Band 10, Heft 2 -

Pathogenic microorganism contamination of food and feed is a serious problem worldwide. The use of microorganism to preserve food and feed has gained importance in recent years due to the demand for the reduced use of chemical preservatives by consumers and the increasing number of microbial species resistant to antibiotics and preservatives. Lactic acid bacteria (LAB) not only produce various antimicrobial compounds that are considered important in the bio-preservation of food and feed and are both cost-effective and safe. At present, many pieces of data have shown that LAB, as a bio-preservative, can improve the quality of food and feed and prolong their shelf life. This review summarises these findings and demonstrates that LAB are promising biological agents for food and feed safety.

This study investigated a novel procedure of Solanum aethiopicum Shum fruits extract (SASFE) preparation using multivariate experimental designs as factorial and Box–Behnken. The thermal stability of optimized extract as well as its influence on the milk solids in curd was determined. The results showed that extraction time, fruit maturity and pH did not affect significantly SASFE preparation, while the amount of fruits, extraction temperature and NaCl concentration of extractant had a significant effect ( p < 0.05). The greatest coagulant index was obtained under the following conditions: 12.5% of fruits, 25°C of extraction temperature and 4% NaCl concentration of extractant. It was thermosensitive and exhibited optimum temperature at 50°C. There was no statistical difference between SASFE and calf rennet in terms of solids yield in curd, estimated yield and actual yield. On the basis of these results, SASFE can be used as a vegetable alternative to calf rennet.

To describe the transient heat conduction from or to a product, its thermo-physical properties must be known. If the boundary condition of the heat conduction equation is of the first kind, the process is governed by the thermal diffusivity α. Normally this property is determined by fit of the analytical solution with only the first term of the series to an experimental dataset of the temperature versus time, in which the temperature is measured in a known position. In this case, the value obtained for α contains errors due to the consideration of only one term and the inclusion of the first experimental points in the fit. This article presents an algorithm based on optimal removal of experimental points to minimize errors in the determination of α. The algorithm was validated and applied to heating of Agar gel. The precision and accuracy of the obtained result were, respectively, 0.38 and 0.6%.

Mortadella evaporative pre-cooling process from 70 to 50°C at core was investigated: the thermal diffusivity and the apparent heat transfer coefficient were experimentally estimated. The effects of ventilation and water spraying with different intervals (0, 5, 10 and 15 min) were tested and core and surface temperatures, cooling times and cook values were compared. Water spraying every 5 min combined with ventilation allowed obtaining both lowest cooling time and cook values in the product. On the contrary, continuous spraying (no interval) presented higher cooling times since probably, after a certain time, water formed a continuous film on product surface, which prevented evaporation. Based on the experimental data, a finite differences mathematical model, previously applied to Mortadella cooking process, was developed and validated by means of two cooling procedures. Acceptable approximation and low percentage errors on final core temperature were obtained, confirming the usefulness and reliability of the proposed model.

In the present work, the oxidized corn starch was prepared by using chlorine dioxide as novel oxidant. It was characterized by X-ray diffraction, scanning electron microscope (SEM), and transmission electron microscope (TEM). The main factors that affect the oxidation process were studied, and the oxidation degree of oxidized starch was determined by the carboxyl content and viscosity of the product. The results show that carboxyl groups are introduced into the starch chains successfully, and the oxidation reaction mainly carries out at the amorphous area. Compared with native starch, the light transmittance and anti-retrogradation of oxidized starch increase, whereas the viscosity reduces. The best oxidized starch can be obtained at the sodium chlorate dosage of 3%, hydrochloric acid 4%, and sulfuric acid 3% (all based on the initial starch weight), while the oxidation reaction is conducted at 50°C for 5 h.

