P1: SFK/UKS P2: SFK BLBS107-c01 BLBS107-Sinha June 13, 2012 10:6 Trim: 276mm X 219mm Printer Name: Yet to Come Part 1 Biology, Biochemistry, Nutrition, and Microbiology COPYRIGHTED MATERIAL 1 P1: SFK/UKS P2: SFK BLBS107-c01 BLBS107-Sinha June 13, 2012 10:6 Trim: 276mm X 219mm Printer Name: Yet to Come 2 P1: SFK/UKS P2: SFK BLBS107-c01 BLBS107-Sinha June 13, 2012 10:6 Trim: 276mm X 219mm Printer Name: Yet to Come 1 Physiology and Classification of Fruits Kuo-Tan Li Introduction Berry Development of a Fruit Drupe Pollination and Fertilization Pome Fruit Set Hesperidium Parthenocarpy and Stenospermocarpy Pepo Fruit Growth Compound Fruits Cell Division Aggregate Fruit Cell Enlargement Multiple Fruit Seasonal Growth Curve Accessory Fruit Single Sigmoid Growth Pattern Culinary Classification of Fruits Double Sigmoid Growth Pattern Fruits Maturation, Ripening, and Senescence Fruits used as Vegetables Maturation of a Fruit Nuts Ripening of a Fruit Cereals Senescence of a Fruit References Physiological Changes of a Fruit toward Maturity Color Abstract: Fruits are an essential part of human diet and culture. Seed Maturity Various classification systems have been applied to fruits to meet Carbohydrate Profile various objectives. Physiological and morphological characteristics Acids of a given fruit species or even a given cultivar affect its postharvest Aroma and Flavor Compounds life and processing quality. This chapter provides a fundamental Firmness background on how a fruit develops in the field and how fruits are Tannins categorized in modern society. Respiration Fruit Classification Fruits Classified by Their Origin Fruits Classified by Respiration Rates and Ethylene INTRODUCTION Responses Botanical Classification of Fruits Fruits are indispensable in human diet to supply essential Simple Fruits vitamins, for example, vitamin A, B6, C, E, thiamine, niacin, Simple Dry Fruits minerals, and dietary fiber (Fourie 2001). Fruits are also sa- Achene vories that provide a pleasing taste. The majority of species of Capsule fruits that are grown and consumed in the modern world have Caryopsis been domesticated by the late Neolithic and Bronze Ages be- Cypsela tween 6000 and 3000 bc. In addition, a number of fruits that Fibrous Drupe have been extensively collected from the wild by the native Legume Nut people were not domesticated until the early twentieth cen- Simple Fleshy Fruit tury (Janick 2005). Some other fruits, although commonly Handbook of Fruits and Fruit Processing, Second Edition. Edited by Nirmal K. Sinha, Jiwan S. Sidhu, Jozsef´ Barta, James S. B. Wu and M. Pilar Cano. C 2012 John Wiley & Sons, Ltd. Published 2012 by John Wiley & Sons, Ltd. 3 P1: SFK/UKS P2: SFK BLBS107-c01 BLBS107-Sinha June 13, 2012 10:6 Trim: 276mm X 219mm Printer Name: Yet to Come 4 Part 1: Biology, Biochemistry, Nutrition, and Microbiology utilized by the local people, remain exotic to the rest of the grains from anthers to stigmas. Pollination in some species world. Nowadays, fruit production and processing are among occurs spontaneously at bloom due to their special structure the major industries in many countries, and the trading and of the flower or the specialized arrangement of their stigmas distribution of fruits have become an important international and stamens, for example, grapes and tomatoes. Pollination economic activity. Although world production and consump- in most other species usually will not be completed without tion of fruits have increased significantly, most people’s diets natural vectors, i.e., wind or insects (Stebbins 1970). The still fall short of the mark set by United Nation’s Food and majority of common fruit crops require insect for pollina- Agriculture Organization (FAO 2003). tion, and the pollination efficiency is usually improved by Botanically, a fruit is the reproductive structure of a flow- introducing bee (Apis) hives to the orchard during blooming ering plant in which seeds form and develop. In culinary arts, season (Morse and Calderone 2000). Flowers of some tropi- fruit normally refers to an edible, juicy, and sweet entity de- cal fruit crops, for example, mangos, are not attractive to bees. rived from a flower on any flowering plant. Among so many Instead, their major pollinators are native flies (Sung et al. species of flowering plants with so much anatomical diver- 2006). In commercial production, their pollination can be sity, only a relatively small group of species and fruit types benefited by introducing the oriental latrine fly (Chrysomya are common in human diet. Nevertheless, the physiological megacephala) to the orchard during bloom (Hu et al. 1995). and morphological characteristics of a given fruit species or Some fruits are dioecious, and pollen grains must be trans- even a given cultivar affect its postharvest life and process- ferred from a male flower in a male plant to a female flower in ing quality. Therefore, it is advisable to obtain a fundamental a female plant to complete the pollination process. Examples understanding on how a fruit develops in the field and how of dioecious fruits include the wind-pollinated mulberries fruits