Understanding the effect of temperature and time on protein degree of hydrolysis and lipid oxidation during ensilaging of herring (Clupea harengus) filleting co-products

Abstract

The aims of this study were to investigate the effect of temperature, time and stirring on changes in protein degree of hydrolysis (DH), free amino acids (FAA), lipid oxidation and total volatile basic nitrogen (TVB-N) during ensilaging of herring (Clupea harengus) filleting co-products. Results showed that temperature and time, and in some cases the interaction effect between these two factors, significantly influenced all the studied responses. Increasing ensilaging temperature and time from 17 to 37 °C and 3 to 7 days, respectively, increased DH, FAA, and TVB-N content from 44.41 to 77.28%, 25.31 to 51.04 mg/g, and 4.73 to 26.25 mg/100 g, respectively. The lipid oxidation marker 2-thiobarbituric acid reactive substances (TBARS) did not increase with time at temperatures above 22 °C, while 2-pentylfuran increased up to 37 °C. Based on the process parameters and responses investigated in this study, and considering energy requirements, it was suggested to perform ensilaging at ambient temperatures (i.e. around 20 °C) with continuous stirring at 10 rpm for 1-3 days; the exact length being determined by the desired DH. Along with population growth and an increased awareness about the role of protein in a healthy diet, the demand for seafood convenience products is steadily growing 1-6. As a result, around 70% of all caught/farmed fish is today processed before final sale, in turn generating around 20-80% co-products depending on the type of fish and level of processing 7. These co-products can be valorized to feed or potentially to food ingredients by ensilaging, which according to the definition of green chemistry proposed by Anastas and Warner 8 , can be described as a "green" process. Ensilaging has several advantages over e.g. fishmeal production such as lower energy and investment requirements, and the flexibility to start the process even in smaller scales at small fish processing sites where fishmeal production is not economically feasible 9-11. Another important aspect is that an acid preserved ensilaging product (i.e. silage) does not putrefy and is considered as almost sterile 9. Ensilaging can thus be used to stabilize sensitive fish co-products right after their generation. The principle of ensilaging is quite simple; minced fish co-products are mixed with organic acids (e.g. formic acid) to lower the pH to a value below 4.0, which preserves co-products against bacterial growth and at the same time induces endogenous protease-mediated autolysis 10. Several studies have reported positive outcomes in animals using silage in their diet 12,13 , e.g. improved growth performance, immunological status, health and welfare, which is believed to be due to the short-chain peptide contents of silage. Further, the amino nitrogen is more readily absorbed from short-chain peptides (2-6 amino acids

Hemoglobin-mediated lipid oxidation of herring filleting co-products during ensilaging and its inhibition by pre-incubation in antioxidant solutions

“…The fact that both PV and TBARS values increased significantly ( p < 0.05) over time in all samples was in line with our earlier findings 11 , confirming that herring co-product ensilaging is a system with high sensitivity to oxidation, despite the gradual formation of short-chain, potentially antioxidative, peptides 3 . Several earlier studies have shown that fish protein-derived peptides are efficient chelators for low molecular weight (LMW) iron 27 ; however, their inability to prevent oxidation in herring silage points at heme-bound iron or other compounds as being of higher relevance as pro-oxidants.…”

“…Ensilaging was performed by adding 2.5% (v/w) formic acid (85% purity) to minced herring co-products, stirred for 30 min at 10 rpm, followed by storage at ambient temperature (i.e. ~ 22 °C) 3 . The mixture was stirred for 10 min at 10 rpm every day; and, samples were collected at regular time points and stored in 5-ml Eppendorf tubes at -80 °C until further use.…”

“…Besides, the co-products contain significant amounts of protein and long chained n-3 polyunsaturated fatty acids (LC n-3 PUFAs) which should be handled as gently as possible to maintain them in an intact and digestible form 2 . Ensilaging—preservation under acidic conditions—is one of the “green” process options which can be used to valorize fish co-products into feed and/or potential food applications 3 . The principle of ensilaging is quite straightforward; minced fish co-products are mixed with organic acids to lower the pH below 4.0 to preserve the co-products against microbial growth and at the same time induce endogenous protease-mediated autolysis, resulting in a product known as silage 4 .…”

Optimization of temperature and extraction time for the nutritional and phytochemical contents of corn bran with ultrasonic-method

“…This is because the higher the temperature used causes the protein in the extract to decrease. After all, because protein is a nutrient that is easily damaged when it is exposed to high heat [43], [44]. According to [45], the solubility of the protein generally increased when the temperature rises 0-40 o C, and the longer the time of the dissolution, then the more contact between the solute and solvent is getting long, so the solute that is taken will be higher.…”

Hydrolysis Methods for Protein Extraction from Seafood

“…While the application of chemical solvent can help adjust properties of proteins hydrolysates, processing parameters can optimize cost and yield. Sajib et al [17] enzymatic-based hydrolyzed (Clupea harengus) with Box-Behnken design, which advanced parameter control, achieving in 77.28% of hydrolysis yield. Enzyme can be immobilized on a fixed-media in a continuous reactor, promoting applications on a large scale [18].…”