Nutritional comparison of fresh, frozen and canned fruits and vegetables. Part 1. Vitamins C and B and phenolic compounds

Abstract

The first of a two-part review of the recent and classical literature reveals that loss of nutrients in fresh products during storage and cooking may be more substantial than commonly perceived. Depending on the commodity, freezing and canning processes may preserve nutrient value. The initial thermal treatment of processed products can cause loss of water-soluble and oxygen-labile nutrients such as vitamin C and the B vitamins. However, these nutrients are relatively stable during subsequent canned storage owing to the lack of oxygen. Frozen products lose fewer nutrients initially because of the short heating time in blanching, but they lose more nutrients during storage owing to oxidation. Phenolic compounds are also water-soluble and oxygen-labile, but changes during processing, storage and cooking appear to be highly variable by commodity. Further studies would facilitate the understanding of the changes in these phytochemicals. Changes in moisture content during storage, cooking and processing can misrepresent changes in nutrient content. These findings indicate that exclusive recommendations of fresh produce ignore the nutrient benefits of canned and frozen products. Nutritional comparison would be facilitated if future research would express nutrient data on a dry weight basis to account for changes in moisture. Copyright © 2007 Society of Chemical Industry

Full text

Journal of the Science of Food and Agriculture J Sci Food Agric 87:930–944 (2007)
Review
Nutritional comparison of fresh, frozen and
canned fruits and vegetables. Part 1. Vitamins
C and B and phenolic compounds
Joy C Rickman, Diane M Barrett and Christine M Bruhn∗
Department of Food Science and Technology, University of California – Davis, Davis, CA 95616, USA
Abstract: The first of a two-part review of the recent and classical literature reveals that loss of nutrients in
fresh products during storage and cooking may be more substantial than commonly perceived. Depending on
the commodity, freezing and canning processes may preserve nutrient value. The initial thermal treatment of
processed products can cause loss of water-soluble and oxygen-labile nutrients such as vitamin C and the B
vitamins. However, these nutrients are relatively stable during subsequent canned storage owing to the lack of
oxygen. Frozen products lose fewer nutrients initially because of the short heating time in blanching, but they
lose more nutrients during storage owing to oxidation. Phenolic compounds are also water-soluble and oxygen-
labile, but changes during processing, storage and cooking appear to be highly variable by commodity. Further
studies would facilitate the understanding of the changes in these phytochemicals. Changes in moisture content
during storage, cooking and processing can misrepresent changes in nutrient content. These findings indicate
that exclusive recommendations of fresh produce ignore the nutrient benefits of canned and frozen products.
Nutritional comparison would be facilitated if future research would express nutrient data on a dry weight basis to
account for changes in moisture.
2007 Society of Chemical Industry
Keywords: nutrient; fruit; vegetable; canned; frozen; vitamins; phenolic
INTRODUCTION
Fruits and vegetables are colourful, flavourful and
nutritious components of our diets and are often
most attractive and health-promoting when harvested
at their peak maturity. Unfortunately, most people
do not have home gardens capable of supplying the
recommended 5–13 daily servings year round. Many
fruits and vegetables grow only in certain parts of
the world, under specific temperature and humidity
environments, and at particular times of the year. In
addition, fruits and vegetables are typically over 90%
water and, once they are harvested, begin to undergo
higher rates of respiration, resulting in moisture loss,
quality deterioration and potential microbial spoilage.
Harvesting itself separates the fruit or vegetable from
its source of nutrients, the plant or tree, and it
essentially uses itself as a source of calories. Many
fresh fruits and vegetables have a shelf life of only days
before they are unsafe or undesirable for consumption.
Storage and processing technologies have been
utilised for centuries to transform these perishable
fruits and vegetables into safe, delicious and stable
products. Refrigeration slows down the respiration of
fruits and vegetables and allows for longer shelf lives.
Freezing, canning and drying all serve to transform
perishable fruits and vegetables into products that
can be consumed year round and transported safely
to consumers all over the world, not only those
located near the growing region. As a result of
processing, respiration is arrested, thereby stopping
the consumption of nutritious components, the loss
of moisture and the growth of micro-organisms. The
first objective of fruit and vegetable processing is to
ensure a safe product, but processors also strive to
produce the highest-quality products. Depending on
how processing is carried out, it may result in changes
in colour, texture, flavour and nutritional quality, the
last of which is the subject of the following literature
review.
A substantial amount of research literature has
been published over the past 75 years reporting the
effects of processing, storage and cooking on the
nutritional quality of fruits and vegetables. Washing,
peeling and blanching steps prior to processing are
responsible for some loss of water-soluble nutrients.
However, the thermal processing often associated
with canning and pre-freezing blanching treatments
is especially detrimental to heat-sensitive nutrients
such as ascorbic acid (vitamin C) and thiamin.1When
used prior to canning, blanching serves to expel air
in the tissue and improve thermal conductivity and
packing into the container. The primary purpose of
∗Correspondence to: Christine M Bruhn, Department of Food Science and Technology, University of California – Davis, Davis, CA 95616, USA
E-mail: cmbruhn@ucdavis.edu
(Received 21 April 2006; revised version received 19 October 2006; accepted 1 December 2006)
Published online 14 March 2007;DOI: 10.1002/jsfa.2825
2007 Society of Chemical Industry. J Sci Food Agric 0022– 5142/2007/$30.00

Nutritional comparison of fresh, frozen and canned fruits and vegetables
blanching prior to freezing is to inactivate naturally
occurring enzymes that may still be active in the
frozen product. Blanching is an important preservation
step in the canning and freezing processing of many
vegetables. Fruits, on the other hand, are usually
not blanched prior to freezing owing to their delicate
nature and inherent acidity. Nutrients may also be lost
through oxidation, especially during heat treatment
and storage. Since both unprocessed and processed
fruits and vegetables must undergo some transport
and storage, degradation of some nutrients prior to
consumption is expected. Lower temperatures, even
in frozen goods, tend to prolong the shelf life of fruits
and vegetables.2Additional cooking of the processed
product can also destroy nutrients, although the extent
of degradation is dependent on cooking method,
nutrient and commodity. In Part 1 we discuss vitamins
C and B and phenolic compounds. Part 2 will look at
vitamin A and carotenoids, vitamin E, minerals and
fibre.3
Research approaches
The retention of ascorbic acid is often used as
an estimate for the overall nutrient retention of
food products.4,5Ascorbic acid is by far the least
stable nutrient during processing; it is highly sensitive
to oxidation and leaching into water-soluble media
during processing, storage and cooking of fresh,
frozen and canned fruits and vegetables.6,7Other
vitamins, minerals and bioactive components are more
stable; high retention of certain components, such as
vitamin E, is common during processing, storage and
cooking. Retention of nutrients is highly dependent on
cultivar, production location, maturity stage, season
and processing conditions.8–14
Despite the wealth of research published, under-
standing nutritional differences between fresh, frozen
and canned foods is complex. Researchers often exam-
ine the effects of processing and storage on a single
cultivar by randomly harvesting fruits or vegetables
from the same location to limit variability due to pro-
duction area, harvest time and cultivar. While this
enables researchers to directly understand the effects
of thermal processing on a specific commodity, it
does not accurately represent the choice consumers
have at the supermarket. At the other extreme, some
researchers simply purchase fresh products from the
grocery store and use these as the raw materials for
processing studies, without adequate information on
cultivar, maturity and production location.
