Growers need focus on building local produce brands that are strong on smell, look and taste

Consumers want food that smells, looks and tastes good, which means locking in desirable field qualities through the post-harvest chain, says Geoff Dixon.

Cavity spot on carrot
Cavity spot on carrot

Fresh produce fruit and vegetables must provide interest, originality and convenience. This equates with fun in the minds of consumers and means maximising appearance, eating quality and flavour and minimising risk. These demands are associated with food localisation and the protection of origins, factors that have largely supplanted "organic" concerns.

Identifying with the grower is crucial. Growers are becoming their own brands and should capitalise on this new-found marketing status. Brand protection has major and increasing monetary value as with the Yorkshire Rhubarb Growers (Leeds-Wakefield-Bradford triangle) or the German Tetlow Turnip - a small, yellow-fleshed turnip traditionally grown south-west of Berlin and much sought after for its flavour, shape and colour.

Consumers have rebelled against the UK Treasury's mantra of "cheap food from any source is good enough for Britain". British growers should take advantage of this revolt by sustaining high field-fresh quality through the post-harvest handling chain.

Aroma and flavour

These attributes have been neglected by growers and supermarkets but consumers rate them very highly. Surveys indicate that quality at the point of consumption is based on flavour and mouth-feel.

Cherries, for example, should be dark red in colour with high levels of sweetness, while crispiness and juiciness are prime features for high-quality apples, hence the popularity of Cox's Orange Pippin.

There is a direct association between aroma and flavour and healthy eating. Flavour components in strawberries result from a balance of appearance, aroma, sweetness and texture. Sweetness and volatile content are important factors influencing consumer reaction and acceptance. Breeders are now adding the intense aroma of wild strawberry resulting from high ester and terpene concentrations into new commercial cultivars.

However, husbandry skills will still strongly affect the resultant eating quality. Harvest date and minimising the interval between picking and display greatly affect the retention of strawberry flavours.

Husbandry is especially critical for early and out-of-season crops such as those in Florida, USA. With raised-bed husbandry systems cropping in December, January and February, the most attractive fruit is harvested early in the season. Flavour is strongly affected by the annual variations in sunshine and air temperature, which control phytochemical production.

Strawberries grown in Florida's low organic matter and low cation exchange capacity sandy soils amended with calcium, magnesium and nitrogen fertilisers increase the ascorbic acid content of fruit. Adding organic matter into these soils as compost also enhances the ascorbic acid and flavanoid content.

The message for UK growers is that adding organic matter enhances soil's physical and biological qualities, encouraging beneficial microbes that result in greater availability and uptake of nutrients leading to improved aroma and flavour. The application of jasmonic acid and methyl jasmonate, which enhance the resistance of plants to pathogens, also increases anthocyanin, phenolic and flavanoid content in both raspberries and strawberries. Disease is reduced and flavour is enhanced as a result.

Flavour and aroma in high-bush blueberry result from the aldehyde and terpene contents. These compounds are also antimicrobial agents, which are especially valuable for early season cultivars in reducing anthracnose fruit rot (Colletotrichum acutatum). Most of the UK high-bush blueberry crop is consumed fresh and post-harvest rot is a continuing problem.

Infection takes place on green, unripe fruit. The pathogen remains dormant until ripening is completed, at which point symptoms start to appear. Breeding for aroma and flavour should correlate with increased disease resistance.

Blandness is a criticised characteristic of much supermarket food. Adding aroma and flavour into growers' fresh produce brands builds up their marketing strength. Joint studies between Warwick HRI-Wellesbourne and the German plant breeding centre at Quedlinburg showed a correlation between increased carrot aroma and sweet flavour and increased consumption. Acceptability increases when bitter flavours caused by free volatiles and amino acids are removed.

More than 100 compounds contribute to the enjoyable flavours in carrots but those of major importance are mono and sesquiterpenes. These account for 97 per cent of carrot aroma. Enhancing their concentrations also helps reduce infections from soil-borne pathogens like Pythium spp. - the cause of cavity spot.

