J. Laencina

On-line methods for pork quality detection

Abstract The detection of pale, soft, exudative (PSE) and dry, firm, dark (DFD) meat is one of the most important problems in judging pork quality. The use of PSE meat leads to lower yields and changes in the rate of salt penetration in cured products, and is unsuitable for preparing cooked products while DFD meat has only a limited application in the preparation of cured products and is easily contaminated by microbial growth. For this reason it is important to be able to detect pork meat quality soon after slaughter and, to aid in this task, ‘on-line’ probes have been developed which are capable of rapidly categorizing meat. Most of these probes are based on the optical and electrical properties of muscle. The most interesting are those which measure internal light scattering by fibre optic probe (FOP) and electrical conductivity by quality meter (QM). Pork quality was studied using FOP, QM and pH measurement on the slaughter line in semimembranosus (SM) and longissimus dorsi (LD) muscles at 45 min and 24 h post-mortem. Results showed that pH is a good predictor of meat quality at 45 min and 24 h post-mortem while FOP differentiates between extreme categories and QM is better at detecting PSE meat.

Fresh and eating pork quality from entire versus castrate heavy males

Abstract Pork quality from entire (EM) and castrated (CM) male pigs slaughtered at 105 kg live weight was compared. Two commercial pig crossbreeds were studied: Cross D (Large White×Duroc females and Landrace×Duroc males) and Cross L (Landrace×Large White females and Large White males). Androstenone (AN), skatole (SK) and indole (IN) backfat levels, fresh meat quality (moisture, protein, intramuscular fat, drip and cooking losses, pH and colour) and eating quality by a trained panel (boar odour and flavour, juiciness, tenderness, aroma and taste of freshly cooked loin) and untrained consumers (preference and acceptance) were determined. Results from these studies show that 35% (25%: Cross D; 45%: Cross L) and 10% (5% and 15%) of EM had over 0.5 μg AN and 0.25 μg SK g −1 fat, respectively, the cut-off values to detect boar taint in meat. Castration increased meat fatness and reduced boar taint, the aroma and taste of freshly cooked meat was more appreciable, while its effects on juiciness and tenderness were less clear. Pork acceptance was better in CM than in EM. CM was preferred by 75% of consumers.

Deaeration and pasteurization effects on the orange juice aromatic fraction

Abstract A comparative study between the aromatic profile in fresh orange juice versus deaerated and pasteurized juices, respectively, was conducted in order to understand the evolution of volatile components after deaeration and pasteurization processes. The aromatic fractions isolated by simultaneous distillation and extraction were analysed by capillary gas chromatography–mass spectrometry. At the qualitative level all the volatile components in fresh orange juice were also found in the counterparts after deaeration and pasteurization processes. According to statistical analyses, significant losses in concentration of volatile components occurred during the deaeration process, while there were no statistically significant differences determined among concentrations of volatile components in deaerated and pasteurized juices. These results show that during the industrial processing of orange juice the biggest losses in the concentration of volatile components occurs during deaeration. The pasteurization process does not change the analytical composition of deaerated orange juice in a significant way for any of the 42 quantitated compounds.

Proteolytic activities of some milk clotting enzymes on ovine casein.

Proteolytic activity of some milk clotting enzymes (calf and lamb rennets, bovine chymosin and pepsin, and proteases from Rhizomucor miehei and Cryphonectria parasitica) on ovine whole casein was determined by urea-PAGE and RP-HPLC. Microbial enzymes were more proteolytic than animal enzymes when acting on ovine whole casein. Lamb rennet and C. parasitica protease showed the lowest and the highest degree of proteolysis, respectively. Urea-PAGE results showed that all enzymes hydrolyzed ovine casein resulting in the formation of αs1-I and β-I as initial breakdown products of αs1-CN and β-CN. In addition to these products, C. parasitica protease produced a series of degradation products with lower mobilities than β-CN. Minor quantitative differences between coagulants from animal origin, but great quantitative and qualitative differences between microbial and animal coagulants (assessed throughout the study of the RP-HPLC peptide profiles), were observed.

Effect of calcium and enzyme in cutting time prediction of coagulating goats’ milk using a light scattering sensor

An on-line fibre optic sensor measuring backscatter at 880 nm was used for predicting the cutting time of goats’ milk. A factorial design was utilised to test the kid rennet and enzyme from Mucor miehei at three levels of added CaCl2. A cutting time prediction equation using the diffuse reflectance parameter, Tmax; predicted the cutting time with a standard error of 0.55 min. Tmax and cutting time decreased with CaCl2 addition. Coagulation was faster for kid rennet. The sensor was found useful for comparing the activity of milk-clotting enzymes. r 2002 Elsevier Science Ltd. All rights reserved.

