Effects of pork fat and linseed oil as additives on gel quality of fish cake.

Pork fat (PF) is a necessary ingredient in making traditional fish cakes (TFCs), which contains saturated fatty acids with potential health concerns. While linseed oil (LO) containing α-linolenic acid is a potential nutrient-enhancing fat substitute. In this study, the effect of pork fat and linseed oil level on gel quality, sensory characteristics, microstructure, and protein conformation of TFCs were characterized. Results showed that the TFCs with 30% pork fat (wt/wt) had the highest gel strength. Additionally, sensory evaluation determined that TFCs with 30% pork fat scored the best by a sensory panel with high gel strength, water-holding capacity, and fresh and sweet taste. The gel strength, chewiness, and hardness of nutrient-enriched fish cakes with 20% linseed oil replaced for pork fat were higher than that only with pork fat (wt/wt) without changing in tenderness and elasticity. Visual results showed that the network was uniform at a moderate level of linseed oil addition (20% LO/PF replacement ratio). The results of this study provided technical guidelines for standardizing the TFC manufacture processes, and useful insight for the development of fish cakes with reduced animal fat content for additional health benefits for consumers.

The migration and loss of water in emulsified surimi gels prepared with different phase states of lipids: Effect of freeze-thawing treatments.

The freeze-thawing (FT) stability generally correlates well with the economic value and acceptability of frozen surimi-based products. However, quality changes of emulsified surimi gels under FT conditions are still unclear. Therefore, the gel properties of samples with different phase states of lipids (lard, lard + soybean oil, and soybean oil) were investigated at FT conditions. Results showed that the soybean oil evidently improved the rheological behaviors of sols/gels compared to the lard group. The moisture content of samples with different lipids decreased by 2.40%-2.71% after 4 FT cycles. With increasing FT cycles, the water-holding capacity decreased accompanied by the increase of cooking loss. Spin-spin relaxation spectra and hydrogen proton density images proved the occurrence of water migration of gels during these processes. Better gel integrity was observed in samples consisting of soybean oil, where the proportion of pores was lower than those with lard regardless of FT treatments. Additionally, the intermolecular forces of gels also changed under FT treatments. There results suggested that the lipids with different phase states affected the migration and loss of water in emulsified surimi gels under FT cycles. PRACTICAL APPLICATION: The quality changes of heating-induced surimi gel products under frozen storage have been ignored, especially the emulsified surimi gels. This study discloses the changes of the gel properties in emulsified gel products with different phase states of lipids after FT treatments, which provides critical insights into the quality improvement of this novel emulsified surimi product during processing, storage, and transportation.

The interaction study of soluble pectin fiber and surimi protein network from silver carp (Hypophthalmichthys molitrix) based on a new prediction model.

Pure surimi of silver carp (Hypophthalmichthys molitrix) cannot meet the texture requirements in novel 3D printing of food. In this work, the effect mechanism of adding soluble pectin fiber on the quality of surimi was studied at molecular scale, and the interaction has been discussed by a novel prediction model. In comparison with pure surimi, pH and water-holding capacity decreased with increasing pectin, and texture properties improved. The storage modulus firstly rose and then decreased, reaching a maximum value of 15012 Pa at 0.5 % pectin addition. The thermal transition temperature of myosin was moved from 52.13 to 49.80 °C. Pectin extended the T22 relaxation time, suggesting a decrease in immobilized water. A new Time-series prediction model and interaction analysis further explored the intrinsic correlation of various parameters of surimi with different pectin additions. This work contributes to add our understanding of pectin application in surimi products in future special dietary food.

Application of oil-in-water nanoemulsions based on grape and cinnamon essential oils for shelf-life extension of chilled flathead mullet fillets.