Different cultivars are often used for canned and
frozen products than for those products intended for
fresh consumption, and nutritional differences exist
between cultivars. Furthermore, studies examining the
effects of processing on a food may not subsequently
study the effects of storage and cooking on the
same food. By the time a consumer consumes fresh
purchased goods, the canned or frozen equivalent may
be nutritionally similar owing to oxidative degradation
of the nutrients during handling and storage of the
fresh product. Researchers should simulate conditions
on the known cultivars harvested from selected
locations. Nutritional qualities also vary according to
season and growing location, so individual results may
not be representative of yearly averages or regional
availability.
Some researchers have approached these problems
by examining the differences in fresh, frozen and
canned fruits and vegetables purchased at a retail
market. Although the cultivars are likely not consistent
and the products have undergone different storage and
processing conditions, these retail market studies offer
a representation of the nutritional differences between
fresh, frozen and canned products that are available to
consumers in that location.
Besides variance in methodologies, changes in
nutritional data may be reported on a dry weight (DW)
or a wet weight (WW) basis. Moisture content often
changes during processing, especially during canning
with the addition of aqueous media. Furthermore,
changes in moisture content due to weight loss
can occur during storage, the extent of which is
dependent on conditions such as relative humidity.
Measurements of changes in bioactive components
on a wet weight basis may thus be misleading.
Some researchers avoid this dilemma by comparing
results on both bases or by adjusting their wet weight
products for content of soluble solids. However, many
studies still report results only on a wet weight basis,
complicating the interpretation of results.
Nutritional guidelines
Despite possible degradation of nutrients during
processing, storage and cooking, fruits and vegetables
are rich sources of many vitamins and minerals, as
well as fibre. The United States Food and Drug
Administration (FDA) defines a ‘good source’ of a
nutrient as one serving of food containing 10–19%
of the Recommended Dietary Allowance (RDA) or
Adequate Intake (AI) for that nutrient. However,
nutrient retention data are often reported in units
per 100 g rather than per serving. Since serving size
for labelling depends on commodity, a single serving
may be more or less than 100 g.
When interpreting data, it is important to consider
intake guidelines for each nutrient, such as the Dietary
Reference Intakes (DRIs) used in the USA and
Canada and published by the Food and Nutrition
Board of the National Academy of Sciences (Table 1).
DRIs refer to intake recommendations for various
nutrients and include the aforementioned RDA and
AI in addition to Estimated Average Requirement
(EAR) and Tolerable Upper Intake Level (UL). EARs
are based on the daily requirements of 50% of healthy
individuals in a particular group, while RDAs are set
slightly higher to meet the needs of most (97 – 98%)
individuals. When there are insufficient data to set
an EAR for a particular nutrient, such as potassium,
an AI is specified as an approximation. Nutrients
that may pose health risks above a certain level,
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JC Rickman, DM Barrett, CM Bruhn
Table 1. Dietary Reference Intakes (mg day−1) for healthy adults (www.iom.edu)
Vit. C
(RDA)
Thiamin
(RDA)
Riboflavin
(RDA)
Vit. B6
(RDA)
Niacin
(RDA)
Folate
(RDA)
Vit. A
(RDA)
Vit. E
(RDA)
Calcium
(RDA)
Potassium
(AI)
Sodium
(AI)
Fibre
(AI)
RDA or AI 82.5 1.15 1.2 1.3 15 0.40 0.80 15 1000 4.7 1.5 30
EAR 67.5 0.95 1.0 1.2 11.5 0.32 0.56 12 – – – –
RDA, Recommended Dietary Allowance; AI, Adequate Intake; EAR, Estimated Average Requirement.
such as sodium, are assigned a UL. In September
2005 the United States Department of Agriculture
(USDA), Agricultural Research Service published a
review of 2001 – 2002 food intake data, finding that
most Americans have significantly lower intakes of
vitamins A, C and E, as well as magnesium, than
the EAR for each nutrient. Additionally, although no
EAR is set for vitamin K, fibre, potassium or calcium,
these nutrients may also be consumed in less than
desirable quantities. These findings may reflect the
insufficient consumption of fruits and vegetables by
most Americans.
While nutrient intakes vary by location, inade-
quate fruit and vegetable consumption is a worldwide
concern. The World Health Organisation (WHO)
estimates that worldwide consumption of fruits and
vegetables is only 20 – 50% of the recommended
daily minimum of 400 g per person (Food and
Agriculture Organisation of the United Nations:
http://www.fao.org/ag/magazine/0606sp2.htm) In fact,
low fruit and vegetable intake is sixth on WHO’s list
of 20 risk factors for mortality worldwide. WHO esti-
mates that sufficient fruit and vegetable consumption
could save up to 2.7 million lives annually (WHO:
http://www.who.int/dietphysicalactivity/media/en/
gsfs fv.pdf). Reasons for insufficient fruit and veg-
etable intake vary among different climates, cultures
and countries. Postharvest loss due to perishabil-
ity may be up to 50% in some developing nations.
In developed nations where different forms of fruits
and vegetables are plentiful, low intake is sometimes
attributed to consumers’ desire for more convenience
foods.
Health agencies in many countries, including the
USA, support a Five-A-Day goal to encourage
the consumption of fruits and vegetables. Although
barriers to consumption vary, the recommendation
to increase consumption of fruits and vegetables
is a global standard. The Food and Agricultural
Organisation (FAO) has collaborated with WHO to
lead the Global Fruit and Vegetables Initiative for
Health. The first phase of this initiative, 2006–2009,
will include support for national action programmes
in up to six pilot countries in developing regions such
as Southern Africa and Latin America.
Government recommendations and current
consumption
In the USA, several different agencies promote the
consumption of all forms of fruits and vegetables.
The 2005 Dietary Guidelines for Americans, pub-
lished jointly by the Department of Health and
Human Services and the Department of Agricul-
ture, suggest that both males and females increase
their overall fruit and vegetable consumption to nine
servings (about 4.5 cups) a day for a 2000 calo-
rie diet. This is an increase of 50 to over 100%
from current consumption. These guidelines specif-
ically state that all types of fruits and vegetables,
including fresh, frozen, canned and dried products,
should be consumed to meet dietary recommenda-
tions. Similarly, the Centers for Disease Control and
Prevention state that ‘all fresh, frozen, dried or canned
fruits and vegetables count towards the Five-A-Day
goal, as long as they don’t have added sugars or fats’
(http://www.cdc.gov/nccdphp/dnpa/5aday/faq/types.
htm). It is important to note that foodstuffs may
only bear the Five-A-Day logo if they meet the FDA
requirements for ‘healthy’ food, which places restric-
tions on fat, saturated fat, cholesterol and sodium.
In particular, sodium levels must be below 480 mg
per serving to bear the Five-A-Day logo. In general,
canned fruits and vegetables meet this requirement
(http://5aday.gov/about/pr.html).
The Women, Infants and Children (WIC) pro-
gramme seeks to improve the nutritional status of
low-income women and their children, in part by
providing food packages designed to address their
nutritional deficiencies. Recent proposed changes to
WIC packages include the addition of monthly $8–10
vouchers for the purchase of fresh fruits and vegeta-
bles. Canned, dried or frozen fruits and vegetables
would be allowable substitutes when fresh forms are
unavailable.15
Clearly, government guidelines encourage the intake
of all fruits and vegetables, whether fresh, frozen,
canned or dried, so long as added ingredients such
as sugar, fat and salt are not significant. This
recommendation is supported by an independent
study at the University of Illinois Department of
Food Science and Nutrition. Researchers at Illinois
compared USDA nutrient data for fresh, frozen
and canned fruits and vegetables (Klein BP and
Kalitz R, personal communication). They determined
that canned fruits and vegetables were nutritionally
similar and sometimes superior for some nutrients to
their fresh and frozen counterparts.