In the present study, banana slices were dried and compared using electrohydrodynamic (EHD) drying method at 4.5, 6.5, and 8.5 kV/cm; oven at 50, 60, and 70°C; and hot-air drying at 50, 60, and 70°C at a constant air velocity of 1.5 m/s. ANOVA showed that drying method had a significant effect on drying time, rehydration capacity, shrinkage, color features ( L* , a* , b* , and ∆ E ), and consumed energy. The values of consuming energy for EHD at 8.5 kV/cm, oven, and hot-air drying at 70°C were 2.99, 20.9, and 81.7 kJ/g run on full capacity of each dryer, respectively. Oven drying led to a greater color change than did hot-air. No significant difference was observed between the color change feature ∆ E for EHD and hot-air dried samples in the orthogonal contrast analysis. The falling rate period for EHD moisture movement showed that diffusion was describing the moisture gradients and the internal moisture transfer was dominant. EHD is not fast; however, its advantages like less energy needed, lower shrinkage, and great rehydration capacity make it a good choice for combining with other convection drying methods.

Influences of mung bean starches treated with different high hydrostatic pressure (HHP) on the properties of batters and crusts from deep-fried pork nuggets were explored. HHP-treated starch increased water retention capacity of batter and consequently the batter pick-up. The increase in pressure at 150–450 MPa could facilitate hydration and swelling of starch granules during gelatinization. The crusts containing HHP-treated starches had higher moisture and less oil content, and the oil content was 15.82 g/100 g dry weight (DW) for 450 MPa treated starch, which was much lower than that of native starch (18.39 g/100 g DW) ( p <0.05). Additionally, HHP-treated starches changed the crispness of crusts with increases in the slope and decrease in the shearing distance. Results indicated that mung bean starch treated with HHP in the range of 150–450 MPa could improve the quality of deep-fried battered food.

The energy and exergy analysis, drying characteristics and mathematical modeling of the thin-layer drying kinetics of white mulberry using microwave drying were investigated. Results indicated that values of exergy efficiency (33.63–57.08%) were higher than energy efficiency (31.85–55.56%). Specific energy consumption increased with increasing microwave power while improvement potential decreased. The specific energy consumption and improvement potential varied from 3.97 to 6.73 MJ/kg water and 0.71 to 2.97 MJ/kg water, respectively. Also, energy efficiency decreased with decrease in moisture content and microwave power level. The best exergy and energy aspect was obtained by drying at 100 W microwave power. Drying took place mainly in warming up, constant rate and falling rate periods. The Page model showed the best fit to experimental drying data. Effective diffusivity increased with decreasing moisture content and increasing microwave power. It varied from 1.06 × 10 −8 to 3.45 × 10 −8 m 2 /s, with an energy activation of 3.986 W/g.

In the present work, the effect of drying was evaluated on some chemical and physical properties of apples, and the functions were modelled using feed-forward artificial neural networks. The drying kinetics and the mass transfer properties were also studied. The results indicated that acidity and sugars were significantly reduced by drying. Regarding colour lightness decreases, whereas redness and yellowness increased. As for texture, the dried samples were softer and less cohesive as compared to the fresh ones. Mass diffusivity increased with temperature, from 4.4×10 −10 m 2 /s at 30°C to 1.4×10 −9 m 2 /s at 60°C, and so did the mass transfer coefficient, increasing from 3.7×10 −10 m/s at 30°C to 7.4×10 −9 m/s at 60°C. As to the activation energy, it was found to be 34 kJ/mol. Neural network modelling showed that all properties can be correctly predicted by feed-forward neural networks. The analysis of the networks’ behaviours input layer weight values also shows which properties are more affected by dehydration or more dependent on variety.

The eggshell crack was detected using flexible piezoelectric film sensors on the basis of dynamic frequency response. The response signal was transformed from the time domain to the frequency domain using fast Fourier transform algorithm. In the normalized power spectrum, the first 10 and 20 features were extracted by interval frequency (IFM), maximum magnitude in turn (HVM), and frequencies by magnitude in turn (MVF). The discrimination between intact eggs and cracked eggs was performed using back-propagation neural network (BPNN) and combination of genetic algorithm and BPNN (GANN). The results were found that intact eggs and cracked eggs could be better identified from their dynamic frequency response using BPNN and GANN based on HVM and MVF. It is suggested that intact and cracked eggs can be distinguished using GANN based on 10 features in MVF.

