New Insights in Active Packaging of Fruits

ANTIMA GUPTA', PRASHANT SAHNI, SAVITA SHARMA, and BALJIT SINGH

Department of Food Science and Technology, Punjab Agricultural University, Ludhiana, Punjab, India

'Corresponding author. E-mail: This email address is being protected from spam bots, you need Javascript enabled to view it

ABSTRACT

Fruits are good source of vitamins, minerals, dietaiy fiber, and various phytochemicals. In spite of that consumer is not getting proper health benefit of nutrients which are present in fruits as they are susceptible to incremental decrease when exposed to improper environmental condition like respiration, physical injuiy, relative humidity, high temperature, ethylene, handling and so on. So, in order to avail maximum benefit from the fruits and to maintain their wholesomeness it very essential to employ some means to preserve its quality. Active packaging can be used as one of the innovative ways to preserve fruits by modifying its environmental condition within the food package without affecting its nutritional quality. Active packaging maintains fruits in an appropriate condition by influencing the various physiological processes (respiration and transpiration) chemical processes (lipid oxidation) and prevention of insect infestation and microbial spoilage. Active packaging methods include oxygen scavengers, ethylene scavengers, carbon dioxide scavengers/emitter, humidity controller, ethanol emitter, flavor/odor absorber, and antimicrobial food packaging. In this chapter, various nuances pertaining to active packaging of fruits is critically reviewed and opportunities for future research are explored.

INTRODUCTION

Fruits are an important part of our diet, due to high concentration of vitamins (particularly Vitamin A and C) and minerals, in addition to it, fruits contain bountiful of phytochemicals and antioxidants (Slavin and Lloyd, 2012). Moreover, high amount of dietary fiber associated with fruits has gained paramount importance looking at the present scenario where there is an increase in the various lifestyle diseases like coronary heart diseases (CHD), obesity, type 2 diabetes and so on due to paradigm shift in faster lifestyle and alteration in the dietary habits. However, it is worth pondering that fruits are living entities because they respire, transpire, and show particular response to the environment to which it is present. Thus, the plethoras of nutrients which are present in fruits are susceptible to incremental decrease when exposed to improper environmental condition. So, in order to avail maximum benefit from the fruits and to maintain their wholesomeness it very essential to employ some means to preserve their quality (Nayik and Muzaffar, 2014).

Though India ranks second in the production of fruits but still the overall output obtained from it is quite low since we suffer major postharvest losses. The estimated postharvest losses have high magnitude in developed as well as in developing countries ranging from 5% to 25% and 20% to 25%, respectively (Kader, 1992). As aforesaid, we need to employ some means to preserve the wholesomeness of fruits, but it is very essential to understand the factors which are responsible for deteriorative reactions in fruits. In order to understand that we must realize that how fresh fruits interact with the environment, since they continue to change even after harvesting. In addition to loss of nutrients due to this response to environment sometimes there is formation of hazardous compounds which pose threat to human health and is a major halt in the safety of food (Mehyar and Han, 2010).

Traditionally, we utilize thermal processing technologies for preservation of fruits; however, those technologies will not allow us to rely on fresh fruits and also render them somewhat nutrient deficient as compared to their fresh counterparts. Even though we have non-thermal techniques for processing of fruits but still these techniques present challenge in their implementation due to high investment cost. These problems can also be solved using modified atmosphere packaging (MAP), but it requires lot of capital investment so to overcome this active packaging comes into picture. Looking at the major driver which has promoted the development of active food packaging includes increased shelf life, wholesomeness and freslmess of produce, reduction in food losses and wastage, convenience, interrupted and scattered cold chain (Fig. 6.1). The paradigm shift in the high consumption of minimally processed fresh-cut fruits is due to new consumer preferences, increase in e-commerce, and change in retail and distribution practices associated with globalization. Active packaging is an innovative concept and refers to a method of packaging in which there is interaction between product package and environment intended for maintaining the wholesomeness of produce and to enhance its shelf life. Some other synonymous terms which are used for active packaging includes “smart,” “functional,” and “freshness preserved packaging.” An active packaging is equipped in such a way with active ingredient which enhances its functionality and allows better quality retention of the stored produce (Singh et al., 2011). The earlier concept of packaging was only revolving around the four basic pillars of packaging functions that is, containment, protection, communication, and convenience. Though the traditional packaging system had important contribution in the early development of food distribution systems but it can no longer satisfy the growing needs of present era. The major challenges surrounding the modern packaging systems include reduction of losses, compliance with legislation, dissolving the barrier to trade, providing convenient, safe and healthy food, and shift toward green packaging (Kerry, 2014).