Although most people do not consume enough total
fruits and vegetables, it is interesting to note that
in the USA more processed fruits and vegetables
are consumed overall than their fresh counterparts.
Table 2 details fruits and vegetables commonly
consumed in their processed form. Since nearly 80%
of all tomatoes consumed in the USA are canned, it is
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Nutritional comparison of fresh, frozen and canned fruits and vegetables
Table 2. Economic Research Service consumption data (lb per
capita) for 2004 (www.ers.usda.gov/data/foodconsumption/)
Commodity Fresh Frozen Canned
Asparagus 1.0 0.07 0.20
Beans, snap 1.9 1.9 3.7
Carrots 8.9 1.6 1.2
Corn 9.6 9.1 8.2
Green peas – 1.9 1.2
Mushrooms 2.6 – 1.6
Peaches and nectarines 5.1 0.55 3.6
Pineapple 4.4 – 4.8
Spinach 2.1 0.93a
Tomatoes 19.3 – 70.4
aTotal for all processed varieties.
especially important to note changes that may occur
during the processing of tomatoes.16 The purpose of
this study is to review the literature on the nutritional
differences between fresh, frozen and canned fruits and
vegetables, concentrating on the years 2000–2005.
Results from this review will be presented in two parts.
Part 1 includes the water-soluble vitamins C and B in
addition to phenolic compounds. Part 2 will focus on
the lipid-soluble vitamins A and E in addition to other
carotenoids, minerals and fibre.3
Whenever possible, the effects of storage and
cooking on the fresh and processed fruits and
vegetables are also compared. Canned foods undergo
thermal processing and are thus most comparable to
cooked fresh or cooked frozen products. However,
canned foods can be served cold or reheated. For
consistency with previous studies, reheated canned
foods will be referred to as ‘cooked’. Values from
the USDA nutrient database, which are usually
yearly averages owing to seasonal variability, are also
considered.
Vitamin C, the B vitamins and phenolic compounds
are all, to varying degrees, water-soluble, thermally
labile and sensitive to oxidation. All these properties
make these nutrients more susceptible to degradation
during processing, storage and cooking than the
nutrients studied in Part 2.
VITAMIN C (ASCORBIC ACID)
Vitamin C is highly water-soluble and sensitive to
heat. These properties make it susceptible to pro-
cessing technologies as well as cooking in the home.
According to the Centers for Disease Control and
Prevention, good sources of vitamin C include broc-
coli, tomatoes, leafy greens, apricots and pineap-
ple (http://www.cdc.gov/nccdphp/dnpa/5ADay/index.
htm).
Processing
Canning
Many recent and classical studies have examined the
effects of thermal processing on ascorbic acid for
various commodities (Table 3). Among the recent
Table 3. Ascorbic acid (g kg−1wet weight) in fresh and canned
vegetables
Commodity Fresh Canned
Loss
(%) Authors Year
Broccoli 1.12 0.18 84 Murcia et al.52000
Corn 0.042 0.032 0.25 Dewanto et al.18 2002
Carrotsa0.041 0.005 88 Howard et al.10 1999
Green peas 0.40b0.096b73 Weits et al .23 1970
Spinach 0.281b0.143b62
Green beans 0.163b0.048b63
0.053 0.050 NS Jiratanan and 2004
Liu20
Beets 0.148 0.132 10
aAverage of two consecutive years.
bBased on USDA nutrient database. Authors did not provide values.
NS, not significant.
Table 4. USDA nutrient data for ascorbic acid (g kg−1wet weight) in
fresh and canned products16
Canned
Commodity Fresh Drained solids Liquids +solids
Green peas 0.40 0.096 0.098
Spinach 0.281 0.143 0.135
Pineapple (juice pack) 0.169 0.094 0.095
Green beans 0.163 0.048 0.034
products studied were tomatoes, asparagus, corn,
broccoli, mushrooms and green beans. All reported
a decrease in ascorbic acid during commercial thermal
processing conditions.5,10,11,13,17– 23
On a wet weight basis, loss of ascorbic acid during
processing ranged from 8% in beets to 90% in
carrots.10,20 Martin-Belloso and Llanos-Barriobero13
reported their results on a dry weight basis, finding
losses of approximately 25–30% for white asparagus,
lentils and tomatoes and 41% for mushrooms. Saccani
et al.22 found similar results for tomatoes. They
reported ascorbic acid losses ranging from 29 to
33% after normalising tomato samples by bringing
concentrations to 5◦Brix. Although most studies
did not analyse the drained liquid, any ascorbic acid
remaining in the liquid would likely be minimal since it
is easily oxidised. This is supported by USDA nutrient
data, which show little difference in ascorbic acid
content when the canning liquid is included in the
analysis along with the fruit or vegetable (Table 4).
Freezing
Several studies considered the effects of freezing on
the same product that was canned.5,10,11,21 In general,
frozen samples contained higher levels of ascorbic
acid than canned samples (Table 5). Favell24 reported
changes in ascorbic acid due to freezing for several
vegetables on a dry weight basis. He found negligible
losses in carrots but 20 and 30% losses in broccoli and
green peas respectively.
These results are consistent with older studies
on blanching and freezing, which show the highest
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JC Rickman, DM Barrett, CM Bruhn
Table 5. Losses of ascorbic acid (% wet weight) due to canning and
freezing processes
Commodity Canning
Blanching
and freezing Authors Year
Broccoli 84 50– 55 Murcia et al.52000
–30Howardet al.10 1999
Carrots 90 0–35
Green beans – 17
63 28 Weits et al.23 1970
Green peas 73 51
84 63 Fellers and 1935
Stepat25
– 20 Hunter and 2002
Fletcher26
Spinach – 50
62 61 Weits et al.23 1970
average losses of vitamin C for spinach and broccoli
and relatively lower amounts for legumes. Asparagus is
reportedly most resistant to losses during the blanching
and freezing process, with retention averaging 90%.
Retention of ascorbic acid can vary tremendously in
all products, depending on cultivar and processing
conditions among other variables. In general, losses
due to the entire freezing process can range from 10
to 80%, with averages around 50%.1This compares
favourably with canning, where average losses are
greater than 60%.
Storage
Fresh
In a study on the effects of storage and freezing on
fresh vegetables, Favell24 found that freshly picked
vegetables consistently contained the greatest amounts
of ascorbic acid in all vegetables studied (Table 6).
Ascorbic acid begins to degrade, however, immediately
after harvest. Green peas, for example, were found
to lose 51.5% WW of ascorbic acid during the first
24 –48 h after picking.25 Furthermore, ascorbic acid
degrades steadily during prolonged storage, although
Table 6. Losses of ascorbic acid (% dry weight) due to fresh and
frozen storage24
Commodity
Fresh, 20 ◦C,
7days
Fresh, 4 ◦C,
7days
Frozen, −20 ◦C,
12 months
Broccoli 56 0 10
Carrots 27 10 –
Green beans 55 77 20
Green peas 60 15 10
Spinach 100 75 30
refrigeration can slow its degradation rate (Tables 6
and 7). The losses of ascorbic acid that occur between
harvest and consumption suggest that processing can
have a preserving effect for some vegetables.10,23,25,26
For instance, levels of ascorbic acid in fresh peas and
fresh spinach stored at 4 ◦C fell below levels in the
frozen product after 10 days. Fresh storage at ambient
temperatures resulted in greater loss; for example,
fresh peas stored at ambient temperatures lost 50% of
their ascorbic acid in 1 week, while fresh spinach stored
at ambient temperatures lost 100% of its ascorbic acid
in less than 4 days.26
Frozen
Ascorbic acid also continues to degrade during
prolonged storage of frozen products (Tables 6 and 7).
