A review of the impact of preparation and cooking on the nutritional quality of vegetables and legumes

Abstract

Vegetables and legumes represent one of the most important components of the human diet. Being informed about their characteristics can improve the health benefits, helping to reduce the risk of cardiovascular disease, type II diabetes and some cancers. Recent studies have demonstrated that the method of preparation and cooking can improve the nutrition quality of food. These two steps induce several changes and interactions among its constituents, in some cases positive, in others negative. Therefore, knowing the changes occurring in food from preparation to table is essential not only for scientific research, but also for the consumer, who can make decisions about how to prepare and cook a selected number of healthy legumes and vegetables. The purpose of this review was to evaluate the most recent studies and draw conclusions that will enable the consumer to make decisions about how to maximize nutrient content of plant foods and identify the critical phases during preparation and cooking, when the nutrients might be lost. For such, some nutrients of specific legumes (peas and beans) and vegetables (broccoli, potatoes and onions) were selected.

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International Journal of
Gastronomy and
Food Science
Available online at www.sciencedirect.com
International Journal of Gastronomy and Food Science 3 (2016) 2–11
Review Article
A review of the impact of preparation and cooking on the nutritional
quality of vegetables and legumes
Adriana D.T. Fabbri
n
, Guy A. Crosby
Department of Nutrition, Harvard T. H. Chan School of Public Health 651 Huntington Avenue, Boston, MA 02115, USA
Received 25 May 2015; accepted 18 November 2015
Available online 24 November 2015
Abstract
Vegetables and legumes represent one of the most important components of the human diet. Being informed about their characteristics can
improve the health benefits, helping to reduce the risk of cardiovascular disease, type II diabetes and some cancers. Recent studies have
demonstrated that the method of preparation and cooking can improve the nutrition quality of food. These two steps induce several changes and
interactions among its constituents, in some cases positive, in others negative. Therefore, knowing the changes occurring in food from preparation
to table is essential not only for scientific research, but also for the consumer, who can make decisions about how to prepare and cook a selected
number of healthy legumes and vegetables. The purpose of this review was to evaluate the most recent studies and draw conclusions that will
enable the consumer to make decisions about how to maximize nutrient content of plant foods and identify the critical phases during preparation
and cooking, when the nutrients might be lost. For such, some nutrients of specific legumes (peas and beans) and vegetables (broccoli, potatoes
and onions) were selected.
&2015 AZTI-Tecnalia. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Keywords: Vegetables; Legumes; Preparation; Cooking methods; Nutritional quality
Contents
Introduction . . ....................................................................................2
Vegetables and legumes: potential health benefits.............................................................3
Factors that affect nutritional quality of vegetables and legumes . ..................................................4
Preparation . .................................................................................. 4
Cooking method ............................................................................... 5
Conclusion . . ....................................................................................8
Acknowledgments..................................................................................9
References . . . ....................................................................................9
Introduction
The nutritional quality provided by vegetables and legumes
consumption has been intensely reviewed (Block et al., 1992;
He et al., 2007;Tiwari and Cummins, 2013). Legumes and
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(http://creativecommons.org/licenses/by-nc-nd/4.0/).
n
Corresponding author.
E-mail address: afabbri@hsph.harvard.edu (A.D.T. Fabbri).

vegetables are rich sources of proteins, fats, carbohydrates,
minerals, antioxidants, fiber and water, as well as being
excellent sources of β-carotene (provitamin A), thiamin (B1),
riboflavin (B2), niacin, pyridoxine (B6), pantothenic acid, folic
acid (folacin), ascorbic acid, and vitamin E and K (Karmas and
Harris, 1988;Prodanov et al., 2004).
Recent studies have shown there are several ways to
enhance the availability of healthy nutrients through proper
selection of the method of cooking. According to these studies,
the most common methods used for cooking legumes and
vegetables are: steaming, roasting, boiling, frying, sautéing,
sous vide, microwave and pressure-cooking. Besides that, the
authors also considered in their researches, factors related to
common domestic processing, including: washing, peeling,
cutting, chopping and soaking (Tiwari and Cummins, 2013).
