Skip to main content
NCBI home page
Australian Journal of Psychology logoLink to Australian Journal of Psychology
. 2024 Sep 15;76(1):2401022. doi: 10.1080/00049530.2024.2401022

Alleviation of physiological stress response by apple aroma

E A Chayani Dilrukshi a, Shu Sato a, Masaki Nakachi a, L Sugeeswari Lekamge a,b, Kosuke Oiwa a, Kanetoshi Ito c, Shusaku Nomura a,✉
PMCID: PMC12218518  PMID: 40666668

ABSTRACT

Objective

The study evaluated the potential of apple aroma to alleviate physiological stress response induced by a short-term cognitive stressor. It investigated the effects of apple aroma on cardiac and peripheral autonomic nervous system activity under stressful conditions.

Methods

Within-subject experiments were conducted with 25 healthy male university students with a 30-minute calculation task under three conditions: Apple, Chamomile (CHA), and Di propylene glycol (DPG) (scentless air). The aroma administration was precisely controlled and counterbalanced. Cardiac activity on electrocardiograms and nose tip temperature were recorded throughout the experiment. A visual analog scale and a scent questionnaire were subjective measures.

Results

Apple aroma demonstrated a significantly smaller increase in heart rate (t [24] = 3.36, p = 0.008 vs. DPG, t [24] = 4.06, p = 0.001 vs. CHA), and a decrease in the high-frequency component of heart rate variability (t [24] = 2.81, p = 0.029 vs. DPG, t [24] = 3.48, p = 0.006 vs. CHA) compared to the other conditions, representing a smaller enhancement of cardiac sympathetic nervous system activity and smaller suppression of cardiac parasympathetic nervous system activity respectively.

Conclusion

Apple aroma showed efficacy in alleviating the physiological stress response in terms of cardiac activity. Apple was also considered significantly preferable and comfortable compared to the other conditions, which would be beneficial in the context of aromatherapy.

KEYWORDS: Heart rate variability, acute stress response, apple aroma, aromatherapy, chamomile, olfactometer

KEY POINTS

What is already known about this topic:

  1. Aromatherapy benefits: Aromatherapy, using volatile plant materials such as essential oils, is recognised for its potential to improve physiological and psychological health. Citrus fruity aromas like orange, bergamot, and yuzu have reduced stress and anxiety and improved mood.

  2. Apple’s health benefits: Apples are rich in bioactive compounds, including polyphenols, which have antioxidant properties. Consumption of apples is linked to reduced risks of lung cancer, cardiovascular diseases, and type II diabetes.

  3. Limited research on apple aroma: While there is extensive research on the health benefits of consuming apples, the effects of apple aroma on physiological and psychological health are underexplored. Preliminary studies suggest that apple aroma may have a relaxing effect on the body and mind.

What this topic adds:

  1. Apple aroma reduces stress response: This study demonstrates that apple aroma significantly reduces the physiological stress response, as indicated by smaller increases in heart rate and less suppression of heart rate variability during a cognitive stressor.

  2. Autonomic nervous system modulation: The findings show that apple aroma leads to smaller cardiac sympathetic nervous system activity enhancements and smaller suppression of cardiac parasympathetic nervous system activity, suggesting a balancing effect on autonomic nervous system activity under stress.

  3. Preference and comfort in aromatherapy: Apple aroma was significantly preferable and more comfortable than chamomile and scentless air, indicating its potential utility in aromatherapy practices aimed at stress alleviation.

Introduction

Aromatherapy – is a branch of complementary and alternative medicine that utilises volatile plant materials, known as essential oils, to improve physiological and psychological health (Herz, 2009). While citrus fruity aromatic essences such as orange, bergamot, and yuzu are widely used in aromatherapy (Cooke & Ernst, 2000; M. S. Lee et al., 2012; Sattayakhom et al., 2023) and have been studied for their potential benefits; other types of fruity aromas have received less attention in the context of aromatherapy.

Several research has shown that inhalation of orange essential oil can alleviate cardiac stress response (Lekamge et al., 2017a), reduce stress and anxiety, and improve mood (Goes et al., 2012), and bergamot essential oil has improved mood states and parasympathetic nervous system (PSNS) activity (E. Watanabe et al., 2015). Yuzu essential oil has been found to relieve emotional stress, contributing to the suppression of sympathetic nervous system (SNS) activity (Matsumoto et al., 2014), and lessen premenstrual emotional symptoms, contributing to the PSNS activity (Matsumoto et al., 2017). Bitter orange (Citrus aurantium) essential oil has effectively reduced anxiety and stress levels in coronary angiography patients (Moradi et al., 2021). Studies have also revealed that lemon aroma inhalation could relieve pain and reduce nausea and vomiting for lower extremity fracture patients who have undergone surgery (Rambod et al., 2023). Despite the potential benefits of citrus fruity aromas in aromatherapy, further research is needed to explore the efficacy of different fruity aromas and their potential physiological and psychological benefits.

Apple (Malus domestica), which belongs to the Rosaceae family, grows worldwide and is mainly cultivated in Asia and Europe. An ancient proverb states, “An apple a day keeps the doctor away”. Apple is packed with essential vitamins, minerals, and other nutrients that promote good health and contains high levels of bioactive compounds such as polyphenols, polysaccharides (pectin), phytosterols, and pentacyclic triterpenes (Patocka et al., 2020). Research has shown that apple polyphenols have antioxidant effects in the prevention of diseases caused by oxidative stress (Zhang et al., 2021). Several epidemiological studies have found that the consumption of apples could reduce the risk of lung cancer (Feskanich et al., 2000), cardiovascular diseases (Sesso et al., 2003), and type II diabetes (Knekt et al., 2002).

The apple aroma, which consists of volatile esters such as ethyl 2-methyl butanoate, 2-methyl butyl acetate, butyl acetate, and hexyl acetate (El Hadi et al., 2013; Espino-Díaz et al., 2016) could affect the human mind and body. In one study, the researchers compared the effects of orange and apple aroma on the anticipatory anxiety or mood of patients awaiting scheduled dental appointments, and the findings suggested that neither the orange aroma nor the apple aroma had any significant effect (Toet et al., 2010). However, it is worth noting that while there have been numerous studies on the health benefits of consuming apples, there is a lack of research on the potential benefits of its aroma. To the best of our knowledge, only one study has investigated the psychophysiological effects of apple fragrance. In the previous study, which only involved six participants, eight aromas, including apple, were tested to identify the prominent aromas with inhibitory potentials to alleviate psychophysiological stress (Lekamge et al., 2017b). The results suggested that apple aroma inhibited the stress response on the cardiac autonomic nervous system (ANS) during a short-term stressor, and apple aroma could potentially relax the body and mind. However, due to the limited sample size and the preliminary nature of the study, the results need to be replicated with a larger sample size and a well-controlled experimental design to confirm the efficacy of apple aroma on psychophysiological responses to acute stress.