Losses after 1 year for fruits and vegetables stored at
−18 to −20 ◦C averaged 20–50% WW for products
such as broccoli and spinach. Asparagus and green
peas, which are generally more resistant to processing,
suffered minimal losses. Hunter and Fletcher26 did
not provide an explanation for the increase observed
during storage of frozen green peas, although a change
in moisture content may be responsible. Table 6 offers
details on specific studies.
Canned
Ascorbic acid losses during storage of canned goods
tend to be small (<15%) when compared with storage
Table 7. Losses of ascorbic acid (% wet weight) due to storage of fresh, frozen and canned vegetables
Fresh Frozen Canned
Commodity Time (days) ◦C Loss (%) Time (months) Loss (%) Time (months) Loss (%) Authors Year
Broccolia21 4 13 12 50 – – Howard et al.10 1999
48
Carrotsa84 5 0 12 NS
10 50
Green beans 16 90 45 – –
––– 6468Weitset al.23 1970
Green peas – – – NS
21 4 40 1 +20b– – Hunter and Fletcher26 2002
72060––––
Spinach 21 4 75 1 NS – –
4 20 100 – – – –
––– 6 26 6 NSWeitset al.23 1970
aResults for two consecutive years.
bAuthors reported an increase.
NS, not significant.
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Nutritional comparison of fresh, frozen and canned fruits and vegetables
losses in fresh and frozen products (Table 7). At
least two studies have shown that no statistically
significant losses of ascorbic acid occur during storage
of canned green beans at room temperature, and one
study showed a slight loss of 6% after 18 months of
storage of canned green beans.9,27,28 These results
are consistent with classical studies suggesting strong
retention (>85%) of ascorbic acid in canned goods
stored at ambient temperature for up to 1 year.2
Cooking
Depending on the cooking method used, losses of
ascorbic acid during home cooking range from 15 to
55%.29 Additional ascorbic acid losses due to cooking
canned products are minimal, since little if any added
water is needed and the heating time is generally less
than the cooking time needed for fresh or frozen
products.4,25 Unheated canned products are thus
usually compared with cooked fresh and/or cooked
frozen foods. Cooked frozen products have often been
shown to be equal or superior to cooked fresh products
in their ascorbic acid levels. This is likely due to the
losses of vitamin C during storage of the fresh produce
(Table 8).4,24,26,30
Howard et al.10 compared uncooked and
microwave-cooked fresh refrigerated, frozen and
canned carrots.10 Interestingly, the cooked versions
did not always contain lower amounts of ascorbic
acid. Microwave cooking may increase the content of
ascorbic acid in a food, although no overall pattern was
observed. Since results were expressed on a wet weight
basis, the apparent increase may be attributed to loss
of soluble solids: the authors suggest that the rate of
diffusion of ascorbic acid out of the cell may be slower
than that of other solids such as sugars. This poses an
avenue for future research. Of the products compared,
cooked canned carrots contained the lowest amounts
of vitamin C, although the results may be nutritionally
insignificant, since carrots are not good sources of the
vitamin (Table 8).
Retail market products and USDA database
Hunter and Fletcher26 compared ascorbic acid levels
in fresh, frozen and canned peas and spinach
purchased at a retail market (Table 9).26 Both
vegetables contained the lowest levels of ascorbic acid
in the canned form, even after cooking fresh and frozen
products. Interestingly, fresh was not always best.
Cooked frozen peas and frozen leaf spinach (versus
frozen chopped) contained amounts of ascorbic acid
greater than or equal to those in the cooked fresh
products. These results are inconsistent with USDA
data for processed spinach, which report the highest
levels of ascorbic acid in the canned form. For green
peas, USDA data report the highest levels of ascorbic
Table 8. Total losses of ascorbic acid (% wet weight (WW)) due to processing, storage and cooking
Fresh Frozen Canned
Commodity
Initial concentration
(g kg−1WW)
Storage time
(days), refrigerated
Loss
(%)
Storage time
(months)
Loss
(%)
Storage time
(months)
Loss
(%) Authors Year
Broccolia1.23 0–21 5 0 –12 35 – – Howard et al.10 1999
1.80 38 62
Carrotsa0.043 0–7 42 0– 12 12 0–12 81
0.039 +50b56 95
Green beans 0.152 0– 21 37 0 – 12 20 – –
0.163c023648668Weitset al.23 1970
Green peas 0.40c028666677
0.354 1–2 61 0 70 0 85 Fellers and Stepat25 1935
Spinach 0.281c064681667Weitset al.23 1970
aAuthors reported total losses as an average of values collected throughout the total storage time. The two values for each vegetable represent
results from consecutive years.
bAuthors reported an increase.
cBased on USDA nutrient database.16 Authors did not provide values.
Table 9. Average ascorbic acid levels (g kg−1wet weight) found in market-purchased products
Fresh Frozen Canned
Commodity Uncooked Cooked Uncooked Cooked Uncooked Cooked Authors Year
Green beans 0.057 – 0.020 – 0.212 – Tinklin and Harrison32 1959
0.21 0.13 0.11 0.03 0.04 0.03 Wills et al .33 1984
Green peas 0.32 0.14 0.21 0.11 0.13 0.06
0.183 – 0.194 – 0.0471 – Hunter and Fletcher26 2002
Spinach 0.289 – 0.35 – 0.029 –
Tomatoes 0.10 0.071 – – 0.107 – Franke et al.62004
0.080 – – – 0.080 – Nagarajan and Hotchkiss31 1999
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Table 10. USDA nutrient data for ascorbic acid (g kg−1wet weight) in selected fruits and vegetables16
Fresh Frozen Canned
Commodity Uncooked Cooked Uncooked Cooked Drained solids Liquids +solids
Green beans 0.163 0.097 0.129 0.041 0.048 0.034
Green peas 0.400 0.142 0.180 0.099 0.096 0.098
Spinach 0.281 0.098 0.243 0.022 0.143 0.135
Peaches 0.066 – 0.942a– 0.028 0.028
Pineapple (juice pack) 0.169 – 0.080 – 0.094 0.095
Tomatoes 0.127 0.228 – – – 0.090
aAscorbic acid may be added during processing to prevent enzymatic browning.
acid in cooked fresh peas, with similar levels in cooked
frozen and canned products (Table 10).
In two other retail market studies, purchased fresh
and canned tomatoes were compared.6,31 The results
for tomatoes are quite different from those found for
peas and spinach. In both studies, canned tomatoes
were found to have similar or higher levels of ascorbic
acid than the fresh product (Table 9). Only one
of these studies cooked the fresh tomatoes, and it
was found that boiling resulted in losses of nearly
30% WW.6On the other hand, USDA data show
higher levels of ascorbic acid in cooked fresh tomatoes
than in unprocessed tomatoes on a wet weight basis
(Table 10). The discrepancy could be due to variation
in cultivars or cooking techniques.
To further examine the differences in retail market
products, we turned to older studies. In one study
conducted for three consecutive years, 1956–1958,
researchers compared fresh, frozen and canned green
beans purchased from a market at various times. The
beans were cooked ‘with minimum liquid and for
as short a time as feasible to conserve the nutritive
value and the general acceptability of the products’.
These researchers found that cooked fresh green beans
contained, on average, significantly higher levels of
ascorbic acid than cooked canned or frozen beans
(Table 9). In comparing cooked canned and frozen
samples, however, the study found variance due to
grade of bean (A, B or C) and brand of product.
