Prospero Di Pierro

Preparation and mechanical properties of edible pectin-soy flour films obtained in the absence or presence of transglutaminase.

Whole soy flour and apple pectin were used as raw materials for producing hydrocolloid edible films. The best ratio between the two components (2:1 mg cm(-2), pectin-soy flour) was determined in order to obtain films which could be perfectly handled for their consistence. Films were also prepared in the presence of transglutaminase, an enzyme able to produce isopeptide bonds among the soy polypeptide chains. The latter films showed a smoother surface and higher homogeneity, as demonstrated by microstructural analyses, whereas studies on the mechanical properties indicated that transglutaminase increased their strength and reduced their flexibility. Our results suggest a possible use of the transglutaminase polymerized pectin-soy protein films as edible food or drug coatings.

Incorporation of whey proteins into cheese curd by using transglutaminase

A Ca2+‐independent microbial TGase (transglutaminase) isolated from Streptoverticillium mobaraense was used to obtain whey protein containing novel dairy products. We evaluated the difference both in the curd formation time as well as in the hardness and deformability of the cheese obtained from cows milk in the presence or absence of the enzyme. The results of our experiments showed that the milk coagulation time was dependent on the step in cheese manufacture at which TGase was added. We analysed the deformability and the hardness of the dairy products obtained either by adding both TGase and the milk‐clotting enzyme to the milk sample at the same time or by adding TGase after treating the milk sample for 30 min with the clotting enzyme and cutting the obtained coagulum. TGase treatment conferred a strongly decreased protein content to derived whey. Moreover, when further amounts of whey were added to the milk during the manufacturing process in the presence of TGase, whey‐protein‐enriched dairy products could also be obtained. Our findings may lead to new biotechnologies for the re‐utilization of by‐products from dairy plants and contribute to reduction of environmental pollution from whey‐protein disposal.

Transglutaminase Crosslinked Pectin- and Chitosan-based Edible Films: A Review

The production of biodegradable and edible films with desired mechanical characteristics and gas barrier properties represents one of the most advanced challenges in the field of food wrapping and coating. New edible films can serve not only to provide food with physical protection but also to reduce loss of their moisture, to restrict absorption of oxygen, to lessen migration of lipids, to improve their mechanical handling features, and as materials, to apply in direct contact with internal food to realize a multilayer food packaging. Polymers derived from natural products, like carbohydrates and proteins, offer the greatest opportunities as component of edible films since their biodegradability and environmental compatibility are assured and they can also supplement the nutritional value of specific foods. However, excessive water solubility and poor water vapor barrier properties, and often poor mechanical resistance, have their application limited until the present time. Numerous studies have been carried out to improve their properties by preparing composite and multi-component films or by physically and chemically crosslinking their natural components. In the present review we summarize the main results obtained by crosslinking with the enzyme transglutaminase different proteins contained in multi-component pectin- and chitosan-based edible films, having the aim to create environmentally-friendly “bioplastics” with mechanical and permeability properties similar to the ones exhibited by plastics of petrochemical origin.

Application of Transglutaminase-Crosslinked Whey Protein/Pectin Films as Water Barrier Coatings in Fried and Baked Foods

Whey protein/pectin edible films were prepared in the presence of transglutaminase and tested as water barrier coatings of both fried doughnuts and french fries as well as of baked food like “taralli” biscuits. Our results demonstrated an undoubted effect of the produced hydrocolloidal films, known to markedly reduce water vapor permeability, in decreasing moisture loss in both doughnuts and french fries when applied before food frying. At the same time, a significant decrease in oil content was observed in the coated fried foods (about 50xa0% in doughnuts and 25xa0% in french fries) with respect to both uncoated controls and whey/soy protein-coated samples. No difference was observed between uncoated and coated both doughnuts and french fries with regard to their texture properties and as confirmed by the data from sensory evaluation tests. Furthermore, since the coating by edible films endowed with low water vapor permeability could be useful to prevent moisture absorption by baked foods, we tested the whey protein/pectin film prepared in the presence of transglutaminase, which was also used to coat taralli biscuits. The proposed methodology resulted to be effective to hinder moisture absorption by biscuits during a long storage period, keeping water content constant from 0 to 50xa0days, thus preventing the food matrix conversion from a glassy state to a rubbery state which is the major cause of baked food rejection by consumers.

Transglutaminase-induced chemical and rheological properties of cheese.

Ca2+-independent transglutaminase isolated from Streptoverticillium mobaraense was used to obtain a novel cheese we called “crosslinked cheese.” We characterized both the cheese obtained by adding transglutaminase and milk clotting enzyme at the same time, and the one produced by adding transglutaminase, following cutting of the coagulum. In both cases, water content and cheese yields were higher, whereas protein content significantly increased from 33.8% to 39.5% only in the second type of crosslinked cheese. Isoelectric focusing of the protein extracted from the prepared cheese samples on a thin layer of polyacrylamide gel indicated that mainly β-caseins were involved in the transglutaminase-catalyzed crosslinks occurring in the curd. Few αs1-casein isoforms were entrapped in the curd matrix only when transglutaminase was added at the same time as the coagulant enzyme. Soluble nitrogen determination and HPLC peptide analysis indicated a markedly reduced proteolysis of crosslinked cheese during ripening, probably responsible for the observed enhancement of their hardness in comparison with the control cheese, obtained in the absence of transglutaminase.

