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. Author manuscript; available in PMC: 2022 May 10.
Published in final edited form as: J Agric Food Chem. 2020 Apr 27;68(18):5241–5248. doi: 10.1021/acs.jafc.0c01681

Concentrations of the Opium Alkaloids Morphine, Codeine, and Thebaine in Poppy Seeds are Reduced after Thermal and Washing Treatments but are Not Affected when Incorporated in a Model Baked Product

Shalaka A Shetge 1, Michael P Dzakovich 2, Jessica L Cooperstone 2,3, Daria Kleinmeier 4, Benjamin W Redan 5,*
PMCID: PMC9087216  NIHMSID: NIHMS1803655  PMID: 32302121

Abstract

Limited information exists on the effectiveness of potential treatments to reduce levels of opium alkaloids that may be present in seeds from poppy (Papaver somniferum L.). Poppy seeds containing morphine at relatively lower (14.7 mg kg−1) and higher (210.0 mg kg−1) concentrations were subjected to dry heat and steam treatments, water washing, and baking. Sample extracts were then analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for the opium alkaloids morphine, codeine, and thebaine. The results indicated that thermal treatment promoted opium alkaloid degradation in poppy seed samples, with a 50% loss of morphine observed after 30–40 min at 200 °C. Water washing reduced concentrations of opium alkaloids in poppy seeds by approximately 50–80%, while steam treatment resulted in a reduction of morphine in only one sample type. Importantly, baking had no significant effect on concentrations of opium alkaloids. Overall, these results indicate that opium alkaloids may not be significantly affected by baking or steam application and that poppy seeds may require water washing or extended thermal treatment to promote reduction of these compounds.

Keywords: Poppy seed, opium alkaloids, morphine, codeine, thebaine, LC-MS/MS, thermal processing

INTRODUCTION

Poppy (Papaver somniferum L.) is a commercial crop grown worldwide that is valued for both its medicinal and culinary uses.14 The pharmacological properties of poppy are mainly due to the presence of opium alkaloids, such as morphine. Aside from the medicinal properties of the plant, poppy is heavily utilized for its seeds, which are used in the food industry in their intact form or pressed for their oil content. While some studies have reported no detectable levels of opium alkaloids in poppy seeds,5 others using sensitive assays have measured these compounds in the seeds and have demonstrated their biological importance in seed development.6 Still, poppy seeds generally contain relatively low levels of opium alkaloids compared to the sap-like substance known as latex that surrounds the seed capsule. The seeds can then become surface contaminated by transfer from the latex to the seeds during pre- and post-harvest events.5, 7 Poppy seeds intended for culinary use are typically obtained mainly from poppy cultivars bred to accumulate lower amounts of opium alkaloids. However, some poppy seeds that enter the food markets may be from cultivars with elevated concentrations of opium alkaloids, perhaps intended for pharmaceutical purposes.8

In light of this, there have been reports of consumers using poppy seeds to prepare extracts enriched in opium alkaloids used for analgesic and recreational purposes.9 These preparations have been reported to result in severe adverse effects and even fatalities, since the dosage of opium alkaloids is typically unknown and is dependent on how the extract is prepared.10, 11 These preparations can contain elevated levels of opium alkaloids other than morphine, including codeine and thebaine.12 While it has long been known that morphine from poppy seed-containing foods is bioavailable and can be detected in biological fluids after intake,13 adverse events demonstrate the need to more thoroughly characterize procedures for controlling opium alkaloid concentrations in poppy seeds.

Although there have been multiple discussions for proposals to set limits on opium alkaloids in poppy seeds, a regulatory limit has yet to be established.5, 14, 15 To ensure that food-grade poppy seeds are lower in opium alkaloids, heating and other treatments have been recommended to reduce their concentrations. For example, dry heat, grinding, washing, and baking have all been reported to remove or degrade these compounds.16 In a document published by the European Commission,17 there are specific recommendations that include heat treatment to reduce opium alkaloid concentrations. Still, there has not been a full characterization of conditions that result in thermal decomposition of the major opium alkaloids in poppy seeds, or when present in foods, such as bakery products.

