The development of food products that contain value-added dietary fi bre beside different classes of phytochemicals is of great interest nowadays. The present research aimed to evaluate the powder obtained from onion processing waste (OPW) for its potential use as a value-added by-product in food sector. Data on chemical and microbiological characterization of onion processing waste powder (OPWP) were obtained. The dietary fi bre content and antioxidant activity were also determined. The results showed that the OPWP was a low-calorie natural source of insoluble fi bres (60.52±0.13 g/100 g dw), total phenols (41.04±1.22 mg GAE/g dw), and total fl avonoids (20.44±1.22 mg QE/g dw). Moreover, the OPWP could be considered as an important source of total fructans (9.04±0.28 g/100 g dw), fructooligosaccharides (2.76 g/100 g dw), and inulin (2.41±0.18 g/100 g dw). In conclusion, this OPWP could be used as a value-added and healthy food ingredient.

Enzyme-assisted extraction of carotenoids from tomato peels of the Bulgarian cultivar "Stela", one of the most widely used cultivars by the canning industry, was examined in this study. The carotenoid content in raw tomato peels was established by HPLC analysis. A two-step protocol was followed: the tomato peels were fi rst treated with enzymes and then extracted by the use of acetone as a solvent for 30 min at 20±1 °C and solid/liquid ratio of 1:30. The total carotenoid, lycopene, and β-carotene extraction yields were increased by the use of pectinase, cellulase, endo-xylanase, and proteinase enzymes in comparison with the non-enzyme-treated samples. The increase in the extraction yield was affected by the enzymes used, the enzyme concentration, the pretreatment time and temperature. Maximum total carotenoid (55.15 mg/100 g d.w.), β-carotene (35.85 mg/100 g d.w.), and lycopene (15.44 mg/100 g d.w.) extraction yields were obtained in peels pretreated with mixed cellulase (100 U g -1 ) and endo-xylanase (400 U g -1 ) for 4 h at 50 °C. Carotenoid recovery by mixed cellulolytic and hemi-cellulolytic enzyme pretreatment of tomato peels is a good approach, which can be used for waste utilization.

The quantity of tomato wastes combined with beneficial characteristics of components of the wastes justifies the great interest of researchers and manufacturers in extracting of carotenoids from this low cost material. In this study the response surface (RSM) approach and Box-Behnken design (BBD) were used to explore the possibility of modelling and optimisation the organic solvent extraction of total carotenoids from Bulgarian tomato processing waste (TPW).  Bulgarian TPW consists of tomato pomace was used in this study. Dried and ground TPW was plased in the extraction flask and stirred with acetone at various extraction conditions. The extract obtained was vacuum filtered through filter paper and was subjected to spectrophotometrically total carotenoids content determination. A three-variable, three-level BBD of RSM was employed in optimisation the extraction conditions for the highest recovery of total carotenoids from Bulgarian TPW. A response surface quadratic model was developed and statistical analysis was carried out. Data concerning model adequacy tests indicated that the values of R2 and Radj2 for quadratic model were the higest in comparison to the other models. The obtained F-value of 38.65 implies the model was significant (p < 0.05) and could be used for optimisation. The effects of extraction temperature, solvent to solid ratio and extraction time were significant in total carotenoids yield. Total carotenoids content ranged from 9.78 to 25.28 mg/100 g dried TPW. The predicted values of total carotenoids content were closed to the experimental observed values. By use of RSM the optimal extraction conditions were determined as follow: extraction time of 90 min, solvent to solid ratio of 60 mL/g and extraction temperature of 50ºC. The results obtained showed that predicted (28.40 mg/100 g dried TPW) and experimental (28.86±0.92 mg/100 g dried TPW) values of total carotenoids content were not significant different (p > 0.05).

Onion processing waste (OPW) was dried in a convective hot-air laboratory scale dryer at 50, 60, 70 and 80ºC. The effect of drying temperature on the drying characteristics and on the total phenolic and total flavonoid content of dried samples was determined. Three mostly used models were applied for fitting the experimental drying curves. The results indicated that the constant rate-drying period was not observed and that the logarithmic model was the most suitable for fitting the experimental drying kinetic data. The drying temperature significantly affected the total phenolic and total flavonoid content of dried OPW. The values of effective diffusivity were calculated and the determined value of activation energy was 28.05 kJ/mol.

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