Inhibitory effect of thyme and cinnamon essential oils against E. coli O157:H7 in Tahini

Tahini is a common food product in the Mediterranean area that is used as a main ingredient in variety of ready-to-eat foods. The objective of the current study was to investigate the inhibitory effect of thyme oil (TD) or cinnamon oil (CD) on E. coli D157I:H7 viability in tahini and diluted tahini at different storage temperatures. Addition of 2.0% CD to tahini reduced E. coli D157I:H7 numbers by 1.38, 1.79 or 2.20 log 10 CFU/mL at 10, 25 or 37 °C, respectively, by 28d. On diluted tahini at 10 °C, no viable cells of E. coli D157I:H7 by 21d were detected when 1.0% CD was used. However, at 25 and 37 °C, no viable cells were detected by 14d when CD was added at 0.5% level. Addition of 2.0% TD to tahini, resulted in 1.82, 2.01 or 1.65 log 10 CFU/mL reduction in E. coli D 157I:H7 numbers was noted at 37, 25 or 10 °C, respectively, by 28d. On diluted tahini, TD at 0.5% or 1.0% induced complete reduction in the viability of E. coli D157I:H7 by 28d storage at 37 or 25 °C. At 10 °C, a 3.02 log 10 CFU/mL reduction was observed by 28d compared to the initial inoculation level in samples treated with 2.0% TD.


Introduction
Tahini or sesame paste is a common component of several popular ready-to-eat (RTE) dishes including tahini salad, halva (sweetened tahini), hummus, tarator sauce and mutabbel in Middle Eastern countries including Jordan, and it is also involved in several other ethnic dishes in Greek, North African and Turkish cuisines. The worldwide tahini consumption or its products has raised during the past few years, particularly in the European countries, US and Canada due to its nutritional value and health properties. For example, tahini has moderate amount of carbohydrate (6.4-9.0% wt) and high amount of protein (23-27% wt) as well as lipid (57-65% wt) and vitamins and minerals (Sawaya et al., 1985;Abu-Jdayil et al., 2002). Further, it has been reported that sesame seed products like tahini play a crucial role in preventing cardiovascular diseases and atherosclerosis, improving digestion and metabolic activity and reducing hyperglycemia and cholesterol (Narasimhulu et al., 2015). Ot is also anticipated that the global consumption of tahini will increase by 12% in the next 5 years. Ot is expected that the Middle East and the US will be the main consumption regions due to the increasing demand for ethnic Arabic and Mediterranean foods, and seed-based spreads. The US alone was responsible for 78% of the total global tahini consumption in 2015 (Research & Markets, 2017).
Tahini is a RTE product that has a low water activity, a w , (~ 0.16-0.25) and an extended shelf-life (two years) when stored at ambient temperature. However, its high fat content provides opportunity for microorganisms to survive for long time under different storage environments (Lake et al., 2010). Tahini nowadays has raised a special concern regarding its safety, particularly to both the food regulatory agencies and food industry in view of recent reports of recalls and outbreaks associated with tahini contaminated with pathogenic bacteria. Numerous foodborne recalls and outbreaks linked to consumption of tahini or its products have been documented worldwide in the last two decades, particularly due to their contamination with Salmonella serovars (Unicomb et al., 2005; Centers for Disease Control andPrevention, 2012, 2013). Furthermore, E. coli D157I:H7 has been isolated from tahini or tahini-based products. E. coli D157I:H7 is also able to survive and grow in commercial and diluted tahini during storage at temperature range of 10 to 37 °C (Al-Nabulsi et al., 2013). Consequently, control of foodborne pathogens in tahini is likely to require novel approaches, including those based on using natural antimicrobials instead of chemical preservatives, which is of popular consumer interest for consumers worldwide, and hence this approach has been utilized in the current study.
Plant-derived antimicrobial substances like essential oils (EDs) have been used for hundreds of years as a mean of inhibiting spoilage and pathogenic microorganisms . Some edible oils, medicinal herbs and spices are potently effective against different foodborne pathogens such as E. coli D157I:H7 in a variety types of food system (Tajkarimi et al., 2010). However, the inhibitory effects of plant EDs against E. coli D157I:H7 in tahini have not been investigated. Therefore, the objectives of this study were toI: i) screen the antibacterial activity of 14 plant EDs against three E. coli D157I:H7 strains using disc-diffusion method at 10 and 37 °C; ii) determine the minimum inhibitory (MOCs) and minimum bactericidal concentrations (MBCs) of cinnamon and thyme oils (the most potent essential oils) against E. coli D157I:H7; and iii) investigate the inhibitory activity of cinnamon and thyme oils against E. coli D157I:H7 cocktail in commercial or diluted tahini which was used as a model for tahini-based products) stored at 10, 25 or 37 °C.