Further, most research on opium alkaloids has focused on morphine, since it is the most biologically active opium alkaloid in terms of analgesic potency. However, codeine and thebaine are also of concern since a certain fraction of codeine is metabolized into morphine in humans and elevated exposure to thebaine may result in toxicity.5, 18 Due to chemical differences between morphine and codeine/thebaine, treatment methods found to reduce levels of morphine in poppy seeds may not extrapolate to other opium alkaloids.5 Additionally, the behavior of these compounds under various treatments may differ across different types of poppy seeds, since there are multiple phytochemicals in poppy seeds that may influence degradation reactions that drive alkaloid oxidation and decomposition.19

The present study proposes to help fill these data gaps by examining how the three major opium alkaloids present in poppy seeds (morphine, codeine, and thebaine) respond to thermal treatments and how to best optimize these conditions to maximize their degradation. After characterizing the major opium alkaloids in a sample of commercially available poppy seeds, two types of seeds were selected for further experiments determining the thermally-driven decomposition kinetics of the three major opium alkaloids. These experiments were then followed by a determination of how opium alkaloids respond under typical baking conditions in a model bakery product, as well as during steam and washing treatments.

MATERIALS AND METHODS

Chemicals

Optima-grade acetonitrile and formic acid were purchased from Thermo Fisher Scientific (Waltham, MA, USA). Deionized (DI) water (18.2 MΩ cm−1 at 25 °C) was obtained from a Milli-Q system (Millipore-Sigma, Burlington, MA, USA). Standards of morphine (1 mg mL−1 in MeOH), codeine (1 mg mL−1 in MeOH), thebaine (1 mg mL−1 in MeOH), morphine-D3 (100 μg mL−1 in MeOH), codeine-D3 (100 μg mL−1 in MeOH), and morphine N-oxide (100 μg mL−1 in MeOH), were all purchased from Sigma-Aldrich (St. Louis, MO, USA).

Poppy seed samples and opium alkaloid extraction

Commercially available poppy seeds (n = 15) were purchased from online retailers. Sample portions were arbitrarily coded from S-1 through S-15. Opium alkaloids from poppy seeds were extracted from a procedure adapted from a previously reported method.20 Briefly, 5.0 g of seeds were weighed on a top-loading balance (Sartorius; Goettingen, Germany) and placed in a 50 mL polypropylene centrifuge tube (Nunc; Rochester, NY, USA). Poppy seeds were extracted by the addition of 25 mL solvent mixture, which consisted of 0.1% formic acid in acetonitrile/water (80/20; v/v), to the seeds in a centrifuge tube. The tube was then placed in a GenoGrinder automated shaker (SPEX SamplePrep; Metuchen, NJ, USA) for 5 min at 550 rpm. The solvent was decanted, and the sample was reextracted using another 25 mL of extraction solvent. The supernatants were pooled, briefly vortexed, and then filtered through a 0.45 μm PTFE filter (Agilent Technologies, Santa Clara, CA, USA). Filtered extract (50 μL) was combined with 900 μL DI water and 50 μL of 1 μg mL−1 morphine-D3 (used as an internal standard to monitor detector response), and then dispensed into a LC-MS vial (Waters Co., Bedford, MA, USA). Extraction recovery was assessed by spiking a set of three poppy seed samples with 200 μL of 100 μg mL−1 morphine-D3 and then carrying out the extraction procedure stated above.

Poppy seed thermal treatments

After an initial screening for opium alkaloids, S-6 and S-13 poppy seeds containing relatively lower and higher concentrations of morphine, respectively, were selected for thermal processing experiments. Poppy seed samples for thermal treatments were weighed on a foil weight boat (Thermo Fisher Scientific) before being placed in an Isotemp circulating oven (Fisher Scientific; Hampton, NH, USA). Independent kinetic timepoint replicate poppy seed samples (n = 3) were treated for 15, 30, 60, 90, and 120 min at 120, 160, 180, and 200 °C. Timing for the thermal treatment began after the surface of the seeds reached the treatment temperature, which was determined using an infrared thermometer (Etekcity Lasergrip; Anaheim, CA, USA). The come-up time to reach the experimental temperature was 5–7 min. After the thermal treatment, poppy seeds were then extracted as described above.

Steam and washing treatments

For steam treatment experiments, a layer of S-6 and S-13 poppy seeds (5.0 g) were placed on a stainless-steel wire fine mesh screen that was positioned over a 1 L glass beaker containing boiling water. The steaming occurred for 30 min, after which the poppy seeds were collected and extracted as previously described. For the washing experiments, 5.0 g of poppy seeds were mixed with 100 mL of room temperature DI water (22 °C) for 5 min using a magnetic stirrer, briefly centrifuged, and then seeds and wash water were collected separately for analysis.

