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Frozen Peas Higher in Vitamin C, β-carotene and Dietary Fibre Content Than Sweet Corn Pay Heed to Cooking and Storage Methods and Time to Avoid Nutrient Loss

  • 2023.09.14

Prepackaged frozen sweet corn and peas are indispensable “reserve” foodstuffs for many families, as they are convenient garnishes while also enriching the nutritional value of dishes. The Consumer Council tested 24 samples of prepackaged frozen sweet corn and peas commonly available on the market. Most were found to be rich in dietary fibre, vitamin C and β-carotene, while the average vitamin C and β-carotene contents of the pea samples were significantly higher than that of sweet corn. However, consumers should be aware that the longer the cooking and storage time, the more vitamin C would be lost. In addition, some samples were detected with traces of metallic contaminants but did not exceed the limits set by relevant Hong Kong regulations.

Between November and December last year, the Council sourced 24 samples of prepackaged frozen sweet corn and peas on the market, of which 10 were sweet corn kernels and 14 were peas. The retail price per 100g of the sweet corn samples ranged from $2.3 to $20, with an over 7-fold difference between the highest and the lowest priced samples, while overall ratings were 4 and 3.5 respectively. As for the green pea samples, the price per 100g ranged from $4.4 to $15.1, with a price difference of over 2 times, but the highest and the lowest priced samples both had an overall rating of 5, reflecting that quality of products may not be directly proportional to the price.

Peas Rich in Vitamin C

Avoid Loss by Minding Cooking Method and Time

Vitamin C is essential for the body to absorb iron and to strengthen joints. 10 pea samples were found to be “source of vitamin C” foods (i.e. containing not less than 15mg per 100g of solid food). Based on the content per 100g sample, the vitamin C content of the pea samples ranged from 7.9mg to 21mg. Consumption of 1 serving (80g) of the pea sample with the highest vitamin C content would provide an intake equivalent to 37.3% of the World Health Organization’s (WHO) recommended daily intake for adults and the elderly. For sweet corn, the average vitamin C content was lower than that of the pea samples, with 2 not detected with vitamin C at all, while the sample with the highest vitamin C content was only found with 6.5mg per 100g.

As vitamin C is highly soluble in water and unstable under heat, light, oxygen and in alkaline environments, consumers should pay attention to not only the temperature and duration of storage, but also the method and time of cooking in order to retain vitamin C in the food. Taking fresh peas as an example, the amount of vitamin C (43.44mg) contained in each 100ml of fresh pea juice would be reduced by almost half to 28.96mg after cooking at 60°C for 15 minutes. Furthermore, as vitamin C is water-soluble, stir-frying instead of blanching could retain more vitamin C. However, it should be noted that stir-frying generally uses more oil than blanching, resulting in a higher fat content. In addition, even if frozen food products were purchased as reserve food, they should be consumed as soon as possible because even though storage at low temperatures could help preserve vitamin C, it would still naturally diminish over time.

Pea Samples Contained More β-carotene than Sweet Corn

Also Rich in Dietary Fibre

β-carotene can be converted into vitamin A in the human body, which helps to maintain the normal functioning of the optic system, integrity of epithelial cells, immune and reproductive functions. Vitamin A is a fat-soluble vitamin, insoluble in water, but is unstable in the presence of heat, light, oxygen and in acidic environments. All pea samples also contained significantly more β-carotene than the sweet corn samples. Based on per 100g sample, the β-carotene content of the pea samples ranged from 233μg to 362μg, while that of the sweet corn samples ranged from 23.5μg to 50.5μg, an over 6-fold difference when comparing the sample with the highest β-carotene content from each type. Taking the pea and sweet corn samples with the highest β-carotene content respectively, each serving (80g) would provide a β-carotene intake of 290μg and 40.4μg respectively. When converted to vitamin A, this would be equal to 48μg of retinol equivalent and 6.7μg of retinol equivalent respectively, which accounted for 8.0% and 1.1% of the recommended daily intake for adult males.

Dietary fibre could promote gastrointestinal health, and the average dietary fibre content of pea samples was found to be higher than that of sweet corn samples. For each 100g sample, the total dietary fibre content of sweet corn ranged from 2.13g to 4.81g, whereas that of peas ranged from 4.76g to 8.42g, a difference of about 75% between the 2 samples with the highest content. Foods containing not less than 6g of dietary fibre per 100g of solid food can be classified as “high in dietary fibre”, whereas foods containing not less than 3g of dietary fibre per 100g of solid food can be regarded as a “source of dietary fibre”. 9 pea samples could be classified as “high in dietary fibre” and 5 could be classified as a “source of dietary fibre”, while 6 samples of sweet corn could be classified as a “source of dietary fibre”.

Some Samples Found with Trace Metallic Contaminants Within Limits

Among the 24 samples, 17 were detected with trace levels of metallic contaminants such as lead, cadmium, or chromium, of which 4 were sweet corn samples and 13 were pea samples. Among them, 1 sweet corn sample was found to contain all 3 metallic contaminants mentioned above. All samples did not exceed limits set out in relevant local regulations.



Most Samples Did Not Contain Sodium

1 Sample Showed Significant Discrepancy Between Labelled and Actual Sodium Content

In the test for sodium, 20 samples were not found with any sodium at all, while the remaining 4 contained 4mg to 13.4mg of sodium per 100g. Among them, the actual sodium content of 1 sample was 95% higher than the value shown on its nutrition label. In addition, the sodium content on the nutrition label of certain samples was ambiguous, labelled as “salt content” without providing an actual value. The relevant information has been passed to the Centre for Food Safety for follow-up. Inaccurate or unclear nutrition labels may mislead consumers into purchasing unsuitable products, especially those with chronic illnesses such as high blood pressure. The Council urges manufacturers and agents to address the problem and improve promptly.

Frozen peas and sweet corn, though milder in flavour, are rich in nutrients and are good choices as complimentary ingredients. Some tips for consumers when cooking and consuming them:

  • Sweet corn and peas can be used in a variety of dishes, and can be combined with other fruits and vegetables for achieving a balanced diet;
  • Peas and sweet corn are low in sodium and milder in flavour. When cooking, consumers should refrain from adding excessive salt and sauces. Instead, consider using natural seasonings such as herbs to reduce sodium intake, so as to avoid increasing the risks of hypertension, stroke, and coronary heart disease;
  • When buying prepackaged peas or sweet corn, read the nutrition labels and try to choose products with lower sodium, sugar and fat content, or without any added sugar or salt.


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