Oxidative stability, volatile components and polycyclic aromatic hydrocarbons of cold-smoked sardine (Sardina pilchardus) and dolphinfish (Coryphaena hippurus)

Although a wide variety of compounds are deposited during the smoking process, much more attention has been given to phenols and polycyclic aromatic hydrocarbons (PAHs). However, even though phenols have an important role to play as food antioxidants, some PAHs have cytotoxic and mutagenic effects. In the present work, two fish species differing in composition (dolphinfish (Coryphaena hippurus) and sardine (Sardina pilchardus)) were salted and cold-smoked. Two different smoking treatments were selected in order to compare phenol content and muscle antioxidant activity employing the ferric reducing power (FRAP) method. Both smoking treatments increased fish lipid oxidation stability compared with the salted muscle. The characterization of the volatile components of the headspace of the more intensely processed smoked products was carried out by SPME/GC/MS, which revealed the presence of typical phenol and carbonyl derivatives, as well as some oxidation products and PAHs of low molecular weight. PAH composition was further investigated by extracting and identifying the PAHs by GC/MS. Neither benzo(a)pyerene nor other high molecular weight PAHs were detected, naphthalene and its derivatives being the most abundant compounds in the smoked products.     

Rheological and microstructural changes in gels made from high and low quality sardine mince with added egg white during frozen storage

 This paper examines the influence of freezing temperature (–40°C or –18°C) and frozen storage temperature (–18°C or –12°C) on gels made from two different sardine minces (M1, high functional quality; M2, low functional quality), with the addition of egg white as a gel enhancing ingredient. To characterize the washed mince, proximate analyses and protein functionality were determined. Freezing at either –40°C or –18°C caused no drastic changes in gel structure. Throughout the course of frozen storage of all samples, a decrease in the water holding capacity (WHC) was detected, along with an increase in the amount of protein soluble in 8 M urea. At 90 days the gels frozen at –40°C exhibited numerous ice micro-crystals; however, they did not affect the external appearance of the gel and had hardly any effect on gel strength, shear strength, hardness, cohesiveness or elasticity. On the other hand, at 90 days the gels frozen at –18°C and stored at either temperature exhibited large, macroscopically visible ice crystals. In these samples, gel strength and shear strength increased while hardness decreased. No definite changes attributable to mince quality were detected during frozen storage. Received: 23 June 1997     

Rancidity development in frozen pelagic fish: Influence of slurry ice as preliminary chilling treatment

The slurry ice technology has shown profitable advantages when employed instead of traditional flake ice for the manufacture of chilled aquatic species. The present work is aimed at evaluating the effect of slurry ice as a preliminary treatment prior to frozen storage. For it, specimens of a small pelagic fatty fish species (sardine; Sardina pilchardus) were stored in slurry ice for 2, 5 and 9 days, then subjected to freezing (-80 °C; 24 h) and finally kept frozen (−20 °C) during 1, 2 and 4 months. At such times, rancidity development in frozen sardine was measured by sensory (odour, skin, colour and flesh appearance) and biochemical (lipid hydrolysis and oxidation) analyses and compared to a control batch previously chilled in flake ice. Sensory analysis indicated an extended shelf-life time for frozen sardine that was preliminary stored under slurry ice for 2, 5 or 9 days, as compared to their counterparts subjected to flake icing. Sensory results were corroborated (P<0.05) by biochemical lipid oxidation indices (thiobarbituric acid reactive substances and the fluorescence formation). The present work opens the way to the use of slurry ice instead of flake ice as preliminary treatment of fish material prior to the frozen storage.     

