Bioactive components and protein content in black carrot leaves

Abstract

Black carrot leaves are considered food waste, even though they may be a multifunctional food commodity. Black carrot leaves contain various bioactive compounds such as phenolics, flavonoids, and proteins, making them a valuable resource for multiple applications in the food industry. In this study, black carrot leaves (BCL) were cold pressed, and 357.47± 40.17 g BCL cold-pressed resulted in 159.51± 14.03 g pulp and 176.50± 28.79 g leaf juice. So, the yield was calculated as 49.22± 4.47 % g leaf juice/ g leaves. The obtained leaf juice was analyzed for TPC (total phenolic content), TFC (Total flavonoid content), CUPRAC (Antioxidant capacity), and DPPH (Antioxidant capacity measurement) analyses by using spectrophotometric methods. The measurements were recorded as 1.912± 0.209 mg Gallic Acid/ g BCL, 2.914± 0.592 mg Quercetin/ g, 6.586± 0.882 mg Trolox/ g BCL, and 0.273± 0.166 mg Trolox/ g BCL, respectively. Subsequently, the protein content in the juice was precipitated by two different methods: acid treatment and heat treatment. The protein yield was calculated as 0.0020± 0.0004 g protein per g BCL via acid-treatment. The protein yield was calculated as 0.0011± 0.0003 g protein per g BCL via heat treatment. The protein content in BCL was determined by the Kjeldahl method. Due to sustainability concerns, the heat-treatment method was chosen in the following steps. The proteins extracted via heat treatment were subjected to in vitro digestion, employing a laboratory setup mimicking the human gastrointestinal tract without symbiotic bacteria in the intestine. This simulation demonstrated that human digestive enzymes can break down Black Carrot Leaves (BCL) proteins, and the Bradford assay examined the results. Moreover, techno-functional properties critical for food and selecting the place to use it were examined. These are water-holding capacity, oil-holding capacity, emulsifying activity and stability, solubility, and foam capacity and stability properties. As a result, the water holding capacity is 4.62± 0.31 g water/ g Pdry, and the oil holding capacity is 5.38± 0.225 g corn oil/ g Pdry. On the other hand, Emulsifying Activity Index (EAI) and Emulsifying Stability Index (ESI) values were examined according to different pH values. EAI increases with increasing pH and reaches its highest value at pH 12. ESI gives very different low or high values with very little pH change. When the solubility was examined as a percentage, it was observed that it increased and as it approached neutral (pH = 7). And, the solubility reached the maximum at pH 12. Foam capacity (FC) and foam stability (FS) values were found to be 0.0516± 0.037% and 33.53± 18.27%, respectively. The evaluation of the antioxidant capacity of BCL, the extraction of protein, and the evaluation of techno-functional properties of BCL, which were commonly considered food waste post-harvest, hold significant importance from a sustainability point of view. Understanding the composition of BCL and its potential applications can contribute to minimizing food waste and exploring sustainable alternatives across multiple sectors.