Pascual López-Buesa

Application of Ultrasound

Publisher Summary Major mechanical effects of ultrasound are provided when the power is sufficiently high to cause cavitation. Like any sound wave, ultrasound is propagated via a series of compression and rarefaction waves induced in the molecules of the medium through which it passes. At sufficiently high power, the rarefaction cycle may exceed the attractive forces of the molecules of the liquid and cavitation bubbles will form. Such bubbles grow by a process known as rectified diffusion, that is, small amounts of vapor (or gas) from the medium enters the bubble during its expansion phase and is not fully expelled during compression. The effectiveness of ultrasound as a food processing tool has been proven in the laboratory and there are a number of examples of scale-up. In most cases, commercially available frequency is used, that is 20 or 40 kHz, and this has proved quite satisfactory. In such cases, the variable parameters are temperature, treatment time, and acoustic power. Little attention has been paid to the use of different frequencies except in a few cases. One such is the use of ultrasound in food preservation using the bactericidal action of sonication combined with other techniques such as heat, ultraviolet light, and the use of a biocide.

Inactivation of proteases and lipases by ultrasound

The inactivation of phospholipase A2, α-chymotrypsin, trypsin and porcine pancreatic lipase by heat and manothermosonication (MTS), and the simultaneous application of heat and ultrasound under moderate pressure, has been studied in different treatment media. MTS sensitivity varied strongly for the different enzymes. Whereas phospholipase A2 was almost insensitive to MTS treatments, α-chymotrypsin and porcine lipase MTS inactivation was much faster than heat inactivation. Trypsin heat inactivation was very different at low than at high temperatures. At low temperatures, it did not follow first order kinetics, contrary to what happened at high temperatures. MTS accelerated trypsin inactivation only at low temperatures. MTS changed also the inactivation order of trypsin (at low temperatures), α-chymotrypsin and porcine lipase; whereas heat inactivation of these enzymes did not follow first order kinetics, MTS inactivation fitted this well.

Incidence in diverse pig populations of an IGF2 mutation with potential influence on meat quality and quantity: An assay based on real time PCR (RT-PCR)

IGF2, insulin-like growth factor 2, is implicated in myogenesis and lean meat content. A mutation in a single base (A for G substitution) of the gene for IGF2 (position 3072 in intron 3) has been recently described as the cause of a major QTL effect on muscle growth in pigs [Van Laere, A. S, Nguyen, M., Braunschweig, M., Nezer, C., Collete, C., & Moreau, L. et al. (2003). Nature, 425, 832-836]. We describe here a rapid assay based on real time PCR (RT-PCR) to detect this mutation. We have evaluated the incidence of the mutation in commercial pig crosses, in three populations of purebred Iberian or Iberian×Duroc crosses, and in cured meat products and wild boars. The incidence of the mutation varies among these groups. Penetrance of the A mutation is about 80% in the commercial population. Purebred Iberian pigs were all homozygous G/G whereas crosses of Iberian pigs were heterozygous (90%) or homozygous A/A (10%). The implications of this gene for the selection of Iberian pigs are discussed.

Burlat cherry quality after long range transport: optimisation of packaging conditions

The purpose of this work was to determine the shelf life of Burlat cherries packaged in modified atmospheres during transportation and commercialisation. Cherries were harvested at commercial maturity and packaged in trays covered with polypropylene films with different permeabilities. All cherries were transported in a refrigerated truck from Zaragoza (Spain) to Milan (Italy) during a transport time of 5 days. After transportation, cherries were submitted to a commercialisation period. Our results show that modified atmosphere packaging using polypropylene films of intermediate permeability (238 ml O2 m−2 h−1 atm−1 or 423 ml O2 m−2 h−1 atm−1) extends postharvest cherry shelf life up to 15–20 days at 5 °C. Under these conditions acidity levels remain higher, anthocyanin synthesis is reduced, lower level of oxidative enzymes are detected, and texture and sensorial quality improve. Moreover, films of intermediate permeability allow a temporal breakage of the cold chain without any reduction in sensorial quality of the cherries.

Allelic incidence in several pig breeds of a missense variant of pig melanocortin-4 receptor (MC4R) gene associated with carcass and productive traits; its relation to IGF2 genotype

MC4R, melanocortin-4 receptor, is involved in feed intake regulation. A mutation in a single base of MC4R, a G/A substitution in position 1426, has been linked to enhanced backfat thickness, average daily gain and daily feed intake. We present in this work a method to diagnose this mutation using real time PCR (RT-PCR) which allows rapid, cheap and reliable analysis of hundreds of samples in just 2h after DNA extraction. We have used this RT-PCR based assay to study the incidence of the mutation in several pig breeds or crosses (Iberian, Duroc, Pietrain, Large White, Large White×Pietrain) and wild boars. IGF2, insuline like growth factor 2, a gene with well demonstrated effects on carcass composition, of all these animals has also been analyzed and we show, using linkage disequilibrium analysis that both genes are independent. The implications of our results for pig selection toward fatty or lean carcasses are discussed.

