Effect of functional edible films and high pressure processing on microbial and oxidative spoilage in cold-smoked sardine (Sardina pilchardus)

The present experiment was an attempt to improve the shelf-life of cold-smoked sardine (Sardina pilchardus) using, singly or in combination, high pressure (300 MPa/20 °C/15 min) and gelatin-based functional edible films enriched by adding an extract of oregano (Origanum vulgare) or rosemary (Rosmarinus officinalis) or by adding chitosan. The uncoated muscle itself exhibited a certain level of antioxidant power (as measured by the FRAP method) ensuing from the deposition of phenols during smoking. Coating the muscle with the films enriched with the oregano or rosemary extracts increased the phenol content and the antioxidant power of the muscle, particularly when used in association with high pressure, due to migration of antioxidant substances from the film. The edible films with the added plant extracts lowered lipid oxidation levels (as measured by the peroxide and TBARS indices) and also, to a lesser extent, reduced microbial growth (total counts), whereas the gelatin–chitosan-based edible films lowered microbial counts (total counts, sulphide-reducing bacteria). Neither luminescent bacteria nor Enterobacteriaceae were detected in any of the batches. The combination of high pressure and edible films yielded the best results in terms of both preventing oxidation and inhibiting microbial growth.     

Extraction of sardine myoglobin and its effect on gelation properties of Pacific whiting surimi

ABSTRACT:  Myoglobin (Mb) was extracted from Pacific sardine and added to Pacific whiting surimi to measure its effects on protein gelation. The purity of Mb extract was determined by SDS-PAGE. Mb extract using ethanol showed higher purity than Mb extract using ammonium sulfate. The addition of 0.2% Mb significantly reduced breaking force. However, a synergistic effect of 1.0% Mb was observed with 1.0% beef plasma protein (BPP) to increase surimi gel strength. The highest storage modulus of gels was observed at 1.0% Mb addition, which corresponded with the nonfracture gel and also supported a synergistic interaction between 1.0% Mb and 1.0% BPP. Differential scanning calorimetry showed Mb addition might have affected myosin denaturation and aggregation.     

Thermodynamic activation and structural analysis of trypsin I from Monterey sardine (Sardinops sagax caerulea)

In this work, we report the molecular characterisation of trypsin I (Try I) from Monterey sardine (Sardinops sagax caerulea). Aspects such as thermodynamic activation parameters, molecular model and cDNA-deduced amino acid sequence allow a more in depth understanding of its activity at low temperatures. The analysis of the thermodynamic activation parameters suggests that this molecule is a cold-adapted protease. From the molecular cloning, we deduced the amino acid sequence and predicted a theoretical structural model of sardine Try I with a classical trypsin fold. Cold-adaptation of this enzyme probably comes from amino acid replacement of key residues to improve flexibility at low temperature, thus increasing k_cat. The cold-adaptation of sardine Try I opens a wide range of biotechnological applications for this protease and also it is interesting from the structure function relationship point of view of serine protease proteins.     

响应面法优化精制沙丁鱼油EPA和DHA富集工艺

以乙酯型精制沙丁鱼油(EPA含量(15.41±0.13)%,DHA含量(8.00±0.03)%)为原料,在尿酯比、包合温度、醇尿比、包合时间4个单因素试验的基础上,采用响应面分析法优化尿素包合法富集工艺。结果表明:最优工艺条件为尿酯比3.5∶1、包合温度0℃、醇尿比2.6∶1、包合时间1.2h,此条件下,产物中EPA+DHA含量为(78.12±0.12)%(EPA含量(53.35±0.10)%;DHA含量(24.77±0.02)%),与理论值78.17%基本一致。     

Biochemical and conformational changes of myosin purified from Pacific sardine at various pHs

ABSTRACT:  Biochemical and conformational changes of purified sardine myosin were investigated at various pHs. The purity of myosin, as determined by SDS-PAGE, was approximately 94.6%. One major band at 205 kDa, corresponding to myosin heavy chain, and 3 light chains at 31, 24, and 23 kDa were observed on the SDS-PAGE gel. The greatest myosin protein solubility was observed at pH 7 and remained constant up to pH 11. Sardine myosin showed no solubility at pHs 2.5 to 5.0. Three endothermic peaks were obtained for samples prepared at pHs 7 and 10, while no peaks were shown for pH 2 samples, indicating chemical denaturation of myosin occurred before thermal treatment. The greatest Ca²⁺-ATPase activity was observed at pH 7, while no activity was observed between pHs 2 and 5 and at pH 11. Total sulfhydryl content was not measured at pHs 2.5 to 4 while the greatest measure was obtained for samples at pH 5.5. Surface hydrophobicity was not detected from pHs 2.5 to 5.0; thereafter the content remained consistent through pH 11. Storage modulus, indicating the elastic element of myosin gels, was minimally affected at pH 2, indicating myosin was chemically denatured before the temperature sweep treatment. However, at pH 10, the thermal exposure of myosin, as evidenced by dynamic thermograms with deeper valleys at 40 to 60 °C, was noted, indicating myosin was not damaged by adjustment to pH 10 and therefore was still able to undergo thermal gelation.     

