Changes in chemical composition and nutritional quality of fried sardine (Clupea pilchardus) produced by frozen storage and microwave reheating

Modifications in proximate composition, fatty acids, amino acids and –SH groups content, as well as changes in solubility and nutritional quality of protein, were studied in fillets of sardine (Clupea pilchardus) that had been successively pan-fried, frozen stored and reheated by two different means, namely conventional oven and microwave oven. Upon pan-frying in olive oil the sardine absorbed C18: 1(n-9) and C18: 2(n-6) and lost saturated (SFA) and polyunsaturated fatty acids (PUFA); this loss continued upon reheating, and as a consequence the percentage of MUFA increased compared to the just-fried sardine. A loss of water was observed during all processes. Upon frying there was a decrease of cyst(e)ine. Upon reheating by both microwave and conventional oven, methionine decreased; however, cyst(e)ine only decreased with the use of a conventional oven. A loss of –SH groups was recorded during frying and this phenomenon continued upon reheating. Biological value (BV) together with net protein utilisation (NPU) decreased upon both frying and reheating. © 1997 SCI.     

Effects of cooking and reheating methods on the fatty acid profile of sea bream treated with rosemary extract

BACKGROUND: The effects of rosemary extract on the fatty acid profile of sea bream fillets cooked by different methods (oven baking, grilling and pan frying) as well as the effects of different reheating methods (microwave and conventional oven) on the fatty acid composition of fish after frozen storage for 4 months were investigated. RESULTS: The proportion of saturated fatty acids increased only slightly in fried samples but significantly in oven‐baked and grilled samples, while the proportion of polyunsaturated fatty acids (PUFAs) increased significantly in fried samples but only slightly in oven‐baked and grilled samples. The proportion of monounsaturated fatty acids remained relatively constant after cooking. Of the fatty acids analysed, the most significant increases (P < 0.05) were observed in C18:1n‐9 and C18:2n‐6 and the most significant decreases (P < 0.05) in C14:0, C16:1, C20:5n‐3 and C22:6n‐3. Although sea bream fillets fried in sunflower oil showed an increase in PUFAs, the lowest eicosapentaenoic and docosahexaenoic acid contents were found in fried samples. CONCLUSION: Sea bream fillets treated with rosemary extract showed slower oxidation than untreated fish. Neither conventional nor microwave reheating after frozen storage for 4 months had a detrimental effect on the fatty acid profile and its stability. Copyright © 2009 Society of Chemical Industry     

Keeping Quality of Sea-Frozen Thawed Cod Fillets on Ice

The objective was to evaluate the suitability of sea‐frozen, thawed cod fillets for the “chilled” seafood market. Fillets were kept frozen for 17 mo. After thawing, fillets were kept iced and at 4°C. Microbiological research on fillets showed higher initial numbers in post‐rigor than pre‐rigor fillets. Pre‐rigor fillets were judged fresher after 2 mo of storage compared to post‐rigor. With longer freezer storage, lower initial freshness scores were obtained, and formation of trimethylamine in thawed fillets was slowed. Thawed fillets frozen prior to rigor merited higher scores for freshness than fillets frozen post‐rigor. This difference decreased with prolonged freezer storage. The results strongly indicate that fillets should be frozen pre‐rigor.     

Capability of the rosemary (Rosmarinus officinalis) extract on the oxidative stability of cooked sea bream (Sparus aurata) during frozen storage

The effects of rosemary extract addition on oxidative stability of cooked sea bream during frozen storage period were investigated. Sea bream fillets were fried, oven baked and grilled. Three groups with rosemary extract were also cooked by the same methods and cooked samples (with and without rosemary extract) were stored in ?18?°C for 4?months. After cooking procedures, the FFA formation was quite similar in fresh-raw and fried sea bream fillets, but significantly increased oven baked (0.31?C0.33% oleic acid) and grilled fillets (0.39?C0.40% oleic acid). The highest value of PV was also obtained from grilled fillets (1.18?C1.58?meq/kg). However, TBA values (1.92?mg MA/kg for fresh-raw fillet) did not increase in sea bream fillets after the frying and grilling procedure except oven baking without rosemary extract (2.41?mg MA/kg). A considerable increase in the FFA, PV and TBA was observed in all cooked groups during frozen storage period. The treated samples with rosemary extract generally showed slower PV and TBA formation than those of the untreated samples. However, the additions of rosemary extract have positive effect on sensory quality of baked sea bream.     

