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Water content of cooked rice is related to variety and cooking method
NUTRITION RESEARCH, Vol. 11, pp. 1397-1402,1991 0271-5317/91 $3.00 + .00 Printed in the USA. Copyright (c) 1991 Pergamon Press plc. All rights reserved.
WATER CONTENT OF COOKED RICE IS RELATED TO VARIETY AND COOKING METHOD B Dibba, LT Weaver MD and GJ Hudson* MRC Dunn Nutrition Unit, Downham's Lane, Milton Road, Cambridge CB4 1XJ, UK and Keneba, West Kiang, The Gambia
ABSTRACT If an average water content is used with records of weighed food intake to calculatenutrient intake, it is important to establish that the value is appropriate. A previous study in three villages in The Gambia, West Africa, reported an average value for the water content of cooked rice of 65.8% and a fairly wide range of values for individual samples (SD 5.52, n 2666). We present values for the water contents of ten varieties of rice that confLrm the results of the previous study. A wide range of values is observed because some varieties of rice, and the same variety cooked in different villages, have average water contents, ranging from 60% to 68%, that differ significantly from the overall mean. Use of the overall mean value for water content for those varieties could lead to underestimates of water intakes of the order of 6%, representing underestimates of nutrient intake of 15%. KEY WORDS: Rice; Variety; Cooking Method; Water Content; Energy Content
INTRODUCTION It is common practice in epidemiological studies to calculate nutrient intake from records of weighed food intake using average compositional data. Hudson & Day (1) investigated the appropriateness of this approach in a sub-Saharan country where there are large seasonal changes in dietary pattern. They concluded that "the use of average analytic values throughout the year is entirely appropriate." In support of this, they presented values for the water content of cooked rice that showed no seasonal changes and reported no difference between the three Gambian villages in that study. However, subsequent investigations have revealed that the people of these villages grow a large number of different varieties of rice, raising the question of whether a single value for the average water content of cooked rice to calculate nutrient intake (2) was appropriate for every variety of rice. Here, we report the results of a study in the same three villages that revealed that different varieties of rice, and the same variety of rice in different villages, do have different water contents when cooked. * Author to whom correspondence should be addressed
1397
1398
B. DIBBA et al.
EXPERIMENTAL PROCEDURES (a) Study villages and subjects, These studies took place in the villages of Keneba, Manduar and Kanton Kunda in the West Kiang District of The Gambia. Women are responsible for growing rice in these communities; 161 women in Keneba, 79 in Manduar and 60 in Kanton Kunda were interviewed to determine which varieties of rice they grew, and to establish their willingness to take part in the study. (b) Varieties of rice A surprisingly large number of varieties of rice was reported; 35 varieties in Keneba, 54 in Manduar and 25 in Kanton Kunda (see Table 3). For each of the three most commonly grown varieties of rice in each village, 32 women were selected randomly to provide samples of raw and cooked rice; and 32 w o m e n were selected random/y from each village to provide samples of raw and cooked Aid rice purchased from local shops. (c) Samples A single sample of raw (approx. 100g) and of cooked rice (approx. 200g) was collected from each subject in exchange for a similar quantity of Aid rice. Samples were placed into plastic pots with clip-on lids and kept in a polyethylene bag in a cool box during transport to the laboratory in Keneba for analysis. Any samples not analysed on the day of collection were stored at -20~ (d) Determination of water content The water content of duplicate 2g samples was determined by drying in a domestic microwave oven as previously described (3). The average value for duplicates was used for calculation of water content. RESULTS AND DISCUSSION The water content of cooked food serves as an index of its nutrient content (2). Table 1 is a stumnm~ of the results obtained for the water content of cooked rice for the three most commonly grown varieties in each of three Gambian villages. The average value for water content of each variety of cooked rice was compared with the value reported by Hudson & Day (1) for the mean water content (65.8%, SD 5.52) of 2666 samples of cooked rice collected from these villages over 13 months; varieties of rice were not identified in that study. In the study reported here, several varieties of rice were found to have a significantly different value (Student's t -test, p < 0.001) for average water content from that reported (1) for all varieties: a summary is presented in Table 2. The average values for the different varieties of rice range from 60 to 68%; so, use of the average value of 65.8% (1) for the calculation of nutrient intake from records of weighed food intake could lead to an average overestimate of water content of the order of 2% or, more seriously, an average underestimate of water content of the order of 6%. At first sight, an error of this magnitude might not seem to be important in the context of the levels of errors often associated with studies of food intake of flee-living subjects. For a mixed Western diet, an underestimate of the water content of cooked rice by 6% and the consequent overestimate of nutrient intake probably is relatively unimportant. However, for a community where rice is the staple food (rice represents approximately 80% of the staple foods eaten in this distric0, the error may be more serious. For example, if the true value for water content of a sample of cooked rice is 60% then, assuming 4 kcal per gram of dry matter, the energy content is 160 kcal/100 g: but if the average value for water content of 66% is used, the energy content is calculated as 136 kcal/100g, which leads to an underestimate of energy intake of 15%.
