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Fresh V's Frozen V's Tinned

Wednesday, 18 November 2009

Today Paula takes a look at some of the staples in our kitchens and compares fresh v's frozen v's tinned. Paula will break down the nutritional value of each item and tell us what she thinks is best. We take a look at peas, sweet corn, orange juice, tuna and strawberries.

Nutritionist Paula Mee

BSc., Dip Dietetics., MSc in Health Sciences., Dip Allergy, M.I.N.D.I.

From Galway, Paula graduated from University College Galway with a BSc in Biochemistry. She then completed her postgraduate qualifications in Dietetics and a Masters in Health Science in Leeds Metropolitan University.

Paula has recently been awarded a Diploma in Allergy from Southampton University. She has also completed the British Dietetic Association's Sports Dietitian course. She is a current member and a past president of the Irish Nutrition and Dietetic Institute.

Paula Mee, Nutrition Consulting was set up in 2004 and offers organisations an extensive range of services in nutrition, product development, and marketing communications.

As part of her working week she also operates a dietetic and weight management clinic.

Paula was one of the presenters of RTE TV's Health Squad programme which ran from 2002 to 2006. Paula is the author of Good Food, Great Life 2008 and a co-author of the Health Squad Guide to Health and Fitness 2005. Her website is www.paulamee.com

Fresh, frozen or tinned: A balancing act

According to a nutritional comparison of fresh, frozen and tinned vegetables carried out in 2007, by the time vegetables are consumed; fresh, frozen, and tinned versions may have similar nutritional values1. Frozen is picked and frozen within hours, whereas fresh fruit and vegetables is often placed in the shipping container and shipped across the world to the supermarket warehouse, then to the supermarket back room, the supermarket shelf, and finally to the consumer's fridge.

While nutrients like vitamin A, minerals, and fibre are stable, others, like vitamin C, react with oxygen after the vegetable is picked and change chemically so that they no longer function the same way in our bodies. This is called oxidative degradation.

The major frozen food companies claim that the majority of their vegetables are harvested, cleaned, cut, and frozen within hours.

This cuts down on nutrient loss due to short-term storage. But because the vegetables are usually blanched before the flash-freezing process, certain heat-sensitive nutrients, such as thiamin, can decrease. Long-term storage of frozen vegetables (6 to 12 months) can further diminish vitamin C because the vegetables are still exposed to oxygen, even in the freezer.

Overall, the comparison in the study above showed losses of vitamin C due to the entire freezing process ranging from 10 to 80 percent, with averages around 50 percent.

When foods are canned, they are exposed to a lot of heat. When foods are frozen, they are exposed to a short burst of heat and then cooled. When it comes to fresh, they aren't heated at all (although they may be chilled) until they are cooked at home by the consumer.

When food is heated (and this includes cooking it), as in canning, the bacteria and enzymes that contribute to spoiling or decay are destroyed or at least slowed down. Freezing food does the same thing. These actions decrease the levels of some nutrients, but in rare instances, also simultaneously increase the levels of others. Tomatoes, for example, are one exception. When tomatoes are heated or cooked, levels of lycopene are increased (an antioxidant) but in the process some vitamin C is lost.

Processing also stops moisture loss and interaction with oxygen but canning can involve adding additional ingredients like sodium, sugar and water that may affect nutrient levels.

Another factor in the overall equation is when the product is harvested. Fresh produce is typically picked before it's ripe, so unlike frozen or tinned products, it often doesn't come with a full load of nutrients from the beginning. What nutrients the produce does have will start to diminish over time. Even if it looks fresh, a premium appearance can be deceiving. Generally, freezing and canning slow nutrient loss.

So it's all about balancing act. Any fruits and vegetables are better than no fruits and vegetables. Tinned and frozen food might be somewhat depleted during processing, but once that initial loss is over, they can start to make gains on fresh food. This means that a 6-month-old tin sitting on the shelf could be healthier for you than its fresh counterpart over in the fruit and vegetable aisle, languishing for weeks waiting to catch a customer's eye.

For peak flavour and good value, fresh fruit and vegetables in season are always a good choice. So try to choose fresh as often as possible, keep frozen veg in the freezer for emergencies and only choose tinned foods that are low in or free from added salt and sugar.

1. Rickman et al. J Sci Food Agric 87:930-944 (2007)


Advantages of fresh food

More attractive appearance
Better taste & texture
Greater choice


Disadvantages of fresh food

By the time most fresh fruits and vegetables get to the shop or supermarket, they've been in transit for up to two weeks, stored in trucks, or even flying in from another part of the world. Then, they sit in the supermarket, losing nutritional value as they wait to be purchased. Once bought, there is another wait before they are consumed, sitting in the fruit bowl on the kitchen counter, or in the vegetable drawer in the fridge.

Advantages of tinned food

Tinned foods are stored easily
The packaging can be recycled
Fruit & vegetables are tinned soon after being picked
Longer shelf-life
More economical in the case of tinned fish versus fresh/frozen fish

Disadvantages of tinned food

Nutrients are lost during the canning process, especially vitamin C and potassium
Salt or sugar are often added to the food to preserve it
Taste and texture not always as good as fresh

Advantages of frozen food

Useful for keeping unseasonal fruit & veg handy e.g. berries in Winter for adding to smoothies

Often more economical than buying fresh versions

Disadvantages of frozen food

Texture not as good as fresh fruit and vegetables due to ice crystals that often form on the surface of the food and within the food itself

Natural, nutrient-rich juices may escape while thawing.