Model baked product

In order to determine the effect of baking on opium alkaloids, a muffin was selected as a model baked product due to it being used in previous research for experiments involving chemical contaminants.21, 22 Batter for one muffin was prepared by mixing 30.0 g of muffin mix (Krusteaz, Seattle, WA, USA) with 15.0 g of DI water directly in a muffin baking tin. Then, either 5.0 g poppy seeds were incorporated directly into the batter or 2.5 g poppy seeds were applied to the surface of the batter. The muffin tin was placed in an Isotemp circulating oven for 16 min at 200 °C. Muffins were then cooled in the baking tin for 5 min before being removed. A thermocouple equipped with a K-type probe (PerfectPrime; Rockaway, NY, USA) was inserted into the center of the muffin at the start of the baking period to record the temperature at the core of the muffin. The surface temperature of the muffin was determined at the end of the 16 min baking period using an infrared thermometer. After baking, the entire muffin was homogenized with 30.0 mL DI water. A matrix-matched control was produced by homogenizing a “blank” baked muffin with either 5.0 or 2.5 g of untreated poppy seeds. A portion of the resulting slurry (15.0 g) was then extracted using the above procedure, with the modification that a total of 45 mL of extraction solvent was used and the sample was centrifuged for 5 min at 3,000 rpm to facilitate separation of the solids. The resulting extract was then prepared for analysis as described in the following section.

UPLC-MS/MS analysis for opium alkaloids

An ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method to quantify the three major opium alkaloids was modified from previously published reports.20, 2325 Separations were achieved using a Waters Acquity UPLC system with a C18 ethylene bridged hybrid column (150 × 2.1 mm, 1.7 μm; Waters Co.) at 40 °C and was in line with a Waters TQD mass spectrometer. Mobile phase A was aqueous 0.1% formic acid (v/v) and mobile phase B was acetonitrile with 0.1% formic acid (v/v). The gradient was set as: initial conditions (0 min), 10% B; 4 min, 70% B; 4.2 min, 100% B; 4.3 min, 10% B; 6 min, 10% B. 5 μL of sample was injected. The mass spectrometer was in positive ionization selected reaction monitoring mode with the following mass transitions used to quantitate the analytes: m/z 286 → 201 (morphine), m/z 289 → 165 (morphine-D3), m/z 300 → 154 (codeine), and m/z 312 → 251 (thebaine). Qualifier mass transitions were set as: m/z 286 → 165 (morphine), m/z 300 → 215 (codeine), and m/z 312 → 266 (thebaine). Other relevant mass spectrometer parameters were as follows: capillary voltage, 3.1 kV; cone voltage, 30 V; source temperature, 125 °C; desolvation gas temperature, 350 °C; desolvation gas, 500 L h−1; cone gas, 50 L h−1; and collision gas, 0.13 mL min−1. Method detection and quantitation limits were estimated by determining the signal-to-noise ratio (SNR) by the peak-to-peak method and then calculating 3× and 10× the SNR of the analyte responses for detection (LOD) and quantitation limits (LOQ), respectively. Data processing was conducted using MassLynx workstation software version 4.1 (Waters Co.) with results exported as Excel worksheets (Microsoft Office, Microsoft Co., Redmond, WA, USA).

Data and statistical analyses

All trials were repeated three times, and data are presented as means ± standard deviation (SD). Data analysis for degradation under thermal treatment was performed by calculating the percent of each opium alkaloid compound remaining in samples and plotting it as a function of time to form an inactivation curve26.The natural logarithm of the first-order rate constant was plotted against inverse temperature to form an Arrhenius curve. From this, the slope parameter was determined using linear regression to obtain the activation energy (Ea) of each opium alkaloid compound for the two poppy seed samples tested.27 Statistical analysis was performed using JMP 13 (SAS Institute, Cary, NC, USA). One-way ANOVA followed by pairwise mean comparisons using the Tukey-Kramer post-hoc correction was used to determine significant differences (P < 0.05) between more than two treatments. Otherwise, a two-tailed t-test was used to determine significance. Data with residuals not normally distributed underwent a Box-Cox transformation before statistical analysis.

