Combined effects of oregano essential oil and salt on the growth of Escherichia coli in salad dressing

There is a broad research interest in the search for alternatives to chemical additives for use as natural food preservatives. Although many natural compounds have biological in vitro properties evidenced, in situ studies are still scarce. This study evaluated the effect of oregano essential oil (OEO) and salt (NaCl) concentrations against Escherichia coli (ATCC 8739), in salad dressing, using the response surface methodology. The experiment included a 2² central composite rotatable design (CCRD) in a total of 11 formulations of salad dressings. Oregano essential oil was characterized by gas chromatography and salad dressings by ash, lipids, proteins and moisture. OEO was composed mainly by carvacrol (65.1%) and p-cymene (12.0%). Salad dressings showed similar chemical profiles. A mathematical model for the prediction of the antibacterial activity in salad dressing was obtained. The results revealed that the interaction between OEO and salt showed effect on the bacterial count. However, the effect of salt was negative suggesting that the highest NaCl concentrations decreases the bacterial count. Therefore, within the parameters studied, the use of OEO to control E. coli in salad dressing can be considered promising and allows reduction in the levels of salt to be incorporated in food.

Oregano essential oil: effect on sensory acceptability

Purpose

– This paper aimed to evaluate sensory acceptability of salad dressing formulated with different quantities of oregano essential oil (OEO) and salt as a starting point for the use of the spice as a natural preservative in food.

Design/methodology/approach

– Sensory assessment of salad dressing with OEO was evaluated in relation to the following attributes: appearance, aroma, consistence, flavour and overall acceptability. Five formulations were developed with variation in the levels of OEO and sodium chloride through a 22 factorial design with a central point. A nine-point hedonic scale was used, besides purchase intent by a structured five-point scale.

Findings

– There was no significant difference in the acceptance of the samples. Cluster analysis showed that formulation with intermediate quantities of salt and OEO was preferred by the consumers. OEO salad dressings with low salt content, regardless of OEO amount, presented higher intention to purchase.

Research limitations/implications

– Due to an increasing interest in the use of natural preservatives to replace chemical additives, this study provided a starting point for further investigations concerning sensory acceptability of OEO in food.

Practical implications

– Finding the balance between pleasant flavour and significant reduction of the use of salt in foods for dietary reasons is a complex challenge. Furthermore, studies need to be performed concerning interaction between amounts of essential oils and salt.

Originality/value

– This study provides insights that suggest a promising usage of OEO in food.