Part I Raw materials
Part I Raw materials
Raw material selection- fruits and Ⅴ egetables L. Bedford, Campden and Chorleywood Food Research Association 1.1 Introduction Fresh fruits and vegetables are utilised in a wide range of chilled products. They may be sold whole, or peeled (for example peeled potatoes and onions)or further prepared(e.g. carrot batons). After washing or further preparation they form ingredients for mixes such as mixed fruit or salad packs or for further processing in a wide range of products. From this it can be seen that raw material requirements can be very varied but are specific to each end use. Sourcing of suitable raw material is essential for the production of final products of consistently high quality and for this both the producer and the user need to have a clear understanding of the requirements In this chapter some of the criteria for selection will be discussed. The examples are drawn from a range of fruit and vegetable crops. Most whole fruits and vegetables are best stored at chill temperatures and thus come naturally under the scope of this book. Some however, such as potatoes and tomatoes and some other fruits are low-temperature sensitive and should ideally be kept at higher temperatures. However even these items, once they are cut and prepared need to be kept chilled, to avoid enzyme-mediated changes and disease-related spoilage, both of which proceed more rapidly at higher temperatures Supply of suitable raw material requires collaboration between the grower and the purchaser of the produce. In effect, the grower forms the first link in the food chain. The decisions made, including variety selection and agronomic practices and the grower's skill in harvesting and where appropriate in storing the crop are crucial steps in the supply of high-quality raw material for chilled fruit and vegetable products
1.1 Introduction Fresh fruits and vegetables are utilised in a wide range of chilled products. They may be sold whole, or peeled (for example peeled potatoes and onions) or further prepared (e.g. carrot batons). After washing or further preparation they form ingredients for mixes such as mixed fruit or salad packs or for further processing in a wide range of products. From this it can be seen that raw material requirements can be very varied but are specific to each end use. Sourcing of suitable raw material is essential for the production of final products of consistently high quality and for this both the producer and the user need to have a clear understanding of the requirements. In this chapter some of the criteria for selection will be discussed. The examples are drawn from a range of fruit and vegetable crops. Most whole fruits and vegetables are best stored at chill temperatures and thus come naturally under the scope of this book. Some however, such as potatoes and tomatoes and some other fruits are low-temperature sensitive and should ideally be kept at higher temperatures. However even these items, once they are cut and prepared need to be kept chilled, to avoid enzyme-mediated changes and disease-related spoilage, both of which proceed more rapidly at higher temperatures. Supply of suitable raw material requires collaboration between the grower and the purchaser of the produce. In effect, the grower forms the first link in the food chain. The decisions made, including variety selection and agronomic practices and the grower’s skill in harvesting and where appropriate in storing the crop are crucial steps in the supply of high-quality raw material for chilled fruit and vegetable products. 1 Raw material selection – fruits and vegetables L. Bedford, Campden and Chorleywood Food Research Association
0 Chilled foods 1.2 Criteria for selection First of all it is necessary to consider the factors which contribute to product variability and what makes raw material suitable for different purposes, particularly for use in chilled food products. Some of the factors are genetically ontrolled. Thus varieties may differ in size, shape and other characteristics Many plant characteristics are also influenced by environmental factors, such as site and climate and seasonal weather patterns. These genetic and environmental aspects interact, contributing to the variability of the produce at harvest The parts of the plant which are consumed may be leaves, stems, roots flowering heads, fruits or seeds, all requiring harvesting at the correct stage of maturity. Further factors apply after harvest, such as the handling and storage of he products before they are sold or prepared for further processing. Post-harvest factors can have a considerable impact on shelf-life and quality 1. 2.1 Variety Plant species have recognisable inherited characteristics, which can be used to distinguish them from other species. Members of a species are generally able to interbreed easily, but much less easily, or not at all with other species. within a species, natural variation gives rise to groups of individuals with small but definite differences. which are known as 'varieties. when the variations are brought about by human intervention as in plant breeding then botanists use the term cultivars. However in common parlance the term ' is used for the an-made products of plant breeding as well When selecting raw material for particular purposes, one of the important criteria under human control, is the choice of suitable varieties. Th are many different ways in which varieties can differ. There may be obvious differences in colour, shape and size. may be differences in field characteristics, such as yield, plant growth habit and disease resistance. In some cases flavour and other sensory characteristics may differ For most crops, a range of varieties can be used for any specific purpose, for example, a number of different varieties of Dutch white cabbage all possess the ick leaf texture and white colour required by the chilled salad producer. In other cases, the choice of a variety suitable for a specific purpose may be more limited; for instance an apple variety such as Cox may be specifically selected for a chilled fruit salad. because of its skin colour. which will enhance the overall appearance. A good variety has to meet the requirements of the primary producer, processor, retailer and ultimately the consumer Agronomic characteristics Traditionally, farmers and growers have selected varieties for their field or agronomic performance. They have been concerned to achieve high yields, this being a major factor affecting profitability. This may be in terms of total yield or, more importantly, of marketable yield. The latter refers to the saleable
