2022 Volume 28 Issue 3 Pages 245-255
This study aimed to find an effective protocol as a cooking pre-treatment for the petioles and young spikes of Petasites japonicus to reduce their contents of pyrrolizidine alkaloids (PAs), a type of natural toxin in plants such as the Asteraceae and Boraginaceae families. After determining the most common cooking pre-treatment methods for petioles and young spikes of Petasites japonicus from a survey of recipes, various treatments were examined for their effectiveness at reducing PAs. It was concluded that both boiling and soaking processes were important for the reduction of PAs in pre-treatment of cooking the petioles and the young spikes of Petasites japonicus, and that a longer soaking time had a greater effect in reducing PAs. PAs in the petioles and young spikes decreased to less than 50% of the original amount in 1 h and 6 h, respectively during soaking after boiling (and peeling).
Petasites japonicus is one of the traditional edible wild plants used for centuries in Japan. It is known that Petasites japonicus includes not only useful ingredients with antioxidant, anti-neuroinflammatory, and anti-adipogenic properties (Hiemori-Kondo and Nii, 2020; Park et al.; 2018, Guo et al., 2019), but also pyrrolizidine alkaloids (PAs), which have carcinogenicity and hepatotoxicity (Mori et al., 1984; Neuman et al., 2015).
The major PAs present in Petasites japonicus are petasitenine, neopetasitenine, and senkirkine (Fig. 1), and these PAs account for approximately 99% of the total PAs in Petasites japonicus (Kitajima et al., 2019). These PAs have a double bond in the ring nucleus, an esterified hydroxyl group, and a branched carbon in the ester side chains. PAs which have those characteristic structure were reported to be especially highly toxic (Neuman et al., 2015). Minor PAs such as secopetasitenine are also found from Petasites japonicus (Kitajima et al., 2019).
Chemical structures of major PAs in Petasites japonicus.
Traditionally, the edible parts of Petasites japonicus are the petioles and young spikes. These parts are generally cooked by boiling, stir-frying or deep frying and are not eaten raw. Generally, fresh Petasites japonicus is available only during a quite limited time of the year and is rarely eaten the rest of the year. In addition, Petasites japonicus is rarely eaten in large quantities at one time due to its unique and strongly bitter flavor, even after cooking. So far, there have been no reports of adverse health effects caused by PAs in Petasites japonicus in Japan. Japan's Ministry of Agriculture, Forestry and Fisheries (MAFF) has indicated no known concern of adverse health effect from intake of Petasites japonicus as long as it is prepared in the traditional way and not overeaten.
However, Joint FAO/WHO Expert Committee on Food Additives conducted risk assessment for PAs in foods and noted that the calculated margins of exposure (MOEs) for honey (high consumers) and tea (mean and high consumers) indicated a potential concern, based on limited occurrence data. The Committee also considered it of concern that exposure to a single food product could result in such low MOEs (JECFA, 2020). It is internationally recognized that the contaminants and toxins level in foods should be reduced to as low as reasonably achievable for consumer health protection. Following this principle, it is necessary to confirm how to reduce PAs during the cooking of Petasites japonicus to mitigate dietary exposure to PAs as much as possible.
As for reduction of contaminants in foods by cooking, verious reports about the reduction of radioactive compounds, mycotoxins, and toxic trace elements such as Hg, Cd, As, and Pb have been published (Nabeshi et al., 2015; Schaarschmidt and Fauhl-Hassek, 2019; Chiocchetti et al., 2020; Menon, et al., 2021). There are also some published reports about natural toxins bio-synthesized by plants. Padmaja reviewed cyanide detoxification in cassava and concluded that treatment by soaking followed by boiling was effective for removing this toxic substance (Padmaja, 1995). Japan's MAFF publishes on the website that traditional pre-treatments of Petasites japonicus such as boiling and soaking are effective at reducing PAs because the PAs in Petasites japonicus are soluble in water i); however, the publication does not include details about the effects of various methods and conditions of pre-treatment on the reduction of PAs, and there is no report focused on the reduction of PAs by cooking pre-treatment of Petasites japonicus. This study aimed to investigate the efficacy of various traditional cooking pre-treatments of the petioles and the young spikes of Petasites japonicus on the retention rate of PAs and to find the optimal method of pre-treatment to reduce PAs.
