Determination of histamine content in vegetable juices by using direct and competitive immunosensors

Figures & data

Figure 1. The schematic arrangement of an optical waveguide lightmode spectroscopy immunosensor. The sensor is constructed of an optical waveguide layer (A) on top of a glass support (B) and of a fine optical grating made in the waveguide. When polarised laser beam (C) (typically He–Ne laser with 632.8 nm wavelength) reaches the grating, it is diffracted. The angle of diffraction (D) depends not only on the optical parameters of the sensor, but also on the refractive index of the covering medium. The waveguide is gradually rotated around its rotation axis (E), and when the diffracted beam is incoupled into the waveguide, it is propagating towards the edge of the sensor through multiple internal reflections. The intensity of the incoupled light is measured with a photodiode (F). The light intensity vs. incoupling angle (α) follows a sharp, resonant peak profile. By measuring the incoupling angle vs. time, one can follow refractive index changes in real time. The change of the effective refractive index due to the presence/association/dissociation of the analyte molecules (G) at the sensor surface results in a shift in the incoupling resonance angle. Association/dissociation of molecules on the surface of the sensor chip can be followed with high precision without labelling and in real time by continuously measuring the change in the incoupling angle.

Figure 2. Calibration curve of the direct histamine detection method for standard solutions.

Figure 3. Immobilisation process of histamine-BSA conjugate and measuring cycles of different dilutions of anti-histamine antibody (A – distilled water, B – glutaraldehyde (2.5%), C – buffer, D – histamine-BSA conjugate (10 µg mL⁻¹), E – HCl, 50 mM, 1 – 1:2000 dilution, 2 – 1:2000 dilution, 3 – 1:1000 dilution of antibody).

Figure 4. Choice of optimal monoclonal antibody dilution for competitive measurement of histamine.

Figure 5. Calibration curve of the competitive histamine detection method for standard solutions.

Figure 6. Antigen selectivity of OWLS immunosensor.

Table 1. The concentrations of the different biogenic amines determined by HPLC.

Samples	Histamine mg L^−1	Putrescine mg L^−1	Cadaverine mg L^−1	Agmatine mg L^−1
Leavened cucumber	75.6	853.7	188.9	n.d.
Sauerkraut 1	44.2	115.9	17.3	n.d.
Sauerkraut 2	7.9	31.1	117.1	n.d.
Pickles 1	2.8	67.4	5.4	n.d.
Pickles 2	19.8	54.5	4.4	n.d.
Fermented vegetable juice 1	n.d.	3.3	113.1	141.9
Fermented vegetable juice 2	n.d.	3.1	118.2	149.6
Fermented vegetable juice 3	n.d.	3.6	142.2	175.7

Figure 7. Histamine content in different samples measured by HPLC and OWLS immunosensor (A – Leavened cucumber; B – Sauerkraut 1; C – Sauerkraut 2; D – Pickles 1; E – Pickles 2; F – Fermented vegetable juice 1; G – Fermented vegetable juice 2; H – Fermented vegetable juice 3).