- Email: [email protected]
FRUITS OF TEMPERATE CLIMATES | Commercial and Dietary Importance
FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance
2753
FRUITS OF TEMPERATE CLIMATES Contents Commercial and Dietary Importance Fruits of the Ericacae Factors Affecting Quality Improvement and Maintenance of Fruit Germplasm
Commercial and Dietary Importance L G Smith and S M Somerset, Queensland Department of Primary Industries, Hamilton, Queensland, Australia Copyright 2003, Elsevier Science Ltd. All Rights Reserved.
Commercial and Dietary Importance Definition 0001
‘Temperate-climate fruits’ refers to all fruits that normally grow further than 23.5 from the equator, but also includes avocado and citrus, fruits often classified as subtropical. Some temperate fruits can be grown at higher altitudes in tropical latitudes, although poor fruit set may occur in some species. ‘Fruits’ could be defined as seed-bearing plant organs that undergo a characteristic process, called ripening, changing from unpalatable to palatable (vegetables have no such sequence). Much of the information in this article is applicable to all fruits, and some tropical fruits are listed here for comparison. Horticultural products that could be classified as temperate fruits (such as many nuts and the tomato) are addressed in separate entries. Production
0002
0003
Temperate fruit production is a major industry. The production and marketing of fresh fruits are much more labor-intensive than that of broadacre crops, so that the temperate fruit industry is a major source of employment. As a consequence of the high labor content of production, large-scale fruit production by major companies is tending to shift towards suitable regions with access to cheap labor. The estimated world production of the major temperate fruits in listed in Table 1. The production for individual countries is shown in Table 2. For many temperate fruits, large quantities are processed in
one form or another (e.g., canned, dried, wine, juice, glace´ ), and the production data in Tables 1 and 2 include that for processed fruit. The specific details of world fruit production are difficult to determine since, in many countries, fruit-production data are unavailable, and reporting countries also lack standards of uniform data presentation. Grapes are the major temperate fruit in terms of tonnes produced, with large quantities going into wine and dried fruits. The major grape-producing countries are Italy, France, the USA, Spain, and countries of the former USSR. Second, in terms of quantity produced, are oranges, many of which are processed into juice, and third are apples, probably the temperate fruit most often eaten fresh, although large quantities are also juiced, dried, and canned. Buying patterns in British households for 12 common fruits are presented in Table 3.
0004
Dietary Importance
There are many different aspects to fruit in the diet. Not only is fruit an important source of dietary fiber, carbohydrate, and vitamin C and A, but because of its flavor, it also influences the intake of many other foods and therefore can exert indirect effects on the diet. Although different fruits are morphologically and botanically diverse, in fruit consumption studies, the nutritional composition is generally considered collectively, rather than in terms of distinct fruits. It is therefore more appropriate to discuss the nutritional impact of fruits as a whole.
0005
Historical Man has been attracted to the sweet taste and full aroma of fruit since prehistoric times, and attempts by man to cultivate various fruits date back over 8000 years. It is not surprising then that the word ‘fruit’ is often used to imply a pleasure or reward (e.g., in expressions such as ‘fruit of our labor’). Their sweet taste is due to the high content of sugars, in particular fructose, sucrose, and glucose. The high sugar content has been recognized for centuries and is exploited, for
0006
2754 FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance tbl0001
Table 1 Characteristics of the major temperate fruits, with four major tropical fruits included for comparison
Temperate Grapes Oranges Apples Watermelons Pears Cantaloupes Peaches Plums Lemons Grapefruit Strawberries Apricots Avocados Currants Raspberries Tropical Bananas Mangoes Pineapples Papaya
World productiond ( 106 t)
Ability toripen after harvest
Recommended storage temperaturea ( C)
57 397 66 212 56 060 47 646 14 379 17 849f 11 065i 8 008 9 335j 5 072l 2 601 2 670 2 325 654 326
No No Yes No Yes Yesg Yes Yes No No No Yes Yes No No
58 618 23 455 12 100 4 801
Yes Yes No Yes
Respirationratesa,b,c (mg CO2 kg1 h1) Ethylene productione
At storage temperature
At 20 C
Likely storage lifea
0 5–7 2–3 5–10 1.5 to 0.5 0–5 h 0 0.5 to 0 10–15k 14–16 0 0.5 to 0 8–10 0.5 to 0 0.5 to 0
1–5 m 3–12 w 3–12 m 2–3 w 2–7 m 1–4 w 2–3 w 1–4 w 1–2 m 1–1.5 m 5–7 d 2–3 w 3–10 w
<0.1 <0.1 10–100 0.1–1.0 10–100 10–100 10–100 10–100 <0.1 <0.1 <0.1 10–100 10–100
1–3 4–7 2–6 3–4 3–7 5–10 4–6 2–3 6–23 10–18 12–18 5–6 20–30
20–25 22–34 20–41 17–25 30–70 45–65 59–102 18–26 7–25 13–26 102–196 29–52 74–150
18–25
>99
13.5–15 10–13 6–20k 7–13
4–21 d 2–6 w 2–4 wk 1–3 w
21–75 45–150 4–7 4–10
33–142 75–200 28–43 22–39
2–3 d 0.1–1.0 <0.1 0.1–1.0 10–100
a Data largely from Hardenburg RE, Watada EE, and Wang CY (1986) The Commercial Storage of Fruits,Vegetables, and Florist and Nursery Stocks. USDA Handbook No. 96. Washington, DC: United States Department of Agriculture, with permission. b Values may vary with production area and cultivar. c Lower value would indicate rate for unripe fruit; a higher value would indicate a peak rate. d Data for 1998 from FAO (1999) Food and Agriculture Yearbook Statistic Series No. 148. Rome: Food and Agriculture Organization, with permission; total production includes processed, alcohol production and includes FAO estimates where individual country data not available. Missing data unavailable. e C2 H4 kg h1 at 20 C. Data largely from Kader AA (1992) Postharvest Technology of Horticultural Crops, 2nd edn. Location: University of California Division of Agriculture and Natural Resources, with permission. f Includes all melons other than watermelons. g Some cultivars (e.g., honeydew) ¼ No. h Not for honeydew melons. i Includes nectarines. j Includes limes. k Very much dependent on production area. l Includes pomelos and similar fruits. Note that storage temperature, storage life, and respiration rates vary according to fruit ripeness, cultivar, production area and other factors, and are presented here as a guide only.
example, in the drying of fruits, the high sugar content allowing their preservation and a water content sufficient to make the fruit palatable in the dried form. The production of alcohol from grapes and other fruits also depends on a high sugar content. Fruit consumption patterns now relate largely to consumer preferences. In the past, the traditional dietary role of temperate fruits was more of a luxury than a staple, but with the vast improvement of cultural practices, postharvest techniques and distribution systems, the availability of both fruit and fruit products has increased dramatically. Fruit is now more available, at an affordable price, to more of the world’s population than ever before. The modern role of fruit in the diet has thus changed from previous generations.
The Modern Dietary Role In the diets of peoples in temperate zones, the most important nutritional features are fruits of high contents of fiber, carbohydrate, and vitamin C, and low fat and protein contents. Fruit is prominent in the official dietary guidelines of many countries. Most developed countries encourage increased consumption of complex carbohydrates and fiber, which are abundant in fruits, and dietary recommendations in the UK and Germany specifically advise increased fruit consumption. One recent study in the USA found that 41% of the test population had no fruit or fruit juice on the day of survey. Substantial public health benefits might be gained if fruit consumption increased among the less affluent groups of people in the USA, and, probably, in other industrialized nations.
0007
FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance tbl0002
2755
Table 2 World production for 1998 (103 t) of eight major temperate fruits (includes all uses, processing, drying, alcohol production, etc.)
