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Vegetables: is fresh best?

Dr Hazel MacTavish-West, a consultant phytochemist, discusses the pros and cons of eating fresh versus frozen vegetables and uncovers some unexpected facts.

Despite improved awareness of campaigns, such as 5ADay, consumers are increasingly turning to foods other than vegetables for their snacks and main meal choices, and to frozen rather than fresh vegetables. So what are the real and perceived differences between fresh and frozen vegetables nutritionally, environmentally and economically? What are the implications for  consumers and for producers of freshand frozen vegetables as a result?

Vegetable consumption trends
Vegetables are very nutrient dense relative to their calorific value, supplying the human body with fibre, water, fat- and water-soluble vitamins (especially Vitamin C) and a diversity of phytonutrients including carotenoids, phenolics, chlorophyll, glucosinolates and alkyl cysteine sulphoxides, to name but a few. Vegetables add colour, flavour and crunch to our diet. The World Health Organisation states that ‘sufficient’ fruit and vegetable consumption is one of 5 major routes to reduce global risk factors for disease. Defining ‘sufficient’ is a work in progress. However, vegetable consumption trends make disturbing reading, with a decline per capita in the UK between 2006 and 2011, and only 18% of children, 24% of men, and 29% of women achieving 5ADay in 2011(1). In most developed countries, the trends are similar.

Frozen vs fresh
Raw materials
Vegetables for processing (i.e. blanching/freezing) are generally grown in the same way as fresh produce. Processing vegetables may be grown specifically, or may be outgrades (too large, misshapen) from fresh production. Globally, the trends are for mega-sized frozen vegetable processors to supply many countries, although most UK-packed frozen vegetables are grown in the UK. The supply of fresh vegetables all year round is achieved by air or truck transportation of produce grown in other countries, when UK-grown produce is not available. Despitemuch hype to the contrary, I have found very little scientific evidence to support claims that vegetables grown in the off-season are nutritionally inferior to in-season produce, apart from higher nitrates in some wintergrown leafy vegetables.

Processing and packaging
ImageVegetables actively respire in aerobic environments until they are cooked. Managing respiration rates and reducing oxidation and other reactions, such as production of bitter or off-flavours, is key for effective processing. This is achieved by maintaining high relative humidity, reducing the temperature, minimising cut surface area and avoiding anaerobic conditions. In Table 1, the processing steps undertaken by producers of fresh (whole) vegetables, and processed, frozen vegetables are compared. The lines highlighted in grey represent when most enzymatic reactions will have ceased due to heat treatments; the asterisks define processes which are known to be most vitamin-depleting.

Blanching stabilises vegetable colour, depletes heat sensitive and water-soluble vitamins (thiamine, folate, Vitamin C) by 25-50%, and may improve the extractability of fat-soluble carotenes. New steam-blanching and air cooling processes minimise nutrient losses. The comparatively earlier ‘kill step’ for enzymatic processes in frozen vegetables means there is less opportunity for depletion of vitamins prior to consumption if frozen produce is stored correctly and is not thawed prior to cooking. Nutritional changes during correct storage of frozen vegetables are less over 12 months than they are in fresh produce stored at 4°C for 7 days (2).

Consumer usage and nutrition
Sporadic or over-purchasing of fresh vegetables may mean produce is stored for an unduly long time prior to consumption. Refrigeration and protective wrapping is recommended for most vegetables (except tomatoes and onions), as it helps maintain moisture content, reduces respiration rates, and improves vitamin retention (2). Several recent studies have shown fresh and commercially frozen vegetables sourced from retail stores to be similar nutritionally. Vitamin C (ascorbic acid), lutein, and beta-carotene were higher (or were more extractable) in frozen broccoli and carrots compared with fresh (3). However, many studies fail to make sensible comparisons, by not sourcing commercially frozen (and thus blanched) vegetables, or not stating comparative country of origin, date code details and retail storage environments (ambient vs chilled) for fresh vegetables. Long cool chains and sub-optimal storage environments can negatively impact the vitamin content of ‘fresh’ produce, especially at home.

Cooking has the biggest impact on nutritional quality of vegetables. It reduces the nutritional differences between fresh and frozen vegetables (2), significantly depleting Vitamin C (sometimes to nil) (4), and making polyphenols and carotenoids more bioavailable. Steaming vegetables has been shown many times to retain water soluble nutrients better than boiling, and even scientists agree: don’t boil broccoli!