Influence of yeast and frozen storage on rheological, structural and microbial quality of frozen sweet dough

The aim of the present study was to investigate the effect of yeast content and frozen storage (9 weeks at −40 °C) on the structural and rheological parameters, and fermentative activity of frozen sweet dough. Two types of dough were studied (to estimate dough shelf life): simple yeasted dough (SY) and double yeasted dough (DY). Fermentative activity (yeast viability, gassing power, and dough volume), rheological and textural parameters were assessed for frozen sweet doughs.These effects were explored by different and complementary methods: Fourier transform infrared (FTIR), dynamic rheology, texture profile analysis (TPA) and differential scanning calorimetry (DSC).The data showed that the longer the frozen storage time at −40 °C, the higher the decreased of frozen sweet dough quality. The rheological attributes such as hardness, ΔS, springiness, tan δ and yeast activity declined significantly during frozen storage. This modification led to lower specific volume of frozen sweet dough during proofing.The observed changes of the frozen sweet doughs rheological properties after thawing may be attributed to the damage on the gluten cross-linking, mainly produced by the ice crystallization during frozen storage. The storage effect was particularly concentrated in the first 27 days of storage.     

Changes of lipids in sardine (Sardinella gibbosa) muscle during iced storage

Changes in lipids of sardine (Sardinella gibbosa) muscle during 15 days of iced storage were investigated. Lipid deterioration, lipolysis and lipid oxidation, occurred throughout the storage. The progressive peroxide formation was monitored by the increase in the absorbance band at 3600–3200 cm⁻¹ in Fourier transform infrared (FTIR) spectra and increased peroxide values were observed in sardine muscle up to 6 days of iced storage, followed by a continuous decrease from then for 9 days (P < 0.05). The increase in thiobarbituric acid reactive substances (TBARS) was noticeable throughout the iced storage (P < 0.05). However, no difference in conjugated diene (CD) of sardine muscle was found within the first 12 days of iced storage (P > 0.05). Marked decreases in unsaturated fatty acids, especially eicosapentaenoic acid (EPA; C20:5(n − 3)) and docosahexaenoic acid (DHA; C22:6(n − 3)) were observed as the storage time increased. Those changes indicated that lipid oxidation occurred in sardine muscle. A gradual increase in free fatty acid formation, with decreases in triglyceride and phospholipid contents, was found during iced storage (P < 0.05), suggesting hydrolysis induced by lipases and phospholipases.     

Influence of frozen storage and packaging on oxidative stability and texture of bread produced by different processes

The influence of packaging barrier properties and frozen storage on phenolic and phytosterol content, oxidative stability and crumb texture of frozen dough, part-baked and fully baked frozen bread was investigated in comparison to conventionally produced bread. Samples were stored either in blue coloured high density polyethylene (PE-HD) or transparent polyester-polyethylene-ethylene-vinyl alcohol copolymer (PET-PE/EVAL/PE) pouches for 22 days at −18 °C. Packaging materials were different in oxygen permeability: 3.67 cm³m⁻²day⁻¹ bar⁻¹ for PET-PE/EVAL/PE and 2080 cm³m⁻²day⁻¹ bar⁻¹ for PE-HD material, which did not significantly change during storage. Total phenolic content and oxidative stability of bread samples decreased during storage depending on the process. Frozen dough bread had the lowest phenolics decrease and the highest oxidative stability. Total phenolic content and oxidative stability of frozen breads during 8 days were similar to conventional bread. The phenolics reduction was higher for samples stored in PET-PE/EVAL/PE laminate than in PE-HD packaging. Total sterol content did not significantly change during bread storage in investigated packaging and did not contribute to the oxidation. Bread firmness was affected only by the process and not by the storage time and packaging material.     

Effect of freezing and frozen storage on microstructure of Mozzarella and pizza cheeses

Scanning electron microscopy was used to assess the effect of aging before (2, 7, and 14 days at 7 °C) or tempering after (1, 7, and 14 days at 7 °C) freezing, and frozen storage (1 and 4 weeks at −20 °C) on protein matrix of pasta filata Mozzarella and non-pasta filata pizza cheeses using unfrozen samples as controls. Pores and ruptures of reticular structure were observed in frozen-stored pasta filata Mozzarella cheese protein matrix, but cracks and clumps of bacteria were found in frozen-stored non-pasta filata pizza cheese. No obvious differences were discernable between the microstructures of pasta filata Mozzarella cheeses frozen stored 1 and 4 weeks. Formation of the reticular structure in frozen-stored pasta filata Mozzarella cheese progressed during tempering. Microstructure of non-pasta filata pizza cheese frozen stored for 4 weeks contained more extensive cracking and more areas of clumps of bacteria than that was frozen stored for 1 week. Aging of cheese before frozen storage was considered responsible for microstructural cracking; fewer cracks were found in the frozen-stored cheese tempered 1 and 2 weeks, but the clumps of bacteria were still observed.     

