Optimizing Processing Conditions for Chemical Peeling of Potatoes using Response Surface Methodology

Using Response Surface Methodology the effects of NaOH concentration (4–20%), process temperature (55–95°C) and time (1–7 min) was determined on the yield, peeling quality, unpeeled skin and total usage of NaOH. Also evaluated were titratable NaOH in the potato tissue, NaOH penetration and “heat ring” depths during one stage chemical peeling of potatoes (Huincul variety). The best peeling quality, maximum yield and minimum total usage of NaOH was obtained for the following ranges: concentration, 11–13%, time 5–5.70 min and temperature, 90–95°C. The maximum temperature for which the “heat ring” and NaOH penetration depths were equal was 72°C where, at 20% NaOH and 7 min, peeling quality was very good and “heat ring” was absent.     

Effect of Surface Freezing on Ascorbic Acid Retention in Water Blanched Potato Strips

The average retention of ascorbic acid in potato strips (10 × 10 × 80 mm) blanched in water at 50°C and 65°C over various blanching times, with and without surface freezing pre-treatment was determined. The strips were frozen in Freon Freezant-12 for 15 sec, with the freezing front penetrating 0.4–0.5 mm. Average retention of ascorbic acid in the surface-frozen potato strips was significantly lower than that in fresh strips and lower at 65°C than at 50°C. At an equal average retention of ascorbic acid, at 50°C the fresh strips required a blanching time four times higher than that for the surface-frozen strips; at 65°C it was twice as high.     

THE LAMINAR FLOW TUBULAR REACTOR WITH HOMOGENEOUS AND HETEROGENEOUS REACTIONS I. Integral Equations for Diverse Reaction Rate Regimes

Design equations for non-isothermal Laminar Flow Tubular Reactors (LFTRs) with homogeneous and heterogeneous - at the reactor wall - reactions with arbitrary kinetic equations have been satisfactorily treated transforming the original P.D.E. problem into a system of integral equations. The kernels of the integral operators are related to an eigenvalue problem which does not depend on the kinetic equations; this avoids repetitive computational effort in the treating of different reaction kinetics.

To render a more efficient numerical treatment and according to the governing reaction rate regime, modified expressions of the general solution were obtained was follows: (i) a solution with kernels depending only on the diffusion and convective times was obtained for a low reaction regime; (ii) another solution with kernels including the reaction lime, besides the diffusion and convective ones, was necessary for a fast reaction regime and (iii) the local quasi-steady-state approximation was obtained as limiting case of solution (ii) for a instantaneous reaction regime.     

Use of Fluorogenic Assays for the Enumeration of Escherichia coli from Selected Seafoods

Escherichia coli was enumerated and immediately confirmed by incorporating 4-methylumbelliferone glucuronide (MUG) into Lactose Broth (LB), Violet Red Bile Agar (VRB) and M-Endo Broth (M-Endo) in selected seafoods. E. coli in the seafood samples ranged from 1.0 × 10¹– 1.0 × 10³ Most Probable Number (MPN)/g, 1.0 × 10¹– 3.5 × 10² cfu/g and 0.9 × 10¹– 2.8 × 10² cfu/g in LB-MUG, VRB-MUG, and M-Endo-MUG, respectively. Although not statistically significant (α= 0.05), LB-MUG resulted in higher counts in fresh finfish, frozen fish and breaded seafoods. Specificity for E. coli in LB-MUG, VRB-MUG and M-Endo MUG was 96.5%, 92.0%, and 90.0%, respectively. All three fluorogenic assays enabled a rapid and sensitive enumeration of E. coli from seafood products.