Africa Algeria Congo Egypt Ethiopia Libya Madagascar Mauritania Morocco Reunion Senegal Somalia South Africa Sudan Tanzania Tunisia Zimbabwe North and Central America Belize Canada Costa Rica Cuba El Salvador Guadeloupe Guatemala Honduras Jamaica Mexico Panama Trinidad and Tobago USA South America Argentina Bolivia Brazil Chile Colombia Ecuador Paraguay Peru Suriname Uruguay Venezuela Asia Afghanistan Bangladesh Armenia Azerbaijan Bhutan Cambodia China Cyprus Gaza Strip Georgia India Indonesia Iran Iraq Israel Japan
Grapes
Oranges
Apples
2 746 159
1415 65
3 298 400
470 47
1125
466 39
117 24
870 4 37 11
4 582 280 145 1 525 14 60 84
410
1 650
57
550
65
4
45 7
210
1 2
25
9 8
1 2
262
1 104
285
31
415
39 1
41
275
23 26
240
35
296
54
84
10
2 545
892
2 033
65 1 1485
934
17
2 120 30 20 3 86 156
56
5
35
490 17
129
79
840 858 540 4 19 250
1 069 399 100
1 300 833 280 36 146 285 23
850 305 132 4
1 273 17 111 2 5 585
30 8 900 17 122 70 17 839 170
53
4
452
5 076 4 704 2 021 23 738 1 665 17 13 76 140 11 12 971 330 106 144
2 287 125 2 275 700 2 200 305 90 251
515
83 6 5 892
Watermelons
8 259 261 24 50 140
510 340 36 1 80 83 72 4 005 27 15 12 571 25 833 841 94 22 987 115 410 217 208 234 12 185 528 12 208 12
8 58 62 2 804 45 105 115 2 000 614 1 800 316 325 131
1
Pears
47 1 100 12 16 500 20 2 1 848 1492 130 21 765 63 54 18 116 72 3 14 237 36 304 90
8 493 2
56 125 6
60 145
16 8
17 508 10
6 728 2
200 13 000
23 338 30 6 225 250
20 135
2 000 86 111 900
2 200 455 260 620
175 3 20 428
27
390 1 4 964 3 226 1 347 9 787 880 25 1 127 50 27 810 18
26 3 16
Cantaloupes
92 77 10 5 30 12 3 70 11613 22 96
Peaches
2 27
Plums
150 8 2 6
25 9 4 452 14
3 724 35
21 15
14 25
2 996 2
2 717 1
640
20 87
38 57
800 226 74 430
132 26 48 176
160 31 18 136
6 372 9 4
4
Continued
2756 FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance Table 2 Continued Grapes Jordan Kazakhstan North Korea South Korea Kuwait Kyrgyzstan Laos Lebanon Malaysia Oman Pakistan Philippines Saudi Arabia Syria Tajikstan Thailand Turkey Turkmenistan Uzbekistan Viet Nam Yemen Europe Albania Austria Belarus Bosnia and Herzegowina Bulgaria Croatia Czech Republic Denmark Estonia Finland France Germany Greece Hungary Ireland Italy Latvia Lithuania Macedonia Moldova Netherlands Norway Poland Portugal Romania Russian Federation Slovakia Slovenia Spain Sweden Switzerland UK Ukraine Yugoslavia Oceania Australia New Zealand
70 20
Oranges 40
22
75 2 130 450 120 26 3 650 177 585 155 30 216 68 234 17 624 421 38
74 28 155 11 1 410 20
9 208
315 830
379 150 3
1
1 814
1 921
25 244 825
764 874 300 76 128 4 842
2 380 588 1176 1 097 78
119
600
438
2 7 000 1 500 1 216 669
65 630 652
384
247
Apples
210
2 403
2 396 369 24
324 82 2 500 30 380 2 16 856 12 392 215 18 152 72 309 67 5 11 2 500 2 154 358 500 9 2 115 15 100 62 485 470 1 687 146 365 1 200 83 122 726 65 180 1 200 235 861 306 501
Watermelons 70 306 100 1 006 1 41 130 145 32 420 70 460 272 155 385 3 925 258 543 200 95 3 908 210
3 246 60
Pears 3 8 120 260
64
36
19 19
Cantaloupes 15
Peaches
Plums
11 2 100 147
36
3
2
50
40
400 16 130 51
46
80
40 27
29 16
1 800
400 5 82
190 9 69
3 718 2 10
2 892 12 77 45 23 78 83 33
100 300 1 33 35
415 32 35 2 605 4 12
2 65 9 8
84 21 6
4 2
1 9
280
512 76
256 387 71 37
590
931
120 25
10 9 7 130
2 520 30 786
395 325 99 88 4
83 160 64 50 12 5 561 16 95 25 160 74 213 172 41
150 6
470 15 480 54
210 416 8 115
518
1 429
149 4 6 20 56 6 12 107 18 404 155 22 4 150 1 10 16 170 480 36 33 3
6 2 3 20
7 72
980
62 18 20 9 3 888
74 72 1
50 46 111 96 15
610 31
FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance tbl0003
Table 3 Fruit-buying patterns of British householdsa Item
Percentage buying
Times per year
Bananas Apples Easy-peel oranges Grapes Pears Regular oranges Strawberries Melons Exotic fruit Peaches Pineapples Avocados
87 86 70 65 64 61 66 53 44 39 17 12
22 17 5 9 9 7 4 5 5 3 2 3
a Source AC Nielson 1998. From Hughes D (1999) Marketing fruit in Europe. In: Good Fruit and Vegetables, pp. 34–35. Melbourne: Rural Press, with permission.
Direct Nutritional Attributes 0008
0009
Fruit is generally high in dietary fiber and low in fats and oils, and is therefore an important food in diets designed to reduce the risk of coronary heart disease in developed countries. An exception is the avocado, which has an unusually high oil content (containing up to 30% fat, depending on the production area), but recent studies indicate a beneficial role of the avocado with respect to heart disease, possibly because 50–75% of the fat is monounsaturated. One dietary feature of fruit in general is the high content of water, ranging from 65% in apples to 88% in papaya. This feature enables fruit to quench thirst in addition to satisfying hunger. Vitamins
0010
0011
Ascorbic acid (vitamin C) is the principal vitamin supplied by fruit in the diet. Some fruit are particularly rich in this vitamin. Citrus have about 50 mg per 100 g, kiwi fruit about 100 mg per 100 g, and blackcurrants and bell peppers (Capsicum annum) have between 200 and 300 mg per 100 g. The orange-colored fruits such as rockmelon, peach, persimmon, tomato, and apricot are rich in b-carotene, which is converted to vitamin A in the body. Certain fruits can be rich in particular vitamins. For example rockmelon strawberry and orange have significant amounts of folic acid. Pantothenic acid is found in appreciable quantities in watermelons currants and berries, and nicotinic acid in apricots, nectarines, peaches, passion fruit, and guavas. Fiber
0012
Fruit is a rich source of pectins and gums, components of fiber, and thus fruit constitutes an important source of dietary fiber. Pectins have been shown to delay gastric emptying, which can lead to favorable
2757
changes in glycemic responses to particular foods. Pectin may also introduce a satiety effect.
Indirect Nutritional Consequences Fruit can be consumed in a number of different forms apart from fresh. The drying of fruit has been a popular preservation technique for many generations. The dehydration process concentrates those nutrients that are not heat- or light-labile. Vitamin C is the major casualty of this process. The dehydration process also decreases the water activity, thus increasing the keeping quality by making microbial growth less likely. Processed fruit is being increasingly used in the dairy industry, as an additive in fermented milk products such as yogurt. This use of fruit has led to a wider acceptability of yogurt and has therefore influenced the intakes of certain nutrients such as calcium and milk protein. This also applies to fruit jams and conserves. Although these fruit products may not have a remarkable nutrient composition themselves, they can be used to improve the palatability of foods such as wholemeal bread, thus increasing the intake of nutrients such as grain fiber and the B-group vitamins. Fruit derivatives are also used in the confectionerymanufacturing industries. Large quantities of fruit are used in the production of fruit juices. The physical processing to which fruit is subjected for juice production leads to a significant reduction in the content of ascorbic acid, but vitamin C is added to processed fruit juice, primarily as an antioxidant preservative, but also to increase consumer appeal. Fruit juice, either processed or fresh, is a significant source of vitamin C in many developed countries.
0013
0014
0015
Pharmacological and Therapeutic Properties Many therapeutic drugs in modern use originated as plant products. It is not surprising, then, that certain fruit components exert pharmacological or therapeutic effects. Limonin and nomilin and other liminoids are present in citrus such as orange, lemon, lime, and grapefruit. These compounds are believed to have a role in inhibiting the development of certain forms of cancer, and research has indicated that the antioxidant forms of b-carotene may also play a role in the prevention of some forms of cancer. Prunes (a variety of dried plums) contain hydroxyphenylostatin derivatives that stimulate colonic smooth muscle, thus explaining their traditional use as a laxative. The effects of some pharmacological agents that occur in some fruits add to the importance of fruit in the diet.
