CHAPTER 1 INTRODUCTION

Transcription

1 CHAPTER 1 INTRODUCTION

2 It is a common knowledge in biological science that mammalian and plant cells are constantly exposed to a variety of oxidizing agents. These oxidizing agents may be present in air, food and water or they may be produced by metabolic activity within the cells. However, it is important to maintain a balance between oxidants and antioxidants to be able to sustain optimal physiological conditions. Overproduction of oxidants can cause an imbalance, leading to oxidative stress (Ames et al., 1993; Adom et al., 2003; Oguntibeju et al., 2013). Oxidative stress can cause oxidative damage to macromolecules such as lipids, proteins, DNA and consequently lead to increased risk for developing chronic diseases such as cancer and cardiovascular disease (Ames et al., 1993; Liu et al., 1995). In order to prevent or reduce the oxidative stress induced by free radicals, sufficient amounts of antioxidants need to be consumed and fruits and vegetables are known to contain a variety of antioxidant compounds such as phenolics and carotenoids which may help protect cellular systems from oxidative damage and reduce the risk of developing chronic diseases (Wang et al., 1996; Vinson et al., 2001; Adom et al., 2003). Fruits and vegetables are major sources of several essential nutrients that include vitamins, minerals and dietary fibers. Their nutritional and health beneficial properties are increasing their demand among consumers. Innumerable studies suggest that a diet rich in fruits and vegetables reduces the risk of developing cancer, cardiovascular, and several other diseases (Kang et al., 2003; Zhao et al., 2004; Scalbert et al., 2005). Human evolution was potentially linked initially to the consumption of naturally available fruits and vegetables, which later might have resulted in the selection of preferred plants and varieties for agriculture. They are also used in medical systems such as Ayurveda (Paliyath et al., 2008). Fruits and vegetables are of immense significance to man. In India, fruits have been given a place of honor on being offered to God at every festival and have also been mentioned in our epics like Mahabharata, Ramayana and writings of Sushrutha and Charaka (Verma & Joshi, 2000). India, with diverse soil and climate types comprising several agro-ecological regions, provides ample opportunity to grow a variety of crops (Nayak & Mukhopadhyay, 2008). Diversified agro-climatic conditions, ranging from tropical to temperate; afford ample opportunities to grow a larger number of fruits and vegetables, in different countries of the world. The production of the fruits and vegetables has received a greater attention even at the expense of conservation of the hard earned crops. Happily the recent past Page 1

3 has witnessed a keen interest both at the research and policy level to focus on the measures to conserve the various horticultural crops (Verma & Joshi, 2000). The aggregate cropping patterns of the country are represented by the gross cropped area allocation among different crops and commodity groups. India has experienced a considerable degree of crop diversification in term of changes in the area under various crops since the Green Revolution, which was largely oriented towards increasing food grains production to meet the objective of self-sufficiency and resolve the country s food security problem. In the past one decade, the change in cropping pattern is more towards the horticulture sector and commercial crops (Mittal, 2007). India's diverse climate ensures availability of all varieties of fresh fruits and vegetables. India ranks second in fruits and vegetables production in the world, after China. India's total fruit and vegetable production according to the Minister of Agriculture was lakh tonnes and 1, lakh tonnes, respectively in and the production has increased and reached to lakh tones and 1, lakh tones respectively in As compared to the , the production of total fruits and vegetables has risen slightly in over the last year (TOI, 2012). India is home to wild species of mangoes, bananas, several cucurbits, beans, tuber crops etc. India ranks second in production of Potatoes, Onions, Cauliflowers, Brinjal and Cabbages etc. The production share of major fruit crops and vegetables are presented in the Figs. 1.1 & 1.2. Amongst fruits, the country ranks first in production of Bananas, Papayas, Mangoes and Lemons and limes (IHD, 2011) Gujarat is occupying 4 th, 6 th and 3 rd places in India in production of fruit, vegetable and spices, respectively. Total agricultural area is 88 lakh hectares and out of that the horticulture area is lakh hectares, i.e. making around 16.5% of the production. The production of horticulture crop is Rs crores i.e. 23% against Rs crores of total agriculture production (ADP, 2013). A Gujarat state account for 10% of fruits produced in India, and is in third position in state-wise production, after Andhra Pradesh and Maharashtra. According to the records of the central and state governments, in , fruit production in Gujarat touched lakh metric tons. In the state produced lakh metric tons. Two reports released recently by the Union Agriculture Department and the State Agriculture Department say that fruit production in the state increased by around 11.13% in as compared to Gujarat government records showed that in , banana topped the state's list followed by papaya and mango (TOI, 2013). Page 2

