ORIGINAL PAPER Effect of High Pressure and/or Temperature over Gelation of Isolated Hake Myofibrils Deysi Cando & Helena M. Moreno & Clara A. Tovar & Beatriz Herranz & A. Javier Borderias Received: 29 November 2013 /Accepted: 30 January 2014 /Published online: 13 February 2014 # Springer Science+Business Media New York 2014 Abstract High hydrostatic pressure (HHP) processing was used to determine its ability to induce protein gelation. Isolated hake myofibrils were processed by HHP at 0, 150, 250, and 500 MPa (10ºC/10 min) and/or by heating (90ºC/ 20 min). The results were analyzed by Fourier transform infrared spectroscopy (FTIR), differential scanning calorime- try (DSC), determination of sulfhydryl group contents, and dynamic rheometry measurements. FTIR data indicated that secondary protein structures exhibited a reduction in α-helix together with an increase in β-sheet as a result of protein denaturation caused by HHP. DSC showed that HHP induced a reduction in myosin denaturation temperature (T peak ) indi- cating protein unfolding. Protein gelation after HHP is based on physical (non-covalent) interactions which make more sulfhydryl groups available, while after heating, it is based on the formation of covalent (disulfide) bonds as a conse- quence of protein denaturation reducing the sulfhydryl groups. The combination of HHP and heating, particularly the latter, improved network stabilization. These results were reflected in the rheological changes, in which heated gels showed more elastic, cohesive, and time-stable networks than pressurized (non-heated) gels. The HHP effect provided softer, more flexible networks. The gel at 500 MPa was the most elastic and time-stable and exhibited the highest level of connectivity. Keywords High pressure . Myofibril . Physicochemical properties . Viscoelastic properties Introduction High hydrostatic pressure (HHP) processing is a novel tech- nique which has attracted growing interest in the food industry in recent years. One of the most widely used is for inactivation of food-spoilage microorganisms and enzymes at low and ambient temperatures with minimal effects on flavor and nutritional attributes of the product (Denys and Hendrickx 1999), but it also has the ability to modify functional food ingredients such as proteins; and therefore, another of its uses is to modify the texture properties of foods (Cao et al. 2012). HHP favors protein solubilization and unfolding, which are both necessary to the first step of gelation (Macfarlane and McKenzie 1976); but the extent of the protein denaturation will depend essentially on the intensity of the pressure, the temperature, and the ionic strength (Yamamoto et al. 1990). HHP-induced gelation works by way of protein aggregation characterized by side-to-side interactions of proteins through covalent and non-covalent bonding (Hwang et al. 2007; Pérez-Mateos et al. 1997; Uresti et al. 2004). Given that, the response to pressure in this case may be due to differences in the contribution of actin and myosin to pressure-induced gelation. But it should also be remembered that pressure can cause solubilization of actomyosin, which works to the benefit of subsequent aggregation for gel network formation (Cheftel and Culioli 1997). Furthermore, when pressure is released, the protein refolding process begins stabilizing new interactions to produce the protein aggregation necessary for the formation of a gel network (Carlez et al. 1995). As noted, HHP-induced changes in protein structure depend on the pressure intensity; thus, at low pressures (<150 MPa), protein quaternary struc- tures may be affected by the formation of hydrogen bonds, while at higher pressures (>200 MPa), the changes in the tertiary structure are maintained by hydrophobic and ionic interactions (Huppertz et al. 2004). Be it noted in this context that hydrophobic interactions, which essentially link actin D. Cando : H. M. Moreno : B. Herranz : A. J. Borderias (*) Instituto de Ciencia y Tecnología de Alimentos y Nutrición (ICTAN-CSIC), José Antonio Novais 10, 28040 Madrid, Spain e-mail: jborderias@ictan.csic.es C. A. Tovar Department of Física Aplicada, Facultad de Ciencias, Universidad de Vigo, As Lagoas, Ourense 32004, Spain Food Bioprocess Technol (2014) 7:3197–3207 DOI 10.1007/s11947-014-1279-9