Nitrared

Implicaciones de la reducción de los niveles de nitratos y nitritos en la seguridad, vida útil y características sensoriales y tecnológicas de los productos cárnicos curados

Nitrates and nitrites have been traditionally added to meat products for various purposes such as inhibiting spoilage and potentially pathogenic microorganisms, providing the stable, bright red-pink colour that characterizes cured meat, and contributing to the achievement of its characteristic aroma and flavour. Meat conservation methods in Food Technology are based on decreasing pH and aw together with the addition of nitrate and nitrite.

Residual nitrite can favour the production of nitrosamines (Pegg & Shahidi, 2000), which implies a direct effect of the nitrifier agents on the abiotic safety of meat products. Nitrite reacts with some meat components and total nitrite content decreases throughout the stages of processing, conservation, preparation and consumption. The transformations that nitrites and/or nitrates undergo during the preparation of a whole piece of meat, such as dry-cured ham, are complex and depend on the diffusion rate from the surface to the inner part of the ham, which is the more critical zone (Arnau et al., 1995; Arnau et al., 2003). Increasing the knowledge on the reduction of nitrite levels (rate and extension) is of great interest both for product stability (colour, lipid oxidation, etc.) and consumers’ health.

 

1. Antimicrobial activity of nitrite

Nitrite is very important for microbial safety of cured products because inhibits the growth of Clostridium botulinum and Salmonella spp.. Microbial safety and stability of raw-cured meat products is improved by the combination of nitrite with other hurdles added during the manufacturing process such as the redox potential, starter cultures activity, pH and aw (Leistner, 1992). However, the addition of nitrite (and nitrate, which is reduced to nitrite), along with the use of sodium chloride are critical in the first stages of the maturating process (Leistner, 1995).

Reducing nitrate and/or nitrite levels in meat products may lead to changes in the growth of technological flora (lactic acid bacteria and cocci gram+ catalase+) due to more abundant and competitive microbiota; the growth of pathogenic microorganisms that are inhibited by nitrites and the development of other microorganisms.

 

2. Nitrate and nitrite effect on the sensory attributes

Aroma is a sensory attribute strongly linked to quality in cured meat products because it conveys the condition of the product and triggers acceptance or rejection by consumers. An appealing colour is very important for the purchase decision, i.e. in cured ham. The use of nitrate and nitrite has great impact on cured meat characteristic colour due to nitrosyl myoglobin pigment formation (Pegg & Shahidi, 1997). However, its influence on aroma has not yet been established because the aroma development is very complex due to the great number of reactions involved (Ordoñez et al., 1999; Toldrá & Flores, 1998). Nitrates and nitrites affect lipolysis and the degradation of amino acids to aromatic compounds (Olesen et al., 2004; Stahnke, 1995).

Reducing the amount of nitrifying agents can change cured meat product aroma, flavour, colour and even texture, leading to low sensory quality products (Wirth, 1993; Lücke, 1998), which could affect consumers’ acceptability. In non-nitrified long maturated hams, e.g. the Parma ham, a pink stable colour can be obtained (Wakamatsu et al., 2004a,b; Parolari et al., 2005). However, their sensory characteristics differ from the ones typical of the Serrano ham (Dirinck et al., 1997). Excessive oxidation (unwanted) has sometimes been observed under the external bones in Spanish hams and shoulders due to a defective nitrification combined with a microaerophile environment (Arnau, not published results).

 

3. Nitrate and nitrite effect on the abiotic safety

The use of nitrites and nitrates is controversial given its potential risk of producing significant amounts of N-nitroso compounds: nitrosamines and nitrosamides, which have proven carcinogenic, mutagenic and teratogenic effects (Hecht, 1997; Martínez et al., 2000a,b). Nitrosamines are the most relevant group and are formed from the reaction of compounds derived from nitrites, such as nitrous acid, with secondary amines mostly (Belitz and Grosch, 1997). Given the presence of amines in meat and the addition of nitrites and nitrates during its manufacturing process, this reaction is common in cured meat products. Different amino acids such as proline, hydroxiproline, sarcosine, glycine, alanine, proline, ornithine act as precursors of nitrosamines. Thermal treatments favour the formation of nitrosamines from such precursors, depending on the selected time and cooking temperature (Cassens, 1997; Antón & Lisazo, 2003).

On the one hand, the use of nitrates and nitrites has an anti-oxidant effect on meat products. Their reduction could increase the product oxidation level, affecting food nutritional and sensorial qualities, as well as safety, given the increase of radicals and compounds derived from oxidation of both lipids and proteins. On the other, nitrite reduction may contribute to a drop in the formation of nitrosamines and other N-nitroso compounds.

 

4. Current dilemma regarding nitrates and nitrites

The amount of nitrates and nitrites allowed in the current European legislation for meat products was considered excessive given the risk of nitrosamine formation. Reducing or avoiding their use in the food industry was regarded as a possibility, and as a consequence, the Directive was reconsidered. A study from the European Food Safety Authority (EFSA, 2003) on nitrate and nitrite safety on meat products concluded that:

i)      there is no simple and direct relationship between the ingoing and the residual amounts of nitrites and nitrates.ii)    nitrite contributes to microbial safety, however, there is no clear evidence of how the residual amount of nitrite contributes to prevent the growth of Clostridium botulinum.iii)    the following new levels were proposed to provide a protective effect against microbial hazards: 50-100 ppm for most products and 50-150 ppm for low salt content and prolonged shelf-life products. It was also proposed that the current “indicative ingoing amount” of nitrite and nitrate should be “maximum ingoing amount”.

 

Consequently, the permitted nitrate and nitrite levels have been changed in the new European Directive (2006/52/CE). This will affect cured products, especially Spanish typical products such as cured ham and fermented sausages. The Spanish meat industry should be prepared to face these changes and future modifications in the legislation and be able to continue producing top quality and safe products.

   
Instituto de Recerca I Tecnologia Agroalimentaria (IRTA)

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