RESULTS

UPLC-MS/MS analysis of poppy seed samples for opium alkaloids

Analysis of morphine, codeine, and thebaine (Figure 1A) exhibited a highly linear response (R2 > 0.9999) using this method in the range of 1–1,000 ng mL−1. This method also resulted in good chromatographic separation of the analytes (Figure 1B). LOD and LOQ were estimated to be 0.2 and 0.8 pg-on-column for morphine, 0.2 and 0.6 pg-on-column for codeine, and 0.7 and 2.3 pg-on-column for thebaine, respectively. Extraction recovery of morphine-D3 was found to be 95 ± 7%. Figure 1C displays the concentrations of the three major opium alkaloids in the analyzed poppy seed samples (see Supplementary Table 1 for numerical values). Overall, there was a large range of opium alkaloid concentrations present in the 15 samples. Morphine ranged from 3.6–261 mg kg−1, codeine from 1.9–378 mg kg−1, and thebaine from 8.1–217 mg kg−1. The overall mean and median of the samples were 73 and 19 mg kg−1 for morphine, 162 and 115 mg kg−1 for codeine, and 116 and 132 mg kg−1 for thebaine. Codeine values were negatively correlated with morphine (R = 0.52; P < 0.05), but thebaine did not exhibit such a relationship.

Figure 1.

Figure 1.

(A) Chemical structures and (B) representative normalized UPLC-MS/MS chromatograms of the target opium alkaloids in poppy seed samples. (C) Concentrations of the three major opium alkaloid compounds in a convenience sample of 15 poppy seeds. Values are shown as means ± SD (n = 3).

It should be noted that a 5 g sample of poppy seeds was necessary for extraction since increased analyte variability was observed with a smaller sample size. This was likely due to natural variation of opium alkaloids in the samples and is consistent with previous reports.20

Effect of thermal treatments on degradation of opium alkaloids

Poppy seed samples S-6 and S-13 were selected to undergo further experiments to model opium alkaloid degradation in samples with relatively low (14.7 ± 4.2 mg kg−1) and high (210.0 ± 19.6 mg kg−1) morphine concentrations, respectively. Figure 2 displays a plot of the effect of time and temperature on the degradation of the three major opium alkaloids in samples S-6 and S-13. The results overall indicated that the opium alkaloid degradation followed apparent first-order kinetics within the temperatures tested (120–200 °C). Several experimental time points exhibited relative error greater than 30% between replicates, which was especially apparent for morphine in sample S-6 (Figure 2A). As noted in the previous section, this variation was likely due to sample heterogeneity and has been noted in other reports.20 Table 1 contains the first-order degradation rates (k) of the opium alkaloids calculated from the data in Figure 2. These data were used to calculate the half-life of the compounds at the tested temperatures, as shown in Table 2. At 200 °C, thebaine exhibited the shortest half-life of approximately 3 min, while codeine and morphine were 32–39 min across both sample types. Post-hoc pairwise mean comparisons of Ea (Table 2) in sample S-6 revealed that codeine had a value significantly (P < 0.05) shorter than either thebaine or morphine. Similarly, codeine exhibited the lowest Ea value in sample S-13. In contrast, the compound with the highest Ea across both sample types was thebaine.

Figure 2.

Figure 2.

Effect of thermal treatment on opium alkaloid retention in poppy seed samples. (A) Morphine retention in S-6 (B) Codeine retention in S-6 (C) Thebaine retention in S-6 (D) Morphine retention in S-13 (E) Codeine retention in S-13 (F) Thebaine retention in S-13. Values are shown as means ± SD (n = 3).

Table 1.

First-order degradation rate constants of the three major opium alkaloids in two poppy seed sample types under thermal treatment.a

Compound 160 °C (min−1) 180 °C (min−1) 200 °C (min−1) ANOVA P value
S-6 Poppy seed sample (k × 10 −3 )
Morphine 5.73 ± 1.53 B 8.27 ± 2.81 B 20.8 ± 0.9 A P < 0.01
Codeine 7.27 ± 0.75 B 7.90 ± 1.11 B 20.6 ± 1.2 A P < 0.001
Thebaine 13.2 ± 1.18 C 26.6 ± 1.25 B 218 ± 14.0 A P < 0.001
S-13 Poppy seed sample (k × 10 −3 )
Morphine 2.97 ± 1.00 B 9.10 ± 1.87 AB 19.1 ± 6.7 A P < 0.01
Codeine 4.80 ± 0.17 B 9.90 ± 1.18 B 22.3 ± 5.2 A P < 0.01
Thebaine 13.3 ± 4.4 C 37.6 ± 2.6 B 254 ± 5.3 A P < 0.001
a

Values are presented as means ± SD. Different letters within a row indicate significant (P < 0.05) pairwise difference with Tukey-Kramer post-hoc correction. Note that rate constants at 120 °C were not calculated due to no significant degradation during the experimental time period.