Viscometric control in the enzymatic extraction of citrus peel oils

Abstract Enzymatic treatment during the industrial extraction of lemon-peel oil allows the aqueous discharges from centrifuges to be recycled towards the extractors. Emulsions with stabilized and reduced viscosity are essential for centrifuges to work efficiently. In citrus processing plants, enzyme is added in a manual operation with no viscosity control. However, the correct measurement of this parameter makes it possible to optimize the concentration of pectinase and to improve control of the flow of emulsion to the centrifuges.

Changes in high and low molecular weight carbohydrates during Rhizopus nigricans cultivation on lemon peel

Rhizopus nigricans was cultivated in a liquid medium using lemon peel as the carbon source. During cultivation, changes were measured in high and low molecular weight carbohydrates from the growth medium, as well as changes in the uronic acid amount of the alcohol insoluble solids from the lemon peel before and after fermentation. The initial amount of carbohydrates in the cultivation medium originated from the solubilisation of small sugars and partial hydrolysis of lemon cell wall polysaccharides in the acidic medium during the autoclaving step of the growth medium preparation. A complex mixture of monosaccharides (fructose, glucose, xylose, inositol), cellobiose, unknown oligosaccharides, galacturonic acid oligomers (penta-, tri-, and monogalacturonic acid), and polysaccharides was solubilised in the cultivation medium. During fermentation the fungus grew, produced the pectic enzyme endopolygalacturonase and consumed free sugars (fructose and glucose) and galacturonic acid. A carbohydrate polymer fraction remained resistant to fermentation, while a fraction of lower molecular weight was consumed.

Cross-flow Filtration through Ceramic Membranes of Enzymes and Degradation Products from Enzymatic Peeling of Satsuma Mandarin Segments

The present work evaluates the possibility of using cross-flow filtration to recover enzymatic activities from commercial enzymes used for peeling mandarin segments. Two ceramic membranes of different pore size and molecular weight cut-off were assayed. The membrane of 40 kDa molecular weight cut-off provided better separation of enzymes and carbohydrates than the membrane of 0.14 μm pore size, since the enzymes were readily retained in the retentate fraction, while carbohydrates easily passed into the permeate fraction. After separation, both fractions (enzymes and carbohydrates) could be further used.

Hot topic: Microstructure quantification by scanning electron microscopy and image analysis of goat cheese curd

Five microstructural parameters of goat cheese curd (number of pores, their area and perimeter, strand thickness, and porosity) were studied by scanning electron microscopy and image analysis. Image analysis was used to characterize and quantify differences in all parameters and to provide a procedure for the measurement of strand thickness. The micrographs provided visual evidence of differences in the protein matrix and were quantified by image analysis at 3 production times: 34 ± 1 min (cutting), 154 ± 6 min (before molding), and 293 ± 35 min (after pressing). The data showed that this procedure is an adequate tool for quantifying differences in the parameters analyzed in industrial samples despite their natural heterogeneity. The procedure was reproducible and repetitive for the first 2 production times because no significant intragroup differences were observed. Significant differences were found when comparing the values of the microstructure parameters analyzed at 34 ± 1 min and those corresponding to 154 ± 6 min and 293 ± 35 min, but no significant differences between samples analyzed at 154 ± 6 min and 293 ± 35 min were found. All microstructure parameters analyzed were related at a significance level of at least 95%. This procedure enables the characterization of the microstructure of industrial goat cheese curd.

Preliminary evaluation of an optical method for modeling the dilution of fat globules in whey during syneresis of cheese curd

An optical sensor designed to measure whey fat concentration was tested on whey samples from a cheese processing plant. Whey samples were collected to determine syneresis kinetics at different times after gel cutting. Normalized spectral sidescatter intensity was measured by mean of a fiber optic spectrometer (300-1100 nm). A sidescatter waveband ratio (S875/425) was calculated by dividing intensity at 875 by that at 425 nm. Whey fat concentrations were predicted by using the power low type equation previously developed by the above authors, [Fat] = .0 ln (.1 S875/425 + .2). Predicted whey fat concentrations were compared to actual concentrations measured by the Gerber method. The change in whey fat concentration with time after gel cutting was used to estimate the syneresis reaction rate. Results confirmed that fat dilution in whey followed a first order response. The light sidescatter technology for determining syneresis kinetics was considered to have potential but requires additional work to improve measurement accuracy.