Band 13, Heft 4 -

This study utilizes liquid-only cans (fitted with a single particle) to gain insight into the heat transfer phenomenon during the novel process of reciprocating agitation thermal processing (RA-TP) for sterilization of food. Overall heat transfer coefficient (U) across the can-wall was evaluated for cylindrical cans, filled with different concentration of glycerin and treated with reciprocating agitation thermal processing (RA-TP). Thermocouple-equipped single spherical particle (diameter = 0.019 m) of various densities were also kept inside the cans to obtain preliminary insights into the heat transfer phenomenon at the liquid–particle interface (h fp ). Seven process variables, viz. operating temperature (110–130 °C), reciprocation frequency (1–4 Hz), reciprocation amplitude (0.05–0.25 m), can headspace (0.006–0.012 m), liquid viscosity (0.001–0.942 Pa.s) and particle density (830–2,210 kg/m 3 ), were varied according to three full-factorial designs and corresponding U & h fp were reported. Depending on the processing condition and product composition, U and h fp varied in the range 197–1,240 W/m 2 K and 210–1,230 W/m 2 K respectively. Higher heat transfer was observed at both can wall and liquid–particle interface with increasing temperature, headspace, frequency and amplitude and decreasing liquid viscosity. The order of heat transfer coefficients for processing conditions was: Frequency > amplitude > headspace > temperature; while for product composition was: Frequency > liquid viscosity > product density. This study is relevant for providing data for process modeling of reciprocating agitation thermal processing.

Acetic acid fermentation is an essential step in the production of high-quality fruit vinegar and typically involves the use of acetic acid bacteria (AAB). The present study showed that the high cell mass and acetic acid yields of ethanol-tolerant AAB under high ethanol conditions were related to the high activities and stability of both pyrroloquinoline quinone (PQQ)-dependent alcohol dehydrogenase and PQQ-dependent aldehyde dehydrogenase. Additionally, in acetic acid fermentation with watermelon wine (8 % ethanol), the main organic acids (acetic, tartaric and malic acids) produced by ethanol-tolerant Acetobacter pasteurianus AAB4 were higher than those by conventional A. pasteurianus AS1.41 (1.42-fold, 3.53-fold and 2.12-fold, respectively). Also, the main esters (ethyl acetate and phenylethyl acetate) produced by AAB4 were higher than those by AS1.41 (1.69-fold and 1.48-fold, respectively). In addition, the total sweet and umami free amino acids produced by AAB4 increased significantly. According to sensory analysis, the flavor, taste and overall acceptance score of watermelon vinegar produced by AAB4 were significantly higher than those by AS1.41. Therefore, high ethanol fermentation with ethanol-tolerant AAB improved the flavor and quality of watermelon vinegar, indicating that this technology can be applied to fruit vinegar production.

This article provides results of an experimental investigation of hybrid- (MIR-FD), mid-infrared- (MIR) and freeze drying (FD) on the drying characteristics, energy consumption and quality parameters of pear. Rehydration ratio, color, texture, water activity, phenolic content and antioxidant activity were measured to evaluate the quality of dried pear products. Mid-infrared-freeze drying (MIR-FD) had the higher drying rate, which reduced the drying time by 14.3–42.9 % compared with FD method. Two empirical models were chosen to fit the drying curves and the models had the suitable R 2 and RMSE values. Temperature characteristics of MIR and MIR-FD dried pear were determined in terms of interior temperature variation. The MIR-FD pear had darker color, better rehydration capacity, similar water activity, lower hardness (except of MIR-FD70°C) and highest content of chemical composition than single stage of FD products. Above all, the MIR50-60°C-FD was suggested as the best drying method for pear in this study.

Drying characteristics of soybeans under different microwave (MW) processing schemes were studied in regard to energy aspects. For drying in a single microwave power density, the experiments were carried out at a constant MW output power throughout the process. It was found that the drying rate is enhanced together with reduced energy consumption at higher single power density, but the soybean cracking ratio is increased gradually from 2 % to 40 % when the power density was changed from 0.2 W/g to 0.8 W/g. Efforts were made to reach a compromise between the drying rate and dried soybean quality by varying the MW power density in several steps overall the drying process, but soybean cracking occurred at a higher ratio due to the fluctuation of drying rate. Microwave drying of soybeans under the power density less than 0.2 W/g with slow and stable drying rate can achieve the soybean cracking ratio controlled within 5 % and lower energy consumption.

The knowledge of electrical properties and their relationship with moisture content is of great importance in operations of post-harvest and storage in grains. The dielectric properties of sorghum samples were studied at different moisture contents and temperatures (25 at 41 °C), at frequencies of 1 and 10 kHz. In order to measure changes in the capacitance and dissipation factor of the samples, the method of impedance bridge was used. Both the dielectric constant and the dielectric loss factor of the samples increased with increasing moisture content and temperature; however, they decreased with increasing frequency. Models were proposed to relate the dielectric properties to either the moisture (exponential and polynomial) or temperature (linear).