Active packaging is designed in such a maimer that they prevent interaction between product and outside environment, thus they act as inert barrier and prevent deterioration of product quality. Active packaging maintains food in an appropriate condition by influencing the various physiological processes (respiration and transpiration), chemical processes (lipid oxidation), and prevention of insect infestation and microbial spoilage (Bodbodak and Rafiee, 2016). Active packaging in fresh produce particularly targets on physiological processes, insect infestation, and microbial spoilage during the process of transportation. The modification of physiological or environmental condition within food package via active packaging is attributed to scavenging or absorption of major threats to the wholesomeness of food, which includes oxygen, carbon dioxide, ethylene, ethanol, moisture, and odor. Compounds such as antioxidants, carbon dioxide, ethanol, flavor, and antimicrobial agents are released in the headspace of the package using sachets, labels, and films. In this chapter, various nuances pertaining to active packaging of fruits is critically reviewed and opportunities for future research are explored.

Major drivers in the development of active packaging of fruits

FIGURE 6.1 Major drivers in the development of active packaging of fruits.

FACTORS INVOLVED IN DETERIORATION OF FRUITS

Appearance of food is a major driver dictating the purchase decision of the consumer. The good appearance and texture of fruits are correlated with their nutritive value. Moreover, the texture and appearance quality has profound role from producer point of view, since they have better salability. It is very essential to understand the major concepts lying beneath the spoilage of fruits for efficient designing of active packaging. Various factors which dictate the spoilage and reduces the shelf life of produce are respiration rate, transpiration rate, and ethylene production which is a cumulative effect of storage temperature, relative humidity (RH), and product handling (Fig. 6.2).

Deteriorative changes in fruits due to biological and environmental factor

FIGURE 6.2 Deteriorative changes in fruits due to biological and environmental factor.

RESPIRATION

Respiration is one of the major metabolic processes which is responsible for senescence and deterioration of fresh produce. During the process of respiration, the breakdown of various food components into simpler substances takes place with subsequent release of energy and thus it reduces the nutritive value of the commodity. Oxygen plays a major role in this process since oxygen used up for the process of respiration and carbon dioxide is released (Nayik and Muzaffar, 2014). The reaction can be represented like:

So, the substrate which is broken down during the process of respiration cannot be replenished, thus high rate of respiration represents major loss of nutritive value, loss of sealable weight, and deterioration of sensory quality. The heat produced in this reaction will lead to building up of high temperature around the commodity which should be removed by appropriate refrigeration or ventilation. Ventilation plays a profound role in maintaining the quality parameter of the product since inadequate ventilation results in carbon dioxide build up around the product and results in the process of fermentation. So, it is interesting to note this contrasting effect of damage due to oxygen and carbon dioxide where high amounts of oxygen around the commodity will deplete the nutrient reserve of the commodity and restricted availability of oxygen will result in the process of breakdown of plant tissues and resultant decay of produce with production of ethanol and off-odor. This type of condition can be observed when we pack a fresh fruit in a sealed plastic bag (Guilbert et al., 1996).

The rate of deterioration of fresh produces is generally proportional to the respiration rate. Fruits are classified on the basis of their respiration rate in Table 6.1. Based on the respiration and ethylene production pattern during maturation and ripening, fruits are either climacteric or non-climacteric. Climacteric fruits tend to exhibit high rates of respiration and ethylene production associated with ripening whereas non-climacteric fruits generally have low carbon dioxide and ethylene production after harvesting (Paul and Pandey, 2014).

TABLE 6.1 Classification of Fruits on the Basis of Respiration Rate.

s.

No.

Class

Range at 5°C (mg CO,/kg-h)*

Fruits

1.

Very low

<5

Dried fruits, dates, nuts

2.

Low

5-10

Citrus fruits, cranberry, apple, grape, kiwifruit, pineapple, papaya, pomegranate, water melon

3.

Moderate

10-20

Banana, gooseberry, pear, peach, plum, apricot

4.

High

20-40

Blackberry, strawberry, avocado

5.

