Impact of high pressure processing on total antioxidant activity, phenolic, ascorbic acid, anthocyanin content and colour of strawberry and blackberry purées

The present study was undertaken to assess the effect of high pressure treatments and conventional thermal processing on antioxidant activity, levels of key antioxidant groups (polyphenols, ascorbic acid and anthocyanins) and the colour of strawberry and blackberry purées. Bioactive compounds (cyanidin-3-glycoside, pelargonidin-3-glucoside, ascorbic acid) and antioxidant activity were measured in strawberry and blackberry purées subjected to high pressure treatment (400, 500, 600 MPa/15 min/10-30 °C) and thermal treatments (70 °C/2 min). Samples were assessed immediately after processing. Different pressure treatments did not cause any significant change in ascorbic acid (p >0.05). In contrast, following thermal processing (P₇₀ >=2 min) ascorbic acid degradation was 21% (p <0.05) as compared to unprocessed purée. However, no significant changes in anthocyanins were observed between pressure treated and unprocessed purées (p >0.05), whereas conventional thermal treatments significantly reduced the levels (p <0.05). In general, antioxidant activities of pressure treated strawberry and blackberry purées were significantly higher (p <0.05) than in thermally processed samples. Colour changes were minor (ΔE) for pressurised purées but the differences were slightly higher for thermally treated samples. Redness of purées was well retained in high pressure treated samples. Therefore processing strawberry and blackberry by high pressure processing could be an efficient method to preserve these products quality. Hence high pressure processing (HPP) at moderate temperatures may be appropriate to produce nutritious and fresh like purées. Industrial relevance: This research paper provides scientific evidence of the potential benefits of high pressure processing in comparison to thermal treatments in retaining important bioactive compounds. Antioxidant activity (ARP), ascorbic acid, and anthocyanins after exposure to high pressure treatments (400-600 MPa) were well retained. Our results also show that redness and colour intensity of strawberry and blackberry purées were better preserved by high pressure processing than conventional thermal treatment. From a nutritional perspective, high pressure processing is an attractive food preservation technology and offers opportunities for horticultural and food processing industries to meet the growing demand from consumers for healthier food products. Therefore high pressure processed foods could be sold at a premium than their thermally processed counterparts as they will have retained their fresh-like properties.