RICE WATER CONTENT AND COOKING METHOD
1399
The findings reported here should be taken as a cautionary note whenever nutrient intakes are calculated on the basis of average values for water content. Although this study was restricted to boiled rice, and studies performed elsewhere have shown that the water content of boiled rice varies with respect to the gelatinization temperature and pasting characteristics of rice varieties (4,5,6), it is probable that similar variety-specific water contents would be found for other cooked plant foods with a high content of starch. Therefore, we suggest that any study designed to calculate nutrient intake on the basis of average compositional data should take cognizance of the possible differences between varieties.
TABLE 1 Water Content of Boiled Rice The Three Most Commonly Grown Varieties and Aid Rice in Each Village
Village
Keneba
Variety
Frequency *
Kunda
SD
n
139/161
66
4.0
23
Jibirokoto
108/161
60
604
27
Jibirokotokoyo
47/161
67
3.4
33
67
3.5
31
Chineso
79/79
62
3.8
28
BuUikisawullengo
70/79
66
3.9
33
Jattaba
42/79
66
3.4
30
68
3.0
32
Aid
Kanton
Mean Banjultunkung
Aid
Manduar
Water content (%, w/w)
Transumano
52/60
68
3.4
28
Chabatunkung
51/60
65
3.4
38
KumbeUi mano
44/60
67
3.2
25
64
5.1
32
Aid
* The number of women who grew this variety/total number of women.
1400
B. DIBBA et al.
TABLE 2 The Five Varieties of Boiled Rice that Differ from the Overall Mean in Water Content Villa.gg Keneba Manduar Kanton Kunda
Variety Jibirokoto Chineso Aid Transumano Aid
Mean 60 62 68 68 64
t-value 8.68 *** 6.55 *** 4.20 *** 3.90 *** 3.10 **
*** p < 0.001; ** p < 0.05 TABLE 3 Varieties of Rice Grown in the Three Villages Variety
Frequency
Variety
Frequency
(/161)
(/60) KANTON
Banjultunkung Bard mano Bcrefet Bolonkono mano Bullildsakoyo Chabatunkung Chinese manisutung Chinesckoyo Chineso Findi maniwulleng Findi mano Jibirokoto Jibirokotokoyo Jibirokotowullengo Kamosori Kartong Kaur Konsunkuto Maningdingkoyo Mankasinoto mano Kumbeli mano
Laminjanko
Lamin mano Mane mano Manikunkoloba Maninding sutung Maniwullengo Meggi messengo Njahaintima Nungfin Nyominding alimatu Pirang mano Pudari mano Sailto mano Transumano
139 2 3 1 43 39 1
15 7 4 18 108 47 30 10 2 1 17 22 1 1
3 3 34 1 16 5 1 4 10 2 1 25 1 5
KUNDA
Acre mano Ba mano Banjulttmkung Btdlikisakoyo Bvnildsafingo Burikisatunkung Chabatunkung Churenso mano Fakari mano Findi mano India mano Jibirokoto Jurunkumusunoringo Katikati mano KumbeUi mano Lang Bojang mano Maninding sutung Manindingo Njahail mano
Njahalltima
Poni mano Pudad mano Putobala Transumano Uncle Ben
4 2 1 6 2 3 51 1 12 I 1 16 i 1 44 8 1 31 6 3 2 6 9 52 3
RICE WATER CONTENTAND COOKING METHOD
1401
~AELE.!_g~aml Variety
Acre mano Agriculture mano Alhagi btmja Bakaramo mano Banjultunkung Bintanding madi Bintu janneh mano Bullildsafingo BuUildsakoyo Bunikisawullengo Bun~usinding Chabatakungo Chinese wullengo Chineso Demba jobr mano Demba mane mano Fabakari mano Faratu kadi mano Fatu ko!limano Ferese koyo Fereso Firio Harnoronding Jaffa mano Jattaba Jilenjakoni Kadi mane mano
Frequency (/79) 1 1 1 2 1 1 1 11 25 70 1 7 1 79 3 7 1 1 2 1 1 1 4 1 42 1 2
Variety
Kamosorr Kartong Katisabo Kaukau mano Kaur Mani koyo Manisutungo ManiwuUengo Mama mani jango Mansa mano Mansasino Mbanyima mano Mendy Momodou sowe mano Mondo mano Mondo mano Musufing Musukebajali Nifingo Njahenn tima Njahenno Nunfing Nyominding alimatu Potofulo Sccfo koyo Sumaila rnano
Frequency (/79) 10 18 1 1 14 5 34 12 1 1 1 2 2 1 4 4 1 21 2 1 16 30 36 2 1 11
ACKNOWLEDGEMENTS We thank Yaya Dibba and Morikeba Sanyang for their invaluable help with the collection of samples, and the women of Keneba, Manduar and Kanton Kunda for their patience and for their co-operation.