Such information has been studied for specific vegetables such
as: broccoli (Dos Reis et al., 2015;Bongoni et al., 2014;
Kahlon et al., 2012;Mahn and Reyes, 2012;Martínez-
Hernández et al., 2013;Miglio et al., 2008;Murador et al.,
2014;Pellegrini et al., 2010;Poelman et al., 2013;Yuan et al.,
2009), onion (Cavagnaro and Galmarini, 2012;Lee et al.,
2008;Németh et al., 2003;Rodrigues et al., 2009;Wilson and
Demmig‐Adams, 2007), potato (Blessington et al., 2010;
García-Segovia et al., 2008;Lachman et al., 2012,2013;
Micklander et al., 2008;Perla et al., 2012) and legumes such as
beans (Ramírez-Cárdenas et al., 2010;Saikia et al., 1999;
Schoeninger et al., 2014;Siqueira et al., 2013;Taiwo and
Akanbi, 1997;Wang et al., 2010a) and peas (Azarnia et al.,
2011;Duhan et al., 2002,2004;Habiba, 2002;Koplı
k et al.,
2004;Wang et al., 2008). It is known that nutrient losses occur
in the preparation and cooking phases, and understanding how
and why these losses occur can help the consumer, chef and
food processor limit losses and enhance the nutritional quality
of the food.
Many reports have found significant differences among the
cooking methods. Kahlon et al. (2007) studied how cooking
could influence in vitro bile acid binding by various vegeta-
bles. It has been demonstrated that bile acid binding lowers the
levels of cholesterol in the blood, helping to reduce the risk of
heart disease. In their first study they found that steam cooking
improved bile acid binding by beets, eggplant, asparagus,
carrots, green beans and cauliflower when compared to the
same vegetables uncooked. In their next study, the authors
obtained similar results by steaming collard greens, kale,
mustard greens, broccoli, Brussel sprouts, spinach, green bell
pepper and cabbage (Kahlon et al., 2008). After four years, the
authors studied some of the same vegetables of the second
study using other cooking methods (sautéing, boiling, steam-
ing). They concluded that sautéing was the cooking method
with the most health potential (binding bile acids) for mustard
greens, kale, broccoli, cabbage and green bell pepper, with
steaming the best method used for collard greens (Kahlon
et al., 2012).
Changes in temperature can modify the flavor, texture and
appearance of food, but this is not the only way that these
modifications can occur. The processing method applied to the
foods is another parameter that can modify food, and
encompasses the entire spectrum from the strength of a knife
to that of a processor. The cutting or processing damages the
cell structure, as well as heating or freezing (America's Test
Kitchen and Crosby, 2012).
As reported by Fennema (1996) without accurate informa-
tion about conditions and methods of food processing, storage
and handling, it is difficult to predict the influence and the
retention of many vitamins, which emphasizes the great need
for more research in this field.
Of the main factors that consumers consider when selecting
food for cooking at home (flavor, texture, nutrition, cost,
safety, convenience), flavor has been shown to be the most
important (Azarnia et al., 2011;Lee et al., 2009;Van Boekel
et al., 2010;Yoo et al., 2012). Enhancing the flavor of legumes
and vegetables through preparation and cooking can increase
the consumption of these healthy foods, especially among
children (Poelman et al., 2013).
Since the early part of the twentieth century many studies
have been conducted to investigate the impact of preparation
and cooking methods on the stability of nutrients in food. The
results of these studies vary widely leading the consumer to
question the best ways of preparing and cooking foods in order
to maintain the nutritional qualities, especially in legumes and
vegetables. Many other researchers have shown that growth
conditions of vegetables and legumes also have a significant
impact on their nutrient content (Elmore et al., 2010;Kopsell
et al., 2003;Lee et al., 2009;Wang et al., 2010b), but this
factor will not be reviewed in this paper, which focuses on the
impact of preparation and cooking on nutrient content. There-
fore, the objective of this review is to evaluate the most recent
studies and draw conclusions that will enable: (a) the consumer
to make decisions about how to maximize nutrient content of
plant foods and (b) identify the critical phases during prepara-
tion and cooking, when nutrients might be lost. For such, some
nutrients of specific legumes (peas and beans) and vegetables
(broccoli, potatoes and onions) were selected. The selection
was based on the increased interest in these foods, according to
the USDA (2010), as well as their availability in most of
the world.
