M.C. Gómez-Guillén

Structural and physical properties of gelatin extracted from different marine species: A comparative study

Gelatin from skins of several marine species were compared on the basis of their rheological characteristics (viscoelasticity and gel strength) and chemical/structural properties (amino acid composition, molecular weight distribution and triple helix formation). Gelatins from flat-fish species (sole and megrim) presented the best gelling ability and the gels were more thermostable than those from cold-adapted fish (cod and hake). This different behaviour may be explained considering the amino acid composition, the α1/α2 collagen-chain ratio, and the molecular weight distribution. Thus, cod gelatin presented a lower alanine and imino acid content, and a decreased proline hydroxylation degree; cod and hake gelatins presented a low α1/α2 ratio (∼1); hake gelatin showed a highly significant decrease in β-components and other aggregates. The squid gelatin presented the most significant changes regarding amino acid composition and molecular weight distribution, most of these differences arising from the low solubility of the squid connective tissue. However, the squid gelatin showed viscoelastic properties intermediate between those from flat-fish and cold-adapted fish species. Circular dichroism analysis reveals that gelling involves a refolding of denatured collagen chains into the typical triple helix conformation and, conversely, unfolding upon reheating. Thermal folding and unfolding curves were similar to those of viscoelastic properties but showing a shift towards lower or higher temperatures upon cooling and heating, respectively. The folding process seem to be directly related in the stabilisation of the gels without disregarding its role in triggering the gelation process. Finally, gel strength evaluation revealed the importance of slow cold maturation.

Biodegradable gelatin-chitosan films incorporated with essential oils as antimicrobial agents for fish preservation

Essential oils of clove (Syzygium aromaticum L.), fennel (Foeniculum vulgare Miller), cypress (Cupressus sempervirens L.), lavender (Lavandula angustifolia), thyme (Thymus vulgaris L.), herb-of-the-cross (Verbena officinalis L.), pine (Pinus sylvestris) and rosemary (Rosmarinus officinalis) were tested for their antimicrobial activity on 18 genera of bacteria, which included some important food pathogen and spoilage bacteria. Clove essential oil showed the highest inhibitory effect, followed by rosemary and lavender. In an attempt to evaluate the usefulness of these essential oils as food preservatives, they were also tested on an extract made of fish, where clove and thyme essential oils were the most effective. Then, gelatin-chitosan-based edible films incorporated with clove essential oil were elaborated and their antimicrobial activity tested against six selected microorganisms: Pseudomonas fluorescens, Shewanella putrefaciens, Photobacterium phosphoreum, Listeria innocua, Escherichia coli and Lactobacillus acidophilus. The clove-containing films inhibited all these microorganisms irrespectively of the film matrix or type of microorganism. In a further experiment, when the complex gelatin-chitosan film incorporating clove essential oil was applied to fish during chilled storage, the growth of microorganisms was drastically reduced in gram-negative bacteria, especially enterobacteria, while lactic acid bacteria remained practically constant for much of the storage period. The effect on the microorganisms during this period was in accordance with biochemical indexes of quality, indicating the viability of these films for fish preservation.

Gel properties of collagens from skins of cod (Gadus morhua) and hake (Merluccius merluccius) and their modification by the coenhancers magnesium sulphate, glycerol and transglutaminase

Abstract The gel properties of two different kinds of fish gelatins prepared from cod ( Gadus morhua ) and hake ( Merluccius merluccius ) and modified by the coenhancers glycerol, salt and microbial transglutaminase, were examined. Gel strength was substantially increased by the addition of coenhancers although results varied, depending on the species. In gelatin from hake ( M. merluccius ) skin, the highest values were obtained with 10 mg/g of transglutaminase, whereas magnesium sulphate was more effective at both concentrations (0.1 and 0.5 M) in gelatin from cod ( G. morhua ) skin. Although, in both gelatins, the addition of any ingredient increased the viscosity modulus (G″), the elastic modulus (G′) was only increased by the addition of glycerol 15% (w/v) and MgSO 4 0.5 M in hake ( M. merluccius ) gelatins; in cod ( G. morhua ) it was increased by all ingredients. The gelling and melting points, very important properties in fish gelatin, showed a notable improvement, the behaviour being different, depending on the species.

The effect of added salts on the viscoelastic properties of fish skin gelatin

Abstract The effects of various salts on the viscoelastic properties of a class A gelatin (obtained by a mild acid pretreatment) from megrim ( Lepidorhombus boscii ) skins were examined and compared with their effects on commercial tilapia skin gelatin. Although salts generally extended the setting time of gelatins, it was found that the melting temperature was increased considerably by the addition of MgSO 4 , (NH 4 ) 2 SO 4 , or NaH 2 PO 4 . Of all the salts assayed, only MgSO 4 improved the rheological characteristics in suitable conditions of pH and ionic strength, which differed between megrim and tilapia gelatin. Notable differences were found in the amino acid compositions of the two species, especially in the hydroxyproline content.

Antimicrobial Activity of Composite Edible Films Based on Fish Gelatin and Chitosan Incorporated with Clove Essential Oil

Edible films based on fish-skin gelatin incorporated with chitosan and/or clove essential oil were elaborated and their antimicrobial activity was tested on Lactobacillus acidophilus, Pseudomonas fluorescens, Listeria innocua, and Escherichia coli. The films incorporated with the clove essential oil were the most effective although differences were observed depending on the biopolymeric matrix in which it was included. When a clove added film was applied to the preservation of raw sliced salmon, a reduction of the growth of total bacteria was observed after 11 days of storage at 2°C. So, edible films based on fish gelatin can be used as an active packaging applied to fish products.

