Removal of lipids and diarrhetic shellfish poisoning toxins from blue mussels (Mytilus edulis) during acid and alkaline isolation of proteins

Role of lingonberry press cake in producing stable herring protein isolates via pH-shift processing: A dose response study

The effects of cross-processing lingonberry press cake (LPC) (2.5-30 %, dw/dw) with herring co-products on protein yield, oxidative stability and color of pH-shift-produced protein isolates were investigated. Even at 2.5 % LPC, the formation of volatile oxidation-derived aldehydes, including hexanal, (E)-2-hexenal, heptanal, octanal, and 2,4-heptadienal, were prevented during the actual protein isolate production. Adding 10 % LPC successfully prevented formation of all these aldehydes also during eight days ice storage which was explained by the partitioning of phenolics, especially ideain (1.09 mg/g dw) and procyanidin A1 (65.5 mg/g dw), into isolates. Although higher amounts of LPC (20-30 %) further prolonged the oxidation lag phase, it reduced total protein yield, increased the consumption of acid and base, and darkened protein isolates. Therefore, it is recommended to use 10 % LPC when pH-shift-processing sensitive fish raw materials as a route to mitigate lipid oxidation and at the same time promote industrial symbiosis and more circular food production.

Cross-processing herring and salmon co-products with agricultural and marine side-streams or seaweeds produces protein isolates more stable towards lipid oxidation

Herring and salmon filleting co-products were pH-shift processed together with seven antioxidant-containing raw materials ("helpers") including lingonberry-, apple-, oat-, barley- and shrimp-co-products, and two seaweeds (Saccharina latissima, Ulva fenestrata) to produce protein isolates stable towards lipid oxidation. Malondialdehyde (MDA) and 4-hydroxy-(E)-2-hexenal (HHE) levels revealed that all helpers, except shrimp shells, to different extents retarded lipid oxidation both during pH-shift-processing and ice storage. The three helpers performing best were: lingonberry press-cake > apple pomace ∼ Ulva. Color of protein isolates was affected by helper-derived pigments (e.g., anthocyanins, carotenoids, chlorophyll) and lipid oxidation-induced changes (e.g., metHb-formation, pigment-bleaching). In conclusion, combining fish co-products with other food side-streams or seaweeds during pH-shift processing appears a promising new tool to minimize lipid oxidation of protein isolates, both during their production and subsequent storage. Lingonberry press-cake was the most efficient helper but provided dark color which may narrow product development possibilities, something which requires further attention.

Monitoring and warning of lipophilic marine algal toxins in mariculture zone based on toxin profiles of phytoplankton

Some toxigenic dinoflagellates can produce lipophilic marine algal toxins (LMATs), which are potent threats to marine breeding industries. In this study, a new method based on the profiling analysis of six LMAT classes in phytoplankton was developed for the monitoring and warning of LMATs in mariculture zones. This method was applied to monitor and evaluate LMATs in the Jiaozhou Bay and the Changjiang estuary in China. Results demonstrated that the occurrence and spatiotemporal variations of LMATs in mariculture zones can be revealed by the toxin profiles of phytoplankton, indicating the method's effectiveness for the comprehensive monitoring of the composition and levels of various LMATs in coastal aquaculture zones. The method was further used as an alarm for potential pollution risk from LMATs in mariculture zones at an early stage. The "alert" thresholds of LMAT pollution in the mariculture zones were preliminarily proposed based on the statistical data analysis of LMATs in phytoplankton in three typical mariculture areas in China. This study is the first to conduct simultaneous monitoring and warning of multi-class LMATs based on toxin profiles of phytoplankton, thereby providing new insight into the monitoring and early warning of natural poisonous pollutants in coastal aquaculture zones around the world.

Bioactive peptides from Atlantic salmon (Salmo salar) with angiotensin converting enzyme and dipeptidyl peptidase IV inhibitory, and antioxidant activities

The pH shift method was utilised for the recovery of proteins from salmon trimmings (ST), yielding 93% (w/w) protein. ST protein (STP) hydrolysates were generated with different enzyme preparations. STP incubated with Corolase PP for 1h (STP-C1) had the most potent angiotensin converting enzyme (ACE) and dipeptidyl peptidase IV (DPP-IV) inhibitory and oxygen radical absorbance capacity (ORAC) activities. Analysis of fractions of STP-C1 using UPLC-MS/MS identified sixteen peptides/amino acids. Tyr-Pro had the highest ACE inhibitory activity (ACE IC₅₀=5.21±0.94μM). The highest DPP-IV inhibitory activity was found with the amino acid Tyr (DPP-IV IC₅₀=75.15±0.84μM). Val-Pro had the highest ORAC activity (19.45±2.15μmol of TEg^-1). To our knowledge, the peptides Gly-Pro-Ala-Val, Val-Cys, and Phe-Phe have not been previously identified to have the activities tested in this study. These results indicate that STP hydrolysates are potential sources of bioactive peptides.