Vegetables and legumes: potential health benefits
The consumption of fresh food has grown considerably in
recent years largely due to the fact that vegetables, legumes
and fruits have been associated with many health recommen-
dations (Hagen et al., 2009;Slavin and Lloyd, 2012;Storey
and Anderson, 2014;Tiwari and Cummins, 2013). According
to the Institute of Medicine, Food and Nutrition Board (IOM,
2005), dietary fiber intake could lower the risk of coronary
disease and cancer. The World Health Organization (WHO/
FAO, 2005) recommends a minimum of 400 g of fruit and
vegetables per day (excluding potatoes and other starchy
tubers) for the prevention of chronic diseases, as well as for
the prevention and alleviation of several micronutrient defi-
ciencies, especially in less developed countries. Block et al.
(1992) have confirmed this fact, by evaluating 200 studies that
examined the relationship between fruit and vegetable intake
A.D.T. Fabbri, G.A. Crosby / International Journal of Gastronomy and Food Science 3 (2016) 2–11 3

and many types of cancer. The authors verified that 128 of 156
dietary studies have presented a statistically significant pro-
tective effect with vegetables and fruit intake. Epidemiologic
and intervention studies have suggested that an intake of 14 g
dietary fiber per 1000 kcal would promote heart health (Storey
and Anderson, 2014).
Legumes are important sources of protein for the human
diet. As reported by Karmas and Harris (1988), there are more
than 13,000 species of legumes, but only 20 are eaten by
mankind. The major legumes used as foods include peas,
beans, lentils, peanuts and soybeans. The structure of peas and
beans consists of a seed coat (hull), hypocotyl-radicle axis,
plummule and two cotyledons. The seed coat works as a
protective barrier during storage and handling. The most
consumed varieties of legumes include: chick-peas (Cicer
arietinum); peas (field or smooth pea and wrinkled pea); broad
beans (Vicia faba or field bean); lentils (Lens esculenta) and
beans (Phaseolus vulgaris,Phaseolus lunatus,Phaseolus aur-
eus and Phaseolus mungo)(Karmas and Harris, 1988).
The nutritional composition of legumes can provide a high
proportion of proteins, fats, carbohydrates, dietary fibers, B-
group vitamins (thiamin, riboflavin, niacin), and minerals
(Prodanov et al., 2004). This composition can vary according
to cultivar, location of growth, climate, environmental factors,
and soil type in which legumes are grown (Karmas and Harris,
1988;Bishnoi and Khetarpaul, 1993). Starch is the major
constituent of available carbohydrates of peas and beans.
Lipids consist primarily of triacylglycerol plus di- and mono-
acyglycerol, free fatty acids, sterols, sterol esters, phospholi-
pids and glycolipids. Peas and beans are very poor sources of
fat soluble vitamins and rich sources of water soluble vitamins;
as well as excellent sources of minerals: calcium, phosphorus,
potassium, sodium, manganese, iron, magnesium, copper,
cobalt, sulfur, zinc and fluorine (Karmas and Harris, 1988).
In some countries, various terms are often substituted for
“legume”. The term “pulse”is commonly used for legumes
having a low fat content, like beans, broad beans, peas, and
lentils. Soybeans and peanuts are sometimes referred to as
leguminous oilseeds (Aykroyd and Doughty, 1982).
Vegetables have also been associated as part of a healthy
diet, by reducing the risk of some chronic diseases. Vegetables
provide vital nutrients for healthiness and maintenance of the
human body, such as vitamin A, vitamin C, folate, fiber and
potassium. According to the WHO (2003), the classification of
vegetables can vary from country to country. The large reason
for this differentiation is related to the inclusion or exclusion of
starchy roots, tubers and legumes, within the vegetable groups.
Besides the related differences between vegetables and
legumes, the USDA (2010) classifies all of them within one
category, namely “Vegetable group”. This category has been
divided into five subgroups: (1) beans and peas; (2) starchy
vegetables; (3) dark green vegetables; (4) red and orange
vegetables and (5) other vegetables. According to this report,
othe consumption of any type of bean (black, brown or white)
is responsible for 89.5% of the consumption of its group, with
Pinto Beans being the most consumed at 44.3%. Potatoes also
have the highest consumption percentile within the Starchy
vegetables subgroup (83%). Onions belong to the group "Other
vegetables" and represent the second most consumed vegeta-
ble, with 19.2% of its group's consumption. Relative to the
Dark green vegetables subgroup, broccoli was the most
consumed (37.7%). Green peas are included into “Starchy
vegetables subgroup”, and not into “Beans and Peas sub-
group”, probably because of the high content of starch. The
percentage of pea consumption is responsible for 4% of their
group. The nutritional composition of these vegetables and
legumes is summarized in Table 1.