4 Fig. 1.1: Production share of major fruit crops in India ( ) Fig. 1.2: Production share of major vegetable crops in India ( ) 1.1. Fruit Ripening: Fruit ripening is a highly coordinated, genetically programmed phenomenon which involves an irreversible phenomenon series of physiological, biochemical, an Page 3

5 organoleptic changes, that finally leads to the development of a soft edible ripe fruit with desirable quality attributes. Ezhilarasi & Tamilmani (2009) and many other researchers stated that the ripening of fruits may be defined as the sequence of changes in colour, flavour and texture which lead to the state at which the fruit is acceptable to eat. A wide spectrum of biochemical changes shown below are involved during fruit ripening (Brady, 1987). Chlorophyll degradation, Biosynthesis of carotenoids, Biosynthesis of anthocyanins, Import/accumulation and modification of sugars and amino acids, Accumulation of essential oils, Flavour and aroma components, Increased activity of cell wall-degrading enzymes, Increased respiration, Transient increase in ethylene production. Fruit species are categorized as either climacteric or non-climacteric based on physiological differences in their ripening patterns (Table 1.1). Climacteric fruits, harvested at full maturity, can be ripened off the parent plant. The respiration rate and ethylene formation though minimal at maturity, raise dramatically to a climacteric peak, at the onset of ripening, after which it declines (Gamage & Rehman, 1999). Nonclimacteric fruits are not capable of continuing their ripening process, once they are detached from the parent plant. Also, these fruits produce a very small quantity of endogenous ethylene, and do not respond to external ethylene treatment. Nonclimacteric fruits show comparatively low profile and a gradual decline in their respiration pattern and ethylene production, throughout the ripening process (Gamage & Rehman, 1999; Prasanna et al., 2007). Table 1.1: Classification of Fruits based on their climacteric nature Climacteric fruits Apple Banana Mango Papaya Peach Pear Persimmon Plum Non-Climacteric fruits Cherry Grape Capsicum Litchi Melon Orange Pineapple Pomegranate Page 4

6 Fruits and vegetables have a high market value and the maintenance of quality after harvest is an important issue to growers. Several factors, such as environmental conditions, cultivars, cultural practices, susceptibility to pests and diseases, time of harvest and postharvest conditions determine the quality of these commodities. As quality greatly affects the consumers preferences, it is a key factor for the marketing of fresh fruits overseas. To gain the best value for growers, storage operators and consumers, it is very important to maintain quality throughout preharvest development, postharvest storage, and subsequent distribution and marketing chains (Sharma et al., 2008) Factors Affecting Quantity and Quality of Fruits: The physiological status is directly or indirectly influenced by extent of diseases, pests infection and mechanical injuries along with the factors influencing the preharvest, harvest and post-harvest aspects of a fruit (Fig. 1.3) (Salunkhe et al., 1991). Therefore, the understanding of post-harvest physiology of fruit is fundamental in deciding different approaches for controlling the losses. The quality attributes are determined by plant variety, stage of maturity or ripening and the pre- and postharvest conditions; and all can change rapidly during postharvest storage. Fig. 1.3: The central role of physiological status of fruit in determining the final quantity and quality of fruits. Page 5