Quality and storage life of par-baked frozen breads

During storage of frozen par-baked breads for a prolonged period of time, bread quality may undergo changes such as increased firmness, moisture and flavour losses resulting in product deterioration. Four categories of par-baked breads namely—variety, white, multi-grain and rye were stored at −18°C for 9 months to evaluate the effects of storage period on product quality, and to develop prediction models that describe kinetics of deterioration of selected quality parameters. The quality was evaluated based on sensory, chemical and physical attributes and properties. Storage life was determined based on the changes in bread quality below certain level. The principal component analysis indicated that approximately 90% of the total variability of 19 quality parameters can be explained with only two principal components. The zero-order kinetic reaction showed good agreement (R²>80%) with quality changes observed by the sensory panel over the storage period. A prediction model, based on the bread quality at zero time and the quality at the time when the bread was rejected by the sensory panel, was developed. The proposed prediction model would provide a useful means of estimating storage life of par-baked breads made with similar formulations.     

Alternative fish species for cold-smoking process

Suitability of sardine (lean and fatty), dolphinfish and blue whiting for cold-smoking was evaluated. Stable water-holding capacity was observed in dolphinfish and blue whiting, but this tended to decrease in sardine throughout the storage. The 2-thiobarbituric acid index was not suitable for lipid oxidation measure in these smoked fishes and rancid flavours were only detected in sardine at the end of storage period. Total volatile basic nitrogen tended to increase in all three species. Lactic acid bacteria became the dominant microflora and Enterobacteriaceae did not show any growth. A bacteriostatic effect of at least 21 days was observable in all the smoked species. Sensory shelf life was 11 weeks for both types of sardine and 9 weeks for dolphinfish and blue whiting. Softening of muscle tissue and the development of bitter and off flavours were the main causes of rejection. Smoking as a processing technology can be used to add value to excess sardine and dolphinfish catches, due to sensory acceptability ratings. In contrast, the blue whiting was not suitable for smoking due to unacceptable soft texture, a characteristic of this species.     

Effects of chitosan coating on quality and shelf life of silver carp during frozen storage

The effects of chitosan coating on quality and shelf life of silver carp during frozen storage were investigated. Fish samples were treated with aqueous solution of 2% chitosan, and then stored at −3 °C for 30 days. The control and the treated fish samples were analyzed periodically for microbiological (total viable count), chemical (pH, TBA, TVB-N, K-value), and sensory characteristics. The results indicated that the effect of chitosan coating on fish samples was to retain their good quality characteristics and extend the shelf life during frozen storage, which was supported by the results of microbiological, chemical, and sensory evaluation analyses.     

Freezing and frozen storage of actomyosin from different species

A comparative study was made of the influence of freezing (–24°C) and frozen storage (–12°C) on the functional properties (viscosity, solubility) and physico-chemical characteristics (aliphatic and aromatic hydrophobicity, ATPase activity) of actomyosin (AM) from myosystems (chicken and hake) of differing freezing and frozen stability. The difference in functional behaviour between chicken and hake AM as a consequence of freezing and frozen storage suggests that, for hake AM, denaturation and aggregation occur essentially through direct aggregation of AM molecules to produce AM aggregates, whereas in chicken proteins, AM first dissociates into myosin and actin to produce myosin and myosin-actin aggregates.     

