Revalorising tomato by-products from salmorejo and gazpacho production for nutritional and functional food ingredients

The food industry generates substantial amounts of by-products, which present both environmental challenges and opportunities for resource recovery. Tomato by-products, particularly from the production of the typical Mediterranean cold vegetable soups salmorejo and gazpacho, retain great amounts of tomato nutrients and are rich in bioactive compounds with potential functional benefits. The main aim of this study was to revalorise tomato by-products into powdered ingredients with a high content of bioactive compounds, protein, and/or fibre to formulate foods for human or animal consumption.

The complete by-product obtained after the industrial production of V-range salmorejo and gazpacho, in addition to the tomato peels and seeds separated from the gazpacho by-product, were dried in an infrared oven at 80 ºC until the moisture content was below 10 %. Then, the dried tomato by-products were ground and sieved to 2 mm particle size, resulting in four potential ingredients. Total carotenoids, phenolic compounds, and antioxidant activity were evaluated spectrophotometrically, whereas individual carotenoids and vitamin C were determined by HPLC-DAD. Protein content was measured using the Dumas method, and fibre fraction contents were also assessed.

The highest carotenoid, phenolic content, and antioxidant capacity were found in gazpacho waste > salmorejo waste > tomato peel > tomato seeds, whereas vitamin C was not detected. However, the highest protein content was found in seeds (26%), while gazpacho and salmorejo wastes had among 18-21%, and peels had 8%. Regarding acid detergent fibre, related to fermentability in the rumen, the content was acceptable in all the by-products except for tomato peel, which had a high content that is difficult to digest.

Therefore, gazpacho waste exhibited the best combination of nutritional and functional properties, making it a promising ingredient for use in food or feed.