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Getty ImagesTinned and frozen fruits and vegetables tend to be seen as less nutritious than fresh versions. But that's not always the case.In recent weeks, as shoppers have looked to stock up on food that lasts, sales of canned and frozen food have surged. Even freezer sales are up. But many of us are taught to believe that when it comes to fruit and vegetables, nothing is as nutritious as fresh produce.
By reaching for tinned or frozen versions, are we doing a disservice to our health?When answering this question, it’s important to remember that food is most nutritious at the point of harvest, says Fatima Hachem, Senior Nutrition Officer at the UN’s Food and Agriculture Organization. Fresh produce starts degrading as soon as it’s picked from the ground or tree, because that ground or tree is its source of nutrients and energy.“Vegetables destined for cooking fresh might lose some of their nutritional value if they stay for long on the shelves,” Hachem says.
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Once picked, that fruit or veg is still using its own nutrients, breaking them down in order to keep its cells alive. And some nutrients are particularly vulnerable. Vitamin C, which helps the human body absorb iron, helps reduce cholesterol levels and protects against free radicals, is also especially sensitive to oxygen and light.
Refrigerating produce slows down the process of nutrition degradation, although the rate at which nutritional value is lost varies from one product to the next.
In 2007, Diane Barrett, a former food science and technology researcher at the University of California, Davis, reviewed numerous studies looking into the nutritional content of fresh, frozen and tinned fruits and vegetables. She found that spinach, for example, loses 100% of its vitamin C content in seven days if stored at a room temperature of 20C (68F); it loses 75% if refrigerated. But carrots, by contrast, only lose 27% of their vitamin C content when stored for a week at room temperature.
“Spinach is very thin, so there’s more loss of moisture and exposure to heat and oxygen compared to, say a carrot, which is denser,” says Barrett. But all other vegetables in Barrett’s research lost significantly less vitamin C when they were frozen. That included spinach, which only lost 30% of its vitamin C when frozen. This is because freezing pauses the process of oxidisation, which is one reason that produce can start to turn brown after being harvested.
Freezing produce on a mass scale is a relatively new innovation for the food industry. Take the humble frozen pea. Today, the pea can be harvested, transported to a factory, washed, blanched and frozen in just over two hours. In the 1970s, it would have taken days.
“Compare that [timescale] to fresh vegetables - most of which are harvested, sent to a packing plant, packed, graded, shipped to retailers, then put in the consumer baskets,” says Richard Harrow, chief executive of the British Frozen Food Federation, the frozen food sector’s trade association in the UK. “About 99% of time, this process takes longer than the time taken to harvest, process and freeze peas.”
Speed is crucial in the frozen food industry: as soon as produce is taken from the ground, it’s a nutritional race against time. Technological innovation has shortened the process of freezing foods over the last few decades, including peas, which are individually quick frozen, Harrow says, using a metal trough that opens at both ends and has a grate on the bottom. Underneath the trough, high-speed fans blow cold air up towards peas, which are “suspended in a cushion of air”. They’re then placed in cold storage until they’re put into packaging. Most other vegetables follow a similar process.
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But it also reduces nutrient content.However, this nutritional loss pales in comparison to the amount of heat that produce is exposed to when it’s tinned. The more intense heat treatment used on food that’s destined for a metal can shows a greater reduction in nutrients than frozen food, Barrett says. But as with fresh food, different nutrients in different kinds of produce degrade at different rates.
In her review, Barrett found that foods with mostly water-soluble nutrients, including vitamin C and B vitamins, retained nutrients differently than those with mainly fat-soluble nutrients, including vitamins A and E. The paper concluded that fresh food is often best for vitamin C content, as this vitamin is highly sensitive to heat - as long as it undergoes minimal storage. Foods with more vitamin E and A, however, which are found in high amounts in canned carrots and tomatoes, fared much better during heat treatment.
But canned food can also have some less desirable contents.“While there’s no reason to be worried about using frozen or canned food, there’s a preference for frozen because of the amount of added salt [in canned], and some canned fruits have added sugar,” says Hachem.
Still, canning also can improve the safety of foods, particularly those prone to harbouring pathogens. “The good thing about canned foods is the process used to sterilise them,” says Barrett. “It results in greater nutrient loss, but once the produce is in the can it can be pretty stable for years, and you can be sure it’s safe because it’s gone through a process that kills all microorganisms.”
What’s most important is to have a diverse diet, says Hachem, which, a lot of time, requires a variety of fresh, frozen and canned.