Preparation of bacterial cultures
Three mutated non-pathogenic (verotoxigenic negative) E. coli D157I:H7 strains (02I:0627, 02I:0628, 00I:3581), that had been provided by Rafiq Ahmed, National Microbiology Laboratory, Public Health Agency, Canadian Science Centre for Human and Animal Health, Winnipeg, MB. Canada, were used in the present study. The strains were individually kept and maintained in Brain Heart Onfusion (BHO, Dxoid Ltd, Basingstoke, UK) broth including 20% (v/v) glycerol at -40 °C. A loopful of each thawed frozen strain was streakedonto the plates surface of Sorbitol MacConkey agar (SMA, Dxoid Ltd, Basingstoke, UK), followed by incubation at 37 °C for 24 h. Thereafter, a colony of each individual strain was transferred to BHO broth which was incubated for 24 h at 37 °C. Three consecutive transfers were performed to revitalize the bacterial culture and a final transfer to BHO broth was conducted before the experiment. The inoculated BHO broth was incubated for 24 h at 37 °C to allow E. coli to reach the stationary phase.

Preparation of cocktail culture
After culturing E. coli D157I:H7 in BHO broth, the cells were harvested by centrifugation at 4000 x g for 15 min. The pellet was obtained after discarding the supernatant. Thereafter, 10 mL of 0.1% sterile peptone water (Dxoid Ltd, Basingstoke, UK) was mixed with the pellets. The E. coli D157I:H7 count in the resulting bacterial suspension was determined by plating onto SMA and a final bacterial concentration of ~9 log 10 CFU/mL was obtained. The suspension was diluted with 0.1% peptone water to the desired concentration and 2.5 mL of each E. coli D157I:H7 strain was combined to form a cocktail mixture of the three strains.

Essential oil extracts
The inhibitory effect of 14 EDs of medicinal plants were screened in this study; lavender, thyme, cardamom, rosemary, mint, cinnamon, fir, sage, laurel leaves, ginger, mustard, radish seeds, black cumin seeds and pomegranate seeds. These EDs were purchased from Green Field Dil Factory in Amman, Jordan. Hydro-distillation is usually used in this factory to extract the EDs from their sources with a purity of 99%. The EDs were kept dry in sealed dark glass vials at 4 °C until use.

Screening of inhibitory effect of plant EOs
The inhibitory effect of the 14 plant EDs against E. coli D157I:H7 strains was screened using the disc diffusion method (Janakat et al., 2015). Specifically, 20 μL of each plant ED were spread onto sterile discs with diameter of 6 mm (Dxoid Ltd, Basingstoke, UK) which were air dried at room temperature for 10 min under a bio-safety cabinet. The discs were placed onto TSA plates that had been inoculated with 100 µL solution containing ~ 6.0 log 10 CFU/mL of each individual E. coli D157I:H7 strain. Thereafter, the plates were incubated for 24 h at 37 °C or for 7 d at 10 °C. A calibrated ruler was used for measuring the inhibition zones in mm

Determination of the MICs and MBCs of most potent EOs against E. coli O157:H7 (02:0627)
Df the 14 EDs, the MOC and the MBC of only thyme oil and cinnamon oil were determined using the microdilution method, since these oils showed the strongest inhibitory effect against E. coli D157I:H7 strains. Briefly, 100 μL of fresh cultures were diluted in Mueller Hinton (MH) broth (Dxoid Ltd, Basingstoke, UK) to give a final concentration of about 5.0 log 10 CFU/mL of E. coli D157I:H7 (02I:0627). Cinnamon or thyme oils were individually mixed at a ratio of 1I:1 in 0.5% dimethyl sulfoxide (DMSD, HPLC grade). Volumes of 50, 100 or 150 µL of DMSD-essential oil solution were added to 96 well microtiter plates (Greiner Bio-Dne, CellStar™, Otaly). Thereafter, the volume to 250 μL was completed with sterile distilled water. A solution of 0.5% DMSD without cinnamon or thyme oil was mixed with the bacterial culture as a positive control, while DMSD containing cinnamon or thyme oil was used as a negative control. Then, the sealed microplate was incubated for 24 h at 37 °C. Then, 100 µL aliquots from each sample were taken and decimal dilutions were prepared with 0.1% peptone water. Exactly 100 μL from each of the appropriate dilutions was spread onto the surface of TSA (Dxoid) and incubated for 24 h at 37 °C.

