Characterization of physicochemical and immunogenic properties of allergenic proteins altered by food processing: a review

Enning Zhou; Qiangqiang Li; Dan Zhu; Gang Chen; Liming Wu

doi:10.26599/FSHW.2022.9250095

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Open Access

Characterization of physicochemical and immunogenic properties of allergenic proteins altered by food processing: a review

Enning Zhou^{^a^,¹}, Qiangqiang Li^{^a^,¹}(), Dan Zhu^{^b}, Gang Chen^{^c}, Liming Wu^{^a}()

Institute of Apicultural Research, Chinese Academy of Agricultural Sciences, Beijing 100093, China

Department of Food Science, University of Otago, Dunedin 9016, New Zealand

School of Food and Health, Beijing Technology and Business University, Beijing 100048, China

¹ These authors contributed equally to this work.

Peer review under responsibility of Tsinghua University Press.

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Highlights

• Food processing can induce allergenic protein aggregation or denaturation.

• Structural change of allergen may lead to masking or destruction of epitopes.

• Improper food processing increases allergenicity by exposing allergen epitopes.

• Other food components may prevent the processing effect on allergen modification.

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Abstract

Food allergens are mainly naturally-occurring proteins with immunoglobulin E (IgE)-binding epitopes. Understanding the structural and immunogenic characteristics of allergenic proteins is essential in assessing whether and how food processing techniques reduce allergenicity. We here discuss the impacts of food processing technologies on the modification of physicochemical, structural, and immunogenic properties of allergenic proteins. Detection techniques for characterizing changes in these properties of food allergens are summarized. Food processing helps to reduce allergenicity by aggregating or denaturing proteins, which masks, modif ies, or destroys antigenic epitopes, whereas, it cannot eliminate allergenicity completely, and sometimes even improves allergenicity by exposing new epitopes. Moreover, most food processing techniques have been tested on purif ied food allergens rather than food products due to potential interference of other food components. We provide guidance for further development of processing operations that can decrease the allergenicity of allergenic food proteins without negatively impacting the nutritional profile.

Keywords

Food allergens Protein structural characterization Immunogenicity evaluation Food processing modif ication

References

[1]

R. Valenta, H. Hochwallner, B. Linhart, et al., Food allergies: the basics, Gastroenterology 148(6) (2015) 1120-1131. https://doi.org/10.1053/j.gastro.2015.02.006.