Capability of the rosemary (Rosmarinus officinalis) extract on the oxidative stability of cooked sea bream (Sparus aurata) during frozen storage

The effects of rosemary extract addition on oxidative stability of cooked sea bream during frozen storage period were investigated. Sea bream fillets were fried, oven baked and grilled. Three groups with rosemary extract were also cooked by the same methods and cooked samples (with and without rosemary extract) were stored in −18 °C for 4 months. After cooking procedures, the FFA formation was quite similar in fresh-raw and fried sea bream fillets, but significantly increased oven baked (0.31–0.33% oleic acid) and grilled fillets (0.39–0.40% oleic acid). The highest value of PV was also obtained from grilled fillets (1.18–1.58 meq/kg). However, TBA values (1.92 mg MA/kg for fresh-raw fillet) did not increase in sea bream fillets after the frying and grilling procedure except oven baking without rosemary extract (2.41 mg MA/kg). A considerable increase in the FFA, PV and TBA was observed in all cooked groups during frozen storage period. The treated samples with rosemary extract generally showed slower PV and TBA formation than those of the untreated samples. However, the additions of rosemary extract have positive effect on sensory quality of baked sea bream.     

Influence of Frozen Storage and Defrosting on the Chemical and Nutritional Quality of Sardine ((Clupea pilchardus)

Studies were carried out on the changes in solubility in SDS+β-mercaptoethanol, the –SH group content, the amino acid and the fatty acid compositions, and nutritional quality of the muscle protein following freezing, storage at −20°C and conventional defrosting of sardines ( Clupea pilchardus ). During the processes, 8% of the total SH– group content was lost and there was a slight drop in solubility in SDS+β-mercaptoethanol. The amino acids which dropped to the greatest extent were the S-amino acids, followed by histidine, tyrosine, leucine, lysine and phenylalanin. The C22:6/C16:0 ratio dropped and this was considered to be related to oxidation phenomena. The digestibility of protein, biological value and net protein utilization (NPU) also dropped as a result of the processes studied.     

Influence of Rapid Cooking Methods on the Survival of Trichinella spiralis in Pork Chops from Experimentally Infected Pigs

Pork chops (1.3, 2.5 or 3.8 cm thick) cooked to an internal temperature of 17 or 77°C by conventional oven, convection oven or flat grill contained no motile trichinae, whereas chops cooked to 66°C sometimes contained motile trichinae. Chops cooked by either charbroil or deep fat fry and pretreated in a microwave oven sometimes had motile trichinae even after cooking to an end point of 77°C. Chops, which had been frozen for 18 hr at -23°C and were thawed by microwave to 0°C then deep fat fried to an end point temperature, sometimes had infectious trichinae as confirmed by tests with rats and mice. Additional research is underway to verify the thermal death times and temperatures for T. spiralis larvae.     

Differentiation of fresh and frozen/thawed fish, European sea bass (Dicentrarchus labrax), gilthead seabream (Sparus aurata), cod (Gadus morhua) and salmon (Salmo salar), using volatile compounds by SPME/GC/MS

BACKGROUND: A simple method based on solid phase microextraction/gas chromatography/mass spectrometry (SPME/GC/MS) was applied for studying the volatile profiles of whole fish samples of European sea bass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata) and fillets of cod (Gadus morhua) and salmon (Salmo salar) during frozen storage in order to be able to differentiate a fresh product from one that has been frozen. Analysis of volatile compounds was performed on these two product types, fresh and after freezing/thawing following storage at ? 20 °C for 30 and 90 days. RESULTS: More than a hundred volatile compounds were found by SPME/GC/MS. Statistical processing by principal component analysis and ascending hierarchical classification was used to classify the samples into categories and verify the possibility of separating fresh samples from those that had been frozen and thawed. The compounds to be used as differentiators were identified. Four compounds were common to all species: dimethyl sulfide, 3‐methylbutanal, ethyl acetate and 2‐methylbutanal. Not only were they found in larger quantities after thawing but they also increased with the duration of storage at ? 20 °C. CONCLUSION: These four compounds can therefore be considered as potential markers of differentiation between a fresh product and one that has been frozen. Copyright © 2012 Society of Chemical Industry     

Comparison of the effects of four cooking methods on fatty acid profiles and nutritional composition of red mullet (Mullus barbatus) muscle