7 1.3. Preharvest Factors: There are numerous preharvest factors affecting the postharvest quality and life of fruits and vegetables, including harvest maturity, cultivar or variety, climate and soil in which the produce grew, chemicals applied and water status (Thompson, 2003a). Within each commodity there is a range of genotypic variation in composition, quality and postharvest life (Kader, 2002). The soil type and its fertility also affect the chemical composition of the produce. In some cases, the mineral content of fruits, such as phosphorous (Knowles et al., 2001), potassium (Cirulli & Ciccarese, 1981; Chiesa et al., 1998), and calcium (Yuen, 1993; Rabus & Streif, 2000) can be used to predict postharvest quality. Rootstock used in fruit production varies in their water and nutrient uptake abilities and in resistance to pests and diseases and thus have a profound effect on the postharvest life of the produce (Tomala et al., 1999). Climatic factors such as light intensity and temperature have strong influences on the composition and nutritional quality of fruits and vegetables. Those constantly exposed to the sun may have different quality and postharvest characteristics from those growing on the shady side (Kader & Rolle, 2004) Postharvest Factors: Fruits and vegetables undergo many physiological changes during postharvest storage, including tissue softening, increase in sugar level, decrease in organic acid levels, degradation of chlorophyll accompanied by the synthesis of anthocyanins or carotenoids upon maturation, production and losses of volatile flavor compounds, decrease in phenolic and amino acid contents and breakdown of cell materials due to respiration (Sharma & Singh, 2000). Harvesting practices determine the extent of variability in maturity and physical injuries. Physical injuries lead to accelerated loss of water and vitamin C and increased susceptibility to decay by fungi or pathogens during storage (Sharma & Singh, 2000; Kader, 2002). Temperature and relative humidity (RH) directly affect postharvest respiration and transpiration of fruits and vegetables. Elevated temperature would speed up respiration, leading to increased ethylene production and high carbon dioxide level (Kader, 1985), and thus changes in flavour, taste, colour, texture, appearance and nutrients of the produce. The most important quality attributes contributing to the marketability of fresh produce includes appearance, colour, texture, flavuor, nutritional value and microbial safety. Page 6

8 Appearance: Appearance is the most important quality attribute of fresh produce, with primary concern for size and colour uniformity, glossiness and absence of defects in shape or skin finish (Aked, 2000). Many fruits and vegetables undergo colour changes as part of the ripening process. Colour is of special importance in fruits and vegetables. The colour change during fruit ripening is due to the unmasking of previously present pigments by degradation of chlorophyll and dismantling of photosynthetic apparatus and synthesis of different types of anthocyanins and accumulation of carotenoids (Tucker & Grierson, 1987; Lizada, 1993) Texture: The texture of fruits and vegetables is often interpreted in terms of firmness, crispness, juiciness and toughness. The major textural changes resulting in the softening of fruit are due to enzyme mediated alterations in the structure and composition of cell wall, partial or complete solubilization of cell wall polysaccharides such as pectins and cellulose (Tucker & Grierson, 1987), and hydrolysis of starch and other storage polysaccharides (Selvaraj et al., 1989; Fuchs et al., 1980). Losses in juiciness often result in dry and tough structures that lead to adverse effects on quality (Lin & Zhao, 2007) Flavor: Flavor involves perception of many taste and aroma components (Kader, 2002). Common taste components in fresh produce are sweetness, acidity, astringency and bitterness. The taste development is due to a general increase in sweetness, which is the result of increased gluconeogenesis, hydrolysis of polysaccharides, especially starch, decreased acidity, and accumulation of sugars and organic acids resulting in an excellent sugar/acid blend (Lizada, 1993; Grierson et al., 1981; Selvaraj et al., 1989). Bitterness and astringency can develop in various fruits and vegetables under certain storage conditions. The aroma profile can change dramatically during the postharvest life of fresh produce, particularly in climacteric fruits, in which the dominant volatile may vary significantly based on maturity of the fruit Nutritional Quality: Fresh fruits and vegetables are important source of nutrients, including vitamins (B6, C, thiamin, niacin), minerals, dietary fibers and significant amounts of phytochemicals that play an important role in human health. Postharvest losses in Page 7