1.2 Criteria for selection First of all it is necessary to consider the factors which contribute to product variability and what makes raw material suitable for different purposes, particularly for use in chilled food products. Some of the factors are genetically controlled. Thus varieties may differ in size, shape and other characteristics. Many plant characteristics are also influenced by environmental factors, such as site and climate and seasonal weather patterns. These genetic and environmental aspects interact, contributing to the variability of the produce at harvest. The parts of the plant which are consumed may be leaves, stems, roots, flowering heads, fruits or seeds, all requiring harvesting at the correct stage of maturity. Further factors apply after harvest, such as the handling and storage of the products before they are sold or prepared for further processing. Post-harvest factors can have a considerable impact on shelf-life and quality. 1.2.1 Variety Plant species have recognisable inherited characteristics, which can be used to distinguish them from other species. Members of a species are generally able to interbreed easily, but much less easily, or not at all with other species. Within a species, natural variation gives rise to groups of individuals with small but definite differences, which are known as ‘varieties’. When the variations are brought about by human intervention as in plant breeding then botanists use the term ‘cultivars’. However in common parlance the term ‘variety’ is used for the man-made products of plant breeding as well. When selecting raw material for particular purposes, one of the most important criteria under human control, is the choice of suitable varieties. There are many different ways in which varieties can differ. There may be obvious differences in colour, shape and size. There may be differences in field characteristics, such as yield, plant growth habit and disease resistance. In some cases flavour and other sensory characteristics may differ. For most crops, a range of varieties can be used for any specific purpose, for example, a number of different varieties of Dutch white cabbage all possess the thick leaf texture and white colour required by the chilled salad producer. In other cases, the choice of a variety suitable for a specific purpose may be more limited; for instance an apple variety such as Cox may be specifically selected for a chilled fruit salad, because of its skin colour, which will enhance the overall appearance. A good variety has to meet the requirements of the primary producer, processor, retailer and ultimately the consumer. Agronomic characteristics Traditionally, farmers and growers have selected varieties for their field or ‘agronomic’ performance. They have been concerned to achieve high yields, this being a major factor affecting profitability. This may be in terms of total yield or, more importantly, of marketable yield. The latter refers to the saleable 20 Chilled foods
Raw material selection -fruits and vegetables 21 produce after all waste and defective material has been removed. Taking a root crop, such as carrots, all the roots will be lifted from the soil and grading will emove undersized and misshapen roots Disease resistance is another major issue. Field diseases can cause complete rop losses, or they may produce blemishes, which cause produce to be downgraded. Chemical pesticides can be applied to control some, but not all diseases. Genetic resistance is preferable, reducing the need for chemicals Disease resistance may be controlled by a single gene or by several genes acting together(multigene resistance). Single gene resistance is easier to work with However the disadvantage is that plant pathogens often rapidly produce new races able to overcome this type of resistance. An example is found in downy mildew of spinach( Peronospora farinosa f sp spinaciae ). The disease is difficult to control chemically and varieties have been bred with specific genes for resistance, originally to races 1, 2 and 3 of the disease. Following the appearance in 1995 of the new race 4, whole crops were wiped out. Plant breeders have now produced a series of new varieties with resistance to race 4 but the resistance of these varieties may also have a limited life. Multigene resistance (field tolerance) gives greater stability. Some varieties of lettuce show this type of resistance to lettuce downy mildew(Bremia lactucae) Plant habit is another varietal characteristic, which is particularly important when the flowering parts of the plant or the seeds are consumed. Plants should have sturdy stems to enable them to remain erect in windy conditions or when the foliage is wet. Varieties are said to have ' good standing abilityand not to lodge' or become flattened. In the green bean crop, plant breeders have given considerable thought to the plant architecture. Stems need to be sufficiently strong to support the combined of pods produced and, as yields increase this becomes more of a problem. If all the pods were to be bunched together at the tops of the plants this might make for easier harvesting, but it could cause increased lodging. Plants on which the pods are distributed more evenly throughout the plant canopy are more likely to remain upright A major change in varieties over the last fifty years is associated with partial complete mechanisation of harvesting. Older varieties of many crops, such as cauliflower and lettuce would have individual plants producing their heads over a period of time. In crops such as peas and beans individual pods were also produced over a long period. With the introduction of machine harvesting, the objective was once-over harvesting and the result, over years of breeding, has been varieties where individual heads mature very evenly. Peas and beans are said to be more 'determinate', that is to say that after producing a certain number of flowering nodes growth tends to stop. The pods then all develop and can be harvested at one time While all these field characteristics are necessary for the growth of crops, successful marketing of the crop requires attention to characteristics required by of the fina,or, the retailer and ultimately by the consumer. These relate to quality roduct