Materials A certain variety of the petioles of Petasites japonicus planted for commercial use in the same area of Japan was used for experiments. For the cooking pre-treatment experiments, 2 cultivation types of the petiole were used, forced cultivation and suppressed cultivation. The forced-cultivation method yields harvests earlier than the natural condition by warming of the crop while the suppressed-cultivation method yields harvest after the natural condition by late planting of the root-stumps. The force-cultivated petioles (FC) were obtained in 2019, and the suppression-cultivated petioles (SC) were in 2019 and 2020. Each lot comprised approximately 150 petioles (30−80 g per a petiole, the length of the long axis is 40−70 cm), and 4 lots of petioles were used for the experiments.
Young spikes of a certain variety of Petasites japonicus which had been planted in the same farm for commercial use and cropped in February and March 2020 was used for experiments. Each lot comprised approximately 300 spikes (3−5 g per a spike), and 4 lots of the young spikes were used for the experiments.
A food-grade salt (The Salt Industry Center of Japan, Tokyo, Japan) and a brewed vinegar made from wheat, rice, and corn (Mizkan, Handa, Japan) were used as additives in some pre-treatments, as was food-additive-grade sodium bicarbonate purchased from Fujifilm Wako (Osaka, Japan).
Chemicals and reagents Pure standards of petasitenine, neopetasitenine and senkirkine, which are major pyrrolidine alkaloids in Petasites japonicus, were purchased from Nagara Science (Gifu, Japan). Heliotrine (internal standard, IS) pure standard was purchased from PhytoLab (Bayern, Germany). Formic acid (LC-MS grade) was purchased from Fujifilm Wako (Osaka, Japan). Acetonitrile (LC-MS grade) was purchased from Kanto Chemical (Tokyo, Japan).
Survey of the recipes Recipes for foods using the petioles and the young spikes of Petasites japonicus were collected from the cooking recipe database of TV cooking shows, food companies, internet sites, and recipe books written by cooking experts. The cooking pre-treatment methods for Petasites japonicus were gleaned from 263 recipes using petioles and 151 recipes using young spikes.
Cooking pre-treatments for Petasites japonicus Three petioles were used for each experimental trial, and four trials were conducted for each experiment (n = 4). Eight experiments were constructed based on results from the recipe survey (experiments 1−8, Table 1). In experiments 1−4, different conditions of soaking time, the length of petioles, and/or temperature during soaking were set. Experiment 5 was conducted to test the effect of salt rubbing, that is, sprinkling salt (10% against the petioles, w/w) over the petioles and rolling them on a board prior to boiling. Experiments 6 and 7 were conducted to test the effect of timing of peeling and the effect of additives, respectively. In experiment 7, boiling water and soaking water were prepared with 0.25−2.5% salt, 0.5−5% vinegar, or 0.1−1% sodium bicarbonate; these concentrations are those traditionally used for cooking pre-treatments of wild plants. In experiment 8, longer boiling time (6 min) was set. The petioles were cut to half of their intact length before boiling in experiments 1−3 and 5−8. When the petioles were boiled and soaked, tap water 10 times weight of the petioles was used. When soaking petioles for 1 hour or more, the soak water was replaced with fresh water in the first 30 min. In experiments 2 and 3 which included slightly different conditions compared with experiment 1, relatively long soaking time (up to more than 3 h) was adopted. In experiments 5−8 which included definitely different conditions compared with experiment 1, relatively short soaking time (0.5 h) was adopted. It was expected that the effect of reduction of PAs could be judged in relatively short soaking time in experiments 5−8. As for experiment 4, it included definitely different conditions compared with experiment 1, but it was assumed that eluting rate of PAs during soaking was quite low, so the soaking time was set up to 24 h. A freezer/refrigerator HRF-90ZFT (Hoshizaki, Toyoake, Japan) set at 4 °C was used for soaking at 4 °C in experiment 3. Room temperature was around 20 °C in all experiments.