0016
0017
2758 FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance
Commercial importance Production 0018
0019
0020
The suitability of a region for commercial fruit production depends on a combination of climate, adequate water, suitable soils, and access to labor and markets. Climatically, the rainfall pattern is most important, as rain can cause major losses from foliar diseases, fruit splitting, and fruit disease, leading to direct losses or downgrading. Consequently, a dry summer climate with abundant good water for irrigation is ideal for fruit production since the water can be applied precisely as required. In production areas with high labor costs, much research is directed towards methods of reducing the labor component of both production and postharvest procedures. Such research includes the use of new dwarfing rootstocks to reduce the cost of harvesting and tree management, planting parameters to facilitate machine pruning, trellising parameters to facilitate machine harvesting, tree shakers for fruit harvest, bulk methods for handling, netting for hail and pest control, and improved postharvest practice and facilities. Varieties and propagation Nearly all major varieties of the major commercially important temperate fruit trees are clonally propagated (rather than grown from seed), either directly by cuttings or by grafting scion varieties on to rootstocks. The grafting process allows a productive variety (the scion) of good eating quality to combine with a different variety (the rootstock) that better resists endemic root diseases. An additional desirable trait of some (dwarfing) rootstocks can be a reduction of tree vigour (wasteful leaf and shoot growth) in the scion, using the incompatibility between rootstock and scion. New varieties introduced from other regions or countries need to be assessed for local suitability, since varieties that produce well in one geographic area often produce poorly in other areas. At rural horticultural research centers (‘field stations’) around the world, a substantial proportion of the work on all major commercial fruits is continually developing new and improved scions and rootstocks and assessing various rootstock–scion combinations. New varieties are selected from either superior bud mutations in existing varieties or, more commonly, concurrent breeding programs, considering fruit quality, crop yield, and freedom from disease. While some varieties have a long history of productive quality, there is a continual search for new varieties to improve both scion and rootstock performance. Many new varieties of many temperate fruits are now being developed purely to
meet changing consumer demands rather than for production factors such as yield or disease resistance. Some important fruits (e.g., certain apples, plums, cherries) require cross-pollination for adequate fruit set, and orchards of these fruits are interplanted with different varieties. Fertilization Fruit tree production can require fewer applied fertilizers than broad-acre farming. The deeper roots have access to nutrients that are more abundant deeper in the soil. Calcium and potassium concentrations can also significantly affect fruit quality. Inadequately fertilized trees result in a poorer fruit set, smaller fruit size, and increased susceptibility to pests and disease. Potassium and phosphorus requirements are relatively low in fruit crops, but calcium and trace elements are usually of particular importance to prevent disorders occurring in fruit, although the trees show no other symptoms. Preharvest pests and disease In most fruit crops, pests (e.g., insects) and disease (e.g., fungi) are major problems. Many commercially bred varieties would be unlikely to survive in nature without human intervention, as they have been selected primarily on the basis of fruit quality and yield, rather than on pest and disease resistance. In most production regions, strict quarantine regulations are enforced to preclude entry of new pests and diseases. There has been a widespread and general acceptance of the need to greatly minimize chemical pesticides by all sectors of the community, including growers, and recent progress in more environmentally friendly pest control has been quite remarkable. Integrated pest management (IPM), the established approach to controlling preharvest pests, is an integration of chemical, biological physical, and procedural methods. IPM fosters effective populations of the natural predators of the pest species, allowing a wellmonitored balance between pest and predator species. If and when the balance is significantly disturbed, a minimum number of carefully applied and precisely timed applications of chemical sprays are applied to keep pests or disease within acceptable limits. The use of insect pheromones that are harmless to humans is now common in controling many pests. These are used either as lures on to treated surfaces containing insecticides or in traps for destruction or by disrupting mating behavior. There still remains much to be done in pest and disease control, and this work constitutes a currently active arena for researchers from many disciplines. Climacteric and nonclimacteric fruits All fruit are living organs and as such continue to live and respire
0021
0022
0023
0024
0025
FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance
0026
0027
after harvest. Fruits such as apples, pears, avocados, tomatoes, and bananas can be harvested slightly immature but ‘green’ (unripe) without significantly reducing the final eating quality when they subsequently ripen. During this ripening process, complex polysaccharides, such as starch or pectins, hydrolyze to sugar resulting in an increase in sweetness and palatability. All climacteric fruits fall into this category. The fruit are called ‘climacteric’ fruit because, concomitantly, their respiration rate develops a climacteric (peak) as they ripen. Some other fruits such as citrus, cherries, strawberries, grapes, pineapples, and some melons do not get better to eat after harvest. Although these fruit may change color, they do not get better to eat the way that a mature but unripe tomato or mango will become notably palatable as ripening proceeds. Concomitantly, these fruit do not have a climacteric peak of respiration, that is, they are ‘nonclimacteric.’ The postharvest ripening nature of major fruits is shown in Table 1. Fruit Maturity
0028
0029
0030
On the tree or bush, an attached fruit undergoes the natural sequence, whereby it grows (develops), matures, and commences to ripen. During ripening, the fruit becomes attractive to eat: softening, changing colour, losing unpalatable off-flavors such as tannins, increasing in sweetness, becoming less acid, and developing attractive flavors. When a fruit is ‘mature,’ it has reached the most appropriate state of development and is now ready for the next stage of its progress, which may be storage, processing, marketing, or ripening for immediate consumption. ‘Under-mature’ or ‘immature’ means that the fruit has not yet reached the state of development most appropriate for a particular destiny, being too hard for processing or too unpalatable if consumed. ‘Over mature’ means that the fruit has developed past the most suitable state of development, for storage, processing, or marketing. Such fruit may be too soft, too colored, or too prone to breakdown during subsequent storage or marketing. A few fruits (e.g., pears and some bananas) do not reach maximum eating quality if left to ripen on the tree, and in that sense, the fresh fruit could become ‘overmature’ for human consumption. Normally, the commercial fruit is harvested somewhat before the ripening has commenced to avoid damage during transport, but most climacteric fruit will improve in eating quality and reach an acceptable quality, even if picked substantially immature. Maturity is thus independent of ripeness. Fruits can be
2759
immature but unripe, immature and ripe, mature but unripe, mature and ripe. Nonclimacteric fruits show a dramatic increase in eating quality during the last several days before natural ripeness begins, but this process halts at harvest, and no increase in palatability occurs (or very little). The exact cause for this different response has not been fully determined. If nonclimacteric fruits are harvested even only a few days too early, they most often lack a full-bodied flavor and palatability. However, if left too late, such fruits can suffer greatly increased rots and breakdown during marketing. Hence, the harvest maturity for nonclimacteric fruits is crucial and is often determined using a refractometer to measure the ‘soluble solids’ (mainly sugar) concentration in the juice of sample fruits. This measurement, either alone (pineapples, strawberries) or in conjunction with titratable acidity measurements (grapes, citrus), is then used to judge the ‘maturity’ of the fruits. The maturity of the fruits is generally most important when judging to harvest the first fruit of a district for the season. For avocados, maturity is commonly judged using percentage dry matter. The maturity indices mentioned (soluble solids; percentage dry matter) are destructive in that the sampled fruit is damaged and usually cannot be marketed. Considerable effort has been applied to develop nondestructive indices of fruit maturity, in particular NIR (near infra-red spectroscopy). This has been quite successfully used in some thin-skinned fruits (stonefruit) where a reflected infrared beam is automatically scanned and analyzed for sugar content. For other fruits such as citrus or pineapple, the thick skins currently pose an obstacle to accurate analysis using NIR. Methods of overcoming this and other problems for different fruits are currently being developed.
