Browsing by Author "Aguilera, JM"

Now showing 1 - 7 of 7
  • Thumbnail Image
    Item
    Limpness of fried potato slabs during post-frying period
    (WILEY, 2005) Miranda, ML; Aguilera, JM; Beriestain, CI
    The rupture stress (RS) of fried potato slices (1.60 mm thick) and of the crust of fried potato slabs (FPS) having lengths of 60 mm and sides of 8, 10 and 12 mm, was determined during the post-frying period by a puncture test. The RS of fried potato slices decreased as water activity increased from 0.22 to 0.85. The RS of FPS diminished in the first 5-6 min when exposed to ambient conditions and remained almost constant thereafter A novel videotape technique and image analysis were used to follow deflection of FPS in the post-frying period. An apparent modulus based on the composite structure of FPS and calculated from beam mechanics decreased with time in a trend similar to that of the textural parameters. We concluded that changes in physical properties of the crust because of moisture accumulation are the major causes of loss of texture (limpness) in FPS during the post-frying period.
  • No Thumbnail Available
    Item
    Microstructure and food product engineering
    (INST FOOD TECHNOLOGISTS, 2000) Aguilera, JM
  • Thumbnail Image
    Item
    Oil absorption during frying of frozen parfried potatoes
    (INST FOOD TECHNOLOGISTS, 2000) Aguilera, JM; Gloria Hernandez, H
    A tracer method was used to assess the uptake of oil by commercial frozen parfried potatoes fried (180 degrees C, 150 s) in colza oil (CO) involving a short post-frying immersion in hot coconut fat (CF), CO and CF were determined directly in the crust by differential scanning calorimetry (crystallization temperature and enthalpy -42.7 degrees C/50 J/g and 10 degrees C/71 J/g, respectively). Oil uptake by the crust during frying in CO or CF was similar (average 25.3%). Potato samples transferred immediately after frying in CO to the CF bath had most of the CO absorbed replaced by CF after a 10 s post-frying, meaning that CO was readily accessible in the crust structure. Samples fried in CO and cooled for up to 60 s before transfer to hot CF showed only partial replacement of CO. Oil wetting the surface of the sample at the end of frying was estimated as 70 to 80% of the total oil uptake. Formation of the crust (frying time > 1 min) was required for oil to migrate into intercellular spaces that are dynamically formed during frying and thus accessible to CF and solvents.
  • Thumbnail Image
    Item
    Rheological, thermal and microstructural properties of whey protein-cassava starch gels
    (INST FOOD TECHNOLOGISTS, 1996) Aguilera, JM; Rojas, E
    Mixed gels of cassava starch (CS) and a whey protein isolate (WPI), obtained by heating solutions of 10% total solids, pH 5.75 to 85 degrees C, were characterized as a function of the starch fraction, U-s by axial compression, small-amplitude oscillatory rheometry, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Gelation did not occur for U-s>0.7. In the range 0
  • Thumbnail Image
    Item
    Structure-mechanical properties of heat-induced whey protein/cassava starch gels
    (WILEY-BLACKWELL, 1997) Aguilera, JM; Baffico, P
    Structure-mechanical properties of heat-induced whey protein isolate/cassava starch (WPI/CS) gels were studied by hot-stage video microscopy (HSVM) and axial compression testing (ACT). Elastic moduli (or compression stress) of pure WPI and CS gels followed a power dependence with concentration. ACT confirmed that reinforcement occurred when CS was added at 10-25% of total solids. HSVM revealed that CS granules swelled first, removed water from the system and concentrated the WPI solution that gelled later. Reinforced gels had a continuous WPI phase filled with swollen CS granules. A modified Takayanagi model accounting for water redistribution during gelatinization accurately fitted the mechanical properties of these gels.
  • Thumbnail Image
    Item
    Textural characterization and kinetics of potato strips during frying
    (WILEY, 2001) Pedreschi, F; Aguilera, JM; Pyle, L
    A single puncture test (SPT) system was designed to determine textural changes in potato strips in situ during frying at 160, 175, and 190 degreesC. Puncture force changed drastically with time and depth in the strip during frying. Force-distance curves were expressed as representative textural parameters as CF (core force), RF (rupture force), and S (springiness). Normalized parameters CF* and S* for core force and springiness were used In modeling textural changes in the core during initial tissue softening and later crust development process, respectively. High frying temperatures accelerated the process, and the finished fried potato strip was a composite structure made of a hard crust and a soft core.
  • No Thumbnail Available
    Item
    Viability of dry Trichoderma harzianum spores under storage
    (1997) Pedreschi, F; Aguilera, JM
    Spores of the potential biocontrol agent Trichoderma harzianum P1 were prepared without (Mi) and with heat shock (40 degrees C for 90 min) after fermentation (M2), filtered into a paste and dried over silica gel. M1 and M2 exhibited high viability (55%) and similar initial trehalose contents (4.0 and 5.4%, respectively) after slow drying. No significant differences in viability were found between treatments during storage for 110 days under different temperatures, T (8, 33 and 42 degrees C) and water activities, a(w) (0.03, 0.33 and 0.75). Viability of spores, after storage at a(w) = 0.03 were 100 and 70% for 8 and 33 degrees C, respectively. During storage, decrease in trehalose content and viability was faster at a(w) = 0.75 and 42 degrees C. Loss of viability was modeled by a first order kinetic model depending on 1/T and a(w). M2 (with heat shock) showed slightly higher trehalose contents than M1 which resulted in 100% viability after 52 days at 8 degrees C.