Fresh, frozen or tinned?

Peas


Food (per 100g)

Calories
kcal
Fibre
g
Salt
g
Other vits/mins

Fresh peas (raw)

83
4.7
0 24mg vitamin C
330mg potassium

Frozen peas (raw)

66
5.1
0 17mg vitamin C
190mg potassium

Tinned peas

80
5.1
0.6 1mg vitamin C
130mg potassium

Fresh is best in terms of peas.
Fresh, frozen and tinned have pretty similar calorie and fibre levels. 100g of fresh peas have 17 more calories than frozen, and a little less fibre (0.4g). Salt is slightly higher in the tinned as you would imagine. In terms of vitamins and minerals like vitamin C and potassium fresh is best. Fresh has nearly three times the vitamin C content and 24 times the vitamin C content.

Vitamin C is an important antioxidant vitamin, protecting against infection by enabling white blood cells to break down bacteria. It is essential for the formation of collagen. It's necessary for growth, tissue repair and wound healing.

Potassium is involved in controlling the amount of water and maintening the correct acid-alkali balance in the body. It's important in helping us to control our blood pressure.


Sweetcorn


Food (per 100g)

Calories
kal
Fibre
g
Salt
g
Other vits/mins

Fresh sweetcorn

93
1.5
0 8mg vitamin C
97ug carotene
260mg potassium

Frozen sweetcorn (on the cob)

24
2.0
0.1 39mg vitamin C
140ug carotene
170mg potassium

Tinned sweetcorn

122
1.4
0.7 1mg vitamin C
110ug carotene
220mg potassium

Frozen is best here.
There's an interesting calorific difference seen here between fresh and frozen. Fibre is also highest in the frozen sweetcorn. There is no significant difference in the salt values for fresh and frozen.

The levels of vitamin C and carotene (vitamin A) are better in frozen too. Fresh and tinned have more potassium but all in all frozen comes out best from this nutrition profile above.

Carotene plays an essential role in vision (especially night vision), normal bone growth, reproduction and the health of mucous membranes.


Orange Juice


Food (per 100g)

Calories
kcal
Fibre
g
Salt
g
Other vits/mins

Freshly squeezed OJ


33
0
0.05
48mg Vitamin C
28ug Folate

Tinned OJ


36
0
0.25 39 mg Vitamin C
18ug Folate

Fresh is best here too.
Both have similar calories. Neither have any significant fibre to offer so that's why its always include the whole fruit as often as possible. Fresh has 5 times less salt but neither are significant sources of salt in the diet. A glass of tinned (200ml) will provide a twelfth of the target 6g salt per day for an adult.

Fresh is significantly higher in vitamin C and folate. However a glass of tinned orange juice (200ml) will provide close to the RDA of 80mg of vitamin C per day.

Folate plays a vital role in making DNA (the substance that makes up our genes). It works with vitamin B12 to form haemoglobin for red blood cells.

Tuna


Food (per 100g)

Calories
Fat
Saturates
Salt
Other vits/mins

Fresh tuna

136
4.6
1.2
0.2
7.2 ug Vitamin D (raw)

Tinned tuna in brine

99
0.6
0.2
0.8
3.6ug Vitamin D

Tinned tuna in oil


189
9.0
1.5
0.7
3ug Vitamin D

All three options are good sources of protein, but I would say fresh is best here too.

Some of the omega 3 fats are lost in processing.

Interesting that tinned in brine has considerably less calories per 100g.

The fat content is much lower in tinned in brine and that probably explains the lower calorie content. Brine is salty water so that's why the salt will be higher in the tinned brine option, even after draining, than the fresh.

Tinned in brine does seem much better lower in saturated fat however neither are significant sources of saturated fat.

The reason we eat fish is to ensure we get protein and the fresh option will mean that we get our protein and more omega 3 essential fats than the other options - with less salt too.

Vitamin D is essential for the absorption and use of calcium and phosphorus.


Strawberries


Food (per 100g)

Calories
Sugars
Fibre
Other vits/mins

Fresh strawberries

27
6.0
1.1 77mg vitamin C
20ug folate
160mg potassium


Frozen strawberries

33
7.8
1.2 48mg vitamin C
20ug folate
170mg potassium


Tinned strawberries (in syrup)

65
16.9
0.7
29mg vitamin C
6 ug folate
87mg potassium


Fresh is best here too.

There are significant less calories and sugar found in the fresh and frozen as opposed to the tinned in syrup. Fibre is similar for fresh and frozen.

Also the tinned in syrup has about a half of the vitamin C, folate and potassium than that of the fresh. Frozen is a very good second of these three.


PEAS

*Fresh has 24 more times Vitamin C than tinned.

* Fresh has 250% more potassium then tinned.

SWEETCORN

*Frozen sweetcorn has 38 times more Vitamin C than tinned.

*Fresh sweetcorn has the highest levels of potassium.

ORANGE JUICE

*Fresh orange juice has higher Vitamin C and folate levels than tinned.

TUNA

*Fresh and tinned tuna are good sources of protein.

*Fresh tuna has high levels of Vitamin D.

STRAWBERRIES

*Fresh has higher levels of Vitamin C.

*Frozen has higher levels of potassium.

*Tinned has half nutritional value than fresh or frozen.

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