Activation of the SNS in response to short-term stress is suggested, resulting in increased blood pressure and heart rate (HR) (McEwen, 2006). The perceived unpleasantness of odours induced the stress response, and the SNS (Hirasawa et al., 2019). Hence, it can be hypothesised that the pleasantness and comfort provided by the apple aroma may effectively alleviate the SNS response, which is activated during the stressor. The experiments employed A cognitive task as an acute stressor to investigate this hypothesis. Furthermore, the psychophysiological evaluations of apple aroma have not been extensively studied, leaving a gap in knowledge regarding evaluation methods and their effects. This study addressed this research gap by focusing on ANS parameters, including HR, heart rate variability (HRV), and nose tip temperature. By examining these physiological measures, the potential effects of apple aroma on the physiological stress response and its modulation of ANS activity are expected to be suggested. A customised olfactometer (Lekamge et al., 2017a, 2017b; Nomura et al., 2016) was installed to precisely handle the dose and duration of aroma administration and maintain the reproducibility of the study.

In summary, this study aims to evaluate the hypothesis that apple aroma can alleviate physiological stress response induced by a short-term cognitive stressor. Therefore, this study investigates the effect of apple aroma on cardiac and peripheral ANS activity under stressful conditions.

Methods

Participants

A power analysis for a two-tailed paired-samples t-test indicated that the minimum sample size to yield a statistical power of at least 0.93 with an alpha (α) of 0.05 and an effect size (d) of 0.59 (Sullivan & Feinn, 2012) is 25. Therefore, the study consisted of 25 healthy male university students with a mean (±SD) age of 22.0 ± 0.8 and a mean (±SD) body mass index of 22.1 ± 2.5 kg/m2. According to their self-reports, none of the participants had olfactory impairment or a history of olfactory impairment.

This study was approved by the Ethics Review Committee of the Nagaoka University of Technology (Approval number: H25. 6). Informed consent was obtained from the participants before the study. The experiments were conducted following the ethical guidelines of the institutional committee and with the 1964 Helsinki Declaration.

Experimental procedure

Experimental protocol

The past experimental protocol of the orange aroma study (Lekamge et al., 2017a) was adopted for this. Within-subject design experiments, which consisted of a 10-minute initial rest period (R1), a 30-minute calculation task (T), and a 15-minute recovery period (R2), were employed, as shown in Figure 1.

Figure 1.

Figure 1.

Open in a new tab

Schematic diagram of the experimental procedure; DPG, Di propylene glycol; ECG, Electrocardiogram; skin temp., skin Temperature; VAS, visual analogue scale.

The Kraepelin calculation task was introduced to induce short-term cognitive stress in the participants, where the participants were instructed to continuously add single-digit numbers displayed on the computer screen as quickly and precisely as possible. It requires sustained attention and concentration from the participants. This test has been used in similar experimental contexts of previous studies (Dilrukshi et al., 2024; Ishikawa et al., 2023; Lekamge et al., 2017a, 2017b).

As illustrated in Figure 1, the aroma was administered exclusively during the task period, ensuring that the effects observed were directly associated with the cognitive stressor and not influenced by pre-task or post-task exposure to the aroma. Each participant performed the experimental trial under each aroma condition: Apple (APL), Chamomile (CHA), and Dipropylene glycol (DPG) (scentless air), on three separate days, where the order of aroma administration was counterbalanced. Chamomile aroma was chosen as a comparative condition due to its established preference among participants and well-documented neutral or mildly calming effects, distinct from the more stimulating effects of fruity aromas like apple. The primary reason for selecting apple and chamomile aromas in this study was based on a preliminary experiment conducted by Lekamge et al. (2017b), where eight different aromas were evaluated. In that study, chamomile, strawberry, and apple were the most preferred scents among participants. Apple was suggested to have the highest physiological effect regarding stress relief, while chamomile showed no significant physiological effect. Based on these findings, this study selected chamomile and apple for further investigation. Previous studies, including (Lekamge et al., 2017b), have demonstrated that chamomile aroma produces physiological responses similar to scentless control (DPG), suggesting it functions as a neutral or mildly calming condition. This allowed us to evaluate the specific effects of apple aroma compared to a scentless control and a neutral aromatic condition. While participants generally prefer apple and chamomile aromas, chamomile typically exhibits a neutral or calming effect, in contrast to the stimulating impact of apple aroma on the ANS. These differences enable a more nuanced comparison, where apple aroma’s specific ability to alleviate stress can be highlighted against the neutral baseline provided by chamomile. Chamomile aroma was also included as a third condition to control potential participant bias, where individuals might attempt to distinguish between aromatic and non-aromatic conditions. This inclusion allowed us to discern whether the observed effects were specific to apple aroma or could be attributed to a general response to any pleasant odour.

The experiments were conducted in an air-controlled laboratory with a mean (±SD) temperature of 23.3 ± 2.5°C and humidity of 42.0 ± 11.4%.

Aroma administration

Apple fragrance (Takasago International Corporation, Japan), composed mainly of Allyl Heptoate, Butyl Acetate, Geranyl Acetate, Hexyl Acetate, and Verdox was prepared at 70 wt% with the odourless solvent DPG and Chamomile fragrance (Takasago International Corporation, Japan), composed mainly of Limonene, Hexyl Acetate, Linalool, Geraniol, Phenyl ethyl alcohol, Hedione, and Musk T was prepared at 90 wt% with the odourless solvent DPG were used as the olfactory stimuli of the study. DPG was used as the control. These are easily reminiscent of common apples and chamomile and were selected for their stability in experiments and palatability.

A trained perfumer prepared the fragrances used in this study. These fragrance preparations are characterised by Butyl Acetate and Hexyl Acetate, found in natural apples, and Limonene, Hexyl Acetate, Linalool, and Geraniol, found in natural chamomile. Table 1 lists the main constituents of the two aromas: apple and Chamomile.

Table 1.

Major constituents of essential oils used in the study.