9 nutritional quality particularly vitamin C content and some phytochemicals, can be substantial (Lin & Zhao, 2007) Safety: Safety factors include naturally occurring toxicants, contaminants such as chemical residues and heavy metals and microbial contamination. Fresh produce items are highly susceptible to fungal spoilage. Proper sanitation and handling procedures can help in reducing the potential risk of contaminations (Lin & Zhao, 2007) Postharvest Activities of Fruits and Vegetables: Postharvest problems of fruits and vegetables include water loss, decreased shelf life, fast ripening process, off flavor, change in firmness, increaes in respiration, increaes in ethylene production and finally unacceptable appearance of the produce. Different types of synthetic and degradative changes that take place after fruit is harvested are presented in Table 1.2. Table 1.2: Postharvest Changes in Fruits and Vegetables Synthetic Synthesis of carotenoids Synthesis of anthocyanins Synthesis of flavour volatiles Synthesis of starch Synthesis of lignin Preservation of selective membranes Interconvertion of sugars Protein synthesis Gene transcription Ethylene biosynthesis Degradative Destruction of chloroplast Breakdown of chlorophyll Starch hydrolysis Organic acid catabolism Oxidation of substrates Inactivation of phenolic compounds Hydrolysis of pectin Breakdown of biological membranes Cell wall softening 1.6. Postharvest Losses: Tropical fruits are very susceptible to qualitative and quantitative deterioration and losses, including sensorial, microbial and nutritional. Major causes of losses are attributed to fungal decay, chilling injury and rapid maturation that enhance senescence process (Chan & Tian, 2006). Huge postharvest losses of fruits and vegetables are a matter of grave concern for any country whose economy is agriculture based. But this is a general phenomenon happening in almost every developing country. Fruits and Page 8

10 vegetables are highly perishable commodities that require to be handled with much care to minimize losses. Because of their high moisture content horticultural crops are inherently more liable to deteriorate especially under tropical conditions. They are biologically active and carry out transpiration, respiration, ripening and other biochemical activities, which result in quality deterioration. Two basic problems of post harvest managements in India are insufficient infrastructure and inadequate post harvest management. The extent of post harvest losses for horticultural commodities in India reaches up to the level of 40%, to the tune of Rs. 44, 000 crore per annum (Rolle, 2006; Pulamte, 2008). Gujarat ranks 2 nd in wasting postharvest fruits and vegetables, according to a national survey by industry body Assocham. Gujarat saw losses to the tune of worth about Rs. 11, 400 crore in postharvest fruits and vegetables (TOI, 2013). The postharvest management of fruit and vegetables in most developing countries in the region is, however, far from satisfactory. The major constraints include inefficient handling and transportation; poor technologies for storage, processing, and packaging; involvement of too many diverse factors; and poor infrastructure (APO, 2006). Minimizing postharvest losses of produce that has invested substantial labor, materials and capital to grow is a very effective way to increase food availability without further boosting crop production (Kader, 2005, Wills et al., 2007). To reduce these losses, understanding the causes of deterioration in fruits and vegetables is the fundamental step, and followed by utilizing appropriate and affordable technological procedures to delay senescence and conserve quality of produce (Wu, 2010). In light of the incidence of the huge postharvest losses in the region and new challenges faced under trade liberalization and globalization, serious efforts are needed to reduce postharvest losses, especially of fruit and vegetables. Although India is a major producer of horticultural crops, many Indians are unable to obtain their daily requirement of fruits and vegetables and the Human Development Index (HDI) is very low. It is well established that the quality of the harvested commodities can be retained till their consumption if the rate of metabolic activities are reduced by adopting the appropriate postharvest handling operations (Sharma & Singh, 2000). Considerable quantities of fruits and vegetables produced in India go waste owing to improper postharvest operations and the lack of processing. This results in a considerable gap between gross food production and net availability. It should be noted that the production of fruits and vegetables is of significance only when they reach the consumer in good condition and at a reasonable price (APO, 2006). Page 9