| Petiole | ||||||||
|---|---|---|---|---|---|---|---|---|
| Exp. No. | Type of petiole | Boiling time | Soaking time | Length* | Temperature** | Salt rubbing | Timing of peeling | Additives |
| [min] | [h] | [cm] | ||||||
| 1 | FC, SC | 3 | 0–24 | L×1/2 | RT | No | After boiling | No |
| 2 | FC | 3 | 3 | L×1/2, 5, 10 | RT | No | After boiling | No |
| 3 | FC | 3 | 6–24 | L×1/2 | 4 °C, RT | No | After boiling | No |
| 4 | SC | 0 | 1–24 | 5 | RT | No | Before soaking | No |
| 5 | SC | 3 | 0.5 | L×1/2 | RT | Yes | After boiling | No |
| 6 | SC | 3 | 0.5 | L×1/2 | RT | No | Before boiling | No |
| 7 | SC | 3 | 0.5 | L×1/2 | RT | No | After boiling | Yes |
| 8 | SC | 6 | 0.5 | L×1/2 | RT | No | After boiling | No |
| Control*** | SC | 3 | 0.5 | L×1/2 | RT | No | After boiling | No |
| Young spike | |||
|---|---|---|---|
| Exp. No. | Boiling time [min] | Soaking time [h] | Temperature** |
| 9 | 1 | 0–24 | RT |
| 10 | 0 | 6–24 | RT |
FC: force-cultivated petiole
SC: suppression-cultivated petiole
L: length of the intact petioles [cm] (40 ≤ L ≤ 70)
RT: room temperature
Twenty-seven to thirty-six spikes were used for one trial of an experiment, and four trials were conducted for each experiment (n = 4). Two experiments were constructed, which had varied conditions of boiling time and soaking time (experiments 9 and 10, Table 1). When the young spikes were boiled and soaked, tap water 20 times weight of the spikes was used. When soaking spikes, the soak water was replaced with fresh water in the first 30 min.
Evaluation of the distribution of PAs in edible and inedible parts of the petiole One petiole of Petasites japonicus that had been suppression-cultivated was peeled to obtain the peel part and peeled part. The latter is usually the edible part. Ratios of the amounts of PAs in the peels and peeled parts were calculated (n = 4).
UPLC-MS/MS analysis conditions A Waters Acquity UPLC H Class-Xevo TQD system (MA, USA) equipped with electrospray ionization operated in positive ionization mode was used. Separation was achieved on an Acquity UPLC BEH C18 (100 × 2.1 mm, 1.7 µm) column using a gradient of 5–45% acetonitrile in water containing 0.1% (v/v) formic acid at a flow rate of 0.4 mL/min and a column temperature of 50 °C. The injected sample volume was 2 µL, and the autosampler was set at 10 °C. The ionization conditions for the Xevo TQD mass spectrometer were set as follows: source voltage, 3 kV; collision energy, 3 V; cone gas flow rate, 50 L/h; desolvation gas flow rate, 1000 L/h; source temperature, 150 °C; desolvation temperature, 500 °C. The optimum values for compound-dependent parameters like cone voltage and collision energy were set at 58 V and 32 eV for petasitenine; 64 V and 34 eV for senkirkine; 56 V and 44 eV for neopetasitenine; and 48 V and 20 eV for IS, respectively. The quantitative analysis of each PA was performed using a multiple reaction monitoring (MRM) method. MRM transitions were m/z 382.03 to m/z 167.96 for petasitenine, m/z 366.10 to m/z 168.02 for senkirkine, m/z 424.10 to m/z 121.97 for neopetasitenine and m/z 314.11 to m/z 137.98 for IS. Data acquisition was performed using MassLynx v 4.1 (Waters, MA, USA).
Extraction and quantification of PAs Stock solutions of petasitenine, senkirkine, neopetasitenine and heliotrine (IS) were prepared by dissolving each compound in 50% (v/v) methanol/water to obtain a concentration of 1.00 mg/mL of each compound and were stored at −80 °C. Before determining PAs in Petasites japonicus samples, we prepared dilutions containing 0, 1.25, 2.5, 5.0, 20, 80, 100, 160, 200 ng/mL of each standard PA with 15 ng/mL of IS.
Raw and treated petioles or young spikes of Petasites japonicus were lyophilized and powdered. PAs were extracted from 0.2 g of lyophilized powder with 10 mL of 50% (v/v) methanol/water containing IS (750 ng/mL for the petioles, 1500 ng/mL for the young spikes) by sonication for 10 min followed by centrifuging at 15,000 g for 10 min. The supernatant was diluted with 50% (v/v) methanol/water 50 times for the petioles or 100 times for the young spikes, respectively, and filtered through a PTFE filter (0.2 µm pore size; Merck, NJ, USA), then subjected to LC-MS/MS analysis. Each PA concentration in petioles or young spikes was calculated using the equation of the calibration curve.
Evaluation of the reduction of PAs in each pre-treatment The reduction of PAs was evaluated by the retention rate of total PAs. The sum of petasitenine, neopetasitenine and senkirkine, the 3 major PAs of Petasites japonicus, in each sample was considered the amount of total PAs. The retention rate of total PA was calculated by dividing the total PAs content in the treated sample by the total PA content in the untreated sample, where the treated sample and the untreated sample were from the same lot. The formula is as follows.
