Supplementary material 1

Questionnaire about Curry, Stew, and Niku-jaga

Our laboratory is studying compounds formed by heat reactions of carbohydrate and amino acids in foods. We are now going to survey about custom of stir-frying potato and onion prior to boiling during cooking of curry, stew, and Niku-jaga, which are popular simmered dishes in Japan. We would appreciate it if you could answer our questionnaire.

Q1. Do you stir-fry potato and onion prior to boiling during cooking of curry at home? A1. Yes, I (we) stir-fry potato. A2. No, I (we) do not stir-fry potato. A3. I (We) do not use potato for curry in my home. A4. Yes, I (we) stir-fry onion. A5. No, I (we) do not stir-fry onion. A6. I (We) do not use onion for curry in my home. A7. I (We) do not cook curry at home.

Q2. Do you stir-fry potato and onion prior to boiling during cooking of stew at home? A1. Yes, I (we) stir-fry potato. A2. No, I (we) do not stir-fry potato. A3. I (We) do not use potato for stew in my home. A4. Yes, I (we) stir-fry onion. A5. No, I (we) do not stir-fry onion. A6. I (We) do not use onion for stew in my home. A7. I (We) do not cook stew at home.

Q3. Do you stir-fry potato and onion prior to boiling during cooking of Niku-jaga at home? A1. Yes, I (we) stir-fry potato. A2. No, I (we) do not stir-fry potato. A3. Yes, I (we) stir-fry onion. A4. No, I (we) do not stir-fry onion. A5. I (We) do not use onion for Niku-jaga in my home. A6. I (We) do not cook Niku-jaga at home.

Q4. Answer age/sex/location of you and /or your family member(s) who usually cook curry, stew, and Niku-jaga at home. If you are living alone and cook at home, answer your age/sex/location. Age: Sex: Location:

Q5. If you or your family member(s) stir-fry potato and/or onion for at least one of the three simmered dishes above, we would like to ask you or your family member(s) for cooperation to our cooking survey. We would ask you or your family member(s) to cut and stir-fry potato and onion with other vegetables and meat in usual way for cooking of curry, stew, or Niku-jaga. We would ask you to send the stir-fried potato and onion to our laboratory for component analysis. We wish to have cooperation of wide range of age/sex/location. We will pay cost of food stuffs (including meat and vegetables used in addition to potato and onion) and recompense. Can you cooperate to our survey cooking? A1. Yes. A2. No. A3. I am not sure.

If you answer A1. Yes or A3. I am not sure in Q5, we may contact you later. Please write your name and affiliation below. Name: Affiliation

We do not use the personal information in your answer other than the purpose of this study.

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Supplementary material 2

Instructions for Preparation of Potato and Onion Samples for Survey (Case of Curry Cooking)

The purpose of this survey is to know changes of potato and onion during stir-frying prior to boiling for cooking of simmered dishes at home. Please prepare potato and onion samples following the instructions below.

1. Cut all foodstuffs for curry as usual way of your home cooking.

2. Take photos of potato and onion pieces. Write you name on Photo Sheet supplied with this instruction sheet. Cover gray area of Photo Sheet with plastic kitchen wrap, and put potato pieces on it. Take a photo of potato pieces with color checkers of Photo Sheet, at least one of which must be uncovered with plastic kitchen wrap and potato. Potato can run off the edge of Photo Sheet. Take a photo of onion pieces as the case of potato. You must use original Photo Sheet. Do not use photocopy of it.

3. Stir-fry foodstuffs for curry in usual way using a pan and a heat source which you usually use at home. (Although targets of this survey are potato and onion, you should stir-fry them with other foodstuffs to realize your usual home cooking condition.)

4. When you finish stir-frying take out all potato and onion from the pan prior to add water for boiling. Take photos of stir-fried potato and onion pieces as written at 2. of this instruction sheet.

5. Write your name and date on plastic bags for potato and onion with your cook number supplied with this instruction sheet. Put stir-fried potato and onion in the bags and send them by cash on delivery refrigerated courier service to our laboratory. If the bags are too small for your sample, you can use any plastic bags of appropriate size marking you cook number, name and date. If you store the samples more than one day, freeze and send them by frozen delivery.

6. Fill the questionnaire sheet, and send with the stir-fried samples.

7. Enclose receipts of foodstuffs of this survey cooking with the stir-fried samples.

8. After sampling of potato and onion, you can use residual stir-fried foodstuffs for your home cooking.

9. Send photos of potato and onion by E-mail.

Thank you very much for your cooperation.

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Supplementary material 3

Questionnaire to Cooperators of Survey Cooking

Cook number: (Cooker number is supplied to each collaborator by laboratory.)

Please fill the tables below and describe your cooking condition. If you are not sure, answer “not sure.”

Foodstuffs Place of Production Cultivar Storage condition at home purchase area Example: before cooking Example: Seiyu Example: Danshaku (refrigeration or room Store, Chofu Hokkaido temperature, duration) City, Tokyo Example: 7 days in refrigerator) Potato Onion Please supply information about foodstuffs stir-fried with potato and onion below.

Cooking condition Serves: Cooking pan: Example: Stainless-steel stew pan, 20 cm; Pressure cooker, 30 cm Type and quantity of oil for stir-frying: Example: Butter; Margarine; Corn oil; Canola oil, 1 table spoon Quantity Size of pieces Stir-frying condition Example: 400 g (4 Example: Cut into 8 Example: 3 min over tubers) equal parts, comb- medium heat shaped Potato Onion Please supply information about foodstuffs stir-fried with potato and onion below.

Cooperator (Person who cooked the samples) Age: Sex: male, female Location:

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