BACKGROUND: The effect of nanoemulsions prepared with grape seed and cinnamon essential oils on the shelf-life of flathead mullet (Mugil cephalus) fillets was evaluated by determining physicochemical (pH, free fatty acids, peroxide value, total volatile base nitrogen (TVB-N), and thiobarbituric acid reactive substances (TBARs)), sensory and microbiological (mesophilic aerobic bacteria, total psychrophilic bacteria, and Enterobacteriaceae counts) properties during 14 day storage at 2 °C. RESULTS: The nanoemulsions showed good stability and low average droplet size. The results indicated that nanoemulsion treatments significantly prolonged the shelf-life of the fillets. Treatment inhibited increases in pH and TVB-N, and retarded lipid oxidation and hydrolysis. Sensory assessment revealed that treatment induced shelf-life extension from 10 to 14 days, compared with controls. Microbiological analyses showed nanoemulsion treatment caused shelf-life extension from 10 to 12 days with reduction of microbiological contamination by up to 1 log cfu g-1 in mesophilic and 1.5 log cfu g-1 in psychrotrophic bacteria. CONCLUSION: Considering the results, grape seed and cinnamon essential oil nanoemulsions could be considered as novel antimicrobial and antioxidant materials for shelf-life extension of flathead mullet fillets during cold storage. © 2021 Society of Chemical Industry.

Strategies to reduce sodium levels in European seabass sausages.

Considering the increasing demand towards "ready-to-cook" processed seafood products, recognised as being potential contributors to high sodium (Na) intake by consumers, this study aimed to assess the effect of sodium chloride (NaCl) reduction on physicochemical, microbiological and sensory properties of European seabass (Dicentrarchus labrax) sausages stored in chilling conditions during 5 weeks. Three formulations were tested in comparison with a control (100% NaCl, CTR): (i) 50% NaCl+50% ME (oleoresins microcapsules) (F1); (ii) 50% NaCl+50% KCl (F2); and (iii) only 50% NaCl (F3). The NaCl reduction mainly affected the texture and the salty taste, resulting in softer and perceived as less salty sausages after processing. However, hardness differences disappeared after 5 weeks. It seems that an antioxidant protection was obtained in sausages formulated with oleoresins microcapsules. No or low growth of psychrotrophic and mesophilic bacteria was observed (≤2.40 log CFU/g). Decreasing NaCl content and/or partially replacing it (50%) by KCl or oleoresins microcapsules seem to be suitable solutions to reduce Na (30.9-36.3%) levels, while maintaining the chilled sausages quality for 5 weeks. The partial replacement of NaCl by KCl also allows obtaining a product richer in K (997.2 mg/100 g), which ingestion may contribute for a cardiovascular protective effect.

Omega-3 phospholipids in Pacific blue mackerel (Scomber australasicus) processing by-products.

The present study investigated phospholipid content, fatty acid composition and the positional distribution (sn-1,3 and sn-2) of n-3 fatty acids in four blue mackerel processing by-products (head, skin, roe, and male gonad). Total lipid was extracted using hexane/ethanol (1:2) and the analyses were carried out using NMR and GC-FID techniques. On the basis of g wet tissue, blue mackerel roe was a better source of phospholipids (38.6 µmol), compared to head (9.89 µmol), skin (13.5 µmol), and male gonad (10.0 µmol). Total lipid extracted from roe was found to have a higher proportion of n-3 fatty acids (44.4%) including EPA (11.3%) and DHA (27.5%), compared to head (total n-3 = 36.6%; EPA, 9.08%: DHA, 21.9%), skin (total n-3 = 34.8%; EPA, 9.63%; DHA, 19.5%) and male gonad (total n-3 = 42.5%; EPA, 12.1%; DHA, 24.7%). The proportion of EPA in the sn-2 position was substantially higher in fish roe (12.6%) compared to the other by-products (head, 1.91%; skin, 2.22%; male gonad, 2.02%). However, the DPA and DHA content in the sn-2 position did not vary significantly among the various parts (p > 0.05). Phospholipid esterified n-3 fatty acids were higher in roe (55.5%) compared to head (40.9%), skin (21.8%) and male gonad (32%). The present study suggests that blue mackerel roe is the best source of marine n-3 phospholipids among the blue mackerel commercially produced by-products.