This study was performed to examine the effects of different cooking methods (frying, steaming, oven cooking, and microwave cooking) on proximate chemical composition, mineral contents, and fatty acids profiles of red mullet (Mullus barbatus) fillets. The frying process caused a significant increase in fat content (from 13.37±0.04 to 34.44±0.20 g/100 g d.w.) and reduced the proportion of the palmitic acid of 50.73% and saturated fatty acids of 56.9%. While, the proportion of polyunsaturated fatty acids (PUFA) increased from 4.04% of total fatty acids for raw fillet to 49.17% of total fatty acids for fried fillets. The steamed, oven-cooked, and microwave-cooked fillets showed the best proportion of fat content, PUFA, and ω-6/ω-3 ratio as compared with fried red mullet fillets. Na, Mg, and Zn contents of cooked fish fillets significantly decreased.     

Storage Quality of Fresh and Frozen-thawed Fish in Ice

The objective was to determine whether traditional quality indexes of fresh (unfrozen) fish like sensory analysis, bacterial counts and trimethylamine content could be applied to thawed whole cod, cod fillets and ocean perch fillets kept in ice. Freezing and short-term freezer storage (≤5 wk at ?25°C) had very little effect on bacterial counts. During long-term freezer storage (≥14 wk at ?25°C) total counts were reduced as well as counts of trimethylamine oxide-reducing bacteria in cod fillets but not in ocean perch fillets. When the thawed fish was unacceptable the trimethylamine was <1 mgN/100g. Trimethylamine as a spoilage indicator was of no value when evaluating spoilage of thawed whole cod, cod fillets and ocean perch fillets kept in ice.     

Reduction of acrylamide formation in French fries by microwave pre‐cooking of potato strips

In this study, the effect of microwave pre‐cooking of potato strips on the resultant acrylamide levels in French fries was investigated. Control and microwaved (10, 20, and 30 s at 850 W) samples were fried at 150, 170 and 190 °C for predetermined times. Surface and core temperatures of potato strips were acquired during frying, and acrylamide content in the surface and the core regions were determined separately. The results showed that microwave application prior to frying resulted in a marked reduction of acrylamide level in the surface region, whereas a slight increase was noted for the core region. When the potato strips were subjected to frying after a microwave pre‐cooking step, acrylamide content in the whole potato strip was reduced by 36%, 41%, and 60% for frying at 150, 170, and 190 °C, respectively, in comparison to the control. Copyright © 2006 Society of Chemical Industry     

Effects of deep‐fat frying temperature on antioxidant properties of whole wheat doughnuts

The total phenolic (TP) content, phenolic acid composition and in vitro antioxidant capacity of whole wheat doughnuts fried at 120–180 °C were determined to identify the effects of frying temperature. Significant differences (P < 0.05) in TP content were observed between doughnuts fried at different temperatures. The TP content of doughnuts decreased significantly when doughnuts were deep‐fat fried. The TP content of doughnuts increased with elevation with frying temperatures. These increases in TP content of doughnuts were also detected in the determination of individual phenolic compounds using HPLC. DPPH radical and iron‐chelating capacity of deep‐fat fried doughnuts exhibited increases with elevation of frying temperature from 120 to 180 °C. Deep‐fat frying at 120 °C lowered lipid peroxidation inhibition capacity of doughnuts prepared from both refined flour and whole‐grain meals and increased consistently with increased frying temperature from 120 to 180 °C. Moderate deep‐fat frying temperature would increase the content and activity of antioxidants of doughnuts.     

Chemical,enzymatical and textural changes during marination and storage period of sardine (<Emphasis Type="Italic">Sardina pilchardus</Emphasis>) marinades

In this study frozen fillets of sardine (Sardina pilchardus) were used to make marinades. The marinating process was performed in 7% acetic acid and 14% sodium chloride in barrels. The fish:solution ratio was (1.5:1). After the marination process, sardine fillets were packed in glass jars in two different formulations fish:solution ratio of (1.5:1); the first formulation contained 2% acetic acid and 4% sodium chloride with tomato sauce and spices and the other was 2% citric acid and 4% sodium chloride with lemon and also the same spices. Pasteurization process had been applied on half of the jars at 70 °C for 20 min. Chemical, enzymatical and textural changes during marination and 6 months storage period of sardine marinades were determined. The results obtained in proteolytic activities correlated well with the observed texture measurements according to time of storage. A decrease in the histidine content and an increase in glutamic acid and aspartic acid contents of marinated sardines were determined. Histamine levels were lower than the toxic limit (100 mg/kg) during the marination and storage period of sardine marinades.     

