Weibiao Zhou

Reaction Kinetics of Degradation and Epimerization of Epigallocatechin Gallate (EGCG) in Aqueous System over a Wide Temperature Range

(-)-Epigallocatechin gallate (EGCG) is the most abundant catechin in green tea, which has been linked with many health benefits. To ensure the conceivable health benefits from thermally processed products, a kinetic study on the stability of (-)-EGCG in aqueous system was carried out using a HPLC-UV system and Matlab programming. Simultaneous degradation and epimerization of (-)-EGCG were characterized during isothermal reactions at low temperatures (25-100 degrees C) combined with previously conducted experimental results at high temperature (100-165 degrees C); the degradation and epimerization complied with first-order reaction and their rate constants followed Arrhenius equation. Mathematical models for the stability of (-)-EGCG were established and validated by the reactions at 70 degrees C and with varied concentrations from different catechin sources. Two specific temperature points in the reaction kinetics were identified, at 44 and 98 degrees C, respectively. Below 44 degrees C, the degradation was more profound. Above 44 degrees C, the epimerization from (-)-gallocatechin gallate (GCG) to (-)-EGCG was faster than degradation. When temperature increased to 98 degrees C and above, the epimerization from (-)-GCG to (-)-EGCG became prominent. Our results also indicated that the turning point of 82 degrees C reported in the literature for the reaction kinetics of catechins would need to be re-examined.

Optimisation of the temperature profile in bread baking

Abstract The common industrial practice in bread making is to bake bread in an oven that is controlled at a constant temperature. Due to the oven structure, the bread effectively experiences four major temperature zones. On the other hand, temperature in each zone is the dominating factor on the baking mechanisms including gelatinisation, enzymatic reaction and browning reaction, therefore the final bread quality. This research aims to establish an optimal temperature profile for white-sandwich bread to achieve the best product quality. Experiments were conducted by a multi-level partial factorial design, where dough was baked in a process with 4 equally divided zones. Mathematical models were established to describe the effects of tin temperature and baking time on bread quality attributes. Based on the models, by solving a constrained minimisation problem, the optimal tin temperature profile for the lowest weight loss was determined to be {115 °C, 130 °C, 156 °C, 176 °C} in the four zones with a baking time of 27.4 min. The crumb temperature was predicted to reach 99 °C, while the top crust colour, side crust colour and averaged crust colour were all within an acceptable range.

An Overview of 3D Printing Technologies for Food Fabrication

Different from robotics-based food manufacturing, three-dimensional (3D) food printing integrates 3D printing and digital gastronomy to revolutionize food manufacturing with customized shape, color, flavor, texture, and even nutrition. Hence, food products can be designed and fabricated to meet individual needs through controlling the amount of printing material and nutrition content. The objectives of this study are to collate, analyze, categorize, and summarize published articles and papers pertaining to 3D food printing and its impact on food processing, as well as to provide a critical insight into the direction of its future development. From the available references, both universal platforms and self-developed platforms are utilized for food printing. These platforms could be reconstructed in terms of process reformulation, material processing, and user interface in the near future. Three types of printing materials (i.e., natively printable materials, non-printable traditional food materials, and alternative ingredients) and two types of recipes (i.e., element-based recipe and traditional recipe) have been used for customized food fabrication. The available 3D food printing technologies and food processing technologies potentially applicable to food printing are presented. Essentially, 3D food printing provides an engineering solution for customized food design and personalized nutrition control, a prototyping tool to facilitate new food product development, and a potential machine to reconfigure a customized food supply chain.

Combined effect of pH and high temperature on the stability and antioxidant capacity of two anthocyanins in aqueous solution

The stability of two cyanidin-based anthocyanins from black rice in an aqueous system containing them with a pH range of 2.2-6.0 was investigated at temperatures ranging from 100 to 165°C. Within these pH and temperature ranges, the stability of the two anthocyanins was found to decrease gradually with increasing pH. The lowest (8.99×10(-4)s(-1)) and highest (0.120s(-1)) degradation rate constants for cyanidin-3-glucoside were obtained at pH 2.2 & 100°C and pH 6.0 & 165°C, respectively, whereas those for cyanidin-3-rutinoside were 5.33×10(-4)s(-1) at pH 2.2 & 100°C and 7.39×10(-2)s(-1) at pH 5.0 & 165°C, respectively. Antioxidant capacity analysis was conducted on thermally processed anthocyanin solutions to further evaluate the effects of pH and thermal treatment on the anthocyanins. The total antioxidant capacity of samples after thermal treatments under various pHs was found to remain at a similar level.

Antibacterial effect of light emitting diodes of visible wavelengths on selected foodborne pathogens at different illumination temperatures.

The antibacterial effect of light emitting diodes (LEDs) in the visible region (461, 521 and 642 nm) of the electromagnetic spectrum was investigated on Escherichia coli O157:H7, Salmonella typhimurium, Listeria monocytogenes and Staphylococcus aureus. The irradiances of the 461, 521 and 642 nm LEDs were 22.1, 16 and 25.4 mW/cm², respectively. Bacterial cultures suspended in tryptic soy broth were illuminated by 10-watt LEDs at a distance of 4.5 cm for 7.5h at 20, 15 and 10 °C. Regardless of the bacterial strains, bacterial inactivation was observed with the range of 4.6-5.2 logCFU/ml at 10 and 15 °C after illumination with the 461 nm LED, while illumination with the 521 nm LED resulted in only 1.0-2.0 log reductions after 7.5h. On the other hand, no antibacterial effect was observed using the 642 nm LED treatment. The photodynamic inactivation by 461 and 521 nm LEDs was found to be greater at the set temperatures of 10 and 15 °C than at 20 °C. The D-values for the four bacterial strains at 10 and 15 °C after the illumination of 461 nm LED ranged from 1.29 to 1.74 h, indicating that there was no significant difference in the susceptibility of the bacterial strains to the LED illumination between 10 and 15 °C, except for L. monocytogenes. Regardless of the illumination temperature, sublethal injury was observed in all bacterial strains during illumination with the 461 and the 521 nm LED and the percentage of injured cells increased as the treatment time increased. Thus, the results show that the antibacterial effect of the LEDs was highly dependent on the wavelength and the illumination temperature. This study suggests the potential of 461 and 521 nm LEDs in combination with chilling to be used as a novel food preservation technology.

