Why the orange juice become bitter if left in room temperature for some time?

The bitterness in orange juice that has been left at room temperature for some time is primarily due to the degradation of certain chemical compounds present in the juice. Here are some key factors that contribute to the development of bitterness:

Limonoids: These are natural compounds found in citrus fruits, including oranges. Limonoids can have a bitter taste, and their concentration increases as the juice is exposed to heat, light, and oxygen. When orange juice is left at room temperature, the limonoids break down and release their bitter flavor into the juice.

Oxidation: Oxidation is a chemical reaction that occurs when certain compounds in the orange juice come into contact with oxygen. This process can lead to the formation of off-flavors, including bitterness. The natural vitamin C (ascorbic acid) present in orange juice acts as a natural antioxidant and helps prevent oxidation. However, as the juice is exposed to air at room temperature, the vitamin C degrades, reducing its antioxidant protection and making the juice more susceptible to oxidation.

Microbial Activity: Leaving orange juice at room temperature for an extended period creates a favorable environment for the growth of bacteria and other microorganisms. These microorganisms can consume the sugars and acids in the juice, leading to the production of various compounds that can contribute to bitterness and other off-flavors.

To minimize the development of bitterness, it is recommended to store orange juice in a cool, dark place, ideally in the refrigerator, to slow down the degradation of limonoids and prevent oxidation and microbial growth.