Quality characteristics of fortified silver carp surimi with soluble dietary fiber: Effect of apple pectin and konjac glucomannan.

The study focused on assessing quality parameters of the surimi incorporated with soluble dietary fibers apple pectin and konjac glucomannan at different levels. The results showed that apple pectin at 0.025% and konjac glucomannan at a 2% level exhibited improved gel-forming ability significantly (p < 0.05). SDS- PAGE revealed high molecular weight protein crosslinks in apple pectin treated surimi gels and disappearance of myosin bands in konjac glucomannan treated surimi gels. The water holding capacity of surimi was the highest when 0.075 g/100 g of apple pectin was added. Konjac glucomannan treated gels exhibited superior whiteness values. The analysis of soluble protein revealed that hydrophobic bonds increased in both the treatments. The hardness values of pectin gels enhanced as the level increased. Other TPA parameters are shown an inconsistent trend. It can be demonstrated that the incorporation of apple pectin and konjac glucomannan at a level of 0.025 and 2.0% may be a novel strategy to improve the gel strength of the surimi.

Carbohydrate-based films containing pH-sensitive red barberry anthocyanins: Application as biodegradable smart food packaging materials.

A novel pH-sensitive colorimetric film was prepared based on immobilizing red barberry anthocyanins (RBAs) within composite chitin nanofiber (CNF) and methylcellulose (MC) matrices. The incorporation of CNFs and RBAs improved their mechanical properties, moisture resistance, and UV-vis screening properties. Moreover, the RBAs could be used as colorimetric indicators to detect food spoilage because they are sensitive to changes in pH and ammonia gas production. The RBA-halochromic indicator changed from reddish/crimson → pink → yellow with increasing pH, and from pink → yellow with increasing ammonia vapor concentration. Furthermore, the smart films possessed good antioxidant and antimicrobial activity owing to the presence of the RBAs and CNFs. Finally, the validity of the indicator to monitor the freshness/spoilage of a model food (fish) was demonstrated. Overall, this study shows that active/smart films can be assembled from food grade ingredients that can protect and monitor the freshness of products, like meat and fish.

Preparation of pH-sensitive food packaging film based on konjac glucomannan and hydroxypropyl methyl cellulose incorporated with mulberry extract.

A pH-sensitive food packaging film was prepared based on konjac glucomannan (KGM) and hydroxypropyl methyl cellulose (HPMC) incorporated with mulberry extracts2 (MBE). FT-IR and XRD analysis revealed that there are good molecular interactions among the three components. The incorporation of MBE into KGM and HPMC (KH) films can significantly improve the mechanical properties and UV resistance. Notably, the KH-MBE-20% film almost completely blocked UV light in the range of 200-600 nm. The best antioxidant and antibacterial properties were obtained when the addition of MBE in the composite film was 20%. In addition, KH-MBE film has good responsiveness to buffers with pH range from 2 to 12. In visual monitoring experiments using the film on fresh fish, the color of the KH-MBE film changed from purple to gray to yellow as the freshness of the fish decreased, and the KH-MBE-20% film had the best color stability. Therefore, intelligent packaging of KH-MBE film has potential applications in real-time monitoring of fish freshness.

Fluorescence detection of malachite green in fish tissue using red emissive Se,N,Cl-doped carbon dots.

Facile detection of malachite green (MG), a toxic dye, in aquaculture is urgently demanded for environment and food safety. Herein, we design a novel fluorescent probe, namely red emissive Se,N,Cl-doped carbon dots (CDs), to accurately determinate MG. CDs are prepared by hydrothermal treatment of selenourea and o-phenylenediamine in HCl solution. This material exhibits excitation-independent dual emissions at 625 and 679 nm, with a high quantum yield of 23.6%. A selective and sensitive fluorescent sensor toward MG is established based on inner filter effect, because both the excitation and emission light of CDs can be strongly absorbed by MG. The fluorescence quenching of CDs is linear to the MG concentration over the range of 0.07-2.50 µM with a low detection limit of 21 nM. Trace-level analysis of MG in fish tissue is successfully explored, demonstrating the great potential of the proposed sensor for MG monitoring in aquatic products.