Essential oil Constituent (%)
Apple Allyl Heptoate 1-3
Butyl Acetate 1-3
Geranyl Acetate 3-5
Hexyl Acetate 1-3
Verdox 5-10
Chamomile Limonene 3-5
Hexyl Acetate 1-3
Linalool 1-3
Geraniol 3-5
Phenyl ethyl alcohol 5-10
Hedione 10-20
Musk T 3-5
Open in a new tab

The discrepancies inherent in aroma research are often due to differences in the dose and duration of aroma inhalation. Previous aroma studies used conventional methods, such as materials filter paper, perfume test strip (Krbot Skorić et al., 2015; Martin, 1998; Sowndhararajan & Kim, 2016), and masks (S. Watanabe et al., 2013) impregnated with aromas, nebuliser nodules (I. Lee, 2016), and aroma diffusers (Matsumoto et al., 2017). The outcome of these studies may have been subjected to the olfactory fatigue of the participants. Therefore, our customised olfactometer was used to precisely control the duration and concentration of aroma administration, preventing olfactory fatigue (Lekamge et al., 2017a, 2017b; Nomura et al., 2016). The cannula placed under the nostrils was connected to the customised olfactometer (Tatsumi Kagaku Co., Ltd., Kanazawa, Japan) designed to minimise olfactory fatigue by delivering the aroma intermittently, specifically for the first 20 s of each 1-minute interval. This intermittent exposure allows brief recovery periods, thereby reducing the likelihood of olfactory adaptation and ensuring that participants maintain olfactory sensitivity throughout the experiment. A series of preliminary studies determined the timing of this interval, confirming that the aroma could be perceived consistently, even during a 30-minute computational task. Prepared fragrances were conveyed to the cannula by regulating the volume and timing. The timing was pre-programmed by an interface on the personal computer to achieve sporadic delivery of the aromas.

Measurements

Physiological parameters

Electrocardiogram (ECG) recordings were obtained using a bio-signal amplifier (MP 150, BIOPAC Systems Inc., CA, USA) throughout the experiment (R1-T-R2) at a sampling rate of 500 Hz and 16-bit resolution. ECG data was used to analyse the HR and HRV, which are known to be parameters to assess cardiac ANS activity. HRV refers to the variation in time intervals between consecutive heartbeats (R-R interval) (Berntson et al., 1997). The high-frequency (HF) component of HRV was determined to be the frequency component between 0.15 and 0.40 Hz for every one-minute time window. This study used the HF component of HRV as an index of vagal (parasympathetic) activity. A decrease in HF during the task period is interpreted as vagal withdrawal, reflecting a reduction in parasympathetic influence on the heart, rather than an increase in sympathetic activation (Quigley et al., 2024).

The temperature at the tip of the nose was obtained using a thermistor probe (NXFT 15H103, Murata Manufacturing Co., Ltd., Japan). Skin temperature depends on skin blood flow through arteriovenous anastomoses (AVA) (Lena Nilsson, 1987). The AVA has numerous vasoconstrictive sympathetic nerves (Donadio et al., 2006). When the enhancement of peripheral SNS is caused by acute stress, the AVA contracts, and skin blood flow is reduced. There are many AVAs in the nose region (Bergersen, 1993), and fluctuations in nose skin temperature reflect the activity of peripheral SNS. The temperature data was recorded at a sampling rate of 1.0 Hz using a data logger (N543R, NIKKISO-THERM Co., Ltd., Japan).

Psychological parameters

A visual analog scale (VAS) comprising of 7 items (“Nervousness”, “Effort”, “Concentration”, “Fatigue”, “Frustration”, “Boredom”, and “Monotony”), with a calibrated line with two endpoints, 0 (min) and 100 (max): strongly disagree – strongly agree, was completed by the participants at the end of R1, T, and R2 (Figure 1). The participants were asked to indicate their perceptions on the line corresponding to their perceptions. In addition, a scent questionnaire, consisting of a 7-point Likert scale ranging from 1 to 7 (1–7; strongly disagree – strongly agree) was given to the participants to rate their subjective impressions of “Comfort”, “Strength”, “Preference” and “Awakening” of each aroma inhalation at the end of the task period.

Figure 2.

Figure 2.

Open in a new tab

(a): changes in HR (mean ± SEM) for all three conditions (n = 25); (b): changes in the mean value of HR during T (mean ± SEM) for all three conditions (n = 25), HR, heart Rate; DPG, Di propylene glycol; APL, Apple; CHA, Chamomile; T, Task; SEM, standard error of the mean.

Behavioral measures

The performance of the calculation task was measured in terms of the correct answer rate and speed of the calculation.

Statistics

The raw values of the physiological data were standardised (z score) concerning each subject and each condition to compensate for significant individual variations (Lewsey, 2006). The values were baseline corrected concerning the mean value of the initial rest (R1) period. The mean and variance used for standardisation were calculated for every 2.5-minute interval during the experimental phases. This approach allowed us to account for temporal fluctuations in physiological responses while maintaining consistency across conditions.

Artefacts in the physiological data, such as ectopic beats and non-stationary segments, were identified and managed using a combination of automated detection algorithms and manual inspection. Non-stationary data segments were excluded from the analysis to ensure the reliability of the HRV measurements. We used custom scripts and built-in analysis functions within the BIOPAC AcqKnowledge 4.0 software suite for processing HRV data, ensuring that the analysis adhered to standard practices in the field.

The normality of the data was tested using the Shapiro-Wilk test. Paired t-tests were performed to compare subjective and objective parameters within and between the conditions if the datasets could be considered normally distributed; otherwise, the Wilcoxon signed-rank test (Scheff, 2016) was performed. Bonferroni corrections were used to compare multiple conditions. The level of statistical significance (α) was set at 0.05. The statistical analysis was performed using R software (version 4.2.2., R Foundation for Statistical Computing, Vienna, Austria).

Results

Heart rate and heart rate variability

Figure 2(a) and Figure 3(a) show the changes in HR and HF components of HRV throughout the experiment (R1-T-R2), respectively. Enhanced HR and a decrease in the HF component of HRV during the task were observed in DPG, which indicates a typical acute stress response of the SNS and PSNS, respectively (Berntson et al., 1997). For CHA and DPG conditions, HR was significantly higher at T than at R1 (CHA: t [24] = 3.46, p = 0.006 and DPG: t [24] = 2.20, p = 0.038), and the HF component of HRV was significantly lower at T than at R1 (CHA: t [24] = 3.50, p = 0.002 and DPG: t [24] = 2.80, p = 0.009). For the HR and HF component of HRV in the APL condition, there was no significant difference between R1 and T (p > 0.05).