0031
0032
0033
Harvesting, Handling, and Packaging
Harvesting constitutes a major production cost. Mechanical harvesting is increasingly used in developed countries, and often where suitable equipment is not currently applicable (e.g., pineapples, melons), research is in progress. Fruits destined for processing are often mechanically harvested because the fruit are processed rapidly before disease can develop from bruised fruits, and partially damaged fruits can be trimmed for processing. Commercial fruit production in developed countries is often large scale and highly capital-intensive, with sophisticated and specialist equipment used for all processes, including unloading, washing, sorting, treating, size-grading, packing, cooling, handling,
0034
0035
2760 FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance
and transporting. Computer tracking and monitoring are essential components. Disinfestation and Phytosanitation 0036
Insect pests are generally only of minor importance on fruit for domestic consumption but are a very serious issue on produce for export. Most importing countries have strict regulations (phytosanitary) for fresh fruit. Many previous chemical dips or fumigants for pests such as fruit fly have now been proscribed on human health or environmental grounds. In many instances, there are no acceptable treatments available. Nonresidual treatments have been intensively studied, with increasing success. Heat disinfestation (formerly termed vapor heat) is the controlled application of hot humidified air between 40 and 60 C and between 80 and 100% RH to fruit in a chamber for a sufficient length of time to heat the innermost fruits and fruit core thoroughly to kill the pests without unacceptably damaging the fruit. The time– temperature ‘window’ for a treatment is very small before damage occurs, and many fruits, or fruits from some growing areas, are unacceptably injured by the disinfestation treatment. Recent research has revealed that ‘preconditioning,’ a pretreatment temperature regimen, is effective in ameliorating damage in otherwise susceptible fruit. Heat disinfestation is currently commercially used on papaya, lychees and mangoes, but current and ongoing research is very active, endeavoring to find suitable treatments for many other fruits. In some instances, it has been found that heat treatments can greatly reduce postharvest disease and thus improve the market quality. Postharvest Aspects of Fresh-market Fruit
0037
0038
Fruits are highly perishable but can be marketed vast distances from the site of production with the application of sound postharvest techniques such as appropriate disease treatment; storage-temperature management, humidity control, controlled atmospheres, correct packaging and palletizing, ventilation, and transport carefulness and timely distribution. Small changes in preharvest conditions, harvest maturity, postharvest handling, storage conditions, new varieties, farm practices, or season can have dramatic affects on product quality. With large-scale handling methods, large-scale losses are a constant hazard to novice and experienced handler alike. Storage temperature and humidity Correct temperature maintenance is the most important factor during marketing, as deterioration from both disease and ripening increases logarithmically with temperature. Fruits generally suffer from disorders if stored
for too long or ripened at too low temperatures (the pear is a notable exception). Such disorders include off-flavors, breakdown, mealiness, flesh and skin browning, skin pitting, and increased susceptibility to disease. For example, peaches and nectarines suffer textural dryness (become ‘woolly’), whereas avocados develop off-flavors if stored for too long below 13 C. If tomatoes have been stored for too long at 10 C or lower, they develop skin diseases from organisms that do not normally infect the fruit (‘saprophytic’ infections). For most fruits, the optimum ripening temperature is 20–22 C. Conversely, some fruits can now be stored at lower temperatures than previously believed (and have a longer marketing life) provided that they are removed from cold storage before ripening commences. Recommended storage temperatures and maximum storage times are shown in Table 1. Different cultivars, different production areas and different seasons can radically affect the tolerance to cold temperatures. Compared with tropical fruits, many temperate fruits can be held at much lower temperatures without any adverse affects, and a few can have relatively long storage lives. Apples can be stored for up to 12 months, citrus for up to 16 weeks, but stone fruit only 2–4 weeks and strawberries only 3–8 days.
0039
Fruit Ripening and Respiration
Harvested fruits, being living tissue, respire during their postharvest life, taking up oxygen, ‘burning’ sugars, and giving out both carbon dioxide and heat at a rate directly proportional to the ambient temperature. When fruit is stacked, stored, or transported, sufficient refrigeration capacity is required to cope with any climacteric (peak) respiratory heat load that is autocatalytic. If not controlled, total breakdown can occur. Certain fruits (e.g., strawberries, peaches), have high rates of respiration and hence need special attention to cooling, but generally, all fruits destined for distant marketing need some refrigeration. Warm fruit that are not promptly cooled have a reduced market life, and runaway deterioration is a risk. In stacked produce, the cardboard cartons act as insulating containers, preventing cooling. Forcing air through such stacked trays or boxes (‘forced-air cooling’) is widely used in warm climates to rapidly remove field heat after harvest or prior to transport, reducing the respiration rate and consequently the rate of the heat production. During ripening, many fruits produce ethylene gas, a potent plant hormone that initiates and catalyzes the commencement of ripening. Ethylene production in fruit follows a similar climacteric production to
0040
0041
FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance
respiration, but some fruit produce much higher ethylene levels than others. Table 1 shows the production rates for the different fruits. Ethylene from fruit can trigger senescent changes such as yellowing or withering in vegetables or flowers, or ripening in adjacent fruits. For this reason, during transport, fruits that produce substantial amounts of ethylene are sometimes isolated. Alternatively, ethylene in store room atmospheres is sometimes destroyed with ozone from special generators, or absorbed, using porous alumina beads impregnated with potassium permanganate and used as small disposable sachets in fruit cartons. 0042
0043
Effects of fertilizers on fruit quality and superior taste Whilst soil mineral composition and/or applied fertilizers have major affects on tree vigour and fruit yield, fruit quality is much less directly affected. The perceived ‘sweetness’ or ‘flavor’ of superior fruits depends on a three-way balance between the concentrations of sugar, acid, and flavor components. In an orchard, the concentration of sugar per fruit, generally an index of the superior taste, can vary from plant to plant or season to season. Sweetness usually decreases proportionally with increasing fruit mass per unit leaf area per plant. In general, for any particular variety, the flavor components depend on fruit maturity, the sugar concentration depends on ambient light intensity and leaf area, and acid concentration depends on ambient temperatures. The flesh color of some fruits at least (e.g., citrus) depends on day/night temperatures. Deficiencies of some elements such as calcium, boron, and molybdenum affect shape, internal and external blemishes and storage disorders in some fruits more than others. A high calcium/potassium ratio in apples is used as an index of storage quality as it reduces softening during storage. In citrus fruits, applying extra potassium increases acidity, sometimes seen as a desirable factor. Applied nitrogen encourages leaf growth and photosynthetic efficiency, which can result in more sugars, thus giving sweeter fruit. In general, prevailing weather, applied water, pests, and diseases have a much greater influence on fruit quality than do mineral nutrition or applied fertilizer. Globalization and the Future of Horticultural Research
0044
Increased economic globalization over recent times has brought about a major decline of both economic
2761
viability and research support within horticulture in first-world countries. Third-world countries are becoming the heirs to the resources as their research institutions have often been fostered with using aid from first-world countries. During this same period, large numbers of horticultural research workers in first-world research systems have steadily been not replaced, while third world horticulture and horticultural research has dramatically expanded. The problem of the deinstitutionalization of the horticultural knowledge base in first world countries is now a serious challenge as career researchers are replaced with casual workers, and the institutional structure is eroded away. Concurrently, domestic horticultural production in first-world countries is being forced to compete with produce from thirdworld regions. The whole issue is contentious and politically challenging, and a situation that has steadily deteriorated for many years without any clear vision of resolution. See also: Ascorbic Acid: Properties and Determination; Physiology; Dietary Fiber: Properties and Sources; Fruits of Temperate Climates: Factors Affecting Quality; Fruits of Tropical Climates: Commercial and Dietary Importance; Fruits of the Sapindaceae; Fruits of the Sapotaceae; Lesser-known Fruits of Africa; Fruits of Central and South America; Gums: Properties of Individual Gums; Pectin: Properties and Determination; Food Use; Vitamins: Overview; Determination
Further Reading Anonymous (1982) Fruit and Vegetables Facts and Pointers. Virginia: United Fresh Fruit and Vegetable Association. Anonymous (1989) Fresh Produce Manual. Handling & Storage Practices for Fresh Produce, 2nd edn. Location: Australian United Fresh Fruit and Vegetable Association Ltd. Block G (1991) Dietary guidelines and the results of food consumption surveys. American Journal of Clinical Nutrition 53: 356S–357S. FAO (1999) Food and Agriculture Yearbook Statistic Series No. 148. Rome: Food and Agriculture Organization. Hardenburg RE, Watada EE and Wang CY (1986) The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Stocks. USDA Handbook No. 96. Washington, DC: United States Department of Agriculture. Hughes D (1999) Marketing fruit in Europe. In: Good Fruit and Vegetables, pp. 34–35. Melbourne: Rural Press. Kader AA (ed.) (1992) Postharvest Technology of Horticultural Crops, 2nd edn. Location: University of California Division of Agriculture and Natural Resources.
