Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

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BIOCHEMISTRY OF FRUITS 31 content is generally very high in ripe mangoes and can reach levels in excess of 90% of the total soluble solids content. Fructose is the predominant sugar in mangoes. In contrast to the bananas, the sucrose levels increase with the advancement of ripening in mangoes, potentially due to gluconeogenesis from organic acids (Kumar and Selvaraj, 1990). As well, the levels of pentose sugars increase during ripening, and could be related to an increase in the activity of the pentose phosphate pathway. 3.3.1.3 Glycolysis The conversion of starch to sugars and their subsequent metabolism occur in different compartments. During the development of fruits, photosynthetically fixed carbon is utilized for both respiration and biosynthesis. During this phase, the biosynthetic processes dominate. As the fruit matures and begin to ripen, the pattern of sugar utilization changes. Ripening is a highly energy-intensive process. And this is reflected in the burst in respiratory carbon dioxide evolution during ripening. As mentioned earlier, the respiratory burst is characteristic of some fruits that are designated as climacteric fruits. The postharvest shelf life of fruits can depend on their intensity of respiration. Fruits such as mango and banana possess high level of respiratory activity and are highly perishable. The application of controlled atmosphere conditions having low oxygen levels and low temperature have thus become a routine technology for the long-term preservation of fruits. The sugars and sugar phosphates generated during the catabolism of starch are metabolized through the glycolysis and citric acid cycle (Fig. 3.4). Sugar phosphates can also be channeled through the pentose phosphate pathway, which is a major metabolic cycle that provides reducing power for biosynthetic reactions in the form of NADPH, as well as supplying carbon skeletons for the biosynthesis of several secondary plant products. The organic acids stored in the vacuole are metabolized through the functional reversal of respiratory pathway, which is termed as gluconeogenesis. Altogether, sugar metabolism is a key biochemical characteristic of the fruits. In the glycolytic steps of reactions (Fig. 3.4), glucose-6-phosphate is isomerized to fructose-6-phosphate by the enzyme hexose phosphate isomerase. Glucose-6-phosphate is derived from glucose-1-phosphate by the action of glucose phosphate mutase. Fructose- 6-phosphate is phosphorylated at the C1 position yielding fructose-1,6-bisphosphate. This reaction is catalyzed by the enzyme phosphofructokinase in the presence of ATP. Fructose- 1,6-bisphosphate is further cleaved into two three-carbon intermediates, dihydroxyacetone phosphate and glyceraldehyde-3-phosphate, catalyzed by the enzyme aldolase. These two compounds are interconvertible through an isomerization reaction mediated by triose phosphate isomerase. Glyceraldehyde-3-phosphate is subsequently phosphorylated at the C1 position using orthophosphate, as well as oxidized using nicotinamide adenine dinucleotide (NAD), to generate 1,3-diphosphoglycerate and nicotinamide adenine dinucleotide plus hydrogen (NADH). In the next reaction, 1,3-diphosphoglycerate is dephosphorylated by glycerate-3-phosphate kinase in the presence of ADP, along with the formation of ATP. Glycerate-3-phosphate formed during this reaction is further isomerized to 2-phosphoglycerate in the presence of phosphoglycerate mutase. In the presence of the enzyme enolase, 2-phosphoglycerate is converted to phosphoenol pyruvate (PEP). Dephosphorylation of phosphoenolpyruvate in the presence of ADP by pyruvate kinase yields pyruvate and ATP. Metabolic fate of pyruvate is highly regulated. Under normal conditions, it is converted to acetyl coA, which then enters the citric acid cycle. Under anaerobic
32 POSTHARVEST BIOLOGY & TECHNOLOGY OF FRUITS, VEGETABLES, & FLOWERS Glucose Hexokinase ATP ADP Glucose-6-phosphate Hexosephosphate isomerase Triose phosphate isomerase Dihydroxyacetone pghosphate Aldolase ATP ADP Fructose-6-phosphate Phosphofructokinase Fructose-1,6-bisphosphate Glyceraldehyde-3-phosphate NAD NADH Glyceraldehyde-3-phosphate dehydrogenase 1,3-Diphosphoglycerate ADP ATP Glycerate-3-phosphate kinase 3-Phosphoglycerate NAD NADH 2-Phosphoglycerate Phosphoglycerate mutase ATP ADP Enolase Ethanol Alcohol dehydrogenase Acetaldehyde Anaerobic metabolism Pyruvate decarboxylase CO 2 Pyruvate Phosphoenol pyruvate NAD Pyruvate dehydrogenase NADH Acetyl CoA Malate dehydrogenase Oxaloacetate Citrate synthse Citrate Aconitase Fumarase Malate Fumarate Succinate dehydrogenase NADH NAD FADH 2 FAD Succinate CoA-SH Citric acid cycle ATP ADP Succinate thiokinase NAD NADH Succinyl CoA NAD NADH CO 2 Isocitrate CO 2 Isocitrate dehydrogenase α-Ketoglutarate CoA-SH Fig. 3.4 Catabolism of sugars through glycolytic pathway and citric acid cycle. conditions, pyruvate can be metabolized to ethanol, which is a byproduct in several ripening fruits. There are two key regulatory steps in glycolysis: one mediated by phosphofructokinase (PFK) and the other by pyruvate kinase. In addition, there are other types of modulation involving cofactors and enzyme structural changes reported to be involved in glycolytic
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Page 7 and 8: vi CONTENTS 9 Structural Deteriorat
Page 9 and 10: Contributors Ishan Adyanthaya Depar
Page 11 and 12: x CONTRIBUTORS Gopinadhan Paliyath
Page 13 and 14: xii PREFACE difficult to find a boo
Page 16 and 17: Chapter 1 Postharvest Biology and T
Page 18 and 19: POSTHARVEST BIOLOGY AND TECHNOLOGY
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Page 34 and 35: Chapter 3 Biochemistry of Fruits Go
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BIOCHEMISTRY OF FLOWER SENESCENCE 8
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PROGRAMMED CELL DEATH DURING PLANT
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(a) (a′) (b) (b′) (c) (d) Fig.
