Canned foods, lead concentrations

Bisphenol A (BPA) mimics the effects of estrogens, which can lead to health effects at high enough concentrations. BPA is used in polycarbonate bottles (see Section 21-16) and in some of the plastic linings of canned foods. Several countries have banned the sale of polycarbonate baby bottles and the use of canned food liners containing BPA because of their concerns that the polymers might hydrolyze and leach free BPA into the food orwaterinthe container. 

The concentrations of lead in foods are typically less than 100 p.g/kg fresh weight. Foods with high surface areas (such as spinach) also tend to have higher concentrations of lead due to atmospheric deposition. Canned foods (especially if the food is at a low pH) often have much higher concentrations of lead than foods packed in another manner (OECD, 1993). 

The lead concentrations found in C. virginica from these coastal lagoons by several authors are presented in Table 17. All the authors compared their results with the US-FDA limit for lead in food of 0.2 mg/kg (1971). As can be seen, except for those from Villanueva, all the results exceeded this limit therefore, these oysters should not have been acceptable for human consumption. However, these results have not been taken into consideration by the responsible authorities and no regulations or controls for the sale of this type of food have been established up to this date. 

In previous chapters attention has been concentrated on the energy and nutrient requirements of farm animals for maintenance and various productive processes. An additional i mportant factor that must be considered is the quantity of food that an animal can consume in a given period of time. The more food an animal consumes each day, the greater will be the opportunity for increasing its daily production. An increase in production that is obtained by higher food intakes is usually associated with an increase in overaii efficiency of the production process, since maintenance costs are decreased proportionately as productivity rises. There are, however, certain exceptions to the generalisation for example, with some breeds of bacon pigs, excessive intakes of food lead to very fat carcasses, which are unacceptable to the consumer and therefore economically undesirable. 

As noted earlier, using lead-seamed cans for canned foods was, in some cases, the major contributor to Pb contamination of foodstuffs in cans. Bolger et al. (1991), for example, reported Pb concentrations in canned foods with and without lead-seamed construction, as seen in Table 6.42. Ratios of Pb levels in lead-seamed can contents were manyfold higher than for containers without Pb. For example, canned vegetable soup Pb levels in lead-seamed cans were 18-fold higher, 0.18, versus 0.01 ppm Pb in cans not lead-seamed. 

The side chains of proteins can undergo post-translational modification in the course of thermal processes. The reaction can also result in the formation of protein cross-links. A known reaction which mainly proceeds in the absence of carbohydrates, for example, is the formation of dehydroalanine from serine, cysteine or serine phosphate by the elimination of H2O, H2S or phosphate. The dehydroalanine can then lead to protein cross-links with the nucleophilic side chains of lysine or cysteine (cf. 1.4.4.11). In the presence of carbohydrates or their degradation products, especially the side chains of lysine and arginine are subject to modification, which is accompanied by a reduction in the nutritional value of the proteins. The structures of important lysine modifications are summarized in Formula 4.95. The best known compounds are the Amadori product -fructoselysine and furosine, which can be formed from the former compound via the intermediate 4-deoxyosone (Formula 4.96). To detect of the extent of heat treatment, e. g., in the case of heat treated milk products, furosine is released by acid hydrolysis of the proteins and quantitatively determined by amino acid analysis. In this process, all the intermediates which lead to furosine are degraded and an unknown portion of already existing furosine is destroyed. Therefore, the hydrolysis must occur under standardized conditions or preferably by using enzymes. Examples showing the concentrations of furosine in food are presented in Table 4.13. 

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