Figure 3.

Figure 3.

Open in a new tab

(a): changes in HF component of HRV (mean ± SEM) for all three conditions (n = 25); (b): changes in mean value of HF component of HRV during T (mean ± SEM) for all three conditions (n = 25), HF, high-frequency component of heart rate variability; DPG, Di propylene glycol; APL, Apple; CHA, Chamomile; T, Task; SE, standard error of the mean.

The enhancement of HR during T (Figure 2(b)) was significantly smaller with APL compared to DPG and CHA (t [24] = 3.36, p = 0.008 vs. DPG, t [24] = 4.06, p = 0.001 vs. CHA), which specified an inhibition of acute stress response by APL compared to other two conditions. The decrease of the HF component of HRV (Figure 3(b)) during T was significantly smaller with APL compared to DPG and CHA (t [24] = 2.81, p = 0.029 vs. DPG, t [24] = 3.48, p = 0.006 vs. CHA). This smaller suppression of HF suggests alleviating the physiological stress response (in terms of cardiac activity) by APL.

No significant differences were observed between the DPG and CHA conditions during the task period for the HR and HF components of HRV (p > 0.05). This indicates that both conditions elicited a similar stress response in terms of the HR and HF components of HRV.

Nose tip temperature

Figure 4(a) shows the changes in temperature at the tip of the nose of the participants. Decreased nose tip temperature during the task shown by DPG indicates a typical acute response (Donadio et al., 2006). For APL and DPG conditions, nose tip temperature was significantly lower at T than at R1 (APL: t [24] = 3.69, p = 0.001, DPG: t [24] = 2.08, p = 0.048). No significant difference between R1 and T was observed in the CHA condition (p > 0.05).

Figure 4.

Figure 4.

Open in a new tab

(a): changes in nose tip temperature (mean ± SEM) for all three conditions (n = 25); (b): changes in mean value of nose tip temperature during T (mean ± SEM) for all three conditions (n = 25), nose TMP, nose tip temperature; DPG, Di propylene glycol; APL, Apple; CHA, Chamomile; T, Task; SE, standard error of the mean.

The mean nose tip temperature at T (Figure 4(b)) was significantly lower with APL than with CHA (t [24] = 3.77, p = 0.003), indicating an enhanced peripheral SNS activity. No significant differences were found between the APL and DPG conditions (p > 0.05) or between the DPG and CHA conditions (p > 0.05) in terms of nose tip temperature during the task period, suggesting that these conditions had a comparable effect on peripheral SNS activity.

Subjective impressions and VAS scores

Subjective impressions on the “Comfort”, “Preference”, “Strength”, and “Awakening” effects of each condition are listed in Table 2. A Wilcoxon signed rank test revealed a significant difference in the perceived strength between APL (n = 25, Z = −3.023, p = 0.001) and DPG. Furthermore, APL was preferred significantly (n = 25, Z = −2.728, p = 0.003), with a higher score for subjective impression towards the sense of comfortability (n = 25, Z = −2.499, p = 0.006) compared to DPG.

Table 2.

Results of subjective impressions for each aroma condition (7-point likert scale).

  Condition Mean (SD)
Comfort DPG 4.40 (0.91)
CHA 4.68 (1.11)
APL 5.20** (1.00)
Preference DPG 4.28 (0.98)
CHA 4.80 (0.87)
APL 5.36** (0.99)
Strength DPG 2.52 (1.23)
CHA 3.40 (1.47)
APL 3.72** (1.40)
Awakening DPG 3.56 (0.96)
CHA 3.28 (1.10)
APL 3.25 (1.26)
Open in a new tab

DPG: Di propylene glycol, CHA, Chamomile, APL, Apple, SD, standard deviation: **p < 0.01 by comparison between conditions with regard to DPG.

Table 3 shows the changes in VAS scores throughout the experiment (R1-T-R2). No significant differences were observed between the conditions in overall VAS scores across the entire experimental period. However, during T, APL and CHA significantly reduced the VAS score for boredom compared to DPG (n = 25, Z = −2.224, p = 0.013 vs APL and n = 25, Z = −2.428, p = 0.011 vs CHA).

Table 3.

Results of subjective measures (VAS scores) for each aroma condition.

VAS score Condition Δ (R1-T)
 Δ (T-R2)
Mean (SD) Mean (SD)
Nervousness DPG 1.60 (20.69) −5.12 (14.34)
CHA 5.60 (21.53) −12.04 (14.89)
APL 7.64 (17.72) −3.36 (15.47)
Effort DPG 15.32 (21.28) −16.68 (18.24)
CHA 13.76 (19.63) −17.44 (16.19)
APL 17.72 (19.40) −19.16 (17.24)
Concentration DPG 9.88 (30.04) −17.68 (24.00)
CHA 7.48 (23.76) −13.16 (22.70)
APL 9.36 (24.79) −23.36 (17.12)
Fatigue DPG 8.72 (24.69) −0.08 (23.25)
CHA 6.88 (23.00) −3.96 (17.79)
APL 10.04 (26.94) −1.80 (15.03)
Frustration DPG 7.48 (14.94) −2.96 (17.74)
CHA 10.16 (23.65) −9.20 (17.92)
APL 13.72 (23.00) −7.96 (20.29)
Boredom DPG 6.00 (26.51) 1.80 (15.50)
CHA −10.12* (22.44) 8.04 (26.94)
APL −3.96* (23.31) 5.28 (27.39)
Monotony DPG 4.80 (16.97) −5.60 (15.68)
CHA 5.32 (17.11) −0.68 (16.69)
APL 9.28 (19.76) −5.44 (16.07)
Open in a new tab

DPG: Di propylene glycol, CHA, Chamomile, APL, Apple, Δ(R1-T), mean differences between the times R1-T, Δ(T-R2), mean differences between the times T-R2, SD, standard deviation: *p < 0.05 by comparison between condition with regard to DPG using Wilcoxon signed rank test results.

Table 4 shows the results of task performance concerning the correct answer rate and speed. There was no significant difference in the participants’ performance among conditions.

Table 4.

Results of task performance for each aroma condition (n = 25).

