Food plant toxicants and safety Risk assessment and regulation of inherent toxicants in plant foods.

The ADI as a tool for risk management and regulation of food additives and pesticide residues is not readily applicable to inherent food plant toxicants: The margin between actual intake and potentially toxic levels is often small; application of the default uncertainty factors used to derive ADI values, particularly when extrapolating from animal data, would prohibit the utilisation of the food, which may have an overall beneficial health effect. Levels of inherent toxicants are difficult to control; their complete removal is not always wanted, due to their function for the plant or for human health. The health impact of the inherent toxicant is often modified by factors in the food, e.g. the bioavailability from the matrix and interaction with other inherent constituents. Risk-benefit analysis should be made for different consumption scenarios, without the use of uncertainty factors. Crucial in this approach is analysis of the toxicity of the whole foodstuff. The relationship between the whole foodstuff and the pure toxicant is expressed in the `product correction factor' (PCF). Investigations in humans are essential so that biomarkers of exposure and for effect can be used to analyse the difference between animals and humans and between the food and the pure toxicant. A grid of the variables characterising toxicity is proposed, showing their inter-relationships. A flow diagram for risk estimate is provided, using both toxicological and epidemiological studies.

Protein quality of feeding-stuffs. 7. Collaborative studies on the microbiological assay of available amino acids.

1. Twenty-two samples of high-protein feeding-stuffs, sixteen of them fish meals, were used in a collaborative study of the precision and the limits of discrimination of the Streptococcus zymogenes assay procedure, as applied to the estimation of available methionine, tryptophan and isoleucine contents. 2. All the participating laboratories ranked the test samples in much the same sequence with respect to content for all three amino acids. There were apparently systematic differences between laboratories which impaired the precision of some of the estimates, and these were greatly reduced by including common reference sample in the tests as an auxilliary standard. 3. Values for available methionine content for eleven test samples were highly correlated (r 0.86) and quantitatively similar to those obtained for chick growth assays, but those for available tryptophan content were markedly lower and were probably in error.