The Center for Nutrition Policy and Promotion –United
States Department of Agriculture –has suggested amounts of
food to be consumed on a daily basis from the basic food
groups, subgroups, and oils to meet recommended nutrient
intakes at 12 different calorie levels. The estimated daily
caloric needs can range according to the sex group/age and on
the physical activity level, from sedentary to active (people
who walk more than 5 km per day, accompanied of light
physical activities) (USDA, 2011). The vegetable Group
includes all fresh, frozen, canned, and dried vegetables and
vegetable juices. According to the USDA (2011) to supply all
the required needs, one person should consume, per day, one
cup of raw or cooked vegetables or two cups of raw leafy
greens (one cup is equivalent to E237 g).
Vegetables and legumes are excellent sources of several
phytochemicals with proposed health-related benefits (Moreno
et al., 2006). Phytochemicals are natural bioactive compounds
found in vegetables and fruits used for combating free radicals
and reducing the oxidative damage responsible by chronic
diseases (Tiwari and Cummins, 2013). Vegetables as broccoli,
provide flavonoids (Lin and Chang, 2005), polyphenols (Faller
and Fialho, 2009), anthocyanin with high antioxidant activity
(Monero et al., 2010) and powerful phytochemicals (glucosi-
nates and isothiocyanates). Isothiocyanates and glucosinolates
are the main biologically active compounds that are known to
exhibit anti-carcinogenic activity in several in vitro and in vivo
studies (Verkerk et al., 2009).
On the other hand, vegetables and legumes also have been
known to contain anti-nutrients: potatoes contain alkaloid
solanine, arsenic and nitrite; green leafy vegetables presents
toxic oxalates and peas contain phytic acid, protease inhibitors
and tannins (Karmas and Harris, 1988;Habiba, 2002).
According to Habiba (2002) the reduction or elimination of
these anti-nutrients is necessary to prevent poisoning and to
improve the biological utilization of legumes. Most anti-
nutrients can be reduced or destroyed by using the proper
cooking method.
Factors that affect nutritional quality of vegetables and
legumes
Preparation
Changes occasioned by food preparation can affect the flavor,
texture, appearance and the nutritional quality of foods (America’s
Test Kitchen and Crosby, 2012). Domestic preparations of
vegetables and legumes normally involve washing, peeling and
A.D.T. Fabbri, G.A. Crosby / International Journal of Gastronomy and Food Science 3 (2016) 2–114

cutting (Tiwari and Cummins, 2013). The preparation methods
most used are summarized in Table 2.
Modifications on texture of vegetables are strongly related to
the transformations in cell wall polymers due to non-enzymatic
and enzymatic reactions (Sila et al., 2008). According to the
literature, the cruciferous vegetables, such as broccoli, have
their flavor constituted by volatiles, sugars, acidity, as well as
the astringency which is influenced by the phenolics’present.
Pungency is increased due to an enzyme called myrosinase.
This enzyme is liberated during food preparation such as
chopping and trimming. When the cells are damaged, myr-
osinase converts glucosinolates into isothiocynates, responsi-
ble for the flavor and pungency of cruciferous vegetables
(Johnson, 2002). In onions, when the Allium cells are
damaged, the enzyme allinase is released and comes in contact
with sulfur compounds. This factor is related to the increase of
the pungency and the flavor of onions. According to Russo
et al. (2013) onion flavor is closely linked to pungency and
thus to the pyruvic acid content. Chopping vegetables can also
alter the bioavailability of bioactive compounds such as
carotenoids, polyphenols and flavonoids (Dos Reis et al.,
2015).
Regarding peas and beans, many authors have cited a
decrease in the cooking time by using soaking prior to cooking
(Taiwo and Akanbi, 1997). During soaking, the water is
dispersed into the starch granules and protein fractions of
beans, which facilitate processes, such as gelatinization and
protein denaturation, which soften the texture (Siddiq and
Uebersax, 2012). This outcome can be improved by adding
salt into soaking water. Soaking in sodium bicarbonate
solution eliminates tannin contents and reduces trypsin inhi-
bitor activity (TIA) in beans (Taiwo and Akanbi,1997).