Environmental impact
In terms of production of greenhouse gases and their equivalents (GHGE), fruit and vegetables produce only 114 GHGE/100g compared with 342 for fats and 612 for fish (5). A Swedish study recently showed that fresh carrots had a higher nutrient value/g CO2 equivalents than frozen carrots (2). The global warming potential (GWP) of fresh vegetable production is low due to high yields; root vegetables, brassicas and onions have a lower GWP than crops grown in glasshouses such as tomatoes, cucumbers and some lettuce. Sorting, washing, packaging and transportation are the dominant contributors to GWP for fresh vegetables. Transportation, distribution, retail and consumer storage of frozen vegetables have significant GWP (6). Keeping foods below ambient for long periods of time is energy intensive although frozen processing/ storage technologies have become more efficient in recent years, using liquid nitrogen to pre-cool cargo containers and increasing the storage temperatures. Some comparative carbon footprint studies have shown frozen vegetables to have a lower carbon footprint than fresh, with decreased in-home waste being the most significant difference. In the UK off-season, fresh vegetables are often flown in from overseas, whereas frozen foods are generally transported by sea, which is more energy efficient; the gains more than compensate for the energy for refrigeration.

Vegetable waste
Globally, one third of all food is wasted, which is simply astounding. For vegetables: farm production waste is approximately 20%; processing waste (washing, processing) is approximately 15- 30%; retail waste (across Europe) is 45%; consumers waste around 30% due to unavoidable (banana peels etc.) and avoidable waste (poor food management). WRAP has studied consumer approaches to waste, finding many fresh vegetables are discarded due to confusion between ‘sell by’ and ‘use by’ date codes. Frozen vegetables are discarded to make room for other foods, as part of a spring clean, or becauseconsumers underestimate the safe storage period. Use of frozen vegetables may reduce unavoidable in-home processing waste, however this waste still occurs, albeit at a different point in the supply chain. Commercial recycling orconversion of processing waste into biogas generates only 10% of the energy used for production. From an environmental perspective, minimising waste throughout the supply chain and encouraging consumers towards composting (or using more of the avoidable waste) may have a greater environmental impact than consumers switching from fresh to frozen vegetables to minimise in-home waste.

The cost of vegetables
The average weekly spend on vegetables in 2011 was £4, which purchased 739g of produce (= £5.41/kg) (1). We recently (April, 2014) undertook a survey of fullprice fresh and frozen vegetables using Tesco online, since 30% of all frozen food in the UK is sold at Tesco. The average price of mixed frozen vegetable packs (broccoli, carrot, cauliflower and peas/beans, not flavoured or chargrilled) and packs of a single vegetable type was £2.19/kg (number of samples =16). Considering edible conversion factors for whole vegetables (7), the cost to make a comparative mixed, ready to cook product by purchasing fresh, whole vegetables was £2.96/kg (number of samples =11), 35% more expensive than the frozen option. Pre-prepared, fresh vegetables had an average price of £4.40/kg (number of samples =17), 100% more than frozen prepared vegetables. Thus the claim that frozen vegetables are cheaper (in-store, at full price) is upheld.

The fresh fruit and vegetable market was valued at £10.7bn in 2014, up by 5.3% (largely on value, not volume) (1). According to ‘The Grocer’ magazine (March, 2014) consumers are buying less fresh vegetables each time, but are purchasing more frequently as a means of reducing waste. The UK is Europe’s largest market for frozen foods with a retail value of £5,293 million in 2011; vegetables comprise £410 million of this market, up 2.5% year on year (value, not volume). The US is currently the world’s largest frozen food market, but increasingly wealthy consumers in China, Brazil and India are adding fridges and freezers to their homes. So watch this space! In a recent French study (8), purchasing of fresh vegetables was linked with increased income, age, education levels and the number of adults at home; purchasing of processed vegetables was greater in larger households, but was not linked with age or education level.

