Chilled storage of high pressure and heat-induced gels of blue whithing (Micromesistius poutassou) muscle

 Microbiological, rheological and chemical characteristics were examined in gels made from the muscle of blue whiting (Micromesistius poutassou) and subjected to three different combinations of pressure, temperature and time: 200 MPa at 3  °C for 10 min (lot L), 375 MPa at 38  °C for 20 min (lot H) and atmospheric pressure at 37  °C for 30 min followed by 90  °C for 50 min (lot T), and kept in chilled storage for 20 days. The microorganism content dropped at the outset as pressurizing took effect, the highest microbial content being found in lot L; however as the effect was not lethal, the total load increased over the following days. Microbial load was significantly lower in lot T. During chilled storage, the values of breaking deformation, breaking force and cohesiveness of lot L were higher than those of the other lots, although they did decrease with storage. The heat-induced gel was much harder, had greater water-holding capacity and was considerably more stable than the high-pressure-induced gels. The lightness value was higher in lot H than in the other two lots. In general, changes in protein solubility tended towards the cleavage of strong bonds as a result of microbial action. The electrophoretic profiles evolved differently in each of the lots over the chilled storage period. However, all of them exhibited large numbers of bands of lower molecular mass which could have been the result of degradation. This was particularly evident in lot H. The heat-induced gels exhibited a highly porous ultrastructure, quite different from the high-pressure-induced gels; these had a more compact matrix which expanded as storage progressed. Received: 26 May 1997     

Effect of a two‐step natural organic acid treatment on microbial activity and lipid damage during blue whiting (Micromesistius poutassou) chilling

Quality loss inhibition in chilled blue whiting (Micromesistius poutassou) was investigated. For it, a natural organic acid‐mixture including ascorbic, citric and lactic acids was applied in a two‐step processing strategy: (i) as an aqueous dipping medium previous to chilling storage and, (ii) included in the flake ice employed as chilling system. As a result of the acid‐mixture addition, a partial inhibition of microbial and biochemical mechanisms involved in the quality loss was obtained. Thus, aerobe and psychrotrophe counts in treated fish showed lower ranges (2.07–4.15 and 2.43–4.39 log CFU g^?1, respectively) than control fish (2.64–5.83 and 2.30–5.30 log CFU g^?1, respectively). Sensory analysis revealed that treated fish was still acceptable at the end of the experiment (day 9), while control fish was rejected at this time. Lipid hydrolysis (free fatty acid formation) proved to be more limiting of fish quality than lipid oxidation (peroxide and thiobarbituric acid‐reactive substance formation).     

Enzymatic hydrolysis of blue whiting (Micromesistius poutassou); functional and bioactive properties

Functional and biochemical properties of fish protein hydrolysates (FPH) from blue whiting (BW) were studied. FPH (2.5%, 5%, 10%, and 15% degree of hydrolysis [DH]) were made from isolated proteins from headed and gutted BW with Alcalase 2.4 L. The properties of dried BW mince and protein isolate compared to 4 reference proteins (soy and milk protein) were studied: color, solubility, water-holding capacity (WHC), oil-binding capacity (OBC), emulsion capacity (EC), and emulsion stability (ES). The angiotensin I-converting enzyme (ACE) inhibitory activities of the soluble fraction of BW powders were also investigated. Furthermore, the products were characterized by analyzing their chemical composition. Chemical composition, solubility, OBC, and EC of the BW powders was significantly (P < 0.05) different with different DH, while color, ES, and WHC were not significantly (P > 0.05) different. Salt content of the FPH was high (4% to 19%) and increased with increased DH. Protein solubility varied from 10% to 70% and increased with increased DH. WHC of the FPH was around 97% and was higher than that of all the reference proteins tested. OBC decreased with increased DH (from 3.5 to 2.1 g oil/g protein) and was higher than OBC of the soy and milk proteins (1.6 to 1.9 g oil/g protein). EC of FPH was similar or lower than the reference proteins. ES of FPH (60% to 90%) was similar to or lower than soy and whey proteins (60% to 98%) but higher than casein (20%). ACE inhibition activity increased as DH was increased. Practical Application: The results from this study demonstrate that a functional bioactive hydrolysate can be produced from BW, which is an underutilized fish species, and may aid the industry in better utilizing this raw material. The novelty of this research was the use of BW as a raw material where the protein has been isolated with the pH shift method. Furthermore, it was novel that bioactivity and functionality was measured in the same samples.     