However, soaking peas in distilled water resulted in an
increase in TIA (3.2–19.3%) (Wang et al., 2008). According
to Taiwo and Akanbi (1997), soaking in simple water did not
reduce the tannin content.
According to Schoeninger et al. (2014), a soaking time of
13.1 h with a concentration of sodium bicarbonate of 2.3 g.100
mL
1
followed by a drying temperature of 50 1C showed a
reduction of 53% on cooking time of common beans (P.
vulgaris L.).
Cooking method
The most common methods of cooking are sautéing,
microwaving, roasting, boiling, and steaming. Other authors
have studied other methods like sous vide, stewing and frying.
Table 1
Nutritional composition of cooked pinto beans, peas, broccolis, onions and
potatoes
n
–value per 100 g of product
nn
.
Nutrient Unit Pinto
Beans
Peas Broccoli Onion Potato
Proximate composition
Water g 62.95 77.87 89.25 87.86 77.46
Energy kcal 143 84 35 44 86
Protein g 9.01 5.36 2.38 1.36 1.71
Total lipid (fat) g 0.65 0.22 0.41 0.19 0.1
Carbohydrate, by
difference
g 26.22 15.63 7.18 10.15 20.01
Fiber, total dietary g 9.0 5.5 3.3 1.4 1.8
Sugars, total g 0.34 5.93 1.39 4.73 0.85
Minerals
Calcium, Ca mg 46 27 40 22 8
Iron, Fe mg 2.09 1.54 0.67 0.24 0.31
Magnesium, Mg mg 50 39 21 11 20
Phosphorus, P mg 147 117 67 35 40
Potassium, K mg 436 271 293 166 328
Sodium, Na mg 1 3 41 3 5
Zinc, Zn mg 0.98 1.19 0.45 0.21 0.27
Vitamins
Vitamin C, total ascorbic
acid
mg 0.8 14.2 64.9 5.2 7.4
Thiamin mg 0.193 0.259 0.063 0.042 0.098
Riboflavin mg 0.318 0.149 0.123 0.023 0.019
Niacin mg 0.229 2.021 0.553 0.165 1.312
Vitamin B-6 mg 0.054 0.216 0.2 0.129 0.269
Folate, DFE mg 172 63 108 15 9
Vitamin B-12 mg0 0 0 0 0
Vitamin A, RAE mg 0 40 77 0 0
Vitamin A, IU IU 0 801 1548 2 3
Vitamin E (alpha-
tocopherol)
mg 0.94 0.14 1.45 0.02 0.01
Vitamin D (D2þD3) mg0 0 0 0 0
Vitamin D IU 0 0 0 0 0
Vitamin K
(phylloquinone)
mg 0.35 25.9 14.1 0.5 2.1
Lipids
Fatty acids, total saturated g 0.136 0.039 0.079 0.031 0.026
Fatty acids, total
monounsaturated
g 0.133 0.019 0.04 0.027 0.002
Fatty acids, total
polyunsaturated
g 0.235 0.102 0.17 0.073 0.043
Cholesterol mg 0 0 0 0 0
n
Source: USDA National Nutrient Database for Standard Reference 27
Software v.2.1.5. (2014).
nn
Pinto beans, mature seeds, sprouted, cooked, boiled, drained, without salt;
Peas, green, cooked, boiled, drained, without salt; Broccoli, cooked, boiled,
drained, without salt; Onions, cooked, boiled, drained, without salt; Potatoes,
boiled, cooked without skin, flesh, without salt.
Table 2
Preparation methods most applied to vegetables and legumes. Source:(Bartz
and Brecht, 2002;Prodanov et al., 2004;America’s Test Kitchen and Crosby,
2012;Smith et al., 1997).
Preparation Description
Chop To cut into small pieces.
Cut To cut across the food, perpendicular to its length.
Dice To cut into uniforms cubes.
Peeling To remove outer skin or peel of certain vegetables.
Soaking Consists of hydration of the seeds in water, usually until they
reach maximum weight, with or without discarding of the soaking
liquid; with or without salt addition. Normally used for legumes,
such as beans.
Trimming To remove all unwanted or inedible parts. Can be used to
improve food appearance.
