27 Aug 2020

WHAT IS THE CAUSE OF RED DRUPES IN BLACKBERRIES?

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The presence of red drupes in the ripe fruits of blackberries bramble is one of the most common and least tolerated defects by customers.

Only recently have scientists begun to understand this phenomenon: several explanations for its causes have been proposed, although the exact mechanisms are not yet fully understood.

WHAT CAUSES RED DRUPES?

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Usually all the drupes on a ripe blackberry fruit are uniformly black. Sometimes the fruit may have white, brownish or red drupes.

The redness of the drupes can occur after and before harvesting. There are several known causes of red drupes and some conditions that are speculation. Regardless of the cause, excessive amounts of red drupes can lead to rejection by customers.

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AFTER THE HARVEST

INVERSION

Reversal is the most common cause of red drupes: drupes are black at harvest and turn red after harvesting. The inversion causes an aesthetic defect, which affects neither the taste nor the sugar content; however, it is unwelcome to consumers who associate it with defects in ripeness or integrity of the fruit.

Research conducted by Max Edgley of the University of Tasmania examined several factors, including nitrogen rates, physical damage during harvesting and transport to refrigeration, air temperatures during harvesting, and slow or fast cooling of the fruit after harvest.

  • Physical damage (dents, impact and compression of the fruit) during harvesting and transport are the main cause of red drupe disorder.
  • High nitrogen fertigation during harvesting can significantly increase the amount of fruit with red drupes after harvesting.
  • Internal berry temperatures above 23C (73F) at harvest significantly increase the amount of red drupes after harvest. It is best to harvest before 10 a.m. while the berries are still fresh from the previous night; shade the berries during harvesting.
  • Harvesting times, techniques and shipping conditions can be manipulated to reduce the incidence of red drupleto disorder.
  • A gradual cooling process that reduces the post-harvest cooling rate has been effective in reducing the incidence of the disturbance
  • Earlier berries are more susceptible to this disturbance.
According to Alejandra Salgado (PhD U Ark) even a weak cell wall can cause reversion.

Learn more about reversion:

BEFORE HARVEST

BRAMBLEBERRY HERIOPHIS

Berries that are infected with a mite called the bramble mite (Acalitus essigi) have drupes that never turn black; red drupes are hard.

Mites inject a toxin into the base of the drupes and consequently the drupes do not develop normally. Brambleberry herophytes are rare in the Eastern United States.

Learn more about the heriophid of the bramble:

EXCESSIVE RAIN.

In case of excessive rain Red drupes are soft and never turn black. It is not easy to confirm that the red drupes in a particular batch were caused by rain. Often we proceed by exclusion, after discarding the reversion and the eryophyte of the bramble.

VIRUS

With current knowledge red drupes have not been identified as symptoms associated with viruses.

COMMERCIAL DEFECT TOLERANCE

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According to the USDA (US Department of Agriculture) red drupes are considered defects only if they extend beyond a certain degree, as shown in the picture.

In the United States, many quality managers classify red drupes as a defect without tolerance; other supermarkets admit them up to 15-20%.

In depth:

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