Valorization of fermented purple carrot pomace, a by-product from shalgam juice, as functional ingredient: A food application and assessment of bioaccessibility

Abstract

Shalgam juice is a traditional beverage produced by lactic acid fermentation. As its commercial production grew over time, it's no longer a local drink. Therefore, shalgam juice is now being promoted and consumed all over Türkiye and the world. The increase in industrial production has led to high-volume production and the processes have resulted in large quantities of important outputs/wastes. The most important of these is purple carrot, which is the main raw material of shalgam juice production. Fresh purple carrot, which can be used in shalgam juice recipes at ratios between 15-25%, is released in fermented form as a result of lactic acid fermentation in the shalgam juice production plants. The fermented purple carrot left at the end of fermentation is considered as fermented purple carrot pomace and handled within the framework of food waste management. Its use as animal feed is the most common evaluation way. However, there is no value-added recycling or upcycling in industrial practice. In this study, fermented purple carrot pulp left over from industrial shalgam juice produced in the traditional process was dried via freeze-drying process. The physicochemical properties, total phenolic compound (TPC), total flavonoid content (TFC), total antioxidant capacity by DPPH and CUPRAC methods (TAC), individual phenolic compounds profile and dietary fibre (DF) characterization of the fermented purple carrot pomace powder were investigated. According to the results regarding characterization of FPCPP, which was studied for valorization purpose, TPC was found as 1041±76 mg GAE/100 g, TFC 1051±62 mg CE/100 g, CUPRAC 2476±143 mg TE/100, DPPH 1224±51 mg TE/100 g. FPCPP exhibited the highest values (p<0.05) among all samples analysed. In indiviual phenolic compound browsing by chromatographic method, epicatechin, caffeic acid, cyanidin-3-O-glucoside, ferulic acid, gallic acid, protocatechuic acid and syringic acid were quantified. Cyanidin-3-O-glucoside which is the anthocyanin source of the powerful purple colour was 67.31±0.78 mg/100 g in undigested of FPCCP. In addition, the dietary fibre value of the pomace powder was found to be 29.3±2%. In order to evaluate the bioaccessibility of the bioactive compounds, in vitro simulated gastrointestinal digestion has been conducted. As for bioaccessibility percentages of FPCPP were measured as follows: 104.8±13% for TPC, 99.6±23% for TFC, 69.0±10 for CUPRAC and 13.3±2% for DPPH. It aims to evaluate pomace powder as an ingredient in a food to develop functional food and to reveal and compare its effect on bioaccessibility during in vitro digestion model for the food to which it is applied. When the enrichment is performed with both pomace powder or commercial apple fibre, raw meatballs, which can already be declared as a source of fibre, would now be declared as increased fibre or more fibre. In the bioaccessibility evaluation by in vitro digestion model, freeze-dried fermented purple carrot pomace powder (FPCPP), commercial apple fibre (CAF), raw meatballs (RM), FPCPP added raw meatballs (5.5%) (RM + FPCPP), commercial apple fibre added raw meatballs (2.7%) (RM + CAF) samples were subjected to analyses. In vitro before and after measurements and comparisons were performed with regard to TPC, TAC, TFC, phenolic compounds profile. Spectrophotometric and chromatographic methods were followed respectively. To sum up, the aim of this study was firstly to characterize the fermented purple carrot pomace from shalgam juice production in terms of bioactive components such as total phenolic content, total flavonoid content, total antioxidant capacity (CUPRAC and DPPH), phenolic profile by HPLC and dietary fibre; secondly to serve the purpose of valorization by using fermented purple carrot pomace as a functional food ingredient in a food (raw meatball) in order to provide functionality in terms of dietary fibre content, bioactive components and thirdly to evaluate the bioaccessibility of the pomace and the other samples including commercial apple fibre which can be a substitute for the pomace. It was deduced that the pomace powder, which was found to be a rich and important source of bioactive components and fibre, can be utilized as a functional food ingredient to improve the nutritional profile. It has also been shown that it has the potential to find a place as a substitute for commercially produced fibres. Furthermore, the enriched raw meatball samples were also subjected to sensory analysis. It cannot be said that this type of addition makes the sensory profile of the foods to which it is added more unfavourable than the control group. It was also found that it did not impair its general acceptability. It was observed that the food application may not be limited to raw meatballs, and FPCPP may support the increase in the nutritional aspect of the foods to which it is added by adding it to other foods. Therefore, it was concluded that the opportunity regarding the valorization of FPCPP is valid for application in foodstuffs and can serve the purpose of upcycling.