Effect of freezing/thawing conditions and long‐term frozen storage on the quality of mashed potatoes

The effects of freezing temperature (−80, −40 or −24 °C) and thawing mode (microwave or overnight at 4 °C) on quality parameters of mashed potatoes made from tubers (cv Kennebec) and from potato flakes were examined, as was the effect of long‐term frozen storage on the quality of mashed potatoes. Mashed potatoes were tested for texture profile analysis (TPA) and cone penetration, oscillatory and steady rheometry, colour, dry matter, Brix and sensory analyses. In natural mashed potatoes, TPA hardness and oscillatory parameters showed that processing resulted in a softer product than the fresh control. The parameters were lower in the samples thawed at 4 °C than in those thawed by microwave at all the freezing temperatures used, which may be ascribed to gelatinisation of the starch released from damaged cells. Differences from the freshly prepared product decreased when the samples were frozen at −80 °C and thawed by microwave. No difference was found in sensory acceptability between samples frozen at −80 and −40 °C, which probably reflects the panellists' mixed preferences for air‐thawed versus microwave‐thawed samples. Increasing the time in frozen storage led to a natural mash with a firmer texture, higher L*/b* value and Brix; nonetheless, panellists found the samples at 0, 3 and 12 months of frozen storage equally acceptable. In commercial mash, penetration and oscillatory parameters showed that processing made for a firmer product than the fresh control, probably owing to retrogradation of gelatinised starch. Thawing mode had a significant effect on parameters, which were lower in the samples thawed at 4 °C. The structure and quality of commercial mash was more detrimentally affected by freezing and, therefore, we would not recommend either freezing or frozen storage of this mashed potato in the used conditions. Natural mash made from Kennebec potatoes should be frozen quickly and thawed by microwave in the conditions described to obtain a product more similar to that freshly made. If the samples are frozen by air blasting at −40 °C, the product can withstand frozen storage for one year. Copyright © 2005 Society of Chemical Industry     

Effect of microwave pre-thawing of frozen potato strips on acrylamide level and quality of French fries

The objective of this study was to reduce frying time, and hence acrylamide level of French fries by microwave pre-thawing of frozen potato strips. Effect of this pre-treatment on acrylamide content and quality attributes of French fries was determined. Frozen par-fried potato strips (8.5 × 8.5 × 70 mm) were thawed in a microwave oven prior to final frying in sunflower oil at 170, 180, and 190 °C. Potato strips that were final fried without pre-thawing were considered as the control. Acrylamide analysis was performed by liquid chromatography–mass spectrometry (LC–MS) method. Microwave pre-thawing of frozen strips reduced the acrylamide level of French fries by 10% (from 17.7 to 15.9 ng/g), 89% (from 72.1 to 8.0 ng/g), and 64% (from 50.5 to 18.4 ng/g) for frying at 170, 180, and 190 °C, respectively, in comparison to the control samples. Quality attributes (texture, color, and oil content) of pre-treated strips were found to be comparable to those of the control.     

High Dietary Vitamin E Affects Storage Stability of Frozen-refrigerated Trout Fillets

Fillets were processed from trout fed a diet containing either 200 (low vitamin E [LVE] diet) or 5000 (high vitamin E [HVE] diet) mg a‐tocopheryl acetate/kg for 0, 4, and 9 wk. These fillets were evaluated fresh and after 6 mo of frozen storage. Frozen fillets were thawed and stored 3 d at 1 °C before analyses. Muscle α‐tocopherol of fish fed the HVE diet continuously increased through 9 wk of feeding. Reduced muscle α‐tocopherol and moisture, and increased muscle redness and fat were observed in frozen‐refrigerated fillets compared with fresh fillets. Thiobarbituric acid‐reactive substances were lower in frozen‐refrigerated fillets produced from fish fed the HVE diet. Proportion of unsaturated fatty acids and omega‐3 fatty acids increased as feeding duration increased from 0 to 9 wk.     

