Lesson- 30 Performance evaluation of packaging on fruits and vegetables and other products
Fruits are generally high acid and vegetables are generally low acid. Major exceptions are tomatoes, which commercially are regarded as vegetables, and melons and avocados, which are low acid. The most popular produce form is fresh and increasingly fresh-cut or minimally processed. Fresh produce is a living, “breathing” entity fostering the physiological consumption of oxygen and production of carbon dioxide and water vapor. From a spoilage standpoint, fresh produce is more subject to physiological than to microbiological spoilage, and measures to extend the shelf life are designed to retard such reactions and water loss. A variety of food products that do not fall clearly into the meat, dairy, fruit or vegetable categories may be described as prepared foods, a rapidly increasing segment of the industrialized society food market during the 1990s. Prepared foods are those that combine several different ingredient components into dishes that are ready to eat or nearly ready to eat.
30.1 Fruits and vegetables products
30.1.1 Fruits and vegetables
Alteration of the atmospheric environment in the form of modified or controlled atmosphere preservation and packaging have been used commercially to extend the refrigerated shelf life of fresh produce items such as apples, pears, strawberries, lettuce, and now fresh-cut vegetables. Controlled atmosphere has been largely confined to warehouse and transportation vehicles such as trucks and seaboard containers. In controlled atmosphere preservation, the oxygen, carbon dioxide, ethylene, and water vapor levels are under constant control to optimize refrigerated shelf life.
Fresh-cut vegetables, especially lettuce, cabbage, and carrots have been a major product in the retail and the hotel/restaurant/ institutional market. Cleaning, trimming and size reduction lead to greater surface to volume of the produce and to the expression of fluids from the interior to increase the respiration and microbiological growth rate. Uncut produce packaging is really a multitude of materials, structures, and forms that range from the old and traditional, such as wood crates, to inexpensive, such as injection-molded polypropylene baskets, to polyethylene liners within waxed corrugated fiberboard cases. Much of the packaging is designed to help retard moisture loss from the fresh produce or to resist the moisture evaporating or dripping from the produce to ensure the maintenance of the structure throughout distribution. Some packaging recognizes the issue of anaerobic respiration and incorporates deliberate openings to ensure passage of air into the package, as, for example, perforated polyethylene pouches for apples or potatoes.
For freezing, vegetables are cleaned, trimmed, cut, and blanched prior to freezing and then packaging, or prior to packaging and then freezing. Blanching and the other processing operations reduce the number of microorganisms. Fruit may be treated with sugar to help retard enzymatic browning and other undesirable oxidations. Frozen food packages are generally relatively simple monolayer polyethylene pouches or polyethylene-coated paperboard to retard moisture loss.
Canning of low-acid vegetables to achieve long-time ambient-temperature microbiological stability is conventional for low-acid foods, with blanching prior to placement in steel cans. Canned fruit is generally placed into lined three-piece steel cans using hot filling coupled with post-fill thermal treatment. Increasingly one end is easy-open for consumer convenience.
30.1.2 Tomato Products
The highly popular tomato-based sauces, pizza toppings, etc., must be treated as if they were low acid if they contain meat as so many do. For marketing purposes, tomato-based products for retail sale are more commonly packaged in glass jars with reclosable metal closures. The glass jars are often retorted after filling and hermetic sealing.
30.1.3 Juices and Juice Drinks
Juices and analogous fruit beverages may be hot filled or aseptically packaged. Traditional packaging has been hot filling into steel cans and glass bottles and jars. Much fruit beverage is currently hot filled into heat-set polyester bottles capable of resisting temperatures of up to 80ºC without distortion. Hermetic sealing of the bottles provides microbiological barriers but the polyester is a modest oxygen barrier and so the ambient temperature shelf life from a biochemical perspective is somewhat limited. The hot filling generates an internal vacuum within the pouch after cooling so that the contents are generally ambient temperature shelf stable. The package materials used are generally laminations of polyester and aluminum foil with a linear low density polyethylene (LLDPE) internal sealant to achieve an hermetic heat seal.
30.2 Other Foods
30.2.1 Dry Foods
Removing water from food products markedly reduces water activity and its subsequent biochemical activity, and thus also significantly reduces the potential for microbiological growth. Moisture can change physical and biological properties. Engineered dry products include beverage mixes such as blends of dry sugars, citric acid, color, flavor, etc.; and soup mixes, which include dehydrated meat stock plus noodles, vegetables, meats, etc., that become particulate-containing liquids on rehydration with hot water. Such products must be packaged in moisture-resistant structures to ensure against water vapor entry which can damage the contents.
30.2.2 Fats and Oils
Fats and oils may be classified as those with and those without water. Cooking oils such as corn or canola oil and hydrogenated vegetable shortenings contain no water and so are stable at ambient temperatures if treated to preclude rancidity. Unsaturated lipids are susceptible to oxidative rancidity. Hydrogenated vegetable shortenings generally are packaged under nitrogen in spiral-wound composite paper-board cans to ensure against oxidative rancidity. Edible liquid oils are packaged in injection blow-molded polyester bottles usually under nitrogen. Fat-resistant packaging such as polyethylene-coated paperboard, aluminum foil/paper laminations and parchment paper wraps, and polypropylene tubs are used to package butter, margarine, and similar bread spreads.
30.2.3 Cereal Products
Dry breakfast cereals generally are sufficiently low in water content to be susceptible to water vapor absorption and so require good moisture- as well as fat-barrier packaging. Breakfast cereals are usually packaged in coextruded polyolefin films fabricated into pouches or bags inserted into or contained within printed paperboard carton outer shells. Sweetened cereals may be packaged in aluminum foil, metalized plastic, or gas barrier plastic films or laminations to retard water vapor and flavor transmission.
Soft bakery goods such as breads, cakes, and muffins are highly aerated structures subject to dehydration and staling. To retard water loss, good moisture barriers such as coextruded polyethylene film bags or polyethylene extrusion coated paperboard cartons are used for packaging. Package structures for cookies and crackers include fat- and moisture-resistant coextruded polyolefin film pouches within paperboard carton shells and thermoformed polystyrene trays over-wrapped with polyethylene or oriented polypropylene film. Soft chewy cookies are packaged in high moisture-barrier laminations containing metallized film to improve the barrier.
30.2.4 Salty Snacks
Snacks include dry cereal or potato products such as potato and corn and tortilla chips, and pretzels, and include roasted nuts, all of which except pretzels have low water and high fat contents. Snacks are usually packaged in flexible pouches made from oriented polypropylene or metallized oriented polypropylene to provide low moisture and gas transmission. Snack food producers depend on rapid and controlled product distribution to minimize fat oxidation. Many salty snacks are packaged under nitrogen both in pouches and in rigid containers such as spiral-wound paperboard composite cans to extend shelf life.
Chocolate, a mixture of fat and nonfat components such as sugar, is subject to slow flavor change. Ingredients such as nuts and caramel are susceptible to water content variation. Chocolates, which are generally shelf stable at ambient temperatures, are packaged in fat-resistant papers and moisture/fat barrier such as pearlized polypropylene film. Hard sugar candies are flavored amorphous sugars which are very hygroscopic because of their extremely low moisture contents. Sugar candies are packaged in low-moisture-transmission packaging such as unmounted aluminum foil, oriented polypropylene film, or metallized oriented polypropylene film.