Brix as a Metric of Fruit Maturity

There are many methods to determine the maturity of fruits. Some methods need an external examination of fruits, while others require a more detailed analysis of the internal composition of fruits. Brix is a measure of internal components. Though it is not universally applicable as some other measures of maturity, Brix provides vital information of interest for the fruit industry and associated processing factories. Therefore, it is important to find out its strengths and limitations.

What is Brix?

Degrees Brix or °Brix (Brix) is a measure of the total soluble solids (TSS) present in the fruit. TSS is mainly made up of sugars but also includes other compounds. The total soluble solids are made up of

• Sugars, which can be monosaccharides, disaccharides, or oligosaccharides, such as sucrose, fructose, etc.
• Organic acids, such as citric, malic, tartaric acids etc.
• Soluble amino acids, but not proteins as they are not soluble.
• Other miscellaneous compounds, such as fat, minerals, alcohol, flavonoids (Vitamin C and Vitamin A), etc.

Sugar content is maximum and can be around 80%, and the portion of other solids is little; Brix is taken as a measure of sugar or sweetness of fruits or fruit juices. The other components of TSS can, however, influence Brix if their proportion increases.

Brix doesn’t differentiate between the different sugars but indicates the total content of all sugars. The °Brix, measured at 200C, is said to be the amount of total sugar in fruit. So, 50 Brix means the fruit has 50% of sugar (or TSS).

How is Brix used?

Brix can be used as a measure of maturity, flavour, and level of sweetness in fruits and vegetables to help in fixing the time of harvest, sales, and processing.

Fruit maturity

To understand how Brix is used, it is necessary to know how fruits mature. There are many stages of maturity (See Figure 1):

• Physiological maturity is the stage when fruit can be harvested and will continue to develop further.
• Horticultural or commercial maturity is the stage when fruit has the qualities needed by consumers.

Stages of fruit maturity in climacteric fruits. ( Image credits: http://www.fao.org/3/y4893e/y4893e04.htm)

In the case of climacteric fruits, harvesting is possible when they have accumulated enough starch to be physiologically mature. They can ripen post-harvest, and the starch is converted to sugars to reach commercial maturity.

In non-climacteric fruits, the fruits have to ripen on the tree, as they accumulate only sugars and no starch. So after harvest, this type can’t ripen further, and thus, physiological and commercial maturity is nearly the same point.

Measuring Harvest Maturity with Brix

As a measure of maturity, Brix is not as useful as other indicators, such as dry matter (DM) which is currently the most preferred index.

• Non-climacteric fruits: Brix, which is a measure of sugar, can be used to determine both the harvest and commercial maturity for non-climacteric fruits, such as capsicum, berries, lemon, olives, citrus fruits, pineapple, grapes, cherry, etc.
• Climacteric Fruits: Brix is, however, best restricted to establishing only commercial maturity for climacteric fruits, such as mangoes, apples, pear, tomatoes, watermelon, etc.

Limitations

One of the disadvantages of using Brix as a measure of maturity is that TSS at harvest is not a good indicator of TSS after a long period of storage in the case of climacteric fruits. Dry matter content at harvest is a much better indicator of TSS after storage. Dry matter is made of all solids – soluble sugars and insoluble starch among other things. So, the starch, which will later change to sugar, is taken into consideration, making DM a good indicator of taste as well in all fruits.

Brix to Determine Flavour and Sweetness

Brix is used to evaluate the flavour and quality of many fruits at different stages of fruit production, such as harvest and processing. In this case, Brix is used in combination with other maturity indices, such as firmness. The value of Brix and firmness and their combination will vary not only based on the type of fruits but also varieties. For example, consumers like Brix values of

• 13 for apples
• 12 for avocados
• 16 for banana
• 14 for mango
• 12 for tomatoes
• 20 for kiwis
• 20 for grapes

As an indicator of sweetness Brix has many uses. Brix is used by:

• Farmers for harvesting non-climacteric fruits meant for processing, such as citrus and grapes.
• Grocery stores and restaurants to check that vegetables and fruits are ready for consumption.
• Processors of fruits and vegetables into wines, juices, sauces or beer to ascertain readiness for processing.

Limitations

It should be remembered that the Brix values of fruit are not constant. TSS and Brix increase as the fruit develops. During senescence, when the fruit is over-mature, the amount of sugar content falls.

Moreover, the rigour of Brix depends on samples and sampling procedure. Inconsistent sampling methods and choice of fruits can influence Brix readings.

DM, which indicates sweetness as it includes sugars and also sourness as it includes acids, is a better indicator of flavour and ultimate consumer preference. People like a combination of tartness and sweetness in their fruits, which Brix alone cannot reflect.

Variation in Brix

Besides the different stages of maturity, Brix values can be affected by several environmental, genetic, and management factors:

• Genetic: The variety and rootstocks of fruit trees can influence the TSS and combination of sugar and acidity in a fruit.
• Weather and season: The amount of sugar in fruit will be higher in dry years or summer season, as the trees will have less water and more exposure to sunlight. During wet years or season, the trees will absorb more water. As a result, fruits have a higher water content, which will dilute the amount of sugar in fruits.
• Nutrition: Higher levels of nitrogen and potassium result in more acid and, therefore, less fruit sweetness and Brix. Phosphorus increases TSS and juice content and, therefore, increases Brix.
• Fruit size and load: When there are fewer fruits on a tree, the fruits have more TSS and higher Brix. When the fruits are smaller, they are sweeter, too.
• Location on a tree: Fruits borne on branches exposed to sunlight will have more TSS and Brix than fruits growing in shaded parts of the trees.
• Management: By regulating irrigation, fertilizer application, and other agricultural practices such as pruning, spacing, etc., it is possible to regulate Brix.
• Area: Due to differences in soil and climate, the growing area of fruits can also influence Brix.

Since TSS levels are sensitive to the growing conditions of crops, it is one of the indicators used to judge the quality of fields.

Relationship with DM

Dry matter accumulation and total soluble solids (TSS) in fruits of Brazilian C. chinense accessions. From Lannes et al. 2007, Image credits: https://doi.org/10.1016/j.scienta.2006.12.029)

Any factor that improves dry matter content will also increase Brix as the two are co-related. As the dry matter increases, so does the total soluble solids. For example, in Capsicum chinense, a 1% increase in dry weight goes with a 0.28% increase in TSS content, until the TSS reaches 10.25%.

Measuring Brix

Brix can be measured by refractometer, hydrometer, or density meter, but none of these methods are non-destructive or suitable for the field. Near Infrared (NIR) spectroscopy, which can be incorporated in small handheld field devices to estimate TSS in the fields, as in the Felix Instruments F-750, is ideal for measuring Brix in the field. NIR spectroscopy, which measures Brix, DM, and Titratable acidity, provides all the maturity indicators needed by growers and producers of fruits and processed products.

—

Vijayalaxmi Kinhal
Science Writer, CID Bio-Science
Ph.D. Ecology and Environmental Science, B.Sc Agriculture

Source

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