Processing technique	Technical principle	Allergenic food or protein	Technological parameters	Effects on protein properties	Reference
Tradition thermal treatment	Destroy the hydrogen and disulfide bonds, and the hydrophobic interaction forces of allergens, causing the changes in allergen conformation and allergenicity.	Peanut allergens(Ara h 1, Ara h 2)	Boiling at 100 ℃ for 2–4 h	Ara h 1 and Ara h 2 were significantly degraded	[20]
		Walnut allergens	Boiling at 100 ℃ for 20 min	IgE-binding ability of walnut allergens was reduced by 50%	[23]
		Walnut allergens	Baking at 160 ℃ for 15 min	No significant effect	[23]
		Rice allergens	Stewing at 100 ℃ for 5 min, drying at 100 ℃ for 30 min	Major allergens (14–16 and 26 kDa) significantly decreased	[129]
Microwave heating	Increase the temperature of food medium, changing protein conformation and allergenicity of the allergen.	Walnut allergens	500 W, 15 min	IgE-binding ability of walnut allergens was reduced by 30%	[23]
		Kiwi fruit allergens(Act d 2)	2.45 GHz, 75 ℃, 1–5 min	The α-helical content significantly decreased, and allergenicity decreased.	[28]
		Shrimp tropomyosin	2.45 GHz, 1000 W, 125 ℃, 15 min	Digestibility increased, allergenicity decreased.	[29]
Ohmic heating	Produce both thermal and electrical effects on allergens, changing the antigenic epitopes and allergenicity of allergens.	Soybean protein isolate(Gly m TI)	2–20 V/cm, 50 Hz, 90 ℃ for 10 min	Allergenicity of Gly m TI was reduced by 36%	[33]
		β-LG	4 V/cm, 25 kHz, 90 ℃ for 1 s	Allergenicity of β-LG decreased	[34]
		β-LG	4 V/cm, 25 kHz, 65 ℃ for 30 min	Allergenicity of β-LG increased	[34]
Ultrasonic treatment	Produce cavitation, thermal and mechanical effects to change the conformation and allergenicity of allergens.	Shrimp tropomyosin	20 kHz, 800 W, 15 min	Secondary structure (α-helix) changed, allergenicity reduced, digestibility increased	[36]
		Peanut allergens(Ara h 1, Ara h 2)	50 Hz, 1–5 h	Protein solubility increased, Ara h 1 significantly decreased, no significant change in Ara h 2	[38]
		Shrimp tropomyosin	20 kHz, 400 W, 50% duty cycle, 20 min	Allergenicity reduced by 76%, digestibility and peptide production increased	[39]
		Kiwifruit allergens(Act d 2)	20 kHz, 400 W, 50% duty cycle, 16 min	Levels of Act d 2 decreased by 50%, secondary structure (α-helix and β-sheet) changed, digestibility increased by 27%	[40]
Ultrahigh pressure treatment	Destroy non-covalent bonds such as hydrogen and ionic bonds in allergens, changing the tertiary and quaternary structures to reduce allergenicity of allergens.	Almond milk allergens	600 MPa, 30 ℃	Allergenicity significantly reduced	[26]
		Apple allergens	800 MPa, 80 ℃, 10 min	No significant effect on IgE-binding ability	[42]
		Apple allergens	800 MPa, 115 ℃, 10 min	IgE-binding ability significantly reduced	[43]
		β-LG	200–600 MPa, 30–68 ℃, 0–30 min	Antigenic properties gradually enhanced	[44]
		β-LG	600 MPa, 20 ℃, 10 min	Digestibility increased	[130]
		Peanut allergens	0.2 MPa, 134 ℃, 10–20 min	Allergenicity reduced by 78%	[131]
Microbial fermentation treatment	Decompose allergens into small peptides and amino acids to destroy the antigenic epitopes and spatial conformation of allergens.	Soybean meal allergens	37 ℃, 48 h, 10% inoculation quantity with Lactobacillus plantarum, Lactobacillus, or Saccharomyces cerevisiae	Total protein and amino acid levels of soybean meal significantly increased, IgE immunoreactivity reduced by 89%	[47]
		Soybean meal allergens	60% water content, 30 ℃, 6% Bacillus subtilis inoculated and grown for 24 h, then 3% Lactobacillus casei and 3%yeast inoculated and grown for 72 h	IgE levels in serum of mice stimulated by fermented soybean meal proteins significantly decreased	[48]
		Peanut allergens	Peanut pulp pressurized at 120 ℃ for 20 min, incubated with Bacillus natto at 37 ℃ for 12–60 h	Protein degraded, conformation changed, α-helixes decreased, protein size changed, IgE-binding ability decreased by 77%	[132]
Cold plasma treatment	Produce active substances to attack the amino acid side chains of allergens, destroy the epitopes, and reduce the allergenicity of allergens.	Peanut allergens(Ara h 1, Ara h 2)	52 kHz, 32 kV, 0–60 min	Relative α-helix content of Ara h 1 and Ara h 2 decreased, allergenicity decreased by up to 65% and 66%, respectively	[53]
		Tropomyosin from L. vannamei	Plasma was ignited in a premixed gas containing 98% argon and 2% oxygen, then blown through a quartz tube at 20 standard liters per min	Free sulfhydryl group content decreased, surface hydrophobicity increased, IgE- and IgG-binding ability decreased by 17.6% and 26.87%, respectively	[55]
		Cashew nut allergens	80 W, 50 kHz	IgE-binding ability of cashew allergens did not change	[56]
Covalent binding to dietary polyphenols	Form covalent binds with the amino acid side chains of allergens, altering allergen spatial conformation to change or mask the antigenic epitopes.	OVA	EGCG	IgE-binding capacity decreased	[60]
		OVA	Quercetin	OVA epitopes were destroyed, IgE-binding capacity was reduced	[63]
		β-LG	EGCG CA	β-LG spatial structure changed; IgE-binding ability decreased	[66]
		Peanut allergen (Ara h 1)	EGCG CA	Denaturation temperature decreased; IgE-binding capacity significantly decreased	[67]
Irradiation	Produce free radicals to attack the amino acid side chains of allergens, or generate energy to change the spatial conformation of allergens.	OVA	1 kGy	Allergenicity decreased by in vivo evaluation	[69]
		α-LA	10 kGy	Allergenicity decreased by in vivo evaluation	[70]
		Tropomyosin	7 kGy	Secondary structure changed, and the IgG-binding ability decreased by 59%.	[71]
Modified by glycosylation	Produce Maillard reaction to change the spatial structure and antigenic epitopes of allergens.	Tropomyosin	Glycosylation with glucose	Allergenicity decreased evaluated by cells	[72]
		Whey allergen	Glycosylation with dextran	Conformational epitope was lost and the IgE-binding ability decreased	[73]
		Chickpea albumin	Glycosylation with glucose	The allergic immune response was reduced in BALB/c mice.	[74]