Washing Rinsing with potable water to remove dirt, insects and small trash.
A.D.T. Fabbri, G.A. Crosby / International Journal of Gastronomy and Food Science 3 (2016) 2 –11 5

To report the changes caused by cooking methods, some key
nutrients were selected for each plant food: glucosinolates and
total antioxidant capacity (TAC) for broccoli; TAC and folate
for potatoes; quercetin for onions; folate for peas and iron for
beans. The description for each method can be seen on Table 3
and the effects of different methods of cooking on vegetables
and legumes are summarized in Tables 4 and 5.
As it can be seen in Table 4, the method of preparation may
greatly affect the content of nutrients and the acceptability of
food. According to studies, steaming seems to be the best
method to maintain the nutritional quality of broccoli (Bongoni
et al., 2014;Mahn and Reyes, 2012;Stea et al., 2007;Wachtel-
Galor et al., 2008). The results have showed that steaming
improves the TAC, glucosinolates, carotenoids, sulphorane
and, folate values. Besides, steaming broccoli presents good
sensory acceptance among children. Cooking time should be
7.5 min to maintain the nutritional quality. Steamed vegetables
are also more flavorsome than boiled vegetables (Poelman
et al., 2013).
In potatoes, Stea et al. (2007) concluded that sous vide is the
best method for folate retention. According to McKillop et al.
(2002),few studies have examined the folate loss associated
with the preparation and cooking of potatoes. The authors
verified that the boiling of whole potatoes (skin and flesh) for
60 min did not result in a significant reduction in folate content
(compared with raw values). Boiling was the preferred method
of cooking potatoes, with 79% of the sample reporting
preference for this method.
Regarding cooking effects on onions, Lombard et al. (2005)
reported an increased concentration of flavonols when onions
were submitted to sautéing (7%) and oven baking (25%).
However, boiling decreased total flavonol concentration
(18%). The authors also verified that cooking less than
5 minutes can retain over 80% of flavonols. In agreement with
the USDA (2007), boiling onions retain less folate (65%),
when compared to baking (85%). Zia-ur-Rehman et al., (2003)
suggested that onions should be cooked, either by the ordinary
method or in a microwave oven instead of a pressure-cooker,
to minimize the losses of insoluble dietary fiber components.
In contrast to broccolis, boiling seems to be the best method
to retain folate in peas (Table 5)(Stea et al., 2007). According
to Bishnoi and Khetarpaul (1993), peas are excellent sources
of dietary carbohydrates, but have relatively low starch
digestibility. Pressure-cooking increases starch digestibility as
well as reduces the level of anti-nutrients.
Concerned about the effect of cooking on beans, Prodanov
et al. (2004) observed a marked reduction in the content of
vitamins when fava beans, lentils and chickpeas were cooked.
AccordingtotheUSDA (2007), cooking beans for more than
2 hours, and then frying or baking them can reduce the folate
retention by 50%. As reported by Léon et al. (1992), soaking
beans in a salt solution, discarding the soaking solution and
cooking with fresh water is the best way to improve the
nutritional quality of beans. Beans contain some complex
sugars of the raffinose family, and if not broken down by
enzymes in the digestive system, can result in gastric issues
such as gas production and flatulence. It can be solved by
soaking the beans, and then cooking them, discarding the
soaking liquid and cooking with fresh water. Besides, this
method of cooking with salt addition can result in a tender
skin due to sodium ions replacing calcium and magnesium
ions bound to pectin in the cell walls (America’s Test Kitchen
and Crosby, 2012). In white beans, traditional cooking has a
positive effect on the bioavailability of Fe. Many studies have
shown that the digestibility and, therefore, absorption of Fe
can be improved by heat processing (Wang et al., 2010a).
Given their health and nutritional benefits, health profes-
sionals should encourage greater bean consumption (Messina,
2014).
AccordingtotheUSDA (2010), cooking is the favorite
way to consume potatoes, onions and broccolis, at 27.3%,
14.7% and 31%, respectively. In the United States, a survey
of a thousand consumers asked how many times a week
Americans were eating out: only 4% eat out more than three
times a week, and 14% eat out twice, 39% once and 41% %
never or rarely (Rasmussen Reports, 2013). Furthermore,
there is a growing demand by consumers for food with less
change or less synthetic additives during processing
(Fellows, 2006).
