Sample comminution for mycotoxin analysis: dry milling or slurry mixing?

A comparison was made between dry milling and slurry mixing as a comminuting step preceding mycotoxin analysis. Sample schemes of up to 30 kg are mandated by European Commission legislation. Cocoa, green coffee, almonds and pistachio samples of 10 kg were milled by a Romer analytical sampling mill and all three subsamples were analysed for aflatoxin B1 or ochratoxin A content. The homogenization process was evaluated in terms of the analytical results, coefficients of variation for different mills and particle size distributions. Coefficients of variation for the comminuting step were higher for dry milling than for slurry mixing. This difference was explained based on measured particle size distributions for both milling types. Measurements also showed slight differences in mycotoxin content of samples based on milling procedures. This might lead to lots being wrongly accepted or rejected based on an erroneous subsample result. It was concluded that sample comminution was best performed by slurry mixing, which produced smaller particles and, consequently, homogeneous samples with lowest coefficients of variation. Additional data are given on analytical results in 10-kg subsamples that originate from the aggregate 30-kg sample as described in Commission Directive 98/53/EC.

Dependence of aflatoxin in almonds on the type and amount of insect damage.

The aflatoxin distribution of single insect damaged Nonpareil almonds (1999 crop) has been measured. Separate distributions were obtained for pinhole, insect (feeding), and gross damage. Only a low level of aflatoxin contamination ( = 0.0003 ng/g) was found for pinhole-only damaged nuts. The distributions for insect and gross damage did not differ, but did differ significantly from the distribution previously obtained for gross damaged Ne Plus almonds from a different producer (Schatzki, T. F.; Ong, M. S. J. Agric. Food Chem. 2000, 48, 489-492; also 1999 crop). The Nonpareil almond distribution could be explained on the basis of a preharvest hull splitting, similar to previous results in pistachios (0-4 weeks versus 2-6 weeks preharvest). The Ne Plus distribution differs in detail from pistachio results and from the Nonpareil results found here. This may indicate additional cultural damage of Ne Plus almonds around harvest time and/or use of different sorting parameters. Aflatoxin lot averages of 31.7 and 3.47 ng/g were obtained for 100% insect damaged Ne Plus and Nonpareil almonds, respectively. (The previous Ne Plus work contained a calculation error, which is corrected here.) The distribution functions were used to compute the seller's risk of nonacceptance of lots in the European Union. To obtain a 95% acceptance rate, aflatoxin B(1) levels of 0.12 and 0.22 ng/g would be required, which would correspond to 3.8 and 1.2% (feeding and gross) insect damage in Nonpareil and Ne Plus almond lots, respectively.

Distribution of aflatoxin in pistachios. 7. Sequential sampling.

Sequential sampling for aflatoxin testing in pistachios is evaluated using the aflatoxin distribution and Monte Carlo results previously obtained (J. Agric. Food Chem. 1999, 47, 3771-3775). The sequential protocol is modeled on the current EU test protocol by applying a three-step sampling, using 10, 20, and 30 kg sample averages. An acceptance level of 15 ng/g of total aflatoxin, under consideration for U.S. standards, is applied. Optimization leads to indifference regions of 2-30 ng/g for the first two steps. The resulting OC curve approximates that for a single 50 kg sample. The sequential protocol is applied to the results for a set of 1293 lots of the 1998 crop year, each tested with a single 10 kg sample. Ninety-five percent of the lots would have been accepted on the basis of the single test and 1.5% would have been rejected, whereas 3.5% of the lots would have required retesting.

Distribution of aflatoxin in almonds. 2. Distribution in almonds with heavy insect damage.

The aflatoxin distribution function in individual insect-damaged NePlus Ultra almonds was determined and found to be the sum of two distributions. Substantially all almonds exhibited a positive aflatoxin level between 0.02 ng/g (the detection level) and 0.3 ng/g, the precise form of this distribution depending on the lot studied. In addition, 1/1000 of the nuts showed contamination between 60 and 600 000 ng/g, independent of the lot. The latter distribution showed a smooth decrease with log concentration in this range, with no evidence of a minimum, as had been found previously for pistachios. No distribution data between 0.3 and 60 ng/g could be obtained. The distribution below 0.3 ng/g was assigned to contamination during post-harvest storage. The distribution above 60 ng/g was tentatively assigned to navel orange worm damage occurring when insects enter the kernel during split hulls late in the growing season. Considerable additional work will be required to verify these assignments.

Distribution of aflatoxin in pistachios. 6. Seller's and buyer's risk.

The seller's risk-the probability of a set of samples exceeding an agreed upon aflatoxin level when the lot mean does not-and the buyer's risk-the probability of a lot exceeding this level when a set of samples do not-have been computed using a parametrized experimental aflatoxin distribution and Monte Carlo simulation. The calculations are exemplified using the proposed EC standards (three 10 kg samples, 4 ng/g of total aflatoxin, basis kernels only) as well as for samples up to 250 kg and for varied lot aflatoxin levels. It is found that within this sample size range the seller's risk is as high as 42% at 10 kg and increases with increasing sample size to 80% at 250 kg. Only by reducing lot levels to 0.2 ng/g of total aflatoxin, basis kernels, can the risk be brought down to 2.5%, independent of sample size. The buyer's risk is as high as 58% at 10 kg but falls to 11% at 250 kg samples. The implications for both seller and buyer strategies are discussed.

Recognition of agricultural objects by shape.

It is desired to enhance the outline of agricultural contraband in X-ray images of passenger luggage. Agricultural contraband consists of fruit, meats, animals, and plants. We suggest most contraband can be distinguished from other material by an elliptic, rather than rectangular, cross section. An algorithm is proposed to recognize such cross section using the erosion of the absolute gradient of the image. Only local convolution calculations are required. This algorithm is tested on a number of computed images as well as on X-ray images of model objects, isolated contraband, and contraband contained and obscured in baggage. The effect of image noise, object size, orientation, and obscuration is tested. It is shown that the proposed algorithm successfully enhances the outlines of desired items as small as 1-2 cm (7-11 pixels) to the exclusion of remaining material under the conditions expected in actual use.

Fruits and fruit products. Non-parametric methods for detection of adulteration of concentrated orange juice for manufacturing.

The composition of organic constituents (total sugars, reactive phenols, total amino acids, arginine, and gamma-aminobutyric acid) has been measured in a large (360 samples) selection of concentrated orange juice for manufacturing and orange pulp wash in the U.S. trade. The detection of adulteration with sugar, reducing sugars, and citric acid addition has been investigated by using non-parametric nearest neighbor classification techniques in the 4-space of log ratios of the compositions. The results show that such detection is possible with a type 1=type 2 error rate of 10% for 20% adulteration if at least 7 samples are taken. The assumptions of such samplings are discussed.