The effect of drying methods on the rheological properties (apparent viscosity, storage ( G ′) and loss ( G ″) moduli, creep behavior) of sugar beet pulp pectin (SBPP) was investigated using steady shear, frequency sweep, activation energy and creep-recovery tests. SBPP was extracted from sugar beet and dried using freeze (FD), hot air (HD), vacuum (VD) and spray (SD) drying methods. The HD sample showed highest apparent viscosity and the VD sample had the highest activation energy. The 1 % (w/v) samples had higher activation energy than 2 % (w/v) samples. The G′ and G ″ versus angular frequency data followed the Power Law model reasonably well ( R 2 > 0.915). The FD sample deformed the most during the creep test.

The purpose of the study was to determine (1) whether baking process (a unit operation) – applied to produce leavened (LFB) and unleavened bread (UFB) – modifies the bioactivity of whey protein (WP) added in these portions and (2) how whey protein can change the textural parameters of these formulations. Reducing power activity (antioxidant potential) in food matrix was evaluated using phosphomolybdenum method. Textural parameters – hardness, cohesiveness, springiness, resilience, chewiness and gumminess – were carried out on a texture analyzer. In addition, this study demonstrated that the biofunctionality of whey protein was maintained in UFB 10 % WP. Nonetheless, this same formulation showed high values of textural parameters (hardness, chewiness and gumminess). Regarding the LFB formulations, the antioxidant potential was restricted after baking process in LFB 10 % WP. In conclusion, addition of bioactive additive in food matrix may not be sufficient to turn it into a functional food considering the effect of unit operations on bioactivity of some potential additives.

Fermentation followed by continuous ultrasonication was applied to release the bound phenolics in sorghum flour (SF). Total phenolic content (TPC) and antioxidant activity (AA) increased with decrease in fermentation time (FT), flour to water ratio (FWR), flow rate (FR) and ultrasonication intensity (UI). The influence of process variables was investigated by Box–Behnken design and multi-layer perceptron neural network. The optimum conditions for maximum TPC and AA were obtained as 12 h FT, 10 % (w/v) FWR, 20 W/cm 2 UI, 4 ml/s FR and 120 s UT. The values observed for TPC and AA at optimum conditions were 90.1 mg GAE/100 g dm and 190.1 µmol TE/100 g dm, respectively, while these values for control SF were observed as 63.9 mg GAE/100 g dm and 133.5 µmol TE/100 g dm. Ultrasonication improved the free phenolic acid content by releasing bound phenolics in SF. The ANN model prediction was more precise compared to the RSM model.

Response surface methodology (RSM) was used to optimize rice bran oil encapsulation using jackfruit seed starch – whey protein isolate blend as wall material by spray drying technique. Oil concentration (20, 25 and 30 %), wall material (Jackfruit seed starch & whey protein isolate) starch-protein ratio (1:1, 3:1 and 5:1) and spray drying inlet air temperature (140, 150 and 160 °C) were considered as process variables for optimization. A three-factor, three-level Box-Behnken design of RSM was used to conduct the experiments with the aim of maximizing encapsulation efficiency and minimizing peroxide value in the encapsulated powder. A polynomial regression model was fitted using design expert software, and the optimum conditions obtained were 20 % oil concentration, 3:1 starch-protein ratio and 140 °C spray drying inlet air temperature. The encapsulated rice bran oil powers obtained at optimized conditions offered 85.90 % of encapsulation efficiency and 1.18 meq/kg oil of peroxide value. The characterization study revealed that powder particles size (diameter) varied from 3.40 to 300.51 µm and most of the particles were smooth spheres with little appendages.

The effect of acid and alkaline pH shift processes on removal of total lipids, cholesterol, nucleic acids and haem pigments during production of protein isolates from broiler meat was investigated. The gel-forming ability of resulting protein isolates were evaluated in comparison with raw broiler meat and water washed broiler meat. Significant reduction of total lipids, cholesterol, nucleic acids and haem proteins was obtained from both pH shift processes ( p < 0.05). Acid process recovered more protein with less total haem pigments resulting in a greater breaking force and whiteness of the isolate gel compared to alkaline counterpart ( p < 0.05). However, protein isolate gels showed inferior deformation and water holding capacity to washed mince gel ( p < 0.05). Therefore, the pH shift processing could be used to produce a functional protein isolate with low nucleic acids, haem pigments and lipids and, thereby, reduced cholesterol level. The protein isolates, particularly acid version, still had good gelling properties.