2753
FRUITS OF TEMPERATE CLIMATES Contents Commercial and Dietary Importance Fruits of the Ericacae Factors Affecting Quality Improvement and Maintenance of Fruit Germplasm
Commercial and Dietary Importance L G Smith and S M Somerset, Queensland Department of Primary Industries, Hamilton, Queensland, Australia Copyright 2003, Elsevier Science Ltd. All Rights Reserved.
Commercial and Dietary Importance Definition 0001
‘Temperate-climate fruits’ refers to all fruits that normally grow further than 23.5 from the equator, but also includes avocado and citrus, fruits often classified as subtropical. Some temperate fruits can be grown at higher altitudes in tropical latitudes, although poor fruit set may occur in some species. ‘Fruits’ could be defined as seed-bearing plant organs that undergo a characteristic process, called ripening, changing from unpalatable to palatable (vegetables have no such sequence). Much of the information in this article is applicable to all fruits, and some tropical fruits are listed here for comparison. Horticultural products that could be classified as temperate fruits (such as many nuts and the tomato) are addressed in separate entries. Production
0002
0003
Temperate fruit production is a major industry. The production and marketing of fresh fruits are much more labor-intensive than that of broadacre crops, so that the temperate fruit industry is a major source of employment. As a consequence of the high labor content of production, large-scale fruit production by major companies is tending to shift towards suitable regions with access to cheap labor. The estimated world production of the major temperate fruits in listed in Table 1. The production for individual countries is shown in Table 2. For many temperate fruits, large quantities are processed in
one form or another (e.g., canned, dried, wine, juice, glace´ ), and the production data in Tables 1 and 2 include that for processed fruit. The specific details of world fruit production are difficult to determine since, in many countries, fruit-production data are unavailable, and reporting countries also lack standards of uniform data presentation. Grapes are the major temperate fruit in terms of tonnes produced, with large quantities going into wine and dried fruits. The major grape-producing countries are Italy, France, the USA, Spain, and countries of the former USSR. Second, in terms of quantity produced, are oranges, many of which are processed into juice, and third are apples, probably the temperate fruit most often eaten fresh, although large quantities are also juiced, dried, and canned. Buying patterns in British households for 12 common fruits are presented in Table 3.
0004
Dietary Importance
There are many different aspects to fruit in the diet. Not only is fruit an important source of dietary fiber, carbohydrate, and vitamin C and A, but because of its flavor, it also influences the intake of many other foods and therefore can exert indirect effects on the diet. Although different fruits are morphologically and botanically diverse, in fruit consumption studies, the nutritional composition is generally considered collectively, rather than in terms of distinct fruits. It is therefore more appropriate to discuss the nutritional impact of fruits as a whole.
0005
Historical Man has been attracted to the sweet taste and full aroma of fruit since prehistoric times, and attempts by man to cultivate various fruits date back over 8000 years. It is not surprising then that the word ‘fruit’ is often used to imply a pleasure or reward (e.g., in expressions such as ‘fruit of our labor’). Their sweet taste is due to the high content of sugars, in particular fructose, sucrose, and glucose. The high sugar content has been recognized for centuries and is exploited, for
0006
2754 FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance tbl0001
Table 1 Characteristics of the major temperate fruits, with four major tropical fruits included for comparison
Temperate Grapes Oranges Apples Watermelons Pears Cantaloupes Peaches Plums Lemons Grapefruit Strawberries Apricots Avocados Currants Raspberries Tropical Bananas Mangoes Pineapples Papaya
World productiond ( 106 t)
Ability toripen after harvest
Recommended storage temperaturea ( C)
57 397 66 212 56 060 47 646 14 379 17 849f 11 065i 8 008 9 335j 5 072l 2 601 2 670 2 325 654 326
No No Yes No Yes Yesg Yes Yes No No No Yes Yes No No
58 618 23 455 12 100 4 801
Yes Yes No Yes
Respirationratesa,b,c (mg CO2 kg1 h1) Ethylene productione
At storage temperature
At 20 C
Likely storage lifea
0 5–7 2–3 5–10 1.5 to 0.5 0–5 h 0 0.5 to 0 10–15k 14–16 0 0.5 to 0 8–10 0.5 to 0 0.5 to 0
1–5 m 3–12 w 3–12 m 2–3 w 2–7 m 1–4 w 2–3 w 1–4 w 1–2 m 1–1.5 m 5–7 d 2–3 w 3–10 w
<0.1 <0.1 10–100 0.1–1.0 10–100 10–100 10–100 10–100 <0.1 <0.1 <0.1 10–100 10–100
1–3 4–7 2–6 3–4 3–7 5–10 4–6 2–3 6–23 10–18 12–18 5–6 20–30
20–25 22–34 20–41 17–25 30–70 45–65 59–102 18–26 7–25 13–26 102–196 29–52 74–150
18–25
>99
13.5–15 10–13 6–20k 7–13
4–21 d 2–6 w 2–4 wk 1–3 w
21–75 45–150 4–7 4–10
33–142 75–200 28–43 22–39
2–3 d 0.1–1.0 <0.1 0.1–1.0 10–100
a Data largely from Hardenburg RE, Watada EE, and Wang CY (1986) The Commercial Storage of Fruits,Vegetables, and Florist and Nursery Stocks. USDA Handbook No. 96. Washington, DC: United States Department of Agriculture, with permission. b Values may vary with production area and cultivar. c Lower value would indicate rate for unripe fruit; a higher value would indicate a peak rate. d Data for 1998 from FAO (1999) Food and Agriculture Yearbook Statistic Series No. 148. Rome: Food and Agriculture Organization, with permission; total production includes processed, alcohol production and includes FAO estimates where individual country data not available. Missing data unavailable. e C2 H4 kg h1 at 20 C. Data largely from Kader AA (1992) Postharvest Technology of Horticultural Crops, 2nd edn. Location: University of California Division of Agriculture and Natural Resources, with permission. f Includes all melons other than watermelons. g Some cultivars (e.g., honeydew) ¼ No. h Not for honeydew melons. i Includes nectarines. j Includes limes. k Very much dependent on production area. l Includes pomelos and similar fruits. Note that storage temperature, storage life, and respiration rates vary according to fruit ripeness, cultivar, production area and other factors, and are presented here as a guide only.
example, in the drying of fruits, the high sugar content allowing their preservation and a water content sufficient to make the fruit palatable in the dried form. The production of alcohol from grapes and other fruits also depends on a high sugar content. Fruit consumption patterns now relate largely to consumer preferences. In the past, the traditional dietary role of temperate fruits was more of a luxury than a staple, but with the vast improvement of cultural practices, postharvest techniques and distribution systems, the availability of both fruit and fruit products has increased dramatically. Fruit is now more available, at an affordable price, to more of the world’s population than ever before. The modern role of fruit in the diet has thus changed from previous generations.
The Modern Dietary Role In the diets of peoples in temperate zones, the most important nutritional features are fruits of high contents of fiber, carbohydrate, and vitamin C, and low fat and protein contents. Fruit is prominent in the official dietary guidelines of many countries. Most developed countries encourage increased consumption of complex carbohydrates and fiber, which are abundant in fruits, and dietary recommendations in the UK and Germany specifically advise increased fruit consumption. One recent study in the USA found that 41% of the test population had no fruit or fruit juice on the day of survey. Substantial public health benefits might be gained if fruit consumption increased among the less affluent groups of people in the USA, and, probably, in other industrialized nations.
0007
FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance tbl0002
2755
Table 2 World production for 1998 (103 t) of eight major temperate fruits (includes all uses, processing, drying, alcohol production, etc.)