In this study, osmotic dehydration of seedless guava was studied through response surface methodology. Seedless guava cubes were dehydrated in sucrose solution at different concentration (30–50% w/w), temperature (30–50°C) and immersion time (15–240 min) with respect to weight reduction, solid gain and water loss. A Box–Behnken design was used to determine the optimum processing conditions that yield maximum weight reduction, water loss and minimum solid gain. The models developed for all responses were significant (p<0.05). The response surface plots were constructed to show the interaction of process variables. Optimum process conditions were found to be sucrose concentration of 33.79% w/w, temperature of 30.00°C and immersion time of 240 min through desirability function method. At these optimum points, weight reduction, solid gain and water loss were found to be 0.189 (gg −1 ), 0.050 (gg −1 ) and 0.237 (gg −1 ), respectively.

Mixtures of sesame cake (0–20%) and corn grits processed in a single-screw extruder to improve the nutritional value of corn-expanded extrudates. Response surface methodology (RSM) was used to analyse the effect of screw speed (X1) and sesame cake level (X2) on the objective (radial expansion ratio (Y1), hardness (Y2), degree of gelatinization (Y3), and water solubility index (Y4)) attributes of a corn-based sesame cake extrudates. The optimum acceptable regions determined from subjective decision and previous studies by referred authors. Therefore, it assumed that radial expansion ratio should be more than 4, hardness should be less than 7.7 kgf, degree of gelatinization should be more than 69%, and water solubility index should be less than 2.9%. Individual contour plots of the different responses were overlaid, and regions meeting the optimum radial expansion ratio of 4.03, hardness of 7.51 (kgf), degree of gelatinization of 69.28(%), and water solubility index of 2.87 (%) were identified at the screw speed of 311 rpm and the sesame cake level of 16%, respectively.

Sweet potato of uniform sizes and shape were subjected to steam peeling (temperature 80–100°C and peeling time 5–15 min) and lye peeling (sodium hydroxide concentration 8–12%, temperature 80–100°C and peeling time 3–5 min). Response surface methodology was used to analyze and optimize the process parameters in each case. For steam peeling, the peel loss and unpeeled surface area were 6.85 and 28.16%, respectively, while optimum peeling conditions where temperature and peeling time of 100°C and 5 min, respectively, for minimum peel loss and unpeeled surface area. For lye peeling, however, the peel loss and unpeeled surface area were 13.19 and 13.35%, respectively, and optimum peeling conditions were lye concentration, temperature and peeling time of 8.89%, 100°C and 4.75 min, respectively, for minimum peel loss and unpeeled surface area. The models developed in each case ( R -squared of 0.9225 and 0.8428; 0.5929 and 0.8346) were adequate in producing responses as a function of the independent variables. From the optimized values and results obtained, lye peeling was more suitable for sweet potato.

Some physical properties of the naked oat seeds were determined as a function of moisture content ranging from 9.56 to 18.07% (wet basis, w.b.). Seed length, width, thickness, and geometric mean diameter were increased from 7.89 to 8.81 mm, 2.32 to 3.09 mm, 1.85 to 2.77 mm, and 3.24 to 4.22 mm, respectively, with the increase of moisture content. The bulk and true densities of the seed samples were decreased from 682.1 to 533.1 kg/m 3 and from 1,280.6 to 1,162.8 kg/m 3 , respectively. The average static friction coefficients of the seeds on the surfaces of plywood, stainless steel, and polypropylene knitted bags were increased from 0.403 to 0.674, from 0.371 to 0.496, and from 0.562 to 0.765, respectively, when the moisture content of these samples were increased from 9.56 to 18.07% (w.b.). The static angle of repose varied from 24.38° to 39.17° in the moisture content range.