produce after all waste and defective material has been removed. Taking a root crop, such as carrots, all the roots will be lifted from the soil and grading will remove undersized and misshapen roots. Disease resistance is another major issue. Field diseases can cause complete crop losses, or they may produce blemishes, which cause produce to be downgraded. Chemical pesticides can be applied to control some, but not all diseases. Genetic resistance is preferable, reducing the need for chemicals. Disease resistance may be controlled by a single gene or by several genes acting together (multigene resistance). Single gene resistance is easier to work with. However the disadvantage is that plant pathogens often rapidly produce new races able to overcome this type of resistance. An example is found in downy mildew of spinach (Peronospora farinosa f sp spinaciae). The disease is difficult to control chemically and varieties have been bred with specific genes for resistance, originally to races 1, 2 and 3 of the disease. Following the appearance in 1995 of the new race 4, whole crops were wiped out. Plant breeders have now produced a series of new varieties with resistance to race 41 but the resistance of these varieties may also have a limited life. Multigene resistance (field tolerance) gives greater stability. Some varieties of lettuce show this type of resistance to lettuce downy mildew (Bremia lactucae). Plant habit is another varietal characteristic, which is particularly important when the flowering parts of the plant or the seeds are consumed. Plants should have sturdy stems to enable them to remain erect in windy conditions or when the foliage is wet. Varieties are said to have ‘good standing ability’ and not to ‘lodge’ or become flattened. In the green bean crop, plant breeders have given considerable thought to the plant architecture. Stems need to be sufficiently strong to support the combined weight of pods produced and, as yields increase, this becomes more of a problem. If all the pods were to be bunched together at the tops of the plants this might make for easier harvesting, but it could cause increased lodging. Plants on which the pods are distributed more evenly throughout the plant canopy are more likely to remain upright. A major change in varieties over the last fifty years is associated with partial or complete mechanisation of harvesting. Older varieties of many crops, such as cauliflower and lettuce would have individual plants producing their heads over a period of time. In crops such as peas and beans individual pods were also produced over a long period. With the introduction of machine harvesting, the objective was once-over harvesting and the result, over years of breeding, has been varieties where individual heads mature very evenly. Peas and beans are said to be more ‘determinate’, that is to say that after producing a certain number of flowering nodes growth tends to stop. The pods then all develop and can be harvested at one time. While all these field characteristics are necessary for the growth of crops, successful marketing of the crop requires attention to characteristics required by the processor, the retailer and ultimately by the consumer. These relate to quality of the final product. Raw material selection – fruits and vegetables 21
Chilled foods Shape and size Within some crops there is a range of shapes and sizes. For instance there is a range of types of carrots with different shapes and size of roots. Nantes varieties have cylindrical roots and so are preferred for pre-packing. Berlicum varieties are also cylindrical. They are generally larger and mature later in the season than Nantes varieties. The other common UK types are the conical Chantenays and Autumn King varieties which have very large roots tapering to a point. Larger roots of cylindrical or slightly conical varieties are suitable for slicing in chilled food products A recent development has been the breeding of specific varieties for ' mini vegetableproduction. The concept is a response to consumer perception that small size equates to high quality and is seen as a way of adding value to vegetable products such as cauliflower. The varieties may also require special growing techniques. Varieties may also be selected according to their ability to produce the correct size of portion for prepared foods. Cauliflowers are often presented ready cut into florets and varieties differ in the ease with which they can be cut up and the size of florets produced. For chopping or dicing, large size consideration. Large cabbages are specified for processing uses sucsant is required and the overall yield of prepared product is an import coleslaw production, the total yield of cabbage shreds being the major concern This contrasts with retail sale where smaller varieties are required Colour and appearance It is often said that the consumer buys by eye, so an attractive colour and appearance is essential. Varieties often vary in colour. The characteristic colours of different apple varieties make them easily identified. They differ not only in the ground colour( Coxes are yellow and red, Bramleys are green) but also in the markings known as russetting. Chilled food manufacturers will consider the flesh colour, as well as the skins and the ability to resist grey discoloration when selecting a variety to provide colour to a mixed fruit salad Modern commercial carrot varieties are orange, but they were arrived at by careful selection from a varied ancestral gene pool in which yellow and purple colours were common. More recently a series of large-rooted varieties were developed for dicing. They had a deeper orange colour that was particularly evenly spread across the core and flesh of the roots. Colour may not be so important where the product is chopped or otherwise prepared. White cabbage for retail sale needs to have bright colour and fresh appearance. Slight greyness may be acceptable if the cabbage is used for coleslaw, as the colour will be masked by the mayonnaise To the consumer, of course, the ultimate requirement is good eating quality, and food products should have good natural flavour and texture. Varieties of some crops such as apples have very distinctive flavours and consumers commonly select their own favourites e.g. Cox, Golden Delicious, Russet. In other crops