Hydrolysis and oxidation of European eel oil during frozen storage for 48 weeks

The quality assessment of the wild European eel (Anguilla anguilla) stored at −20 °C was assessed by sensory, chemical (total volatile basic nitrogen (TVB-N), peroxide value (PV), free fatty acid (FFA), thiobarbituric values (TBA) and pH) methods. The sensory analysis of showed that European eels were acceptable by panellists and can be stored for more than 48 weeks at −20 °C. No effects of frozen storage were observed on the proximate composition of eel. The level of TVB-N showed fluctuations (7.09–14.72 mg TVB-N/100 g) during frozen storage period, thus TVB-N could not be used as an indicator of frozen eel quality. FFA, PV and TBA values showed fluctuations during frozen storage period but remained low at the end of storage period, PV reached to the maximum level of 13.20±1.73 meq/kg, which did not exceed the maximum recommended value for human consumption (20 meq/kg). The release of FFA slightly increased (P>0.05) from the initial value of 0.88 to 2.14 (expressed as % of oleic acid) until 32 weeks of frozen storage while TBA increased from the initial value of 0.085 mg MA/kg to maximum level of 0.7696 mg MA/kg after week 40. After that, their values decreased to 1.82 and 0.5577 at week 48, respectively. This study showed that off-flavour and off-odour was not detected and frozen European eels were still acceptable by panellists and can be stored for more than 48 weeks at −20 °C.     

Effect of chitosan edible coating on the quality of double filleted Indian oil sardine (Sardinella longiceps) during chilled storage

The effectiveness of edible chitosan coating (1 and 2%) on the quality changes of Indian oil sardine (Sardinella longiceps) in iced condition was assessed. The chitosan prepared in the study had higher degree of deacetylation (83%). Edible coating with chitosan was effective in inhibiting bacterial growth and reduced the formation of volatile bases and oxidation products significantly. The muscle pH increased with the storage period for all the samples. On the day of sensory rejection for untreated samples, the formation of total volatile base nitrogen and trimethylamine nitrogen was less by 14.9 and 26.1% for 1% chitosan treated sardine and 32.7 and 49% for 2% chitosan treated samples respectively. The chitosan coating improved the water holding capacity, drip loss and textural properties significantly compared to untreated sample. The eating quality was maintained up to ∼8 and 10 days for 1 and 2% chitosan treated sardine respectively, compared to only 5 days for untreated samples.     

Influence of freezing and of frozen storage on the specific heat capacity of trout and herring fillet

Effects of freezing and frozen storage on the specific heat capacity difference of native (not heat denatured) and heat denatured fillet () of trout and herring have been studied for the first time. Single and double freezing of fillet induced a clear reduction of the of up to 15 mJ g⁻¹ K⁻¹ at each freezing step. Frozen storage at −20 °C reduced the of herring fillet but not of trout fillet. This is in agreement with the earlier detected instability of myosin transition temperature of herring and the stability of myosin transition temperature of trout [1]. The is suggested as a new parameter for the evaluation of protein stability at freezing and frozen storage of fish. It has been shown, that a reversible endothermic effect between 2 and 22 °C in herring fillet is accompanied by a decrease of the storage modulus in the chopped fillet, which characterises the flexibility of the proteins. This mechanical change and the endothermic signal are missed in the chopped trout fillet at heating from 2 to 22 °C. This cold, reversible relaxation of fish proteins can be understood as a requirement for subsequent protein denaturation at frozen storage.     

The interaction between inulin and wheat starch and effects of inulin on frozen storage quality of noodles

In this paper, the effects of adding a different proportion of inulin powder on starch gelatinisation, free amylose content, thermodynamic properties and microstructure of wheat starch were studied. RVA results showed that the addition of inulin could increase the starting temperature of wheat starch gelatinisation, decrease the peak viscosity and the setback value, and reduce the content of the leached amylose. In DSC test, similar trend was observed, starting temperature and peak temperature showed growing results, and retrogradation enthalpy and the ageing rate reduced. SEM results found that with inulin addition, wheat starch presents flocculent and fold structure. The noodles with 5% inulin addition were frozen-stored for 50 days after the cooking process. Inulin addition could retard the hardness and viscosity increase during the frozen storage. Besides, cooking loss rates and sensory property-treated samples were better than the control.     

