International Research Journal of Microbiology

Studies on Antimicrobial Activity of Anthocyanins Extracted from Red Sorghum (Sorghum bicolor .L) Bran

P.Suganyadevi^1*, M Saravanakumar² and S. Mohandas^{3 1}Department of Biochemistry, Karpagam Academy of Higher Education, Coimbatore, India
²Department of Biochemistry, P.S.G College of Arts and Science, Coimbatore, India
³Senior Scientists, Rasi Seeds, Salem, India
^*Corresponding Author:
P.Suganyadevi, Department of Biochemistry, Karpagam Academy of Higher Education, Coimbatore, India, Email: suganyadevibiotech@gmail.com

Received: 29-Oct-2021 Published: 26-Nov-2021

Introduction

Sorghum (Sorghum bicolor (L)) is the fifth leading cereal crop in the world and is used primarily in Asia and Africa as a food crop (Rooney, 2000). Speciality of sorghum have high levels of phytochemicals, including proanthocyanins (Awika; 2003, Hahn;1996), 3-deoxyanthocyanins(Gous; 1989, Awika; 2004a, Awika; 2004b), phenolic acids (Wansika; 1989), phytosterols (Singh; 2003) and policosanols (Huang; 2004) in their bran layers. In addition, sorghum bran is rich in dietary fiber (Rooney; 1992). This sorghum bran are potentially useful ingredients in various functional food applications and were shown to produce desirable attributes (e.g., attractive natural color) without adversely affecting other sensory properties of foods such as bread, cookies and expanded snacks (Acosta; 2003, Gordon; 2001, Mitre-Dieste; 2000).

Anthocyanins are belonging to water – soluble plant pigments and representatives of flavonoids. They are responsible for the blue, purple and red colour of many plant tissues. They play a definite role in the attraction of animals for pollination and seed dispersal, and hence they are of considerable value in the co-evolution of these plant- animal interactions (Han; 2006).

Antibiotic – resistant bacteria is still of world – wide concern. Since the use of antibiotics became wide spread over 50 years ago, bacteria have progressively developed resistance (Hsueh; 2005). Consequently, scientific efforts have been made to study and develop new compounds to be used beyond conventional antibiotic therapy.

The objective of the present study was to evaluate the antimicrobial activity of anthocyanins isolated from red sorghum bran.

Materials and Methods

Samples

Sorghum bicolor was collected from the village area (Coimbatore district, India) and raised in the college campus under normal climatic conditions. The plant was identified and authenticated (No.BSI/SRC/5/23/2011-12/Tech.1486) by Botanical survey of India (BSI), Tamil Nadu Agricultural University (TNAU), Coimbatore, India. The bran was collected and was stored at -20⁰C.

Anthocyanin extraction

The bran of red Sorghum were extracted by incubating with two solvent systems like methanol and with 1% Hydrochloric acid in methanol, overnight at room temperature, followed by a filtration through whatman filter paper no 4. Methanol was removed by a rotary evaporation under 35°C and the pigmented fraction extracts were stored for a further study.

Microorganisms

Escherichia coli, Klebsiella oxytoca, Klebsiella pneumonia, Pseudomonas aeruginosa, Staphylococcus aureus, Aspergillus niger and Aspergillus fumigatus were the micro-organisms used and they were stored at freeze temperature until use.

Determination of antibacterial activity

An agar –well diffusion methods was employed for determination of antibacterial activity. The anthocyanin extracts were tested for microbial resistance using such technique with an inoculum volume equivalent to 0.5% Mc Farland’s Standard in Mueller – Hinton agar and examined after 24 hrs. The anthocyanin extracts containing 1 mg, 2.5 mg, 5 mg, 7.5 mg, 10 mg and 12.5 mg were dissolved in DMSO. Negative controls were prepared using DMSO solution. Streptomycin was used as positive reference standards to determine the sensitivity of each bacterial species tested and Nystin was used as reference standard for fungal cultures. The inoculated plates were incubated at 37°C for 24 hrs. Antibacterial activity was evaluated by measuring the inhibition zones formed on the medium were evaluated in mm of the tested bacterial cultures and for fungal culture it was incubated at room temperature for 48 hours. All the tests were performed in triplicates.

Results and Discussion

Antibacterial activities of anthocyanin extracted by methanol solvent

One out of five bacteria used Staphylococcus aureus is Gram positive and four (Escherichia coli, Klebsiella pneumoniae, Klebisella oxytoca, Pseudomonas aerginosa) are Gram negative. There was significant variation in the antibacterial activities of anthocyanin extracts. In all four Gram negative bacterias the methanol extract of anthocyanin showed no inhibitory zone even at 12.5 mg concentrations. For Staphylococcus aureus, the zone of inhibition values of anthocyanin extracts were between 5-9 mm. The results of methanolic extracts on bacteria are presented in Table 1. The moderate antifungal activity was observed in Aspergillus fumigates and Aspergillus niger. (Table 1). The results observed in anthocyanin extracted from red Sorghum bran methanol extracts indicating that gram positive strain was more sensitive than gram negative. This observation can be attributed in the difference in the structure of bacterial cell wall. The less complex structure of the cell wall in the gram positive bacteria makes it more permeable to the antibacterial compounds (Chrissanthy et al. 2005).

Antibacterial activites of anthocaynin extracted by acidified methanol solvent

There was a significant variation in the antibacterial activities of anthocyanin extracted from acidified methanol. The acidified methanol extracts of anthocyanin samples showed inhibitory effect in gram positive and gram negative bacteria. The highest antibacterial activity was observed in K. oxytoca with zone of inhibition of 3- 6 mm with the concentration ranging from 1 to 12.5 mg. The moderate antifungal activity was observed in Aspergillus fumigates and Aspergillus niger (Table 2). The Suganya et al. 2011 reported the anthocyanin content was found to be higher in acidified methanol extract than methanol extract. Deividas et al. 2009 reported that phenolic compounds and anthocyanin content was higher in the extracts of skin and berry extracts of biliberry and blue berry showed highest inhibitory zone against gram negative bacteria than other extracts, which coincides with our results.

Conclusion

The present study confirms the potential antimicrobial activity of the extract of red sorghum bran. The presence of anthocyanin as major active constituents may be responsible for these activities. Further studies are necessary to isolate characterize the active constituents of the plant to evaluate their modes of action and render this species interesting for future.

Acknowledgments

This work was supported by Department of science and technology, New Delhi, India (Grant No: 100/(IFD)/1398/2011-12) under Women Scientist Scheme.

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