Table 2.

Half-life and activation energies of the three major opium alkaloids in two poppy seed sample types under thermal treatments.a

Compound 160 °C 180 °C 200 °C Ea (kJ mol−1)b
P-6 Poppy seed sample (min)
Morphine 127 ± 32.0 89.7 ± 25.8 33.4 ± 1.8 94.0 ± 15.5 A
Codeine 96.1 ± 10.6 89.0 ± 13.1 33.7 ± 2.4 44.0 ± 2.2 B
Thebaine 52.8 ± 4.6 26.1 ± 1.2 3.20 ± 0.3 118 ± 6.6 A
P-13 Poppy seed sample (min)
Morphine 250. ± 74.4 78.6 ± 17.9 39.2 ± 12.8 79.4 ± 25.7 B
Codeine 145 ± 5.1 70.7 ± 8.8 32.2 ± 6.7 59.7 ± 3.17 B
Thebaine 56.7 ± 21.2 18.4 ± 1.2 2.73 ± 0.1 127 ± 14.8 A
a

Values are presented as means ± SD. Different letters indicate within activation energy column indicate a significant (P < 0.05) pairwise difference with Tukey-Kramer post-hoc correction.

b

Activation energy (Ea) was calculated without kinetic values obtained at 120 °C due to no significant degradation observed during the experimental time period.

Effect of steam and washing treatments on opium alkaloid concentrations

Figure 3 shows the effect of steam and washing treatments on levels of opium alkaloid concentrations in S-6 and S-13 poppy seed samples. Figure 3A indicates that there was no significant (P > 0.05) effect of a 30 min steam treatment on sample S-6, while 3B indicates that the steam treatment significantly (P < 0.05) decreased morphine concentrations in S-13 by 21%. Figure 3C and 3D show the effect of a 5 min water washing treatment, which indicated a significant (P < 0.05) reduction in opium alkaloid levels in both poppy seed samples. For sample S-6, morphine, codeine and thebaine were reduced by approximately 80%, 75%, and 60%, respectively, after the wash treatment; for S-13, morphine, codeine, and thebaine were reduced by 79%, 69%, and 46%, respectively. Mass balance of the summation of the major opium alkaloids in the washed poppy seed sample S-6 and wash water was calculated to be 97.2 ± 23.6%, 98.4 ± 9.9%, and 75.9 ± 9.5% for morphine, codeine, and thebaine, respectively. Mass balance of sample S-13 and wash water was determined to be 102 ± 11.0%, 115 ± 12.1%, and 88.1 ± 12.8% for morphine, codeine, and thebaine, respectively.

Figure 3.

Figure 3.

Effect of steam and washing treatments on retention of opium alkaloid concentrations. (A) S-6 30 min steam treatment (B) S-13 30 min steam treatment (C) S-6 5 min washing treatment (D) S-13 5 min washing treatment. Values are shown as means ± SD (n = 3). Calculation of significant differences (P < 0.05) were measured using a two-tailed t-test. *P < 0.05; **P < 0.01.

Effect of opium alkaloids in a model baked product

Opium alkaloids were found to be stable after undergoing thermal treatment in a baked product model (Figure 4; see Supplementary Figure 1 for images of baked muffins). After 16 min of baking at 200 °C, Figure 4A and 4B indicate that there was no significant (P > 0.05) differences in opium alkaloid concentrations when either sample S-6 or S-13 was incorporated into the model baked product. Similarly, no reduction in opium alkaloid concentrations were observed for poppy seeds applied to the surface of the muffin (Figure 4C and 4D). Temperatures recorded at the core of the muffin indicated that it reached 99.6 ± 1.7 °C at 8 min and remained at this temperature until the baking was complete at 16 min. The temperature at the surface of the muffin determined at the end of the baking period was 136 ± 1 °C.

Figure 4.

Figure 4.