11 1.7. Postharvesting Methods: The term shelf-life or the synonyms storage life and storability, can be defined as the time periods that a fruit or vegetable can be expected to maintain a predetermined level of quality under specified storage conditions. Various technologies have been implemented to prolong horticultural products shelf life, including low temperature storage, plastic packaging usage aiming to create modified atmospheres, as well as hydrothermal treatments application and formulations containing biological agents, among others (Quezada et al., 2003). But even with the accessibility of several modern technologies the postharvest losses of fruit are still high. Therefore, there is a need to find alternative adequate postharvest technologies for reducing postharvest losses, thus extending the shelf life and maintaining the keeping quality at low costs. These techniques should be simple, easily available, environmentally friendly and reasonable, and having no known harmful effects on human health, hence the possibility of using chemical treatments (Conforti & Zinck, 2002) and edible coatings (Tharanathan & Kittur, 2003). Both quantitative and qualitative losses occur in horticultural commodities between harvest and consumption. Qualitative losses, such as loss in edibility, nutritional quality, caloric value and consumer acceptability of fresh produce, are much more difficult to assess than are quantitative losses. The goals of postharvest research and extension are to maintain quality and safety and minimize losses of horticultural crops and their products between production and consumption. Reduction of postharvest losses increases food availability to the growing human population decreases the area needed for production and conserves natural resources (Kader, 1999) 1.8. Chemical Treatments: The storage or marketable life of crops can be extended by various treatments applied to them postharvest. A variety of chemicals is applied to crops after harvest to control diseases, delay or prevent sprouting or affect the crop s metabolism. Crops may be exposed to certain gases such as ethylene, or in other circumstances precautions have to be taken to protect the crops from gases including ethylene. Chemicals are applied to crops to control pest infestations, to correct nutrient imbalances in the crop which may shorten its storage life or cause physiological disorders (Thompson, 1996). Various plant growth regulators (PGRs) (Salunkhe et al., 1991) and chemicals (Singh & Sharma, 2000) are being used at various stages of production and post harvest Page 10

12 handling for delaying ripening and colour alteration. These chemicals can be applied as dip, spray or through injection. Some commonly used chemicals and respective effects on some fruits are presented in Table 1.3. Table 1.3: Some examples of Plant Growth Regulators (PGRs) and Chemicals PGRs and Chemicals Cytokinins, kinetin Benzyl adenine Gibberellins used to extend the shelf life of fruits and vegetables. Effects Fruit Reference Delays chlorophyll degradation and senescence Delays chlorophyll degradation and senescence Retards maturation, ripening, delay chlorophyll degradation, increases peel firmness Cucumber Cherry Tomato, Kiwi, banana, citrus. Salunkhe et al. (1991) Salunkhe et al. (1991) Salunkhe et al. (1991) Salicylic acid Delays ripening Banana Srivastava & Dwivedi (2000) Calcium nitrate Calcium chloride Reduces weight loss and decay Grape Gupta et al. (1980) Enhances keeping quality; delayed fruit ripening Mango, strawberry Waskar & Gaikwad (2005); Andrea (1999) 1.9. Edible Coatings: Another potentially viable technology for shelf life extension of fruits and vegetables is the use of edible coatings. There are several reasons for investigating edible coatings. One of them is the introduction of new food product categories, such as safe, convenience and high quality products (Buonocore et al., 2003; Kokoszka & Lenart, 2007). Yet the main reason is the need to reduce the volume of waste through the use of packaging made of naturally occurring polymers which replace synthetic materials. Edible coatings offer such a solution. They protect food against the loss of nutrients (i.e. permit water vapor, oxygen and carbon dioxide permeation) (Buonocore et al., 2003). An edible film is defined as a thin layer, which can be consumed, coated on a food or placed as barrier between the food and the surrounding environment. For the past 10 years, research on edible films and coatings in foods is driven by food engineers due to the high demand of consumers for longer shelf-life and better quality of fresh foods as well as of environmentally friendly packagings (Siracusa et al., 2008). Indeed, edible films and coatings can be used as a vehicle for incorporating natural or Page 11