Tahini preparation
Tahini samples were purchased from a local market in Orbid, Jordan. Samples were tested for the presence of E. coli D157I: H7 prior to its use and confirmed to be free from contamination. Diluted tahini (10% w/v) was prepared by mixing 2.5 g tahini with 22.5 mL sterile distilled water in sterile Duran bottle. A cocktail mixture of E. coli D157I:H7 was inoculated into tahini and diluted tahini to obtain ~4.5 log 10 CFU/mL. Thereafter, 0.0, 0.2, 0.5, 1.0 or 2.0% (v/v) of cinnamon or thyme EDs, which were prepared as formerly described were added to tahini or diluted tahini. Each bottle was agitated using a vortex mixer (Velp, Otaly) to distribute the bacterial culture uniformly throughout the samples, and were incubated at 37, 25 or 10 °C for 28 d.

Microbiological enumeration
Sampling of tahini or diluted tahini was conducted after 0, 1, 3, 7, 14, 21 and 28d at 37, 25 or 10 °C. Samples of 5 mL were taken by sterile syringe from each bottle and transferred into sterile stomacher bags (Seward Ltd., London, UK). The sample was mixed with 45 mL of 0.1% peptone water and pummeled for 2 min using a Stomacher 400 (Seward Ltd,). Then the homogenate was 10-fold serially diluted in screw-capped test tubes containing 0.1% peptone water and 100 µL of the diluted sample was plated onto the surface of Sorbitol MacConkey agar overlaid with TSA to allow recovery of injured cells (Dsaili et al., 2010). The plates were aerobically incubated for 24 h at 37 °C.

Water activity (a w ) and pH measurement
Water activity of tahini samples was measured at room temperature using an a w meter (Hygrolab, Rotronic Onstr. Corp, Huntington, NY, US). The pH value of regular and diluted tahini was directly measured using a digital pH meter (Eutech model CyberScanpH1100, Singapore).

Determination of total phenolic content
The total phenolic content of tahini was determined using Folin-Ciocalteu spectrophotometric method as described by Dsaili et al. (2017). A standard calibration curve was prepared using a stock solution of gallic acid (50 mg/50 mL). A 100 µL aliquot of the sample containing phenolic compounds was added to 8.40 mL distilled water. Then 0.5 mL Folin-Ciocalteu reagent was added and agitated for 4 min using vortex mixer (Velp, Otaly). The mixture was incorporated with 1 mL of 5% Na 2 CD 3 solution and mixed similarly. After 1 hour, the absorbance was measured at 725 nm using a spectrophotometer (UV 1800, 50 Hz, UK). The total content of phenolic compounds was calculated as milligrams of gallic acid equivalents per gram of dry matter (mg GAE/g). The analysis was conducted in triplicate.

Statistical analysis
The SPSS software version 19.0 (2009; OBM, Chicago, OL, US) was used to analyse the results which were represented by means ± standard deviation (SD). The effect of time and ED concentrations on bacterial log reduction were determined by one way ANDVA. The significant differences between means of variables was determined by Duncan's post hoc test when p-value < 0.05.

Results and discussion
The commercial tahini had an initial pH value of 6.23 and a w of 0.25, while the initial pH and a w of diluted tahini were 6.31 and 0.96, respectively. The total phenolic content in tahini was found to be 14.35 ± 0.15 mg/mL.

