# Freshness Monitoring of Packaged Vegetables
## 6 Active Packaging (AP)  
Active packaging can be defined as a system that uses active components such as scavers and releasing objects as a part of packaging material or inside the headspace, for the purpose of extending the shelf-life of the packaged product [83; 170]. The target of such a system is to adjust and improve the environment inside the package to keep the packaged product fresh and free from contamination. Active packaging has several applications in different fields such as pharmaceuticals and health care, energy and power, and food packaging. This packaging system can be classified according to its functionality or the active components used. For functionality, the system is divided into: scavenging that capture objects from headspace of a package such as oxygen scavengers, moisture absorbers, and odor absorbers; or releasing the release components for specific purposes such as antimicrobial, antioxidants, and carbon dioxide emitters. This system can also be classified based on the active components used into oxygen scavengers, carbon dioxide absorbers or emitters, moisture absorbers, temperature compensating films, or preservative releases. Oxygen scavengers help to control the amount of oxygen inside the package and are usually in the form of sachets, labels or plastic films. Oxygen scavengers contain either metallic powders such as iron, which reacts with the water inside the package using the oxygen to produce a stable oxide, or non-metallic scavengers that uses a reducing agent such as ascorbate salts or enzymic systems. Carbon dioxide scavengers or emitters are used to maintain carbon dioxide within a specific limit which in turn reduces the effect of vegetable injury and color change. For example, the prolonged freshness of shitiake mushroom and eggplant were observed with the use of CO\({}_{2}\) absorbers [198; 199]. Furthermore, keeping the percentage of this gas within a certain limit shows a difference on the freshness of different vegetables such as potato, onions, lettuce, cucumber, and cauliflower [200]. These scavengers or emitters use a valve to release a gas; or powders as physical absorbers, or in sachets or granules form that uses chemicals such as calcium hydroxide mixed with oxygen scavengers [1; 201]. Moisture absorbers play a key role in vegetable packaging, since they absorb accumulated water and/or water vapor inside the package, inhibiting mold and bacterial growth, and hence prolonging the shelf-life of the packaged vegetables. These absorbers controls humidity either in the liquid phase or in the vapor phase. Liquid-state absorbers are usually sachets filled with silica gel such as natural clays or drip absorbing pads that consists of strong absorbent polymer sandwiched between microporous polymers. Vapor-state absorbers are typically humectant layers between permeable plastic films [201]. Temperature compensating films rely on the use of polymer-based membranes that adjust their permeability for oxygen and carbon dioxide depending on the temperature variation to help control the percentage of these gases within a certain range [1; 23; 202]. These films allow for CO\({}_{2}\) penetration at rates that are four time faster than O\({}_{2}\) to ensure a slower rate of respiration and dehydration inside the package. In this way the freshness is prolonged. A schematic illustration of the method is given in Figure 18. Low-density polyethylene (LDPE) is an example of such materials that can be used as a temperature compensating film [16]. These films are available for manufacturers packaging and even for home use [1; 201]. Preservative releases such as antimicrobial and antioxidants are components that can be added directly to the food or can be mixed with packaging materials to release objects to inhibit the growth of bacteria or to reduce the oxidation process that leads to loss of packaged food nutritional value and change its color. For antimicrobial packaging, commercialization is still limited due to the safety concerns and masking the spoilage of packaged food.