Statistical analyses Statistical analyses were performed using IBM SPSS Statistics, version 25 (IBM Japan, Ltd, Tokyo, Japan). The homogeneity of variances was carried out by Levene's test. The data were analyzed using one-way analysis of variance (ANOVA), with the Tukey-Kramer multiple comparison test. When the variance was not homogenous, the non-parametric Kruskal-Wallis test was used to detect significance between groups, with Dunnett's multiple comparison test. Furthermore, two-way ANOVA was performed either to determine the effects of temperature and soaking time, in experiment 3, or the effects of soaking time and boiling, in experiment 6. When an interaction was significant, we examined the simple main effect of two factors using the Bonferroni method. The level of statistical significance was set at p < 0.05.
The cooking pre-treatment for petioles of Petasites japonicus The survey of 263 recipes revealed that boiling, peeling, and soaking are the major cooking pre-treatment methods. Ninety-seven percent of recipes included a boiling process, 87% included a peeling process, and 81% included a soaking process. Fifty-six percent of all recipes included the process of salt rubbing. In the recipes where the boiling time was specified, the majority said 2−3 min (Fig. 2). Eighty-one percent of the recipes included a soaking process, but most did not specify the soaking time. In the recipes in which the soaking time was specified, 92% of the recipes used a soaking time less than 1 hour (Fig. 3). As a minority, there were some recipes that used condiments or additives such as salt, vinegar or sodium bicarbonate during boiling or soaking. There were also some recipes that included a soaking process without boiling.
Proportion of the number of recipes of each boiling time (X) in the cooking pre-treatment of petioles of Petasites japonicus among 263 recipes.
Proportion of the number of recipes of each soaking time (X) in the cooking pre-treatment of petioles of Petasites japonicus among 263 recipes.
Reduction of PAs by cooking pre-treatment of petioles of Petasites japonicus Total PAs in the untreated petioles of Petasites japonicus were 1.5−2.7 and 6.4−7.9 mg/kg (wet base) for FC and SC, respectively. The ratio of the amounts of PAs contained in the peel part and peeled part of Petasites japonicus petioles was 2:98. Experiment 1 showed that when the petioles were boiled for 3 min and soaked in water, a longer soaking time reduced the retention of total PAs in the petioles of both FC and SC (Fig. 4). After boiling for 3 min and peeling, total PAs were reduced to 81% and 66% of untreated petioles in FC and SC, respectively. The retention rate of PAs after soaking for more than 30 min for FC and more than 3 h for SC was significantly lower than that in petioles without soaking. After soaking for 24 h, total PAs fell to less than 20 and 10% of untreated petioles in FC and SC, respectively. Since there was not remarkable difference between FC and SC in reduction of PAs in the experiment 1, the other experiments were carried out using either FC or SC. Experiment 2 showed that the length of the petioles during soaking did not have a significant effect on the total PAs (Fig. 5). Experiment 3 showed that the temperature during soaking and the soaking time did not have a significant main effect on the retention rate of total PAs in FC (Fig. 6). Experiment 4 showed that approximately 80% of PAs remained after soaking for 24 h in the petioles that were peeled and cut to 5 cm without boiling; however, there was no significant difference in the retention rate of PAs among groups with soaking times of 1, 6 and 24 h (Fig. 7). This result shows that peeling, cutting and soaking without boiling does not reduce PAs in petioles. Experiments 5−8 showed that salt rubbing, the timing of the peeling the use of additives in boiling and soaking, and boiling time did not have significant effect on the retention rate of total PAs (Table 2).
Time-dependent changes of retention rate of total PAs by soaking as a cooking pre-treatment (boiling for 3 min → peeling → soaking) of the petioles of Petasites japonicus (n = 4). [Experiment 1]
Each data is expressed as mean ± standard deviation.
FC: Data were analyzed by one-way ANOVA (p < 0.001), followed by Tukey-Kramer test (p < 0.05).
SC: Data were analyzed by Kruskal-Wallis test (p < 0.001), with Dunnett's test (p <0.05).
Different letters (a, b, c) indicate significant differences in each value.
Effects of length of the petioles on retention rate of total PAs in soaking as a cooking pre-treatment (boiling for 3 min → peeling → cutting to 10 or 5 cm → soaking for 3 h) of the petioles of Petasites japonicus (n = 4). [Experiment 2]
Data are expressed as means ± standard deviations.
