Valorization of carrot processing by-products through fermentation and extrusion for enhanced bioactive content and bioaccessibility

Abstract

The valorization and effective utilization of food processing by-products and food waste have become crucial for sustainable food production with the growth of the food industry. Carrots (Daucus carota), among the most consumed vegetables worldwide, come in various colors like orange, red, purple, white, and yellow. These vegetables are rich in bioactive compounds such as dietary fibers, carotenoids, anthocyanins, and phenolic compounds. However, the carrot processing industry produces pomaces rich in these bioactive compounds. These by-products hold significant potential and can be transformed into valuable components through sustainable techniques, contributing to healthier food options and environmental sustainability. This research aims to convert carrot pomace into high-value functional food ingredients by optimizing fermentation and extrusion processes. Fermentation is a common method that contributes to the nutritional profile of food by-products. In this study, carrot pomace was fermented using different strains of lactic acid bacteria (LAB), including Lactobacillus plantarum, Lactobacillus casei, and Lactobacillus acidophilus. The fermentation process was optimized to enhance the bioactivity of compounds of the final product. Conditions were optimized to increase the bioactive potential of black and orange-colored carrot pomace, with measurements of total phenolic content, antioxidant capacity, and individual phenolic profile. Fermentation affected total titratable acidity and lactic acid production, with L. plantarum showing the highest increases in orange-colored carrot pomace (OCP). While citric acid levels initially increased, ascorbic acid levels decreased across all cultures. Black carrot pomace (BCP) fermented with L. casei had the highest phenolic content (611.42 mg GAE/100 g dw) and antioxidant activity on the third day. The total phenolic content of OCP reached its highest level on the third day with both L. casei and L. plantarum. Variations in phenolic acid profiles were observed based on carrot type; BCP was rich in neochlorogenic and chlorogenic acids, while OCP was rich in gallic and p-coumaric acids. Particularly high anthocyanin content (especially cyanidin derivatives) was found in black carrot pomace fermented with L. casei. Similarly, OCP showed increases in α-carotene and β-carotene levels on the third day with L. casei. Carotenoid analysis revealed that BCP contained only α-carotene, reaching the highest levels after four days of fermentation with L. plantarum. For beverages with broad consumption, fermented carrot pomace was added to orange juice to develop a functional beverage. When added at 2.5% and 5%, both fermented (optimized condition in the study before, with L. casei with 3 day) and unfermented black and orange-colored carrot pomaces significantly improved the bioactive profile of orange juice, enhancing total phenolic content, antioxidant capacity, and anthocyanin levels. Particularly, adding 2.5% and 5% fermented black carrot pomace led to notable increases in these metrics. This suggests that fermented carrot pomace is a valuable component for functional beverages, offering multiple bioactive compounds that support consumer health. Orange juice enriched with carrot pomace offers many bioactive compounds supporting consumer health, presenting a healthier beverage alternative. Especially, black carrot pomace added orange juice showed elevated antioxidant capacity, phenolic content, and anthocyanin levels, enhancing the drink's health benefits. Extrusion is a commonly used method for producing snack products. This study examined mixtures containing black carrot pomace and chickpea flour (10-20% BCP and 20-30% CF) extruded into products, analyzing total phenolic content, antioxidant capacity, and physical properties. Black carrot pomace, a by-product of color production, contains valuable health-promoting components. Using it in starch-based extruded snacks combined with wheat semolina and corn starch, the physical and functional properties, such as expansion rate, hardness, water absorption index (WAI), and water solubility index (WSI), were analyzed in detail. The expansion rate varied from 2.07 to 2.71, increasing with higher chickpea flour concentrations. The extrusion process and resulting molecular structure influenced protein and fiber content, gelatinization, and expansion characteristics, highlighting the need for optimal mixture ratios. High fiber content can break cell walls, limiting air bubble expansion and reducing overall expansion rate. Black carrot pomace concentration correlated with increased product hardness, ranging from 47.14 to 60.50 N versus 23.95 N for the control group. Higher BCP content produced a more compact structure, increasing hardness, evidenced by a negative correlation between hardness and expansion rate. WAI (5.27 to 5.49 g/g) and WSI (20.57 to 22.95 g/100 g) values, influenced by starch gelatinization and molecular breakdown, were significantly higher than initial mix values (3.68 g/g and 10.06 g/100 g), respectively. Extrusion efficiency and flexibility are essential for snack production, especially regarding different ingredient impacts, physical properties, chemical profiles, and bioactive stability. The physical and chemical changes occurring during the extrusion process have had a direct impact on the nutritional value of the products. The effects of adding black carrot pomace to functional foods during the extrusion process were thoroughly examined. Total phenolic content and antioxidant capacities are fundamental components determining the bioactive properties of extruded products, and these values significantly increased following the extrusion process. In addition, the effects on phenolic acids and anthocyanins were investigated through a simulated gastrointestinal digestion process. During in vitro simulated gastric digestion, phenolic acid and anthocyanin levels increased by 48-382%, however, anthocyanins were not detectable after simulated intestinal digestion. This highlights the adverse effect of high temperature and pressure on the molecular integrity of anthocyanins, indicating a need for further research to preserve these compounds. Despite promising results, some challenges were noted. Anthocyanin levels decreased during extrusion, suggesting the need for process optimization to preserve these compounds. Fermentation's specific biochemical effects and the stability of altered bioactive compounds need deeper investigation. Findings based on in vitro digestion simulations should be supported by in vivo studies to understand health benefits and bioavailability fully. Sensory evaluations for consumer acceptance and effects of higher carrot pomace concentrations should be further explored. Optimizing extrusion parameters, such as high temperature and pressure, and developing new technologies to enhance the stability of phenolic compounds in black carrot pomace are essential. Future research should refine fermentation parameters to improve phytochemical content, taste, and commercial viability. Integrating fermented carrot pomace into various food products, such as probiotic-rich drinks, dairy, and plant-based foods, offers significant opportunities. Optimizing extrusion to preserve anthocyanins and incorporating higher carrot pomace levels can lead to nutritionally rich snacks. Understanding bioactive compound interactions during processing and digestion requires comprehensive in vivo studies, increasing commercial viability and consumer acceptance. Developing new formulations and extrusion techniques will promote wider use of black carrot pomace in snack products. Optimizing fermentation and extrusion processes can convert carrot pomace into high-value functional food ingredients, supporting a sustainable circular economy and enhancing food security and environmental sustainability. By valorizing agricultural by-products such as orange and black carrot pomaces, we can not only reduce food waste but also create innovative food solutions that meet consumer demands for healthier, nutrient-rich options. This research underscores the potential for integrating bioactive-rich orange and black carrot pomaces into mainstream food production, ultimately contributing to global sustainability initiatives and encouraging more responsible consumption and production designs within the food industry.