1. Hudson, GJ, Day, KC. Water content of the rural Gambian diet. Nutr Rep Int 1989; 40:335 - 339.
2. Hudson, G J, John, PMV, Paul, AA. Variation in the composition of Gambian foods: The importance of water in relation to energy and protein content. Ecol Fd Nutr 1980; 10:9 - 17. 3. Hudson, GJ.. Using a domestic microwave oven for the measurement of water in food. Nmr Rep Int 1989; 40:67 - 70.
1402
B. DIBBA et al.
4. Halick, JV, Kelly, VJ. Gelatinization and pasting characteristics of rice varieties as related to cooking behavior. Cereal Chem 1957; 36:91 - 98. 5. Juliano, BO, Bautista, GM, Lugay, JC, Reyes, AC. Studies on the physicochemical properties office. J Agric Fd Chem 1964; 12:131 - 138.
6.
Singh,N, Sekhon, KS, Kaur, A. (1990). Effect of pre-harvest flooding of paddy on the milling and cooking quality office. J Sci Fd Agric 1990; 52:23 - 34. Accepted for publication October 8, 1991.
WATER CONTENT OF COOKED RICE IS RELATED TO VARIETY AND COOKING METHOD B Dibba, LT Weaver MD and GJ Hudson* MRC Dunn Nutrition Unit, Downham's Lane, Milton Road, Cambridge CB4 1XJ, UK and Keneba, West Kiang, The Gambia
ABSTRACT If an average water content is used with records of weighed food intake to calculatenutrient intake, it is important to establish that the value is appropriate. A previous study in three villages in The Gambia, West Africa, reported an average value for the water content of cooked rice of 65.8% and a fairly wide range of values for individual samples (SD 5.52, n 2666). We present values for the water contents of ten varieties of rice that confLrm the results of the previous study. A wide range of values is observed because some varieties of rice, and the same variety cooked in different villages, have average water contents, ranging from 60% to 68%, that differ significantly from the overall mean. Use of the overall mean value for water content for those varieties could lead to underestimates of water intakes of the order of 6%, representing underestimates of nutrient intake of 15%. KEY WORDS: Rice; Variety; Cooking Method; Water Content; Energy Content
INTRODUCTION It is common practice in epidemiological studies to calculate nutrient intake from records of weighed food intake using average compositional data. Hudson & Day (1) investigated the appropriateness of this approach in a sub-Saharan country where there are large seasonal changes in dietary pattern. They concluded that "the use of average analytic values throughout the year is entirely appropriate." In support of this, they presented values for the water content of cooked rice that showed no seasonal changes and reported no difference between the three Gambian villages in that study. However, subsequent investigations have revealed that the people of these villages grow a large number of different varieties of rice, raising the question of whether a single value for the average water content of cooked rice to calculate nutrient intake (2) was appropriate for every variety of rice. Here, we report the results of a study in the same three villages that revealed that different varieties of rice, and the same variety of rice in different villages, do have different water contents when cooked. * Author to whom correspondence should be addressed