  Condition Mean (SD)
Correct answer rate DPG 0.98 (0.01)
CHA 0.98 (0.02)
APL 0.98 (0.01)
Speed (number/s) DPG 0.96 (0.23)
CHA 1.00 (0.29)
APL 1.07 (0.34)
Open in a new tab

Di propylene glycol, CHA, Chamomile, APL, Apple, SD, standard deviation.

Discussion

The study investigated apple aroma’s physiological and psychological effects on peripheral and cardiac ANS activity under a short-term cognitive stressor in a highly reproducible manner using a customised olfactometer. The significantly smaller increase in HR and the smaller decrease in the HF component of HRV during the task in the APL condition indicate that the apple aroma alleviates the physiological stress response (in terms of cardiac activity). Additionally, the subjective impressions showed that apple was considered significantly preferable and more comfortable than the other conditions, suggesting that apple aroma could be a beneficial scent in aromatherapy.

During the task, the mean nose tip temperature in the APL condition was significantly lower than in the other conditions. This decrease in nose tip temperature indicates vasoconstriction and reduced peripheral blood flow (Donadio et al., 2006; Lena Nilsson, 1987). Simultaneously, the increase in HR observed during the task was lower in the APL condition. Enhanced peripheral SNS activity is typically observed during a cognitive task, leading to increased peripheral vascular resistance and a decrease in the amount of blood flowing through the blood vessels (DeLalio et al., 2020). However, the findings of nose tip temperature observed in this study cannot be attributed to SNS stress response, as the HR and HF components of HRV did not show a greater increase or decrease compared to the other conditions. A lavender aroma study by Nomura et al. (2016) showed consistent results regarding the decrease in nose tip temperature in terms of peripheral SNS activity (Nomura et al., 2016). This similarity may be because of a small percentage of hexyl acetate in apple aroma and lavender essential oil (Ciocarlan et al., 2021). Moreover, during R2, it was observed that the nose tip temperature in the APL condition returned to a level similar to that before the task despite the decrease in HR. Even if there was a pharmacological effect of the chemical constituents in apple on peripheral response, considering lower HR and higher HF during R2, a higher PSNS activation with apple aroma could be suggested. This study can reveal another positive efficacy of apple aroma.

Based on these findings, apple aroma could be effective in cardiac SNS and PSNS activity, but it does not appear to significantly impact peripheral SNS activity. The biological mechanism of these discrepant effects of apple aroma inhalation on ANS response remains unclear. Butyl Acetate, contained in natural apples and the aroma sample used in this study, is the ester derived from n-butanol and acetic acid. It is found in many fruits, including apples and bananas, imparting their characteristic flavours and smell (Clark, 2001). Hexyl Acetate also contained in natural apples, is the acetate ester of hexane-1-ol and is typically used as a perfume compound (Wright, 2019). Although these compounds are believed to have pharmacological effects such as antioxidant, anti-cholesterol, and anti-cancer (Nur Azizah et al., 2020), their effects on physiology have not been investigated in previous studies.

To the best of our knowledge, apple aroma has not been popularly used in the context of aromatherapy so far, as it is technically difficult and cost-ineffective to extract aroma compounds to form apple essential oil. Only one study investigated the effect of anticipatory anxiety at a dental clinic with apple and orange odours and reported that these two aromas do not have any significant effect on anticipatory anxiety or mood of patients waiting for scheduled dental appointments (Toet et al., 2010).

The current study could be compared with some previous studies done under the same or related experimental protocols (Lekamge et al., 2017a; Nomura et al., 2016). Lekamge et al. (2017a) reported that mild orange (1%) essential oil inhalation inhibits cardiac stress response, showing a significantly smaller increase in HR and a smaller decrease in the HF component of HRV during the task. This finding aligns with our study, although the positive efficacy in alleviating stress response with apple aroma, indicated by the overall effect sizes for HR and HF components of HRV, is slightly smaller (effect size for orange oil: 0.65 vs. effect size for apple aroma: 0.59). This similarity in stress-alleviating effects may be attributed to the fruity nature of both aromas. Moreover, Nomura et al. (2016) found that lavender aroma inhalation promoted the physiological stress response whilst showing consistent study findings concerning the decrease in nose tip temperature.

On the other hand, Chamomile (Matricaria recutita), a medicinal herb that comes from the chicory plant family has been investigated under a variety of clinical conditions. For example, chamomile aromatherapy has been effective in reducing the scale of nausea after chemotherapy of cervical cancer patients (Putri et al., 2019), decreasing the number of contractions during the first stage of labour in primipara women (Heidari-Fard et al., 2018), reducing the depressive symptoms in institutionalised patients with newly diagnosed acute leukaemia (Blackburn et al., 2017), and significantly decreasing the depression, anxiety, and stress scores of community-dwelling older people (Ebrahimi et al., 2022). Limonene, contained in natural chamomile, is a major compound found in citrus aromas that inhibits physiological stress (Fukumoto et al., 2008). Nonetheless, few studies have focused on the effect of chamomile on the physiological acute stress response. The previous study with eight different aromas found that chamomile does not significantly affect cardiac or peripheral ANS response. However, it was a highly preferred aroma by the participants (Lekamge et al., 2017b). In contrast, this study found a significantly lower decrease in nose tip temperature during the task for the CHA condition compared to the APL condition and a significantly higher increase in nose tip temperature compared to DPG during the recovery period (R2). Our findings suggest that while chamomile aroma may have a mild stress-alleviating effect on peripheral ANS activity, it does not produce the significant reduction in HRV and HR seen with apple aroma. This distinction highlights the specific efficacy of apple aroma in modulating cardiac sympathetic and parasympathetic activity under stress, whereas chamomile appears to offer a more neutral or mildly calming effect without significantly altering these physiological markers. However, the discrepancy between the two studies might be due to the inclusion of a small sample size in the previous study.

This study contributes to our understanding of alleviating acute stress response under different aromas. Although citrus fruity aromas were commonly used in previous aroma studies, non-citrus fruity aromas such as apples are given less focus in the context of aromatherapy. Therefore, the acute stress alleviation effect suggested by apple aroma in this study could be effective in the context of aromatherapy in the future. As Apple is a preferred fruit worldwide, its benefits in aromatherapy under stressful conditions could be widely used in complementary medicine and cosmetology practice.

