COMPLEX METHOD FOR NONLINEAR CONSTRAINED MULTI-CRITERIA (MULTI-OBJECTIVE FUNCTION) OPTIMIZATION of THERMAL PROCESSING

The goal in a multi‐objective function optimization problem is to optimize the several objective functions simultaneously. the complex method is a powerful algorithm to find the optimum of a general nonlinear function within a constrained region. the objective of this study was to apply the complex method to two different shapes (a sphere and a finite cylinder) subjected to the same thermal processing boundary conditions to find a variable process temperature profile (decision variable) to maximize the volume‐average retention of thiamine. A process temperature range of 5 to 150C was used as an explicit constraint. Implicit constraints were center temperature and accumulated center lethality of the sphere and the finite cylinder. the objective functions for both shapes were combined into a single one using a weighting method. Then, the previously developed complex algorithm was applied using Lexicographic Ordering to order the objective functions with respect to their significance. the results were reported as optimum variable process temperature profiles using the given geometries and objective functions. the thiamine retentions were also compared with a constant process temperature process, and 3.0% increase was obtained in the combined objective function. the results showed that the complex method can be successfully used to predict the optimum variable process temperature profiles in multi‐criteria thermal processing problems.     

NONLINEAR CONSTRAINED OPTIMIZATION of THERMAL PROCESSING II. VARIABLE PROCESS TEMPERATURE PROFILES to REDUCE PROCESS TIME and to IMPROVE NUTRIENT RETENTION IN SPHERICAL and FINITE CYLINDRICAL GEOMETRIES

Conventional methods for thermal processing of foods use constant processing temperature profiles (CPTPs) for a prescribed processing time, which is based on achieving a required microbial lethality to comply with public health standards. This also results in degradation of nutrients and quality factors. the variable process temperature profiles (VPTPs) obtained by using optimization methods can reduce quality losses and/or processing time compared to CPTPs. the objective of this research was to evaluate VPTPs using the Complex Method to reduce the processing time and/or improve quality retention for a specified level of lethality in thermal processing of conduction heated foods. the VPTPs were obtained for volume average retention of thiamine considering different sizes of spheres (small and large) and finite cylinders (small and large), and the thiamine retention and processing time results were compared with a conventional method (processing at 121.1C) for a specified lethality level. the use of VPTPs resulted in a 37 and 10% decrease in processing times in spherical and 40 % and 6 % for finite cylindrical shapes, for the same objective function value and specified lethality compared to the CPTP process. For the same processing time, the improvements in thiamine destruction were 3.7 and 2 % for spheres, and 3.9 and 2.2% for finite cylinders.     

改进的随机定向搜索法及系统可靠性的优化计算

在对几种随机搜索法进行比较分析的基础上，提出了改进的随机定向搜索法，并以具体算例在ＩＢＭ－ＰＣ微机上求解了高维非线性整数规划问题，计算结果表明，改进的随机定向搜索法比Ｌｕｕｓ提出的非线性整数规划算法更有效、可靠，并具有适用性强、计算工作量少等特点。     

TEXTURAL CHANGES IN VEGETABLES DURING THERMAL PROCESSING. I. A DESCRIPTIVE METHOD to SEGREGATE EFFECTS of PROCESS TREATMENTS

Criteria for assessing the effect of processing treatments on the texture of processed foods were developed. Five parameters were defined, relating the hardening or softening of a food material and allowing for the comparison between different processing procedures. In order to determine the usefulness of this method, the parameters were applied to experimental data reported in literature for thermal processing of fruits and vegetables. Three parameters were defined for identifying the effect of a given preprocessing treatment on the raw material texture, the effect of the preprocessing treatment on the sensitivity of the vegetable tissue to the thermal processing and the overall effect. the two remaining parameters were used to describe additional information regarding the process kinetics, that is, to assess the effect of time and temperature on the rate of softening/hardening.     

MODELING AND OPTIMIZATION OF CONSTANT RETORT TEMPERATURE (CRT) THERMAL PROCESSING USING COUPLED NEURAL NETWORKS AND GENETIC ALGORITHMS

Coupled artificial neural network (ANN) models and genetic algorithms (GA) were applied for developing prediction models and for optimization of constant temperature retort (CRT) thermal processing of conduction heating foods. ANN prediction models were developed for process time (Pt), average quality retention (Qv), surface cook value (Fs), equivalent energy consumption (En), final temperature difference (T_g) at can center, and lethality ratio (p, heating/total lethality). The processing conditions as inputs for ANN models were as follows: retort temperature (RT = 110–140C), thermal diffusivity (α= 1.1–2.14*10^?7m²/s), volume of can (V = 1.64–6.55*10^?4m³), ratio of height to diameter of can (R_dh= 0.2–1.8), total desired lethality value (F₀= 5–10 min) at can center and quality kinetic destruction parameters: decimal destruction time (D_q– 150–300 min) and their temperature dependence (z_q= 15–40C). The data for training and testing ANN models were obtained from a finite difference computer simulation program. A second order central composite design was used for constructing the experimental data for training ANN models, while an orthogonal experimental design with 6 factors and 3 levels was used for the generalization of trained ANN models. ANN model linked Genetic Algorithms (GA) were employed for searching for the optimal quality retention and corresponding retort temperature, and for investigating the effects of main processing factors. ANN‐based prediction models successfully described the various outputs of CRT thermal processing (correlation coefficients: R² > 0.98; relative errors: Er ≤ 3%). The coupled ANN‐GA models, verified under several typical processing conditions, could be effectively used for optimization of CRT thermal processing. The main processing conditions and their interactions in the order of their importance with respect to the optimal quality retention and corresponding retort temperature were: V >z_q >R_dh >; and z_q >F_d > R_dh >V, respectively.     