Mechanisms of gelation of sardine proteins: influence of thermal processing and of various additives on the texture and protein solubility of kamaboko gels

Surimi prepared from freshly caught sardines was mixed with NaCl and other additives and used to prepare kamaboko gels. Protein-protein interactions involved in the setting (at 4 or 37°C) and/or the cooking (at 90°C) gelation steps were investigated (i) by assessment of kamaboko texture as a result of the type and concentration of additive added; (ii) by partial solubilization of kamaboko gels in buffers containing mercaptoethanol, sodium dodecyl sulphate (SDS) and/or urea, followed by determination of the soluble protein constituents by polyacrylamide gel electrophoresis. Cooked gels of high elasticity and of varying rigidity and gel strength were obtained in the 73–80% water range. Adequate gel texture required a NaCl content of 1.7–3.5% and a pH range of 6.4–8.4. Low concentrations of reducing agents (mercaptoethanol, dithiothreitol, cysteine) or of divalent cations (Ca²⁺, Mg²⁺) improved the texture of gels obtained by setting at 37°C with and without subsequent cooking at 90°C. On the other hand, the addition of N -ethyl maleimide or of ethylene diamine tetra-acetate led to texture deterioration after cooking. These data demonstrate the involvement of disulphide bonds and of electrostatic interactions in surimi gelation. Gel solubilization experiments indicate that the aggregation of myosin heavy chains through various types of protein-protein interactions may be responsible for the elastic gel network formed during setting at 37°C (30 min) or 4°C (24h). Strengthening of the gel network after cooking appears to be due to additional disulphide and hydrophobic interactions.     

Lipid composition and palatability of canned sardines. Influence of the canning process and storage in olive oil for five years

Lipid variations of canned sardines in olive oil, both quantitative and in fatty acid composition, have been studied during various stages of the canning process: raw sardines (RS), precooked sardines (PS), just canned sardines (CS) and sardines stored for 6 months (6MS), 12 months (12MS) and 5 years (5YS). The effect of maturation on the palatability of sardines has also been observed by means of triangle tests using a panel of 60 tasters. Our results show a significant loss of SFA in fish during the canning process (C16: 0, 273±6 g kg⁻¹ of fat in RS and 169±11 g kg⁻¹ of fat in CS) and a rise in MUFA (C18:1 207±2 g kg⁻¹ of fat in RS and 506±14 g kg⁻¹ of fat in CS); PUFA showed almost no variation. The maturation and canning processes both yielded similar qualitative modifications. The palatability of the sardines was significantly higher after 6 months of maturation than immediately after canning, and this quality was maintained, for at least 5 years of storage. © 1998 SCI.     

Stereospecific analysis of triacyl-sn-glycerols in Docosahexaenoic acid-rich fish oils

This paper presents the positional distribution of fatty acids in docosahexaenoic acid (22∶6n-3)-rich fish oil triacyl-sn-glycerols (TG). Stereospecific analysis of TG was carried out by a nonenzymatic method. The TG of bonito head oil, obtained after a winterization process, contained 22∶6n-3 at concentrations of 28,7, and 49 mole % in thesn-1,sn-2, andsn-3 positions, respectively. In the TG of oil before the winterization process, 22∶6n-3 was concentrated in thesn-3 position, followed evenly by thesn-1 andsn-2 positions. Tuna orbital oil, obtained after winterization, showed the preferential association of 22∶6n-3 to thesn-3 position, followed by thesn-1 position. This distribution pattern was similar to that observed for seal oil TG rather than sardine oil TG. The bonito head and tuna orbital oils are useful as fish oils with characteristics different from those of common fish oils, such as menhaden, sardine, and herring oils.     

Microstructure of suwari and kamaboko sardine surimi gels

In a previous work it was suggested that the texture of kamaboko (set and cooked) gels made from sardine surimi under varying setting conditions was predetermined by the specific matrix forming in each suwari (set) gel. This paper describes the microstructure of the networks formed in suwari and kamaboko gels set at 25, 35 and 40 °C for 30 or 60 min as examined by scanning electron microscopy (SEM). Cooking conditions for kamaboko gels were fixed at 90 °C for 30 min; other preparation conditions were invariable. At low magnification (≤×500) the gel matrixes were compact, with practically no differences among lots. At higher magnification (×20 000), the suwari gel matrixes formed at low temperature consisted of globules. At higher temperatures the globules joined up to form fibrillar structures (fibres) and zones of disordered globule aggregation (coagula); at longer setting times, lateral bonding of the fibres became apparent. Kamaboko gels produced from unstructured globular matrixes exhibited only a few fibrillar zones and large areas of coagula. Where there was already an incipient fibrous formation, these developed into individual fibres or bundles of fibres that correlated with the best texture characteristics. Suwari gels with extensive lateral bonded fibres gave rise to kamaboko gels with a highly compact appearance under SEM; this correlated with a decline in texture values. These different structures suggest that the protein–protein bonds in the suwari networks have different levels of stability to heat, and these levels determine whether or not the proteins can subsequently be reorganised when the kamaboko gel forms. © 1999 Society of Chemical Industry     

响应面法优化精制沙丁鱼油乙酯化工艺

为研究精制沙丁鱼油乙酯化工艺,以精制沙丁鱼油为原料,在无水乙醇用量、NaOH用量、反应时间、反应温度4个单因素试验的基础上,采用响应面分析法优化精制沙丁鱼油乙酯化工艺,确定乙酯化工艺的回归模型,考察各个因素及其交互作用对乙酯率的影响。结果表明:乙酯化最优工艺条件为无水乙醇用量60 g、NaOH用量1.2 g、反应时间75 min、反应温度50℃。在此条件下,精制沙丁鱼油乙酯率为88.12%±0.08%,乙酯化工艺合理、可行,为乙酯型精制沙丁鱼油的大规模开发利用提供了一定的理论依据。