Shape and size Within some crops there is a range of shapes and sizes. For instance there is a range of types of carrots with different shapes and size of roots. Nantes varieties have cylindrical roots and so are preferred for pre-packing. Berlicum varieties are also cylindrical. They are generally larger and mature later in the season than Nantes varieties. The other common UK types are the conical Chantenays and Autumn King varieties which have very large roots tapering to a point. Larger roots of cylindrical or slightly conical varieties are suitable for slicing in chilled food products. A recent development has been the breeding of specific varieties for ‘mini vegetable’ production. The concept is a response to consumer perception that small size equates to high quality and is seen as a way of adding value to vegetable products such as cauliflower. The varieties may also require special growing techniques. Varieties may also be selected according to their ability to produce the correct size of portion for prepared foods. Cauliflowers are often presented ready cut into florets and varieties differ in the ease with which they can be cut up and the size of florets produced.2 For chopping or dicing, large size is required and the overall yield of prepared product is an important consideration. Large cabbages are specified for processing uses such as coleslaw production, the total yield of cabbage shreds being the major concern. This contrasts with retail sale where smaller varieties are required. Colour and appearance It is often said that the consumer buys by eye, so an attractive colour and appearance is essential. Varieties often vary in colour. The characteristic colours of different apple varieties make them easily identified. They differ not only in the ground colour (Coxes are yellow and red, Bramleys are green) but also in the markings known as ‘russetting’. Chilled food manufacturers will consider the flesh colour, as well as the skins and the ability to resist grey discoloration when selecting a variety to provide colour to a mixed fruit salad. Modern commercial carrot varieties are orange, but they were arrived at by careful selection from a varied ancestral gene pool in which yellow and purple colours were common. More recently a series of large-rooted varieties were developed for dicing. They had a deeper orange colour that was particularly evenly spread across the core and flesh of the roots. Colour may not be so important where the product is chopped or otherwise prepared. White cabbage for retail sale needs to have bright colour and fresh appearance. Slight greyness may be acceptable if the cabbage is used for coleslaw, as the colour will be masked by the mayonnaise. Flavour and texture To the consumer, of course, the ultimate requirement is good eating quality, and food products should have good natural flavour and texture. Varieties of some crops such as apples have very distinctive flavours and consumers commonly select their own favourites e.g. Cox, Golden Delicious, Russet. In other crops, 22 Chilled foods
Raw material selection -fruits and vegetables 23 many varieties have quite similar flavour. A consumer would be unlikely to be able to tell the difference between many varieties of, say, iceberg lettuce On the other hand, flavour has been a particular issue with Brussels sprouts Varieties differ in flavour, particularly in levels of bitterness and excess bitterness has caused some varieties to be unacceptable. The flavour and aroma characteristics of varieties are governed by their chemical constituents. Breeders may be able to manipulate these, in order to improve varietal quality. The chemicals responsible for bitterness in Brussels sprouts have been identified as the glucosinolates, sinigrin and progoitrin. In the 1970s and 80s deep green coloured varieties appeared on the market, which had been selected for resistance to insect pests. However, taste panel assessments showed these varieties to be bitter and chemical analysis confirmed that they were high in glucosinolates Some varieties, such as Topline, Rasalon and Lunet had consistently good quality over several years. Van Doorn et al. conducted consumer studies with a ange of different Brussels sprout varieties and suggested that at a level of glucosinolates(sinigrin plus progoitrin) of above 2.2g per kg negative consumer reaction was registered. Breeders can now select for lower levels of these chemicals either by analysis or by tasting Flavour can vary even within the portion of the crop that is consumed. Both leeks and celery have white tissue at the base of their stems and greener tissue and leaves higher up. There are differences in flavour between white and green portions. EU regulations' dictate the proportions of white and green in celery for sale and varieties vary in their ability to satisfy this requirement The texture of a product also contributes to eating quality. This is often related to maturity, with an over-mature product becoming tough. However, there may be variety differences. Potatoes have obvious texture differences being either waxy or floury. Waxy varieties are firm and will retain their shape after cooking. They are preferred for salad use or for products such as potato scallops. Floury varieties, which soften on cooking, are used for mashed Chilled food manufacturers use large volumes of sliced and diced onions to add flavour to their products. Onion varieties differ in pungency. In the UK the majority of main crop onions are of the rijnsburger type which are relatively high in pungency. Some of the varieties grown in Spain are less pungent and hence"Spanish'onions are used if the onion is to be eaten raw. The American Vidalia type is noted for its sweetness Sweetness is an important flavour attribute of most crops but sugar levels can also be important for other reasons. Amounts of reducing sugars in potatoes influence colour after frying and there is a strong variety-related component to this effect. Maris Piper is a preferred variety for the chipping trade because it is lower in reducing sugars. Flavour ariations in tomatoes are related to differences in the amounts of sugars and acids in the fruit. If both are at low levels the flavour will be bland. Commercial varieties with high levels of both acid and sugar are preferred
many varieties have quite similar flavour. A consumer would be unlikely to be able to tell the difference between many varieties of, say, iceberg lettuce. On the other hand, flavour has been a particular issue with Brussels sprouts. Varieties differ in flavour, particularly in levels of bitterness and excess bitterness has caused some varieties to be unacceptable. The flavour and aroma characteristics of varieties are governed by their chemical constituents. Breeders may be able to manipulate these, in order to improve varietal quality. The chemicals responsible for bitterness in Brussels sprouts have been identified as the glucosinolates, sinigrin and progoitrin.3 In the 1970s and 80s deep green coloured varieties appeared on the market, which had been selected for resistance to insect pests. However, taste panel assessments showed these varieties to be bitter and chemical analysis confirmed that they were high in glucosinolates. Some varieties, such as Topline, Rasalon and Lunet had consistently good quality over several years.4 Van Doorn et al.5 conducted consumer studies with a range of different Brussels sprout varieties and suggested that at a level of glucosinolates (sinigrin plus progoitrin) of above 2.2g per kg negative consumer reaction was registered. Breeders can now select for lower levels of these chemicals either by analysis or by tasting. Flavour can vary even within the portion of the crop that is consumed. Both