Heliyon (Jun 2024)
Sour orange (Citrus aurantium) seed, a rich source of protein isolate and hydrolysate – A thorough investigation
Abstract
Sour orange (Citrus aurantium) seeds are typically discarded by juice processors as waste. This study aimed to extract protein isolates, produce hydrolysates from de-oiled sour orange seeds (SOS), and characterize their physicochemical properties. Previous studies have described methods to obtain protein isolates and hydrolysates from agricultural residues. However, there is limited data on the SOS. This research characterized protein isolates and hydrolysates from SOS, emphasizing yield, purity, and amino acid composition. Protein isolates were extracted using borate saline buffer, saline, and distilled water. Enzymatically hydrolysis was conducted using Protamex® (a commercial protease) at concentrations ranging from 0.2 to 5 g enzyme/100g protein isolate. Differential scanning calorimetry, electrophoresis, and FT-IR spectroscopy were utilized to characterize the isolates and hydrolysates. Data showed that using 5 % saline resulted in protein extraction with a yield and purity of 30 and 86 %, respectively. DSC analysis revealed that the denaturation temperature of the protein isolate was 68 °C, while the hydrolysates exhibited structural instability, as indicated by a decrease in enthalpy change compared to the isolate. The protein isolate had a 76° contact angle. The amino acid profile showed a significant presence of glutamic acid (130.530 mg/g) and arginine (70.210 mg/g). Electrophoresis analysis exhibited four major bands of the protein. The bands' intensity decreased, and new bands appeared after hydrolysis. The enzyme hydrolysis was confirmed using the O-phthaldialdehyde method and FTIR. Findings revealed that based on the free amine group quantity, the hydrolysate obtained using 5 g enzyme/100g protein isolate was 14.220 ± 0.299 μmol/mg protein. The study concluded that sour orange seeds are a good source of protein, with protein isolates and hydrolysates exhibiting desirable characteristics. More research needs to be conducted to acquire further information about their functional properties and potential applications.
