http://informahealthcare.com/ijf ISSN: 0963-7486 (print), 1465-3478 (electronic) Int J Food Sci Nutr, 2014; 65(7): 797–802 ! 2014 Informa UK Ltd. DOI: 10.3109/09637486.2014.917155
FOOD COMPOSITION AND ANALYSIS
Evaluation of iodine content and stability in recipes prepared with biofortified potatoes Lorenzo Cerretani1, Patrizia Comandini1, Davide Fumanelli2, Francesca Scazzina2, and Emma Chiavaro2 Pizzoli S.p.A., Via Zenzalino Nord 1, Budrio, Italy and 2Dipartimento di Scienze degli Alimenti, Universita` degli Studi di Parma, Parma, Italy
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1
Abstract
Keywords
Iodine is an essential micronutrient of the human diet. Deficiency of iodine is diffused in many areas of the world and mild deficiency is present also in developed countries around Europe. Biofortification of vegetables could represent a better strategy with respect to iodized salt in order to increase iodine intake. The aim of this study was evaluating the stability of iodine, derived from biofortified potatoes, in the preparation process of three Italian typical dishes: dumplings, vegetable pie, and focaccia bread. The obtained results showed a good stability of iodine in cooking processes, in particular, during baking of focaccia bread. Significant losses of iodine were detected during boiling of dumplings and baking of vegetable pie. Although the different stability during the cooking processes, the three dishes maintained a good final content of iodine, ranging from the 33.3% to 52.7% of daily recommended intake in adults for individual serving size.
Biofortification, cooking, energy balance iodine, meal, nutritional analysis
Introduction Iodine is an essential micronutrient and a component of thyroid hormones thyroxine (T3) and triiodothyrosine (T4) (Zimmermann, 2011). Thyroid hormones are involved in a variety of physiological processes, including reproductive functions, growth, development, and resting metabolic rate (Zimmermann, 2013). Low iodine intake exerts several effects on human health, altogether defined as iodine deficiency disorders (IDD) (Untoro et al., 2010). The symptoms are goitre, a noncancerous enlargement of the thyroid gland, cretinism, and hypothyroidism, but the most serious effect is represented by possible damage to the fetus (Zimmermann, 2011). Severe iodine deficiency during pregnancy may cause stillbirths, abortions, and congenital abnormalities (Zimmermann et al., 2008). An adequate iodine intake during pregnancy, lactation, and early childhood has been reported to be essential for optimal brain development of the fetus and of children from 7 to 24 months of age (Pearce, 2012; Untoro et al., 2010). Moreover, metabolic changes in thyroid function occurring during pregnancy lead to increased loss of iodine and, as a consequence, to higher iodine need (Olivares et al., 2012; Skeaff, 2012; Trumpff et al., 2013). The recommended dietary allowance of iodine is 90 mg/d for 0–5 years old, 120 mg/d for 6–12 years old, 150 mg/d for 12 years, and older and 250 mg/d for pregnant and lactating woman (WHO, 2007). Iodine deficiency remains a major threat to the health and development of population around the world, particularly in children and pregnant women in low-income countries
Correspondence: Francesca Scazzina, Dipartimento di Scienze degli Alimenti, Universita` degli Studi di Parma, Parco Area delle Scienze 47/A, 43124 Parma, Italy. Tel: +39 0521 903830. Fax: +39 0521 903832. E-mail: [email protected]
History Received 24 February 2014 Revised 1 April 2014 Accepted 5 April 2014 Published online 14 May 2014
(Andersson et al., 2010). Nineteen European populations are affected by a mild and 4 by a moderate iodine deficiency (WHO, 2004). In particular, Europe has a very high rate (59.9%) of school children with insufficient iodine intake (Melse-Boonstra & Jaiswal, 2010; WHO, 2004). Several strategies in contrast to iodine malnutrition have been described, such as mineral supplementation, food fortification, and biofortification of crops. Salt iodization is currently the most widely used strategy to control and eliminate IDD (WHO, 2007). Universal salt iodization (USI) is a term used to describe the iodization of salts for human (food industry and household) and livestock consumption (Zimmermann, 2008). Nevertheless, the use of salt as a vehicle for food fortification has been recently questioned after the recommendations for reducing salt intake to prevent cardiovascular diseases (Andersson et al., 2010; Sˇtimec et al., 2009). Increasing the concentration of bioavailable micronutrients in edible crops tissues (biofortification) is a very promising strategy for increasing the intake of micronutrient (Hotz, 2013; Miller & Welch, 2013; Saltzman, 2013) and preventing iodine deficiency (Charlton & Jooste, 2013; Tonacchera et al., 2013; White & Broadley, 2005). The edible part of vegetables is an excellent target for iodine supplementation and can be readily incorporated into the human diet (Weng et al., 2013). Specific agricultural practices have been developed in order to increase iodine content in several vegetables and crops as tomato (Caffagni et al., 2011; Landini et al., 2011), spinach (Smolen & Sady, 2012; Weng et al., 2013), barley and wheat (Caffagni et al., 2011), potato (Caffagni et al., 2011; Zanirato & Mayerle, 2009), cabbage, coriander, cucumber, eggplant, long cowpea, and hot pepper (Weng et al., 2013), carrot and onion (Zanirato & Mayerle 2009). Many common vegetables are consumed only cooked and iodine, being volatile, can be readily lost during food processing operations (Winger et al., 2008). The critical problem
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with iodine stability is the potential transformation to elemental iodine (I2) that readily sublimes at room temperature (Diosady et al., 2002). Several investigations carried out on the stability of iodine in iodized salt showed that, on one hand, iodine content significantly decreased during storage (Patel et al., 2012) and cooking procedures (Caffagni et al., 2012; Goindi et al., 1995; Longvah et al., 2012, 2013). On the other hand, the iodine stability in biofortified vegetables during cooking was only recently investigated (Caffagni et al., 2012; Comandini et al., 2013; Rana & Raghuvanshi, 2013). In particular, these studies concern the effect of boiling, baking, and pasteurization on iodine content in potatoes, tomatoes, and carrots. However, at the best of authors’ knowledge, there are no publications dealing with iodine stability and/or loss in recipes prepared with biofortified vegetable. Thus, the aim of this study is to evaluate the cooking effect on iodine content in three dishes: dumplings, vegetable pie, and focaccia bread, prepared with biofortified potatoes.