leeks and celery have white tissue at the base of their stems and greener tissue and leaves higher up. There are differences in flavour between white and green portions.6 EU regulations7 dictate the proportions of white and green in celery for sale and varieties vary in their ability to satisfy this requirement. The texture of a product also contributes to eating quality. This is often related to maturity, with an over-mature product becoming tough. However, there may be variety differences. Potatoes have obvious texture differences being either waxy or floury. Waxy varieties are firm and will retain their shape after cooking. They are preferred for salad use or for products such as potato scallops. Floury varieties, which soften on cooking, are used for mashed potatoes. Chilled food manufacturers use large volumes of sliced and diced onions to add flavour to their products. Onion varieties differ in pungency. In the UK the majority of main crop onions are of the Rijnsburger type which are relatively high in pungency.8 Some of the varieties grown in Spain are less pungent and hence ‘Spanish’ onions are used if the onion is to be eaten raw. The American Vidalia type is noted for its sweetness. Sweetness is an important flavour attribute of most crops but sugar levels can also be important for other reasons. Amounts of reducing sugars in potatoes influence colour after frying and there is a strong variety-related component to this effect.9 Maris Piper is a preferred variety for the chipping trade because it is lower in reducing sugars. Flavour variations in tomatoes are related to differences in the amounts of sugars and acids in the fruit. If both are at low levels, the flavour will be bland. Commercial varieties with high levels of both acid and sugar are preferred. Raw material selection – fruits and vegetables 23
24 Chilled foods Recently there has been interest in the health-promoting effects of some of the mponent substances found in fruit and vegetables. Varieties may differ in amounts of these so called bioactive substances. Schonhof et al. working on calabrese determined concentrations of carotenoids, chlorophylls and glucosino- lates in three different varieties. They reported that although there were seasonal influences on the concentrations of these, the genetic differences were constant 1. 2. 2 Crop maturity Another major consideration in raw material production and selection is arvesting of crops at the optimal stage of maturity. Visual indications often reflect the stage of development of the plant and aid the grower in timely harvesting. When bulb onions are mature the leaves begin to wilt and bend over Growers refer to the 'fall-over' date. assessment criteria are different for vegetables and fruits and assessment of the correct stage depends on the part of the plant that is consumed eafy crops are harvested according to size and firmness. Most types of cabbage and lettuce are allowed to produce a heart and the heads should be firm and of the size required by the particular outlet. Cabbage greens are harvested before the hearts have had time to form Lettuce and spinach for leafy salads are harvested only a few weeks after drilling, when leaf size is very small. In crops such as cauliflower and calabrese, where the flowering heads are consumed assessment is also by eye and development is monitored until firm heads have formed. Once this stage is passed the heads will open out as flower development proceeds. In over-mature calabrese, the yellow flower petals may be seen Harvest time is less critical with root crops such as carrots, swedes, turnips,or parsnips. They may be harvested when they reach the size required by a particular outlet but are often stored in the field for several months. Carrots may be considered to have reached maturity when there is no white coloration at the tip of the root but will continue to grow after this. Bunching carrots may be harvested immature, with some white roots. Other types are harvested at a later stage when roots have achieved a sufficient size to meet specific market equirements. Similarly early potatoes are harvested immature, but other maincrop'orware' potatoes are harvested after the leaves have died down, this being a sign that the crop has completed bulking up In some crops the immature pods or immature seeds are consumed(e.g. runner beans, dwarf French beans, peas, sweetcorn). As the seeds develop and swell they accumulate carbohydrates, first of all in the form of sugars and these are then converted to starch as the seed dries out. At the same time the pods are drying out and the texture becomes tough or mealy. Maturity assessment particularly critical for these crops as they rapidly become tough if left in the field after optimum maturity In beans the seed development is monitored and aturity is related to pod and bean size for specific varieties Fruits are divided into two ripening types. Climacteric fruits such as 'pe fruits(apples and pears)apricots, peaches, plums and kiwifruit continue to
Recently there has been interest in the health-promoting effects of some of the component substances found in fruit and vegetables. Varieties may differ in amounts of these so called bioactive substances. Schonhof et al.10 working on calabrese determined concentrations of carotenoids, chlorophylls and glucosinolates in three different varieties. They reported that although there were seasonal influences on the concentrations of these, the genetic differences were constant. 1.2.2 Crop maturity Another major consideration in raw material production and selection is harvesting of crops at the optimal stage of maturity. Visual indications often reflect the stage of development of the plant and aid the grower in timely harvesting. When bulb onions are mature the leaves begin to wilt and bend over. Growers refer to the ‘fall-over’ date. Assessment criteria are different for vegetables and fruits and assessment of the correct stage depends on the part of the plant that is consumed. Leafy crops are harvested according to size and firmness. Most types of cabbage and lettuce are allowed to produce a heart and the heads should be firm and of the size required by the particular outlet. Cabbage greens are harvested before the hearts have had time to form. Lettuce and spinach for leafy salads are harvested only a few weeks after drilling, when leaf size is very small. In crops such as cauliflower and calabrese, where the flowering heads are consumed, assessment is also by eye and development is monitored until firm heads have formed. Once this stage is passed the heads will open out as flower development proceeds. In over-mature calabrese, the yellow flower petals may be seen. Harvest time is less critical with root crops