Evaluation of ELISA kits for the screening of four nitrofuran metabolites in aquaculture products according to the European guideline for the validation of screening methods.

The administration of nitrofurans to livestock to treat or prevent animal diseases has been banned in the EU for the production of food of animal origin. The corresponding marker residues are tissue-related metabolites AMOZ, AHD, SEM, and AOZ. The MRPL (minimum required performance limit)/RPA (Reference point for action) was set at 1 µg kg-1 in the EU. Thus, all the laboratories involved in the control of nitrofuran metabolites must detect at least at this analytical limit of performance. The objectives of the work reported here were to evaluate the performance of ELISA kits from two different manufacturers (R-Biopharm, Germany; Europroxima, the Netherlands) for the individual screening of the four nitrofuran metabolites (AOZ, AMOZ; AHD; and SEM) in aquaculture products (fish, shrimps), and then to validate the kits according to the European Decision EC/2002/657 and to the European guideline for the validation of screening methods. The false positive rates were below 9 % for the kits from both manufacturers. The detection capabilities CCß determined were all below the current RPA (1 µg/kg). However, regarding the updated RPA at 0.5 µg/kg that shall apply in 2022, the AMOZ and SEM kits from R-Biopharm and the SEM kit from Europroxima will not be able to reach it.

Synergistic effects of UVA irradiation and phlorotannin extracts of Laminaria japonica on properties of grass carp myofibrillar protein gel.

BACKGROUND: Oxidized phlorotannin can be used as a protein crosslinking agent to produce high-quality fish gel products. Phlorotannin can be easily induced to form quinone compounds in an oxidizing environment, while o-quinone has been proven to be a reactive, electrophilic intermediate that easily reacts with proteins to form rigid molecular crosslinking networks. The objective of this study was to investigate the synergistic effects of ultraviolet A (UVA) irradiation (1 h, 15 W m-2 ) and various concentrations of Laminaria japonica phlorotannin extracts (PTE) on the gel properties of grass carp myofibrillar protein (MP). RESULTS: UVA treatment and PTE could synergistically improve the MP gel properties more than PTE alone (P < 0.05). At 625 mmol kg-1 MP PTE alone, the gel strength and cooking yield reached 3.10 ± 0.16 g cm and 47.45 ± 0.35%, respectively, while with the same level of PTE plus UVA they became 4.26 ± 0.19 g cm and 53.89 ± 1.54%, respectively. The three-dimensional network structure of the gel (with PTE + UVA) showed higher connectivity and tightness than that of the control group (no treatment). CONCLUSIONS: The synergistic effects of PTE and UVA could effectively induce crosslinking of grass carp MP, which could lead to an improvement of MP gel quality. These findings would provide a new technical approach to produce high-quality protein gel products in the fish processing industry. © 2020 Society of Chemical Industry.

The Role of Lipid Composition in the Sensory Attributes and Acceptability of the Salted and Dried Mullet Roes (Bottarga): A Study in Human and Animal Models.

A taste component is implicated in the oro-sensory detection of dietary lipids and free fatty acids seem to be involved in fatty food recognition. Bottarga, the salted and semi-dried ovary product of mullet (Mugil spp.), is a rich-fat food. A comparative sensory assessment of different commercial bottarga samples was performed in insect and human models in relation to their lipid composition. The bottarga attractant effect to Ceratitis capitata was assessed by behavioral tests. The subjective odor and taste perception of bottarga samples was investigated in human determining the rate of pleasantness, familiarity, and intensity dimensions using the 7-points Likert-type scale. Bottarga samples showed similar lipid profiles, but differences emerged in total and free fatty acid levels. Significant differences were observed in the attractant effect/acceptability of samples to medflies, negatively correlated to their total and free fatty acids. Insect female exhibited the ability to select among bottarga samples based on their visual and olfactory properties. In the human model, a potential contribution of free fatty acid amount in the pleasantness and familiarity dimensions of taste of bottarga samples was evidenced. Women exhibited a greater ability than men to select bottarga samples based on their better olfactory perception. Our results increase the knowledge about this outstanding product with nutritional and nutraceutical properties.