Methods Chemicals Tetramethylammonium hydroxide (TMAH, 1 M) solution was bought from Sigma Aldrich (St. Louis, MO). All the solvents used were of high purity grade, and ion exchanged water (18 M ) was generated by a Millipore Direct Q5 system (Millipore Co., Bedford, MA). Samples Potatoes (Cupido variety) and carrots (Maestro variety) were kindly donated by Pizzoli S.p.A. (Budrio, Italy). Iodine potatoes were obtained by a patented procedure (Zanirato & Mayerle, 2009) of agronomic biofortification through foliar fertilization. The other ingredients used for the dishes preparation were purchased in a local market. Dishes preparation Three dishes containing potatoes as the main ingredient were selected for this study, taking into account a balanced nutritional intake. The dishes and their preparation are reported below. Dumplings: 500 g of mashed potato were kneaded with 200 g of wheat flour, 60 g of boiled and mashed carrots, 35 g of egg, and 6 g of salt. Dumplings were manually formed and were boiled in tap water for 3 min. Forty grams of olive oil were mixed with 20 g of hard grated cheese and 3 g of sage leave and the mixture obtained was added to dumpling as seasoning. Vegetable pie: 100 g carrots were cut in long slices and were boiled in tap water for 20 min. A bakery mould was covered with blanched carrot slices and filled with a mash thus obtained: 670 g of mashed potato, 200 g of peas, 115 g of egg, 100 g of milk, 80 g of ham, 60 g of hard grated cheese, 2 g of salt, and 1 g of pepper. Twenty grams of olive oil were added on the surface and the vegetable pie was baked in an oven set at 180 C for 30 min. Focaccia bread: 550 g of mashed potato were kneaded with 770 g of wheat flour, 250 g of tap water, 30 g of olive oil, 25 g of brewer’s yeast, 5 g of sugar, and 1 g salt. The dough was spread out on a baking tray and was kept rising for 2 h. Thereafter, 150 g of small tomatoes, 10 g of olive oil, 2 g of oregano, and 1 g of salt were spread on the surface of raw focaccia bread. Focaccia bread was baked in an oven set at 200 C for 20 min. Sampling for iodine and composition analyses The iodine analysis has been carried out on raw potatoes, boiled potatoes, raw, and cooked dishes. Raw potatoes were
Int J Food Sci Nutr, 2014; 65(7): 797–802
homogenized with a mixer and stored at 20 C until iodine determination. Boiled potatoes were cooked in tap water for 30 min, peeled, and mashed. The mashed sample was also used for the preparation of dishes. Iodine was determined in raw and cooked dishes, after homogenization of a serving of about 150 g. In particular, dumplings were analyzed before and after boiling, vegetable pie, and focaccia bread were analysed before and after baking. Composition analyses (moisture, ash, fat and fatty acid composition, protein, carbohydrate and sugar content, energy) have been performed on cooked dishes after homogenization of a serving of about 150 g. Samples were stored at 20 C until iodine and composition analyses. Iodine determination Iodine was extracted by an alkaline procedure with TMAH assisted by a mineralization in microwave oven (Mars Express 5, CEM srl, Cologno al Serio, Italy). After extraction, the sample was diluted with ultrapure water, centrifuged, and filtered following the method used by Comandini et al. (2013). The measurements were carried out with an inductively coupled plasma mass spectrometer (ICP-MS) (Agilent, Palo Alto, CA). RF power used was 1550 W, argon flow rates were 1.05 l/min and 0.2 l/min, respectively, for carrier gas and make up gas. Instrument calibration was performed by employing iodine standards of up to a concentration of 100 mg/l in dilute TMAH solutions. The iodine content was expressed as mg/100 g on wet cooked weight (WCW) and as mg/100 g on wet raw weight (WRW) in potatoes and dishes, as specified in the Results section. Composition analyses Dry matter was determined by oven drying for 3 h at 105 C (AOAC 930.15, 1990). Water content was calculated from the following expression: Water content ðg=100 gÞ ¼ 100 dry matter ðg=100 gÞ Ash content was determined with a muffle furnace set at 550 C (AOAC 923.03, 2000). Fat content was determined by Soxhlet extraction (6 h) using dyethilether as a solvent (AOAC 920.39a, 1990). Determination of fatty acid composition was realized by saponification and methil-esterification on fat samples previously extracted (UNI EN ISO 12966-2:2011). Then, fatty acid methylesters were analysed by gas chromatography (Agilent 6890 series II gas chromatograph, Agilent Technologies, Palo Alto, CA) using a SP 2560 fused-silica capillary column (100 m 0.25 m, 0.2 mm film thickness; Supelco Inc., Bellefonte, PA) (UNI EN ISO 5508:1998). The amount of sample proteins was determined from the nitrogen content (N 6.25), using the Kjeldhal method (AOAC 968.06). Fibre content was analysed by a gravimetric method, after enzymatic digestion (AOAC 962.09, 2000). The total carbohydrates content was calculated by the following formula (Chen et al., 2013): Carbohydrates ðg=100 gÞ ¼ 100 water ðg=100 gÞ protein ðg=100 gÞ ash ðg=100 gÞ fat ðg=100 gÞ fibre ðg=100 gÞ Sugars were determined by HPLC-RID (Agilent 1100 series HPLC system, Agilent Technologies, Palo Alto, CA) on a NH2 column (Aminex HPX-87H ion exchange column, 300 mm 7.78 mm), as reported by Eye´ghe´-Bickong et al. (2012).
Evaluation of iodine content and stability in recipes
DOI: 10.3109/09637486.2014.917155
The nutritional profile of the three preparations was reported on WCW referred to one adult portion size for the Italian population (Turconi & Roggi, 2007). The macronutrient content of fat, saturated fat, carbohydrate, sugar, and protein was reported as % of energy contribution. Sodium and water content was reported as grams per portion size. The fibre content was reported both as % of energy contribution and grams. Finally, the iodine content was reported as mg per portion size. Energy content of dishes Energy of dishes is calculated by the following expressions (EU, 2011): Energy ðkcal=100 gÞ
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¼ protein ðg=100 gÞ 4 þ fat ðg=100 gÞ 9 þ carbohydrates ðg=100 gÞ 4 þ fibre ðg=100 gÞ 2 Energy ðkJ=100 gÞ ¼ protein ðg=100 gÞ 17 þ fat ðg=100 gÞ 37 þ carbohydrates ðg=100 gÞ 17 þ fibre ðg=100 gÞ 8 Statistical analysis Food preparations and analytical determinations were repeated three times. All the statistical analyses were performed with Statistica 7.0 software (Statsoft Inc, Tulsa, OK). The effect of cooking on iodine content was evaluated with a paired t-test (p50.05) while the statistical differences for iodine content on the three dishes were evaluated with a one-way ANOVA followed by a Tukey test (p50.05).