Manothermosonication of heat-resistant lipase and protease from Pseudomonas fluorescens: effect of pH and sonication parameters.

The effect of different parameters (pH, ultrasonic amplitude and pressure) on the resistance to heat and manothermosonication (MTS) treatments of heat resistant lipase and protease produced by Pseudomonas fluorescens B52 and NCDO 2085, respectively, were studied. Lipase B52 thermoresistance decreases with an increase of pH. However, inactivation by MTS seems to be pH independent. There were only slight increases in the MTS efficiency when increasing pressure at UHT temperatures and the effect of amplitude was different depending on treatment temperature. Protease NCDO 2085, which was very resistant to MTS at 30 degrees C. was very sensitive to MTS at 76 degrees C. Increases in applied pressure had no effect on MTS efficiency at 140 degrees C and its inactivation by MTS was almost temperature independent between 76-109 degrees C. Data obtained are compared with previous published data and inactivation mechanisms are discussed.

The effects of two alleles of IGF2 on fat content in pig carcasses and pork.

The different fat infiltration capabilities of two alleles of IGF2 (G3072A) have been investigated in pigs of a Landrace-Large White×Duroc cross. Paternally inherited G allele carrier pigs show an increased content of adipose rich meat cuts such as the lard or the belly and 4mm larger backfat thickness values. Paternally inherited A carrier pigs on the other hand contain larger muscle tissue rich cuts such as the loin, the ham and the tenderloin and have 0.19 units lower feed conversion index. No substantial differences have been found neither in intramuscular fat content in several muscles nor in meat quality in both pig groups. Hams of paternally inherited G carrier pigs are richer in both subcutaneous adipose tissue (23.1 vs 19.1mm backfat thickness) and intermuscular fat content. The suitability and the economics of using any of the two of both genotypes for cured ham production are discussed.

Amino acid and nucleotide contents and sensory traits of dry-cured products from pigs with different genotypes

The free amino acid and nucleotide contents of dry-cured ham, shoulder and loin from two genetic lines selected from pigs according to the paternal allele (homozygous AA and heterozygous AG) of the insulin-like growth factor-II gene were studied by HPLC. Their influence on the flavor and taste characteristics was also studied. The increase of lean content caused by the IGF-II mutation could affect proteolysis during the ripening process and therefore the sensory characteristics. The lower intramuscular fat content in the AA ham batch had a positive effect on the free amino acid content. However, similar flavor traits between ham batches were found, but the AG loin batch showed greater value. The enhancing effect of the IMP on the overall flavor intensity was limited by the amino acid and the IMF contents in dry-cured ham and loin, while in dry-cured shoulder, the IMP could be the reason for the significant differences in after taste and cured flavor scores.

Effect of IGF-II (insulin-like growth factor-II) genotype on the quality of dry-cured hams and shoulders

The aim of this study was to investigate the effect of the paternal allele (homozygous AA and heterozygous AG) of the IGF-II gene on the fat content, fatty acid composition and sensory characteristics of dry-cured hams and shoulders. The effects were more evident in the subcutaneous fat thickness than in the intramuscular fat (IMF) content, and in the dry-cured hams rather than the dry-cured shoulders. Subcutaneous fat thickness was significantly higher in AG dry-cured hams and shoulders; however, IMF content was only significantly higher in AG dry-cured hams. These effects produce changes in fatty acid composition and sensory characteristics when comparing both batches of each product, but the behavior differed with the type of product. Sensory characteristics were similar in both batches of dry-cured hams in spite of the differences in IMF content. Nevertheless, AG dry-cured shoulders showed higher scores in most of the attributes evaluated, despite the IMF content being similar between batches.

c.A2456C-substitution in Pck1 changes the enzyme kinetic and functional properties modifying fat distribution in pigs.

Cytosolic phosphoenolpyruvate carboxykinase, PCK1, is one of the main regulatory enzymes of gluconeogenesis and glyceroneogenesis. The substitution of a single amino acid (Met139Leu) in PCK1 as a consequence of a single nucleotide polymorphism (SNP), c.A2456C, is associated in the pig to a negative phenotype characterized by reduced intramuscular fat content, enhanced backfat thickness and lower meat quality. The p.139L enzyme shows reduced kcat values in the glyceroneogenic direction and enhanced ones in the anaplerotic direction. Accordingly, the expression of the p.139L isoform results in about 30% lower glucose and 9% lower lipid production in cell cultures. Moreover, the ability of this isoform to be acetylated is also compromised, what would increase its susceptibility to be degraded in vivo by the ubiquitin-proteasome system. The high frequency of the c.2456C allele in modern pig breeds implies that the benefits of including c.A2456C SNP in selection programs could be considerable.