VARIABLE CONTROL of A BATCH RETORT and PROCESS SIMULATION FOR OPTIMIZATION STUDIES

A microcomputer was interfaced with a batch retort for digital PI control of the retort temperature. Six retort temperature profiles (three isothermal, sinusoidal, step, and ramp) were examined for processing pea puree to nearly the same lethality values in 211 × 400 cans. Thiamine content and steam consumption were measured. Thiamine retentions in non-isothermal processes were greater than in the isothermal processes, but there was no significant difference in the steam consumption.
Lethality and thiamine retention were also simulated using a finite difference model for the same heating profiles, with good agreement with experimental results. the simulation suggests that differences in thiamine retention due to differing heating regimes are significant only for large lethality values and smaller cans. For F₀ values smaller than 10 min, the simulation suggests that the sinusoidal heating regime will provide better thiamine retention. Limitations of the model and suggestions for future improvement are also discussed.     

Selected Rheological Properties of pH-Adjusted or Succinylated Egg Albumen

Apparent viscosities of pH-adjusted or succinylated raw egg albumen were measured at 10, 20, and 30°C using a Haake rotary viscometer. Viscosities decreased with increasing temperature. Rheological power law model parameters indicated that as pH approached 5–6 and 11, albumen became more Newtonian. Control albumen (pH 9.0) and succinylated albumen were pseudoplastic. Intrinsic viscosities of DH 9.0, 10.0, and 11.0 albumens were 0.083, 0.092, and 0.102 dl/g, respectively, and that of succinylated albumend (0, 0.1, 0.2, and 0.4% w/w) were 0.052, 0.147, 0.149, and 0.184 dl/g, respectively. Apparent viscosities of coagulated albumen, measured by capillary extrusion, increased with pH but did not change with succinylation. Yield forces and rigidity moduli of these gels increased with pH but not with succinylation level.     

Correction Factors for Nondestructive Measurement of Residual Volume of Air in Retort Pouches

A destructive and a nondestructive method of estimating residual volume of air in retort pouches were compared. The difference between the volumes of air given by two techniques were found to be significant (P < 0.05) by paired t-test. An indirect calculation method was developed for estimation of internal pressure at neutral buoyancy and when used in conjunction with Archimedes’ Principle and Boyle's Law significantly improved the results. This method of calculating residual air in flexible pouches did not show any significant difference (P > 0.01) when compared to the standard destructive technique. The procedure outlined is easy to use.     

RHEOLOGICAL BEHAVIOR OF PROCESSED MUSTARD. II. STORAGE EFFECTS

Samples of processed yellow mustard with three different particle size distributions (slightly-coarse, standard, and fine) were prepared according to a standard formulation and pilot-plant replication of the commercial methodology and stored for 3 months at 5°C, 25°C, and 45°C. After 3-month storage at 45°C, all samples showed visible liquid separation (syneresis) and aggregation of colloidal particles, as indicated by increase in d _pop and decrease in % colloids. The fine milled samples exhibited syneresis and an increase in d _pop after 3-month storage even at 25°C. The bimodal distribution did not show significant changes as a result of aggregation. In general, increase in d _pop increased apparent viscosity (η _ap ), flow behavior index (n) from the Herschel-Bulkley model, and exponent n" from the loss modulus (G") power law equation. As d _pop increased, Bingham yield stress _o), plastic apparent viscosity (η _p ), shear stress constant (A) from the Weltman stress decay model, yield stress (_o) and consistency index (m) from the Herschel-Bulkley model, exponent n' from the storage modulus (G') power law equation, and minimum values of loss tangent (tan δ) decreased. In heterodisperse semi-solid foods such as processed mustard, the particle size distribution influences the structure (i.e., packing) and the rheological behavior. Therefore, time and temperature dependent instabilities such as syneresis may be minimized by controlling particle size distribution during processing.     

