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Altering Acid Levels In Fruit

Perfecting The Taste - Altering Acid Levels In Fruit


It's difficult to get the acidity level in fruit just right for the consumer, yet along with sweetness it has a major influence on flavour.

Once acid metabolism is fully understood, New Zealand growers will be better able to produce fruit that has the optimum taste. The average acid content of New Zealand mandarins is 1.2 percent but the ideal is approximately 1 percent.

HortResearch scientist Ken Marsh has been working alongside researchers in Florida to discover which enzymes control acidity in citrus, with the intention of using this research to create the optimum balance of sugar and acid in other fruit.

"If we understand acid metabolism, we will be able to target orchard processes, or even modify the growing environment, to effect appropriate enzymes and produce a better acid to sugar ratio."

Dr Marsh said initial research, although not conclusive, suggests the enzyme pyrophosphatase, present in all fruit, influences the acid to sugar ratio in horticulture crops.

In Florida the hot climate means oranges tend to lack acidity, whereas New Zealand suffers a related, yet different conundrum. "Our problem is that the colder climate means oranges often don't drop their acidity levels and can therefore have a sharp, tangy taste."

Because pyrophosphatase increases late in the season as fruit mature, it may play an important role in influencing their final acidity level, Dr Marsh said.

After measuring the activity of enzymes involved in the transport and accumulation of acid in different varieties of orange, Dr Marsh found low acid varieties had greater pyrophosphate levels than high acid varieties. "If we want to influence high acid varieties of orange, we need to look for ways to increase pyrophosphate activity."

Dr Marsh said he is interested in the acidity of all crops. The reason he began his research using citrus fruit is because they are easy to study. "This research [with citrus] will be used as a model system for continued work on the acid and sugar ratio of other fruit."

This most recent research grew from a project Dr Marsh worked on with another HortResearch scientist Annette Richardson where they looked at the influence of temperature on acid and sugar levels in mandarins. Words 356

For further information contact: Dr Ken Marsh, scientist Caleb Hulme-Moir, writer HortResearch Mt Albert HortResearch Palmerston North Tel: 09 815 4200, ext 7151 Tel: 06 351 7000, ext 7728 Fax: 09 815 4201 Fax: 06 354 6731 Email:kmarsh@hortresearch.co.nz Email:chulme-moir@hortresearch.co.nz


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