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Chapter 6 Ethylene Perception and G
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ETHYLENE PERCEPTION AND GENE EXPRES
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Chapter 7 Enhancing Postharvest She
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ENHANCING POSTHARVEST SHELF LIFE AN
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THE BREAKDOWN OF CELL WALL COMPONEN
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Table 8.3 Transgenic genetics to de
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Chapter 9 Structural Deterioration
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PHOSPHOLIPASE D, MEMBRANE DETERIORA
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Fig. 9.3 Fracture face of a fully o
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PHOSPHOLIPASE D INHIBITION TECHNOLO
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HEAT TREATMENT FOR ENHANCING POSTHA
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THE ROLE OF POLYPHENOLS 261 mainly
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THE ROLE OF POLYPHENOLS 263 Table 1
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THE ROLE OF POLYPHENOLS 265 Pentose
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THE ROLE OF POLYPHENOLS 267 Phenyla
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THE ROLE OF POLYPHENOLS 269 3' OH H
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THE ROLE OF POLYPHENOLS 271 OH OH O
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THE ROLE OF POLYPHENOLS 273 compoun
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THE ROLE OF POLYPHENOLS 275 washing
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THE ROLE OF POLYPHENOLS 277 (Fujita
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THE ROLE OF POLYPHENOLS 279 Boyer,
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THE ROLE OF POLYPHENOLS 281 Peschel
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ISOPRENOID BIOSYNTHESIS IN FRUITS A
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Chapter 14 Postharvest Treatments A
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POSTHARVEST TREATMENTS AFFECTING SE
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Chapter 15 Polyamines and Regulatio
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POLYAMINES AND REGULATION OF RIPENI
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Chapter 16 Postharvest Enhancement
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POSTHARVEST ENHANCEMENT OF PHENOLIC
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RHIZOSPHERE MICROORGANISMS 361 the
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RHIZOSPHERE MICROORGANISMS 363 Rese
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RHIZOSPHERE MICROORGANISMS 365 Tabl
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RHIZOSPHERE MICROORGANISMS 367 Toma
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RHIZOSPHERE MICROORGANISMS 369 Such
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RHIZOSPHERE MICROORGANISMS 371 Gian
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Chapter 18 Biotechnological Approac
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BIOTECHNOLOGICAL APPROACHES 375 tec
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BIOTECHNOLOGICAL APPROACHES 379 suc
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BIOTECHNOLOGICAL APPROACHES 389 Kik
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BIOSENSOR-BASED TECHNOLOGIES 419 20
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BIOSENSOR-BASED TECHNOLOGIES 425 Li
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BIOSENSOR-BASED TECHNOLOGIES 427 So
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Cl O O O OH Cl O OH Cl Cl Cl 2,4-Di
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BIOSENSOR-BASED TECHNOLOGIES 441 Le
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Chapter 21 Changes in Nutritional Q
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CHANGES IN NUTRITIONAL QUALITY OF F
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Index Abscisic acid (ABA), 65, 210,
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INDEX 469 Biosensor-based technolog
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INDEX 471 Cryptochlorogenic acid (4
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INDEX 473 French bean, 95 Fresh-cut
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INDEX 475 LePLDα3 (AY013253), 213-
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INDEX 477 Pectin methylesterase (PM
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INDEX 479 PSY1 expression, 289 PSY1
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INDEX 481 Sugars, biosynthesis of,
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