Effect of dissolved oxygen and deoxygenation on the quality of orange juice

Orange juice was the most consumed fruit juice in the 2007/08 season, representing 50% (14.4 L, Single Strength Equivalent per capita) of the total per capita consumption of fruit juices. Because processing conditions influence the quality of the end product, it is important to understand the changes that orange juice experiences during processing. Deaeration is a processing step applied immediately before pasteurization to remove air, in particular oxygen, incorporated into orange juice during extraction or mixing. Vitamin C is believed to be the compound the most affected (oxidized) by dissolved oxygen (DO) in orange juice. However, there is a lack of information about changes in color and aroma under different levels of DO. The objective of this study was to understand the effect of initial DO, presence of air in the headspace and storage temperature on vitamin C, color and aroma of not from concentrated (NFC) orange juice in order to preserve fresh-like characteristics.;The first storage study correlated changes in vitamin C (ascorbic and dehydroascorbic acid) and aroma compounds of commercial NFC orange juice (cultivar Valencia,) with selected initial DO levels during storage for 60 days at 5°C in amber glass containers. The same study also evaluated the effect of having air in the headspace. The selected initial levels of DO in juice with no headspace were: deaerated (42.3 +/- 2.7 muM), oxygen saturated (494.7 +/- 1.8 muM), control (177.6 +/- 7.9 muM), and juice with air in the headspace (180.3 +/- 9.3 muM). The juice with air headspace had the highest loss of ascorbic acid (AA) of 42% after 60 days of storage at 5C. Pseudo-first order rate constant of DO consumption was 2.8x10-1 +/-4.1x10-2 d-1. No changes in color were visually perceived among treatments or over time. Pseudo-first order rate constant of AA oxidation at 5°C was 1.9x10-2 +/- 3.0x10 -3.;Aroma active and volatile compounds were analyzed in all juices by GC-O and GC-MS using solid phase micro extraction (SPME) headspace sampling. Among aroma active compounds, methional was perceived at higher intensity in orange juice samples with air headspace compared to control only. Nonanal had the main contribution to aroma intensity of control, oxygen saturated and air headspace orange juices. At day 1 of storage beta-elemene, alpha-selinene and delta3-carene had the highest amounts in deaerated orange juice compared with the other juices. At day 60 of storage, the content of most of the compounds decreased with respect to day 0 except for E-2-hexenal and limonene oxide whose content increased in orange juice with air headspace. Principal component analysis (PCA) of volatile compounds allowed to differentiating orange juices deaerated and with air headspace between days 0 and 6 of storage.;A second storage study with not-from concentrated (NFC) orange juice (cultivar Hamlin) described the impact of DO and storage temperature on volatile compounds, AA and color during storage at 5, 13, 21.5, 30.5 and 40°C.;The DO content in the juice samples was modified by gas sparging, followed by pasteurization and storage in amber glass containers at the specified temperatures. Similar to the previous study, the different initial levels of DO in juice with no headspace were: deaerated (58.7+/- 6.3 muM), oxygen saturated (209.7 +/- 76.3 muM), control (152.4 +/- 21.3 muM), and juice control with air headspace (340.9 +/- 64.5 muM). The juice with the highest loss of AA was the one air headspace with 100%, 73.5% and 54.4% of AA loss after 60 days of storage at 5°C, 3 days of storage at 40°C and 6 days of storage at 30.5°C respectively. Color change was perceived by direct observation only in air headspace orange juice stored 3 days at 40°C, Color change was also measured using a and b parameters than changed toward the red and blue respectively. No correlation with dissolved oxygen content was established.;Volatile compounds were measured by SPME headspace and GC-MS after gas sparging and pasteurization and identified by matching with database and LRI values. Each replicate was obtained from a different batch of orange juice and relative standard deviations of more than 50 were observed in the raw peak areas of the replicates of the same sample. Although it was initially thought that differences in oil content could be the cause of the variability, differences between replicates were not detected by Scott oil measurement. Three different normalizations were applied to volatiles raw peaks: normalization with 4-heptadecanone added as internal standard to all the samples, normalization with total peak area and normalization with respect to day 0. Normalization with total peak area gave relative standard deviations smaller than the other two normalizations and was selected for further ANOVA and PCA analysis.alpha-pinene content was higher in juice with air headspace juice, beta-myrcene and beta-elemene were lower in control and oxygen saturated juices and octanal was lower in deaerated and oxygen saturated juices. Furfural, alpha-terpineol, beta-terpineol were only detected at day 6, and 1-hexanol content increased over the time. These observations were significantly different and confirmed with PCA.;The results of this research suggest that since dissolved oxygen does not have an important impact on vitamin C, color and aroma of orange juice, deaeration of juice may not be necessary in citrus processing for short term storage. Rather, removing air headspace from storage containers or replacing air headspace with nitrogen will reduce the oxidation of vitamin C during storage. The results of this research may possibly be applied to other fruit juices, nectars or purees containing oxygen sensitive compounds and high concentration of vitamin C.