Processing techniques	Advantages	Disadvantages	Reference
Tradition thermal treatment	Convenient, low-cost	Not applicable to allergens with high heat resistance, and nutrient loss	[17]
Microwave heating	Rapid, high efficiency	Uneven heat or partial overheating	[28]
Ohmic heating	Heat evenly and quickly	Lead to interaction between metal ions and food materials	[33]
Ultrasonic treatment	Safe, environmental-friendly, timesaving, low-cost	Intensity-dependent	[16,133]
Ultrahigh pressure treatment	High efficiency, low nutrient loss	Intensity-dependent	[16]
Microbial fermentation treatment	Improve nutritional properties and reduce anti-nutrient substances	Parameter-dependent, and bitter peptides production	[134]
Cold plasma treatment	Low residual, low energy input	Limited safety evaluation	[16,53]
Covalent binding to dietary polyphenols	Stable, and improve the added value of food	Harsh covalent reaction conditions	[62]
Irradiation	High energy penetration, large processing capacity, high efficiency	Potential safety hazards and nutrient loss	[135]

Protein detection technique	Food allergen	Modified condition	Structural characterization	Reference
Mass spectrometry (MS)	Almond (Pru du 6)	-	Conformational epitopes of Pru du 6 were mapped	[84]
	Cashew (Ana o 2)	-	Epitope-bearing segments were identified	[85]
	Wheat gluten	-	Wheat gluten peptides were identified and quantified	[86]
Circular dichroism spectrometry (CD)	β-LG	Covalent binding to CA	Relative content of α-helixes and β-sheets decreased, random coils increased, protein structure extended	[66]
	Tropomyosin from Exopalaemon modestus	Glycosylation with glucose	Relative α-helix content decreased from 78.7% to 18.5%; β-sheets, β-turns, and random coils increased from 0 to 20%, 5.1% to 21.7%, and 14.2% to 39.8%, respectively	[72]
	Egg white allergen	Microwave processing	Relative content of α-helixes decreased, significant increases in β-sheets and random coils	[87]
	Tropomyosin from Penaeus chinensis	Glycosylation with ribose, galacto-oligosaccharide, chitosan-oligosaccharide	Relative α-helix content decreased	[88]
	OVA	Covalent binding to CA	Relative content of α-helixes and β-sheets decreased	[95]
Fourier transform infrared spectrometry (FTIR)	β-LG	Covalent binding to CA	Amide Ⅰ bands moved from 1641.4 cm^-1 to 1642.4 cm^-1, amide Ⅱ bands moved from 1534.8 cm^-1 to 1537.0 cm^-1	[66]
	Shrimp tropomyosin	Microwave processing	Relative content of β-sheets increased, α-helix to β-turn ratio decreased, random coil content fluctuated	[68]
	Peanut allergens	Microwave processing	Relative content of α-helixes increased; random coils were eliminated	[91]
	Wheat gluten	High hydrostatic pressure (HHP)	β-Sheet to β-turn ratio increased, α-helix content decreased	[136]
Fluorescence spectrometry (FS)	Soybean 7S protein	Covalent binding to CA or EGCG	FS intensity of conjugated protein decreased; maximum emission wavelength was red-shifted	[64]
	β-LG	Covalent binding to plant dietary polyphenols	Maximum emission wavelength was red-shifted, FS intensity decreased, microenvironment of tyrosine residue changed	[66]
	WPI	Covalent binding to EGCG	Maximum emission wavelength was red-shifted 3 nm, FS intensity decreased significantly, polar microenvironment of main fluorophore tryptophan increased	[96]
	β-Conglycinin	High hydrostatic pressure	FS intensity significantly increased at 200–400 MPa	[97]
	SPI	Covalent binding to anthocyanins	Tertiary structure loosened, polypeptide chain stretched and was more easily hydrolyzed	[98]
Ultraviolet absorption spectrometry (UV)	β-Conglycinin	Heat treatment	UV absorption exhibited a slight increase at 65 ℃; absorption intensity then significantly decreased with increased temperature	[82]
	SPI	Covalent binding to anthocyanin-3-galactose; ultrasonic processing	UV absorption peak changed	[100]
	Zein	Covalent binding to EGCG	UV absorption peak changed	[137]
Differential scanning calorimetry (DSC)	OVA	Covalent binding to quercetin	Denaturation temperature and thermal stability of OVA–quercetin copolymer decreased	[63]
Differential scanning calorimetry (DSC)	β-LG	Covalent binding to CA	Denaturation temperature and thermal stability improved	[66]

Techniques	Primary structure	Secondary structure				Tertiary structure	Thermal stability
Techniques	Primary structure	α-Helix	β-Sheet	β-Turn	Random coil	Tertiary structure	Thermal stability
Mass spectrometry (MS)	√	×	×	×	×	×	×
Circular dichroism spectrometry (CD)	×	√	√	√	√	×	×
Fourier transform infrared spectrometry (FTIR)	×	√	√	√	√	×	×
Fluorescence spectrometry (FS)	×	×	×	×	×	√	×
Ultraviolet absorption spectrometry (UV)	×	×	×	×	×	√	×
Differential scanning calorimetry (DSC)	×	×	×	×	×	×	√