such as carrots, swedes, turnips, or parsnips. They may be harvested when they reach the size required by a particular outlet but are often stored in the field for several months. Carrots may be considered to have reached maturity when there is no white coloration at the tip of the root but will continue to grow after this. Bunching carrots may be harvested immature, with some white roots. Other types are harvested at a later stage when roots have achieved a sufficient size to meet specific market requirements. Similarly early potatoes are harvested immature, but other ‘maincrop’ or ‘ware’ potatoes are harvested after the leaves have died down, this being a sign that the crop has completed bulking up. In some crops the immature pods or immature seeds are consumed (e.g. runner beans, dwarf French beans, peas, sweetcorn). As the seeds develop and swell they accumulate carbohydrates, first of all in the form of sugars and these are then converted to starch as the seed dries out. At the same time the pods are drying out and the texture becomes tough or mealy. Maturity assessment is particularly critical for these crops as they rapidly become tough if left in the field after optimum maturity. In beans the seed development is monitored and maturity is related to pod and bean size for specific varieties. Fruits are divided into two ripening types. Climacteric fruits such as ‘pome’ fruits (apples and pears) apricots, peaches, plums and kiwifruit continue to ripen 24 Chilled foods
Raw material selection -fruits and vegetables 2 naturally after harvest. As the fruit matures, carbohydrates are accumulated as starch and as ripening proceeds starch is broken down to sugars. When they are allowed to mature on the tree the climacteric begins, respiration rate increases and there is an increase in the production of ethylene gas, which promotes ripening. If allowed to ripen fully on the tree the crop is only suitable for immediate sale. Fruit destined for long-term storage is harvested immature and torage conditions are designed to control ripening. Non-climacteric fruit, for example raspberries, strawberries and cherries, accumulate sugars as they on the plant and do not continue ripening after they are harvested. They harvested at maturity Maturity of both types of fruit can be assessed using a refractometer, which measures total soluble solids, and in the case of fruits this is mostly sugar. Where applicable, starch can be measured using the iodine test. This has be apples and pears but has been most successful as a maturity indicator for pears 1. 2.3 Growing and environmental influences on suitability In addition to variety and maturity, in the production of high-quality raw material, the other major influences are environmental Growing site and season and the growers production techniques may in fact be as, or more, important to the final crop quality but the effects are more difficult to define or control Site When selecting suitable sites, consideration must be given to climatic conditions and soil type. The former influences the ability to grow crops successfully. In England, some crops such as sweetcorn are best suited to growing in southern counties where overall temperatures are warmer and there are sufficient frost- free days. Low temperatures slow down growth of the plants and cob development. Frosts after sowing will kill young seedlings and at the end of the season will destroy the cobs. Other crops, more suited to growing in the UK are able to grow at lower temperatures, e.g. cabbages, potatoes, or to complete their development in a shorter time period, e.g. peas. Research on carrots, mainly in Scandinavia and the Usa has also shown latitude and other site differences to be influential l, 12 Martens et al. 13 found that season and site had a major influence on sensory quality and chemical composition, with variety being much less important Selection of suitable soil type is important, particularly for root crops. When carrots are grown on stony soils the result is fanged and twisted carrots. Hence in England either sand or peat soil types have historically been chosen. Root growth has been found to be different on these two soil types and roots from peat soils are longer than the same variety from sand sites. Site may also influence chemical composition and through this sensory quality. Heany and Fenwick reported differences in glucosinolate concentrations and hence bitterness of Brussels sprout varieties from five UK sites. In Ireland, Gormley found that soil type influenced chemical composition and sensory quality. Carrots from
naturally after harvest. As the fruit matures, carbohydrates are accumulated as starch and as ripening proceeds starch is broken down to sugars. When they are allowed to mature on the tree the climacteric begins, respiration rate increases and there is an increase in the production of ethylene gas, which promotes ripening. If allowed to ripen fully on the tree the crop is only suitable for immediate sale. Fruit destined for long-term storage is harvested immature and storage conditions are designed to control ripening. Non-climacteric fruit, for example raspberries, strawberries and cherries, accumulate sugars as they ripen on the plant and do not continue ripening after they are harvested. They are harvested at maturity. Maturity of both types of fruit can be assessed using a refractometer, which measures total soluble solids, and in the case of fruits this is mostly sugar. Where applicable, starch can be measured using the iodine test. This has been used for apples and pears but has been most successful as a maturity indicator for pears. 1.2.3 Growing and environmental influences on suitability In addition to variety and maturity, in the production of high-quality raw material, the other major influences are environmental. Growing site and season and the growers’ production techniques may in fact be as, or more, important to the final crop quality but the effects are more difficult to define or control. Site When selecting suitable sites, consideration must be given to climatic conditions and soil type. The former influences the ability to grow crops successfully. In England, some crops such as sweetcorn are best suited to growing in southern counties where overall temperatures are warmer and there are sufficient frostfree days. Low temperatures slow down growth of the plants and cob development. Frosts after sowing will kill young seedlings and at the end of the season will destroy the cobs. Other crops, more suited to growing in the UK are able to grow at lower temperatures, e.g. cabbages, potatoes, or to complete their development in a shorter time period, e.g. peas. Research on carrots, mainly in Scandinavia and the USA has also shown latitude and other site differences to be influential11, 12 Martens et al.13 found that season and site had a major influence on sensory quality and chemical composition, with variety being much less important. Selection of suitable soil type is important, particularly for root crops. When carrots are grown on stony soils the result is fanged and twisted carrots. Hence in England either sand or peat soil types have historically been chosen. Root growth has been found to be different on these two soil types and roots from peat soils are longer than the same variety from sand sites. Site may also influence chemical composition and through this sensory quality. Heany and Fenwick14 reported differences in glucosinolate concentrations and hence bitterness of Brussels sprout varieties from five UK sites. In Ireland, Gormley15 found that soil type influenced chemical composition and sensory quality. Carrots from Raw material selection – fruits and vegetables 25