Africa Algeria Congo Egypt Ethiopia Libya Madagascar Mauritania Morocco Reunion Senegal Somalia South Africa Sudan Tanzania Tunisia Zimbabwe North and Central America Belize Canada Costa Rica Cuba El Salvador Guadeloupe Guatemala Honduras Jamaica Mexico Panama Trinidad and Tobago USA South America Argentina Bolivia Brazil Chile Colombia Ecuador Paraguay Peru Suriname Uruguay Venezuela Asia Afghanistan Bangladesh Armenia Azerbaijan Bhutan Cambodia China Cyprus Gaza Strip Georgia India Indonesia Iran Iraq Israel Japan
Grapes
Oranges
Apples
2 746 159
1415 65
3 298 400
470 47
1125
466 39
117 24
870 4 37 11
4 582 280 145 1 525 14 60 84
410
1 650
57
550
65
4
45 7
210
1 2
25
9 8
1 2
262
1 104
285
31
415
39 1
41
275
23 26
240
35
296
54
84
10
2 545
892
2 033
65 1 1485
934
17
2 120 30 20 3 86 156
56
5
35
490 17
129
79
840 858 540 4 19 250
1 069 399 100
1 300 833 280 36 146 285 23
850 305 132 4
1 273 17 111 2 5 585
30 8 900 17 122 70 17 839 170
53
4
452
5 076 4 704 2 021 23 738 1 665 17 13 76 140 11 12 971 330 106 144
2 287 125 2 275 700 2 200 305 90 251
515
83 6 5 892
Watermelons
8 259 261 24 50 140
510 340 36 1 80 83 72 4 005 27 15 12 571 25 833 841 94 22 987 115 410 217 208 234 12 185 528 12 208 12
8 58 62 2 804 45 105 115 2 000 614 1 800 316 325 131
1
Pears
47 1 100 12 16 500 20 2 1 848 1492 130 21 765 63 54 18 116 72 3 14 237 36 304 90
8 493 2
56 125 6
60 145
16 8
17 508 10
6 728 2
200 13 000
23 338 30 6 225 250
20 135
2 000 86 111 900
2 200 455 260 620
175 3 20 428
27
390 1 4 964 3 226 1 347 9 787 880 25 1 127 50 27 810 18
26 3 16
Cantaloupes
92 77 10 5 30 12 3 70 11613 22 96
Peaches
2 27
Plums
150 8 2 6
25 9 4 452 14
3 724 35
21 15
14 25
2 996 2
2 717 1
640
20 87
38 57
800 226 74 430
132 26 48 176
160 31 18 136
6 372 9 4
4
Continued
2756 FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance Table 2 Continued Grapes Jordan Kazakhstan North Korea South Korea Kuwait Kyrgyzstan Laos Lebanon Malaysia Oman Pakistan Philippines Saudi Arabia Syria Tajikstan Thailand Turkey Turkmenistan Uzbekistan Viet Nam Yemen Europe Albania Austria Belarus Bosnia and Herzegowina Bulgaria Croatia Czech Republic Denmark Estonia Finland France Germany Greece Hungary Ireland Italy Latvia Lithuania Macedonia Moldova Netherlands Norway Poland Portugal Romania Russian Federation Slovakia Slovenia Spain Sweden Switzerland UK Ukraine Yugoslavia Oceania Australia New Zealand
70 20
Oranges 40
22
75 2 130 450 120 26 3 650 177 585 155 30 216 68 234 17 624 421 38
74 28 155 11 1 410 20
9 208
315 830
379 150 3
1
1 814
1 921
25 244 825
764 874 300 76 128 4 842
2 380 588 1176 1 097 78
119
600
438
2 7 000 1 500 1 216 669
65 630 652
384
247
Apples
210
2 403
2 396 369 24
324 82 2 500 30 380 2 16 856 12 392 215 18 152 72 309 67 5 11 2 500 2 154 358 500 9 2 115 15 100 62 485 470 1 687 146 365 1 200 83 122 726 65 180 1 200 235 861 306 501
Watermelons 70 306 100 1 006 1 41 130 145 32 420 70 460 272 155 385 3 925 258 543 200 95 3 908 210
3 246 60
Pears 3 8 120 260
64
36
19 19
Cantaloupes 15
Peaches
Plums
11 2 100 147
36
3
2
50
40
400 16 130 51
46
80
40 27
29 16
1 800
400 5 82
190 9 69
3 718 2 10
2 892 12 77 45 23 78 83 33
100 300 1 33 35
415 32 35 2 605 4 12
2 65 9 8
84 21 6
4 2
1 9
280
512 76
256 387 71 37
590
931
120 25
10 9 7 130
2 520 30 786
395 325 99 88 4
83 160 64 50 12 5 561 16 95 25 160 74 213 172 41
150 6
470 15 480 54
210 416 8 115
518
1 429
149 4 6 20 56 6 12 107 18 404 155 22 4 150 1 10 16 170 480 36 33 3
6 2 3 20
7 72
980
62 18 20 9 3 888
74 72 1
50 46 111 96 15
610 31
FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance tbl0003
Table 3 Fruit-buying patterns of British householdsa Item
Percentage buying
Times per year
Bananas Apples Easy-peel oranges Grapes Pears Regular oranges Strawberries Melons Exotic fruit Peaches Pineapples Avocados
87 86 70 65 64 61 66 53 44 39 17 12
22 17 5 9 9 7 4 5 5 3 2 3
a Source AC Nielson 1998. From Hughes D (1999) Marketing fruit in Europe. In: Good Fruit and Vegetables, pp. 34–35. Melbourne: Rural Press, with permission.
Direct Nutritional Attributes 0008
0009
Fruit is generally high in dietary fiber and low in fats and oils, and is therefore an important food in diets designed to reduce the risk of coronary heart disease in developed countries. An exception is the avocado, which has an unusually high oil content (containing up to 30% fat, depending on the production area), but recent studies indicate a beneficial role of the avocado with respect to heart disease, possibly because 50–75% of the fat is monounsaturated. One dietary feature of fruit in general is the high content of water, ranging from 65% in apples to 88% in papaya. This feature enables fruit to quench thirst in addition to satisfying hunger. Vitamins
0010
0011
Ascorbic acid (vitamin C) is the principal vitamin supplied by fruit in the diet. Some fruit are particularly rich in this vitamin. Citrus have about 50 mg per 100 g, kiwi fruit about 100 mg per 100 g, and blackcurrants and bell peppers (Capsicum annum) have between 200 and 300 mg per 100 g. The orange-colored fruits such as rockmelon, peach, persimmon, tomato, and apricot are rich in b-carotene, which is converted to vitamin A in the body. Certain fruits can be rich in particular vitamins. For example rockmelon strawberry and orange have significant amounts of folic acid. Pantothenic acid is found in appreciable quantities in watermelons currants and berries, and nicotinic acid in apricots, nectarines, peaches, passion fruit, and guavas. Fiber
0012
Fruit is a rich source of pectins and gums, components of fiber, and thus fruit constitutes an important source of dietary fiber. Pectins have been shown to delay gastric emptying, which can lead to favorable
2757
changes in glycemic responses to particular foods. Pectin may also introduce a satiety effect.
Indirect Nutritional Consequences Fruit can be consumed in a number of different forms apart from fresh. The drying of fruit has been a popular preservation technique for many generations. The dehydration process concentrates those nutrients that are not heat- or light-labile. Vitamin C is the major casualty of this process. The dehydration process also decreases the water activity, thus increasing the keeping quality by making microbial growth less likely. Processed fruit is being increasingly used in the dairy industry, as an additive in fermented milk products such as yogurt. This use of fruit has led to a wider acceptability of yogurt and has therefore influenced the intakes of certain nutrients such as calcium and milk protein. This also applies to fruit jams and conserves. Although these fruit products may not have a remarkable nutrient composition themselves, they can be used to improve the palatability of foods such as wholemeal bread, thus increasing the intake of nutrients such as grain fiber and the B-group vitamins. Fruit derivatives are also used in the confectionerymanufacturing industries. Large quantities of fruit are used in the production of fruit juices. The physical processing to which fruit is subjected for juice production leads to a significant reduction in the content of ascorbic acid, but vitamin C is added to processed fruit juice, primarily as an antioxidant preservative, but also to increase consumer appeal. Fruit juice, either processed or fresh, is a significant source of vitamin C in many developed countries.
0013
0014
0015
Pharmacological and Therapeutic Properties Many therapeutic drugs in modern use originated as plant products. It is not surprising, then, that certain fruit components exert pharmacological or therapeutic effects. Limonin and nomilin and other liminoids are present in citrus such as orange, lemon, lime, and grapefruit. These compounds are believed to have a role in inhibiting the development of certain forms of cancer, and research has indicated that the antioxidant forms of b-carotene may also play a role in the prevention of some forms of cancer. Prunes (a variety of dried plums) contain hydroxyphenylostatin derivatives that stimulate colonic smooth muscle, thus explaining their traditional use as a laxative. The effects of some pharmacological agents that occur in some fruits add to the importance of fruit in the diet.