Effect of supercritical CO2 plant extract and berry press cakes on stability and consumer acceptance of frozen Baltic herring (Clupea harengus membras) mince.

A promising way of processing Baltic herring, Clupea harengus membras, is turning the fish into boneless mince. However, Baltic herring is prone to lipid oxidation, which possesses a challenge for industrial applications. The aim of this work was to study the efficacy of press cakes from Finnish berries and a supercritical CO2 plant extract to limit lipid oxidation during frozen storage of Baltic herring mince and to determine the impact of these additions on consumer acceptance in a fish product. Peroxide value, formation of volatile oxidation products and loss of polyunsaturated fatty acids showed that the tested natural additives decreased oxidation to a greater or similar extent as conventional antioxidants during 10-month storage. While potential of berry press cakes and plant extracts as "green label antioxidants" was shown, consumer study indicated need for further research to reach both optimal antioxidative efficacy and sensory properties.

Collaborative study: Quantification of total folate in food using an efficient single-enzyme extraction combined with LC-MS/MS.

Quantification of the specific folate vitamers to estimate total folate in foods is not standardized. A collaborative study, including eight European laboratories, was conducted in order to determine the repeatability and reproducibility of the method for folate quantification in foods using the plant-origin γ-glutamyl hydrolase as part of the extraction procedure. The seven food samples analyzed represent the food groups; fruits, vegetables, dairy products, legumes, offal, fish, and fortified infant formula. The homogenization step was included, and six folate vitamers were analyzed using LC-MS/MS. Total folate content, expressed as folic acid equivalent, was 17-490 µg/100 g in all samples. Horwitz ratio values were within the acceptable range (0.60-1.94), except for fish. The results for fortified infant formula, a certified reference material (NIST 1869), confirmed the trueness of the method. The collaborative study is part of a standardization project within the Nordic Committee on Food Analysis (NMKL).

Enhancement of gel properties of Scomberomorus niphonius myofibrillar protein using phlorotannin extracts under UVA irradiation.

The effect of phlorotannin extracts (PTE) (from sporophyll of Undaria pinnatifida) added at different levels (0, 25, 125, 625 µmol/g protein) on the gel properties of mackerel (Scomberomorus niphonius) myofibrillar protein (MP) was studied with and without ultraviolet A (UVA) irradiation. The results showed that the gel strength and cooking yield increased in a PTE dose-dependent manner, and at the level of 625 µmol/g protein PTE, the highest gel strength of 308.43 ± 8.12 (mN·cm) and cooking yield of 76.16 ± 1.40% were obtained in the samples treated with UVA irradiation. The same samples also showed increased carbonyl content, decreased total sulfhydryl, unwinding of α-helix, and quenching of fluorescence intensity of endogenous tryptophan, all of which indicated that elevated protein oxidation in these samples led to enhanced protein cross-linking. Results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated aggregation of myosin heavy chains (MHCs) in the UVA-treated gels with PTE, also evidenced by the dense three-dimensional network structure in these samples visualized by scanning electron microscopy (SEM). Electron spin resonance (ESR) and spin trapping results indicated that free radicals were produced during the gelation process, possibly originated from UVA-treated PTE, which played a critical role of oxidizing fish MPs, and eventually led to the improvement of the textural properties of the mackerel MP gel. PRACTICAL APPLICATION: Brown algae are a family of high-yield marine algae. Phlorotannin extracts are highly active natural substances extracted from brown algae that can have many applications. Ultraviolet A (UVA) as a green and environmentally friendly physical processing method has been widely used in food processing in recent years. The method proposed in this study could be utilized to improve properties of fish protein gel made from poorly performing low-priced fishes, and provide workable guidance for industry to expand the application of brown algae in food processing to better meet consumer's demand for high-quality marine foods.

