Photo Credit: Sagarmanis

Researchers found that frozen fruit and vegetable juice was comparable to fresh fruit and vegetables for conducting year-round food allergy screening.

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A team of researchers recently evaluated whether frozen fruit and vegetable juice was a comparable alternative to fresh food for conducting prick-to-prick (PTP) and skin prick tests (SPT).

“Some fresh food allergens lose their allergenic properties rapidly during the extraction process,” wrote Severina Terlouw and colleagues. “Furthermore, not all fruits and vegetables can be bought throughout the whole year. Corresponding commercially available extracts of fruit and vegetables have a low allergenic activity; the proteins are destroyed during the manufacturing process of the extracts.”

However, frozen aliquots could be defrosted and individually stirred for use in SPTs, allowing clinicians to perform testing at any time. Terlouw and colleagues analyzed whether frozen juice from apples, kiwis, peaches, tomatoes, and carrots could be used in SPTs as an alternative to PTP tests performed with fresh foods. They published their findings in Clinical and Translational Allergy.

Selecting Patients

The researchers included 36 patients in the study. The participants’ average age was 40.7 years (range, 22-68), and they were primarily women. All patients reported having at least one inhalant allergy, including grass pollen (67%), birch pollen (94%), house dust mites (42%), and pets (53%). Most patients (92%) reported using some form of anti-allergy medication, largely antihistamines (89%), but stopped taking them 72 hours prior to the study.

The most common food allergic symptom was oral allergy syndrome with/without gastrointestinal symptoms (94%), followed by respiratory symptoms (44%) and skin reactions (33%).

“The total number of patients who experienced symptoms after ingestion of the specific food allergen were: 27 (75%) for apple, 19 (53%) for kiwi, 16 (45%) for peach, nine (25%) for tomato, and eight (22%) for carrot. The total number of patients consuming the specific food allergen without any symptoms was nine (25%) for apple, 14 (39%) for kiwi, 13 (36%) for peach, 25 (69%) for tomato, and 22 (61%) for carrot,” the researchers reported.

Comparing Test Accuracies

The investigators conducted 360 tests, including 180 SPTs with frozen food and 180 PTP tests with fresh food. Per the findings, the mean Histamine Equivalent Prick indices for SPT compared with PTP were:

• 86 versus 0.94 for apple
• 35 versus 0.65 for kiwi
• 10 versus 1.14 for peach
• 20 versus 0.22 for tomato
• 43 equal for carrot

The ICCs between SPT and PTP were moderate for apple (0.72) and kiwi (0.71), strong for peach (0.75) and tomato (0.89), and very strong for carrot (0.94).

“These differences can be due to different methods applied to obtain the fruit extracts. Another aspect could be due to the rapid degradation of less stable allergens when being extracted and exposed to a different pH environment. Similarly, freezing and thawing could also destroy some of the food allergens in fruits such as apples and kiwifruit,” the researchers noted. 

The researchers compared food allergen-specific symptoms obtained through patient questionnaires and reported the following accuracies for the SPT and PTP tests:

• 78 equal for apple
• 41 vs 0.50 for kiwi
• 52 equal for peach
• 71 vs 0.68 for tomato
• 57 equal for carrot

The test methods showed comparable sensitivity and specificity for apples, peaches, tomatoes, and carrots. However, the kiwi tests showed discrepancies in mean and range Histamine Equivalent Prick index, sensitivity and specificity.

“This could be a consequence of the fact that by performing the PTP test, we chose to prick the needle into the fresh, unpeeled kiwi near the stalk just under the fruit peel, where most proteins are located. For the SPT with frozen juice, the kiwi juice was obtained from the whole kiwi.”

Testing Year-Round

The study was limited by its small sample size, potential cross-reactivity with birch pollen, and lack of comparison with the double-blind, placebo-controlled food challenge (DBPCFC).

“Comparing SPT results with a food allergy-focused clinical diet history questionnaire must be seen as a first step in the diagnosis of a food allergy. Although the use of the DBPCFC presumably will change the sensitivity and specificity calculations, the main goal of this study was to compare the SPT and PTP test results,” Terlouw and colleagues noted.

The researchers also did not perform oral provocation tests, so it was unclear whether the patients could tolerate frozen apples, kiwis, peaches, tomatoes, or carrots.

Nevertheless, Terlouw and colleagues advised that frozen juice could be a suitable alternative to fresh foods when conducting allergy tests.

“We recommend the use of frozen juice of fruits and vegetables. The juice was stored in small aliquots at −20°C and could easily and quickly be defrosted before single use in SPTs. This enables the allergist to perform SPTs throughout the year, without limitations of the availability of seasonal fruits and vegetables,” the authors concluded.