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The natural approach to food stabilisation is at the forefront of research on plant compounds for food use. Matrix interactions and stability studies of the incorporated foods are necessary prior to further food processing. In this study, apple peel phenolic fractionated based on acidity (flavonoids and phenolic acids) were added to a commercial bottled tomato juice. The juice was left open i.e. air in the headspace at 4°C for 4 days to assess its physical-chemical quality, and for 10 days for the microbiological analysis. Quality markers were analysed (colour and turbidity) and showed that apple peel phenolics, particularly procyanidins, could form insoluble complexes with colloidal pectins thus affecting the turbidity; this led to brighter juice colours with enhanced yellowness due to added flavonol glycosides. The presence of other natural antioxidants (i.e. ascorbic acid and carotenoids) in the tomato juice was not affected by the presence of peel phenolics. Ascorbic acid was partially reduced during storage in all the juice samples. However, such decrease was counterbalanced by the presence of the added peel phenolics whose amount remained constant over time, thus contributing to a higher radical scavenging capacity compared to the control. The microbiological spoilage of the opened tomato juice was also delayed by 2-3 days in the presence of apple peel phenolics compared to the control. As a result, the open-package shelf-life of the bottled tomato juice was extended. The antimicrobial capacity was possibly due to the acidity of phenolic acids and the presence of apple flavonoids such as flavan-3-ols and flavonols that are likely to affect the transportation of nutrients across the cell membranes of the spoilage microflora.
Massini, L., Rico, D., Martin-Diana,A. and Barry-Ryan, C. (2016) Quality markers of functional tomato juice with added apple phenolic antioxidants. Beverages 2016, 2(1), 4. doi:10.3390/beverages2010004