0016
0017
2758 FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance
Commercial importance Production 0018
0019
0020
The suitability of a region for commercial fruit production depends on a combination of climate, adequate water, suitable soils, and access to labor and markets. Climatically, the rainfall pattern is most important, as rain can cause major losses from foliar diseases, fruit splitting, and fruit disease, leading to direct losses or downgrading. Consequently, a dry summer climate with abundant good water for irrigation is ideal for fruit production since the water can be applied precisely as required. In production areas with high labor costs, much research is directed towards methods of reducing the labor component of both production and postharvest procedures. Such research includes the use of new dwarfing rootstocks to reduce the cost of harvesting and tree management, planting parameters to facilitate machine pruning, trellising parameters to facilitate machine harvesting, tree shakers for fruit harvest, bulk methods for handling, netting for hail and pest control, and improved postharvest practice and facilities. Varieties and propagation Nearly all major varieties of the major commercially important temperate fruit trees are clonally propagated (rather than grown from seed), either directly by cuttings or by grafting scion varieties on to rootstocks. The grafting process allows a productive variety (the scion) of good eating quality to combine with a different variety (the rootstock) that better resists endemic root diseases. An additional desirable trait of some (dwarfing) rootstocks can be a reduction of tree vigour (wasteful leaf and shoot growth) in the scion, using the incompatibility between rootstock and scion. New varieties introduced from other regions or countries need to be assessed for local suitability, since varieties that produce well in one geographic area often produce poorly in other areas. At rural horticultural research centers (‘field stations’) around the world, a substantial proportion of the work on all major commercial fruits is continually developing new and improved scions and rootstocks and assessing various rootstock–scion combinations. New varieties are selected from either superior bud mutations in existing varieties or, more commonly, concurrent breeding programs, considering fruit quality, crop yield, and freedom from disease. While some varieties have a long history of productive quality, there is a continual search for new varieties to improve both scion and rootstock performance. Many new varieties of many temperate fruits are now being developed purely to
meet changing consumer demands rather than for production factors such as yield or disease resistance. Some important fruits (e.g., certain apples, plums, cherries) require cross-pollination for adequate fruit set, and orchards of these fruits are interplanted with different varieties. Fertilization Fruit tree production can require fewer applied fertilizers than broad-acre farming. The deeper roots have access to nutrients that are more abundant deeper in the soil. Calcium and potassium concentrations can also significantly affect fruit quality. Inadequately fertilized trees result in a poorer fruit set, smaller fruit size, and increased susceptibility to pests and disease. Potassium and phosphorus requirements are relatively low in fruit crops, but calcium and trace elements are usually of particular importance to prevent disorders occurring in fruit, although the trees show no other symptoms. Preharvest pests and disease In most fruit crops, pests (e.g., insects) and disease (e.g., fungi) are major problems. Many commercially bred varieties would be unlikely to survive in nature without human intervention, as they have been selected primarily on the basis of fruit quality and yield, rather than on pest and disease resistance. In most production regions, strict quarantine regulations are enforced to preclude entry of new pests and diseases. There has been a widespread and general acceptance of the need to greatly minimize chemical pesticides by all sectors of the community, including growers, and recent progress in more environmentally friendly pest control has been quite remarkable. Integrated pest management (IPM), the established approach to controlling preharvest pests, is an integration of chemical, biological physical, and procedural methods. IPM fosters effective populations of the natural predators of the pest species, allowing a wellmonitored balance between pest and predator species. If and when the balance is significantly disturbed, a minimum number of carefully applied and precisely timed applications of chemical sprays are applied to keep pests or disease within acceptable limits. The use of insect pheromones that are harmless to humans is now common in controling many pests. These are used either as lures on to treated surfaces containing insecticides or in traps for destruction or by disrupting mating behavior. There still remains much to be done in pest and disease control, and this work constitutes a currently active arena for researchers from many disciplines. Climacteric and nonclimacteric fruits All fruit are living organs and as such continue to live and respire
0021
0022
0023
0024
0025
FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance
0026
0027
after harvest. Fruits such as apples, pears, avocados, tomatoes, and bananas can be harvested slightly immature but ‘green’ (unripe) without significantly reducing the final eating quality when they subsequently ripen. During this ripening process, complex polysaccharides, such as starch or pectins, hydrolyze to sugar resulting in an increase in sweetness and palatability. All climacteric fruits fall into this category. The fruit are called ‘climacteric’ fruit because, concomitantly, their respiration rate develops a climacteric (peak) as they ripen. Some other fruits such as citrus, cherries, strawberries, grapes, pineapples, and some melons do not get better to eat after harvest. Although these fruit may change color, they do not get better to eat the way that a mature but unripe tomato or mango will become notably palatable as ripening proceeds. Concomitantly, these fruit do not have a climacteric peak of respiration, that is, they are ‘nonclimacteric.’ The postharvest ripening nature of major fruits is shown in Table 1. Fruit Maturity
0028
0029
0030
On the tree or bush, an attached fruit undergoes the natural sequence, whereby it grows (develops), matures, and commences to ripen. During ripening, the fruit becomes attractive to eat: softening, changing colour, losing unpalatable off-flavors such as tannins, increasing in sweetness, becoming less acid, and developing attractive flavors. When a fruit is ‘mature,’ it has reached the most appropriate state of development and is now ready for the next stage of its progress, which may be storage, processing, marketing, or ripening for immediate consumption. ‘Under-mature’ or ‘immature’ means that the fruit has not yet reached the state of development most appropriate for a particular destiny, being too hard for processing or too unpalatable if consumed. ‘Over mature’ means that the fruit has developed past the most suitable state of development, for storage, processing, or marketing. Such fruit may be too soft, too colored, or too prone to breakdown during subsequent storage or marketing. A few fruits (e.g., pears and some bananas) do not reach maximum eating quality if left to ripen on the tree, and in that sense, the fresh fruit could become ‘overmature’ for human consumption. Normally, the commercial fruit is harvested somewhat before the ripening has commenced to avoid damage during transport, but most climacteric fruit will improve in eating quality and reach an acceptable quality, even if picked substantially immature. Maturity is thus independent of ripeness. Fruits can be
2759
immature but unripe, immature and ripe, mature but unripe, mature and ripe. Nonclimacteric fruits show a dramatic increase in eating quality during the last several days before natural ripeness begins, but this process halts at harvest, and no increase in palatability occurs (or very little). The exact cause for this different response has not been fully determined. If nonclimacteric fruits are harvested even only a few days too early, they most often lack a full-bodied flavor and palatability. However, if left too late, such fruits can suffer greatly increased rots and breakdown during marketing. Hence, the harvest maturity for nonclimacteric fruits is crucial and is often determined using a refractometer to measure the ‘soluble solids’ (mainly sugar) concentration in the juice of sample fruits. This measurement, either alone (pineapples, strawberries) or in conjunction with titratable acidity measurements (grapes, citrus), is then used to judge the ‘maturity’ of the fruits. The maturity of the fruits is generally most important when judging to harvest the first fruit of a district for the season. For avocados, maturity is commonly judged using percentage dry matter. The maturity indices mentioned (soluble solids; percentage dry matter) are destructive in that the sampled fruit is damaged and usually cannot be marketed. Considerable effort has been applied to develop nondestructive indices of fruit maturity, in particular NIR (near infra-red spectroscopy). This has been quite successfully used in some thin-skinned fruits (stonefruit) where a reflected infrared beam is automatically scanned and analyzed for sugar content. For other fruits such as citrus or pineapple, the thick skins currently pose an obstacle to accurate analysis using NIR. Methods of overcoming this and other problems for different fruits are currently being developed.