1397
1398
B. DIBBA et al.
EXPERIMENTAL PROCEDURES (a) Study villages and subjects, These studies took place in the villages of Keneba, Manduar and Kanton Kunda in the West Kiang District of The Gambia. Women are responsible for growing rice in these communities; 161 women in Keneba, 79 in Manduar and 60 in Kanton Kunda were interviewed to determine which varieties of rice they grew, and to establish their willingness to take part in the study. (b) Varieties of rice A surprisingly large number of varieties of rice was reported; 35 varieties in Keneba, 54 in Manduar and 25 in Kanton Kunda (see Table 3). For each of the three most commonly grown varieties of rice in each village, 32 women were selected randomly to provide samples of raw and cooked rice; and 32 w o m e n were selected random/y from each village to provide samples of raw and cooked Aid rice purchased from local shops. (c) Samples A single sample of raw (approx. 100g) and of cooked rice (approx. 200g) was collected from each subject in exchange for a similar quantity of Aid rice. Samples were placed into plastic pots with clip-on lids and kept in a polyethylene bag in a cool box during transport to the laboratory in Keneba for analysis. Any samples not analysed on the day of collection were stored at -20~ (d) Determination of water content The water content of duplicate 2g samples was determined by drying in a domestic microwave oven as previously described (3). The average value for duplicates was used for calculation of water content. RESULTS AND DISCUSSION The water content of cooked food serves as an index of its nutrient content (2). Table 1 is a stumnm~ of the results obtained for the water content of cooked rice for the three most commonly grown varieties in each of three Gambian villages. The average value for water content of each variety of cooked rice was compared with the value reported by Hudson & Day (1) for the mean water content (65.8%, SD 5.52) of 2666 samples of cooked rice collected from these villages over 13 months; varieties of rice were not identified in that study. In the study reported here, several varieties of rice were found to have a significantly different value (Student's t -test, p < 0.001) for average water content from that reported (1) for all varieties: a summary is presented in Table 2. The average values for the different varieties of rice range from 60 to 68%; so, use of the average value of 65.8% (1) for the calculation of nutrient intake from records of weighed food intake could lead to an average overestimate of water content of the order of 2% or, more seriously, an average underestimate of water content of the order of 6%. At first sight, an error of this magnitude might not seem to be important in the context of the levels of errors often associated with studies of food intake of flee-living subjects. For a mixed Western diet, an underestimate of the water content of cooked rice by 6% and the consequent overestimate of nutrient intake probably is relatively unimportant. However, for a community where rice is the staple food (rice represents approximately 80% of the staple foods eaten in this distric0, the error may be more serious. For example, if the true value for water content of a sample of cooked rice is 60% then, assuming 4 kcal per gram of dry matter, the energy content is 160 kcal/100 g: but if the average value for water content of 66% is used, the energy content is calculated as 136 kcal/100g, which leads to an underestimate of energy intake of 15%.
RICE WATER CONTENT AND COOKING METHOD
1399
The findings reported here should be taken as a cautionary note whenever nutrient intakes are calculated on the basis of average values for water content. Although this study was restricted to boiled rice, and studies performed elsewhere have shown that the water content of boiled rice varies with respect to the gelatinization temperature and pasting characteristics of rice varieties (4,5,6), it is probable that similar variety-specific water contents would be found for other cooked plant foods with a high content of starch. Therefore, we suggest that any study designed to calculate nutrient intake on the basis of average compositional data should take cognizance of the possible differences between varieties.
TABLE 1 Water Content of Boiled Rice The Three Most Commonly Grown Varieties and Aid Rice in Each Village
Village
Keneba
Variety
Frequency *
Kunda
SD
n
139/161
66
4.0
23
Jibirokoto
108/161
60
604
27
Jibirokotokoyo
47/161
67
3.4
33
67
3.5
31
Chineso
79/79
62
3.8
28
BuUikisawullengo
70/79
66
3.9
33
Jattaba
42/79
66
3.4
30
68
3.0
32
Aid
Kanton
Mean Banjultunkung
Aid
Manduar
Water content (%, w/w)
Transumano
52/60
68
3.4
28
Chabatunkung
51/60
65
3.4
38
KumbeUi mano
44/60
67
3.2
25
64
5.1
32
Aid
* The number of women who grew this variety/total number of women.