Results Iodine analysis Iodine content of each ingredient used in the preparation of dishes was analysed and reported in Table 1. Ingredients with the highest iodine content were hard cheese (232.0 mg/100 g), biofortified potatoes (76.1 mg/100 g), eggs (30.4 mg/100 g), milk (19.7 mg/100 g), and wheat flour (16.0 mg/100 g). Taking into account the amount of ingredients in each dish, biofortified potatoes were the main sources of iodine, accounting for 81.0% of total iodine contribution in dumplings, 72.6% in vegetable pie, and 76.9% in focaccia bread. Hard cheese had the highest iodine value (232.0 mg/100 g) but its contribution to the total iodine content of each dish was reduced due to the low amount used in each recipe (2.3% and 4.3% in dumplings and vegetable pie, respectively). Ham, peas, and carrots had low iodine levels (0.2–3.3 mg/100 g). Iodine content in all the other ingredients was not detectable under the analytical conditions used. As reported in Table 2, iodine content was evaluated in potatoes and dishes before (raw) and after cooking (cooked). To avoid differences due to the moisture content as a result of cooking, all samples were weighted before and after cooking, and iodine values were reported as mg/100 g on WCW and as mg/100 g on WRW (McKillop et al., 2002). Weight loss (WL) detected during the different cooking process ranged between 0.3% and 12.5% (Table 2). In potatoes, no significant differences in the iodine content were detected before and after boiling. Cooking process of dumplings and vegetable pie caused a significant loss of iodine equal to 27.5% and 55.3%, respectively. In focaccia bread, no significant differences were detected before and after cooking.
Table 1. Iodine content in ingredients and contribution to raw dishesa.
Dish
Ingredient
Ingredient amount (%)
Iodine in single ingredient (mg/100 g WRW)
Iodine contribution in raw dishes (%)
Dumplings
Potatoes Hard cheese Wheat flour Eggs Carrots Olive oil Salt Sage leaves
57.9 2.3 23.3 4.1 7.0 4.4 0.7 0.3
76.1 ± 7.7 232.0 ± 12.2 16.0 ± 2.7 30.4 ± 3.1 0.22 ± 0.02 n.d. n.d. n.d.
81.0 10.0 6.9 2.2 0.0 – – –
Vegetable pie
Potatoes Hard cheese Eggs Milk Ham Peas Carrots Salt Pepper Olive oil
49.5 4.3 8.5 7.5 6.0 14.8 7.5 0.1 0.1 1.6
76.1 ± 7.7 232.0 ± 12.2 30.4 ± 3.1 19.7 ± 4.2 3.3 ± 1.1 0.8 ± 0.5 0.22 ± 0.02 n.d. n.d. n.d.
72.6 19.0 5.0 2.8 0.4 0.2 0.0 – – –
Focaccia bread
Potatoes Wheat flour Water Tomatoes Olive oil Brewer’s yeast Sugar Salt Oregano
30.7 42.9 13.9 8.4 2.3 1.4 0.3 0.1 0.1
76.1 ± 7.7 16.0 ± 2.7 n.d. n.d. n.d. n.d. n.d. n.d. n.d.
76.9 23.1 – – – – – – –
a
799
Values are mean ± SD of three measurements. WRW, wet raw weight; n.d., not detectable, under limit of detection.
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Table 2. Iodine content of potato and dishes before and after cooking processa. Iodine content Raw (mg/100 g WRW) Potatoes Dumplings Vegetable pie Focaccia bread
aA
76.1 ± 7.7 54.3 ± 2.3aB 69.5 ± 0.6aAB 31.9 ± 3.1aC
Cooked (mg/100 g WCW) aA
96.4 ± 5.9 39.5 ± 4.0bB 35.5 ± 3.6bB 33.3 ± 3.3aB
Cooked (mg/100 g WRW) aA
94.9 ± 5.8 39.4 ± 3.9bB 31.1 ± 2.9bB 29.8 ± 2.7aB
WL (%) 1.6 0.3 12.5 10.4
a
Values are mean ± SD of three measurements. Means with different letter on the same row (a, b) are significantly different; means with different letter on the same column (A, B, C) are significantly different (one-way ANOVA, Tukey test, p50.05). WL, weight loss; WRW, wet raw weight; WCW, wet cooked weight.
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Table 3. Nutritional composition of cooked dishes related to one adult portion size (Turconi & Roggi, 2007).
Portion size (g) Energy (kcal) Energy (kJ) Water (g) Fat (E%)a – Saturated (E%)a Carbohydrate (E%)a – Sugars (E%)a Protein (E%)a Fibre (E%)* (g) Sodium (g) Iodine (mg)
RDIb
Dumplings
Vegetable pie
Focaccia bread
– 2000 8368 – 31.5 9 52 18 10 – 2.4 150.0
200 329 1384 128 26 6 59 12 12 3 (4.2) 0.4 79.0
165 198 829 120 37 14 36 5 22 5 (5.0) 0.4 58.6
150 316 1335 74 16 3 70 7 11 4 (5.6) 0.1 50.0
a
E%: % of energy contribution compared with 100% of portion size. RDI, Reference Daily Intake of a 2000 calories diet (EU Reg., 2011).
b
Composition analysis The nutritional composition of cooked dishes is reported in Table 3. The values were related to one adult portion size of WCW. The biggest differences were related to water, fat, and carbohydrate content. One portion of focaccia bread contained less water (74 g) than dumpling and vegetable pie (128 g and 120 g, respectively). Energy from saturated fat was higher for vegetable pie (14%) with respect to dumpling (6%) and focaccia bread (3%). Finally, dumpling and focaccia bread contained, respectively, 59% and 70% of energy from carbohydrate, compared with 36% in vegetable pie. The sodium content in the three dishes was low and ranged between 0.1 g and 0.4 g. In relation to iodine content, one portion of dumpling had the highest quantity of iodine (79.0 mg) followed by one portion of vegetable pie (58.6 mg) and one portion of focaccia bread (50.0 mg).