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“You can have a balanced meal by cooking vegetables from frozen or in a can, but this doesn’t replace the importance of having fresh salads,” Hachem says. “The problem with the lockdown is how to ensure fruit and vegetables retain their maximum nutrient value in light of the fact we’re advised to shop only once per week. If we can manage one salad on a daily basis, with cooking from frozen or canned, we’re not risking nutritional intake - on the contrary, it’s a good way of diversifying.”
Some experts also advise that buying local and organic also help ensure the fresh fruit and vegetables on your plate are as nutritious as possible. A number of studies have found that the content of phenolics - healthy compounds found in high amounts in red wine and tea - is higher in organic crops than conventionally grown ones.
Sušená zelenina sa stala základnou súčasťou modernej potravinovej výrobe a objavuje sa v instantných nudliach, korení, hotových jedlách a snackoch. Je však sušená zelenina skutočne rovnocenná čerstvej?
Aj keď obe formy pochádzajú z rovnakých surovín, procesy, ktorými prechádzajú, vytvárajú rozdiely v obsahu vlhkosti, textúre, intenzite chuti, kulinárskom využití a nutričnom profile. Pochopenie týchto rozdielov je nevyhnutné pre spotrebiteľov aj vývojárov potravín.
Čerstvá zelenina obsahuje vysoké percento vody, obvykle medzi 70 % a 95 %. Táto vlhkosť prispieva k jej chrumkavosti a žiarivému vzhľadu, ale tiež ju činí náchylnou k mikrobiálnemu rastu a enzymatickej aktivite. Po zberu zelenina okamžite začína kaziť kvalitu. V chladničke ju možno skladovať iba krátko, čo ovplyvňuje logistiku a dostupnosť.
Pri sušení zeleniny sa väčšina tejto vlhkosti odstráni. Znížením aktivity vody proces dehydratácie spomaľuje enzymatické reakcie a zabraňuje rastu mikroorganizmov. Preto možno sušenú zeleninu skladovať mesiace či roky bez chladenia. Transformácia je však viac než len odstránenie vody - je to kontrolovaný proces s cieľom zachovať čo najviac barvu, nutričnú hodnotu a chuť.
Obsahuje sušená zelenina stále živiny? Gram sušenej mrkvy obsahuje viac beta-karoténu než gram čerstvej mrkvy, pretože voda bola odstránená. Vitamíny citlivé na teplo, ako vitamín C a niektoré vitamíny skupiny B, sa môžu počas sušenia strácať. Technológie nízkoteplotného alebo lyofilizovaného sušenia však túto stratu významne znižujú. Minerály, antioxidanty a vláknina zostávajú vo veľkej miere nedotknuté, čo zo sušenej zeleniny robí cennú zložku pre produkty zamerané na zdravie.
Naopak, chuť je jedným z najvýraznejších rozdielov medzi sušenou a čerstvou zeleninou. Sušená zelenina dodáva koncentrované arómy a zvýrazňuje prírodné cukry a tieňové látky zodpovedné za chuť. Rehydratovaná zelenina môže znovu získať väčšinu pôvodnej textúry, čo ju robí vhodnou pre hotové jedlá a instantné použitie.
Trvanlivosť a priemyslové výhody: pre výrobcov potravín sušená zelenina znižuje plytvanie a zjednodušuje výrobné plány. Bez sušenej zeleniny by neboli dostupné instantné nudle, lyofilizované polievky, koreninové zmesi a trvanlivé jedlá. Čerstvé vs. sušené: dopĺňajú sa, nie vylučujú.
Čerstvé produkty sú najlepšie na priame tepelné úpravy, konzumáciu bez tepelného spracovania a jedlá vyžadujúce křupavosť a vlhkosť. Sušená zelenina sa vyznačuje vynikajúcou spracovateľnosťou, dlhodobým skladovaním, ľahkou prepravou a aplikáciami, kde je konzistentná chuť a trvanlivosť nevyhnutná. Namiesto toho, aby sme jeden z komponentov považovali za lepší, treba ich vnímať ako dve fázy tej istej suroviny prispôsobené rôznym potrebám.