Rheological Behavior of Frozen and Thawed Low-Moisture, Part-Skim Mozzarella Cheese

Stress relaxation and dynamic profiles of low-moisture, part-skim (LMPS) Mozzarella cheese cylinders refrigerated 14 days (control), frozen and thawed, and stored frozen and refrigerated up to 90 days were compared. Samples were frozen at ?30°C and stored at ?20°C. Thawing and refrigerated storage were at 5°C. Stress relaxation tests were conducted at 20°C and dynamic spectrometry at 20°C and 60°C. The frozen and thawed Mozzarella cheese tested at 20°C became harder and more elastic with storage time, while refrigerated stored samples became softer and more elasticoviscous with time. Upon melting, both go-day-frozen and go-day-refrigerated cheeses were less elastic and less viscous than 14-day-refrigerated samples.     

Phase Equilibria and Distribution Coefficients of δ-Lactones in Supercritical Carbon Dioxide

A static method was used to measure the solubilities and distribution coefficients of δ-lactones (pure), inherent (natural levels) δ-lactones of anhydrous milk fat (AMF) and fortified (added) δ-lactones in AMF in supercritical carbon dioxide (SC-CO₂) at 40°C with pressures of 5–30 MPa. At 40°C distribution coefficients of δ-lactones increased with pressure and exhibited molecular weight-dependency. Using experimental data, a mathematical model based on thermodynamic equilibria and material balance was developed and used to predict the distribution of inherent δ-lactones of AMF in a continuous SC-CO₂ extraction system. At 24.1 MPa/40°C column conditions, AMF was separated into a raffinate and 5 fractions. Predicted δ-lactones distribution coefficients in the raffinate and extract were in good agreement with experimental data.     

Characterization of Thixotropic Behavior of Soft Cheeses

Time-dependent structural decay (γ) of four different spreadable cheeses was established using a Wells-Brookfield cone and plate viscometer. The γ values were determined at constant values of shear rate, (10 set⁻¹ to 200 sec⁻¹). The products studied were two samples of commercial Neufchatel cheese (one plain and one chocolate flavored) and two different saqples of cheese prepared using the Maubois, Mocquot and Vassal (MMV) method, which utilizes milk concentrated by ultrafiltration. All samples presented a structural decay characterizable by two different rate constants. Yield stress for Neufchatel cheese was observed to be one-third of the values obtained for MMV cheeses.     

ANTI-OXIDANT EFFECT OF QUERCETIN ON TYPE 2 DIABETIC ERYTHROCYTES

There is much evidence that oxidative stress is involved in the etiology of several diabetic complications. Many in vitro and in vivo studies have demonstrated that several parameters of red blood cell function and integrity are negatively affected by increased oxidative stress. Quercetin (3,3', 4',5,7-pentahydroxyflavone) is one of the most abundant bioflavonoids commonly present in most edible fruits and vegetables. Quercetin has been reported to prevent oxidant damage and cell death by scavenging free radicals. The present study was undertaken to evaluate the antioxidant effect of quercetin on markers of oxidative stress in erythrocytes from type 2 diabetic patients. Quercetin (at micromolar concentration) shows significant antioxidant effect in protecting erythrocytes from tert- butylhydroperoxide induced oxidative changes. These results suggest that a diet rich in quercetin may provide protection to diabetic patients against some late complications.

PRACTICAL APPLICATIONS

In recent years, there has been heightened interest in the possible therapeutic role of plant polyphenols for large number of human diseases. Among other known biological effects, plant polyphenols are known to have strong antioxidant properties. Out of more than 4,000 different types of plant polyphenols, relatively few are known to be effectively absorbed in the human digestive system. Among this group is the flavonoid quercetin that is present in many fruits and vegetables. We present here experimental proof of the protecting effect of this bioflavonoid on erythrocytes subjected to increased oxidative stress. Since diabetic patients are known to have increased oxidative stress, our results add to the scientific knowledge that a higher intake of diet rich in quercetin may protect diabetic patients from some late complications arising due to oxidative stress.     

Fractional Conversion for Determining Texture Degradation Kinetics of Vegetables

Fractional conversion (f) takes into account the nonzero texture property upon prolonged heating. This was applied as an alternate technique for reanalyzing texture degradation kinetics based on published data which indicated that the softening of vegetables followed a dual mechanism first order kinetic model. The plot of the logarithm of 1-f vs heating time was linear through log cycles indicating the reaction was first order with a single rate constant and the substrate b was better characterized by the equilibrium (or maximum retainable) texture property. A possible explanation was developed for negative activation energies which had been reported for the second mechanism with some vegetables.