In-store, fresh and frozen vegetables are stocked in completely different sections of the supermarket. Promotional activity is different, with frozen food being more price oriented; quality guarantees are more often made on-pack, as there is greater control throughout the supply chain and the product has been stabilised. Internet shopping is the great equaliser, wherein the appearance of produce has little impact. Consumer perceptions
Fig 1. In which ways are fresh vegetables better than frozen vegetables, in your opinion?Mintel advises that 40% of UK consumers believe frozen vegetables are as healthy as fresh, an increase of 5% between 2008 and 2012 (1). We recently surveyed over 300 consumers in Australia and the UK about their perceptions of fresh and frozen vegetables. Respondents used the following words (larger fonts relate to more frequent mention) when describing why they valued fresh vegetables, illustrating the perceptions of provenance and identification with farmers:

Fig 2. In which ways are frozen vegetables better than or equal to fresh vegetables?When asked about important factors when buying frozen vegetables, convenience came through, as well as perceptions that produce was not local:

Given that we hear repeatedly that lack of preparation time is seen as one of the biggest barriers to sufficient (or greater) vegetable consumption, there would seem to be some obvious benefits in using more frozen vegetables. We also asked about perceived differences between fresh and frozen vegetables (Figs 1 and 2).

The differences in flavour and texture consistently put fresh vegetables ahead of frozen. Visually, frozen vegetables are not as dissimilar as one would imagine from fresh vegetables.

New product development
In the fresh vegetable sector, the UK is well served with many prepared, ready to eat, or ready to cook and eat options. Washed and pre-prepared salads are the largest component of the fresh vegetable category, at 40%. New products have focused on convenience, combinations, additions of flavoured butters, different formats (salad bowls, for example), new varieties with visual differences (colour, shape), new packaging options (to increase fresh shelf-life) and the emergence of brands (Naked & Fresh, Albert Bartlett, Steve’s Leaves). Building value around the farming provenance is promoted rather than specific claims around nutrition, health or quality, which are more difficult with a whole product supplied all-year-round that may vary in variety and growing region/country.

In the frozen vegetable category, new products include new combinations for specific usage, such as Mexican-style, stir-fry and microwavable packs, with additions, such as garlic and ginger. The aim has been to try and engage consumers in the convenient meal preparation process by encouraging them to stir-fry the product. An emerging trend is frozen salads, such as Moroccan couscous salad, and other salads with legumes and grains. Claims include convenience, health claims (low/no/reduced allergens, high in protein, fibre, wholegrains, and the number of vegetable servings) and an increasing focus on seasonal offerings.

Summary and conclusions
• Fresh vegetables represent an important source of dietary fibre, vitamins and phytonutrients, as well as adding flavour, colour and crunch to meals and snacks.
• Air transportation of out of season fresh produce from other countries, and in-home preparation waste increases the carbon footprint significantly compared with frozen vegetables.
• Inappropriate and prolonged storage and cooking depletes nutrients in fresh vegetables significantly.
• Consumers value the provenance, flavour and texture of fresh vegetables, especially for salads, stir-frys and snacks.
• Frozen vegetables may have a greater environmental impact in terms of processing and storage, however decreasing in-home waste dramatically reduces the carbon footprint compared with fresh vegetables.
• Blanching and freezing provides nutrient rich, relatively shelf-stable biomass that is convenient and cost effective.
• Consumers value the convenience and price, and for many meal options, frozen vegetables are equivalent to fresh (soups, stews, some stir-frys etc).
• For both fresh and frozen vegetables, education regarding optimal storage and cooking techniques are imperative to ensure maximum sensory and health benefits are received.
• Vegetables are a diverse, flavoursome, healthy and tasty addition to our diet, with fresh and frozen variants providing consumer options. Neither is ‘better’ than the other, it’s a case of horses for courses.

Dr Hazel MacTavish-West is a consultant phytochemist, experienced in communicating the attributes of flavour, colour and bioactivity (health benefits) of plants and plant extracts to stakeholders including consumers. Hazel helps to promote the health benefits of vegetables (www.veggycation.com.au). Her client base includes many of the largest horticultural producers in the UK and Australia.
MacTavish West Pty. Ltd. 1st Floor, 445 Macquarie St, South Hobart, Tasmania AUSTRALIA 7004.
Tel: +61 (0)362 244 905 Email: hazel@mactavishwest.com.au Web: www.mactavishwest.com.au www.Twitter.com/vegdoctor

Disclaimer: As a freelance consultant, Dr Hazel MacTavish-West undertakes projects on behalf of producers of both fresh and frozen vegetables in the UK and Australia. No commercial funds were offered, sought or received for producing this independent article.



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