Effect of the Degree of Hydrolysis on Nutritional, Functional, and Morphological Characteristics of Protein Hydrolysate Produced from Bighead Carp (Hypophthalmichthys nobilis) Using Ficin Enzyme

Valorization of fish processing by-products for protein hydrolysate recovery: Opportunities, challenges and regulatory issues

Protein-rich fish processing by-products, often called rest raw materials (RRM), account for approximately 60% of the total fish biomass. However, a considerable amount of these RRM is utilized for low-value products such as fish meal and silage. A promising and valuable approach for maximizing the utilization of RRM involves the extraction of bioactive fish protein hydrolysate (FPH). This review assesses and compares different hydrolyzation methods to produce FPH. Furthermore, the review highlights the purification strategy, nutritional compositions, and bioactive properties of FPH. Finally, it concludes by outlining the application of FPH in food products together with various safety and regulatory issues related to the commercialization of FPH as a protein ingredient in food. This review paves the way for future applications by highlighting efficient biotechnological methods for valorizing RRM into FPH and addressing safety concerns, enabling the widespread utilization of FPH as a valuable and sustainable source of protein.

Sour orange (Citrus aurantium) seed, a rich source of protein isolate and hydrolysate - A thorough investigation

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.

Potential of Subcritical Water Hydrolysis to Valorize Low-Valued Ray-Finned Fish (Labeobarbus nedgia): Effects of Hydrolysis Temperature and Pressurization Agent

Subcritical water (SCW) hydrolysis was applied to valorize the low-valued ray-finned fish (Labeobarbus nedgia) into valuable protein hydrolysates, employing N2 and CO2 as pressurization agents at varying temperatures (140, 160, 180, and 200 °C). The degree of hydrolysis (DH) and total free amino acid content increased with temperature for both pressurizing agents. The highest DH (54.5 ± 0.4%) and total free amino acid content (210 ± 1 mg/gprot) were observed at 200 °C when CO2 gas was used as the pressurizing agent. Predominantly, glycine and alanine were released for both pressurizing agents. The antioxidant activity, evaluated through three different assays, increased with temperature and was found to be the highest at 200 °C. This study illustrated the advantages of the intensified SCW technology by using CO2 as a pressurization agent in valorizing low-valued ray-finned fish (Labeobarbus nedgia), as animal residue rich in proteins, for the production of valuable protein hydrolysates with a high fraction of valuable free amino acids, which could offer potential applications as a functional ingredient in the food industry.

Flavor improving effects of cysteine in xylose-glycine-fish waste protein hydrolysates (FPHs) Maillard reaction system

A promising way to utilize fish by-products is to develop hydrolysis of fish proteins with enzymes. The obtained fish protein hydrolysates (FPHs) are rich in peptides and amino acids, but bitterness and aroma defects impede further utilization of FPHs. The present study adopted Maillard reaction to improve FPHs' flavor and illustrated the role of cysteine in this system. We investigated the impact of cysteine (0, 0.25%, 0.5%, 0.75%, and 1%) on the browning intensity, free amino acids (FAAs), molecular weight distribution, structure of MRPs, volatile compounds changes and organoleptic characteristics of xylose-glycine-FPHs Maillard reaction systems. Results showed that the addition of cysteine lowered the browning degree of Maillard reaction products (MRPs) by inhibiting the cross-linking of small peptides and reducing the production of melanin. GC-MS and GC-IMS analysis indicated that cysteine inhibited the formation of furans and nitrogen-containing compounds and facilitated the formation of sulfur-containing compounds contributing to the meaty flavor. Sensory analysis revealed that 0.25-0.75% range of cysteine increased the meaty, caramel, umami, mouthfulness and salty notes, and caused a decrease in bitter taste of the MRPs as confirmed by GC-MS. A highly significant correlation between the organoleptic characteristics and physicochemical indicators of MRPs was found by Mantel test. These results elucidated the influence of cysteine on the formation of Maillard reaction products and will help improve the flavor profile of meat flavorings.

Maximizing Use of Pelagic Capture Fisheries for Global Protein Supply: Potential and Caveats Associated with Fish and Co-Product Conversion into Value-Add Ingredients

Globally, capture fisheries contribute significantly to protein supply and the food security of a third of the world's population. Although capture fisheries production has not significantly increased in tonnes landed per annum during the last two decades (since 1990), it still produced a greater tonnage of protein than aquaculture in 2018. Policy in the European Union and other locations favors production of fish through aquaculture to preserve existing fish stocks and prevent extinction of species from overfishing. However, aquaculture production of fish in order to feed the growing global population would need to increase from 82 087 kT in 2018 to 129 000 kT by 2050. The Food and Agriculture Organization states that global production of aquatic animals was 178 million tonnes in 2020. Capture fisheries contributed 90 million tonnes (51%) of this. For capture fisheries to be a sustainable practice in alignment with UN sustainability goals, ocean conservation measures must be followed and processing of capture fisheries may need to adapt food-processing strategies already used extensively in the processing of dairy, meat, and soy. These are required to add value to reduced fish landings and sustain profitability.