Natural Additives in Bioactive Edible Films and Coatings: Functionality and Applications in Foods

Incorporation of natural additives to active packaging systems or biopolymer-based edible films can modify the film structure and, as a result, modify their functionality and application to foods. This paper reviews the effect of the incorporation of natural additives from plant extracts or their isolated active compounds and vitamins on the functionality of edible films and the application of these films to foods. The final functionality of edible films is related to their bioactive properties (such as antioxidant, antimicrobial, and antibrowning activities) and functional properties (such as barrier to oxygen, carbon dioxide, and UV–vis light); water vapor permeability; tensile stress; elongation at break; and physical properties (such as opacity and color). Several categories of natural antioxidants found in plant, spices, and herbs (organic acids, plant natural extracts, and plant essential oils) have been incorporated into edible films and coatings, resulting in an improvement of the bioactive properties of the films. However, a wide range of plant natural sources with bioactive properties has not yet been characterized with respect to their ability to be applied directly on foods and used to develop active packaging or biopolymer-based edible films for preserving and adding value to foods. In addition, in vivo studies of the use of bioactive films to preserve the quality, shelf life, and nutritional value of foods remain limited.

Functional characterisation of muscle and skin collagenous material from hake (Merluccius merluccius L.)

Abstract The purpose of this paper was to examine the modifications occurring in certain functional hydration properties (protein solubility in 0.5 M acetic acid, apparent viscosity and water-binding capacity) of the collagenous material from skin and muscle of hake ( Merluccius merluccius L.) in relation to the pH and the ionic strength (expressed as variation in NaCl concentration) of the medium. At the same time, these modifications were compared with those reported for collagenous material from trout in a previous paper. Generally speaking, skin collagenous material showed higher functionality than muscle collagenous material. It was found that protein solubility, apparent viscosity and water-binding capacity presented maximum values at pH levels between 2 and 4, and at concentrations of less than 0.25 M NaCl. Finally, the functional values were found to be higher in collagenous material from hake than from trout, especially in the skin material. ©

Collagen characteristics of farmed Atlantic salmon with firm and soft fillet texture

The possible role of collagen in texture variations among Atlantic salmon (Salmo salar L.) grown under commercial conditions at a Norwegian farm was studied. The texture was determined instrumentally as the breaking strength, and collagen and its salt (SSC), acid (ASC), pepsin (PSC) and insoluble (IF) fractions were analysed in order to determine the collagen aggregation degree. The collagen solubility and its overall amino acid (AA) composition showed no correlation to the breaking strength, but a positive correlation was observed between the breaking strength and glycine (r=0.74) and alanine (r=0.87) contents of the PSC fraction. Salmon with high breaking strength had higher T(peak) (temperature of transition) and ΔH (enthalpy of transition), and the collagen seemed to have triple helix structures mainly stabilized by covalent associations as compared to salmon with low breaking strength. The glycosylation degree was also positively correlated to the breaking strength (r=0.88, p ≤ 0.05). It is concluded that firmness of salmon muscle was not related to the total amount of collagen in the muscle, but rather higher collagen stability.

Influencia de la subespecie, estacionalidad y procedimientos de estabilización en la aptitud gelificante del músculo de sardina (Sardina pilchardus) congelado/Influence of subspecies, season and stabilization procedures in gel-forming ability of frozen minced muscle of sardine (Sardina pilchardus)

This paper examines the gel-forming ability of minced muscle of sardine - caught from the Bay of Biscay and the Mediterranean at different seasons - kept in frozen storage for 150 days. The influence of atmospheric and vacuum packaging on the gel-forming capacity of minced muscle, and the addition of tocopherol as antyoxidant were also studied. From the outset of frozen storage, Mediterranean sardine muscle exhibited greater gel strength than that from the Bay of Biscay. Sardines from the Bay of Biscay caught in November produced the best gels from any area. Generally, when frozen muscle was vacuum-packed, rancidity was less and gel strength improved. Activity of tocopherol does not seem sufficiently clear. In nearly all cases, gel strength was greater the longer the muscle was kept in frozen storage, although in Bay of Biscay sardine muscle there was progressive myofibrillar protein aggregation throughout the storage.

Partial protease activity characterization of squid (Todaropsis eblanae) mantle / Caracterización parcial de la actividad proteolítica del manto de pota (Todaropsis eblanae)

Proteolytic activity in mantle of Todaropsis eblanae was maximum at 40 and 65 °C. Several peaks of activity were detected over the pH range studied (1.5-9.5), indicating the presence of acidic, neutral and alkaline proteases, depending on the temperature. The substantial enzymic inhibition at acidic pH by the inhibitor trans-epoxysuccinyl-L-leucylamine-4-guanidine butane (E-64) revealed the pre dominance of lysosomal cysteine proteases (cathepsins) which showed higher activity at 65 °C than at 40 °C. At 65 °C and pH 5.5 metallo-proteases were also detected by the inhibition with phenanthroline. Serine protease activity predominated at neutral pH (higher at 40 °C than at 65 °C), and cysteine proteases were detected at alkaline pH. There was evidence of cathepsin B and L activity at 65 °C and to a lesser degree at 40 °C.