Waste salt from the manufacturing process of mullet bottarga as source of oil with nutritional and nutraceutical properties.

BACKGROUND: The Sardinian food delicacy 'bottarga' is the final product of a number of treatments (salting and drying) on the ovaries of mullet (Mugil spp) and represents an important natural source of n-3 polyunsaturated fatty acids (n-3 PUFA) with nutraceutical properties. During the salting process of mullet roes to obtain bottarga, huge amounts of waste salt are generated, rich in residual ovary material. RESULTS: We evaluated the lipid composition (main lipid components and fatty acids) and bioactivity of oil obtained from the ovary material separated from waste salt (waste salt oil). Oil was obtained by supercritical fluid extraction with carbon dioxide (SFE-CO2 ), an environmentally friendly separation technique. The lipid composition of waste salt oil was determined by carbon-13 nuclear magnetic resonance (13 C-NMR) spectroscopy and reversed-phase high-performance liquid chromatography with diode array detector and an evaporative light scattering detector (HPLC-DAD/ELSD) chromatography. The oil was characterized by a relatively high level of n-3 PUFA (122 ± 7 g kg-1 of oil), and these beneficial health compounds were mainly present in the form of wax esters. Waste salt oil showed a marked cytotoxic effect [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay] in cancer B16F10 melanoma cells, with a slight cytotoxic effect in normal cells (3T3 fibroblasts). Waste salt and its derivatives (salt oil and residual material after oil extraction) were also tested for the attractant effect and acceptability to insects (Ceratitis capitata) to gain preliminary information about their potential application for animal supplementation. CONCLUSION: The results qualify waste salt as a potential resource for veterinary dietary supplements, nutraceuticals, and pharmaceutical applications. © 2020 Society of Chemical Industry.

Characteristic and shelf life of fish sausage: fortification with fish oil through emulsion and gelled emulsion incorporated with green tea extract.

BACKGROUND: Silver carp (Hypophthalmichthys moltrix) fish sausages incorporated with three forms of refined cod liver oil (as a source of polyunsaturated fatty acids: fish oil, oil-in-water emulsion (E), gelled oil-in-water emulsion (G)) and lyophilized aqueous extract of green tea (Camellia sinensis; 700 and 900 mg kg-1 ) were developed. The composition, technological properties (cooking loss, pH, texture, and color), sensory analysis, and microbial and oxidative stability of fish sausages during storage (4 °C) were evaluated. RESULTS: Lower value of cooking loss and thiobarbituric acid value were observed by addition of fish oil in emulsions forms. The incorporation of green tea showed no significant differences in preventing oxidation in related samples. Gelled-emulsified fish oil had better textural properties, including hardness and decreased springiness of the sausages. The G and E sausages showed higher values of lightness (L* ) than the control did. Emulsification had no significant effect on total viable count. Panelists could not distinguish between samples incorporated with fish oil whether in emulsified, gelled-emulsified, or control. Gelled-emulsified treatments were awarded higher scores by panelists for all of the sensory attributes (P < 0.05). Eicosapentaenoic acid and docosahexaenoic acid quantities significantly increased from control (0.48 mg g-1 and 0.46 mg g-1 sample respectively) to the enriched batches (>1.50 mg g-1 sample). The lowest ratio of ω6 to ω3 in batches was observed for gelled-emulsified samples. CONCLUSION: Overall, the addition of free fish oil affected the properties of the sausages. The gelled-emulsified treatment was a suitable fish oil delivery system in fish sausages, which maintained sensory properties during refrigerated storage.