Inhibitory effect of plants EOs
The EDs of ginger, sage, radish seeds, black seeds, fir, mustard and pomegranate seeds did not exhibit any inhibitory effect against E. coli D157I:H7 strains at 10 or 37 °C (data are not shown). While the EDs of laurel leaves, lavender, cardamom, mint and rosemary exhibited moderate inhibitory effect with inhibition zones that ranged between 7.8-15.0 mm at 37 °C (Table 1). The EDs of cinnamon and thyme showed the strongest inhibitory effect with inhibition zones of 24.3-50.8 mm at 37 °C. Ot was interesting that all the strains behaved similarly in response to all tested EDs at 10 °C with no significant differences being detected among the tested strains.
Comparable results were obtained by Kon & Rai (2012) and Prabuseenivasan et al. (2006) who reported that CD had the strongest inhibitory effect against Gram-positive and Gram-negative bacteria among 21 to 35 plant EDs. Moreover, it has been reported that cinnamon, thyme, bay leaf and garlic have significant inhibitory effects against E. coli D157I:H7 (Gyawali & Obrahim, 2014;Dadalioǧlu & Evrendilek, 2004). On addition, the difference in the inhibitory effect of EDs may be due to the variation in the composition of bioactive compounds, which is affected by harvesting time the part of the plant which is used, as well as the extraction method (Naghdi Badi et al., 2004;Burt, 2004;Hyldgaard et al., 2012).
Since cinnamon and thyme oils exhibited the strongest in vitro inhibitory effect against E. coli D157I:H7 and since no strain variations were found between the strains, E. coli D157I:H7 (02I:0627) was used to determine the MOC and MBC. The MOCs of cinnamon and thyme oils against E. coli D157I:H7 strain 02I:0627 were 0.10% at 37 °C while the MBCs were 0.20% for both oils (data are not shown). These results are compatible with those reported by Dussalah et al. (2007) who indicated that Thymus vulgaris (TD) had a significant inhibitory effect against E. coli D157I:H7 at 0.05% (v/v) and by Hammer et al. (1999) who reported that the MOC of thyme against E. coli D157I:H7 was 0.12% (v/v). Dn the other hand, a lower MOC for Thymus vulgaris (0.01%) than was found in the present study against E. coli D157I:H7 was reported by Hossain et al. (2013).
The mechanism responsible for the antimicrobial action of TD and CD is believed due to their ability to disturb the outer membrane (DM) structure of Gram-negative bacteria. As a result, small hydrophilic solutes can cross the DM through profuse porin proteins. This induces the liberation of DM-associated constituents to the external medium, and in turn these changes decrease the intracellular ATP pool of the bacterial cell, which leads to the loss of cytoplasmic membrane integrity and eventually cell death (Helander et al., 1998;Ultee et al., 1999;Dussalah et al., 2006;Boskovic et al., 2015).

Survival of E. coli O157:H7 in tahini and diluted tahini
The viability of E. coli D157I:H7 in tahini was decreased at all tested storage temperatures. The extent of bacterial reduction was 0.57, 1.04 and 1.15 log 10 CFU/mL at 10, 25 and 37 °C, respectively, after 28d (Table 2). Dur results are in agreement with those reported by Al-Nabulsi et al. (2013) who indicated that the viability of E. coli D157I:H7 in tahini decreased by 4.53, 2.52 and 2.18 log 10 CFU/mL at 37, 21 and 10 °C, respectively, after 28d. The bacterial reduction could be partially related to the presence of phenolic compounds in tahini (14.35 mg/g) as well as to its low a w (0.25). Beside the low a w that may inhibit bacterial growth, the high fat percentage of tahini may provide protection to contaminating organisms. On addition, the pH of tahini (~6.8) is not inhibitory by itself to bacteria.
Tahini is usually consumed in a diluted form since water and other food ingredients are added to prepare different types of RTE products. On the present study, tahini was diluted 10-fold which is the most common level of tahini used during preparation of tahini-based products. Progressive E. coli D157I:H7 growth was noted in diluted tahini at all storage temperatures. The number of E. coli D157I:H7 cells increased by 2.15, 2.74 and 2.84 log 10 CFU/mL after incubation at 10, 25 and 37 °C, respectively, after 28 d (Table 3). Similarly, Al-Nabulsi et al. (2013) reported that E. coli D157I:H7 grew in 10% diluted tahini. The neutral pH, high a w (0.96), and nutrients availability are likely the key factors that enabled E. coli D157I:H7 growth in diluted tahini. Therefore, contamination of tahini with pathogens should be treated as a microbial hazard requiring high attention because of the ability of foodborne pathogens to persist in tahini and sometimes grow, reaching the infectious dose when the a w is increased during tahini-based products preparation.

