Tofu Test Reveals Vast Variations in Nutrient Contents – Protein & Calcium Differ by More than a Double & 25 Times

15 October 2018
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Tofu Test Reveals Vast Variations in Nutrient Contents –  Protein & Calcium Differ by More than a Double & 25 Times

Tofu (bean curd), long being regarded as a health food which is “low fat” and “high calcium”, is popular with many consumers (aside from vegetarians), who opt for tofu as a source of protein to cut down on their meat intake and live a low-carbon lifestyle.  The Consumer Council tested 40 models of tofu and found vast variations in their nutrient content, with levels of protein and 6 different minerals varying between 1.6 times to 25 times.  Furthermore, some of the nutrient labels of the prepackaged tofu samples were at variance with the test findings, with the discrepancy exceeding the tolerance limit of the Centre for Food Safety’s (CFS) Technical Guidance.   When making a purchase decision, consumers especially if they are vegetarians, are advised to carefully compare the nutrient contents on the product labels of the different products, to ensure that they have sufficient and balanced nutrition intake.  

Included in this test were 34 prepackaged and 6 non-prepackaged (plate tofu) totaling 40 models.  Of the prepackaged samples, 8 were hard tofu and 26 were soft tofu.  All samples were tested against required standards in Hong Kong, the Mainland, Taiwan, Japan and the United Nations CODEX Alimentarius Commission to evaluate their safety and nutrient content.

Protein

The main ingredients of tofu are water and soybeans.  Soybeans are rich in plant protein.  Test results show that all samples tested complied with CODEX requirements on protein, containing 3.5g/100g or more. However, significant differences in protein levels were observed among individual samples, with the highest protein level at 9.4g/100g and the lowest at 3.6g/100g, a difference of 1.6 times.

According to the Taiwan’s Standard for Packaged Soybean Curd (Tofu) (CNS12729), the protein content of hard and soft tofu should be more than 8% and 4.3% respectively.  Of the 34 prepackaged test samples, the protein content measured in hard tofu was on average 6.5%, which meant that only 2 out of 8 models complied with the standard while the protein content of 26 soft tofu was on average 5.9%, with only 4 models slightly below the standard; and the average protein content in 6 plate tofu samples was 5.5%.

According to the Centre for Food Safety’s Technical Guidance Notes on Nutrition Labelling and Nutrition Claims, foods containing not less than 6g protein per 100g food are classified as a “source of protein”, while those with not less than 12g in 100g are classified as “high in protein”.  Based on these standards, out of the 40 samples, only 17 (5 hard and 12 soft tofu) measured up to the “source of protein” standard.  But none of the samples reached the requirement of being “high in protein”. 

Vegetarians are generally reliant on tofu and other bean products as meat substitute for their source of protein.  The same is true for the health-conscious who may substitute eating some tofu in place of meat.  According to the recommendation of the Chinese Nutrition Society, an adult male requires a daily intake of 65g protein.  In the case of the sample containing the highest protein level, one needs to consume 700g i.e. 2.3 boxes of tofu to meet the recommended daily intake.  In contrast, for the sample containing the least protein, 1,900g of tofu will have to be consumed a day to meet the recommended daily intake, equivalent to 7 boxes (each 300g).

Minerals

The test also examined the content of 6 types of minerals, namely: calcium, phosphorous, magnesium, iron, zinc, and manganese.  Although tofu is generally believed to be “high-calcium”, the prepackaged samples were found to contain wide variation in the levels of calcium ranging from 16mg/100g to 420mg/100g, a significant discrepancy of 25 times.  In general, the plate tofu fared better than the prepackaged in calcium content, with an average of 122mg/100g, almost double the calcium content of the prepackaged samples.   This could be due to plate tofus being mostly made with calcium sulphate or edible Gypsum (which contains mainly calcium sulphate) as a firming agent.

According to the CFS Technical Guidance, only 4 models of tofu (1 hard, 2 soft and 1 plate) are classified as food containing “source of calcium” (not less than 120mg/100g), and 2 models (1 hard tofu and1 non-prepackaged tofu) as food which are “high in calcium” (not less than 240mg/100g).   As indicated in the ingredients list of the prepackaged tofu, samples with higher calcium content used calcium sulphate or edible Gypsum as the firming agent, which as mentioned above, both are rich in calcium.

For the other 5 minerals, the respective contents in the samples varied between 2 to 5 times, with 12 samples defined as a “source of phosphorous” (not less than 105mg/100g), 13 as a “source of magnesium” (not less than 45mg/100g), 17 as a “source of manganese” (not less than 0.5mg/100g), and 2 as “high in manganese” (not less than 0.9mg/100g).  As iron and zinc contents are generally low in tofu samples, consumers should supplement their daily intake with other foodstuffs such as dried fruit, nuts and green vegetables etc. 

Total Fat

Tofu is generally perceived to be “low-fat” but the test results indicated otherwise, with the total fat content of the samples measuring between 2g/100g to 6.5g/100g, a differential of more than 2 times.  Only 1 hard tofu, 9 soft tofu and 1 plate tofu samples reached the CFS “low-fat” standard, i.e. containing not more than 3g/100g.  Although over 70% of the samples were not “low-fat” food, the fat in tofu is mainly unsaturated fatty acids which can reduce the levels of bad cholesterol and total cholesterol in the body.

Nutrition Labeling

Furthermore, some of the nutrient labels of the prepackaged samples were at variance with the test findings.  Looking at the level of protein, for instance, the discrepancy in 3 of the samples exceeded the tolerance limit of the CFS Technical Guidance Notes on Nutrition Labelling and Nutrition Claims of 20%, with their declared values falling short of the actual measured values by 22%, 31% and 39% respectively.  The discrepancy in total fat content was even more acute, with 7 samples measuring higher than their declared values, ranging from 36% to 212%, far in excess of the CFS tolerance limit of 20%.

The samples in question have been referred to the CFS for follow-up. Some of the samples have also been taken off the shelves and sales discontinued.  Inaccurate nutrition information on product labeling could mislead consumers into purchasing products unsuitable for them, in particular for people suffering from chronic illnesses, for instance, diabetes or osteoporosis.  Manufacturers and agents are strongly urged to provide accurate information for the reference of consumers.

For the tests on food safety, all samples were found to be satisfactory with a clean bill of health for heavy metals and preservatives tests.  Only 2 non-prepackaged samples were detected with trace amounts of lead (0.01 and 0.02ppm), which were far below the maximum permitted concentration (6ppm) prescribed by the Food Adulteration (Metallic Contamination) Regulations.  All samples were also found free of arsenic, mercury, tin and 8 types of commonly used preservatives. 

Consumers consuming tofu are advised to pay heed the following:

- People who are allergic to soy should avoid consuming tofu;

- Due to the high content of purine in tofu, people suffering from gout should pay attention to the amount of tofu they consume and should avoid consuming other foods “high in purine” such as mushrooms, fish and internal organs at the same time;

- It is said that tofu cannot be eaten together with spinach at the same time. As tofu and spinach contain calcium and oxalic acid respectively, the combination of the two will form kidney stones. But in fact, only prolonged and volumionous consumption of tofu and spinach at the same time will pose this risk. People who have suffered or are suffering from kidney stones should eat tofu and spinach separately to avoid the recurrence of kidney stones;

- There are studies which show that phytoestrogens in soybeans may interfere with the effectiveness of breast cancer drugs. Therefore, people with breast cancer who are undergoing treatment should consult their doctors and dietitians before eating tofu.

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