Effect of protein concentration on whey protein gels obtained by a two-stage heating process

 The influence of protein concentration on the properties of gels obtained by a two-stage heating process was determined. In the first stage, whey protein dispersion (3–10%) was heated at pH 8.0, and in the second stage it was diluted to 3% protein, adjusted to pH 7.0 and heated again. Increased protein concentration in the first stage of polymerization resulted in the gels obtained in the second stage having a lower phase angle, increased storage modulus and increased hardness. Increased protein concentration also resulted in gels with an increased optical density, which suggests thathigher protein concentration leads to more and larger aggregates. Gels obtained from dispersions preheated at a higher protein concentration had higher permeability coefficient (B _gel) values. The increase in B _gel suggests that the higher protein concentration increased the size of the aggregates, which in a second stage of heating formed a gel matrix with a larger pore size. Received: 11 February 1999     

Effect of high‐pressure treatments prior to cooking on gelling properties of unwashed protein from barramundi (Lates calcarifer) minced muscle

Heat‐induced gelling properties of barramundi minced muscle with 1.5% and 2% added salt were assessed after application of pressures at 300, 400 and 500 MPa at 4 °C (initial temperature) for 10 min and subsequent cooking at 90 °C for 30 min. Whiteness, gel‐forming ability, water‐holding capacity, hardness and springiness of the barramundi gels increased as applied pressure and salt concentration increased. At 2% salt concentration, high‐pressure treatment results in barramundi gels with higher gel strength, mechanical properties and smoother texture as compared to conventional heat‐induced gels (0.1 MPa, 90 °C for 30). At a reduced salt concentration (1.5%) and pressure ≥ 400 MPa, the quality (gel strength, water‐holding capacity, hardness and springiness) of pressurised cooked gels is comparable to those heat‐induced gels with 2% added salt, but the microstructure is smoother. Scanning electron microscope images of pressurised cooked gels showed dense and compact network with smoother surface than those of heat‐only‐induced gels. Thus, application of high‐pressure treatment prior to cooking could be an effective method to enable reduced salt concentration in barramundi gels.     

Functional properties of fish protein hydrolysates from Pacific whiting(Merluccius productus) muscle produced by a commercial protease

Pacific whiting (Merluccius productus) muscle was used to produce hydrolysates with 10%, 15% and 20% degree of hydrolysis (DH) using the commercial protease Alcalase^® and were characterized at pH 4.0, 7.0 and 10 according their solubility, emulsifying and foaming properties. Protein recovered in soluble fractions increased proportionally with the hydrolytic process, yielded 48.6 ± 1.9, 58.6 ± 4.1 and 67.8 ± 1.4 of total protein after 10%, 15% and 20% DH, respectively. Freeze-dried hydrolysates presented almost 100% solubility (p > 0.05) at the different pHs evaluated. Emulsifying properties (EC, EAI and ESI) were not affected by DH as most samples showed similar (p > 0.05) results. Higher EC (p ? 0.05) than sodium caseinate, used as control, were obtained at pH 4 for most hydrolysates. Hydrolysates showed very low foaming capacity not affected by pH; but foam stability was equal or even better (p > 0.05) than bovine serum albumin (BSA), except at pH 4.0. Results suggest that hydrolysates from Pacific whiting muscle can be produced with similar or better functional properties than the food ingredients used as standards.     

Contribution to the identification of the pigments responsible for the browning of anthocyanin-flavanol solutions

 The formation of pigments responsible for the browning of solutions of pH 3.2 containing malvidin-3-monoglucoside (Mv3g) and (+)-catechin (cat), stored at 32  °C, was studied by liquid chromatography with double detection by diode array spectrophotometry and mass spectrometry. The progressive accumulation of yellowish pigments, with λ_max in the visible region between 439 nm and 458 nm, was observed throughout the assay period. The results obtained allowed the hypothesis that these pigments result from anthocyanin-flavanol condensation to be discounted, and instead suggested that they derive from cat and involve products from the oxidation of ethanol and tartaric acid. Phloroglucinol, produced in the degradation of Mv3g, was seen to participate in the formation of one of the pigments. A colourless dimer resulting from the direct cat-Mv3g condensation was also found; this product was stable and did not evolve towards the formation of pigments during the period of the assay (90 days). Structures for the principal compounds detected were postulated, taking as a basis the data obtained from their mass spectra. Received: 25 January 1999     

