Garlic: a potential food allergen?

Abstract

Background:

Garlic, Allium sateevum, is one of the most commonly used spices worldwide but a rare cause of immunoglobulin E (IgE) mediated allergy. Six garlic proteins have been associated with sensitization. Alliin lyase has been classified as the major garlic allergen and demonstrated to be heat labile. Thus, some patients with garlic allergy have reported the ability to ingest cooked garlic without symptoms.

Methods:

We report two cases of patients with reaction to garlic, the first to both raw and cooked garlic, and the second to only raw but not cooked garlic. We further examined the proteins found in raw, cooked, and powdered garlic by Sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE), then assessed the patients’ sera for IgE to these proteins with immunoblot.

Results:

We confirmed that most garlic proteins, to include alliin lyase are degraded with heat and discovered that garlic powder is most consistent with raw garlic on SDS-PAGE. In addition, we corroborated the potential for binding of serum IgE to a rare garlic allergen at ∼70 kDa and demonstrated its heat lability for the first time with immunoblot.

Conclusion:

These findings would suggest that patients with garlic allergy could ingest cooked garlic without symptoms but not raw or powdered forms. However, our patient with garlic sensitization reported symptoms with both raw and cooked garlic, which further illustrated the need for further studies.

Adverse food reactions can be classified as either food allergy or food intolerance. Food allergy is defined as an “adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food” whereas food intolerance is defined as “nonimmune reactions that include metabolic, toxic, pharmacologic, and undefined mechanisms.”¹ Garlic, Allium sateevum, is one of the most common garnishes used worldwide and known to cause dermatitis, urticaria, rhinitis, and asthma, most frequently secondary to occupational exposure.² Anaphylaxis to garlic is reported less frequently, although there are a few reports of immunoglobulin E (IgE) mediated allergy in the literature.²

Kao et al.² studied a small population of patients with garlic allergy from a region of Taiwan with garlic fields. Alliin lyase was determined to be the major garlic allergen, with a molecular weight of 56 kDa.² Later studies demonstrated that heat degraded the proteins into small fragments with molecular weights < 10 kDa.³ Five other garlic proteins (at ∼10–12, 20, 30, 40, and 75 kDa) have been associated with sensitization.^3–6 We present two cases that highlight the potential risk of garlic in individuals who are susceptible.

The first patient is a 25-year-old woman with a medical history of irritable bowel syndrome, allergic rhinitis, and moderate persistent asthma who presented with a history of abdominal cramping 30 minutes after ingestion of garlic, with spontaneous resolution of symptoms after 60 minutes. She experienced recurrence of these symptoms both with raw and cooked garlic. Serum IgE (sIgE) to garlic was positive at 3.88 kUA/L. The patient declined oral provocation.

The second patient is of a 23-year-old woman who was nonatopic and with a medical history of von Hippel-Lindau disease with renal cell carcinoma in remission who presented with urticaria, dizziness, diarrhea, abdominal pain immediately after ingestion of pasta with raw garlic. Her symptoms resolved within 30 minutes of taking an oral antihistamine. She reported recurrence of symptoms with raw garlic but not cooked garlic and continued to eat all other ingredients without reaction. The sIgE to garlic was not detectable (<0.1 kUA/L). Skin-prick testing results to garlic extract, raw garlic (R), cooked garlic (C) (which was baked at 350°F for 30 minutes), and garlic powder (P) were also negative. This patient also declined oral provocation.

We decided to investigate further by assessing the major proteins in different garlic preparations (R, C, and P), then compared patient sIgE binding patterns to extracted proteins from these samples. Proteins were extracted and lyophilized with equivalent concentrations assessed by the Lowry protein assay. Next, we performed an Sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) by loading garlic extracts (R, C, and P) onto wells in serial dilutions along with a protein marker. Prominent bands of raw garlic extract were noted at ∼5, 9, 23, 28, 39 and 50 kDa (Fig. 1A). A prominent band from the cooked preparation at ∼10 kDa was noted, which suggested the previously reported raw proteins are heat labile, including alliin lyase at 56 kDa. Powder extract had the same prominent bands as raw except for absent bands at 28 and 39 kDa. Alliin lyase has been reported to be the major garlic allergen, with a molecular weight of 56 kD. This same protein was visualized on our SDS-PAGE test results for raw and powder extracts but not for cooked extracts.

Figure 1.

Sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) (A) and immunoblot (B) incubated with serum from patient no. 1, serum from patient no. 2, and cord plasma (control). Pt = Patient; R = raw garlic; C = cooked garlic; P = garlic powder.

After twofold dilutions, the best protein band pattern was chosen for all three garlic preparations (concentrations: R, 2.5 µg/µL; C, 0.325 µg/µL; and P, 2.5 µg/µL) and then loaded into separate lanes (Fig. 1B). The protein bands were transferred onto a nitro cellulous membrane and incubated with serum from patient no. 1, serum from patient no. 2, and cord plasma (negative control). Lastly, these were incubated with tagged monoclonal antihuman IgE. IgE from patient no. 1 bound to a protein at ∼50 kDa in both the raw and powder lanes, consistent with IgE to alliin lyase. In addition, IgE from patient no. 1 bound to a protein at ∼70 kDa in only the raw extract, which has otherwise only been reported once in the literature.⁵ Binding at 70 kDa with cooked and powder extracts was not appreciated, which seems to be the first time that this garlic allergen has been assessed for heat lability with immunoblot. Theoretically, this may be a polymerized, previously known garlic allergen and only mass spectrometry could further delineate this band. There was no IgE binding to cooked garlic. Serum from patient no. 2 appreciated no IgE binding to any garlic proteins. No binding was noted for cord plasma, as expected.

Patient no. 1, who reported recurrent abdominal cramping after garlic ingestion and had garlic IgE demonstrated IgE binding on immunoblot to raw and powder extracts at ∼50 kDa where the major allergen, alliin lyase is found. In addition, IgE binding at ∼70 kDa on immunoblot was noted with only raw garlic. Consequently, we recommended that this patient abstain from raw in addition to powder garlic. There was no IgE binding appreciated to cooked garlic. This would infer that this patient could potentially eat cooked garlic without a reaction; however, because the patient also reported symptoms with cooked garlic, we hypothesize that differences in cooking preparation is likely playing a role. Furthermore, a limitation of our laboratory evaluation is that it did not investigate the temperature or time required to degrade alliin lyase or the 70 kDa protein. Patient no. 2, who reported symptoms more consistent with anaphylaxis, had a negative sIgE value to garlic. Her immunoblot was also negative to all three preparations. The mechanism for her reaction is undefined. However, because the sensitivity of our assays in unknown, it is possible that low levels of sIgE to garlic are present but remain undetected. Future investigation could include serial electrophoresis to increasing garlic concentrations. Both patients declined further evaluation with oral garlic food challenge.

CONCLUSION

Most garlic proteins, to include alliin lyase are degraded with heat. We report for the first time that a rare garlic allergen at 70 kDa is also heat labile, confirmed by immunoblot. Patients with garlic allergy could potentially ingest cooked garlic safely. However, the heat and length of time required to degrade allergenic garlic proteins is unknown and requires further investigation. Garlic powder (dehydrated pulverized garlic) is more consistent with raw garlic and includes the major garlic allergen, alliin lyase, although not the rare garlic allergen at 70 kDa. More investigation is required to fully assess the potential allergenicity of garlic.