0031
0032
0033
Harvesting, Handling, and Packaging
Harvesting constitutes a major production cost. Mechanical harvesting is increasingly used in developed countries, and often where suitable equipment is not currently applicable (e.g., pineapples, melons), research is in progress. Fruits destined for processing are often mechanically harvested because the fruit are processed rapidly before disease can develop from bruised fruits, and partially damaged fruits can be trimmed for processing. Commercial fruit production in developed countries is often large scale and highly capital-intensive, with sophisticated and specialist equipment used for all processes, including unloading, washing, sorting, treating, size-grading, packing, cooling, handling,
0034
0035
2760 FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance
and transporting. Computer tracking and monitoring are essential components. Disinfestation and Phytosanitation 0036
Insect pests are generally only of minor importance on fruit for domestic consumption but are a very serious issue on produce for export. Most importing countries have strict regulations (phytosanitary) for fresh fruit. Many previous chemical dips or fumigants for pests such as fruit fly have now been proscribed on human health or environmental grounds. In many instances, there are no acceptable treatments available. Nonresidual treatments have been intensively studied, with increasing success. Heat disinfestation (formerly termed vapor heat) is the controlled application of hot humidified air between 40 and 60 C and between 80 and 100% RH to fruit in a chamber for a sufficient length of time to heat the innermost fruits and fruit core thoroughly to kill the pests without unacceptably damaging the fruit. The time– temperature ‘window’ for a treatment is very small before damage occurs, and many fruits, or fruits from some growing areas, are unacceptably injured by the disinfestation treatment. Recent research has revealed that ‘preconditioning,’ a pretreatment temperature regimen, is effective in ameliorating damage in otherwise susceptible fruit. Heat disinfestation is currently commercially used on papaya, lychees and mangoes, but current and ongoing research is very active, endeavoring to find suitable treatments for many other fruits. In some instances, it has been found that heat treatments can greatly reduce postharvest disease and thus improve the market quality. Postharvest Aspects of Fresh-market Fruit
0037
0038
Fruits are highly perishable but can be marketed vast distances from the site of production with the application of sound postharvest techniques such as appropriate disease treatment; storage-temperature management, humidity control, controlled atmospheres, correct packaging and palletizing, ventilation, and transport carefulness and timely distribution. Small changes in preharvest conditions, harvest maturity, postharvest handling, storage conditions, new varieties, farm practices, or season can have dramatic affects on product quality. With large-scale handling methods, large-scale losses are a constant hazard to novice and experienced handler alike. Storage temperature and humidity Correct temperature maintenance is the most important factor during marketing, as deterioration from both disease and ripening increases logarithmically with temperature. Fruits generally suffer from disorders if stored
for too long or ripened at too low temperatures (the pear is a notable exception). Such disorders include off-flavors, breakdown, mealiness, flesh and skin browning, skin pitting, and increased susceptibility to disease. For example, peaches and nectarines suffer textural dryness (become ‘woolly’), whereas avocados develop off-flavors if stored for too long below 13 C. If tomatoes have been stored for too long at 10 C or lower, they develop skin diseases from organisms that do not normally infect the fruit (‘saprophytic’ infections). For most fruits, the optimum ripening temperature is 20–22 C. Conversely, some fruits can now be stored at lower temperatures than previously believed (and have a longer marketing life) provided that they are removed from cold storage before ripening commences. Recommended storage temperatures and maximum storage times are shown in Table 1. Different cultivars, different production areas and different seasons can radically affect the tolerance to cold temperatures. Compared with tropical fruits, many temperate fruits can be held at much lower temperatures without any adverse affects, and a few can have relatively long storage lives. Apples can be stored for up to 12 months, citrus for up to 16 weeks, but stone fruit only 2–4 weeks and strawberries only 3–8 days.
0039
Fruit Ripening and Respiration
Harvested fruits, being living tissue, respire during their postharvest life, taking up oxygen, ‘burning’ sugars, and giving out both carbon dioxide and heat at a rate directly proportional to the ambient temperature. When fruit is stacked, stored, or transported, sufficient refrigeration capacity is required to cope with any climacteric (peak) respiratory heat load that is autocatalytic. If not controlled, total breakdown can occur. Certain fruits (e.g., strawberries, peaches), have high rates of respiration and hence need special attention to cooling, but generally, all fruits destined for distant marketing need some refrigeration. Warm fruit that are not promptly cooled have a reduced market life, and runaway deterioration is a risk. In stacked produce, the cardboard cartons act as insulating containers, preventing cooling. Forcing air through such stacked trays or boxes (‘forced-air cooling’) is widely used in warm climates to rapidly remove field heat after harvest or prior to transport, reducing the respiration rate and consequently the rate of the heat production. During ripening, many fruits produce ethylene gas, a potent plant hormone that initiates and catalyzes the commencement of ripening. Ethylene production in fruit follows a similar climacteric production to
0040
0041
FRUITS OF TEMPERATE CLIMATES/Commercial and Dietary Importance
respiration, but some fruit produce much higher ethylene levels than others. Table 1 shows the production rates for the different fruits. Ethylene from fruit can trigger senescent changes such as yellowing or withering in vegetables or flowers, or ripening in adjacent fruits. For this reason, during transport, fruits that produce substantial amounts of ethylene are sometimes isolated. Alternatively, ethylene in store room atmospheres is sometimes destroyed with ozone from special generators, or absorbed, using porous alumina beads impregnated with potassium permanganate and used as small disposable sachets in fruit cartons. 0042
0043
Effects of fertilizers on fruit quality and superior taste Whilst soil mineral composition and/or applied fertilizers have major affects on tree vigour and fruit yield, fruit quality is much less directly affected. The perceived ‘sweetness’ or ‘flavor’ of superior fruits depends on a three-way balance between the concentrations of sugar, acid, and flavor components. In an orchard, the concentration of sugar per fruit, generally an index of the superior taste, can vary from plant to plant or season to season. Sweetness usually decreases proportionally with increasing fruit mass per unit leaf area per plant. In general, for any particular variety, the flavor components depend on fruit maturity, the sugar concentration depends on ambient light intensity and leaf area, and acid concentration depends on ambient temperatures. The flesh color of some fruits at least (e.g., citrus) depends on day/night temperatures. Deficiencies of some elements such as calcium, boron, and molybdenum affect shape, internal and external blemishes and storage disorders in some fruits more than others. A high calcium/potassium ratio in apples is used as an index of storage quality as it reduces softening during storage. In citrus fruits, applying extra potassium increases acidity, sometimes seen as a desirable factor. Applied nitrogen encourages leaf growth and photosynthetic efficiency, which can result in more sugars, thus giving sweeter fruit. In general, prevailing weather, applied water, pests, and diseases have a much greater influence on fruit quality than do mineral nutrition or applied fertilizer. Globalization and the Future of Horticultural Research
0044
Increased economic globalization over recent times has brought about a major decline of both economic
2761
viability and research support within horticulture in first-world countries. Third-world countries are becoming the heirs to the resources as their research institutions have often been fostered with using aid from first-world countries. During this same period, large numbers of horticultural research workers in first-world research systems have steadily been not replaced, while third world horticulture and horticultural research has dramatically expanded. The problem of the deinstitutionalization of the horticultural knowledge base in first world countries is now a serious challenge as career researchers are replaced with casual workers, and the institutional structure is eroded away. Concurrently, domestic horticultural production in first-world countries is being forced to compete with produce from thirdworld regions. The whole issue is contentious and politically challenging, and a situation that has steadily deteriorated for many years without any clear vision of resolution. See also: Ascorbic Acid: Properties and Determination; Physiology; Dietary Fiber: Properties and Sources; Fruits of Temperate Climates: Factors Affecting Quality; Fruits of Tropical Climates: Commercial and Dietary Importance; Fruits of the Sapindaceae; Fruits of the Sapotaceae; Lesser-known Fruits of Africa; Fruits of Central and South America; Gums: Properties of Individual Gums; Pectin: Properties and Determination; Food Use; Vitamins: Overview; Determination
Further Reading Anonymous (1982) Fruit and Vegetables Facts and Pointers. Virginia: United Fresh Fruit and Vegetable Association. Anonymous (1989) Fresh Produce Manual. Handling & Storage Practices for Fresh Produce, 2nd edn. Location: Australian United Fresh Fruit and Vegetable Association Ltd. Block G (1991) Dietary guidelines and the results of food consumption surveys. American Journal of Clinical Nutrition 53: 356S–357S. FAO (1999) Food and Agriculture Yearbook Statistic Series No. 148. Rome: Food and Agriculture Organization. Hardenburg RE, Watada EE and Wang CY (1986) The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Stocks. USDA Handbook No. 96. Washington, DC: United States Department of Agriculture. Hughes D (1999) Marketing fruit in Europe. In: Good Fruit and Vegetables, pp. 34–35. Melbourne: Rural Press. Kader AA (ed.) (1992) Postharvest Technology of Horticultural Crops, 2nd edn. Location: University of California Division of Agriculture and Natural Resources.