3.4.1. Minimum Inhibitory Concentration (MIC) Test Results
Generally, the MIC test for bacteria and fungi
n-hexane extract was better than ethyl acetate and ethanol extracts. The MIC of
S. mutans and
S. aureus showed that the
n-hexane and ethyl acetate extracts had low values at concentrations of 0.5, 1.5, and 1% for
S. mutans,
S. aureus,
C. Albicans, and
C. tropicalis. In the ethanol extract, up to a concentration of more than 50%, bacteria and fungi were not found in MIC. This indicated that the colony could still grow at a concentration of more than 50%. The difference in the MIC concentration of each extract tended to occur because the solvent’s varying polarity determined the yield. The MIC test results of
Cinnamon bark extract against bacteria and fungi are shown in
Table 5.
The difference in solvent polarity can affect the concentration of the extracted active compound and the MIC. The minimum inhibitory concentration can be used as a reference in the IAW test. The smaller the concentration of extract obtained in the MIC test, the better the antibacterial activity. The compounds with antifungal activity are essential oils from the bark of C. burmanii against C. Albicans. Meanwhile, essential oils that can be extracted by non-polar and semi-polar solvents, in this case, are n-hexane and ethyl acetate. Similarly, the MIC of C. burmanii stem bark extracted using the multilevel maceration method for the n-hexane and ethyl acetate extracts produced 2.5%, while for the ethanol extract, 25% was obtained.
3.4.2. Inhibitory Area Width (IAW) Test Results
The IAW test was conducted to determine the effect of the concentration of the extract on the antibacterial power. This was conducted using the paper disc diffusion method because it is more sensitive to antimicrobial compounds whose activity is unknown. According to Banjara et al., growth inhibition in this method was indicated by forming a clear zone around the paper disc [
49]. The antibacterial activity category was determined. The diameter of the inhibition zone of 5, 5–10, 11–20, and 21 mm are categorized as weak, moderate, strong, and very strong (
Table 6).
The test results showed that the three extracts have antibacterial activity against S. mutans and were categorized from weak to medium. The concentration of the extract had a significant effect on IAW. The higher the n-hexane extract concentration, the wider the IAW. Although IAW produced the widest concentration at 4%, this result was still in the weak category and under positive control. Similarly, even though the ethyl acetate extract produced the best extract concentration at 4% extract with 3.66 mm, it was in the weak category. The lowest IAW test results were ethanol extract with a concentration of 15% against S. mutans.
One of the non-polar
n-hexane solvents that attracted compounds from the bark of
C. burmanii was cinnamaldehyde, which could inhibit energy metabolism in bacteria and has been widely reported to have antibacterial properties. This was evidenced by the synthetic inhibition of the cell wall of
S. mutans bacteria and biosynthetic enzymes used for energy formation [
50].
In addition to cinnamaldehyde compounds, the bark of
C. burmanii contains other secondary metabolites, such as alkaloids, flavonoids, tannins, saponins, and terpenoids. Flavonoids are polar compounds and belong to the phenol group that contains a hydroxyl on a carbon ring and functions as an antimicrobial and antiviral [
51]. Flavonoid compounds can change the physical and chemical properties of cytoplasm-containing proteins and denature bacterial cell walls by binding to proteins through hydrogen bonds. It also interferes with membrane permeability function, active transport function, and control of protein composition.
Terpenoids have the same polarity as the phenol group and bind to fats and carbohydrates, causing the permeability of bacterial cell membranes to be disturbed. Tannins are complex organic compounds acting as antimicrobials, reacting with cell membranes, inactivating enzymes, destroying bacteria, and functioning as bacterial genetic material. The alkaloids have a mechanism of action by influencing the osmotic pressure between bacteria and their environment [
52]. Polyphenols are phenol group compounds that play a role in damaging the cytoplasmic membrane of bacteria. Therefore, it causes instability in the controlling protein composition function of bacterial cells.
The IAW test on
S. aureus and
S. mutants showed that the extract concentration had a significant effect. All the extracts tested showed antibacterial properties from weak to moderate, and the higher its concentration, the greater the IAW
S. aureus. Duncan’s test showed that the extract concentration produced the highest IAW at a concentration of 6% with a strong category and quantitatively exceeded the control. The mouthwash preparations containing
C. burmanii oil can inhibit bacteria with an IAW of up to 13.80 mm. In contrast to the
n-hexane extract, the ethyl acetate extract significantly affected IAW until the category was under positive control, while the ethanol extract was in the weak category. The results of IAW testing in
cinnamon bark extract against
S. aureus bacteria are shown in
Table 7.