Data were analyzed by one-way ANOVA (n.s.).
L: length of the intact petioles [cm]
Effects of temperature and soaking time on retention rate of total PAs in cooking pre-treatment (boiling for 3 min → peeling → soaking) of the petioles of Petasites japonicus (n = 4). [Experiment 3]
Data are expressed as means ± standard deviations.
Data were analyzed by two-way ANOVA (main effect of temperature; n.s., main effect of soaking time; n.s., interaction effect of temperature × soaking time; n.s.).
Time dependent changes of retention rate of total PAs in soaking process in cooking pre-treatment (peeling → cutting to 5 cm → soaking) of the petioles of Petasites japonicus (n = 4). [Experiment 4]
Data are expressed as means ± standard deviations.
Data were analyzed by one-way ANOVA (n.s.).
| Exp. No. | Condition* | Retention rate of total PAs*** (%) |
|---|---|---|
| 5 | Salt rubbing before boiling | 90.0 ± 17.3 |
| 6 | Peeling before boiling | 80.4 ± 27.3 |
| 7 | Boiling in water with 1% salt | 62.3 ± 28.4 |
| Boiling in water with 2% vinegar | 66.7 ± 35.3 | |
| Boiling in water with 0.4% sodium bicarbonate | 68.6 ± 6.6 | |
| Soaking in water with 1% salt | 102.6 ± 28.7 | |
| Soaking in water with 2% vinegar | 90.6 ± 31.3 | |
| Soaking in water with 0.4% sodium bicarbonate | 78.0 ± 14.9 | |
| 8 | Boiling for 6 min | 68.8 ± 18.0 |
| Control | ** | 60.5 ± 19.7 |
For experiment 7, representative results are shown.
The cooking pre-treatment method for young spikes of Petasites japonicus The survey of 151 recipes revealed that boiling and soaking are the major methods of cooking pre-treatment for young spikes. Twenty-two percent of all recipes did not include a boiling process, and 35% did not include a soaking process. In the recipes where the boiling time was specified, most recommended a boiling time of 1−3 min (Fig. 8). In the recipes where the soaking time was specified, the soaking time varied greatly from 0 (no soaking) to more than 12 h (Fig. 9).
Proportion of the number of recipes of each boiling time (X) in the cooking pre-treatment of young spikes of Petasites japonicus among 151 recipes.
Proportion of the number of recipes of each soaking time (X) in the cooking pre-treatment of young spikes of Petasites japonicus among 151 recipes.
Reduction of PAs by cooking pre-treatment of young spikes of Petasites japonicus Total PAs in untreated young spikes of Petasites japonicus were 8.4−23.3 mg/kg (wet base). Experiment 9 showed that when the young spikes were boiled for 1 min and soaked in water, the longer soaking time made the retention rate of total PAs lower, and the retention rate of PAs after soaking for more than 6 h was significantly lower than that of young spikes without soaking in water as a pre-treatment. After soaking for 24 h, total PAs fell to 28% of that of untreated young spikes (Fig. 10).
Time-dependent changes of retention rate of total PAs in soaking process in cooking pre-treatment (boiling for 1 min → soaking) of young spikes of Petasites japonicus (n = 4). [Experiment 8]
Data are expressed as means ± standard deviations.
Data were analyzed by one-way ANOVA (p < 0.001), with post-hoc Tukey-Kramer test (p < 0.05).
Different letters (a, b) indicate significant differences in each value.
In experiment 10, when two-way ANOVA was performed either to determine the effects of soaking time (6 and 24 h) or boiling (with, without), a significant main effect of boiling was observed (p < 0.001), whereas the main effect of soaking time was not significant. Since the interaction of the two components was significant, a simple main effect was examined using the Bonferroni method. The retention rate of PAs was significantly lower in young spikes that were boiled first, then soaked, compared to those only soaked (p <0.001); among the boiling conditions, it was significantly lower in young spikes soaked for 24 h than in those soaked for 6 h (p <0.05). It was suggested that the boiling process was essential for reducing PAs in young spikes (Fig. 11).
Effect of boiling process on retention rate of total PAs in soaking process in cooking pre-treatment (boiling for 1 min or no boiling → soaking) of the young spikes of Petasites japonicus (n = 4). [Experiment 9]
Data are expressed as means ± standard deviations.