There are several limitations of the study that need to be acknowledged. The study included a homogeneous sample of male university students on purpose to avoid discrepancies in the results related to the variations in SNS and PSNS activity in women due to their hormonal imbalance during specific phases of the menstrual cycle (Gómez-Amor et al., 1990; Saperova & Filippova, 2022), and a simple calculation task as the acute stressor. Moreover, the study utilised prepared aroma samples containing natural apples and chamomile components. Hence, it is worth testing whether the prepared fragrances demonstrate the same efficacy as the essential oils in terms of aromatherapy. While nose tip temperature was utilised as a novel measure in this study, it is important to acknowledge that it may not have the same extensive scientific foundation as other measures of sympathetic activity, such as finger temperature or skin conductance. However, previous studies have suggested its potential utility in assessing peripheral sympathetic responses. For instance, research has shown that facial skin temperature, including the nose, correlates with HRV during sympathetic activation tests, such as the cold pressor test (Engert et al., 2014). Additionally, the relationship between facial skin temperature and autonomic responses, such as HRV and electrodermal activity (EDA), has been evaluated, demonstrating its relevance in stress assessment (Gioia et al., 2023). Furthermore, thermal infrared imaging studies have demonstrated that changes in facial skin temperature, including the nose, are associated with emotional responses, including stress (Ioannou et al., 2014). The current findings should be interpreted with this limitation in mind, and further research is necessary to validate nose tip temperature as a reliable measure of sympathetic activity. Future research should concentrate on these limitations and various aromas in a similar experimental setting to better understand the psychophysiological effects of aromatherapy under stressful situations.

Conclusion

Apple is considered a fruit with a wide range of health benefits. However, apple aroma is not popularly used in the context of aromatherapy. This study investigated the potential of apple aroma to alleviate physiological stress response induced by a short-term cognitive stressor in a highly reproducible manner using an olfactometer. The study’s findings substantiated that apple aroma exhibits notable positive efficacy in alleviating physiological stress response, particularly concerning cardiac activity, while it is significantly preferred comfortably compared to other conditions. These benefits in aromatherapy under stressful conditions could be utilised in complementary medicine and cosmetology practice in the future.

Acknowledgements

The authors are incredibly thankful to the participants of this study. This research is a collaborative work with Takasago International Corporation, Japan, and includes company employees in the author list. K. Ito was an employee of the company and received a salary for this work. Takasago International Corporation partially funded this study. The company prepared and provided the aroma substances. However, this study was not aimed to promote apple aroma and was conducted purely for scientific interest.

Funding Statement

The work was supported by the Nagaoka University of Technology and Takasago International Corporation.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availablity statement

The data that supports the findings of this study are available in open repository. https://osf.io/s2geu/?view_only = 97693b27091240f5abe7cec068282a5b