On average, cooked canned green beans contained
comparable amounts of ascorbic acid to cooked frozen
beans.32 A 1984 Australian study found similar results
for market-purchased green beans, with cooked fresh
beans having the greatest amount of ascorbic acid,
while cooked frozen and canned beans contained the
same amount (Table 9).33
Conclusions
Research supports the common perception that fresh
is often best for optimal vitamin C content, as
long as the fresh product undergoes minimal storage
at either room or refrigerated temperatures. While
the canning process causes significant initial loss
of ascorbic acid, further losses due to storage and
cooking are minimal. In contrast, the blanching and
freezing process is not as destructive to ascorbic acid,
but continued storage and subsequent cooking of
frozen products result in significant degradation of the
vitamin. Studies of produce on the retail market and
USDA nutrient data reveal that cooked canned and
frozen products can contain similar or higher levels of
ascorbic acid as cooked fresh products, depending on
commodity. Moreover, canned foods such as tomatoes
and pineapples can make significant contributions to
the RDA for vitamin C. More studies with greater
sample sizes are needed to compare ascorbic acid
levels in foods available to the consumer.
B VITAMINS
The B vitamin family includes thiamin (B1), riboflavin
(B2), niacin (B3), biotin, pantothenic acid, B6, folate
and B12. Their water solubility renders them prone to
leaching during cooking and processing. Additionally,
many of the B vitamins, especially thiamin, are
sensitive to degradation during processing. Next to
vitamin C, thiamin is the least stable of the vitamins
to thermal processing, so its losses are the most
studied of the B vitamins.29,34 However, fruits and
vegetables are generally not good sources of thiamin,
so its retention may not be representative of the overall
nutrient retention of a food.29 Riboflavin is unstable to
light, so processing and storage conditions play a role
in its retention. Since biotin and pantothenic acid are
widespread in food, changes in these B vitamins during
processing are generally not of nutritional concern. B12
is found mostly in animal products, so its sensitivity is
not reported here.
Moshfegh et al.35 reported that most Americans
consume adequate intakes of riboflavin and niacin.
Thiamin and folate intakes are lower than desirable
among female populations, while inadequate intake of
vitamin B6was identified as a potential problem for
older females. Many fruits and vegetables, especially
leafy greens, can contribute B vitamins to the diet.
Processing
Much of the original research on the effects of
processing on the B vitamins was completed between
1960 and 1990. Few researchers in recent years have
focused their studies on B vitamin losses as a result
of canning, freezing and subsequent storage. With
continual advances in technology, it may be important
to update these data.
936 J Sci Food Agric 87:930–944 (2007)
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Nutritional comparison of fresh, frozen and canned fruits and vegetables
Canning
Thiamin (B1). Several studies have shown significant
decreases in thiamin content during thermal process-
ing, although the extent of degradation depends on the
commodity.9,13,27 Losses may range from 25% DW in
asparagus to 66% DW in spinach.13,36 At least two
recent reports suggest no significant thiamin losses
(WW) after canning tomatoes, although one study
reported a loss of 53% DW.13,22,36 This difference
may be due to the expression of nutrient content on a
dry rather than a wet basis, but the deviation suggests
the need for additional research.
Riboflavin (B2). Retention of riboflavin during the
canning process is much higher than that of thiamin.
Research suggests retention of 68% in mushrooms and
lentils to 95% or higher in asparagus, sweet potatoes
and peaches (DW).9,13 Again, there are discrepancies
among tomato studies due to different dry versus wet
weight reporting practices. One study of tomatoes
reported a 61% DW retention rate for riboflavin, while
another found no significant decreases during canning
(WW).13,22
Vitamin B6.Retention of B6during the canning
process ranges from 54% DW in mushrooms to
80% DW in cherries and lentils.13,27 Schroeder37
found 57–77% WW less vitamin B6in canned
vegetables than in their fresh counterparts. Saccani
et al.22 brought all tomato samples to 5◦Brix before
analysis to account for the change in moisture content.
They found significant increases of 14–38% in B6
after canning tomatoes, depending on the type of can
(lacquered or plain) and the temperature used for
sterilisation.
Niacin (B3). Most data suggest that niacin is stable
to processing.36 Retention rates of 93% or higher
were found after canning and subsequent storage of
green peas, green beans, peaches and sweet potatoes
on both wet and dry weight bases.9,33 In fiddlehead
greens, however, nearly 50% WW of the original niacin
concentration was lost after canning.38
Folate. Only one recent study examined folate reten-
tion after canning. Jiratanan and Liu20 found a 30%
WW loss of folate as a result of canning beets but
did not find a reduction in folate after canning green
beans. They attributed the results to the reducing
environment in green beans created by packing and
processing in water, whereas the beets were packed
without a filling medium. The authors suggested that
the reducing environment created by the addition of
water might allow for the recycling of folate or slow its
degradation.
Freezing
The use of blanching as a pre-freezing treatment is
responsible for the loss of water-soluble B vitamins.
Losses of 9–60% thiamin and up to 20% riboflavin
have been reported for vegetables such as green peas
and beans.39 Hebrero et al.40 reported a 30% DW loss
of thiamin in spinach due to blanching before freezing.
Bushway et al.38 found 30, 38 and 35% WW lower
levels of thiamin, riboflavin and niacin respectively
after blanching and freezing fiddlehead greens.
A few recent studies have compared B vitamins in
frozen and canned legumes. On a wet weight basis,
frozen legumes contained significantly higher levels of
thiamin than their canned counterparts.21,33 USDA
nutrient data, which report data on a wet weight basis,
support this finding (Table 11). Lisiewska et al.,21
however, found that the differences were insignificant
when dry matter content was considered.
Storage
Fresh
Spinach has been found to lose 13 and 46% DW of
its original thiamin content during storage for 1 and
3 weeks respectively at 4– 6 ◦C. Green peas retained
much more thiamin, losing only 23% DW after
3 weeks of storage at 4 ◦C. Riboflavin also degrades
during storage. After 3 weeks at 4 ◦C, losses of 39
and 24% DW were determined for spinach and
peas respectively.41 Storage temperature can have a
significant effect; even greater losses were found in
spinach stored at room temperature.40
Frozen and canned
The few studies on changes in B vitamins during
canned and frozen storage suggest that there is
some degradation of these vitamins during storage
for most products.9,38 During long-term storage
(6–18 months) at room temperature, significant losses
(DW) of thiamin were observed in canned tomatoes
and peaches, but only small losses (DW) were found
in canned green beans.9,22,27 Canned tomatoes also
lost significant amounts of riboflavin, vitamin B6
and niacin during 8 months of storage.22 Canned
cherries and green beans lost vitamin B6during 4
and 6 months of storage respectively.27 For canned
and frozen fiddlehead greens, no significant changes
in thiamin, riboflavin and niacin were found during
10 months of storage.38 Hebrero et al.40 found a 25.4%
DW increase in thiamin after 40 days in frozen spinach.
The authors suggest that further research is needed to
satisfactorily explain the increase.
Cooking
Cooking vegetables can result in thiamin losses ranging
from 11 to 66% WW, depending on the commodity
and cooking process.42 Retention of other B vitamins is
generally high, although losses due to leaching can be
significant, depending on cooking conditions. In one
study on green peas and green beans, cooked fresh
products consistently contained more thiamin and
riboflavin than both cooked frozen and canned samples
on a wet weight basis. Thiamin, riboflavin and niacin
contents were the same in cooked frozen and canned
J Sci Food Agric 87:930 – 944 (2007) 937
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JC Rickman, DM Barrett, CM Bruhn
green beans. In the case of green peas, thiamin and
niacin were significantly lower in the cooked canned
sample than in the cooked frozen sample.33 Since the
results were reported on a wet weight basis, dilution of
the vitamins may account for some of the differences.