.6 Chilled foods mineral soil had higher dry matter and higher levels of carotene and, after cooking, taste panels rated them higher for flavour and softer in texture However Day, in a three-year project on sand and peat soils, found neither type to be consistently better for yield or quali Season Crop production is greatly influenced by seasonal weather conditions. For optimum crop growth, the right balance of temperature and moisture are required. This not only has a great influence on crop growth and yield, but may also affect post-harvest quality. In wet conditions, leafy plant material often takes lot of water and results in soft tissue. If this occurs at harvest it can lead to tissue which bruises easily and leads to shorter shelf-life. Conversely, too little water leads to plants suffering from moisture stress and they may wilt or fail to develop properly as in cauliflowers which are said to button. They produce only very small heads, too small to market Disease and pest development also require very specific temperature and moisture conditions and sophisticated prediction methods have been developed based on weather data collected nationally, as in potato blight prediction, or locally. Some diseases prefer wet (e.g. powdery mildew) and some dry conditions(downy mildew) but this is to oversimplify the topic. Different regimes are required for different parts of the life cycle of the disease. The yield of tomatoes is dependent on light levels during the growing season Light levels also influence the growth of lettuce crops and the accumulation of nitrates in the plants. Manufacturers of chilled baby foods will be particularly concerned that their raw materials are low in nitrates For chopped lettuce products a dense head will give the most efficient throughput for use in a chilled salad product. Recent research has shown that day and night temperatures have large effects on the shape and density of heads of iceberg lettuce Growing techniques Production techniques constitute the one area where the grower can have a major impact on the yield, quality and suitability for purpose of his crops. This includes time of drilling, plant spacing and plant protection throughout the growing season and the provision of all the nutrients needed to optimise production. The application of fertilisers to provide the plants with sources of nitrogen, phosphorus and potassium and other major and minor nutrients has been researched over many years. Nitrogen is essential for crop growth, but excess nitrates in the tissues are perceived as a possible health hazard. There are EU prescribed levels for lettuce and spinach. Field studies on a range of crops showed that some of the variation in nitrate levels may be attributed to rate of fertiliser application, but that there is likely to be an interaction with other factors affecting absorption, translocation and assimilation. Nitrate concentra- tions also varied in different parts of the plant, being higher for instance in the outer leaves of lettuce than at the heart. New research on lettuce aims to
mineral soil had higher dry matter and higher levels of carotene and, after cooking, taste panels rated them higher for flavour and softer in texture. However Day16, in a three-year project on sand and peat soils, found neither type to be consistently better for yield or quality. Season Crop production is greatly influenced by seasonal weather conditions. For optimum crop growth, the right balance of temperature and moisture are required. This not only has a great influence on crop growth and yield, but may also affect post-harvest quality. In wet conditions, leafy plant material often takes in a lot of water and results in soft tissue. If this occurs at harvest it can lead to tissue which bruises easily and leads to shorter shelf-life. Conversely, too little water leads to plants suffering from moisture stress and they may wilt or fail to develop properly as in cauliflowers which are said to ‘button’. They produce only very small heads, too small to market. Disease and pest development also require very specific temperature and moisture conditions and sophisticated prediction methods have been developed, based on weather data collected nationally, as in potato blight prediction, or locally. Some diseases prefer wet (e.g. powdery mildew) and some dry conditions (downy mildew) but this is to oversimplify the topic. Different regimes are required for different parts of the life cycle of the disease. The yield of tomatoes is dependent on light levels during the growing season. Light levels also influence the growth of lettuce crops and the accumulation of nitrates in the plants.17 Manufacturers of chilled baby foods will be particularly concerned that their raw materials are low in nitrates. For chopped lettuce products a dense head will give the most efficient throughput for use in a chilled salad product. Recent research has shown that day and night temperatures have large effects on the shape and density of heads of iceberg lettuce.18 Growing techniques Production techniques constitute the one area where the grower can have a major impact on the yield, quality and suitability for purpose of his crops. This includes time of drilling, plant spacing and plant protection throughout the growing season and the provision of all the nutrients needed to optimise production. The application of fertilisers to provide the plants with sources of nitrogen, phosphorus and potassium and other major and minor nutrients has been researched over many years. Nitrogen is essential for crop growth, but excess nitrates in the tissues are perceived as a possible health hazard. There are EU prescribed levels for lettuce and spinach. Field studies on a range of crops showed that some of the variation in nitrate levels may be attributed to rate of fertiliser application, but that there is likely to be an interaction with other factors affecting absorption, translocation and assimilation. Nitrate concentrations also varied in different parts of the plant, being higher for instance in the outer leaves of lettuce than at the heart.19 New research on lettuce aims to 26 Chilled foods