Use of image analysis to determine fat and connective tissue in salmon muscle

 An attempt was made to measure connective tissue and fat in salmon fillets using image analysis. Farmed salmon fillets were digitized by video camera and transferred to an image analysis program. A Laplace transformation was performed, and the image was segmented into different scales of grey. Particle analysis was applied to the binary pictures to calculate the percentage of white stripes in the total surface of the fillet, which were related to the percentage of connective tissue (CT) and fat. Although low correlation coefficients were obtained, it could be assumed that the video image analysis method is sensitive enough to detect great variations in fat content, which could prove useful in industrial applications. In contrast, CT was found to have less influence on the visual appraisal of the fillet surface. Received: 17 July 1998 / Revised version: 20 October 1998     

Effect of a new vacuum leaching technology on the textural characteristics of sardine mince

 In order to determine the effect of the vacuum level and leaching time used during the washing process on the gelation characteristics and water-holding capacity (WHC) of sardine mince, a Response Surface Methodology was used. The use of vacuum leaching for short time periods was highly efficient and produced a 50% decrease in the fat content of the washed mince. The leaching under atmospheric pressure produced minces characterised by a low water content and a high residual fat content. The minces’ WHC was shown to be conditioned exclusively by the vacuum pressure produced during stirring, with the lowest WHC results corresponding to the highest fat contents in the minces, which result from the leaching at atmospheric pressure. The determination of gel strength showed that the highest values are obtained with intermediate values of air pressure, and correspond to minces with high protein contents. Harder gels were also obtained with intermediate levels of vacuum. In general, the gels tended to be more cohesive when medium levels of vacuum are used (200–300 mmHg, 26.7–40.0 kPa) for short periods (5 min), or low vacuum levels (550– 650 mmHg, 73.2–86.5 kPa) for longer periods. Hardness, as well as gel strength and breaking force, presented a behaviour that followed the evolution of the protein content in the mince, i.e. higher values were measured at higher protein contents. Received: 27 November 1995 / Revised version: 1 April 1996     

Use of principal component analysis to evaluate the physical properties of Mahon cheese

 The texture, colour and water activity of the seven existing types of Mahon cheese, manufactured under the Mahon cheese Appellation of Origin, were studied using eight physical variables. Four of the types are industrially manufactured [fresh (less than 10 days of ripening), half-ripened (2–5 months of ripening), ripened (5–10 months of ripening) and old-ripened (more than 10 months of ripening)] and three are traditionally manufactured (half-ripened, ripened and old-ripened). ANOVA, Tukey's multiple range test and principal component analysis (PCA) were used. Mahon cheeses from different ripening periods exhibited significant differences in water activity and yellowness values (P<0.001). PCA reduced the eight physical variables to two independent components, which accounted for 84.4% of the total variance. The first principal component (PC1) separated cheeses characterised by high water activity, high springiness values and slight yellowness from those with high hardness and puncture force; PC1 therefore distinguished among samples from different ripening periods. Cohesiveness, chewiness and gumminess were highly correlated in the second principal component, which could be interpreted as an index of cohesiveness. Received: 8 February 1999     

Hydrolysis of alanine oligopeptides by porcine muscle alanyl aminopeptidase

 Alanyl aminopeptidase from porcine skeletal muscle was purified and its activity against alanine oligopeptides studied using capillary electrophoresis. The purpose was to determine the effect of the chain length of alanine oligopeptides on aminopeptidase activity. The enzyme showed high specificity against penta- and tetraalanine and absence of activity against dialanine. In this way, dipeptides and free amino acids would be generated in meat processing. Thus, the presence of a specific amino acid on the N-terminal end of a peptide is determinant for the enzyme activity and the length of that peptide also affects the hydrolysis rate. Received: 25 May 1998 / Revised version: 10 July 1998     