Discussion Iodine analysis The iodine amount of each ingredient used in the preparation of dishes was analysed in order to better understand the sources of iodine in raw dishes (Table 1). In regular raw potatoes, iodine content usually ranges between 0.1 and 0.3 mg/100 g (Comandini et al., 2013; Haldimann et al., 2005). Thanks to the biofortification procedure used in this investigation (Zanirato & Mayerle, 2009), potatoes of the Cupido variety had an iodine level of 76.1 mg/100 g. The results of iodine content for the other ingredients were in agreement with those reported in the literature (Bhagat et al., 2009; Haldimann et al., 2005; Longvah et al., 2013;
Wenlock et al., 1982). In particular, an iodine level of about 20 mg/100 g was previously found in milk by Bhagat et al. (2009) and Longvah et al. (2013). Regarding eggs, the iodine amount detected in this investigation (30.4 mg/100 g) was in line with the results of Haldimann et al. (2005) that verified that iodine was located principally in yolk. Finally, an iodine level of about 10 mg/100 g was reported in wheat flour by Wenlock et al. (1982). The hard cheese used in the preparation of vegetable pie and dumplings was an industrial grated cheese. The high content of iodine detected (232.0 mg/100 g) was probably due to the high amount of milk used for the production of hard cheese. In the preparation of dishes, rock salt was used. Its iodine content was not detectable by ICP-MS. This kind of salt was chosen to avoid the contribution of sea salt or iodized salt on the total content of iodine of the dishes and to better focus the investigation on biofortified vegetable. Moreover, the stability of iodine during storage and cooking processing of sea and iodized salt was largely discussed in previous investigations (Chavasit et al., 2002; Longvah et al., 2012; Patel et al., 2012; Rana & Raghuvanshi, 2013). The first step in the preparation of each dish involved boiling of whole, unpeeled potatoes to obtain cooked mashed potato. So, the first investigated aspect was the effect of boiling on the iodine content of biofortified potatoes. Results showed that boiling of whole potatoes had no effect on iodine content confirming previous results by Comandini et al. (2013), describing the effect of boiling in several varieties of biofortified potato. The high capacity of retention of iodine content was probably due to the presence of starch, composed by amylose (Mottiar & Altosaar, 2011; Yu et al., 1996) and amylopectin fractions (Shen et al., 2013), that might be involved in iodine– starch complex formation. In addition, the presence of potato skin
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DOI: 10.3109/09637486.2014.917155
during boiling might have represented a physical barrier that limited the leaching of iodine into water. This barrier effect of potato skin has been previously reported by Barba et al. (2008) and by Ezekiel et al. (2013) for phenolic compounds that were better preserved during boiling of unpeeled potatoes in comparison with peeled tubers. However, owing to different chemical properties of iodine and phenolic compounds, further investigations are needed to support this hypothesis. Preparation of the first dish involved dumpling manual formation, with boiled mashed potatoes, followed by a second boiling step in tap water for 3 min. Iodine content of cooked dumplings was reduced of about 27.5% with respect to the raw mixture (39.4 versus 54.3 mg/100 g WRW). As previously discussed, boiling of whole potatoes did not cause an iodine loss, so the iodine reduction observed during dumpling preparation derived from a leakage of iodine into cooking water during the second boiling step, despite the boiling time, which was shorter for dumplings (3 min) than whole potatoes (30 min). The different stability of iodine between whole potato and dumpling boiling was probably due to the absence of a protective skin in dumplings that increased leakage of iodine, and to the small size of dumplings (about 4 g each) that increased the contact surface with boiling water. Similar results were obtained by Goindi et al. (1995) with average losses of 36.6 ± 14.8% in iodine content during boiling of six different Indian recipes, and by Longvah et al. (2012) with average losses of 47.2 ± 27.2% during boiling of nine Indian recipes prepared with the addition of iodized salt. During focaccia bread baking (200 C, 20 min), no significant iodine losses were detected. The high iodine stability in this dish might derive from its high starch content (Mottiar et al., 2011; Shen et al., 2013; Yu et al., 1996), due to potato and wheat flour. Vegetable pie showed the highest iodine loss (55.3%) during baking. Despite the cooking procedure was similar to that of focaccia bread, the high iodine loss might have been due to the absence of wheat flour and, therefore, to the lower starch content. Moreover, vegetable pie was cooked in small aluminum moulds that have increased the surface to volume ratio of the dish, causing a slight rise of WL, as compared with focaccia bread (12.5% versus 10.4%). The higher cooking time (30 min) compared with focaccia bread might also have enhanced the iodine loss in the vegetable pie. Despite the different iodine stabilities during preparation of dumplings, vegetable pie, and focaccia bread, the final iodine content after cooking was similar for all the dishes, and ranged between 33.3 and 39.5 mg/100 g WCW. Composition analysis The three preparations were chosen among the most consumed recipes containing potatoes in the Italian diet. To better understand the overall nutritional characteristics of the three preparations, energy, macronutrient profile and iodine content were standardized to one adult portion size (Turconi & Roggi, 2007) (Table 3). Vegetable pie was the highest in saturated fats due to its specific ingredients (egg, ham, and cheese) that, even if added in low quantity, contain high amounts of these fatty acids. The presence of wheat flour in dumpling and focaccia bread affected the carbohydrate content of these preparations.
Conclusions Although these recipes cannot be considered individually from a nutritional viewpoint and must be evaluated in the context of a well-balanced diet, they certainly represent a good strategy to increase iodine intake. For example, considering the dietary reference value for an adult population, one portion size of
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dumplings, vegetable pie, and focaccia bread, prepared with biofortified potatoes (Zanirato & Mayerle, 2009), can provide the 52.7%, 39.1%, and 33.3%, respectively, of the daily adequate intake of iodine, as recommended by WHO (2007), while keeping the intake of sodium very low. These data showed that the biofortified potatoes represent a good source of iodine, comparable with iodized salt, without increasing sodium intake in the diet. Nevertheless, only few recipes were tested and more investigations are necessary for better understand the mechanisms of the iodine stability, and the effects of different food components.
Acknowledgements The authors gratefully acknowledged Mr. Alberto Bini in performing part of the experiments and Mr Fabio Bianchini (Madegus Srl, Parma, Italy) for the assistance and the suggestions in preparing dishes.
Declaration of interest The authors declare that they have no conflict of interest. Vegetables were supplied free of charge with no obligation from the researchers to the manufacturers.
