Bio-sanitation treatment using essential oils against E. coli O157:H7 on fresh lettuce

Figures & data

Table 1. Chemical constituents of the essential oils used in this study.

Essential oil	Major component	RI	RRI	GC–FID (%)
Thyme (Thymus vulgaris)	Thymol	1291	1290	31.20
Tea tree (Melaleuca alternifolia)	α-Terpineol	1843	1843	41.00
Ylang-ylang (Cananga odorato)	Benzyl acetate	1165	1167	27.48
Sage (Salvia dolomitica)	Eucalyptol (1,8-cineole)	1207	1196	36.00

Notes: RI, retention indices measured relative to n-alkanes (C₁₀–C₂₆) on the HP-5MS column. RRI, retention indices taken from the literature.

Figure 1. Total phenolic content of the thyme oil (stand-alone) and in combination with ylang-ylang, tea tree and sage oils separately tested. Bars with different letters are significantly different at Fisher’s protected t-test for LSD at the 5% significance level.

Figure 2. Determination of the antioxidant activity of thyme oil stand-alone and in combination of tea tree, ylang-ylang and sage oils at different concentrations using the DPPH assay. LSD = 0.58 at the 5% significance level.

Table 2. Interaction effect of thyme oil and tea tree oil combination treatment and storage time on reduction of Escherichia coli O157:H7 at the retail shelf condition (10°C).

Essential oils	Day 1		Day 3		Day 5
	Log	Reduction	Log	Reduction	Log	Reduction
Distilled water (control)	8.00 ± 0.45a		7.80 ± 0.25 a		7.81 + 0.62a
NaOCl	7.40 ± 0.52a	−0.60	7.41 ± 0.31a	−0.40	5.21 + 0.23c	−2.60
Stand-alone treatment
Thyme oil (1%)	7.55 ± 0.12a	−0.45	7.11 ± 0.28a	−0.70	6.66 + 0.13ab	−1.15
Thyme oil (1.5%)	6.90 ± 0.23ab	−1.10	6.80 ± 0.44ab	−1.00	4.53 + 0.32c	−3.28
Thyme oil (3%)	6.60 ± 0.34b	−1.40	5.41 ± 0.18b	−2.39	3.81 + 0.41cd	−4.01
Tea tree oil (1%)	7.55 ± 0.41a	−0.45	7.12 ± 0.22a	−0.68	6.33 + 0.27b	−1.48
Tea tree oil (1.5%)	7.24 ± 0.54ab	−0.76	6.45 ± 0.14ab	−1.35	5.32 + 0.18c	−2.49
Tea tree oil (3%)	6.89 ± 0.12ab	−1.11	5.73 ± 0.46b	−2.07	3.82 + 0.22cd	−4.01
Combination treatment
Thyme + Tea tree oil (0.5% + 0.5%)	7.01 ± 0.32ab	−1.00	7.04 ± 0.31a	−0.76	5.45 + 0.34c	−2.36
Thyme + Tea tree oil (0.75% + 0.75%)	6.91 ± 0.22ab	−1.10	5.65 ± 0.17b	−2.15	3.94 + 0.19cd	−3.87
Thyme + Tea tree oil (1.5% + 1.5%)	6.01 ± 0.13b	−1.99	4.16 ± 0.21c	−3.64	1.72 + 0.25e	−6.09

Note: Means in each column followed by the same letter are not significantly different at p < .05 using Fisher’s protected least significant test.