MODELING OF PREHEAT TREATMENT OPTIMIZATION APPLIED TO FRESH‐CUT “ROCHA” PEAR

ABSTRACT

Response surface methodology based on a five‐level, three‐variable central composite rotatable design was used for modeling the effects of preheat treatments on fresh‐cut “Rocha” pear quality. Studied variables were time (t: 0–150 min), temperature (T: 20–50C) and posttreatment storage time (St: 0–20 days, 5C). The quality‐affecting parameters including color, firmness, pH, soluble solid content, and total ascorbic acid content were the monitored dependent variables. Results provide reasonable estimation of the impact of preheat treatments on the quality of fresh‐cut “Rocha” pear and its shelf life. The time–temperature range of 33–41C during less than 20 min was selected as the conditions that best provided surface browning control, without impairing other studied quality parameters, with an estimated 8‐day shelf life period. The achieved kinetic changes of polyphenoloxidase, partial reduction in enzyme activity (ca. 23%) and depletion of phenolic content (ca. 11%) could be responsible for the browning control.

PRACTICAL APPLICATIONS

Minimal processing, namely cutting operations, triggers physiological reactions which limit fresh‐cut Rocha pear shelf life. Superficial browning is one of the major concerns to this industry, and new “clean” methodologies aiming at the inhibition of such reaction and maximization of the product shelf life will benefit not only from product marketability but also will respond to the consumers' demand of “chemical free” products. Heat treatments have been used to improve fresh‐cut commodities' browning resistance. The present work evaluated the use of preheat treatments against this physiological disorder during storage. Results will provide an optimized preheat treatment that grants high‐quality fresh‐cut Rocha pear with suitable shelf life.

     

3D map distribution of metallic nanoparticles in whole cells using MeV ion microscopy

In this work, a new tool was developed, the MORIA program that readily translates Rutherford backscattering spectrometry (RBS) output data into visual information, creating a display of the distribution of elements in a true three‐dimensional (3D) environment. The program methodology is illustrated with the analysis of yeast Saccharomyces cerevisiae cells, exposed to copper oxide nanoparticles (CuO‐NP) and HeLa cells in the presence of gold nanoparticles (Au‐NP), using different beam species, energies and nuclear microscopy systems. Results demonstrate that for both cell types, the NP internalization can be clearly perceived. The 3D models of the distribution of CuO‐NP in S. cerevisiae cells indicate the nonuniform distribution of NP in the cellular environment and a relevant confinement of CuO‐NP to the cell wall. This suggests the impenetrability of certain cellular organelles or compartments for NP. By contrast, using a high‐resolution ion beam system, discretized agglomerates of Au‐NP were visualized inside the HeLa cell. This is consistent with the mechanism of entry of these NPs in the cellular space by endocytosis enclosed in endosomal vesicles. This approach shows RBS to be a powerful imaging technique assigning to nuclear microscopy unparalleled potential to assess nanoparticle distribution inside the cellular volume.     

SPARSE MATRIX METHODS FOR USE IN ELECTRICAL IMPEDANCE TOMOGRAPHY

The objective of electrical impedance tomography is to reconstruct images representing the electrical impedance properties within a region from measurements on its surface. The region of interest is usually first discretized into finite elements and its impedance distribution updated using an iterative process. This iterative process comprises two problems: the forward problem and the inverse problem. The inverse problem is the term given to the procedure to find the internal impedance distribution from a set of boundary measurements, and the forward problem is the determination of the internal voltages given the impedance distribution and boundary conditions. In this paper several finite element labelling algorithms, implemented by the authors in C, are investigated and their impact on the forward problem solver efficiency analysed. The algorithms investigated are: Nested Dissection (ND), Minimum Degree (MDG), Minimum Deficiency (MDF) and Simulated Annealing for Fill-in (SAFR) Reduction during Cholesky Factorization. These renumbering strategies were applied to a collection of representative two-dimensional meshes used in electrical impedance tomography and a number of sparse symmetric matrices from the Harwell–Boeing sparse matrix collection for comparison purposes. © 1997 by John Wiley & Sons, Ltd.     

