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I am indebted for the following report on "Brown Heart " to Inspector Turner:—
Brown Heart in Apples and Pears.
The abnormal condition sometimes found in stored fruit to which the name "Brown Heart" .
has been given, is due, not to bruising, frost injury, or infection by moulds or bacteria, but to a defect
in the living processes. It is a functional disease causing death of living tissue cells with subsequent
browning by oxidation. It is the evidence of a form of suffocation.
Appearance.
Affected fruit may be perfect in external appearance, but on being cut open, clearly defined
brown areas are seen. In the early stages the patches may be small and isolated, increasing in size
as the condition advances until a continuous brown mass is formed in the centre of the fruit. The
texture of the affected tissue is at first firm and juicy and similar to the living tissue. Fruit once
affected when removed from the influence of the causal condition and held in a ventilated store, do not
deteriorate, the brown areas do not develop and the dead tissue dries out leaving cavities and becoming
tough and spongy in texture.
Causal Agents.
During respiration every live cell consumes oxygen and produces carbon dioxide, which owing
to low permeability of the skin and consequent slow rate of gas exchange with the external air by,
diffusion through pores, increases the concentration of CO2 in the intercellular spaces, called the internal
atmosphere. This condition is aggravated by the capacity of the cells to produce CO2 in the absence
of oxygen.
So long as free ventilation is maintained and the fruit bathed in pure air the CO2 concentration
by reason of constant diffusion does not reach the danger limit. When, however, ventilation is
stopped a condition likely to be met with in a closed ship's hold, the CO2 concentration increases
beyond the danger limit, with a correspondingly low concentration of O2 and brown heart develops.
At low temperatures respiration is slowed up and brown heart develops with lower concentrations
of CO2 in the presence of subnormal concentration of O2.
Brown heart does not develop in the entire absence of oxygen, but a condition called "Deep
Scald" may make its appearance, the affected tissue is somewhat similar in appearance to brown
heart, being sharply delimited, but extending from the surface inward.
There are therefore three variables which determine the incidence of brown heart.
1. Concentration of Carbon Dioxide.
2. Concentration of Oxygen.
3. Temperature.
Brown heart may be prevented by adequate occasional ventilation, so that the carbon dioxide
produced during respiration is not permitted to accumulate beyond a certain limit, having regard to the
temperature and variety being stored. Susceptibility varies with different varieties and among fruit
of the same variety from different sources and with degree of ripeness—the more mature being less
susceptible, possibly due to the enlarging of skin pores and more rapid diffusion between the internal
and external atmosphere.