Retention of opium alkaloids in a model baked product (muffin) prepared with poppy seeds. (A) Muffin with incorporated S-6 poppy seeds (B) Muffin with surface addition S-6 poppy seeds (C) S-13 poppy seeds baked with incorporated poppy seeds (D) S-13 poppy seeds with surface addition. Values are shown as means ± SD (n = 3). Calculation of significant differences (P < 0.05) were conducted using a two-tailed t-test.

DISCUSSION

Due to the potential for poppy seeds to contain elevated concentrations of opium alkaloids, we tested various processes to reduce levels of these compounds. We first performed an analysis of the three major opium alkaloids found in samples of poppy seeds obtained from online retailers and found a large variation of the opium alkaloid concentrations present in the samples. As a comparison, data published in 2005 from the German Federal Institute for Risk Assessment (Bundesinstitut fur Risikobewertung; BfR) indicated that poppy seed samples contained levels ranging from 0.1–620 mg kg−1 morphine, 0.1–57.1 mg kg−1 codeine, and 0.3–41 mg kg−1 thebaine. A separate analysis of opium alkaloids in poppy seeds performed by the Hungarian Food Safety Office found maximum concentrations of 530, 60, and 120 mg kg−1 for morphine, codeine, and thebaine, respectively.28 An analysis of blue poppy seeds (n = 32) from 2018 found concentrations ranged from 0.2–241 mg kg−1 for morphine, < 0.1–348 mg kg−1 for codeine, and < 0.1–106 mg kg−1 for thebaine.20 Even variation within a sample type can be large, as noted by previous research stating that relative standard deviation can reach as high as 40%.20 The present analysis found morphine values similar or lower than previously reported, but the maximum codeine value was 6-fold greater than highest value reported by BfR, and the maximum thebaine concentration was approximately two-fold greater than the highest value reported by two different authors.20, 28

It is interesting to note the high concentrations of thebaine in certain samples, since it is a precursor to codeine and morphine in the biosynthetic pathway of poppy.29 While there was no correlation between thebaine and the other opium alkaloids analyzed, the negative relationship between codeine and morphine may reflect codeine being the precursor to morphine in the biosynthesis pathway. Thebaine is not known to have analgesic or other pharmacological properties in humans, but since there are generally limited data on the toxicity of this compound, it is still important to characterize the levels of this compound in poppy seeds and to determine how it is affected by thermal treatments due to potential safety concerns.18 Additionally, this compound is important to monitor since thebaine can be a precursor in the commercial synthesis of opiate compounds.1

The results from the heat treatment experiments indicated that the three major opium alkaloids are relatively stable. At 120 °C, minimal, if any, alkaloid degradation was observed after 120 min. With the experimental temperature at 200 °C, the half-life of morphine and codeine was found to be approximately 32–39 min, while thebaine was only 3 min. As a comparison, a previous report found that 80–90% of morphine and codeine degraded after 20 min at 220 °C, although the actual starting opium alkaloid concentration was not indicated.30 Use of heat treatments in this range of temperatures to promote opium alkaloid degradation would not likely be useful, as they will likely affect the sensory aspects of poppy seeds.

Morphine has been shown to undergo pseudo first-order thermal degradation by an oxidative mechanism.26 Similarly, thermal degradation of codeine follows first-order kinetics.31 Oxidation of morphine has been shown to yield degradation products such as the pharmacologically active compound morphine N-oxide and pseudomorphine, which is not pharmacologically active. An exploratory analysis of thermally treated samples detected an ion with a mass consistent with the molecular weight of morphine N-oxide, but these results were inconclusive due to coelution of this compound with morphine. Future work should attempt to identify and quantify opium alkaloid degradation products in thermally treated samples.

Calculation of the Ea of the opium alkaloid compounds indicated that thebaine in both poppy seed samples was most sensitive to temperature increases, while codeine was least affected. Although Ea values for opium alkaloids in a poppy seed matrix have not been previously reported, the pharmaceutical literature provides information on the pure compounds.26 Morphine in solution was determined to have an Ea of 95 kJ mol−1, which is comparable to the values determined in the present experiments across the two types of poppy seeds (80–94 kJ mol−1). Codeine sulfate Ea in solution was determined to be 88 kJ mol−1,31 which is greater than the Ea determined by our experiments (44–60 kJ mol−1). Codeine in aqueous solution is reported to be more sensitive to thermostress than in its solid state, which could explain the lower observed Ea in our experiments.31 Differences in chemical behavior between an alkaloid in solution and in the context of a food are to be expected, since factors such as oxygen and water exposure could be markedly different.

