Nora C. Bertola

Partial least squares correlations between sensory and instrumental measurements of flavor and texture for Reggianito grating cheese

Abstract Visual, manual and oral texture descriptors for Reggianito grating cheese were correlated with parameters obtained from an instrumental compression test. Aroma and flavor descriptors were correlated with organic acid concentrations. Linear partial least squares regression was used for the multivariate correlations and proved to be a useful tool. Measurements were done between 30 and 290 days of ripening time. Strain at breaking point was the instrumental texture parameter which best correlated with sensory descriptors: negatively wth visual, manual and oral fracturability; and positively with manual elasticity. Sensory hardness was related to instrumental hardness although the correlation coefficients were not high. Total flavor and aroma intensity were well correlated with propionic acid, suggesting this acid could be a flavor indicator for this type of cheese. Uric and orotic acids changed during ripening yet remained below sensory threshold values.

Modelling phenol biodegradation by activated sludges evaluated through respirometric techniques

In this paper respirometric techniques were used to study the effect of pH, phenol and dissolved oxygen (DO) concentrations on the phenol biodegradation kinetics by activated sludges. In addition, a mathematical model was developed to interpret the obtained respirometric curves. Closed respirometer experiments showed that phenol inhibited the respiration rate of unacclimated sludges. On the contrary, oxygen uptake rate (OUR) of phenol acclimated sludges exhibiting the typical Haldanes substrate inhibition curve. The Monod equation adequately represented the relation between OUR of acclimated biomass and DO concentration. Within the tested pH range (4-12) the oxygen saturation coefficient was independent of pH. On the contrary, the maximum OUR was strongly affected by the pH, being its maximum between 9.5 and 10.5. Open respirometer experiments shows that as pH decreased from 10.2 to 5.8, the maximum OUR also decreased, in accordance with the trend observed in the closed respirometer experiments. Although the respiration rate of phenol degrading bacteria was strongly affected by pH, a constant phenol oxidation coefficient was observed within the studied pH interval. A mathematical model was proposed to interpret the open respirometry curves. The coefficients of the model were estimated using both pseudo steady state and dynamic conditions for different biomass concentrations. The model adequately predicted the whole OUR and DO profiles as a function of time during the biodegradation of phenol under different DO conditions. The mathematical model proposed in the present work is useful for predicting transient responses such as substrate concentration and DO concentrations as a function of time in bioreactors treating phenolic wastewaters under an overload of phenolic compounds.

Effect of processing conditions on the hardness of cooked beef

Abstract Changes in meat tenderness that occur during cooking are generally associated with heat-induced alterations of the components (collagen and myofibrillar proteins) of the primary structure of the muscle tissue. Heat transfer during the cooking process and the related textural changes were simulated numerically in irregular domains by integrating both the differential equation for unsteady state heat conduction and the temperature-dependent kinetic equation that corresponds to textural changes of the cooked meat. A code employing a boundary-fitted grid method was implemented in a numerically conservative form (control volume formulation). The proposed model was verified experimentally on irregularly shaped pieces of beef. The effects of heat transfer coefficient, temperature of the cooking medium, and size of the meat piece on the hardness distribution and average final hardness of the cooked product were studied. When the temperature of the cooking medium was above 85 °C the average hardness was always high, regardless of processing time, even for small pieces of meat. Conversely, low temperatures produce a more tender product, although on large beef cuts this advantage is overcome because of the long cooking times required.

Stoichiometry and kinetic of the aerobic oxidation of phenolic compounds by activated sludge.

The aerobic degradation of phenol (PH), catechol (CA), resorcinol (RE), pyrogallol (PY), and hydroquinone (HY) by phenol-acclimated activated sludge was investigated. A Haldane-type dependence of the respiration rate on PH, RE, and HY was observed; CA and PY exhibited a biphasic respiration pattern. According to the initial biodegradation rate, tested compounds were ordered as follows: CA>PH>>PYRE>HY. Also, they exhibited the following degree of toxicity to their own degradation: PY>>CARE>>PH>HY. Oxidation coefficients for PH, PY, RE, and HY were constant as a function of the consecutive additions of the compound. Conversely, an increase of YO/S from 1 to 1.5 molO2 molCA(-1) was observed during repeated additions of CA. The role of some enzymes involved in the aerobic degradation pathways of the tested compounds is discussed and related to the obtained results.

Edible methylcellulose-based films containing fructo-oligosaccharides as vehicles for lactic acid bacteria

The goal of this work was to investigate the physicochemical properties of methylcellulose (MC) based films as stabilizers of two strains of lactobacilli: Lactobacillus delbrueckii subsp. bulgaricus CIDCA 333 and Lactobacillus plantarum CIDCA 83114. The incorporation of 3% w/v fructo-oligosaccharides (FOS) into the MC film formulation improved the viability of L. delbrueckii subsp. bulgaricus CIDCA 333 after film preparation. L. plantarum CIDCA 83114 was intrinsically more resistant as no viability loss was observed upon preparation of the films in the absence of FOS. Scanning electronic microscopy images also showed a good incorporation of microorganisms without affecting the homogeneity of the films. FTIR spectroscopy provided structural information about the bacteria-loaded films. Water sorption isotherms showed an impervious behavior at low aw but on exceeding 0.7 of aw the film started to dissolve and form syrup, causing a drastic drop of bacterial viability (log N/N0≤-5). Dynamic mechanical analysis (DMA) demonstrated that the incorporation of microorganisms into the MC films had no effect on vitreous transition temperatures. FOS incorporated into the MC films had a plasticizing effect. Microorganism-loaded films were stored at relative humidities (RH) ranging from 11 to 75%. Both strains could be stored at 11% RH for 90days. At 33 and 44% RH L. delbrueckii subsp. bulgaricus CIDCA 333 could be stored up to 15days and L. plantarum CIDCA 83114 up to 45days. At 75% RH only L. plantarum CIDCA 83114 could be equilibrated (log N/N0: -2.05±0.25), but CFU/g films were undetectable after 15days of storage. The results obtained in this work support the use of MC films containing FOS as a good strategy to immobilize lactic acid bacteria, with potential applications in the development of functional foods.

