Quality markers of functional tomato juice with added apple phenolic antioxidants

Using natural antioxidants instead of synthetic additives for food stabilisation is at the forefront of research in food formulation. Matrix interactions and stability studies of the incorporated foods are necessary prior to further processing. In this study, apple peel phenolics were added to a commercial bottled tomato juice. The juice was opened and then stored in the presence of air in the headspace at 4^˝C for four days to assess its physical-chemical stability (pH, turbidity, colour and total phenolic content) and nutritional content (ascorbic acid and total carotenoids); it was also stored at 4^˝C for 10 days for the microbiological analysis. The antimicrobial capacity of the phenolic extracts was tested against a range of food borne pathogens and spoilage microorganisms. Results showed that apple peel phenolics could form complexes with colloidal pectins thus increasing the turbidity, even though this effect was not significant during the four-day storage; the colour of the enriched juice was brighter with enhanced yellowness due to added pigments such as flavonol glycosides. The presence of other natural antioxidants (ascorbic acid and carotenoids) in tomato juice was not affected by the addition of peel phenolics. Ascorbic acid was partially reduced during storage in all the juice samples; however, the presence of the added peel phenolics whose amount remained constant over time significantly contributed to a higher radical scavenging capacity compared to the control. The microbiological spoilage of the opened tomato juice was also delayed by two to three days in the presence of apple peel phenolics compared to the control. The antimicrobial capacity was due to a bacteriostatic effect of the phenolic extracts mostly against the growth of yeasts; the antimicrobial capacity was related to the acidity of phenolic acids and the presence of apple flavonoids such as flavan-3-ols.