Another study showed that cooked fresh and frozen
green peas contained similar amounts of thiamin and
riboflavin on a wet weight basis.41 The frozen product,
however, did not undergo any storage. Since these
vitamins may undergo continued degradation during
storage, these results may be nutritionally insignificant.
Other studies suggest that cooked frozen and canned
legumes contain similar amounts of thiamin, although
both contain less than cooked fresh legumes.21,33
USDA nutrient database
USDA nutrient data on selected fruits and vegetables
can be found in Table 11. Canned green beans, green
peas and spinach generally contain the least amount of
B vitamins when compared with their fresh and frozen
counterparts. Canned peaches are similar to frozen
peaches in B vitamin content, although both contain
lower amounts than fresh peaches. Canned tomatoes
generally contain higher levels of B vitamins than fresh
tomatoes.
Conclusions
Although there are inconsistencies with methodology
and data reporting, most data suggest that the B
vitamins are sensitive to thermal processing, storage
and cooking. However, more studies should be
completed to determine the differences in fresh, frozen
and canned products available to the consumer at
retail markets. Most importantly, dry weight results
should be reported to avoid apparent differences due
to changes in moisture content during processing and
storage.
PHENOLIC COMPOUNDS
Epidemiological studies show positive correlations
between a diet high in phenolic-rich fruits and
vegetables and reduced risk of chronic diseases such
as cancer and cardiovascular disease. In general,
phenolic compounds are thus considered a positive
quality of fruits and vegetables.43 However, phenolic
compounds are not considered vital nutrients for
humans, and their potential benefit to human
health is still under discussion. Their nutritional
benefits are often attributed to their substantial
antioxidant activity. Some researchers have suggested
that phenolic compounds are responsible for stalling
or stopping the ‘initial trigger’ of chronic disease by
serving as sacrificial antioxidants to damaging oxidants
in the body.43,44 Since there are hundreds of phenolic
compounds found in fruits and vegetables, many
authors report composite total phenolic (TP) values.
Processing
The phenolic composition of fruits and vegetables is
dependent on commodity, cultivar, maturity stage and
postharvest conditions. Since phenolic compounds are
antioxidants, they are subject to oxidation during
storage and processing of foods.44 The blanching
process often used prior to canning and freezing
inactivates enzymes that cause the oxidation of
phenolics.45 However, chemical degradation can still
occur during storage, depending on available oxygen
and exposure to light.
Phenolic compounds are also water-soluble, ren-
dering them susceptible to leaching. Furthermore,
phenolic compounds and other phytochemicals are
found in significant amounts in the peels of fruits, so
some content is lost during the peeling step of process-
ing. Removal of peach peel resulted in 13– 48% loss
of total phenolics, depending on the maturity stage of
the fruit.46 Separation of other plant tissues, such as
removal of mushroom stems, may also influence the
final phenolic composition of a food.
Canning
Several researchers have reported significant declines
in TP content due to thermal processing. The
Table 11. USDA data for B vitamins (g kg−1wet weight) in selected fruits and vegetables16
Commodity Thiamin Riboflavin Niacin B6Folate
Green beans Cooked from fresh 0.00074 0.00097 0.00614 0.00056 0.00033
Cooked from frozen 0.00035 0.00090 0.00383 0.00060 0.00023
Canned 0.00015 0.00056 0.00201 0.00037 0.00032
Green peas Cooked from fresh 0.00259 0.00149 0.0202 0.00216 0.00063
Cooked from frozen 0.00283 0.00100 0.0148 0.00113 0.00059
Canned 0.00121 0.00078 0.00732 0.00064 0.00044
Tomatoes Cooked from fresh 0.00036 0.00022 0.00532 0.00079 0.00013
Canned 0.00045 0.00047 0.00735 0.00090 0.00008
Peaches Cooked from fresh 0.00024 0.00031 0.00806 0.00025 0.00004
Cooked from frozen 0.00013 0.00035 0.00653 0.00018 0.00003
Canneda0.00012 0.00026 0.00614 0.00019 0.00003
Spinach Cooked from fresh 0.00095 0.00236 0.00490 0.00242 0.00146
Cooked from frozen 0.00078 0.00176 0.00439 0.00136 0.00121
Canned 0.00018 0.00106 0.00271 0.00080 0.00058
aCanned in heavy syrup; drained.
938 J Sci Food Agric 87:930–944 (2007)
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Nutritional comparison of fresh, frozen and canned fruits and vegetables
evidence suggests, however, that the decline is largely
due to leaching into the brine or syrup rather
than oxidation.47,48 Furthermore, vegetables vacuum
packed and/or canned without a liquid topping juice
(beets, tomatoes and corn) were found to have very
slight changes in their TP content (Table 12). In fact,
beets experienced a further increase (+17% WW from
control) after additional heating for a total of 45 min.20
Interestingly, Bing cherries also experienced an overall
increase in TPs due to thermal processing when the
canning syrup was included in the analysis. However,
50% WW of the TPs were transferred from the fruit
to the syrup.47
The largest loss of TPs due to canning was found
in mushrooms (Table 12), which underwent several
washing and immersion steps in addition to thermal
processing.49 The stems of the mushrooms were also
removed, but the authors did not quantify the TPs
that may have been lost in this step. This may be
important, since other authors have suggested stem
removal as a significant reason for nutrient loss in
mushrooms.13 Two brines were used in canning to
determine the effects of adding ascorbic acid to the
canning medium. As expected, mushrooms canned
with ascorbic acid had a retention rate 20% WW higher
than those canned without ascorbic acid, suggesting
that oxidation is also a significant cause of loss of TPs
in mushrooms.
When analysing specific phenolic compounds,
similar results were found. Total flavonoids decreased
by 60% WW in green beans packed in water but
increased by 30–50% WW in beets in which no
topping juice was used.20 No significant change was
found in total flavonoids after canning tomatoes.8
Anthocyanins were found to increase slightly in
Bing cherries after canning with syrup, but nearly
50% WW of the anthocyanins were transferred to
the syrup.47 Although procyanidin values for fresh
clingstone peaches were not reported, Hong et al.48
compared frozen peaches with canned peaches and
reported that the apparent losses observed during
thermal processing may be attributed to migration
of procyanidins into the canning syrup.
Freezing
In general, freezing causes minimal destruction
of phenolic compounds in fruits, with retention
levels dependent on cultivar.49 – 51 Increases in the
phenolic content of some fruit varieties have also
been reported (Table 13). After freezing raspberries,
Gonz´
alez et al.50 found a 12% WW loss in one early
harvest cultivar but a 12% WW gain in another.
The authors also found increases (up to 40% WW)
in total anthocyanins for early harvest cultivars but
decreases (−17% WW) for late harvest varieties.