Influence of storage temperature and duration on lipid and protein oxidation and flavour changes in frozen pork dumpling filler

This study was conducted to evaluate the effect of storage temperature and duration on oxidation and flavour changes in frozen pork dumpling filler. Freshly prepared dumplings were stored for 0, 30, 60, 90, and 180 d at − 7 °C, − 18 °C, and an oscillation between − 7 °C and − 18 °C. The samples stored at − 7 °C for 180 d had significantly higher levels of TBARS and protein carbonyls than those stored at − 18 °C and the fluctuating − 7 °C/− 18 °C (P < 0.05). The percentage of unsaturated fatty acids in total lipids decreased with extended storage times. The volatile compounds with pleasant odours decreased with time, while the compounds with pungent tastes and smells increased (P < 0.05). The sensory results showed that the dumplings stored at higher frozen temperatures for long periods of time had significantly lower acceptability scores (P < 0.05). The results suggest that oxidation is a primary cause of quality deterioration in pork dumpling filler during frozen storage.     

Aggregation of minced hake during frozen storage

 Aggregation in minced hake muscle (Merluccius merluccius) during storage at –20  °C was studied in conditions where there is progressive deterioration of functionality and texture as measured by apparent viscosity and shear resistance. Natural actomyosin was extracted with 0.6 M NaCl over a period of 49 weeks. Insoluble residue was extracted successively with 2% sodium dodecyl sulphate (SDS) and 2% SDS plus 5% β-mercaptoethanol (ME) solutions. SDS–polyacrylamide gel electrophoresis was performed on the extracted fractions. The results showed a 75% decrease in 0.6 M NaCl extractability by the end of the storage period. Initially the remaining precipitate was all extracted in 2% SDS and although the amount extracted in this solution increased as storage time progressed, its proportion decreased, accounting for as little as 40–50% of the protein aggregate by the end of storage. The proteins most involved in formation of the aggregate not extracted in 0.6 M NaCl were myosin and actin. Neither of these proteins was fully recovered in the fractions extracted with 0.6 M NaCl, 2% SDS, or 2% SDS plus 5% ME, and therefore it was inferred that they were forming part of the aggregates, bound by covalent bonds. Received: 17 November 1998     

Suitability of whey and buttermilk for the growth and frozen storage of probiotic lactobacilli

The growth of six probiotic commercial strains of lactobacilli was assessed in reconstituted dried whey and buttermilk supplemented with yeast extract, meat peptone, soy peptone, tryptone or casein acid hydrolysate at 0.3%, 0.6% or 1%. The addition of 1% glucose was also tested. Growth and acidification kinetics were determined at 37°C using MRS broth and a commercial culture medium as references. The suitability of whey and buttermilk as cryoprotectants at –20°C and –70°C was also assessed. Whey and buttermilk with 0.3% yeast extract were chosen for the growth of probiotic lactobacilli, since no satisfactory growth was observed without an external nitrogen source, whereas glucose did not improve the growth of any of the strains assayed. In general, buttermilk performed as satisfactorily as the reference media. The effectiveness of these media as cryoprotectants was strain dependent: skimmed milk and whey were the most suitable ones, especially for long-term storage at –20°C. However, at –70°C, no significant differences were observed between the culture media assessed. The use of whey or buttermilk as culture media for the production of probiotic lactic acid bacteria and for their cryopreservation implies a novel use of these low-cost products, offering an alternative way of utilizing the by-products of the dairy industry, helping to minimize their negative impact on the environment.     

冻藏对不同处理形态青梅果品质的影响

为了解决青梅常温不易保存的问题,开展了冻藏对青梅果品质影响的研究。在-18℃下,将青梅整果、果浆、果汁分别冻藏30 d,每5 d取样分析比较青梅果不同加工形态的可溶性固形物、糖类、总酸、氨态氮、黄酮、V_C含量的变化规律,评价冻藏对青梅果品营养物质的影响。研究结果表明,冷藏过程中,青梅整果、果浆和果汁的可溶性固形物、总糖、还原糖、总酸、氨态氮含量呈下降趋势,而且下降比较显著;黄酮和V_C含量有所降低,但其含量下降较少,其含量与青梅鲜果接近。在青梅整果、果浆、果汁三种保存形态中,营养物质保持状况,整果优于果浆、果汁。