Visual appeal

Presentation is a key marketing tool, enticing consumer interest. Spraying natural harpin proteins onto lettuce five days prior to harvest increases their visual appeal and extends shelf life.

Harpin is derived from the bacterium Erwinia amylovora. It switches on defence responses that allow plants to resist pathogens. Treated lettuce that is bagged and stored at 1-3 degsC has improved visual quality and lower microbial populations.

The fresh-cut produce sector has shown substantial growth in both UK and American consumer markets despite the recession. Consumers expect to use the produce direct from the bag without washing, hence high standards of hygiene are vital. Sanitisers are approved for use after cutting but limiting microbial loads before harvesting as with the use of harpin is an alternative option.

Respiration damages fresh fruit and vegetables after harvest by consuming carbohydrates and organic and fatty acids. Rapid respiration correlates with the onset of early senescence. Oxygen uptake increases with the number of respiratory enzyme adsorption sites per unit mass of the produce being stored.

For example, oxygen uptake is rated as highest in broccoli florets followed by spinach leaves with lowest values in onion bulbs. Consequently, reducing the oxygen and increasing the carbon dioxide concentrations surrounding fruit and vegetables slows ripening and extends their shelf life.

The use of modified atmosphere packaging (MAP) started in the late 1940s when plastic film polymers first became available for civilian use. The Americans Gebhardt and Wright were early users of this technology for packaging cherries.

Plastic film technology and packaging techniques have advanced substantially in the subsequent 50 years and MAP is now a major marketing tool, especially for cut and diced vegetables and increasingly for fruit.

Problems remain, however, when shelf life is over-extended for rapidly respiring produce such as lettuce and broccoli. Then off-flavours and fermentation develop, which can damage brand image. Nonetheless, few consumers probably realise that on opening a pack of baby leaf salads they are releasing a short burst of concentrated carbon dioxide acting as a preservative.

Developing environmentally-friendly packaging that is either self-degrading or edible would be a large advance and a big marketing prize. Recent experiments in Chile with apricots showed that extracts from the leaves of their native myrtle 'murta' (Ugni molinae) could offer natural forms of packaging material that are biodegradable.

Risk avoidance

Food scares of the 1990s led to the fresh produce chain becoming highly risk-averse, particularly at the supermarket end. Fresh produce is open to microbial contamination particularly by human bacterial pathogens such as Escherichia coli 0157:H7, Listeria, Salmonella or Yersinia spp.

For this reason, the supermarket quality assurance protocols have specified absolute and rigorous food hygiene standards and in some instances take their demands to rather extreme "box-ticking" lengths. British growers have responded magnificently to these demands, ensuring that cleanliness is absolute when crops are delivered into packing and handling buildings.

Extending shelf life might increase the risks to health when using MAP by increasing the period when food remains edible and allowing slow-growing pathogens to form toxins and retarding the development of competing organisms.

Microbes such as E. coli decline in vegetables such as shredded lettuce, sliced cucumber and shredded carrot held at 5 degsC and increase when they are held at 14 and 21 degsC for up to 14 days. Automatic identification of conditions favourable to pathogens would be very useful. Indicator inks that show when packaging is damaged would provide this.

Professor Andrew Mills from the University of Strathclyde chemistry department in Glasgow has formulated inks that change colour when exposed to oxygen. These show when oxidation is happening in fresh produce packs or indeed other types of food product.

Labelling that links growers with their consumers increases producers' power. Consumers will look for and ask for produce from particular growers especially where they have enjoyed the aroma, flavour and freshness of a product. This could introduce greater stability into the fresh produce chain and decrease opportunities for cavalier and penal attitudes by the supermarkets. Such power brings responsibilities for growers to ensure consistent quality and safety that satisfies the consumer without fail.

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