Comparison of manual and automatic sampling for monitoring ochratoxin A in barley grain

Figures & data

Figure 1. Sampling schemes for a comparison of manual and automatic sampling of OTA in barley. Figures illustrate the positions of incremental samples in the container. (a) Increments during the monitoring of OTA formation where open and filled circles indicate aggregate samples 1 and 2, respectively. (b) End-point manual sampling where aggregate samples are formed from incremental samples collected at positions 1–8. (c) Formation of eight aggregate samples by interpenetrating automatic sampling.

Figure 2. OTA estimations in barley, experimental design and procedures for sampling and sample preparation. Aggregate samples were formed by manual and automatic sampling. After sample splitting, milling and reduction, four test samples were obtained in the manual sampling procedure and two test samples in the automatic sampling, respectively. Each test sample was analysed twice for OTA concentration by means of immunoaffinity clean up and HPLC-FLD. Brackets indicate total uncertainty (u _t) and uncertainty from sampling with automatic (u _as) or manual (u _ms) sampling, sample reduction (u _r), subsampling (u _sub1) and analysis (u _a) (analysis = subsampling2 + extraction + HPLC).

Figure 3. Monitoring of temperature, moisture content and concentration of OTA (µg kg⁻¹) in barley inoculated with Penicillium verrucosum at ambient temperature. Bars represent OTA concentration of aggregate samples (A, B), respectively. Graphs indicate the temperature (°C) near the surface and in the centre of the lot and the average moisture content (%).

Table 1. Concentrations of OTA (µg kg⁻¹) at the end-point sampling (week 10) in individual analytical samples from manual and automatic sampling.

Aggregate sample	Analytical sample								Mean	SD
	a1a	a1b	a2a	a2b	b1a	b1b	b2a	b2b
Manual
#1	35.50	31.95	41.75	28.90	30.72	30.41	37.79	39.09	34.51
#2	2.02	2.21	3.82	3.56	1.86	2.13	2.79	2.84	2.65
#3	11.77	7.69	12.31	11.62	8.87	9.72	13.58	15.66	11.40
#4	14.64	19.02	16.81	16.93	18.91	15.40	15.68	15.87	16.66
#5	35.06	35.51	27.31	23.68	18.29	19.03	22.39	18.32	24.95
#6	90.23	78.50	86.56	67.05	77.51	79.87	73.83	62.15	76.96
#7	9.89	10.24	17.40	19.44	13.93	12.45	22.59	14.23	15.02
#8	23.55	28.55	17.98	15.08	20.89	18.21	19.17	20.13	20.45
								Batch	25.33	22.88
Automatic
#1	21.57	17.53	12.36	18.34					17.45
#2	14.74	23.89	15.85	24.84					19.83
#3	14.07	15.70	18.66	14.39					15.70
#4	20.08	18.10	12.37	14.64					16.30
#5	11.12	12.79	14.13	17.67					13.93
#6	21.87	21.26	13.51	18.30					18.74
#7	17.70	20.14	22.46	21.58					20.47
#8	18.15	18.25	18.17	18.44					18.25
								Batch	17.58	2.20
Note: Highest and lowest values are indicated by bold font.

Table 2. ANOVA results for manual and automatic sampling of OTA in barley.

Source of variability	Relative uncertainty at p = 0.05^a	Percentage variance contribution to total variance^b
		… versus manual (lower estimate)	… versus automatic
Manual sampling: total (u t)	114–118%	100%	–
Manual sampling (u ms + u r)	110%
Sample reduction (u r)	17%
Automatic sampling: total (u t)	43%	–	100%
Automatic sampling (u as)	13%
Preparation and analysis (u sub1 + u a)^c	37–42%	11%	76%
Sample preparation only	37–42%	11%	76%
Chromatography (u c)	1.5%	0.017%	0.12%
Sub-sampling1 (u sub1)	31–34%	7.06%	51%
Analysis (u a) (fractional shovelling)	22–26%	3.6%	26%
Analysis (u a-spoon) (spooning)	32–36%		48–53%
Notes: ^a100*2*u/x.
^b u2/u t2.
^cAlternative estimates from manual sampling or from all 24 sub-samples.

Table 3. Distribution of OTA in fractions of coarsely ground barley after sieving.

Particle size (mm)	Fraction mass (g)	Fraction mass (%)	OTA (ng g^−1)	SD	OTA (ng/fraction)	OTA (%)
>2	78	3.4	0.4	0.1	31	0.1
>1	1026	45.2	4.9	0.2	5027	14.4
>0.5	682	30.0	9.7	1.4	6615	19.0
>0.25	244	10.7	32.5	2.1	7930	22.7
<0.25	240	10.6	63.7	1.7	15,288	43.8
Aggregate	2270	100.0	15.4		34,892	100.0