140 Chilled foods Table 6.4 Oxygen and water vapour transmission rates of selected packaging materials film (25m) T 23°C:0%RH 38°:90%RH EVOH 0.2-1.6b 24-120 PVDC 0.8-92 0.3-3.2 MXDE 2.4b 50-100 20-30 PA6 PETG MOPP 1.5-3.0 UPVC 22-35 PAIl PVC 2000-10000° 200 OPP 2000-2500 HDPE 2100 2500-5000 110160 OPS 2500-5000 PP 3000-3700 PC 4300 LDPE 7100 EVA 12000 110-160 Microperforated 0000-2000000 Dependent on pinhole Dependent on moisture and level of plasticiser a technique to improve product image, reduce wastage and extend the quality shelf-life of a wide range of foods(Day 1992). Established chilled products now available in MAP include red meats, fish, seafood, poultry, crustaceans, offal cooked and cured meats and fish, pasta, pizza, kebabs, cheese, cooked and dressed vegetable products, dairy and bakery goods, ready meals, and whole and prepared fresh fruit and vegetables(Day and wiktorowicz 1999, Air Products Plc1995) Gases The gas mixture used in MAP (see Table 6.5)must be chosen to meet the needs of the specific food product, but for nearly all products this will be some combination of carbon dioxide( co2), oxygen(O2)and nitrogen(N2)(Day and wiktorowicz 1999). Carbon dioxide has bacteriostatic and fungistatic properties and will retard the growth of mould and aerobic bacteria. The combined negative effects on various enzymic and biochemical pathways result in an increase in the lag phase and generation time of susceptible spoilage microorganisms. However, CO2 does not retard the growth of all types of
a technique to improve product image, reduce wastage and extend the quality shelf-life of a wide range of foods (Day 1992). Established chilled products now available in MAP include red meats, fish, seafood, poultry, crustaceans, offal, cooked and cured meats and fish, pasta, pizza, kebabs, cheese, cooked and dressed vegetable products, dairy and bakery goods, ready meals, and whole and prepared fresh fruit and vegetables (Day and Wiktorowicz 1999, Air Products Plc 1995). Gases The gas mixture used in MAP (see Table 6.5) must be chosen to meet the needs of the specific food product, but for nearly all products this will be some combination of carbon dioxide (CO2), oxygen (O2) and nitrogen (N2) (Day and Wiktorowicz 1999). Carbon dioxide has bacteriostatic and fungistatic properties and will retard the growth of mould and aerobic bacteria. The combined negative effects on various enzymic and biochemical pathways result in an increase in the lag phase and generation time of susceptible spoilage microorganisms. However, CO2 does not retard the growth of all types of Table 6.4 Oxygen and water vapour transmission rates of selected packaging materials Packaging film Oxygen Water vapour (25 m) Transmission rate transmission rate (cm3 m2 day1 atm1 ) (g m2 day1 ) 23ºC: 0% RH 38ºC: 90% RH Al foil neg.a neg.a EVOH 0.2–1.6b 24–120 PVDC 0.8–9.2 0.3–3.2 MXDE 2.4b 25 PET 50–100 20–30 PA6 80b 200 PETG 100 60 MOPP 100–200 1.5–3.0 UPVC 120–160 22–35 PA11 350b 60 PVC 2000–10 000c 200 OPP 2000–2500 7 HDPE 2100 68 PS 2500–5000 110160 OPS 2500–5000 170 PP 3000–3700 10–12 PC 4300 180 LDPE 7100 16–24 EVA 12 000 110–160 Microperforated 20 000–2 000 000d – a Dependent on pinholes. b Dependent on moisture. c Dependent on moisture and level of plasticiser. d Dependent on degree of microperforation. 140 Chilled foods
Chilled food packaging 141 Table 6.5 Gas-mix guide for MAP of retail chilled food products Chilled food item %o CO, Meat(red 60-85 Meat(cured) Meat(cooked) 25-30 Offal(raw) Poultry(white) Poultry(reddish) 25-35 Fish(oily) 55-65 ceans and molluscs 333 25-35 3 25-35 65-75 25-35 65-75 25-35 65-75 25-35 65-75 Quiche 25-35 65-75 Meat pies 25-35 65-75 Cheese(hard) 25-35 Cheese(mould-ripened) --------1 fruit/vegetable 3-1 tables(cooked) 5-35 microorganisms. For example, the growth of lactic acid bacteria is improved in the presence of CO2 and a low O2 content. CO2 has little effect on the growth of yeast cells. The inhibitory effect of CO2 is