Fresh, frozen, canned, and dried fruits and vegetables are all nutritious and count toward your 5-a-day. Frozen and canned fruits and vegetables are nutritionally comparable to their fresh counterparts and sometimes superior. Because they last much longer, they’re less likely to spoil before being eaten, which helps reduce food waste at home. The belief that “fresh is best” is largely a perception, not a scientific fact. Fresh fruits and vegetables are often seen as the gold standard of healthy eating. But frozen, canned, and dried options can be just as nutritious. Dried fruits are nutrient-dense, offering concentrated fibre, vitamins, and minerals in small portions. A 20-30 g serving can provide 10-16% of your daily fibre needs, depending on the fruit. Regularly eating dried fruits has been linked to a lower risk of cardiovascular disease, type 2 diabetes, obesity, and other chronic conditions.5 Since they're calorie-dense, enjoy them in mindful portions. A 30 g serving of dried fruit (the equivalent to around 80 g or 1 portion of fresh fruit) counts as 1 portion of your 5-a-day. This is about 1 heaped tablespoon of raisins, currants or sultanas, 1 tablespoon of mixed dried fruit, 2 figs, 3 prunes or 1 handful of dried banana chips.
On top of their nutritional benefits, frozen, canned, and dried fruits and vegetables have a much longer shelf-life than fresh fruits and vegetables, which means they’re less likely to spoil before being eaten and therefore can help reduce food waste at home.
It’s easy to assume that fresh is always better. The word fresh brings images of just-picked produce, bursting with flavour, and vitamins. But that’s not always what ends up on your plate. In many cases, fresh fruits and vegetables are harvested early, stored, transported across long distances, and then kept in shops and home fridges for days or weeks. During this time, maturation continues, which can improve taste but doesn’t necessarily improve the nutritional quality. For example, spinach can lose all its vitamin C within a week at room temperature; 75% if refrigerated, but only about 30% when frozen. Freezing, canning and drying help lock in nutrients, and in some cases even improve their bioavailability.
It is worth noting that drying - and to a lesser extent freezing - requires energy, which can affect their environmental footprint. However, these impacts need to be balanced against reduced food waste, longer shelf life, and fewer transport losses compared to fresh produce.
While freezing, canning and drying can protect some nutrients, some others like vitamin C and B vitamins, can degrade during certain heating methods. Many people associate fresh produce with being “natural,” “pure,” and “healthy,” while viewing canned or frozen options as “processed” or “second-best.” These assumptions create a halo effect, where freshness feels better even if the nutrient content is similar. In reality, frozen, canned, and dried fruits and vegetables are all nutritious, affordable, long-lasting, and convenient options that can help you reach your 5-a-day.
Sušené datle sú koncentrovaným zdrojom živín: energia, vlákniny a minerálnych látok, ako je draslík a hořčík. Sušené plody goji sú ceněny pre svoj obsah antioxidantov, vitamínov a karotenoidov. Sušené brusinky sú bohaté na fenolické zlúčeniny, ale ich zdravotná hodnota do značnej miery závisí na zložení. Sušené aronie vynikajú mimoriadne vysokým obsahom antioxidantov, najmä antokyanov. Sušené plody šípku a sušené jeřabiny sú menej zvyčajné, ale z hľadiska výživovej hodnoty zaujímavé plody.
Stručná odpoveď znie: áno, sušené ovocie môže byť súčasťou zdravej stravy - ale iba za určitých podmienok. Kľúčovú úlohu hrá kvalita i množstvo, ktoré denne konzumujeme. Vláknina prevažuje medzi významnými zložkami a prítomné minerály ako draslík, horčík a železo a bioaktívne látky ako polyfenoly a antioxidanty sú hlavnými piliermi.
Najvhodnejšie sušené ovocie s ohľadom na výživovú hodnotu sú tie bez pridaného cukru a bez zbytočných prísad, ktoré obsahujú veľa vlákniny a minerálnych látok. Pri vyššom obsahu cukru v sušenom ovocí treba dbať na porcie a frekvenciu konzumácie, najmä pri inzulínovej rezistencii alebo cukrovke. Striedmosť a kvalita výrobkov sú kľúčom.
Fresh, frozen, canned, and dried fruits and vegetables all contribute to daily fruit and vegetable intake, availing different advantages and trade-offs. Sušená zelenina a ovocie majú svoje miesto v modernom potravinárstve aj vo verejnom zásobovaní; dôležité je pochopiť, že ide o dve fázy jednej ingrediencie, prispôsobené rôznym kulinárskym a logistickým potrebám.
Najdôležitejšie je mať pestrú stravu, ktorá zahŕňa čerstvé, mrazené a konzervované potraviny. Rozumné je striedanie foriem podľa dostupnosti, chuti a nutričného profilu podľa aktuálnych potrieb tela a životného štýlu.
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