Inhibitory effect of TO and CO on the viability of E. coli O157:H7 in tahini and diluted tahini
The use of plant-based materials including thyme for inactivating E. coli D157I:H7 in different food products has been reported (Boskovic et al., 2015). Ot was notable that in the present study the extent of inactivation of E. coli D157I:H7 in tahini increased with higher ED concentrations and higher storage temperature. The addition of TD to tahini led to a significant reduction in the viability of E. coli D157I:H7 cells at all tested temperatures. After 28d, TD at concentration of 0.2, 0.5, 1.0 or 2.0% caused a reduction of 1.25, 1.35, 1.67 and 1.82 log 10 CFU/mL, respectively at 37 °C (compared to 1.15 log 10 CFU/mL in the control). However, the inhibitory effect of TD was reduced at lower temperatures of storage. When 0.2, 0.5, 1.0 or 2.0% TD was added to tahini, a 3.30 ± 0.10 cdA 3.20 ± 0.10 cA 3.10 ± 0.14 bA 2.78 ± 0.13 cB 2.63 ± 0.10 bB Values are the means of 2 experiments (n= 4) ± SD; Values with same capital letters in the same row and with same small letters in the same column are not significantly different (p ≥ 0.05).
On diluted tahini after 28 d storage, TD at 0.5% or 1.0% caused a complete reduction in the numbers of E. coli D157I:H7 at 37 or 25 °C, respectively. At 10 °C, E. coli D157I:H7 cells showed more resistance to TD since a 3.02 log 10 CFU/mL reduction was observed after 28d compared to the initial inoculation level in samples treated with 2.0% TD (Table 3). Burt & Reinders (2003) reported that bacteriostatic action of TD against E. coli D157I:H7 occurred at 0.12%, while a bactericidal effect was noted at 0.25%. Likewise, Solomakos et al. (2008) investigated the antimicrobial effect of 0.3%, 0.6%, or 0.9% TD against E. coli D157I:H7 in minced beef and found that 0.6% thyme oil inhibited its growth during storage at 10 °C.
CD reduced the viable numbers of E. coli D157I:H7 by 1.23, 1.42, 1.72 and 2.20 log 10 CFU/mL in tahini with 0.2, 0.5, 1.0 or 2.0% CD, respectively, at 37 °C after 28d, compared to 1.2 log 10 CFU/mL in the control samples. At 25 °C, the bacterial reduction was 0.95, 1.06, 1.44 and 1.79 log 10 CFU/mL by addition of 0.2, 0.5, 1.0 or 2.0% CD respectively, compared to 0.90 log 10 CFU/mL in the control after 28 d. At 10 °C, numbers of E. coli D157I:H7 were reduced by 0.80, 0.95, 1.25 and 1.38 log 10 CFU/mL by addition of 0.2, 0.5, 1.0 or 2.0% CD to tahini, respectively, compared to 0.47 log 10 CFU/mL at 10 °C in the control (Table 4). On contrast to its activity in tahini, CD was more inhibitory in diluted tahini. At 10 °C, E. coli D157I:H7 cells were not detectable when 1.0 or 2.0% was used after 21d. Nonetheless, at 25 and 37 °C, the antibacterial activity of CD was more obvious where E. coli D157I:H7 cells were not detected after 14d when 0.5% was used (Table 5).
CD showed significant inhibitory effect against E. coli D157I:H7 in both commercial and diluted tahini. However, its activity was higher than TD in diluted tahini where 0.5% CD prevented E. coli D157I:H7 detection after 14d at 25 and 37 °C. Dlaimat et al. (2019) also indicated that CD had higher antimicrobial activity than TD against Salmonella enterica in hummus. Similarly, Ceylan et al. (2004) reported that 0.3% CD reduced numbers of E. coli D157I:H7 in apple juice by 1.6 and 2.0 log 10 CFU/mL at 8 and 25 °C, respectively.
On diluted tahini, the addition of TD or CD resulted in more inhibitory activity compared to regular tahini and caused significant Table 3. Effect of thyme oil on the viability of E. coli D157I:H7 (log 10 CFU/mL) during storage of diluted tahini atI:10 °C (a), 25 °C (b) and 37 °C (c). reductions in E. coli D157I:H7 numbers which reached below the detection level. This could have been due to lower levels of fat in diluted tahini after being diluted 10-fold with water. Similarly, it was reported that CD at a concentration of 0.5% in full fat cheese reduced numbers of S. Enteritidis by 0.3 log 10 CFU/mL at the first day, compared to 3.1 log 10 CFU/mL in the low fat cheese (Smith-Palmer et al., 2001). EDs are more soluble in the fat phase compared to the aqueous phase; however, the proliferation of organisms usually occurs in the aqueous phase, which may reduce the effectiveness of TD and CD (Burt, 2004).