Stress-life fatigue assessment of pipelines with plain dents

This paper presents a new algorithm for assessing the fatigue life of dented pipelines. The proposed methodology was conceived according to the current stress-life fatigue theory and design practice: it employs S–N curves inferred from tensile test material properties and uses well established methodologies to deal with the stress concentration, the mean stress and the multi-axial stress state that characterizes a dented pipe. Finite element analyses are carried out to model the denting process and to determine the stress concentration factors of several pipe-dent geometries. Using dimensional analysis over the numerical results, a non-dimensional number to characterize the pipe-dent geometry is determined and linear interpolation expressions for the stress concentration factors of dented pipelines are developed. Fatigue tests are conducted with the application of cyclic internal pressure on small-scale dented steel pipe models. In view of the fatigue test results, the more appropriate S–N curve and mean stress criteria are selected.     

THE INFLUENCE of pH ON the KINETICS of ACID HYDROLYSIS of SUCROSE

Sucrose acid hydrolysis was studied as a potential chemical time-temperature integrator to use under pasteurization conditions. A nonisothermal method was used to determine the kinetic parameters of this reaction at different pH values in the range of 0.8 to 2.5 and covering the range of temperatures from 50 to 90G. the nonisothermal method was first validated with the classical two-step isothermal method at pH 2.5. Kinetic parameters showed to be highly collinear (correlation of 0.99), but it was concluded that the activation energy can be assumed independent of pH and equal to 99 kJ/mole with the preexponential factor being proportional to the H⁺ concentration. Results are favorable for the future application of this system in the evaluation of pasteurization processes. Since the activation energy was found to be independent of the pH, this system is useful as a TTI for validation of mathematical models, but not so much for monitoring quality factors, except those with an equal activation energy.     

The effect of different sweeteners in low-calorie yogurts — a review

Recently, increased demand for low-calorie products and foods with alternative sweeteners has gained special attention. Intense sweeteners avoid the problems of health risks associated with caloric sweeteners. This paper presents information about the technical characteristics of the more widely used artificial sweeteners and the possibility of their application in low-calorie yogurts.     

The effect of inulin as a prebiotic on the production of probiotic fibre-enriched fermented milk

We investigated the effect of inulin as a prebiotic on the production of probiotic fibre-enriched fermented milk. The kinetics of acidification of inulin-supplemented milk (0, 0.01, 0.02 and 0.04 g/g), as well as probiotic survival, pH and firmness of fermented milk stored at 4°C for 24 h and 7 days after preparation were examined. Probiotic fibre-enriched fermented milk quality was influenced both by the amount of inulin and by the co-culture composition. Depending on the co-culture, inulin addition to milk influenced acidification kinetic parameters, probiotic counts, pH and the firmness of the product.     

PHOSPHOLIPASE A2 ACTIVITY IN POULTRY PSE, PALE, SOFT, EXUDATIVE, MEAT

The interrelationship between phospholipase A2 activity (PLA (2)) and the development of pale, soft, exudative meat (PSE) in chicken was evaluated. Pectoralis major m. from female birds of 45 days of age after hatch was studied and determination of the enzyme activity was estimated by the formation of long‐chain fatty acids. The occurrence of PSE was evaluated by measuring pH, L* values, water holding capacity and sarcoplasmic Ca²⁺ concentration from both heat‐stressed and nonstressed birds. In addition, the occurrence of the syndrome was monitored with birds advancing in age. Our studies revealed that PLA(2) plays an important role towards the occurrence of PSE symptoms and its activity increased as the birds became older. The enzyme activity was detected from the beginning of our experiment at 36 days and increased up to 70 days after hatch. The overall average activity was 1.25 times more pronounced in PSE samples from heat‐treated birds when compared to control animals (P ≤ 0.05).