The late harvest raspberries, however, still contained
significantly higher levels of total anthocyanins after
freezing. The same study found 8 and 15% WW
losses of TPs and total anthocyanins respectively
after freezing wild blackberries. In another study
on raspberries, no significant difference in total
anthocyanins and TPs was found after freezing.51
Table 12. Total phenolics (g gallic acid equivalents kg−1wetweight(WW))infreshandcannedproducts
Commodity
Fresh
product
Canned product
(drained)
Total canned product
(fruit or vegetable
+canning liquid)
Change due to
canning
(% WW) Authors Year
Beets 1.20 1.30 No liquid used +5 Jiratanan and Liu20 2004
Green beans 0.78 0.53 Not reported −32
Bing cherries 1.94 1.13a233 −40bChaovanalikit and Wrolstad47 2004
1.17a259
Clingstone peaches 0.397 0.314 Not reported −21 Asami et al.46 2002
Corn 0.72 0.68 No liquid used −5Dewantoet al.18 2002
Tomatoes 0.142 – 0.149 NS
Mushrooms 1.80 0.162 Not reported −91 Vivar-Quintana et al.49 1999
0.603c−67c
aResults for canned product correspond to different batches.
bDoes not include syrup.
cAscorbic acid was added to canning brine.
NS, not significant.
Table 13. Total phenolics (g gallic acid equivalents kg−1wet weight) in selected fresh and frozen fruits
Commodity Fresh Frozen % change Authors Year
Raspberries 0.576 0.565 NS Mullen et al .51 2002
1.134–1.782 0.996 – 1.885 −12to +12aGonz ´
alez et al.50 2003
Blackberries 9.7771 9.036 −8
Peaches (peeled) 0.326 0.423 +30 Asami et al.46 2003
aResults varied by cultivar.
NS, not significant.
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JC Rickman, DM Barrett, CM Bruhn
Asami et al.46 found a significant (30% WW) increase
in the TPs of clingstone peaches after freezing.
Puupponen-Pimi¨
aet al.52 studied the effects of
blanching and freezing on phenolic compounds of
peas, carrots, cauliflower, cabbage and potatoes. The
authors reported an average loss of 20 – 30% DW
of TPs in most vegetables, although no change was
observed in most carrot samples and a 26% DW
increase was observed in cabbage.
Storage
Fresh
Mullen et al.51 simulated the storage of fresh raspber-
ries to predict levels in fruits available at retail market
(3 days of storage) and at home (additional 24 h).
The levels of TPs increased slightly but significantly
during the 3 days of storage and the additional 24 h
period. The authors suggest that continued secondary
metabolic activity in the stored fruits is responsible for
the increases observed in TPs. No significant change
was found in total anthocyanin content.
Asami et al.46 reported no significant loss of TPs
during cold storage of peeled and unpeeled peaches.
Interestingly, they found significant gains (69 and
36% WW respectively for peeled and unpeeled fruits)
during 24 h of storage at 30 ◦C. Levels began to drop
off after 24 h, although at 48 h the peeled and unpeeled
fruits still contained 50 and 28% WW more TPs
respectively than fresh fruits. The authors attributed
these gains to the possibility of increased activity
of enzymes involved in phenolic synthesis, due to
elevated temperatures and tissue stress induced by
peeling.
Vegetables may not experience the same beneficial
increase reported during fresh storage of fruits. Vallejo
et al.53 stored freshly harvested broccoli for 7 days
to simulate maximum time spent in transport and
distribution and for a further 3 days to simulate
time spent in a retail market. After the 10 days,
large amounts of phenolic compounds were lost. The
authors reported losses of 44 – 51, 59 – 62 and 73 –74%
WW for sinapic acid derivatives, total flavonoids and
caffeoyl-quinic acid derivatives.
Frozen
Changes in TPs during frozen storage seem to depend
heavily on commodity. No statistically significant
change was observed in TPs of frozen peaches
during 3 months of storage on a wet weight basis.46
Puupponen-Pimi¨
aet al.,52 however, found some losses
of TPs on a dry weight basis during 12 months of
frozen storage of broccoli, carrots, cauliflower, peas
and potatoes (Table 14). Significant decreases in TPs
and total anthocyanins were also found during frozen
storage of Bing cherries (Table 15). Losses of 50 and
87% WW of TPs and total anthocyanins respectively
were recorded after 6 months of storage at −20 ◦C.
Cherries stored for 6 months at −70 ◦C, however,
retained 88% of total anthocyanins and 100% of
TPs.47
Changes in TPs are also dependent on cultivar.
Gonz´
alez et al.50 studied four raspberry cultivars and
found different results for each, ranging from no
change to an increase of 12% and decreases of
21 and 28%, during 12 months of frozen storage.
Since retention of phenolic compounds seems to be
quite erratic during frozen storage, further research
Table 14. Changes in total phenolics (g gallic acid equivalents kg−1dry weight) during freezing and 12 months of frozen storage of vegetables52
Commodity Fresh Initial frozen
% change
due to freezing Final frozen
% change during
frozen storage
Broccoli – 3.20 NA 3.10 −3
Cabbage 1.90 2.40 +26 1.90 −21
Carrots 1.10 – 1.30 0.80 – 1.30 0 to −33 0.80– 1.20 −17 to +20
Cauliflower 5.60 4.90 −13 4.50 −8
Peas 0.80–1.20 0.60– 0.90 −13 to −25 0.60–0.90 0 to −14
Potatoes 0.50– 0.60 0.30 – 0.60 −16 to −40 0.40 – 0.50 −20 to +67
NA, not applicable.
Table 15. Total phenolics (g gallic acid equivalents kg−1wet weight) in fresh, frozen and canned fruits after storage
Commodity
Original
content
Storage
time
(days)
Fresh
stored
(4 ◦C)
Storage
temp.
(◦C)
Storage
time
(months)
Frozen
stored
Storage
temp.
(◦C)
Storage
time
(months)
Canned,
drained
Canned,
including
syrup Authors Year
Bing 1.94 – – −23 3 1.45 2 5 1.27 2.35 Chaovanalikit 2004
cherries 6 0.96 and Wrolstad47
−70 3 2.10 22 5 1.21 2.31
62.00
Peeled 0.398 7 38.5 −12 3 0.50 Ambient 3 0.221 – Asami et al.46 2003
peaches 14 37.8 6 0.247 –
Unpeeled 0.468 7 43.9 −12 3 0.526 – – – –
peaches 14 44.3
940 J Sci Food Agric 87:930–944 (2007)
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Nutritional comparison of fresh, frozen and canned fruits and vegetables
should be completed to specify other variables, such
as packaging, that may influence retention rates.
Canned
Peaches canned in enamel-coated cans lost 30 – 43%
WW of TPs after 3 months of storage at room
temperature (Table 15).46 The authors did not assay
the syrup in this study, but in a subsequent study they
reported that the procyanidins lost during canning had
actually migrated to the syrup.48 Chaovanalikit and
Wrolstad47 found similar results for cherries canned
in enamel-coated cans (Table 15). Significant losses
of anthocyanins were found in canned cherries and
their syrup stored for 5 months at room temperature.
Slight but insignificant decreases in TPs, however,
were found after 5 months of storage at both chilled
and room temperatures. The level of TPs in the
cherries and syrup was still higher than that in fresh
cherries, however, owing to the apparent increases
during thermal processing.
Some authors have suggested that the degradation
of phenolic compounds during canned storage may be
dependent on the type of can used. Tin-plated cans
can sacrifice tin to compete for available oxygen, thus
sparing some of the phenolic compounds.46 Research
is needed to determine if this is a viable method
for increasing retention rates of phenolic compounds
during canned storage.
Cooking
Changes in TPs of vegetables during cooking depend
on commodity, cooking method and cooking time.
Dewanto et al.8found that the gains of TPs and
flavonoids during thermal processing of tomatoes were
not significant on a wet weight basis.8Gahler et al.,19
however, found up to a 44% gain of TPs during the
baking of tomatoes and up to a 64% increase in TPs
during the cooking of tomato sauce on a wet weight
basis. Franke et al.6found that retail-purchased fresh
tomatoes lost 30 –60% WW quercetin upon boiling.