Protein isolation from blue mussels (Mytilus edulis) using an acid and alkaline solubilisation technique--process characteristics and functionality of the isolates

BACKGROUND

The pH shift method was developed to isolate proteins from low-value raw materials by solubilisation at high or low pH followed by precipitation. In this paper the application of the pH shift method on isolated mussel (Mytilus edulis) meat and whole mussels is reported.

RESULTS

Highest protein solubilisation was achieved at pH values of 2.6 and 12. The optimum precipitation pH values were established as around 5.8 following acid solubilisation and 5.2 following alkaline solubilisation. Protein recoveries were 430 and 580 g kg(-1) with the acid and alkaline processes respectively. Using whole crushed mussels, the corresponding recoveries were 310 and 480 g kg(-1). Process modifications to further improve protein recovery resulted in only a marginal increase. Lipid oxidation was not induced during pH shift processing, but heavy proteolysis occurred during the acid process version. Proteolysis could not be prevented by porcine plasma protein. Alkali-produced proteins performed better in all functionality tests compared with acid-produced proteins. The acid process removed slightly more lipids, recovered relatively more cysteine, methionine and lysine and resulted in whiter isolates.

CONCLUSION

The pH shift method can be successfully used to extract functional proteins from mussels and add value to blue mussels unsuitable for human consumption (with or without shells).

Effect of pretreatment on lipid oxidation and fishy odour development in protein hydrolysates from the muscle of Indian mackerel

Impact of different pretreatments on chemical compositions of Indian mackerel mince was studied. Mince prepared using washing/membrane removal/alkaline solubilisation process (W-MR-Al) contained the lowest remaining myoglobin and haem iron content and also showed the lowest total lipid and phospholipid contents. When mince and W-MR-Al were hydrolysed using Alcalase for up to 120 min, a higher degree of hydrolysis (DH) was found in W-MR-Al after 30 min of hydrolysis. Furthermore, hydrolysate from W-MR-Al had lower peroxide value (PV), thiobarbituric acid reactive substances (TBARS) and non-haem iron content throughout hydrolysis period (P<0.05). When hydrolysate powder produced from mince and W-MR-Al (0-0.3%w/v) were fortified in milk, the former resulted in the lower likeness score (P<0.05) at all levels used. The addition of the latter, for up to 0.2%, had no effect on likeness of all attributes, compared with milk without fortification (P>0.05). Therefore, the appropriate pretreatment of mince yielded hydrolysate with lower fishy odour.

Mercury distribution and lipid oxidation in fish muscle: effects of washing and isoelectric protein precipitation

Nearly all the mercury (Hg) in whole muscle from whitefish (Coregonus clupeaformis) and walleye (Sander vitreus) was present as methyl mercury (MeHg). The Hg content in whole muscle from whitefish and walleye was 0.04-0.09 and 0.14-0.81 ppm, respectively. The myofibril fraction contained approximately three-fourths of the Hg in whitefish and walleye whole muscle. The sarcoplasmic protein fraction (e.g., press juice) was the next most abundant source of Hg. Isolated myosin, triacylglycerols, and cellular membranes contained the least Hg. Protein isolates prepared by pH shifting in the presence of citric acid did not decrease Hg levels. Addition of cysteine during washing decreased the Hg content in washed muscle probably through the interaction of the sulfhydryl group in cysteine with MeHg. Primary and secondary lipid oxidation products were lower during 2 °C storage in isolates prepared by pH shifting compared to those of washed or unwashed mince from whole muscle. This was attributed to removing some of the cellular membranes by pH shifting. Washing the mince accelerated lipid peroxide formation but decreased secondary lipid oxidation products compared to that of the unwashed mince. This suggested that there was a lipid hydroperoxide generating system that was active upon dilution of aqueous antioxidants and pro-oxidants.

Protein isolation from gutted herring (Clupea harengus) using pH-shift processes

Herring ( Clupea harengus ) and other pelagic fish species are mainly used for fish meal and oil production and not for human consumption. In this study, acid pH-shift processing and alkaline pH-shift processing were used to isolate proteins from whole gutted herring with the aim to investigate the potential use of herring proteins as a food ingredient. The acid and alkaline processes gave rise to similar protein yields, 59.3 and 57.3%. The protein isolates from both processes had a significantly (p < 0.05) whiter color and higher protein and lower lipid contents than the starting material. The removal of ash was >80% for both processes, with a trend (p = 0.07) toward higher removal during the alkaline process. Also, Ca and Mg removal was significantly (p < 0.05) higher during the alkaline process. The isolated proteins from the acid process contained myosin degradation products and had a lower salt solubility than proteins from the alkaline process. Both protein isolates had an amino acid profile meeting the recommendations for adults according to FAO/WHO/UNU and could produce a surimi gel of medium strength. The results show that pH-shift processing could be a valuable method for the production of functional food proteins from gutted herring.