytotoxic activity against human primary dermal fibroblast (HDFa, ATCC® PCS-201-012™, Primary Dermal Fibroblast; Normal, Human, Adult). Eight variables, including inoculum concentration, carbon and nitrogen source concentration, NaCl concentration, pH, incubation time, temperature, and stirring speed, were analyzed using the Plackett-Burman experimental design. Subsequently, factors significantly influencing pigment and antioxidant metabolite production, such as temperature, inoculum concentration, and agitation speed, were further optimized using response surface methodology and Box-Behnken design. The results demonstrated a substantial increase in absorbance (from 0.091 to 0.32), DPPH radical scavenging capacity (from 27.60% to 84.61%), and ABTS radical scavenging capacity (from 17.39% to 79.77%) compared to responses obtained in the isolation medium. The validation of the mathematical model accuracy exceeded 90% for all cases. Furthermore, liquid chromatography coupled with mass spectrometry (LC-MS) facilitated the identification of compounds potentially responsible for enhanced pigment production and antioxidant capacity in extracts derived from G. hongkongensis. Specifically, six carotenoids, red-orange pigments with inherent antioxidant capacity, were identified as the main enhanced compounds. This comprehensive approach effectively optimized the culture conditions and medium of a G. hongkongensis strain, resulting in enhanced carotenoid production and antioxidant capacity. Beyond identifying bioactive compounds and their potential cosmetic applications, this study offers insights into the broader industrial applicability of these extracts. It underscores the potential of G. hongkongensis and hints at the future utilization of other untapped sources of rare actinomycetes within the industry.

Keywords: Actinomycetota; Gordonia hongkongensis; antioxidants; carotenoids; fermentation; optimization; pigments.

Figure 1.

Effect of cultural media on the (a) dry weight of biomass production, (b) absorbance of pigmented ethanolic extracts measured at 490 nm, (c) DPPH radical scavenging capacity of pigmented ethanolic extracts measured at 515 nm, and (d) ABTS radical scavenging capacity of pigmented ethanolic extracts measured at 735 nm. G. hongkongensis EUFUS-Z928 grown on GYM and Zobell medium. The points and bars represent the mean of three independent assays with their respective standard deviation (SD).

Figure 2.

Effect of carbon sources on the (a) absorbance of pigmented ethanolic extracts measured at 490 nm, (b) DPPH radical scavenging capacity measured at 515 nm, and (c) ABTS radical scavenging capacity measured at 735 nm. G. hongkongensis EUFUS-Z928 grown on GYM medium. The bars represent the mean of three independent assays with their respective standard deviation (SD). ns: no significant differences. *, **; ***, ***,**** described significant differences.

Figure 3.

The pareto chart illustrates the standardized effects of various factors on the absorbance measurements (at 490 nm) of pigmented ethanolic extracts from G. hongkongensis EUFUS-Z928 cultivated on GYM medium. These factors were scrutinized using the Plackett-Burman design. The bars depict the t-value derived from three independent assays along with their corresponding standard deviations. Factors displaying a negative effect are highlighted in red, while those positively impacting the absorbance of pigmented extracts are depicted in blue.

Figure 4.

The pareto chart illustrates the standardized effects of various factors on the DPPH radical scavenging (measured at 515 nm) of pigmented ethanolic extracts from G. hongkongensis EUFUS-Z928 cultivated on GYM medium. These factors were scrutinized using the Plackett-Burman design. The bars depict the t-value derived from three independent assays along with their corresponding standard deviations. Factors displaying a negative effect are highlighted in red, while those positively impacting the absorbance of pigmented extracts are depicted in blue.

Figure 5.

The pareto chart illustrates the standardized effects of various factors on the ABTS radical scavenging (measured at 735 nm) of pigmented ethanolic extracts from G. hongkongensis EUFUS-Z928 cultivated on GYM medium. These factors were scrutinized using the Plackett-Burman design. The bars depict the t-value derived from three independent assays along with their corresponding standard deviations. Factors displaying a negative effect are highlighted in red, while those positively impacting the absorbance of pigmented extracts are depicted in blue.

Figure 6.

The pareto chart illustrates the standardized effects of various factors on the absorbance and DPPH/ABTS radical scavenging capacities of pigmented ethanolic extracts from G. hongkongensis EUFUS-Z928 cultivated on GYM medium. Absorbance was measured at 490 nm, DPPH radical scavenging at 515 nm, and ABTS radical scavenging at 735 nm. These factors were scrutinized using the Plackett-Burman design. The bars depict the t-value derived from three independent assays along with their corresponding standard deviations.

Figure 7.

Contour response surface plots depict the impact on pigmented extract absorbance due to the interaction between various factors: (a) temperature and inoculum concentration at an optimal agitation speed, (b) agitation speed and inoculum concentration at an optimal temperature, and (c) temperature and agitation speed, showcasing their combined effect on the absorbance with the inoculum concentration set at an optimal level. The absorbance measurement in the pigmented extract was conducted at 490 nm, utilizing G. hongkongensis EUFUS-Z928 cultivated on a modified GYM medium. The factors were analyzed by a Box-Behnken design. Each contour plot represents the mean of three independent assays along with their respective standard deviation.

Figure 8.

Contour response surface plots depict the impact on pigmented extract DPPH radical scavenging capacity due to the interaction between various factors: (a) temperature and inoculum concentration at an optimal agitation speed, (b) agitation speed and inoculum concentration at an optimal temperature, and (c) temperature and agitation speed, showcasing their combined effect on the absorbance with the inoculum concentration set at an optimal level. DPPH radical scavenging capacity of pigmented extract was conducted at 515 nm, utilizing G. hongkongensis EUFUS-Z928 cultivated on a modified GYM medium. The factors were analyzed by a Box-Behnken design. Each contour plot represents the mean of three independent assays along with their respective standard deviation.

Figure 9.

Contour response surface plots depict the impact on pigmented extract ABTS radical scavenging capacity due to the interaction between various factors: (a) temperature and inoculum concentration at an optimal agitation speed, (b) agitation speed and inoculum concentration at an optimal temperature, and (c) temperature and agitation speed, showcasing their combined effect on the absorbance with the inoculum concentration set at an optimal level. ABTS radical scavenging capacity of pigmented extract was conducted at 735 nm, utilizing G. hongkongensis EUFUS-Z928 cultivated on a modified GYM medium. The factors were analyzed by a Box-Behnken design. Each contour plot represents the mean of three independent assays along with their respective standard deviation.

Figure 10.

Total ion chromatogram of the pigmented ethanolic extract with antioxidant activity from G. hongkongensis EUFUS-Z928 grown on GYM medium.