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Sˇtimec M, Kobe H, Smole K, Kotnik P, Sˇirca-Cˇampa A, Zupancˇicˇ M, Battelino T, et al. 2009. Adequate iodine intake of Slovenian adolescents is primarily attributed to excessive salt intake. Nutr Res 29:888–896. Tonacchera M, Dimida A, De Servi M, Frigeri M, Ferrarini E, De Marco G, Grasso L, et al. 2013. Iodine fortification of vegetables improves human iodine nutrition: in vivo evidence for a new model of iodine prophylaxis. J Clin Endocrinol Metab 98:694–697. Trumpff C, De Schepper J, Tafforeau J, Van Oyen H, Vanderfaeillie J, Vandevijvere S. 2013. Mild iodine deficiency in pregnancy in Europe and its consequences for cognitive and psychomotor development of children: a review. J Trace Elem Med Bio 27:174–183. Turconi G, Roggi C. 2007. Atlante fotografico alimentare. Uno strumento per le indagini nutrizionali. Roma, Italia: EMSI Editore. Untoro J, Timmer A, Schultink W. 2010. The challenges of iodine supplementation: a public health programme perspective. Best Pract Res Clin Endocrinol Metab 24:89–99. Weng HX, Hong CL, Xia TH, Bao LT, Liu HP, Li DW. 2013. Iodine biofortification of vegetable plants – an innovative method for iodine supplementation. Chi Sci Bull 17:2066–2072. Wenlock RW, Buss DH, Moxon RE, Bunton NG. 1982. Trace nutrients 4. Iodine in British food. Brit J Nutr 47:381–390. White PJ, Broadley MR. (2005). Biofortifying crops with essential mineral elements. Trends Plant Sci 10:586–593. WHO. 2004. Iodine status worldwide: WHO global database on iodine deficiency. Geneva, Switzerland: World Health Organization. WHO. 2007. Assessment of iodine deficiency disorders and monitoring their elimination: a guide for programme managers, 3rd ed. Geneva, Switzerland: World Health Organization. Winger RJ, Konig J, House DA. 2008. Technological issues associated with iodine fortification of foods. Trends Food Sci Technol 19:94–101. Yu X, Houtman C, Atalla RH. 1996. The complex of amylose and iodine. Carbohydr Res 292:129–141. Zanirato VM, Mayerle M. 2009. Method for enriching crops with iodine, and crops thus obtained. International Patent PCT/EP2009/050142. Zimmermann MB. 2008. Iodine requirements and the risks and benefits of correcting iodine deficiency in populations. J Trace Elem Med Bio 22:81–92. Zimmermann MB. 2011. The role of iodine in human growth and development. Semin Cell Dev Biol 22:645–652. Zimmermann MB. 2013. Deficiency disorders and prevention programs. In: Caballero B, Allen L, Prentice A, editors. Encyclopedia of human nutrition, vol. 3. Oxford, UK: Elsevier. p 28–32. Zimmermann MB, Jooste PL, Pandav CS. 2008. Iodine-deficiency disorders. Lancet 372:1251–1262.
FOOD COMPOSITION AND ANALYSIS
Evaluation of iodine content and stability in recipes prepared with biofortified potatoes Lorenzo Cerretani1, Patrizia Comandini1, Davide Fumanelli2, Francesca Scazzina2, and Emma Chiavaro2 Pizzoli S.p.A., Via Zenzalino Nord 1, Budrio, Italy and 2Dipartimento di Scienze degli Alimenti, Universita` degli Studi di Parma, Parma, Italy
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1
Abstract
Keywords
Iodine is an essential micronutrient of the human diet. Deficiency of iodine is diffused in many areas of the world and mild deficiency is present also in developed countries around Europe. Biofortification of vegetables could represent a better strategy with respect to iodized salt in order to increase iodine intake. The aim of this study was evaluating the stability of iodine, derived from biofortified potatoes, in the preparation process of three Italian typical dishes: dumplings, vegetable pie, and focaccia bread. The obtained results showed a good stability of iodine in cooking processes, in particular, during baking of focaccia bread. Significant losses of iodine were detected during boiling of dumplings and baking of vegetable pie. Although the different stability during the cooking processes, the three dishes maintained a good final content of iodine, ranging from the 33.3% to 52.7% of daily recommended intake in adults for individual serving size.
Biofortification, cooking, energy balance iodine, meal, nutritional analysis
Introduction Iodine is an essential micronutrient and a component of thyroid hormones thyroxine (T3) and triiodothyrosine (T4) (Zimmermann, 2011). Thyroid hormones are involved in a variety of physiological processes, including reproductive functions, growth, development, and resting metabolic rate (Zimmermann, 2013). Low iodine intake exerts several effects on human health, altogether defined as iodine deficiency disorders (IDD) (Untoro et al., 2010). The symptoms are goitre, a noncancerous enlargement of the thyroid gland, cretinism, and hypothyroidism, but the most serious effect is represented by possible damage to the fetus (Zimmermann, 2011). Severe iodine deficiency during pregnancy may cause stillbirths, abortions, and congenital abnormalities (Zimmermann et al., 2008). An adequate iodine intake during pregnancy, lactation, and early childhood has been reported to be essential for optimal brain development of the fetus and of children from 7 to 24 months of age (Pearce, 2012; Untoro et al., 2010). Moreover, metabolic changes in thyroid function occurring during pregnancy lead to increased loss of iodine and, as a consequence, to higher iodine need (Olivares et al., 2012; Skeaff, 2012; Trumpff et al., 2013). The recommended dietary allowance of iodine is 90 mg/d for 0–5 years old, 120 mg/d for 6–12 years old, 150 mg/d for 12 years, and older and 250 mg/d for pregnant and lactating woman (WHO, 2007). Iodine deficiency remains a major threat to the health and development of population around the world, particularly in children and pregnant women in low-income countries
Correspondence: Francesca Scazzina, Dipartimento di Scienze degli Alimenti, Universita` degli Studi di Parma, Parco Area delle Scienze 47/A, 43124 Parma, Italy. Tel: +39 0521 903830. Fax: +39 0521 903832. E-mail: [email protected]
History Received 24 February 2014 Revised 1 April 2014 Accepted 5 April 2014 Published online 14 May 2014
(Andersson et al., 2010). Nineteen European populations are affected by a mild and 4 by a moderate iodine deficiency (WHO, 2004). In particular, Europe has a very high rate (59.9%) of school children with insufficient iodine intake (Melse-Boonstra & Jaiswal, 2010; WHO, 2004). Several strategies in contrast to iodine malnutrition have been described, such as mineral supplementation, food fortification, and biofortification of crops. Salt iodization is currently the most widely used strategy to control and eliminate IDD (WHO, 2007). Universal salt iodization (USI) is a term used to describe the iodization of salts for human (food industry and household) and livestock consumption (Zimmermann, 2008). Nevertheless, the use of salt as a vehicle for food fortification has been recently questioned after the recommendations for reducing salt intake to prevent cardiovascular diseases (Andersson et al., 2010; Sˇtimec et al., 2009). Increasing the concentration of bioavailable micronutrients in edible crops tissues (biofortification) is a very promising strategy for increasing the intake of micronutrient (Hotz, 2013; Miller & Welch, 2013; Saltzman, 2013) and preventing iodine deficiency (Charlton & Jooste, 2013; Tonacchera et al., 2013; White & Broadley, 2005). The edible part of vegetables is an excellent target for iodine supplementation and can be readily incorporated into the human diet (Weng et al., 2013). Specific agricultural practices have been developed in order to increase iodine content in several vegetables and crops as tomato (Caffagni et al., 2011; Landini et al., 2011), spinach (Smolen & Sady, 2012; Weng et al., 2013), barley and wheat (Caffagni et al., 2011), potato (Caffagni et al., 2011; Zanirato & Mayerle, 2009), cabbage, coriander, cucumber, eggplant, long cowpea, and hot pepper (Weng et al., 2013), carrot and onion (Zanirato & Mayerle 2009). Many common vegetables are consumed only cooked and iodine, being volatile, can be readily lost during food processing operations (Winger et al., 2008). The critical problem
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with iodine stability is the potential transformation to elemental iodine (I2) that readily sublimes at room temperature (Diosady et al., 2002). Several investigations carried out on the stability of iodine in iodized salt showed that, on one hand, iodine content significantly decreased during storage (Patel et al., 2012) and cooking procedures (Caffagni et al., 2012; Goindi et al., 1995; Longvah et al., 2012, 2013). On the other hand, the iodine stability in biofortified vegetables during cooking was only recently investigated (Caffagni et al., 2012; Comandini et al., 2013; Rana & Raghuvanshi, 2013). In particular, these studies concern the effect of boiling, baking, and pasteurization on iodine content in potatoes, tomatoes, and carrots. However, at the best of authors’ knowledge, there are no publications dealing with iodine stability and/or loss in recipes prepared with biofortified vegetable. Thus, the aim of this study is to evaluate the cooking effect on iodine content in three dishes: dumplings, vegetable pie, and focaccia bread, prepared with biofortified potatoes.