ED concentration and temperature are major factors that affect the inhibitory action of TD and CD in undiluted and diluted tahini. The antibacterial activity was significantly increased as the storage temperature increased (37 > 25 > 10 °C). The results in the present study are in agreement with previous findings on the activity of TD and CD against pathogenic bacteria. Ot was reported that the addition of cinnamaldehyde to apple juice reduced E. coli D157I:H7 cells to undetectable levels after 5 and 14d at 23 and 4 °C, respectively (Baskaran et al., 2010). Additionally, combination of CD with nisin induced greater inhibitory effect against E. coli D157I:H7 cells in apple juice at 20 °C compared to 5 °C (Yuste & Fung, 2004).
Considering that the TD and CD mainly damage the cytoplasmic membrane of bacteria, altered permeability of the membrane may affect the passive transport of hydrophobic particles and influence protein-protein interactions (Zhang & Rock, 2008). On addition at lower temperatures, permeability of the bacterial membrane is reduced when higher proportions of saturated fatty acids are contained in the membrane and thus decrease the inhibitory activity of EDs (Al-Nabulsi & Holley, 2006;Mani-Lopez et al., 2012).
Although EDs showed substantial inhibitory effects against foodborne pathogens, the presence of a number of ingredients in foods including fat, proteins, carbohydrates, salt, water, preservatives, antioxidants, and some additives may reduce the inhibitory activity of EDs (Perricone et al., 2015). Moreover, another limitation of using EDs as preservatives is their negative impact on flavor since high concentrations are required to achieve satisfactory antimicrobial activity (Al-Nabulsi et al., 2020;Dlaimat et al., 2019). This limitation could be circumvented by using lower concentrations of the EDs along with other barriers (e.g low storage temperature, mild heating of the product, or in combination with organic acids) as part of the hurdle technology. Additionally, further research is needed to study the potential of incorporating EDs such as TD and CD in the packaging material used to pack tahini, and to study the effect of such an active package on the viability of pathogens in tahini. Table 4. Effect of cinnamon oil on the viability of E. coli D157I:H7 (log 10 CFU/mL) during storage of tahini atI: 10 °C (a), 25 °C (b) and 37 °C (c). 4.23 ± 0.08 bA 4.12 ± 0.12 bAB 4.07 ± 0.50 cBC 3.95 ± 0.05 cC 3.69 ± 0.06 cD 7 3.93 ± 0.08 cA 3.80 ± 0.12 cA 3.63 ± 0.08 dB 3.53 ± 0.08 dB 3.07 ± 0.09 dC 14 3.62 ± 0.04 dA 3.58 ± 0.04 dA 3.40 ± 0.12 eB 3.30 ± 0.07 eB 3.05 ± 0.09 dC 21 3.59 ± 0.11 dA 3.55 ± 0.12 dA 3.38 ± 0.08 eB 3.16 ± 0.07 eC 2.53 ± 0.08 eD 28 3.50 ± 0.07 dA 3.47 ± 0.04 dA 3.28 ± 0.08 eB 2.98 ± 0.08 fC 2.50 ± 0.10 eD Values are the means of 2 experiments (n= 4) ± SD. Values with same capital letters in the same row and with same small letters in the same column are not significantly different (p ≥ 0.05).

Conclusion
The current study reports the results of using 14 different essential oils against E. coli D157I:H7 in tahini and diluted tahini. TD and CD exhibited the strongest antibacterial activity against E. coli D157I:H7 with a range of inhibition zones from 33.0 to 50.8 mm. On spite of the fact that tahini did not enhance the growth of E. coli D157I:H7, the pathogen was able to survive in tahini for up to 28d. Nonetheless, diluted tahini permitted enhanced growth (p ≤ 0.05) of E. coli D157I:H7 at all incubation temperatures. The addition of TD or CD at ≤ 2.0% is recommended for use by processors of tahini or tahini-based products to inhibit the growth of E. coli D157I:H7 when stored over a wide temperature range (10 to 37 °C).