Antibacterial activity is influenced by the extracted polarity compound of the solvent, and each compound can have a different effect in inhibiting bacterial growth [
53]. The effective concentration ion intense antibacterial activity is in the inhibition zone. Therefore, the 6% concentration of
n-hexane extract of
C. burmanii stem bark effectively inhibits the growth of
S. aureus. The antibacterial activity of the
n-hexane extract was more significant than the ethyl acetate and 96% ethanol extracts because it contained many essential oils, such as cinnamaldehyde, which are effective antibacterial and antifungal.
Pracheeta et al. stated that flavonoids inhibit bacterial growth by damaging cell walls and cytoplasmic membranes. The ability of saponins to act as an antibacterial compound is because they cause leakage of proteins and enzymes from within the cell [
54]. Similarly, Wiyanto [
55] stated that steroids could inhibit microbes by damaging the plasma membrane and causing the release of the cytoplasm due to leakage, leading to cell death [
55]. According to Rahmawati et al. [
56], antibacterial compounds containing terpenoids damage the cell wall structure and interfere with the work of active transport as well as the strength of protons in the bacterial cytoplasmic membrane.
In a study of active antifungal compounds conducted to determine the category of antifungal activity by Davis and Stout, IAW is in the weak, medium, and strong categories when it is <5, 5–10, and 10–20 mm, respectively. The results of the variance analysis showed that the concentration of n-hexane extract had a very significant effect on the IAW of C. albicans. The higher the extract concentration, the greater the IAW. Hence the n-hexane extract with concentrations of 2% and 3% has an average inhibition area of 11.33 mm and 13.83 mm in the strong category and higher than the positive control. The ethyl acetate extract also showed that the concentration had a very significant effect on IAW C. albicans. The 32% ethyl acetate extract indicates significantly inhibited bacterial growth with an IAW of 13.67 mm above the positive control.
Meanwhile, the ethanol extracts up to a concentration of 70% did not form an inhibition zone; therefore, increasing the test concentration will not affect its utilization. This extraction process did not have antifungal activity against C. albicans. The extraction using a multilevel maceration method obtained n-hexane extract concentrations of 2.5% and 5%, which are included in the weak category (<5 mm) and 10% in the strong category (0–20 mm). Ethyl acetate extract at a concentration of 10% (5–10 mm) and 96% ethanol extract (<5 mm) were included in the medium and weak categories.
The variance analysis results showed that the concentration of
n-hexane extract had a very significant effect on IAW
C. tropicalis, with 3% having an average inhibition area of 10 mm and in the strong category with a positive control value of 4.83 mm. In addition, the extract ethyl acetate results in variance analysis showed that the concentration also had a very significant effect on IAW
C. tropicalis at a concentration of 32% in an IAW of 7 mm with a positive control value of 4.83 mm. IAW test results for ethanol extract up to a concentration of 70% were not produced. The average value of the IAW test results for
C. burmanii bark extract against
C. albicans and
C. tropicalis is shown in
Table 8.
The positive control treatment using nystatin 350 ppm had an average inhibition area of 4.83 mm and was included in the weak category. Nystatin is an antifungal recommended for patients infected with the fungi Candida sp. Meanwhile, the negative control treatment was 1% DMSO due to the use of DMSO as the extracting solvent without antifungal activity. It was also used to dissolve the extract in polar or non-polar compounds and has no antifungal activity.
Essential oil compounds can inhibit fungal growth; therefore, the antifungal effect is the presence of phenolic groups in essential oils to form complexes with proteins in cell membranes, thereby leading to clumping. This process undergoes denaturation, which can reduce cell membrane permeability and interfere with the transport of nutrients into cells while inhibiting fungi growth. In addition to essential oils, tannin compounds can also inhibit fungi growth because they prevent the synthesis of chitin, which is used to form cell walls in fungi and damage cell membranes [
57]. The mechanism of tannin action compounds in inhibiting fungi growth prevents the biosynthesis of ergosterol, the main sterol constituent of fungi cell membranes. Sterols are structural and regulatory components found in eukaryotic cell membranes and the final product of sterol biosynthesis in fungi cells. It is similar to cholesterol in mammals, which plays a role in the permeability of fungal cell membranes [
58].