Methods Chemicals Tetramethylammonium hydroxide (TMAH, 1 M) solution was bought from Sigma Aldrich (St. Louis, MO). All the solvents used were of high purity grade, and ion exchanged water (18 M ) was generated by a Millipore Direct Q5 system (Millipore Co., Bedford, MA). Samples Potatoes (Cupido variety) and carrots (Maestro variety) were kindly donated by Pizzoli S.p.A. (Budrio, Italy). Iodine potatoes were obtained by a patented procedure (Zanirato & Mayerle, 2009) of agronomic biofortification through foliar fertilization. The other ingredients used for the dishes preparation were purchased in a local market. Dishes preparation Three dishes containing potatoes as the main ingredient were selected for this study, taking into account a balanced nutritional intake. The dishes and their preparation are reported below. Dumplings: 500 g of mashed potato were kneaded with 200 g of wheat flour, 60 g of boiled and mashed carrots, 35 g of egg, and 6 g of salt. Dumplings were manually formed and were boiled in tap water for 3 min. Forty grams of olive oil were mixed with 20 g of hard grated cheese and 3 g of sage leave and the mixture obtained was added to dumpling as seasoning. Vegetable pie: 100 g carrots were cut in long slices and were boiled in tap water for 20 min. A bakery mould was covered with blanched carrot slices and filled with a mash thus obtained: 670 g of mashed potato, 200 g of peas, 115 g of egg, 100 g of milk, 80 g of ham, 60 g of hard grated cheese, 2 g of salt, and 1 g of pepper. Twenty grams of olive oil were added on the surface and the vegetable pie was baked in an oven set at 180 C for 30 min. Focaccia bread: 550 g of mashed potato were kneaded with 770 g of wheat flour, 250 g of tap water, 30 g of olive oil, 25 g of brewer’s yeast, 5 g of sugar, and 1 g salt. The dough was spread out on a baking tray and was kept rising for 2 h. Thereafter, 150 g of small tomatoes, 10 g of olive oil, 2 g of oregano, and 1 g of salt were spread on the surface of raw focaccia bread. Focaccia bread was baked in an oven set at 200 C for 20 min. Sampling for iodine and composition analyses The iodine analysis has been carried out on raw potatoes, boiled potatoes, raw, and cooked dishes. Raw potatoes were
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homogenized with a mixer and stored at 20 C until iodine determination. Boiled potatoes were cooked in tap water for 30 min, peeled, and mashed. The mashed sample was also used for the preparation of dishes. Iodine was determined in raw and cooked dishes, after homogenization of a serving of about 150 g. In particular, dumplings were analyzed before and after boiling, vegetable pie, and focaccia bread were analysed before and after baking. Composition analyses (moisture, ash, fat and fatty acid composition, protein, carbohydrate and sugar content, energy) have been performed on cooked dishes after homogenization of a serving of about 150 g. Samples were stored at 20 C until iodine and composition analyses. Iodine determination Iodine was extracted by an alkaline procedure with TMAH assisted by a mineralization in microwave oven (Mars Express 5, CEM srl, Cologno al Serio, Italy). After extraction, the sample was diluted with ultrapure water, centrifuged, and filtered following the method used by Comandini et al. (2013). The measurements were carried out with an inductively coupled plasma mass spectrometer (ICP-MS) (Agilent, Palo Alto, CA). RF power used was 1550 W, argon flow rates were 1.05 l/min and 0.2 l/min, respectively, for carrier gas and make up gas. Instrument calibration was performed by employing iodine standards of up to a concentration of 100 mg/l in dilute TMAH solutions. The iodine content was expressed as mg/100 g on wet cooked weight (WCW) and as mg/100 g on wet raw weight (WRW) in potatoes and dishes, as specified in the Results section. Composition analyses Dry matter was determined by oven drying for 3 h at 105 C (AOAC 930.15, 1990). Water content was calculated from the following expression: Water content ðg=100 gÞ ¼ 100 dry matter ðg=100 gÞ Ash content was determined with a muffle furnace set at 550 C (AOAC 923.03, 2000). Fat content was determined by Soxhlet extraction (6 h) using dyethilether as a solvent (AOAC 920.39a, 1990). Determination of fatty acid composition was realized by saponification and methil-esterification on fat samples previously extracted (UNI EN ISO 12966-2:2011). Then, fatty acid methylesters were analysed by gas chromatography (Agilent 6890 series II gas chromatograph, Agilent Technologies, Palo Alto, CA) using a SP 2560 fused-silica capillary column (100 m 0.25 m, 0.2 mm film thickness; Supelco Inc., Bellefonte, PA) (UNI EN ISO 5508:1998). The amount of sample proteins was determined from the nitrogen content (N 6.25), using the Kjeldhal method (AOAC 968.06). Fibre content was analysed by a gravimetric method, after enzymatic digestion (AOAC 962.09, 2000). The total carbohydrates content was calculated by the following formula (Chen et al., 2013): Carbohydrates ðg=100 gÞ ¼ 100 water ðg=100 gÞ protein ðg=100 gÞ ash ðg=100 gÞ fat ðg=100 gÞ fibre ðg=100 gÞ Sugars were determined by HPLC-RID (Agilent 1100 series HPLC system, Agilent Technologies, Palo Alto, CA) on a NH2 column (Aminex HPX-87H ion exchange column, 300 mm 7.78 mm), as reported by Eye´ghe´-Bickong et al. (2012).