Data were analyzed by two-way ANOVA (main effect of boiling; p < 0.001, main effect of soaking time; n.s., interaction effect of boiling × soaking time; p < 0.05). When the interaction effect of two components (boiling × soaking time) was significant, the simple main effect of boiling and soaking time was examined using Bonferroni method (boiling; p < 0.001).
Different letters (a, b, c) indicate significant differences among values.
From the evaluation of the retention rate of PAs in the series with pre-treatment, it was clarified that the processes of boiling and soaking are important, and that a longer soaking pre-treatment reduces the retention rate of PAs in cooked petioles and young spikes of Petasites japonicus. The preliminary sensory evaluation also supported that the pre-treatment of petioles to reduce PAs does not degrade the flavor or texture (data not shown).
Traditionally, various cooking pre-treatments such as boiling in water, soaking in water, sometimes using salt, vinegar, sodium bicarbonate, or ash have been used for various edible wild plant including Petasites japonicus. Izumo et al. reported that higher eluting rates of minerals such as Ca and K were confirmed when the petioles of Petasites japonicus were boiled in 1 or 2% salt solution compared with plain water (Izumo et al., 1981). Hata and Nanko reported that when the leaves of bracken were soaked with hot water containing sodium bicarbonate, the tissue was softened, and contents of some inorganic substances were reduced (Hata and Nanko, 1983). A survey of recipes using the petioles of Petasites japonicus showed that more than half of all recipes included the process of salt rubbing; however, our study found no significant effect on reduction of PAs in the petioles of Petasites japonicus by salt rubbing. Likewise, there was no significant effect of using salt, vinegar or sodium bicarbonate as additives to water used for boiling or soaking.
In the review on cyanide detoxification in cassava, it was reported that the treatment of 10 min boiling after 15 to 24 h soaking reduced 79% of the total cyanide, and the retention rate was lower than those for soaking or boiling alone (Padmaja, 1995). In the report on the arsenic removal in rice cooking, it was reported that the treatment of parboiling and absorbing water reduced 54% and 73% of the inorganic arsenic in cooking brown and white rice, respectively (Menon et al., 2021). In these studies, the combination of boiling and soaking together had a greater effect on removing the hazards than either single treatment. A similar tendency was observed in the results for the pre-treatment of Petasites japonicus in this study.
As for the softening of vegetable tissues by boiling, Tamura explained that when the root of radish or burdock is boiled, the adhesive property between cell walls is lowered by degradation of high-methoxylated pectin in the cell wall, and the sponging between cellulose microfibrils brought about the softening of tissues (Tamura, 1994). In boiling the petioles or the young spikes of Petasites japonicus, similar changes may occur; the tissues are softened, and water-soluble substances including PAs may become easier to eluted. Salt rubbing or using sodium bicarbonate in the boiling or soaking pre-treatment of petioles or the young spikes of Petasites japonicus may promote softening of the tissues. But it is assumed that without these treatments, boiling (for 3 min for the petioles and for 1 min for the young spikes) may soften the tissues enough to elute PAs.
Peeling is not an effective treatment to reduce PAs in the petioles because most of the PAs are contained in the peeled part of the petioles; however, the peeling process may be necessary to improve the texture and palatability of the petioles.
Among the cooking recipes using petioles and the young spikes of Petasites japonicus collected in this study, many recipes did not clearly describe the conditions of cooking pre-treatment. Among recipes with pre-treatment conditions, many seemed not to satisfy the condition of reducing PAs in petioles and young spikes: for example, peeling and soaking without boiling for the petioles, only boiling (not including soaking) or boiling and soaking for only a short time (for example 30 min).
The series of examinations of cooking pre-treatment for the petioles and young spikes of Petasites japonicus revealed that the optimal method to reduce PAs is to boil, peel and soak in water for more than 3 h for the petioles and to boil and soak in water for about 1 day for the young spikes. Even if those pre-treatments are performed at room temperature, Petasites japonicus is generally eaten after cooking with heating, so there are few food hygiene concerns. It is assumed that this information about PA-reduction pre-treatment methods for the petioles and the young spikes of Petasites japonicus should be properly communicated to consumers from the relevant government authorities to ensure food safety.
Acknowledgements This study was conducted under the research project on “Regulatory research projects for food safety, animal health and plant protection (JPJ008617. 18066596) funded by the Ministry of Agriculture, Forestry and Fisheries of Japan.
Conflict of interest There are no conflicts of interest to declare.
pyrrolizidine alkaloids
MAFFMinistry of Agriculture, Forestry and Fisheries
FCforce-cultivated petiole
SCsuppression-cultivated petiole.