A SYSTEM FOR CONTINUOUS THERMAL PROCESSING OF FOOD POUCHES USING MICROWAVE ENERGY

ABSTRACT— A system for continuous microwave sterilization of foods packaged in plastic pouches has been designed, constructed and tested. Air pressure was used to prevent pouch rupture. Pouches containing food for use in military rations were sealed and introduced through an air lock on to a conveyor inside a plastic pipe within a microwave cavity. Microwave energy was supplied up to 10 kw at 2,450 MHz. Conveyor speed and power were regulated to provide the process time and temperature. Cooling was achieved in a cooling bath. Pouches were overpackaged in a foil laminate for additional protection. Several food products were processed. Total process times of 9–14 min were achieved.     

OPTIMIZATION OF PROCESSING CONDITIONS FOR KUNUN-ZAKI, A SPONTANEOUSLY FERMENTED CEREAL-BASED BEVERAGE

Kunun-zaki production was monitored at six sites for the evaluation of microbiological quality, potential hazards and identification of critical control points, with the aim of setting critical limits for process optimization. Samples were collected at various stages of production and examined microbiologically for potential pathogens, before and after optimization. Critical limits were established for the critical control points identified, and two producers were selected for testing the effectiveness of corrective actions in an optimized process. Samples of kunun-zaki recorded total viable counts ranging from 3.84 to 4.80 log₁₀ cfu/mL. Bacillus cereus, salmonellae and staphylococci were isolated in samples at 0.00–0.01, 0.57–0.76 and 1.70–2.04 log₁₀ cfu/mL, respectively. The application of corrective measures, such as hand-washing practices, washing of processing areas and utensils, hygienic handling of materials during processing and pasteurization of final product proved effective in significantly reducing (up to 80%) the microbiological hazards associated with kunun-zaki.

PRACTICAL APPLICATIONS

The findings of this study have shown that with minimum hygienic food-handling practices, the incidence of food-borne pathogens in local foods and drinks can be reduced if not eliminated, even at household level of production. The work itself is practicable at the current level of kunun-zaki production and holds application for pilot-scale processing. The results can be used to set national standards for this and other related drinks. It also provides baseline data for standardization of kunun-zaki production, the focus of ongoing research by the authors.     

VICINAL DIKETONES IN BEER. PART I: A MODIFIED EBC METHOD FOR THE DETERMINATION OF DIACETYL AND OTHER VICINAL DIKETONES IN BEER

A rapid and reliable analytical method for the determination of diacetyl and other vicinal diketones in beer is described. Like Analytica EBC, the new assay is based on the spectrophotometric estimation of 2,3-dialkylquinoxalines. A comparison between these two methods is made, from which it can be concluded that both the recovery figures for added diacetyl and the coefficient of variation found in the modified method show a notable improvement compared with the EBC method. This method is recommended for quality control use on the basis of its speed and accuracy.     

DEEP-FAT FRYING OF YAM SLICES: OPTIMIZATION OF PROCESSING CONDITIONS USING RESPONSE SURFACE METHODOLOGY

The deep-fat frying of yam slices was investigated with the aim of optimizing the processing conditions. During frying, frying temperature, initial dry matter and frying time have a significant effect on moisture loss and oil uptake. Response surface methodology central composite rotatable design was used to study the effects of the independent variables on quality attributes of yam chips. Breaking force, oil content, moisture content and color parameters were determined. Statistical analysis with response surface regression showed that breaking force, oil and moisture contents and color parameters ( L* and a* ) were significantly ( P <  0.05) correlated with frying temperature, initial dry matter and frying time. The optimum conditions were a frying temperature of 175–180C, using tubers of initial dry matter of 0.179–0.214 kg/kg with a frying time of 4–5 min. It was suggested that the regression equation can be used to estimate the dependent variables for fried yam chips except b* (yellowness) parameter.

PRACTICAL APPLICATIONS

It is expected that the optimized processing conditions highlighted in this work will be useful in obtaining fried yam chips of acceptable quality attributes. This optimized condition would be a good prospect for commercialization in small-scale industries.     

COLORIMETRIC DETERMINATION OF PHENOLS IN PEATED MALTS USING A MODIFIED KLEBER'S METHOD

Kleber's method was modified to determine the amount of volatile phenolic compounds, that is, the pasting degree of peated malt. Steam distillation was done using a specially designed apparatus directly with the malt instead of the wort. The modified Kleber's method, when compared with Macfarlane's method by quantitative analysis using gas chromatography, was more sensitive and showed higher reproducibility and accuracy.     

DEVELOPMENT AND USE OF A METHOD FOR DETERMINATION OF MALT FERMENTABILITY

A method for the determination of the fermentability of unboiled, filtered, malt Hot Water Extracts has been developed. The wort is fermented under carefully controlled conditions, using fresh distillers' yeast. Knowledge of a malt's extract and fermentability allows calculation of its fermentable extract content, which allows spirit yield prediction, and the method is in use as a basis for Malt Purchase Specifications.