Influence of the Enzymatic Hydrolysis Using Flavourzyme Enzyme on Functional, Secondary Structure, and Antioxidant Characteristics of Protein Hydrolysates Produced from Bighead Carp (Hypophthalmichthys nobilis)

In the current study, bighead carp fish were used in conjunction with the flavourzyme enzyme to obtain (FPH) fish protein hydrolysates. The optimum conditions of the hydrolysis process included an enzyme/substrate ratio of 4% and a temperature of 50 °C and pH of 6.5. The hydrolysis time was studied and investigated at 1, 3, and 6 h, and the (DH) degree of hydrolysis was recorded at 16.56%, 22.23%, and 25.48%, respectively. The greatest yield value was 17.83% at DH 25.48%. By increasing the DH up to 25.48%, the crude protein and total amino acid composition of the hydrolysate were 88.19% and 86.03%, respectively. Moreover, more peptides with low molecular weight were formed during hydrolysis, which could enhance the functional properties of FPH, particularly the solubility property ranging from 85% to 97%. FTIR analysis revealed that enzymatic hydrolysis impacted the protein's secondary structure, as indicated by a remarkable wavelength of amide bands. Additionally, antioxidant activities were investigated and showed high activity of DDPH radical scavenging, and hydroxyl radical scavenging demonstrated remarkable activity. The current findings demonstrate that the functional, structural, and antioxidant characteristics of FPH might make it an excellent source of protein and suggest potential applications in the food industry.

Collagen and Keratin Hydrolysates to Delay the Setting of Gypsum Plaster

Leather and wool waste represent a high concern due to the low level of valorization and circular economy demands for upcycling of biomass resources. Both biomasses can be easily processed as protein hydrolysates and used as functional additives due to the amphiphilic and tunable properties of collagen and keratin proteins. The chemical, physical, and structural investigations of collagen and keratin hydrolysate properties showed that the chelating abilities due to carboxylic groups can be exploited for gypsum retardant additives. The molecular weights and amino acid compositions of three different hydrolysates showed only slight influences on the setting time of gypsum; all three proteins delayed the setting time of gypsum between 60 and 120 min, as compared to the commercial plaster with a 30 min setting time. Higher molecular weight and more carboxylic active groups showed slight improvements in the setting time of mortars. The improved properties of keratin hydrolysate as compared to low molecular collagen hydrolysate were attributed to foaming and conductive properties. The mechanism of mortar setting delaying through calcium ions complexation by protein hydrolysates was shown by electric conductivity evolution of plasters with and without protein additives over time, supported by foaming properties, amino acid, and functional groups' composition. Lower bending strength values for the higher concentration of proteins do not reduce the potential to use the protein hydrolysates as retardant additives in mortar fabrication.

Factors affecting sericin hydrolysis and application of sericin hydrolysate in sericin films

Sericin is a natural protein and a by-product obtained from silk processing. To enhance the antioxidant properties of sericin, sericin hydrolysis was studied. The solvent effects (distilled water, citric acid and hydrochloric acid) and hydrolysis methods (heat treatment (water bath) and mild ultrasonic treatment at 20%, 40% or 60% amplitude) were investigated on the properties of sericin hydrolysate (SH). Furthermore, solvent effects (distilled water and 15% ethanol) were examined for the properties of the sericin films incorporated with selected SH. The SH samples from acid hydrolysis and the ultrasonic method had a darkened visual appearance. However, the degree of hydrolysis and antioxidant activity of SH increased with ultrasonic-assisted acid hydrolysis. The molecular weight (MW) of sericin was notably reduced. As expected, hydrochloric acid hydrolysis resulted in a lower MW for the SH than from citric acid. Thus, SH from hydrochloric acid and 20% amplitude in the ultrasonic method were selected to produce a sericin film. As revealed, using distilled water as a general solvent provided films with lower solubility and water vapor permeability but higher tensile strength. Furthermore, the addition of SH enhanced the antioxidant properties of its hydrolysate as a novel protein packaging film material for various applications.