Considering that much of the population prepares food at
home, the knowledge of how these foods are prepared and
how these different methods of preparation affect the nutri-
tional quality of the food is extremely relevant for today’s
consumer.
Table 3
Cooking methods most applied to vegetables and legumes. Source:Adapted from America’s Test Kitchen and Crosby (2012), Baldwin (2012), and Fellows (1996).
Method Definition
Boil To cook foods in boiling liquid in a pot set on a hot burner.
Fry To cook in a hot oil in a skillet on a hot burner.
Microwave To cook by placing the food in the path of microwaves (the induced molecular friction in water molecules will to produce heat).
Pressure-cooking To cook food using water or other liquid in a sealed pot, normally a pressure cooker or an autoclave (Laboratory simulation).
Roast To cook foods in a pan in a hot oven.
Sauté To cook foods in a thin film of hot oil in a skillet set on a hot burner.
Simmer To cook foods in liquid (below the boiling point in a pot set or hot burner).
Sous-vide To cook in a vacuumed plastic pouches at precisely controlled temperatures.
Steam To cook food that is suspended, generally in a basket, over simmering liquid in a covered pot set on the stovetop.
Stew To sauté the food, and then simmer.
A.D.T. Fabbri, G.A. Crosby / International Journal of Gastronomy and Food Science 3 (2016) 2–116

Table 4
Effects of cooking methods on the nutrients in vegetables
n
.
Cooking method Effects Main conclusion Reference
Broccoli
Basket Fresh Broccoli: The total content of glucosinolates of fresh
broccoli increased by steaming methods
Pellegrini et al. (2010)
Steaming (BS) BS/OS:↑glucosinolates (37–39%) Steam cooking: best procedure to preserve and
enhance nutritional quality of fresh broccoli
Boiling (BL) BL:↓glucosinolates (5%)
Microwaving (MW) MW: No differences
Oven Frozen Broccoli:
Steaming (OS) All methods↓glucosinolates:
BL (64%), MW(27%), BS (11%),
OS (26%)
Boiling (BL) TAC: BL↑(98%), FR↑(163%)
and S↑(221%)
Each vegetable should use a different cooking
method.
Miglio et al. (2008)
Frying (FR) Glucosinolates: BL ↓(71%), ↓FR
(84%), and S ↑(30%)
S: Best for retention of nutrients.
Steaming (S)
Boiling (BL) SV:↑TAC All processes contributed in some way to an
increased content of antioxidant compounds
Dos Reis et al. (2015)
Microwaving (MW) SV: Best for TAC retention.
Sous vide (SV)
Steaming (S)
Boiling (BL) S and DR:↑sulphorane and TAC S and DR: have demonstrated best retention on
sulphorane and TAC.
Mahn and Reyes (2012)
Drying (DR)
Freezing (FZ)
Steaming (S)
Boiling with a cold
water start (BLC)
S↑glucosinates (17%) S: Best cooking method for nutrient retention. Bongoni et al. (2014)
Boiling with a hot
water start (BLH)
BLH↓glucosinates (41%)
BLC↓glucosinates (50%)
Steaming (S) No sensorialawere found
(n¼99)
Potato
Boiling (BL) Purple Majesty potatoes BL: Seems to be the most promising method for
preserving the bioactive composition.
Lemos et al. (2015)
Microwaving (MW) BL, MW, and S:↑Antioxidant
Activity
Oven Baking (OB) OB:↓Antioxidant Activity
Steaming (S)
Blanching (BLA) Folate retention Folate retention: BL (59%) and OB of unpeeled
potatoes (63%) caused a significant (po0.05)
reduction of the folate content compared with
raw potatoes on Dry Matter basis.
Stea et al. (2007)
Boiling (BL)
Microwaving (MW) SV (103%) 4BL (72%)4OB
(63%)
Oven Baking (OB) Results indicates that the skin may give
protection against folate losses.Steaming Boling (SB)
Sous vide (SV)
Boiling (BL) Folate retention (82%) BL of whole potatoes (skin and flesh) for 60 min
did not result in a significant reduction in folate
content.
McKillop et al. (2002)
The presence or absence of potato skin had no
significant impact on folate retention during
boiling.
