To Your Health
Is there a good and cheap way to judge the nutritional content of fruit?
A. "Brix value," a term seldom heard in casual conversation, is a measure of the total amount of all the substances dissolved in a solution, whether it is sugar, a mineral, a vitamin, or an amino acid. Named for the Austrian scientist Adolph Brix, who developed it in the 1800s to measure sugar content, the Brix value of a solution is now measured with an instrument known as a refractometer. With a mixed solution such as vegetable or fruit juice, the Brix value cannot be related to the concentration of any specific substance. The cost of a Brix meter, $100-$1000, is probably a deterrent to its widespread use.
There are several assumptions that underlie the use of a Brix meter to determine the nutritional quality of produce, fruit in particular. One is that the sugar content of produce will increase as it ripens. Sugar content is a major, though not the only, contributor to its Brix value and the most important in judging the ripeness of fruit. The increase in sugar content with ripening is usually accompanied by a decrease in the amount of tannins and other substances that lend a bitter taste to unripe fruits and also prevent minerals from being easily absorbed by the body, so produce with a high Brix value generally tastes better and would be more nourishing.
It is not as clear that there is an increase in protein and mineral levels in produce as it ripens. These factors would influence Brix values, but Brix readings vary at different times of the day and with changing weather and temperature, so the small changes in Brix value due to changes in mineral or amino acid content may be hard to spot.
Because fruits and vegetables carry the next generation of plants in their seeds, which need to be scattered by the animals that eat the fruit, they have ways of signaling when they are ripe and ready to eat. Unfortunately, different fruits and vegetables have different indicators of ripeness. With most fruits, color is the most obvious change that occurs with ripening, but blueberries, for example, color up days before the berries are truly ripe. It helps if you are able to pick blueberries right off the bush. To separate the ripe berries from the unripe berries, cup your hand beneath a cluster of berries, then "tickle" them. The ripe fruits fall into your hand. For any fruit, the ease with which it can be detached from the plant is a good signal of ripeness.
Although some fruit tastes terrible if it is eaten when unripe, a few can or must be picked underripe, then ripened indoors. Pears (with the exception of Seckel and Asian pears) turn mushy and brown if allowed to ripen on the tree, so they must be picked underripe. Other fruits that ripen well off the plant include avocado, banana, and persimmon.
If you are interested in a book on the subject, check your library for a book with the odd title Fruit the Ripe Pick: Fruit Selection Made Easy! by T.M. Gorman, for simple instructions on picking the best produce, both common and exotic, in the supermarket.