Very high

>40

Passion fruit, raspberry, melons

♦Vital heat (Btu/ton/24 h) = mg CO,/kg-h * 220 Vital heat (kcal/1000 kg/24 h) = mg CO,/kg-h x61.2

Respiration rate can be influenced by various factors as follows:

  • (1) Temperature'. Rate of respiration is directly proportional to the temperature. So, the rate of respiration increases with the increase in temperature.
  • (2) Oxy-gen concentration : Rate of respiration is directly proportional to the oxygen. So, the rate of respiration increases with the increase in oxygen.
  • (3) Carbon dioxide concentration: Effect of carbon dioxide on the rate of respiration is mainly dependents upon the type of fruit. In general, it decreases the rate of respiration.
  • (4) Stress in fruits: Physical or mechanical injury to the fruit accelerates the rate of respiration.
  • (5) Ripening: Climacteric fruits continue to ripen after they are being harvested. So, as ripening progresses the rate of respiration increases, but after they attain full maturity the rate of respiration decreases.

ETHYLENE

Ethylene is a plant growth hormone that dictates various physiological processes during the growth, development, and storage of fruits and is associated with metabolism of plant. Ethylene is stimulant to the respiration and concentration even at part-per-million (ppm) to part-per-billion (ppb) will lead to high increment in the respiration, however, the fact of ethylene is further influenced by the temperature and the exposure time. Even concentration as low as 0.1 ppm of ethylene can deteriorate the commodity if they are stored for prolonged period of times as such concentration (Ozdemir and Floras, 2004). Introspection will be particularly required when surplus fresh produce is stored for long time for temporal arbitrage.

Increased ethylene production as a result of physical injury or decay will result in avalanche of detrimental changes in the commodity leading to death. Physical injury induces increased release of ethylene from the plant tissue due to its effect on the rate-limiting enzyme (1-aminocyclopropane-1- carboxylic acid synthase) in the biochemical pathway (Fig. 6.2) leading to ethylene formation and increases tissue sensitivity to ethylene (Kato et al., 2002).

Biochemical pathway of ethylene production

FIGURE 6.3 Biochemical pathway of ethylene production.

Though ethylene accelerates the process of aging in fresh produce, but no fixed relationship exists between the perishability and ethylene production. Ethylene production is particularly more important phenomenon while dealing with perishability of climacteric fruits and this is an important consideration for employing appropriate active packaging technique for a desired commodity (Fig 6.3).

STORAGE TEMPERATURE

Storage temperature plays an important role in deterioration of fresh commodities. For eveiy increase of 10°, the rate of deterioration increases by 2-3 folds. Every commodity has an optimal temperature for storage at which it maintains maximum quality and wholesomeness. Usually, the ideal temperature for storage of fresh commodity depends on its geographical origin, that is why majority of tropical fruits have an ideal temperature of 12°C in contrast to fruits from temperate regions whose ideal temperature of storage is 0°C (Tucker et al., 2009). This can be easily observed at a household level in case of storage of banana under refrigerated condition where it tends to results in “chill injury.” The interaction of active packaging and storage temperature can be made clearer when the big picture of reduced respiration rate, reduced sensitivity to ethylene, and decreased transpiration are brought into consideration. So, general trend is observed that products have longer shelf life at low temperature, however as mentioned earlier the lowest safe storage temperature used earlier might not be same for each commodity. Thus optimum temperature for storage is relatively higher for the produce susceptible to chill injury.

RELATIVE HUMIDITY

RH is considered to be one of the important environmental factors to be controlled for maintaining optimal quality of foods. Since fruits tend to lose their moisture due to transpiration as a result of deficit in the vapor pressure between produce and the ambient ah. This not leads to the reduction of seal- able weight but also results in destruction of nutrients and sensoiy attributes of the produce. “Who -would like relish the wilted berries of the grapes?” RH is an important parameter to prevent quality loss, since fruits will rapidly lose moisture at low RH. These interventions are important even when we make sure that we safeguard the quality of products in a cold store. Condition of water loss exacerbation is observed in case of high rate of ah flow and large temperature differential on refrigeration coil. The overall effect of the enthe above- mentioned factor in relation to RH should be considered in a holistic manner. Since the cumulative effect of all the measures taken to prevent quality loss should be well balanced. For example, if we are storing a commodity in a packaging material we will make sure appropriate porosity of the packaging material for the marginal respiration of the produce, so package with moisture scavenger will be appropriate for executing this approach.

HANDLING

Handling plays an important role in maintaining quality since physical damage in the form of bruises, compression, results in high respiration rate. So, maintaining the integrity of the product is veiy essential to maintain its wholesomeness. Various instances of physical damage in case of fruits include finger bruises, inappropriate removal of plant parts (inappropriate berry separation) and impact bruising because of rough surfaces. So, appropriate handling will ensure good product quality.

 
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