The experiments evaluating the impact of baking on opium alkaloids concentrations in poppy seed muffins showed no significant effects. Food processing, including baking, has previously been reported to reduce morphine from poppy seeds by up to 90% based on limited experiments.32 One possible reason for a divergence in these results may be related to the specifics of the baking process in the experimental design. In a publication that reported significant reductions in opium alkaloid concentrations in baked products, the authors followed a traditional German recipe where the poppy seeds were soaked for a period of time in a mixture of milk, table sugar, and egg before the cooking process occurred.30 The authors reported that only 10–50% of morphine and codeine was recovered after baking the poppy seed mixture for 20 min at 180 °C, while we observed no significant differences after baking for 16 min at 200 °C. Although not directly tested, it is possible that the soaking treatment may have affected the stability of the opium alkaloids during the thermal treatment. In the present experiments, poppy seeds were added to the batter immediately before baking to more directly assess the effect of the thermal treatment. In addition, we compared the treated poppy seeds to an appropriate matrix-matched control in order to prevent differences in experimental values due to the background matrix. Further, we monitored the temperature of the core of the baked product, which did not exceed 100 °C. This temperature is consistent with other research that has used a muffin as a model baked product, where the high moisture content of the batter typically prevents core temperatures from exceeding the boiling point of water.22 In contrast, the surface of the baked product reached 136 °C at the end of the baking period. Our data from the kinetic experiments suggests that even the poppy seeds applied to the surface of the muffin would need to be treated for more than 2 h to reduce morphine and codeine concentrations by 50%. Overall, these experiments demonstrate the importance of characterizing heat transfer in a baking system when considering thermal degradation of select chemical compounds.

Washing poppy seeds with water has previously been shown to reduce the presence morphine concentrations by approximately 60–100%,16 but information on reduction of codeine and thebaine has not previously been published. Our results indicated that water washing for a relatively short time period reduced all three opium alkaloids by 46–79%. Morphine is somewhat water soluble (log P = 0.89), but concentrations of the more lipophilic compounds, codeine (log P = 1.19) and thebaine (log P = 1.53), were reduced by the washing treatment. Since analysis of the wash water and the washed seeds showed high mass balance for morphine and codeine (~80–100%) and good mass balance for thebaine (~70–80%), the compounds were likely only removed from the surface of the seed by dissolution and did not undergo degradation. While we only tested the effect of room temperature water washing on reduction of opium alkaloids, other research found that there was no difference in morphine, codeine, and thebaine concentrations of a water extraction performed at 23 °C versus 94 °C.12 Results on the effect of a steam treatment found a moderate 21% reduction in morphine in one sample type (S-13). However, use of steam for this period of time (30 min) or direct water washing may not likely be used in an industrial setting since spice suppliers often avoid high moisture environments to prevent microbial growth.5

The current study examined the effect of thermal treatments, baking, and washing treatments on the morphine, codeine, and thebaine concentrations in two poppy seed samples containing different initial levels of opium alkaloids. These data were used to fully characterize the thermal degradation kinetics of the three major opium alkaloids in poppy seed samples. Thebaine exhibited the greatest reduction in response to thermal treatment, followed by morphine and then codeine. Water wash treatments were effective in reducing opium alkaloid levels, in contrast to the steam treatments. Baking experiments using muffins as a model baked product demonstrated the stability of opium alkaloids, as there was no significant reduction in these compounds after baking. Information obtained from this research will be useful to both industry and governmental bodies in order to help evaluate control conditions that spice suppliers use to reduce opium alkaloids in poppy seeds supplied to the food industry and can also be used to assist in estimating consumer exposure to these alkaloid compounds.

Supplementary Material

Table S1

Supplementary Table 1. Concentrations of major opium alkaloids in poppy seed samples obtained from online retailers.

Figure S1

Supplementary Figure 1. Images of experimental poppy seed muffins.

Acknowledgments

The authors would like to thank Emily Pettengill (FDA/CFSAN/Office of Food Safety) for providing valuable feedback on the manuscript.

Footnotes

Declaration of interest

The authors have no competing interests.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Table S1

Supplementary Table 1. Concentrations of major opium alkaloids in poppy seed samples obtained from online retailers.

Figure S1

Supplementary Figure 1. Images of experimental poppy seed muffins.

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