Comparison of the physicochemical and functional properties of some fruit and vegetable by-products

The fruit and vegetable processing industry generates a significant amount of by-products, and the disposal of these materials plays a critical role from environmental and economic perspectives. However, these by-products are rich in pigments, polyphenols, and other bioactive compounds, presenting substantial potential for the development of functional foods. The aim of this thesis is to determine the changes in the physicochemical and functional properties of fruit and vegetable by-products after convective drying and to contribute to further studies on their potential for revalorization. Within the scope of this thesis, by-products such as peels, pomace, and seeds generated during the processing of various fruits and vegetables (pineapple, avocado, tomato, apple, grapefruit, mandarin, banana, black carrot, cauliflower, celery, red beet, and leek) were evaluated in both fresh form and as powders after drying at 60 °C. For this purpose, the following analyses were conducted; moisture and ash content, pH, color parameters (L*, a*, b*, C*, h°), water activity, water solubility index, water and oil holding capacities, total phenolic content, total flavonoid content, antioxidant activity, and total carotenoid content. According to the analysis results, avocado seed stood out in terms of bioactive properties. The total phenolic content of fresh and dried avocado seeds was found to be 2816.87 and 1363.96 mg/100g DM, respectively; total flavonoid content was 967.23 and 1165.67 mg/100g DM, and antioxidant activity values were 121.90 and 54.13 µM Trolox/100g DM, respectively. In terms of total carotenoid content, fresh (85.37 mg/100g DM) and dried (64.40 mg/100g DM) cauliflower leaves showed the highest values. The highest water solubility index was observed in pineapple peel (44.88%) and grapefruit residue (49.71%). Black carrot pomace exhibited the highest water and oil holding capacities, at 14.86 g water/g sample and 3.25 g oil/g sample, respectively. This study identified important properties of by-products generated in the food industry and provided scientific data for their transformation into value-added products in future research. With the results obtained, it is predicted that fruit and vegetable by-products might shed light on new applications in terms of sustainability.