Turkmen et al.54 studied the effects of cooking
(boiling, steaming and microwaving) on TPs in the
dry matter of fresh purchased pepper, squash, green
beans, leeks, peas, broccoli and spinach. Some losses of
up to 40% DW were found after cooking squash, peas
and leeks, although pepper, green beans and spinach
experienced increases in TPs during all cooking
methods. Broccoli increased in TP content by 16%
DW after steaming or microwaving but lost a slight
(6% DW) amount of TPs from boiling.
These results differ from those of Zhang and
Hamauzu,55 who found that broccoli lost up to 70%
WW of its TPs after boiling or microwaving. This
difference could be due to the change in moisture
content of the broccoli during cooking, since Zhang
and Hamauzu reported their results on a wet weight
basis.
Clearly, more research is needed to determine
the effects of cooking on total phenolics as well as
individual phenolic compounds. Research is especially
needed to determine any further changes in the
phenolic make-up of frozen and canned products
during cooking.
Retail market products
Since phenolic compounds can undergo oxidation
during storage and transport to the retail market, it
is important to measure the phenolic composition
of market-available food products. As mentioned
previously, several authors have simulated these
conditions as fresh, frozen and/or canned storage
of single cultivars. Several other researchers opted
to purchase fresh tomatoes and canned tomato
products to quantify what is available to the consumer.
Nagarajan and Hotchkiss31 found significantly higher
levels of TPs in canned tomato products compared
with fresh tomatoes on a wet weight basis. When
they adjusted their results for the same amount
of total soluble solids, however, they found similar
levels in most products. Tomato paste and juice
were exceptions, with canned tomato paste containing
about 40% less TPs and canned tomato juice
containing about 67% more TPs than fresh tomatoes.
Franke et al.6measured individual flavonoids and
total flavonoids in canned, fresh and boiled fresh
tomatoes. Total flavonoids were highest in fresh
tomatoes purchased at a market; boiled and canned
tomatoes contained similar amounts of flavonoids.
On average, canned tomatoes contained 44% WW
less quercetin than fresh tomatoes.6Finally, Podsedek
et al.56 measured the polyphenol content in bottled
tomato juices and canned tomatoes but not in fresh
tomatoes. They found that the content in their
purchased products was similar to the values reported
for fresh tomatoes by other authors.
The phenolic composition of other fruits and
vegetables and their processed products available to
the consumer should be studied in the future. Since
different cultivars are used for fresh, frozen and canned
products, the phenolic make-up of retail goods is likely
to vary significantly within individual commodities.
Conclusions
Changes in phenolic compounds during processing,
storage and cooking appear to be quite variable and
may depend highly on commodity. Future studies may
clarify some of the reported discrepancies. Thermal
treatment via cooking, blanching or canning appears
to increase the extractability of phenolic compounds.
However, since phenolic compounds are both water-
soluble and sensitive to oxidation, degradation of TPs
is possible during fresh and frozen storage. Decreases
in stored canned foods may be due to migration of TPs
from the fruit or vegetable to the canning medium;
however, further research is necessary. Currently, the
USDA does not include TP values in the nutrient
database. Since the reported data are rather erratic,
future evaluation of TP contents of retail market foods
may be germane. A standardised method of analysis
J Sci Food Agric 87:930 – 944 (2007) 941
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JC Rickman, DM Barrett, CM Bruhn
and reporting (wet or dry weight) is also essential for
comparing study results.
IMPLICATIONS
Losses of nutrients during fresh storage may be more
substantial than consumers realise. Depending on
the commodity, freezing and canning processes may
preserve nutrient value. While the initial thermal
treatment of canned products can result in loss,
nutrients are relatively stable during subsequent
storage owing to the lack of oxygen. Frozen products
lose fewer nutrients initially because of the short
heating time in blanching, but they lose more nutrients
during storage owing to oxidation. In addition to
quality degradation, fresh fruits and vegetables usually
lose nutrients more rapidly than canned or frozen
products. Other variables such as storage and cooking
conditions will also influence the final nutrient content
of a food. Consumers should consider such variability
when utilising nutrient guidelines such as the USDA
nutrient database.
Updates to nutritional recommendations for
humans of all ages are ongoing. Exclusive recom-
mendations of fresh produce ignore the nutritional
value of canned and frozen products and may conceal
the sensitivity of fresh products to nutrient loss. Since
nutrient retention is highly variable, a diet filled with
diverse fruits and vegetables is ideal. The results pre-
sented here suggest that canned, frozen and fresh fruits
and vegetables should all continue to be included in
dietary guidelines. The Global Fruit and Vegetables
Initiative for Health should consider the benefits of
including all forms of fruits and vegetables in their
recommendations. There are, however, limitations to
the present work. Some of the nutrient losses reported
during processing, storage and/or cooking may be sta-
tistically significant but not significant in terms of
human nutrition. For instance, carrots lose significant
amounts of vitamin C during canning, but they are not
good sources of this nutrient to begin with. Similarly,
other products such as pineapple contain high enough
levels of vitamin C that they remain good sources of
the nutrient despite degradation during thermal pro-
cessing. Our research also did not examine the effects
of other ingredients, such as added sugar, that may
affect the overall nutritional value of processed fruits
and vegetables. This may be particularly important for
canned fruits, which are often filled with syrup. While
draining the syrup may minimise sugar intake, it may
also result in nutrient loss: our research suggests some
nutrients may migrate into the syrup or canning liq-
uid. Vacuum-packed fruits and vegetables appeared to
experience less degradation of phenolic compounds;
however, further research is also necessary to deter-
mine the significance of these results.
Nutrition labels do not impart the significant
degradation of nutrients that may occur during
storage and cooking of fresh and frozen fruits and
vegetables. Since minimal degradation occurs during
storage of canned goods owing to the lack of oxygen,
nutritional labels are valuable sources of information
for these products. Nutritionists thus must interpret
our results carefully. Fresh cut vegetables were not
examined in this study owing to the lack of research.
However, we might assume that these products would
experience more rapid degradation of oxygen-sensitive
nutrients during storage compared with their intact
fresh counterparts owing to the increased exposure to
oxygen.
GENERAL CONCLUSIONS
While canned foods are often regarded as less
nutritious than fresh or frozen products, research
reveals that this is not always true. The effects of
processing, storage and cooking are highly variable by
commodity. In general, while canning often lowers
the content of these water-soluble and thermally labile
nutrients, storage and cooking of fresh and frozen
vegetables can also significantly lower the nutritional
content. Unfortunately, very few studies followed
the same product from harvest through processing,
storage and cooking. Since nutrient and phytochemical
content is highly dependent on commodity, cultivar
and growing practices, more studies following the
same food throughout the consumer chain would be
beneficial. Analysis of fresh, frozen and canned fruits
and vegetables available in retail markets would also
be more appropriate for understanding the nutritional
content of fruits and vegetables available to the
consumer. Additionally, these retail market studies
would be a useful supplement to the USDA nutrient
database.
Understanding nutrient data is quite complex.
Variance in methodologies and practices makes
interpretation of data difficult. Changes in moisture
content during storage, cooking and processing often
misrepresent changes in nutrient content. Future
research should focus on nutrient data expression
on a dry weight basis to account for such changes.
Furthermore, many current reports in the literature
refer to nutrient retentions for processing, storage and
cooking that were compiled more than 25 years ago.
It is necessary to update these data, standardising
process and reporting methods.
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