Evaluation of iodine content and stability in recipes
DOI: 10.3109/09637486.2014.917155
The nutritional profile of the three preparations was reported on WCW referred to one adult portion size for the Italian population (Turconi & Roggi, 2007). The macronutrient content of fat, saturated fat, carbohydrate, sugar, and protein was reported as % of energy contribution. Sodium and water content was reported as grams per portion size. The fibre content was reported both as % of energy contribution and grams. Finally, the iodine content was reported as mg per portion size. Energy content of dishes Energy of dishes is calculated by the following expressions (EU, 2011): Energy ðkcal=100 gÞ
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¼ protein ðg=100 gÞ 4 þ fat ðg=100 gÞ 9 þ carbohydrates ðg=100 gÞ 4 þ fibre ðg=100 gÞ 2 Energy ðkJ=100 gÞ ¼ protein ðg=100 gÞ 17 þ fat ðg=100 gÞ 37 þ carbohydrates ðg=100 gÞ 17 þ fibre ðg=100 gÞ 8 Statistical analysis Food preparations and analytical determinations were repeated three times. All the statistical analyses were performed with Statistica 7.0 software (Statsoft Inc, Tulsa, OK). The effect of cooking on iodine content was evaluated with a paired t-test (p50.05) while the statistical differences for iodine content on the three dishes were evaluated with a one-way ANOVA followed by a Tukey test (p50.05).
Results Iodine analysis Iodine content of each ingredient used in the preparation of dishes was analysed and reported in Table 1. Ingredients with the highest iodine content were hard cheese (232.0 mg/100 g), biofortified potatoes (76.1 mg/100 g), eggs (30.4 mg/100 g), milk (19.7 mg/100 g), and wheat flour (16.0 mg/100 g). Taking into account the amount of ingredients in each dish, biofortified potatoes were the main sources of iodine, accounting for 81.0% of total iodine contribution in dumplings, 72.6% in vegetable pie, and 76.9% in focaccia bread. Hard cheese had the highest iodine value (232.0 mg/100 g) but its contribution to the total iodine content of each dish was reduced due to the low amount used in each recipe (2.3% and 4.3% in dumplings and vegetable pie, respectively). Ham, peas, and carrots had low iodine levels (0.2–3.3 mg/100 g). Iodine content in all the other ingredients was not detectable under the analytical conditions used. As reported in Table 2, iodine content was evaluated in potatoes and dishes before (raw) and after cooking (cooked). To avoid differences due to the moisture content as a result of cooking, all samples were weighted before and after cooking, and iodine values were reported as mg/100 g on WCW and as mg/100 g on WRW (McKillop et al., 2002). Weight loss (WL) detected during the different cooking process ranged between 0.3% and 12.5% (Table 2). In potatoes, no significant differences in the iodine content were detected before and after boiling. Cooking process of dumplings and vegetable pie caused a significant loss of iodine equal to 27.5% and 55.3%, respectively. In focaccia bread, no significant differences were detected before and after cooking.
Table 1. Iodine content in ingredients and contribution to raw dishesa.
Dish
Ingredient
Ingredient amount (%)
Iodine in single ingredient (mg/100 g WRW)
Iodine contribution in raw dishes (%)
Dumplings
Potatoes Hard cheese Wheat flour Eggs Carrots Olive oil Salt Sage leaves
57.9 2.3 23.3 4.1 7.0 4.4 0.7 0.3
76.1 ± 7.7 232.0 ± 12.2 16.0 ± 2.7 30.4 ± 3.1 0.22 ± 0.02 n.d. n.d. n.d.
81.0 10.0 6.9 2.2 0.0 – – –
Vegetable pie
Potatoes Hard cheese Eggs Milk Ham Peas Carrots Salt Pepper Olive oil
49.5 4.3 8.5 7.5 6.0 14.8 7.5 0.1 0.1 1.6
76.1 ± 7.7 232.0 ± 12.2 30.4 ± 3.1 19.7 ± 4.2 3.3 ± 1.1 0.8 ± 0.5 0.22 ± 0.02 n.d. n.d. n.d.
72.6 19.0 5.0 2.8 0.4 0.2 0.0 – – –
Focaccia bread
Potatoes Wheat flour Water Tomatoes Olive oil Brewer’s yeast Sugar Salt Oregano
30.7 42.9 13.9 8.4 2.3 1.4 0.3 0.1 0.1
76.1 ± 7.7 16.0 ± 2.7 n.d. n.d. n.d. n.d. n.d. n.d. n.d.
76.9 23.1 – – – – – – –
a
799
Values are mean ± SD of three measurements. WRW, wet raw weight; n.d., not detectable, under limit of detection.
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Table 2. Iodine content of potato and dishes before and after cooking processa. Iodine content Raw (mg/100 g WRW) Potatoes Dumplings Vegetable pie Focaccia bread
aA
76.1 ± 7.7 54.3 ± 2.3aB 69.5 ± 0.6aAB 31.9 ± 3.1aC
Cooked (mg/100 g WCW) aA
96.4 ± 5.9 39.5 ± 4.0bB 35.5 ± 3.6bB 33.3 ± 3.3aB
Cooked (mg/100 g WRW) aA
94.9 ± 5.8 39.4 ± 3.9bB 31.1 ± 2.9bB 29.8 ± 2.7aB
WL (%) 1.6 0.3 12.5 10.4
a
Values are mean ± SD of three measurements. Means with different letter on the same row (a, b) are significantly different; means with different letter on the same column (A, B, C) are significantly different (one-way ANOVA, Tukey test, p50.05). WL, weight loss; WRW, wet raw weight; WCW, wet cooked weight.
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Table 3. Nutritional composition of cooked dishes related to one adult portion size (Turconi & Roggi, 2007).
Portion size (g) Energy (kcal) Energy (kJ) Water (g) Fat (E%)a – Saturated (E%)a Carbohydrate (E%)a – Sugars (E%)a Protein (E%)a Fibre (E%)* (g) Sodium (g) Iodine (mg)
RDIb
Dumplings
Vegetable pie
Focaccia bread
– 2000 8368 – 31.5 9 52 18 10 – 2.4 150.0
200 329 1384 128 26 6 59 12 12 3 (4.2) 0.4 79.0
165 198 829 120 37 14 36 5 22 5 (5.0) 0.4 58.6
150 316 1335 74 16 3 70 7 11 4 (5.6) 0.1 50.0
a
E%: % of energy contribution compared with 100% of portion size. RDI, Reference Daily Intake of a 2000 calories diet (EU Reg., 2011).
b
Composition analysis The nutritional composition of cooked dishes is reported in Table 3. The values were related to one adult portion size of WCW. The biggest differences were related to water, fat, and carbohydrate content. One portion of focaccia bread contained less water (74 g) than dumpling and vegetable pie (128 g and 120 g, respectively). Energy from saturated fat was higher for vegetable pie (14%) with respect to dumpling (6%) and focaccia bread (3%). Finally, dumpling and focaccia bread contained, respectively, 59% and 70% of energy from carbohydrate, compared with 36% in vegetable pie. The sodium content in the three dishes was low and ranged between 0.1 g and 0.4 g. In relation to iodine content, one portion of dumpling had the highest quantity of iodine (79.0 mg) followed by one portion of vegetable pie (58.6 mg) and one portion of focaccia bread (50.0 mg).
