Special edition: joy in juice and smoothies
Carotenoid chameleons: Scientists chart how orange juice changes color
Carotenoids are organic pigments that give orange juice its color. In a study published in the journal Food Chemistry, scientists investigated the correlation of carotenoid changes with color degration of juice.
The authors believe they are the first to investigate the changes of carotenoids during storage both at ambient and elevated storage temperatures, and specifically the impact of this on color.
Color and perceptions of quality
“Orange juice is one of the most popular beverages in the world, with its attractive color, refreshing taste and high nutritional value; it remains the most widely consumed fruit juice,” wrote Ann Van Loey, one of the authors.
“In fresh juice, the bright orange color is determined by the composition and concentration of its naturally occurring pigments, carotenoids.”
“Color is an important characteristic of food. The deliverance of a good impression through color will determine consumers’ acceptability and their purchase decision.
"Also, color plays an important role as a quality indicator. Different chemical and biochemical reactions which occur in a food product can be detected visually by its color.”
During processing and storage, color of orange juice can change depending on the conditions that favour degradation reactions. Since degradation is complex, scientists believe there is more than one mechanism responsible for color adjustment.
“It is known that each carotenoid has its own distinctive color properties,” said Loey.
“Due to their highly unsaturated structure, carotenoids are prone to various degradation reactions, which affect not only their color but also their biological activity. The presence of oxygen, especially in combination with light and heat, can lead to oxidative degradation, forming an epoxide and free radicals.”
Stability of carotenoids is influenced by a number of factors: including processing intensity, storage time and temperature, availability of light and oxygen, and the specific carotenoid.
How do you measure color?
Juice was stored in dark incubators at 20 and 28 °C for 32 weeks; 35 °C for 12 weeks; and 42 °C for 8 weeks.
Color changes were measured using CIELAB, an objective method of color measurement. “Although color can be evaluated through visual analysis, it is pertinent to determine the color objectively, since visual assessment is subjective and can be biased,” said Loey.
“Results from this study indicated color degradation was influenced by storage temperature and time,” said Loey. “Browning was clearly detected and became more evident at elevated storage temperatures and at prolonged storage.
“With respect to the carotenoid profile, several carotenoids showed important changes and appeared to have different susceptibilities to storage. Due to the relatively limited decrease of carotenoids, isomerisation [the re-arrangement of atoms] could be more important than oxidation reactions [change in electrons].”
More carotenoids displayed important decreases as temperature and time increased, which implied differences in individual carotenoids due to storage, Loey added.
“Other reactions such as non-enzymatic browning reactions could play an important role in the perceived color changes. Since orange juice contains an appreciable amount of ascorbic acid, its degradation may contribute to browning.
“Also, interaction between different pathways or compounds may occur. Therefore, further research is needed to understand the mechanisms responsible for the color instability in orange juice, not just focusing on the influence of carotenoids.”
Source: Food Chemistry, Volume 171. March 15, 2015.
‘Colour and carotenoid changes of pasteurised orange juice during storage’
S. Wibowo; L. Vervoort; J. Tomic; J.S.Santiago; L. Lemmens; A. Panozzo; T. Grauwet; M. Hendrickx; A.V. Loey.