An approach to mass produce peppermint oil-sodium alginate composite microcapsules by drop-on-demand system loaded with stabilized nanoemulsion

Figures & data

Table 1. HLB values of composite surfactants prepared by various ratios of span/Tween.

	N1	N2	N3	N4	N5	N6	N7	N8
Span:Tween (w/w)	0:10	0.5:9.5	1:9	1.5:8.5	2:8	3:7	4:6	5:5
HLB value	15.00	14.465	13.93	13.395	12.86	11.79	10.72	9.65

Figure 1. DLS testing results of different PO/SA nanoemulsions illustrating the effects of (a) surfactant HLB value; (b) emulsification temperature; (c) PO/oil phase ratio; (d) oil phase/emulsion ratio on the mean droplet size and PDI.

Table 2. Factors and levels of the response surface methodology.

Factors	Levels
H (HLB value)	13.395	13.93	14.465
P (PO/oil phase)	0.1	0.3	0.5
O (oil phase/emulsion)	0.05	0.10	0.15

Table 3. Analysis of variance for regression model.

Source	Sum of Squares	df	Mean Square	F Value	P-value, Prob > F
Model	39253.60	9	4361.51	270.68	<0.0001	significant
H	3370.21	1	3370.21	209.16	<0.0001	significant
P	228.98	1	228.98	14.21	0.0070
O	218.40	1	218.40	13.55	0.0078
HP	19.80	1	19.80	1.23	0.3042
HO	214.62	1	214.62	13.32	0.0082
PO	7.02	1	7.02	0.44	0.5303
H^2	33110.31	1	33110.31	2054.85	<0.0001	significant
P^2	108.55	1	108.55	6.74	0.0357
O^2	913.26	1	913.26	56.68	0.0001
Residual	112.79	7	16.11
Lack of Fit	91.12	3	30.37	5.61	0.0646	not significant
Pure Error	21.67	4	5.42
Cor Total	39366.40	16

Table 4. Model fit summary for quadratic model statistics.

Std. Dev.	4.01	R-Squared	0.9971
Mean	101.57	Adj R-Squared	0.9935
C.V. %	3.95	Pred R-Squared	0.9621
PRESS	1491.86	Adeq Precision	44.330

Table 5. Groups of PO/SA nanoemulsion set for appearance and stability check.

	HLB value	PO/oil phase ratio (w/w)	oil phase/emulsion ratio (w/w)	Emulsification Temperature (℃)
NE1	14.465	0.1	0.15	25
NE2	13.93	0.3	0.1	25
NE3	13.93	0.3	0.1	55
NE4	13.886	0.407	0.085	25

Figure 2. (a) appearance of four groups of PO/SA nanoemulsions, (b) mean droplet size of different nanoemulsions at day0 (6h) and day7 (174h), and (c) PDI of different nanoemulsions at day0 (6h) and day7 (174h).

Figure 3. Optical microscopy images of PO/SA microcapsules prepared by different pulse durations of (a)100, (b) 80, (c) 60, (d) 40, and (e) 20 ms.

Figure 4. Optical microscopy and FESEM images of pure sodium alginate microcapsules (a) and PO/SA microcapsules with different shell/core ratios of (b) 2 (S/C-2), (c) 1 (S/C-1), and (d) 0.5 (S/C-0.5).

Figure 5. (a) size and (b) shape distribution of PO/SA microcapsules fabricated with different pulse durations and shell/core ratios (***: p < 0.001, **: p < 0.05, *: p < 0.01).

Figure 6. The effect of PO contents on the UV-Vis absorbance: (a) the UV-Vis spectra of peppermint oil, (b) the relationship of UV-Vis absorbance with the concentration of core contents of PO/SA microcapsules in CaCl₂, and (c) the encapsulation efficiency of PO/SA microcapsules fabricated with different parameters (***: p < 0.001, **: p < 0.05, *: p < 0.01).

Figure 7. Killing experiments on E. coli at 0h and 24h for (a) pure SA microcapsules, (b) S/C-2, (c) S/C-1, and (d)S/C-0.5 PO/SA microcapsules.