are categorized in modern society. and the insect-pollinated kiwifruit (Hopping 1990). In mo- noecious fruit crops such as wind-pollinated chestnuts, wal- nuts, and pecans; and insect-pollinated lychee (Stern 2003), DEVELOPMENT OF A FRUIT watermelons, and cucumbers, pollen grains must be trans- A fruit is developed from a flower and its associate tissues. ferred from a male flower to a female flower either on the The onset of fruit development begins as early as the differ- same plant or on separate plants to continue the fertilization entiation of flower by which the apical meristem on a shoot process. forms a flower or inflorescence instead of a leaf or a shoot. Fertilization takes place after the germination of pollen Anatomical changes begin at the edge of the meristem, first grains on the stigma. A pollen grain after successful germi- generating the calyx and the corolla, and later the androecium nation contains two sperm cells. Upon entering the ovule, (male) and the gynoecium (female) tissues. The process of one sperm cell fertilizes the egg cell and the other unites flower differentiation can be completed within a few days in with the two polar nuclei of the embryo sac. The sperm annual plants to nearly a year in some perennial plants. The and haploid egg combine to form a diploid zygote and later differentiation of gynoecium continues to form the carpel or the embryo of the seed. The other sperm and the two hap- pistil in which the ovule is hosted. A gynoecium may con- loid polar nuclei form a triploid nucleus and later the en- sist of a single carpel, multiple distinct (unfused) carpels, dosperm, a nutrient-rich tissue nourishing the developing or multiple connate (fused) carpels. Inside gynoecia ovules, embryo (Raghavan 2006). The ovary, which encompasses within one or more ovaries develop and later become seeds the ovule, develops into the pericarp of the fruit and helps to upon fertilization. When mature, gynoecia may function to protect and disperse the seeds. attract pollinators through aroma or nectar. At bloom or in In self-fertilized fruit crops, for example, in most peach and some instances prior to bloom, gynoecia receive pollen grains nectarine cultivars, successful fertilization can occur within on their specialized surface structure called a stigma and in one flower, and pollen grains from other flowers or from some cases actively select genetically different pollen grains other cultivars are not necessary (Weinbaum et al. 1986). On so as to avoid inbreeding. Gynoecia may facilitate the growth the other hand, fertilization in cross-pollinated fruit crops, of pollen tube to the ovule and the delivery of sperm to the for example, in most apple, pear, almond, and rabbiteye egg. The gynoecium forms the pericarp. The pericarp in most blueberry (Vaccinium ashei) cultivars, will not succeed with fruits differentiates into three distinct layers. The outer layer pollen grains from flowers of same cultivars or other cul- is called exocarp and normally becomes the peel of the fruit. tivars with incompatible genetic background. Therefore, it The middle layer is the mesocarp, the major edible part of requires the mixed planting of two genetically compatible most fleshy fruits. The inner layer is the endocarp, which cultivars in an orchard block to achieve a satisfactory yield directly surrounds the ovary and the seed. (Visser and Marcucci 1984, Dedej and Delaplane 2003). In some fruit crops, for example, northern highbush blueberries (Vaccinium corymbosum), although self-pollination is pos- Pollination and Fertilization sible to set fruit, cross-pollination by mixed planting two Most flowering plants will not set fruit without pollination or cultivars will increase the fruit size and quality (Huang et al. fertilization. Pollination is the process of transferring pollen 1997, Ehlenfeldt 2001, Bieniasz 2007). P1: SFK/UKS P2: SFK BLBS107-c01 BLBS107-Sinha June 13, 2012 10:6 Trim: 276mm X 219mm Printer Name: Yet to Come 1 Physiology and Classification of Fruits 5 The embryo of the developing seed produces plant hor- carpel. Seedless fruits can be a result of parthenocarpy or mone gibberellins at early development stages to trigger the stenospermocarpy. production of auxins and stimulates fruit growth (Ozga et al. In parthenocarpic fruit set, a flower continues to develop 2002). In conclusion, pollination and fertilization are nor- into a fruit without pollination or fertilization. Partheno- mally required to initiate fruit growth. carpy can be a natural event or induced by cultural practices (Gustafson 1942). Commercial banana and pineapple cul- Fruit Set tivars are naturally parthenocarpy, requiring no pollination (Simmonds 1953). Many citrus fruits will also set partheno- Fruit set refers to the retention of fruit on the plant after carpic fruits but require pollination to stimulate fruit growth. bloom. Most fruit crops produce numerous functional flowers Seedless watermelons are commercially produced by cross- but only a small percentage of the flowers continue to develop pollination between diploid and tetraploid parents (Terada into mature fruits.