Foodstuffs fish products

Acetic acid is used as a preservative in many foods, for example, pickles, mayonnaise, bread, and fish products, because it prevents bacteria and fungi growing. However, its fungicidal nature is not due to any lowering of the pH of the foodstuff. In fact, it is the undissociated acid that acts as a bactericide and a fungicide in concentrations as low as 0.1-0.3%. Besides, such a low concentration has little effect on the pH of the foodstuff anyway. 

The method involving the Mo-V-P acid has been used in determinations of phosphorus in biological tissues [127], plant material [128], fruits [129], fish products [130], foodstuffs [131], phosphate minerals [132], cast iron and steel [133,134], niobium, zirconium and its alloys, titanium and tungsten, aluminium, copper, and white metal [135], nickel alloys [134,135], metallurgy products [136], molybdenum concentrates [137], silicon tetrachloride [7], cement [138], and lubricants[139]. The flow injection technique has been applied for determining phosphate in minerals [140] and in plant materials [141]. 

Information of foodstuffs showed that in the period 1986-1990, there was a trend of increased levels of HCH, Lindane and DDT in fish products for 1986. However, absolute values did not exceed maximum allowable concentrations (MAC) (Figure 24.10) for meat products trends show an increase of HCH, in 1990 (Figure 24.2), The same trend was observed for residues of HCH in milk in 1990 (Figure 24.3). 

In contrast, fish and fish products can be highly burdened with mercury, especially methylmercury. The highest concentrations are found both in marine and freshwater fish at the highest trophic levels of the aquatic food chain, caused by bioaccumulation [4-6] (see Sec. 2.1). The mean mercury concentration in the edible parts of these problem fishes is approximately 1 mg/kg, but peak values even of 10 mg/kg have been reported [16,17]. Shellfish also accumulate methylmercury to a high extent. For instance, the weekly consumption of 200 g of fish containing only 0.5 mg mercury/kg results in the intake of 100 p,g mercury per week [2]. This amounts to one-half of the PTWI (provisional tolerable weekly intake), as recommended by the World Health Organization (WHO) [4,18]. The feeding of animals like chickens with fish meal may raise the mercury burden of terrestrial animal foodstuffs too. 

In foodstuffs preserved by smoking (such as fish and meat products) oxides of nitrogen present in the smoke act as nitrosating agents. 

Niacin is present in foods mainly as coenzyme NAD and NADP, which are hydrolyzed in the intestine, and it is adsorbed as nicotinamide or nicotinic acid. The free forms, nicotinamide and nicotinic acid, only allowed to be added in fortified foods [403], occur naturally in limited amounts. Instead, niacin occurs as nicotynil ester bonded to polysaccharides, peptides, and glycopeptides. In general, niacin is widespread in foodstuffs (cereals, seeds, meat, and fish). High concentrations are present in roasted coffee beans as a primarily product of the roasting process [417]. 

In commercial rearing of fish, it is essential to know how much foodstuff should be given for mere support (balancing metabolic output) and how much for actual growth. Present knowledge is insufficient for us to calculate the nutritional requirements for a steady state in a population, i.e. one which would not stimulate production but which would not reduce the number or weight of individuals. 

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