Review of Rapid Tests Available for Measuring the Quality Changes in Frying Oils and Comparison with Standard Methods

Repeated use of oils and fats for frying of food brings about many changes in their physical and chemical properties. Due to increasing health concerns, the assessment of the quality of reused oils has received much attention, since such assessment is useful in determining the discarding point of the oils. The official analytical methods used in laboratories for this purpose need skill, time, and a large consumption of solvents. To make the oil testing simpler, several rapid test kits have been developed based on either physical parameters (such as viscosity or dielectric changes) or chemical parameters (such as free fatty acids, oxidized fatty acids, or carbonyl compounds). These test kits usually comprise a portable instrument or colorimetric reaction sticks, capable of providing a direct or indirect measurement of a single parameter. The review presented in this paper evaluates the use of such rapid test kits and highlights the need to develop multi-parameter test kits in order to establish the quality of reused oil and the point at which it should be discarded. The review also encompasses pertinent details on the standard analytical methods, and deterioration of frying oils that occur during and after their use and the associated health consequences.

Impact of caramelization on the glass transition temperature of several caramelized sugars. Part I: Chemical analyses.

This study aims to investigate the relationship between caramelization of several sugars including fructose, glucose, and sucrose and their glass transition temperature (Tg). Differential scanning calorimetry (DSC) was used for creating caramelized sugar samples as well as determining their glass transition temperature, which was found to decrease first and then increase as the holding time at the highest temperature increased. The extent of caramelization was quantified by UV-vis absorbance measurement and high-performance liquid chromatography analysis. Results showed that the amount of small molecules from the degradation of sugar increased very fast at the beginning of heating, and this increase slowed down in the later stage of caramelization. On the other hand, there was a lag phase in the formation of large molecules from the degradation of sugar at the beginning of heating, followed by a fast increase in the later stage of caramelization. The obtained results clearly indicate the impact of melting condition on the T g of sugars through formation of intermediates and end products of caramelization. Generally, when the heating condition is relatively mild, small molecules are formed first by decomposition of the sugar, which leads to a decrease of the overall Tg, and as the heating time becomes longer and/or the heating condition becomes more severe, polymerization takes over and more large molecules are formed, which results in an increase of the overall Tg. Mathematical modeling of the relationship will be presented as part II of the study in a separate paper.

Two-dimensional CFD modelling and simulation of an industrial continuous bread baking oven

In an industrial continuous bread baking oven, dough/bread is travelling inside the oven chamber and it is the oven temperature distribution in this whole travelling period that dominates the product quality variations. To establish a model covering the temperature distribution of the whole oven chamber, computational fluid dynamics (CFD) may be the most effective method. This paper presents the results of a CFD study on an industrial continuous bread baking oven. A two-axis CFD model was established to simulate the temperature profile and airflow pattern due to the convective and radiation heat transfer. With several oven operating parameters including heat supply and fan volume, the heat distribution trend in the oven was satisfactorily simulated. Based on the simulation results, positioning of the controller sensors was investigated through a sensitivity study. The simulation results can also be used to modify the oven configuration for better heat distribution.

Chemical composition and sensory profile of pomelo (Citrus grandis (L.) Osbeck) juice.

Two cultivars (Citrus grandis (L.) Osbeck PO 51 and PO 52) of Malaysian pomelo juices were studied by examining their physicochemical properties (i.e. pH, °Brix and titratable acidity), volatile and non-volatile components (sugars and organic acids). Using solvent extraction and headspace solid-phase microextraction, 49 and 65 volatile compounds were identified by gas chromatography-mass spectrometer/flame ionisation detector, respectively. Compared to pink pomelo juice (cultivar PO 52), white pomelo juice (cultivar PO 51) contained lower amount of total volatiles but higher terpenoids. Descriptive sensory evaluation indicated that white pomelo juice was milder in taste especially acidity. Furthermore, principal component analysis and partial least square regression revealed a strong correlation in pomelo juices between their chemical components and some flavour attributes (i.e. acidic, fresh, peely and sweet). Hence, this research enabled a deeper insight into the flavour of this unique citrus fruit.

Development in the Combined Treatment of Coating and Osmotic Dehydration of Food – A Review

Osmotic dehydration is gaining considerable attention as a minimal processing method because of its advantages such as saving energy to compliment drying process, better control of flavor loss and tissue damage problems and improved retention of color and nutritional constituents. The problems of flavor loss, tissue damage, color degradation and nutritional loss are present in traditional hot air drying due to the high temperature involved. However, except for candied food, large penetration of solute into the food becomes a major problem in osmotic dehydration. The application of a coating on food prior to osmotic dehydration is a promising solution to alleviate the large solute intake problem. Edible coatings serve as a barrier to limit the penetration of solute without having an adverse effect on water removal. This paper focuses on this combined technology and its potentials. The effects of edible coatings on both water and solute mass transfer in osmotic dehydration are reviewed. Suitable coating materials and their applicable concentration range for osmotic dehydration of food are evaluated. Mathematical models describing the mass transfer in osmotically dehydrated food with coatings are also reviewed.