Onion
Boiling (BL)
Oven Baking (OB) OB and SUT:↑7-25% quercetin
concentration
SUT and OB:↑flavonol
BL:↑5 min↓flavonol
Lombard et al. (2005)
A.D.T. Fabbri, G.A. Crosby / International Journal of Gastronomy and Food Science 3 (2016) 2 –11 7

Conclusion
This review is intended to reduce the uncertainly about how
the different methods of preparation and cooking can affect the
nutrient content of certain vegetables and legumes. According
to this review, it is possible to conclude that:
1. Onion's pungency is increased during food preparation,
such as chopping and trimming.
2. Steaming seems to be the best method to maintain the
nutritional quality (TAC, carotenoids, glucosinolates, sul-
phorane, folate and phytochemicals).
3. Onions should be cooked or baked to improve flavonols’
content.
Table 5
Effects of cooking methods on the nutrients in legumes
n
.
Cooking method Effects Main conclusion Reference
Peas
Sous vide (SV) Folate retention: No method (BL, MW, SB) caused any
significant (po0.05) losses of folates.
Stea et al. (2007)
Boiling (BL)
Oven Baking (OB) BL 77%4MW 75% 4SB 73%
4BLA 71%Microwaving (MW) Storage at various temperatures and length of
times (followed by reheating) caused no
further significant losses of total folate.
Steaming Boling (SB)
Blanching (BLA)
Blanching (BLA) Folate retention: The significant loss of folate in peas Czarnowska and Gujska
(2012)Freezing (FRZ) 79% (BLA þFRZ) Resulting from blanching may be associated
not only with the influence of heat treatment,
but also with the size and degree of product
fragmentation.
Beans
Ordinary Cooking (OC) No awere found for Fe content in
7 different beans.
Concentrations of Fe were unaltered by
cooking. Cooking increases soluble iron
content in the cooking water.
Ferreira et al. (2014)
Soaking (SO)
No Soaking (NSO) SO and POC↓Fe cooked grain, but↑Fe
in the bean broth
Beans should be consumed in a combined
form, i.e. grain with bean broth.
Carvalho et al. (2012)
Ordinary Cooking (OC)
Pressure Cooking (POC)
Soaking (SO)
n
The data of this Table has been focused on broccolis, onions, potatoes, peas and beans. The references used in this table can be studied more than one nutrient;
vegetable or legume.
Table 4 (continued )
Cooking method Effects Main conclusion Reference
Sautéing (SUT) BL: ↓18% quercetin
concentration
Flavonol content more dependent on variety than
cooking method.
Boiling for 30 min
(BL 30)
White onion The greatest losses of flavonoids occurred in
boiled onions as a result of its migration into the
cook water.
Rodrigues et al. (2009)
Boiling for 60 min
(BL 60)
BL 30: ↓37% quercetin 3,40-
diglucoside (QdG) and ↓29%
quercetin 40-glucoside (QmG)
Frying (FR) BL 60: ↓53%(QdG) and ↓44%
(QmG)
Moderate
Microwaving (MW)
MW did not affected flavonols
content
Intense Microwaving
(IMW)
Oven Roasting IMW: ↓16% (QdG) and↓18%
(QmG)
(OR)
TAC¼Total Antioxidant Capacity.
n
The data of this Table has been focused on broccolis, onions, potatoes, peas and beans. The references used in this table can be
studied more than one nutrient; vegetable or legume.
A.D.T. Fabbri, G.A. Crosby / International Journal of Gastronomy and Food Science 3 (2016) 2–118

4. Sous vide cooking has shown good results in cooking
potatoes and should be investigated further.
5. Soaking and cooking peas and beans are effective in
removing or reducing anti-nutrients such as tannins, TIA
and acid phytic.
6. Boiling seems to be the best method to retain folate in peas
and should be further investigated.
7. Soaking with salt, discarding water and cooking in fresh
water is the best method to reduce cooking time, and to
improve the protein quality, texture and appearance of
beans, while reducing gastric issues.
8. The absorption of Fe can be improved by heat processing.
9. Other factors besides cooking –such as growth conditions
and variety/cultivar –can affect sensory parameters.
All the steps included before vegetables and legumes
consumption can affect directly their nutrition quality. Being
informed about these factors might make the consumer more
aware on how to optimize the nutrients obtained during a meal.
Acknowledgments
The authors are grateful to Ciências sem Fronteiras from
CNPq for the scholarship.
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