increased at low temperatures because of its enhanced solubility in water to form a mild carbonic acid. The practical significance of this is that MAP does not eliminate the need for refrigeration. The absorption of CO2 is highly dependent on the water and fat content of the product. Excess CO2 absorption can reduce the water-holding capacity of meats, resulting in unsightly drip. In addition, some dairy products can be tainted, and fruit and vegetables can suffer physiological damage owing to high CO2 levels. If products absorb excess CO2, the total volume inside the package will be reduced, giving a vacuum package look known as pack collapse In MAP, Oz levels are normally set as low as possible to inhibit the growth of aerobic spoilage microorganisms and to reduce the rate of oxidative deterioration of foods. However, there are exceptions; for example, O2 is needed for fruit and vegetable respiration, colour retention in red meats or to avoid anaerobic conditions in white fish MA packs Nitrogen is effectively an inert gas and has a low solubility in both water and fat. In MAP, N2 is used primarily to displace O2 in order to retard aerobic spoilage and oxidative deterioration. Another role of N2 is to act as a filler gas so as to prevent pack collapse. Other gases such as carbon monoxide, ozone ethylene oxide, nitrous oxide, helium, neon, argon, propylene oxide, ethanol vapour, hydrogen, sulphur dioxide and chlorine have been used experimentally or on a restricted commercial basis to extend the shelf-life of a number of food
microorganisms. For example, the growth of lactic acid bacteria is improved in the presence of CO2 and a low O2 content. CO2 has little effect on the growth of yeast cells. The inhibitory effect of CO2 is increased at low temperatures because of its enhanced solubility in water to form a mild carbonic acid. The practical significance of this is that MAP does not eliminate the need for refrigeration. The absorption of CO2 is highly dependent on the water and fat content of the product. Excess CO2 absorption can reduce the water-holding capacity of meats, resulting in unsightly drip. In addition, some dairy products can be tainted, and fruit and vegetables can suffer physiological damage owing to high CO2 levels. If products absorb excess CO2, the total volume inside the package will be reduced, giving a vacuum package look known as pack collapse. In MAP, O2 levels are normally set as low as possible to inhibit the growth of aerobic spoilage microorganisms and to reduce the rate of oxidative deterioration of foods. However, there are exceptions; for example, O2 is needed for fruit and vegetable respiration, colour retention in red meats or to avoid anaerobic conditions in white fish MA packs. Nitrogen is effectively an inert gas and has a low solubility in both water and fat. In MAP, N2 is used primarily to displace O2 in order to retard aerobic spoilage and oxidative deterioration. Another role of N2 is to act as a filler gas so as to prevent pack collapse. Other gases such as carbon monoxide, ozone, ethylene oxide, nitrous oxide, helium, neon, argon, propylene oxide, ethanol vapour, hydrogen, sulphur dioxide and chlorine have been used experimentally or on a restricted commercial basis to extend the shelf-life of a number of food Table 6.5 Gas-mix guide for MAP of retail chilled food products Chilled food item % CO2 % O2 % N2 Meat (red) 15–40 60–85 0–10 Meat (cured) 20–35 – 65–80 Meat (cooked) 25–30 – 70–75 Offal (raw) 15–25 75–85 – Poultry (white) 20–50 – 50–80 Poultry (reddish) 25–35 65–75 – Fish (white) 35–45 25–35 25–35 Fish (oily) 35–45 – 55–65 Crustaceans and molluscs 35–45 25–35 25–35 Fish (cooked) 25–35 – 65–75 Pasta (fresh) 25–35 – 65–75 Ready meals 25–35 – 65–75 Pizza 25–35 – 65–75 Quiche 25–35 – 65–75 Meat pies 25–35 – 65–75 Cheese (hard) 25–35 – 65–75 Cheese (mould-ripened) – – 100 Cream – – 100 Fresh fruit/vegetables 3–10 210 80–95 Vegetables (cooked) 25–35 – 65–75 Chilled food packaging 141