References

  1. Bergersen, T. K. (1993). A search for arteriovenous anastomoses in human skin using ultrasound doppler. Acta Physiologica Scandinavica, 147(2), 195–12. 10.1111/j.1748-1716.1993.tb09489.x [DOI] [PubMed] [Google Scholar]
  2. Berntson, G., Bigger, J. R. J. T., Eckberge, W., Grossman, P., Kaufmann, P., & Malik, M. (1997). Heart rate variability: Origins, methods, and interpretive caveats. Psychophysiology, 34(6), 623–648. 10.1111/j.1469-8986.1997.tb02140.x [DOI] [PubMed] [Google Scholar]
  3. Blackburn, L., Achor, S., Allen, B., Bauchmire, N., Dunnington, D., Klisovic, R. B.,Naber, S. J., Roblee, K., Samczak, A., Tomlinson-Pinkham, K., & Chipps, E. (2017). The effect of aromatherapy on insomnia and other common symptoms among patients with acute leukemia. Oncology Nursing Forum, 44(4), E185–E193. 10.1188/17.ONF.E185-E193 [DOI] [PubMed] [Google Scholar]
  4. Ciocarlan, A., Lupascu, L., Aricu, A., Dragalin, I., Popescu, V., Geana, E. I., Ionete, R. E., Vornicu, N., Duliu, O. G., Hristozova, G., & Zinicovscaia, I. (2021). Chemical composition and assessment of antimicrobial activity of lavender essential oil and some by-products. Plants, 10(9), 1829. 10.3390/plants10091829 [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Clark, G. (2001). The butyl acetates. Perfumer & Flavorist, 26(July/August), 20–28. [Google Scholar]
  6. Cooke, B., & Ernst, E. (2000). Aromatherapy: A systematic review. British Journal of General Practice, 50(455), 493–496. [PMC free article] [PubMed] [Google Scholar]
  7. DeLalio, L. J., Sved, A. F., & Stocker, S. D. (2020). Sympathetic nervous system contributions to hypertension: Updates and therapeutic relevance. The Canadian Journal of Cardiology, 36(5), 712–720. 10.1016/j.cjca.2020.03.003 [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Dilrukshi, E. A. C., Nishiyama, Y., Ito, K., & Nomura, S. (2024). Alleviation of acute stress response by black pepper aroma administration. Journal of Physiological Anthropology, 43(1), 3. 10.1186/s40101-023-00352-1 [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Donadio, V., Nolano, M., Provitera, V., Stancanelli, A., Lullo, F., Liguori, R., & Santoro, L. (2006). Skin sympathetic adrenergic innervation: An immunofluorescence confocal study. Annals of Neurology, 59(2), 376–381. 10.1002/ana.20769 [DOI] [PubMed] [Google Scholar]
  10. Ebrahimi, H., Mardani, A., Basirinezhad, M. H., Hamidzadeh, A., & Eskandari, F. (2022). The effects of lavender and chamomile essential oil inhalation aromatherapy on depression, anxiety and stress in older community-dwelling people: A randomized controlled trial. Explore, 18(3), 272–278. 10.1016/j.explore.2020.12.012 [DOI] [PubMed] [Google Scholar]
  11. El Hadi, M. A. M., Zhang, F. J., Wu, F. F., Zhou, C. H., & Tao, J. (2013). Advances in fruit aroma volatile research. Molecules, 18(7), 8200–8229. 10.3390/molecules18078200 [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Engert, V., Merla, A., Grant, J. A., Cardone, D., Tusche, A., Singer, T., & Xiong, M. (2014). Exploring the use of thermal infrared imaging in human stress research. PLoS One, 9(3), e90782. 10.1371/journal.pone.0090782 [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Espino-Díaz, M., Sepúlveda, D. R., González-Aguilar, G., & Olivas, G. I. (2016). Biochemistry of apple aroma: A review. Food Technology and Biotechnology, 54(4), 375–394. 10.17113/ftb.54.04.16.4248 [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Feskanich, D., Ziegler, R. G., Michaud, D. S., Giovannucci, E. L., Speizer, F. E., Willett, W. C., & Colditz, G. A. (2000). Prospective study of fruit and vegetable consumption and risk of lung cancer among men and women. Journal of the National Cancer Institute, 92(22), 1812–1823. 10.1093/jnci/92.22.1812 [DOI] [PubMed] [Google Scholar]
  15. Fukumoto, S., Morishita, A., Furutachi, K., Terashima, T., Nakayama, T., & Yokogoshi, H. (2008). Effect of flavour components in lemon essential oil on physical or psychological stress. Stress & Health, 24(1), 3–12. 10.1002/smi.1158 [DOI] [Google Scholar]
  16. Gioia, F., Nardelli, M., Scilingo, E. P., & Greco, A. (2023). Autonomic regulation of facial temperature during stress: A cross-mapping analysis. Sensors, 23(14), 6403. 10.3390/s23146403 [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Goes, T. C., Antunes, F. D., Alves, P. B., & Teixeira-Silva, F. (2012). Effect of sweet orange aroma on experimental anxiety in humans. The Journal of Alternative and Complementary Medicine, 18(8), 798–804. 10.1089/acm.2011.0551 [DOI] [PubMed] [Google Scholar]
  18. Gómez-Amor, J., Martínez-Selva, J. M., Román, F., & Zamora, S. (1990). Electrodermal activity in menstrual cycle phases: A comparison of within- and between-subjects designs. International Journal of Psychophysiology, 9(1), 39–47. 10.1016/0167-8760(90)90006-Y [DOI] [PubMed] [Google Scholar]
  19. Heidari-Fard, S., Mohammadi, M., & Fallah, S. (2018). The effect of chamomile odor on contractions of the first stage of delivery in primpara women: A clinical trial. Complementary Therapies in Clinical Practice, 32, 61–64. 10.1016/j.ctcp.2018.04.009 [DOI] [PubMed] [Google Scholar]
  20. Herz, R. S. (2009). Aromatherapy facts and fictions: A scientific analysis of olfactory effects on mood, physiology and behavior. The International Journal of Neuroscience, 119(2), 263–290. 10.1080/00207450802333953 [DOI] [PubMed] [Google Scholar]
  21. Hirasawa, Y., Shirasu, M., Okamoto, M., & Touhara, K. (2019). Subjective unpleasantness of malodors induces a stress response. Psychoneuroendocrinology, 106, 206–215. 10.1016/j.psyneuen.2019.03.018 [DOI] [PubMed] [Google Scholar]
  22. Ioannou, S., Gallese, V., & Merla, A. (2014). Thermal infrared imaging in psychophysiology: Potentialities and limits. Psychophysiology, 51(10), 951–963. 10.1111/psyp.12243 [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Ishikawa, M., Okawa, Y., Wakabayashi, E., Hirono, A., Oshima, Y., & Nomura, S. (2023). Physiological effects of using citrus mint flavored mouthwash. Transactions of Japan Society of Kansei Engineering, 22(1), 51–55. 10.5057/jjske.tjske-d-22-00034 [DOI] [Google Scholar]
  24. Knekt, P., Kumpulainen, J., Järvinen, R., Rissanen, H., Heliövaara, M., Reunanen, A., Hakulinen, T., & Aromaa, A. (2002). Flavonoid intake and risk of chronic diseases. The American Journal of Clinical Nutrition, 76(3), 560–568. 10.1093/ajcn/76.3.560 [DOI] [PubMed] [Google Scholar]
  25. Krbot Skorić, M., Adamec, I., Jerbić, A. B., Gabelić, T., Hajnšek, S., & Habek, M. (2015). Electroencephalographic response to different odors in healthy individuals: A promising tool for objective assessment of olfactory disorders. Clinical EEG and Neuroscience, 46(4), 370–376. 10.1177/1550059414545649 [DOI] [PubMed] [Google Scholar]
  26. Lee, I. (2016). Effects of inhalation of relaxing essential oils on electroencephalogram activity. International Journal of New Technology and Research, 2(5), 263522. [Google Scholar]
  27. Lee, M. S., Choi, J., Posadzki, P., & Ernst, E. (2012). Aromatherapy for health care: An overview of systematic reviews. Maturitas, 71(3), 257–260. 10.1016/j.maturitas.2011.12.018 [DOI] [PubMed] [Google Scholar]