Raw material selection- fruits and vegetables 27 investigate the extent to which nitrate accumulation of protected lettuce can be adjusted by different crop management and fertiliser treatments. 20 The primary producer can also influence the suitability for purpose of particular crops by growing and harvesting suitably sized material. A major requirement of batoning carrots is that they are of suitable size and shape to maximise throughput of the batoning equipment. The optimum size is produced by a combination of suitable varieties and growing techniques and this has to be related to the requirements of different makes of equipment 1. 2.4 Post-harvest handling and storage Once a crop is harvested its quality cannot be improved. At this stage, the objective must be to maintain the produce in good condition through any short- or long-term storage until it is delivered to the customer. Thus, the ultimate quality and shelf-life of a final product depends not only on growing conditions but also on harvesting and on post-harvest handling. Avoidance of handling damage at this stage is important. Rough handling leads to bruises which spoil the appearance of produce and can become a focus of infection by spoilage diseases. Bruising can be a major reason for losses of fruit in store as well as for vegetable crops such as Dutch white cabbage aintenance of suitable post-harvest temperature is extremely important to maximise shelf-life, both for produce for immediate use and for that to be stored Crops continue to respire after harvesting using up reserves and shortening shelf-life through wilting and yellowing. Respiration rate is temperature related and is roughly halved for every 10C that the temperature is reduced. The general rule is to remove field heat as quickly as possible after harvest and then to maintain the produce at chill temperature. This is achieved by various methods such as vacuum cooling for lettuce, hydrocooling of carrots and tomatoes and storage in various types of refrigerated stores(see Ch. 4) Increasingly, use of the cool chain' aims to retain the produce at the required low temperature during packing and transport to the retailer Some delicate crops such as lettuce are not suitable for other than very short- term storage. Others such as root crops, cabbage and many fruit crops can be stored for many months to provide the continuity of supply required by the hilled food manufacturer and customer. Storage may be in field, for example for carrots which are covered with straw or in am bient stores for beetroot and other root crops. For longer storage, refrigerated stores are used. Many use moist air cooling to maintain the desired relative humidity and prevent dehydration and positive ventilation to draw air through the stored crop Specialised storage methods are required for some crops. For example there is a three-stage procedure for onion curing and storage, each stage requiring a different temperature and humidity. In the first stage the aim is to dry the surface of the bulbs. At the next stage moisture is removed from their necks at high temperature. The temperature is then reduced to prepare the onions for ong-term storage
investigate the extent to which nitrate accumulation of protected lettuce can be adjusted by different crop management and fertiliser treatments.20 The primary producer can also influence the suitability for purpose of particular crops by growing and harvesting suitably sized material. A major requirement of batoning carrots is that they are of suitable size and shape to maximise throughput of the batoning equipment. The optimum size is produced by a combination of suitable varieties and growing techniques and this has to be related to the requirements of different makes of equipment . 1.2.4 Post-harvest handling and storage Once a crop is harvested its quality cannot be improved. At this stage, the objective must be to maintain the produce in good condition through any shortor long-term storage until it is delivered to the customer. Thus, the ultimate quality and shelf-life of a final product depends not only on growing conditions but also on harvesting and on post-harvest handling. Avoidance of handling damage at this stage is important. Rough handling leads to bruises which spoil the appearance of produce and can become a focus of infection by spoilage diseases. Bruising can be a major reason for losses of fruit in store as well as for vegetable crops such as Dutch white cabbage. Maintenance of suitable post-harvest temperature is extremely important to maximise shelf-life, both for produce for immediate use and for that to be stored. Crops continue to respire after harvesting using up reserves and shortening shelf-life through wilting and yellowing. Respiration rate is temperature related and is roughly halved for every 10ºC that the temperature is reduced. The general rule is to remove field heat as quickly as possible after harvest and then to maintain the produce at chill temperature. This is achieved by various methods such as vacuum cooling for lettuce, hydrocooling of carrots and tomatoes and storage in various types of refrigerated stores (see Ch. 4). Increasingly, use of the ‘cool chain’ aims to retain the produce at the required low temperature during packing and transport to the retailer. Some delicate crops such as lettuce are not suitable for other than very shortterm storage. Others such as root crops, cabbage and many fruit crops can be stored for many months to provide the continuity of supply required by the chilled food manufacturer and customer. Storage may be in field, for example for carrots, which are covered with straw, or in ambient stores for beetroot and other root crops. For longer storage, refrigerated stores are used. Many use moist air cooling to maintain the desired relative humidity and prevent dehydration and positive ventilation to draw air through the stored crop. Specialised storage methods are required for some crops. For example there is a three-stage procedure for onion curing and storage, each stage requiring a different temperature and humidity.21 In the first stage the aim is to dry the surface of the bulbs. At the next stage moisture is removed from their necks at high temperature. The temperature is then reduced to prepare the onions for long-term storage. Raw material selection – fruits and vegetables 27