Food processing in a Dow Water & Process Solutions installation.
Food processing in a Dow Water & Process Solutions installation.

The bitterness in orange juices due to limonin develops after the extraction from oranges and is referred to as delayed bitterness, becoming a serious economic problem for the citrus industry. But scientific developments have helped producers to overcome this problem.

In Chinese tradition, the orange is widely considered a symbol of good fortune. Perhaps this is due to its health benefits, as its high concentration of Vitamin C neutralizes free radicals that cause chronic diseases, like cancer and heart disease. However, the sweet taste of orange juice is down to more than just good fortune, but good chemistry.

At the beginning of the 20th century, oranges were consumed principally as fresh, whole fruit. It was only in 1916, when California growers found themselves with an overabundance of oranges, that orange juice became more widely popular and solidly established itself as a key player in the global beverage industry.

However, orange juice back then wasn’t the sweet-tasting nectar that we know today. One of the biggest problems throughout the juice’s commercial history was controlling taste, as orange juice loses taste over time and can also be extremely bitter. The compound that is primarily responsible for bitterness in navel orange juice is limonin.

In fact, the development of unpleasant flavours is a consequence of food processing that results in the thermal degradation of components. As a matter of fact, the intact fruit barely contains limonin.

Delayed bitterness

Bitterness due to limonin in a variety of citrus juices is generally referred to as delayed bitterness, and it’s a major problem of the citrus industry worldwide. In fact, only a very small amount of this compound is needed to render the juice unpalatable.

Although the sensitivity to limonin among individuals varies, generally most people will perceive bitterness in orange juice when its concentration is about 5 parts per million (ppm), and will consider an orange juice to be unpalatable when its concentration is about 10 ppm or higher. However, a nonbitter precursor limonoat A-ring lactone is present in the insoluble fruit sections and passes into the juices after its preparation and is converted to limonin under acidic conditions.

Scientific advances in the second half of the century allowed orange juice producers to alter the taste such as by removing bitterness. Today, annual orange juice production is expected to reach 1.7 billion liters, the equivalent of 680 Olympic-sized swimming pools. It has become a really popular product within the drinks department, as orange juice is perceived as ‘healthy’ by consumers.

So, how is orange juice made and how is the bitterness issue solved? First, oranges are harvested and shipped to the processing facility, where they are washed and screened before being squeezed for juice extraction. Citrus juices have natural bitter components, such as limonin and naringin, and removal of these bitter molecules is important for taste and shelf life stability.

During the squeezing process, the orange rind emits a bitter flavour into the juice, so before it can be bottled and commercialized, the juice passes through a resin column to remove the bitterness.

Ion exchange resin technology is used to optimize this removal process. Polymeric adsorbent resins, such as DOW Amberlite FPX66, help to debitter the juice by removing components through hydrophobic interaction. Ultrafiltration diverts the citrus pulp around the resin, and regeneration with hot dilute caustic removes the limonin and prepares the resin for reuse.

Early efforts to remove the citric acid from citrus juices date back to the 1960’s, where electrodialysis was tried on an experimental basis. Other methods were also attempted, but with little success. Nowadays, fruit juice purifications are quite diverse and serve the producer and the customer in a variety of different ways.

Bitter compounds

From the purification of waste streams, to the select adsorption of bitter compounds, the use of Dow Water & Process Solutions’ ion exchange technology makes vital contributions to the juice and beverage industry. These techniques provide juice suppliers with the possibility to improve both the quality of their products and the yield from their raw materials. In addition, they make fruit juice products and their respective beverage products palatable and available to the consumer at reasonable prices.

With stocks at historically low levels, in part due to recent surcharges such as the ‘soda tax’, as well as an historic drop in the orange harvest in Brazil, prices for orange and juice have almost quadrupled in 2016. The rise in prices is reinforced by the continued strong global demand from Brazil, which alone produces more than 50% of the world's orange juice, through three large family companies Cutrale, Citrosuco/Citrovia and Louis Dreyfus Commodities, of French origin.

Dow Water & Process Solutions is a global leader in sustainable water separation and purification technologies. Its product line, expertise, and global reach allow for performance of complex manufacturing processes or simply producing a delicious glass of orange juice.