Characterization of Citrus pectin edible films containing transglutaminase-modified phaseolin

The growing social and economic consequences of pollution derived from plastics are focusing attention on the need to produce novel bioprocesses for enhancing food shelf-life. As a consequence, in recent years the use of edible films for food packaging is generating a huge scientific interest. In this work we report the production of an edible hydrocolloid film made by using Citrus pectin and the protein phaseolin crosslinked by microbial transglutaminase, an enzyme able to covalently modify proteins by formation of isopeptide bonds between glutamine and lysine residues. The films were characterized and their morphology was evaluated by both atomic force microscopy and scanning electron microscopy. Mechanical properties and barrier properties to CO2, O2 and water vapor have demonstrated that these films possess technological features comparable to those possessed by commercial plastics. It is worth noting that these characteristics are maintained even following storage of the films at 4°C or -20°C, suggesting that our bioplastics can be tailored to protect food at low temperature. Moreover, gastric and duodenal digestion studies conducted under the same conditions found in the human digestion system have demonstrated that transglutaminase-containing films are regularly digested encouraging an application of the proposed materials as food coatings.

Effect of transglutaminase on the mechanical and barrier properties of whey protein/pectin films prepared at complexation pH.

The behavior of pectin and thermally denatured whey proteins at both different protein/polysaccharide ratios and different pH values was investigated. Our findings suggest the formation at pH 5.1 (complexation pH) of transglutaminase-catalyzed cross-links among soluble ionic whey protein/pectin complexes, which could be responsible for the observed increase of both tensile strength (2-fold) and elongation to break (10-fold) of films obtained in the presence of enzyme. Conversely, a significant reduction of elasticity, probably due to the formation of covalent bonds among single whey protein molecules, was observed when the films were prepared in the presence of the enzyme at pH 6.0. In addition, the presence of the enzyme at complexation pH significantly reduced film permeability. Atomic force and scanning electron microscopy revealed significant changes in the microstructure of the films prepared in the presence of TGase as well as in the morphology of their surface.

Transglutaminase-mediated modification of ovomucoid: effects on its trypsin inhibitory activity and antigenic properties

Hen egg can cause food hypersensitivity in infants and young children, and ovomucoid is the most allergenic factor among proteins contained in egg white. Since proteinase treatment, a well-recognized strategy in reducing food allergenicity, is ineffective when applied to ovomucoid because of its ability to act as trypsin inhibitor, we investigated the possibility of reducing the ovomucoid antiprotease activity and antigenic properties by covalently modifying its structure. The present paper reports data showing the ability of the Gln115 residue of ovomucoid to act as an acyl donor substrate for the enzyme transglutaminase and, as a consequence, to give rise to a covalent monodansylcadaverine conjugate of the protein in the presence of both enzyme and the diamine dansylated derivative. Moreover, we demonstrated that the obtained structural modification of ovomucoid significantly reduced the capability of the protein to inhibit trypsin activity, also having impact on its anti-ovomucoid serum-binding properties.

Substance P and its transglutaminase-synthesized spermine derivative elicit yawning behavior via nitric oxide in rats.

Previously, we showed that intranigrostriatal injection of substance P (SP) cause behavioral changes in rats. Those effects, such as locomotion and food intake, resulted related to catecholamines release modulated by nitric oxide [18]. Here we report that intranigrostriatal injection of SP elicited yawning in rats. Moreover, since in previous studies we demonstrated that transglutaminase-synthesized gamma-(glutamyl5)spermine derivative of SP (Spm-SP) could be a useful tool in differentiating NK1 receptors [5,19,26], we reports the effects of injecting the selective septide-sensitive NK1 receptor agonist Spm-SP into the nigrostriatal region of the rat brain on yawning. The administration of L-N(omega)-nitroarginine methyl ester, a NO-synthase inhibitor, stereospecifically reduced in a dose related manner both SP and Spm-SP-induced yawning. In contrast, L-arginine pretreatment prevented the effect of NO-synthase inhibitor. Moreover, the NK1 antagonist RP,67580 blocked yawning behavior induced by both SP and Spm-SP, whereas the pretreatment with systemic reserpine determined its increase. The administration of NO-synthase inhibitor resulted ineffective in reducing SP and Spm-SP-induced yawns in reserpinized rats. Finally, yawns elicited by SP or Spm-SP were blocked when rats were treated with scopolamine but not with methylscopolamine. These results indicate that yawning induced in rats by SP injection is dependent upon endogenous dopamine levels in brain nigrostriatal area. Moreover, we demonstrate, by using Spm-SP, that septide-sensitive NK1 receptor are specifically involved in yawning behavior.

Trehalose-containing hydrocolloid edible films prepared in the presence of transglutaminase

In this article, edible hydrocolloid films were prepared by using Citrus pectins and the protein phaseolin in the presence of microbial transglutaminase, an enzyme able to catalyze isopeptide bonds between endo‐protein‐reactive glutamine and lysine residues. For the first time, trehalose, a nonreducing homodisaccharide into which two glucose units are linked together by a α‐1,1‐glycosidic linkage, was used as a component of hydrocolloid films constituted of both proteins and carbohydrates. Our data have demonstrated that these films act as very effective barriers to gases, especially to CO2. They also present a high antioxidant capability as measured by the 2,2‐diphenyl‐1‐picrylhydrazyl scavenging assay. In addition, the films were characterized using Atomic Force Microscopy, a powerful tool used to evaluate film surface topography and roughness. The results of our experiments clearly indicate that the trehalose‐containing films prepared both in the presence and absence of transglutaminase are composed of nanoparticles with a smooth surface, having similar roughness values (Rα). In conclusion, according to barrier and antioxidant properties and to their structure, it is possible to consider the trehalose‐containing films as innovative bioplastics potentially able to protect different kinds of foods.