Optimisation of the design parameters in an activated sludge system for the wastewater treatment of a potato processing plant

Abstract Aerated biological reactors at a laboratory scale, fed continuously with a model wastewater system, were used to obtain design parameters of an activated sludge process for the wastewater treatment of a potato processing plant. Experiments were performed using different dilution rates ( D ) ranging between 0.01 and 0.13 h −1 to determine parameters such as: maximum specific microbial growth rate ( μ max ), saturation constant ( K s ), coefficient of microbial decay ( k d ) and true biomass yield ( Y X/S ). Design parameters were calculated from the mass balances of substrate consumption and biomass production under steady state, considering a Monod-type equation to represent the effect of substrate concentration on biomass production rate. The values of Y X/S and k d were obtained from the linear plot of q S (specific rate of substrate consumption) vs. D . Experimental data regression led to Y X/S =0.45 gVSS/g COD and k d =0.024 h −1 . By non-linear regression of q S vs. substrate concentration ( S S ) data the following values were obtained μ max =0.09 h −1 and K s =0.006 g/l. Critical dilution rate was also calculated; it corresponds to the D value for which the cells of a reactor operating under such conditions are destroyed or are eliminated from the system at the same rate than they are produced.

Rheological behaviour of Reggianito Argentino cheese packaged in plastic film during ripening

The effect of plastic film packaging (BK1, Grace) was analysed during ripening of hard cheese (Reggianito Argentino). Cheeses packaged 30 and 45 days after manufacture were compared with traditionally ripened cheeses. The values of soluble and nonprotein nitrogen were determined. No significant differences were found among the three cheese lots in spite of the slightly higher average water content of packaged cheeses. Hardness, breaking force and strain at breaking point were analysed. Packaged cheeses exhibited less hardness and lower breaking force values. Relaxation curves were used to analyse the visco-elastic behaviour. The visco-elastic parameters, (elastic modulus and viscosities) were obtained using the generalized Maxwell model. Results showed that traditionally ripened cheeses were harder and less elastic than packaged cheeses. The relationships between the texture parameters (hardness, breaking force and strain at breaking point) and both the percentage of water-soluble nitrogen compounds and water content variations were mathematically modelled.

Development and Characterization of a Baked Snack from Rings of Green Apples

Apple snacks were developed from green apple (Granny Smith) by baking. The effect of several pretreatments on properties such as color, texture, moisture, and water activity was studied. Blanching with steam, impregnation with calcium salts (calcium carbonate/calcium lactate), impregnation with sugars (fructose and maltodextrin), and addition of ascorbic acid were some of the pretreatments used. The addition of calcium proved to be favorable since it caused a reduction in the porous structure of the apple tissue associated with a greater firmness. The optimum selection of pretreatments on the rings of green apples gave as a result a snack with a higher acceptability in the evaluated attributes (color, sour taste, sweetness, and texture). Irrespective of the composition of the used solution of sugars, moisture, water activity, and lightness (L) of the baked apple rings did not differ significantly. The antioxidant activity of the obtained snack increased compared to that of fresh fruit due to the addition of ascorbic acid. The ascorbic acid content of apple snacks also turned out to be higher than that of fresh apples.

Stability of methylcellulose-based films after being subjected to different conservation and processing temperatures

Methylcellulose films with and without sorbitol addition were developed. The major objective of this study was to attempt insights into the stability of the methylcellulose-based film properties after having been subjected to freezing, storage or a combination of both procedures. The importance of the sorbitol concentration and process temperature was also to be elucidated. As-prepared film solubility decreased at 100 °C, as a result of the methylcellulose thermogelation property when the samples were exposed to high temperatures. By analyzing the film pattern behavior and its properties 0.25% w/v sorbitol concentration turned out to be an inflexion point. The moisture content as well as the mechanical and thermal properties made this fact evident. Moreover the elastic modulus (Ec) and glass transition temperature (Tg) did not undergo significant changes for higher plasticizer concentrations. The methylcellulose film properties remained more stable in the presence of sorbitol, which would act as a protective agent due to its hydrogen bonding capacity. This stability is crucial for film and coating applications in the food industry.

Improvement of Fatty Acid Profile and Studio of Rheological and Technological Characteristics in Breads Supplemented with Flaxseed, Soybean, and Wheat Bran Flours

Functional breads constitute an interesting alternative as vehicle of new essential fatty acids sources. The aim of this study was to improve the fatty acids (FA) profile of bakery products, producing breads with low saturated fatty acid (SFA) content and with high polyunsaturated fatty acid (PUFA) content, through partial substitution of wheat flour by other ingredients (soy flour, flax flour, and wheat bran) and to analyze the effect of this change on the technological, rheological, and sensorial characteristics of breads. Flaxseed flour (FF), soybeans flour (SF), or wheat bran (WB) was used to replace 50, 100, and 150 g kg−1 of wheat flour (WF) in breads. FF or SF produced a decrease in monounsaturated and SFA and an increase of PUFA in these breads. Furthermore, breads replaced with FF presented considerable increase in the content of n3 FA, while, SF or WB contributed to rise of linoleic and oleic FA, respectively. The substitution percentage increase of FF, SF, or WB to formulation produced changes in the colour, rheological, textural, and technological characteristics of breads. This replacement resulted in improved lipid profile, being breads with 50 g kg−1 SF, the better acceptance, baking features, and enhanced fatty acid profile.