Discussion Iodine analysis The iodine amount of each ingredient used in the preparation of dishes was analysed in order to better understand the sources of iodine in raw dishes (Table 1). In regular raw potatoes, iodine content usually ranges between 0.1 and 0.3 mg/100 g (Comandini et al., 2013; Haldimann et al., 2005). Thanks to the biofortification procedure used in this investigation (Zanirato & Mayerle, 2009), potatoes of the Cupido variety had an iodine level of 76.1 mg/100 g. The results of iodine content for the other ingredients were in agreement with those reported in the literature (Bhagat et al., 2009; Haldimann et al., 2005; Longvah et al., 2013;
Wenlock et al., 1982). In particular, an iodine level of about 20 mg/100 g was previously found in milk by Bhagat et al. (2009) and Longvah et al. (2013). Regarding eggs, the iodine amount detected in this investigation (30.4 mg/100 g) was in line with the results of Haldimann et al. (2005) that verified that iodine was located principally in yolk. Finally, an iodine level of about 10 mg/100 g was reported in wheat flour by Wenlock et al. (1982). The hard cheese used in the preparation of vegetable pie and dumplings was an industrial grated cheese. The high content of iodine detected (232.0 mg/100 g) was probably due to the high amount of milk used for the production of hard cheese. In the preparation of dishes, rock salt was used. Its iodine content was not detectable by ICP-MS. This kind of salt was chosen to avoid the contribution of sea salt or iodized salt on the total content of iodine of the dishes and to better focus the investigation on biofortified vegetable. Moreover, the stability of iodine during storage and cooking processing of sea and iodized salt was largely discussed in previous investigations (Chavasit et al., 2002; Longvah et al., 2012; Patel et al., 2012; Rana & Raghuvanshi, 2013). The first step in the preparation of each dish involved boiling of whole, unpeeled potatoes to obtain cooked mashed potato. So, the first investigated aspect was the effect of boiling on the iodine content of biofortified potatoes. Results showed that boiling of whole potatoes had no effect on iodine content confirming previous results by Comandini et al. (2013), describing the effect of boiling in several varieties of biofortified potato. The high capacity of retention of iodine content was probably due to the presence of starch, composed by amylose (Mottiar & Altosaar, 2011; Yu et al., 1996) and amylopectin fractions (Shen et al., 2013), that might be involved in iodine– starch complex formation. In addition, the presence of potato skin
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DOI: 10.3109/09637486.2014.917155
during boiling might have represented a physical barrier that limited the leaching of iodine into water. This barrier effect of potato skin has been previously reported by Barba et al. (2008) and by Ezekiel et al. (2013) for phenolic compounds that were better preserved during boiling of unpeeled potatoes in comparison with peeled tubers. However, owing to different chemical properties of iodine and phenolic compounds, further investigations are needed to support this hypothesis. Preparation of the first dish involved dumpling manual formation, with boiled mashed potatoes, followed by a second boiling step in tap water for 3 min. Iodine content of cooked dumplings was reduced of about 27.5% with respect to the raw mixture (39.4 versus 54.3 mg/100 g WRW). As previously discussed, boiling of whole potatoes did not cause an iodine loss, so the iodine reduction observed during dumpling preparation derived from a leakage of iodine into cooking water during the second boiling step, despite the boiling time, which was shorter for dumplings (3 min) than whole potatoes (30 min). The different stability of iodine between whole potato and dumpling boiling was probably due to the absence of a protective skin in dumplings that increased leakage of iodine, and to the small size of dumplings (about 4 g each) that increased the contact surface with boiling water. Similar results were obtained by Goindi et al. (1995) with average losses of 36.6 ± 14.8% in iodine content during boiling of six different Indian recipes, and by Longvah et al. (2012) with average losses of 47.2 ± 27.2% during boiling of nine Indian recipes prepared with the addition of iodized salt. During focaccia bread baking (200 C, 20 min), no significant iodine losses were detected. The high iodine stability in this dish might derive from its high starch content (Mottiar et al., 2011; Shen et al., 2013; Yu et al., 1996), due to potato and wheat flour. Vegetable pie showed the highest iodine loss (55.3%) during baking. Despite the cooking procedure was similar to that of focaccia bread, the high iodine loss might have been due to the absence of wheat flour and, therefore, to the lower starch content. Moreover, vegetable pie was cooked in small aluminum moulds that have increased the surface to volume ratio of the dish, causing a slight rise of WL, as compared with focaccia bread (12.5% versus 10.4%). The higher cooking time (30 min) compared with focaccia bread might also have enhanced the iodine loss in the vegetable pie. Despite the different iodine stabilities during preparation of dumplings, vegetable pie, and focaccia bread, the final iodine content after cooking was similar for all the dishes, and ranged between 33.3 and 39.5 mg/100 g WCW. Composition analysis The three preparations were chosen among the most consumed recipes containing potatoes in the Italian diet. To better understand the overall nutritional characteristics of the three preparations, energy, macronutrient profile and iodine content were standardized to one adult portion size (Turconi & Roggi, 2007) (Table 3). Vegetable pie was the highest in saturated fats due to its specific ingredients (egg, ham, and cheese) that, even if added in low quantity, contain high amounts of these fatty acids. The presence of wheat flour in dumpling and focaccia bread affected the carbohydrate content of these preparations.
Conclusions Although these recipes cannot be considered individually from a nutritional viewpoint and must be evaluated in the context of a well-balanced diet, they certainly represent a good strategy to increase iodine intake. For example, considering the dietary reference value for an adult population, one portion size of
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dumplings, vegetable pie, and focaccia bread, prepared with biofortified potatoes (Zanirato & Mayerle, 2009), can provide the 52.7%, 39.1%, and 33.3%, respectively, of the daily adequate intake of iodine, as recommended by WHO (2007), while keeping the intake of sodium very low. These data showed that the biofortified potatoes represent a good source of iodine, comparable with iodized salt, without increasing sodium intake in the diet. Nevertheless, only few recipes were tested and more investigations are necessary for better understand the mechanisms of the iodine stability, and the effects of different food components.
Acknowledgements The authors gratefully acknowledged Mr. Alberto Bini in performing part of the experiments and Mr Fabio Bianchini (Madegus Srl, Parma, Italy) for the assistance and the suggestions in preparing dishes.
Declaration of interest The authors declare that they have no conflict of interest. Vegetables were supplied free of charge with no obligation from the researchers to the manufacturers.
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