Umami peptides: assessment of their alleged taste properties

 In the literature there are reports that 31 di-and tripeptides elicit umami (i.e. monosodium L-glutamate-like or MSG-like) or savoury tastes. However, the occurrence of “umami peptides” is questioned with regard to the high specificity of those that give an umami taste. A total of 12 dipeptides and 4 tripeptides were selected for a re-examination of their taste properties. Criteria were that: (1) their taste has been described as umami, savoury or brothy; (2) they have a threshold value; and (3) they should fit into the theoretical framework of L-glutamyl peptides discussed. The peptides – in aqueous solutions, at room temperature, at pH 6.0 and 4.0, and at concentrations well above the reported threshold values – were tasted. Panel members were selected on the basis of their ability to perceive the umami taste of 2.67 mM MSG at pH 6.0. None of the peptides tested was found to elicit an umami taste. The taste of L-glutamic acid in the peptides was lost and furthermore the taste of bitter amino acids in the peptides was no longer perceivable. Within the range of Glu-X peptides, even Glu-Glu and Glu-Asp, which have previously been reported to elicit umami tastes, did not taste MSG-like either in pure solution or in the presence of sodium chloride. The tripeptide Ala-Glu-Ala, reported to have an “umami threshold” value as low as 0.8 mM, was found not to have an umami taste or any other specific taste up to 10 mM. The general occurrence of umami peptides appears to be highly unlikely. Received: 6 December 1996     

The effect of blanching on the mechanical and rehydration properties of dried potato slices

 Short-time blanched (2 min, 90  °C), long-time blanched (30 min, 90  °C) and non-blanched potato slices were dried in a convective air drier and their mechanical and rehydration properties were compared. Blanching increased the flexibility and strength of dried potato slices, although the effects of short and long blanching were not significantly different. Unblanched potato slices did not have larger rehydration ratios than blanched ones. After rehydration for 30 min, samples from all treatments had higher strength and flexibility than cooked potatoes. Received: 2 November 1998 / Revised version: 15 February 1999     

Binding of sulphadimidine to glucose in sausage

 The presence of an adduct of sulphadimidine with glucose, i.e. N⁴-glucopyranosyl-sulphadimidine, was demonstrated in raw fermented sausage and batter to which sulphadimidine was added. Identification was performed by HPLC followed by diode array detection. This study demonstrates the need for a hydrolysis step prior to the determination of sulphadimidine for inspection purposes, in food samples containing glucose. Received: 21 October 1998     

Thermal properties of doughs formulated with enzymes and starters

 Thermal properties (gelatinization, amylose-lipid complex dissociation and amylopectin retrogradation) of bread samples formulated with two different quality wheat flours, two enzymes (α-amylase/pentosanase, lipase and their mixture), and three microbial sourdough starters were studied with a differential scanning calorimeter. The carbohydrases modified gelatinization temperature and enthalpy, whilst the lipase modified the amylose-lipid complex dissociation. The enthalpy of amylopectin retrogradation was significantly influenced only by the storage of breads. Second-order interactive effects of enzymes with flour or starter were found for gelatinization and/or amylose-lipid complex dissociation parameters. Some interesting relationships were observed between thermal and textural properties of fresh and stored breads. Received: 22 September 1998 / Revised version: 28 October 1998     

Effect of frozen storage on lipids and lipolytic activities in the longissimus dorsi muscle of the pig

 Samples of longissimus dorsi muscle from pigs were vacuum-packed and stored at –18  °C for a 6-month period. The quantity of total lipids, non-polar lipids, phospholipids and cholesterol remained unchanged during storage. However, there was a decrease (1.4%) in the polyunsaturated fatty acid percentage of the phospholipid fraction after 6 months of frozen storage, mainly due to the decrease in linoleic fatty acid. Nevertheless, there was no change in fatty acid composition of the non-polar lipid fraction. Phosphatidylethanolamine was the phospholipid most affected during the frozen storage, with a significant decrease from an intial percentage of 26.6% to 23.0% after 6 months of storage. Important activities of muscle lipolytic enzymes were still recovered after the storage, which explains the continuous release of free fatty acids reported during the process, with a net increase of 50.6 mg/100 g dry matter. The highest release of free fatty acids was reported during the 1st month of frozen storage. At the 6th month of frozen storage the compositions of both the free fatty acid and phospholipid fractions were similar. With respect to oxidation, the thiobarbituric acid test number showed a slight increase during the process while the peroxide value remained unchanged. Received: 16 March 1998 / Revised version: 17 June 1998     