Freezing and Thawing Conditions Affect the Gel Stability of Different Varieties of Rice Flour

The freeze‐thaw stabilities of three different rice flour gels (amylose rice flour with 28% amylose, Jasmine rice flour with 18% amylose and waxy rice flour with 5% amylose) were studied by first freezing at –18 °C for 22 h and subsequent thawing in a water bath at 30 °C, 60 °C and 90 °C, or by boiling in a microwave oven. The freeze‐thaw stability was determined for five cycles. Starch gels thawed at higher temperature exhibited a lower syneresis value (percent of water separation) than those thawed at lower temperature. Amylose rice flour gels gave the highest syneresis values (especially at the first cycle). The Jasmine rice flour gels gave a higher syneresis value than the waxy rice flour gel. Except for freezing by storage at –18 °C and thawing at 30 °C, there was no separation of water at any cycle when waxy rice flour gel was thawed at any temperature, irrespectively of the freezing methods used. Cryogenic Quick Freezing (CQF) followed by storage at –18 °C and then thawing (by boiling or by incubation at any other temperatures) gave lower syneresis values than all comparable samples frozen by storage at –18 °C. The order of syneresis values for the three types of rice flour was waxy rice flour < Jasmine rice flour < amylose rice flour. The syneresis values and the appearance of starch gels, which had gone through the freeze‐ thaw process, suggested that the order of freeze‐thaw stability of gels for the three types of rice flour was waxy > Jasmine > amylose rice flour.     

Effect of modified atmosphere and vacuum packaging on microbial,chemical and sensory quality indicators of fresh,filleted Sardina pilchardus at 3 °C

The self‐life, quality and safety of refrigerated sardine fillets (Sardina pilchardus) were determined at 3 °C in atmospheric air, vacuum and modified atmosphere (50% CO₂/50% N₂) packaging conditions. Microbiological, physico‐chemical and sensory parameters were utilised as quality indicators. The microbial flora of sardine comprised—according to order of occurrence—Shewanella putrefaciens, pseudomonads, Brochothrix thermosphacta, lactic acid bacteria and, finally, Enterobacteriaceae. Bacteria grew most quickly in sardines stored in air, followed by those in vacuum packaging, and the lowest counts were found in modified atmosphere packaging. The concentrations of moisture, ash, protein, fat and polyunsaturated fatty acids were not affected during the storage period compared to the pH values and the concentrations of lactate and ammonia that showed significant differences. Copyright © 2007 Society of Chemical Industry     

Effects of contact‐dehydrating sheets on preference for fried food and deterioration of frying oil

The purpose of this study was to investigate the effects of contact‐dehydrating sheets on preferences for fried food and the deterioration of frying oil. Mackerel or chicken breast were dehydrated by wrapping with the contact‐dehydrating sheets at 4°C for 1.5 h and subsequently fried at 180°C for 3 min; those were referred to as the dehydrated samples. The same fried materials not wrapped with the contact‐dehydrating sheets were referred to as the control. The frying procedure was repeated 15 times under the above conditions and the amount of frying oil was adjusted to 1000 g by addition of new oil each time. Sensory analysis showed that the dehydrated samples were preferred to the control. Acidic values, anisidine values and ΔE values of the frying oil used for the dehydrated mackerel were significantly lower than for that used for preparing the control. These results indicate that the use of contact‐dehydrating sheets for the dehydration of the frying materials was effective in both significantly increased preference for the fried food and the retardation of the deterioration of the frying oil. Copyright © 2004 Society of Chemical Industry     

Oil Absorption During Frying of Frozen Parfried Potatoes

A tracer method was used to assess the uptake of oil by commercial frozen parfried potatoes fried (180 °C, 150 s) in colza oil (CO) involving a short post-frying immersion in hot coconut fat (CF). CO and CF were determined directly in the crust by differential scanning calorimetry (crystallization temperature and enthalpy −42.7 °C/50 J/g and 10 °C/71 J/g, respectively). Oil uptake by the crust during frying in CO or CF was similar (average 25.3%). Potato samples transferred immediately after frying in CO to the CF bath had most of the CO absorbed replaced by CF after a 10 s post-frying, meaning that CO was readily accessible in the crust structure. Samples fried in CO and cooled for up to 60 s before transfer to hot CF showed only partial replacement of CO. Oil wetting the surface of the sample at the end of frying was estimated as 70 to 80% of the total oil uptake. Formation of the crust (frying time > 1 min) was required for oil to migrate into intercellular spaces that are dynamically formed during frying and thus accessible to CF and solvents.