13 chemical antimicrobial agents, antioxidants, enzymes or functional ingredients such as probiotics, minerals and vitamins (Siracusa et al., 2008). The functional properties of edible coatings on fruits and vegetables are presented in the Fig The edible films are classified into three categories taking into account the nature of their components: Hydrocolloids (containing proteins, polysaccharides or alginates), lipids (constituted by fatty acids, acylglycerols or waxes) and composites (made by combining substances from the two categories) (Greener-Donhowe & Fennema, 1994). Figure: 1.4 Functional properties of edible coating on fruits and vegetables The main research challenges to be considered include developing the formulations for each type of food, having biochemical, physicochemical and antimicrobial stability with no adverse effect on food sensory quality, as well as to be completely safe for human consumption and to possess sufficient mechanical strength and a competitive cost to replace current synthetic materials and also eliminating the synthetic preservative addition. These are the primary reasons for having it called the packaging technology of the future (Ramos-Garcia et al., 2010). Despite significant Page 12

14 benefits from using edible coatings for extending shelf life, enhancing quality and microbial safety of fresh fruits and vegetables, commercial applications on a broad range of fruits and vegetables are still very limited. It it toxically safe and regarded as a Generally Regarded as Safe (GRS), from the FAO, the FDA and several other food legislations (Baldwin, 1994). Park (1999) reported that edible coating material that is non-phytotoxic, tasteless, odorless, biodegradable and effective in preserving fruit quality. Thus, the concept of biodegradability enjoys both user-friendly and eco- friendly attributes and the raw materials are essentially derived from either replinishable agricultural feedstocks or marine food processing industry wastes, and therefore it capitalizes on natural resource conservation with an underpinning on environmentally friendly and safe atmosphere (Tharanathan, 2003). In addition, their functions fall entirely into green-packaging applications, such as the US EPA suggested plan for improved municipal waste management and reduction (Dan garan et al., 2009; Falguera et al., 2011). Table 1.4 summarizes the reports on using edible coatings for fresh fruits and vegetables. Table 1.4: Some examples of Edible coatings used to extend the shelf life of fruits and vegetables. Edible coatings Effects Fruit Reference Alginate Shelf life extension Peach Maftoonazad et al. (2008) Chitosan Carboxymethyl cellulose (CMC) Antimicrobial, shelf life extension Strawberry; Carambola Hernandez- Munoz et al. (2008); Gol et al. (2013 Shelf life extension Banana Malmiri et al. (2011) Gum arabic (GA) Delayed ripening Tomato Ali et al. (2010 & 2013) Hydroxypropyl methyl cellulose (HPMC) Zein Gelatin Carrageenan Postharvest quality retention & shelf life extension Maintains overall quality Lowest weight loss percentage Influences physical and chemical characteristics Sweet orange Apple Sweet cherries Pear Adetunji et al. (2012) Bai et al. (2003a) Lim et al. (2011) Moraes et al. (2012) Page 13

15 In view of these facts, the present study is proposed with an aim to investigate the impact of postharvest treatments (chemical as well as edible coating treatment) to improve the shelf life and quality of some commercially important horticultural commodities, with the following objectives: OBJECTIVES: Evaluation of the quality characteristics and shelf life of commercially important tropical fruits (Mango, Tomato and Banana) treated with selected chemical treatments. By elucidating the physico- chemical and biochemical responses of selected fruits to different chemical treatments. By determining the influence of postharvest treatments on the activities of cell wall degrading and antioxidant enzymes. Determination of the efficacy of the treatments in delaying the fruit ripening and extend the shelf life of above mentioned fruits. To investigate the effectiveness of different polysaccharide and protein based edible coatings to enhance the shelf life and maintain the valuable quality attributes of selected horticultural commodities such as Jamun, Strawberry, Capsicum, Guava, Tomato, Mango and Banana. By elucidating the changes in total antioxidants along with other physicochemical and biochemical changes during storage, as a result of different edible coating treatments. By improving the fruit quality in terms of fruit texture by delaying the changes in softening and antioxidant enzymes. Making recommendations for the use of essentially safe edible coatings on fruits to assure high quality and wholesomeness. Screening of antibacterial activity of Guava and Jamun fruit coated with different edible coating treatments. Elucidation of certain histo-architectural and histo-chemical changes in relation to physiological changes in the selected fruits (Mango and Banana) treated with chemical treatments and edible coatings. Page 14