Ascorbic acid, aroma compounds and browning of orange juices related to PET packaging materials and pH

The ascorbic acid content of orange juice made from concentrate was measured after 9 months of storage at 20°C in glass, standard monolayer polyethylene terephthalate (PET,), multilayer PET (PET2) and plasma-treated PET (PET3) containers. Glass enabled the best preservation of ascorbic acid and, in plastic packaging materials, ascorbic acid losses were correlated with their oxygen permeability. PET2 and PET3, which exhibit oxygen permeability 10 times less than that of PET1, enabled a gain of 100 mg L-1 after 9 months of storage. Freshly hand-squeezed orange juice samples were adjusted to various pH values using sodium hydroxide; a rise in the pH from 3.2 to 4.0 significantly reduced the amounts of off-flavours (i.e., furfural and a-terpineol) appearing during storage, by 79% and 65%, respectively. Moreover, an increase in the pH from 3.2 to 4.0 enabled the protection of ascorbic acid levels without detrimentally increasing non-enzymatic browning. © 2006 Society of Chemical Industry.