1400
B. DIBBA et al.
TABLE 2 The Five Varieties of Boiled Rice that Differ from the Overall Mean in Water Content Villa.gg Keneba Manduar Kanton Kunda
Variety Jibirokoto Chineso Aid Transumano Aid
Mean 60 62 68 68 64
t-value 8.68 *** 6.55 *** 4.20 *** 3.90 *** 3.10 **
*** p < 0.001; ** p < 0.05 TABLE 3 Varieties of Rice Grown in the Three Villages Variety
Frequency
Variety
Frequency
(/161)
(/60) KANTON
Banjultunkung Bard mano Bcrefet Bolonkono mano Bullildsakoyo Chabatunkung Chinese manisutung Chinesckoyo Chineso Findi maniwulleng Findi mano Jibirokoto Jibirokotokoyo Jibirokotowullengo Kamosori Kartong Kaur Konsunkuto Maningdingkoyo Mankasinoto mano Kumbeli mano
Laminjanko
Lamin mano Mane mano Manikunkoloba Maninding sutung Maniwullengo Meggi messengo Njahaintima Nungfin Nyominding alimatu Pirang mano Pudari mano Sailto mano Transumano
139 2 3 1 43 39 1
15 7 4 18 108 47 30 10 2 1 17 22 1 1
3 3 34 1 16 5 1 4 10 2 1 25 1 5
KUNDA
Acre mano Ba mano Banjulttmkung Btdlikisakoyo Bvnildsafingo Burikisatunkung Chabatunkung Churenso mano Fakari mano Findi mano India mano Jibirokoto Jurunkumusunoringo Katikati mano KumbeUi mano Lang Bojang mano Maninding sutung Manindingo Njahail mano
Njahalltima
Poni mano Pudad mano Putobala Transumano Uncle Ben
4 2 1 6 2 3 51 1 12 I 1 16 i 1 44 8 1 31 6 3 2 6 9 52 3
RICE WATER CONTENTAND COOKING METHOD
1401
~AELE.!_g~aml Variety
Acre mano Agriculture mano Alhagi btmja Bakaramo mano Banjultunkung Bintanding madi Bintu janneh mano Bullildsafingo BuUildsakoyo Bunikisawullengo Bun~usinding Chabatakungo Chinese wullengo Chineso Demba jobr mano Demba mane mano Fabakari mano Faratu kadi mano Fatu ko!limano Ferese koyo Fereso Firio Harnoronding Jaffa mano Jattaba Jilenjakoni Kadi mane mano
Frequency (/79) 1 1 1 2 1 1 1 11 25 70 1 7 1 79 3 7 1 1 2 1 1 1 4 1 42 1 2
Variety
Kamosorr Kartong Katisabo Kaukau mano Kaur Mani koyo Manisutungo ManiwuUengo Mama mani jango Mansa mano Mansasino Mbanyima mano Mendy Momodou sowe mano Mondo mano Mondo mano Musufing Musukebajali Nifingo Njahenn tima Njahenno Nunfing Nyominding alimatu Potofulo Sccfo koyo Sumaila rnano
Frequency (/79) 10 18 1 1 14 5 34 12 1 1 1 2 2 1 4 4 1 21 2 1 16 30 36 2 1 11
ACKNOWLEDGEMENTS We thank Yaya Dibba and Morikeba Sanyang for their invaluable help with the collection of samples, and the women of Keneba, Manduar and Kanton Kunda for their patience and for their co-operation.
1. Hudson, GJ, Day, KC. Water content of the rural Gambian diet. Nutr Rep Int 1989; 40:335 - 339.
2. Hudson, G J, John, PMV, Paul, AA. Variation in the composition of Gambian foods: The importance of water in relation to energy and protein content. Ecol Fd Nutr 1980; 10:9 - 17. 3. Hudson, GJ.. Using a domestic microwave oven for the measurement of water in food. Nmr Rep Int 1989; 40:67 - 70.
1402
B. DIBBA et al.
4. Halick, JV, Kelly, VJ. Gelatinization and pasting characteristics of rice varieties as related to cooking behavior. Cereal Chem 1957; 36:91 - 98. 5. Juliano, BO, Bautista, GM, Lugay, JC, Reyes, AC. Studies on the physicochemical properties office. J Agric Fd Chem 1964; 12:131 - 138.
6.
Singh,N, Sekhon, KS, Kaur, A. (1990). Effect of pre-harvest flooding of paddy on the milling and cooking quality office. J Sci Fd Agric 1990; 52:23 - 34. Accepted for publication October 8, 1991.