Effect of low sodium on eating quality, shelf-life and functional properties
The eating quality of a meat product is usually assessed from its meat content, firmness and flavour. However, sensory quality such as colour, mouth feel, aroma, juiciness and tenderness are also important when they contribute to the overall acceptability or appreciation of the product by consumers. Consumers demand healthier products but expect the products to taste and look the same. In practice, however, lowering sodium in processed meat products has an effect on eating and other sensory qualities, quite often affecting them adversely. Many studies have been carried out to measure the effects of salt reduction. Most effects vary depending on the product and the choice of other cations, phosphates and hydrocolloids. This will be explored later in this section (Optimum concentrations), but some common findings are:
- Saltiness perception has been found to be negatively correlated with meat protein content. In other words, when meat protein content increases, perceived saltiness decreases (Ruusunen et al., 2001, 2005).
- Conversely, saltiness perception can correlate positively with fat content (Matulis et al., 1995; Ruusunen et al., 2001, 2005; Sheard et al., 2010).
In the present context "shelf-life" means the period during which the meat product should be safe to eat from a microbiological perspective. An alternative term would be expiration date.
Salt has been used as a preservative for centuries; however, when it started to be used hygiene measures were rather poor. Nowadays hygiene practices have changed enormously. Hygiene regulations have been put in place and meat processors have to follow them. In addition, meat microbiology and chemistry are much better understood, which has permitted the development of different techniques to decrease the risk of contamination and enhance shelf-life. Other ways of enhancing shelf life, such as vacuum packing and modified atmosphere packing, could be use to replace some of the salt. This means that the preservative properties of salt are not as important as they used to be centuries ago.
The main techniques developed and used for increasing shelf-life in commercial meat products are lowering temperature (to between -1 °C and 4 °C) and using appropriate packaging. Vacuum packaging and modified-atmosphere packaging are commonly used for processed pig-meat products. Finished products should be packed in such a way that any further loss in weight is avoided and a barrier is placed between the product and bacteria in the environment.
- Vacuum packing
Vacuum packing removes O2 and delays microbiological spoilage by anaerobic bacteria (such as Pseudomonas spp.). The materials used must be oxygen-impermeable and the degree of vacuum applied has to be really strong, -0.99 bar is recommended before the bag is sealed.
1 Which types of micro-organisms could spoil vacuum-packed products?
2 What types of bacterial problems can occur in vacuum-packaged products, and how can they be recognised ?
Some approaches are used in combination with vacuum packing to extend shelf-life. The following are most common:
- Low storage temperature - keeping vacuum-packed products at a low storage temperature (around 0 °C) is a good way of combating bacterial growth and extending shelf-life.
- Post-pack pasteurisation (PPP) - short exposure to high temperatures is often used in chilled and unsliced products. Processed meat products are dipped into hot water (85-95°C) for 2-3 seconds after being vacuum packed. PPP results in a significant reduction in the number of bacteria on the surface of the product, enhancing shelf life.
Vacuum packing, however, should not be used in trimmed or sliced products, mainly because slices stick together and the product is squeezed, resulting in increased drip formation and affecting presentation. Modified-atmosphere packaging is normally used for these products.
- Modified atmosphere
In the case of sliced products, the advantage of packing products under a modified atmosphere is that the individual pieces lie loosely in their packaging, which is especially convenient for cutlets and trimmed or sliced products. The meat can be displayed in an attractive form and shelf-life is extended by the modified atmosphere.
The gas mixture normally used in modified-atmosphere packing is a combination of 50-70% N2 and 30-50% CO2. Carbon dioxide induces changes in the permeability of the bacterial cell membranes and inhibits enzyme-catalysed reactions within the bacterial cells disrupting cell membrane activity. This contributes to reducing bacteria growth and extending shelf-life. Nitrogen is used to displace oxygen; N2 is an inert gas so it does not react with the product. The O2 level should not exceed 0.6% in order to avoid aerobic spoilage. In fresh meat, low concentrations of oxygen are needed to maintain a red colour; cured meat products, however, have a stable red colour (when nitrites have been used) so they could be packed in a CO2 atmosphere (Feiner, 2006; Warriss, 2006).
1 What would be the consequences if an excess of carbon dioxide was introduced into the packing?
2 What would be the consequences if an excess of nitrogen was introduced into the packing?