Can someone comment on what happens to % DM (dry matter) as the fruit ripens?
Are there any data showing the % weight loss over time when harvested fruit is refrigerated and with high humidity?
This is an interesting question and I may have some information that can shed light on this.
Several years ago when conducting a project to look at acceptable dry matter levels for new California avocado varieties I came across a paper from Peter Hofman (DPI, Queensland, Australia) and others where it was hypothesized that one could back calculate the harvest dry matter of an avocado using weight loss that occurred during ripening. I and other colleagues found this assumption interesting and decided to test this hypothesis. The first challenge was to figure out a way to measure both fresh (hard fruit) and ripe fruit dry weights on the same fruit. We found that we could take out plugs of tissue (in our situation we used plugs from opposite sides at the fruit equator) and still get the fruit to ripen without decaying. When we sealed the holes made by plugging the fruit we obtained an intermediate weight loss in the fruit (when it ripened with ethylene) as compared to non-plugged ethylene treated fruit and non-plugged non-ethylene treated fruit. This serendipitous finding led us to be able to conduct two projects that were able to relate harvest dry matter to eating acceptability of the ripe fruit…. That is another story in itself. This work also ultimately led to the current California approved method for determining harvest dry matter.
However, back to the main point of this reply; once we confirmed that fruit could be successfully ripened in this manner, we could examine in greater detail the relationship between unripe and ripe dry matter on individual fruit. We ultimately looked at 148 individual fruit (varieties, Hass and Lamb Hass) recording both the ripe and unripe dry matter. Much to our amazement, we observed that the dry matter DECREASED with ripening in 140 of the 148 fruit. The average drop in dry matter was 1.54% but ranged from -5.06 to +0.98. For example if we measured an initial dry matter of 22.0%, after the fruit ripened, the dry matter had decreased to 20.46%. The average weight loss of the fruit when ripened was approximately 4%. We conducted these tests over a range of dry matter (17.5 – 36.9%) and looked to see if harvest dry matter (maturity) impacted the trend towards a decrease in dry matter after ripening. We observed no such trend as demonstrated in the graph below.
This data clearly shows that although the fruit does lose weight during ripening, that this weight loss does not translate into an increase in dry matter. Why? There are several possible explanations. First, as the fruit ripens, we really do not know where the weight loss occurs. I believe that weight loss in the peel contributes to the net loss in weight. Another factor to consider is the high level of respiratory activity that occurs during fruit ripening. The avocado has one of the higher rates of respiration (carbon dioxide production) of all fruits. The fruit’s respiratory activity during ripening will result in a net loss of carbon from the fruit. In some very simplistic calculations based on respiratory values provided in the USDA Handbook 66 we calculated that the net loss of carbon from the fruit could account for the majority of the dry matter loss as a result of ripening.
The question poised on this discussion forum has prompted us to design a study to look at weight loss during ripening and storage. We should have some preliminary data by mid-August to share on this forum.