Use of different thermal indices to assess the quality of pasteurized milks

 Lactoperoxidase activity and lactulose, furosine and undenatured whey protein contents were determined in Spanish commercial milks labelled as pasteurized (group A) and high-temperature pasteurized (group B), in order to assess their quality. Three samples of group A and all of the samples of group B were lactoperoxidase negative. Most samples of group A had measurable amounts of lactulose, even though their concentrations of undenatured β-lactoglobulin were higher than 2600 mg/l. In general, samples of group B showed higher lactulose and furosine and lower undenatured whey protein contents. High levels of furosine and lactulose accompanied by high levels of undenatured β-lactoglobulin could indicate the addition of milk heated at high temperatures, whereas high levels of furosine and relatively low levels of lactulose may have been due to the presence of reconstituted milk powder. Received: 29 June 1998     

Development of a novel fermented soymilk product with potential probiotic properties

 The study was carried out to test the ability of Enterococcus faecium, Lactobacillus acidophilus, L. jugurti, Streptococcus thermophilus and L. delbrueckii ssp bulgaricus to decrease cholesterol in vitro and to grow in the presence of bile salts. Both properties were dependent on the species under study. The cultures were also inoculated into soymilk fortified with dry milk whey powder as single or mixed starters. The physicochemical and sensory evaluations of the fermented products showed that E. faecium plus L. jugurti (ratio 1 : 1) is the best combination, and this mixture also produces a 43% decrease in cholesterol. Received: 14 October 1998 / Revised version: 5 February 1999     

Lipid oxidation in high-pressure processed chicken breast muscle during chill storage: critical working pressure in relation to oxidation mechanism

 The oxidative stability of chicken breast muscle subjected to high-pressure treatment at 300, 400, 500, 600, 700 or 800 MPa for 5 min or 10 min, or to heat treatment (80  °C for 10 min) and subsequent storage at 5  °C was evaluated over a 2-week period. Lipid oxidation in pressure-treated chicken breast muscle monitored as formation of thiobarbituric acid reactive substances depended to a high degree on the working pressure and less on the pressurizing time. The pressure treatment at 800 MPa for 10 min was found to enhance lipid oxidation to the same extent as the heat treatment. Pressure treatment at 600 MPa and 700 MPa resulted in less oxidation. Chicken breast muscle exposed to pressure at or below 500 MPa showed no indication of rancidity, similar to what was found for untreated meat during chill storage; accordingly 500 MPa is a critical pressure for pressure treatment of chicken breast muscle. Analysis of non-heme iron in pressure-treated chicken breast muscle revealed that the notable increase in lipid oxidation caused by high pressure above 500 MPa did not result from the release of iron ions during high-pressure treatment. Furthermore, no influence of high-pressure treatment on the catalytic activity of metmyoglobin on lipid oxidation was observed in a model system, and it is concluded that increased lipid oxidation is probably related to membrane damage. Received: 23 August 1999     

Differential lipid damage in various muscle zones of frozen hake (Merluccius merluccius)

 A comparison of the lipid damage produced in different hake zones was carried out during frozen storage at –11 and –18  °C. Three light muscle zones and the dark muscle were considered. Lipid oxidation [conjugated dienes; thiobarbituric acid index (TBA-i); fluorescence formation] and hydrolysis (free fatty acids, FFA) were determined. The most predominant lipid damage in all zones was hydrolysis, at the end of storage reaching values of about 40% (for the light muscle zones) and 12% (for the dark muscle) of the total lipids at –11  °C. Significant (P<0.05) correlation value (r=0.67–0.85) relationships between the frozen storage time and the FFA content were obtained for the four muscle zones at both temperatures. A comparison of the regression lines slopes in the different zones showed that a lower (P<0.05) lipolitic activity was produced in the dark muscle compared to the three light zones at both temperatures. A low lipid oxidation development was produced in the three light muscle parts, so that no significant differences between them could be assessed. However, the dark muscle showed a higher oxidation development (TBA-i and fluorescence formation) as a result of a higher lipid content and the presence of prooxidant constituents. Received: 16 June 1998