  28. Lekamge, S., Nakachi, M., Sato, S., Ito, K., & Nomura, S. (2017a). Alleviation of the acute stress response following mild orange essential oil administration. IEEJ Transactions on Electrical and Electronic Engineering, 12(S1), S158–S163. 10.1002/tee.22428 [DOI] [Google Scholar]
  29. Lekamge, S., Nakachi, M., Sato, S., Ito, K., & Nomura, S. (2017b). Psychophysiological effects of aroma inhalation during a short-term cognitive stressor: A preliminary study using eight different aromas. International Journal of Affective Engineering, 16(3), 213–220. 10.5057/ijae.ijae-d-17-00001 [DOI] [Google Scholar]
  30. Lena Nilsson, A. (1987). Blood flow, temperature, and heat loss of skin exposed to local radiative and convective cooling. The Journal of Investigative Dermatology, 88(5), 586–593. 10.1111/1523-1747.ep12470202 [DOI] [PubMed] [Google Scholar]
  31. Lewsey, J. (2006). Medical statistics: A Guide to data analysis and critical appraisal. Annals of the Royal College of Surgeons of England, 88(6), 603–603. 10.1308/rcsann.2006.88.6.603 [DOI] [Google Scholar]
  32. Martin, G. N. (1998). Human electroencephalographic (EEG) response to olfactory stimulation: Two experiments using the aroma of food. International Journal of Psychophysiology, 30(3), 287–302. 10.1016/S0167-8760(98)00025-7 [DOI] [PubMed] [Google Scholar]
  33. Matsumoto, T., Asakura, H., & Hayashi, T. (2014). Effects of olfactory stimulation from the fragrance of the Japanese citrus fruit yuzu (citrus junos Sieb. ex Tanaka) on mood states and salivary chromogranin a as an endocrinologic stress marker. The Journal of Alternative and Complementary Medicine, 20(6), 500–506. 10.1089/acm.2013.0425 [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Matsumoto, T., Kimura, T., & Hayashi, T. (2017). Does Japanese citrus fruit yuzu (citrus junos Sieb. ex Tanaka) fragrance have lavender-like therapeutic effects that alleviate premenstrual emotional symptoms? A single-blind randomized crossover study. The Journal of Alternative and Complementary Medicine, 23(6), 461–470. 10.1089/acm.2016.0328 [DOI] [PubMed] [Google Scholar]
  35. McEwen, B. S. (2006). Protective and damaging effects of stress mediators: Central role of the brain. Dialogues in Clinical Neuroscience, 8(4), 367–381. 10.31887/dcns.2006.8.4/bmcewen [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Moradi, K., Ashtarian, H., Danzima, N. Y., Saeedi, H., Bijan, B., Akbari, F., & Mohammadi, M. M. (2021). Essential oil from Citrus aurantium alleviates anxiety of patients undergoing coronary angiography: A single-blind, randomized controlled trial. Chinese Journal of Integrative Medicine, 27(3), 177–182. 10.1007/s11655-020-3266-5 [DOI] [PubMed] [Google Scholar]
  37. Nomura, S., Maeyama, K., & Ito, K. (2016). Enhancement of autonomic stress response and reduction of subjective stress by lavender inhalation during a short-term calculation task. Advanced Biomedical Engineering, 5(), 7–12. 10.14326/abe.5.7 [DOI] [Google Scholar]
  38. Nur Azizah, P., Misfadhila, S., & Author, C. (2020). Review of phytochemical and pharmacological effects of apple. International Journal of Research and Review (Ijrrjournal.Com), 7(9), 231. [Google Scholar]
  39. Patocka, J., Bhardwaj, K., Klimova, B., Nepovimova, E., Wu, Q., Landi, M., Kuca, K., Valis, M., & Wu, W. (2020). Malus domestica: A review on nutritional features, chemical composition, traditional and medicinal value. Plants, 9(11), 1–19. 10.3390/plants9111408 [DOI] [PMC free article] [PubMed] [Google Scholar]
  40. Putri, I. N., Amelia, R., & Rahayu, S. (2019). The chamomile aromatherapy reduce the scale of nausea. International Journal of Public Health Science (IJPHS), 8(3), 294. 10.11591/ijphs.v8i3.20252 [DOI] [Google Scholar]
  41. Quigley, K. S., Gianaros, P. J., Norman, G. J., Jennings, J. R., Berntson, G. G., & de Geus, E. J. C. (2024). Publication guidelines for human heart rate and heart rate variability studies in psychophysiology—part 1: Physiological underpinnings and foundations of measurement. Psychophysiology, 61(9). 10.1111/psyp.14604 [DOI] [PMC free article] [PubMed] [Google Scholar]
  42. Rambod, M., Pasyar, N., Karimian, Z., & Farbood, A. (2023). The effect of lemon inhalation aromatherapy on pain, nausea, as well as vomiting and neurovascular assessment in patients for lower extremity fracture surgery: A randomized trial. BMC Complementary Medicine and Therapies, 23(1), 208. 10.1186/s12906-023-04047-z [DOI] [PMC free article] [PubMed] [Google Scholar]
  43. Saperova, E. V., & Filippova, I. (2022). Heart rate variability during different phases of menstrual cycle. FASEB Journal, 36(S1), 36. 10.1096/fasebj.2022.36.S1.L7996 [DOI] [Google Scholar]
  44. Sattayakhom, A., Wichit, S., & Koomhin, P. (2023). The effects of essential oils on the nervous system: A scoping review. Molecules, 28(9), 3771. 10.3390/molecules28093771 [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Scheff, S. W. (2016). Chapter 8 - Nonparametric Statistics. Fundamental Statistical Principles for the Neurobiologist; A Survival Guide (pp. 157–182). Elsevier. [Google Scholar]
  46. Sesso, H. D., Gaziano, J. M., Liu, S., & Buring, J. E. (2003). Flavonoid intake and the risk of cardiovascular disease in women. The American Journal of Clinical Nutrition, 77(6), 1400–1408. 10.1093/ajcn/77.6.1400 [DOI] [PubMed] [Google Scholar]
  47. Sowndhararajan, K., & Kim, S. (2016). Influence of fragrances on human psychophysiological activity: With special reference to human electroencephalographic response. Scientia Pharmaceutica, 84(4), 724–751. 10.3390/scipharm84040724 [DOI] [PMC free article] [PubMed] [Google Scholar]
  48. Sullivan, G. M., & Feinn, R. (2012). Using effect size—or why the P value is not enough. Journal of Graduate Medical Education, 4(3), 279–282. 10.4300/jgme-d-12-00156.1 [DOI] [PMC free article] [PubMed] [Google Scholar]
  49. Toet, A., Smeets, M. A. M., Van Dijk, E., Dijkstra, D., & Van Den Reijen, L. (2010). Effects of pleasant ambient fragrances on dental fear: Comparing apples and oranges. Chemosensory Perception, 3(3–4), 182–189. 10.1007/s12078-010-9078-9 [DOI] [PMC free article] [PubMed] [Google Scholar]
  50. Watanabe, E., Kuchta, K., Kimura, M., Rauwald, H. W., Kamei, T., & Imanishi, J. (2015). Effects of bergamot (citrus bergamia (Risso) Wright & Arn.) essential oil aromatherapy on Mood States, parasympathetic nervous system activity, and salivary cortisol levels in 41 healthy females. Complementary Medicine Research, 22(1), 43–49. 10.1159/000380989 [DOI] [PubMed] [Google Scholar]
  51. Watanabe, S., Hara, K., Ohta, K., Iino, H., Miyajima, M., Matsuda, A., Hara, M., Maehara, T., Matsuura, M., & Matsushima, E. (2013). Aroma helps to preserve information processing resources of the brain in healthy subjects but not in temporal lobe epilepsy. Seizure: European Journal of Epilepsy, 22(1), 59–63. 10.1016/j.seizure.2012.10.008 [DOI] [PubMed] [Google Scholar]
  52. Wright, J. (2019, June). Flavor bites: Hexyl acetate. Perfumer & Flavorist, 44(6), 22–25. [Google Scholar]
  53. Zhang, S., Hu, C., Guo, Y., Wang, X., & Meng, Y. (2021). Polyphenols in fermented apple juice: Beneficial effects on human health. Journal of Functional Foods, 76, 104294. 10.1016/j.jff.2020.104294 [DOI] [Google Scholar]

Articles from Australian Journal of Psychology are provided here courtesy of Taylor & Francis

RESOURCES