Zhongli Pan

Continuous and pulsed ultrasound-assisted extractions of antioxidants from pomegranate peel

There is a great demand for developing efficient extraction methods in order to reduce extraction time and increase the yield and activity of functional antioxidants. The yields, activities, and extraction kinetics of antioxidants from the dry peel of pomegranate marc were studied using ultrasound-assisted extraction in continuous and pulsed modes and the results were compared with conventional extraction (CE) at a temperature of 25±2 °C and water/peel ratio of 50/1, w/w. The studied factors were intensity level and treatment time for continuous ultrasound-assisted extraction (CUAE), and intensity level, number of pulse repetition, and pulse duration and interval for pulsed ultrasound-assisted extraction (PUAE). The results showed that all factors significantly affected the antioxidant yield, but only treatment time had a significant effect on the antioxidant activity. Compared to CE, PUAE at an intensity level of 59.2 W/cm(2), and a pulse duration of 5s and a resting interval of 5s increased the antioxidant yield by 22% and reduced the extraction time by 87%. Similarly, CUAE at the same intensity level increased the antioxidant yield by 24% and reduced the extraction time by 90%. Since PUAE had 50% energy saving compared to CUAE, we recommend using PUAE for the extraction with antioxidant yield of 14.5% and DPPH scavenging activity of 5.8 g/g. A second-order kinetic model was successfully developed for describing the mechanism of ultrasound-assisted extractions under PUAE and CUAE. This research clearly demonstrated the superiority of PUAE for producing antioxidants from peel of pomegranate marc.

Kinetic modeling for enzymatic hydrolysis of pretreated creeping wild ryegrass.

A semimechanistic multi‐reaction kinetic model was developed to describe the enzymatic hydrolysis of a lignocellulosic biomass, creeping wild ryegrass (CWR; Leymus triticoides). This model incorporated one homogeneous reaction of cellobiose‐to‐glucose and two heterogeneous reactions of cellulose‐to‐cellobiose and cellulose‐to‐glucose. Adsorption of cellulase onto pretreated CWR during enzymatic hydrolysis was modeled via a Langmuir adsorption isotherm. This is the first kinetic model which incorporated the negative role of lignin (nonproductive adsorption) using a Langmuir‐type isotherm adsorption of cellulase onto lignin. The model also reflected the competitive inhibitions of cellulase by glucose and cellobiose. The Matlab optimization function of “lsqnonlin” was used to fit the model and estimate kinetic parameters based on experimental data generated under typical conditions (8% solid loading and 15 FPU/g‐cellulose enzyme concentration without the addition of background sugars). The model showed high fidelity for predicting cellulose hydrolysis behavior over a broad range of solid loading (4–12%, w/w, dry basis), enzyme concentration (15–150 FPU/ g‐cellulose), sugar inhibition (glucose of 30 and 60 mg/mL and cellobiose of 10 mg/mL). In addition, sensitivity analysis showed that the incorporation of the nonproductive adsorption of cellulase onto lignin significantly improved the predictability of the kinetic model. Our model can serve as a robust tool for developing kinetic models for system optimization of enzymatic hydrolysis, hydrolysis reactor design, and/or other hydrolysis systems with different type of enzymes and substrates. Biotechnol. Bioeng. 2009;102: 1558–1569.

Characteristics of soybeans as affected by soaking conditions

The water absorption of soybeans in soaking is directly related to the changes in textural characteristics and grinding properties of soybeans for processing. In this study, we determined the characteristics of water absorption, solid loss, and moisture content, textural characteristics and grinding properties of soybeans at four different soaking temperatures, 10°C, 20°C, 30°C, and 40°C, and various soaking times up to 8 h. We found that the solid loss increased significantly when the soaking temperature increased from 30°C to 40°C. The measured moisture data of soaked soybeans fitted well with the data predicted using Pelegs equation. Rupture force and maximum tangent and secant modulus measured by the compression test decreased as the moisture increased, up to 122%. The grinding property of soaked soybeans was related only to the final moisture content and not to the soaking conditions. High soaking temperature could significantly reduce the required soaking time. Based on these results, we recommend that soybeans be soaked to minimal final moisture content of 120% before grinding.

Quantitative determination of major polyphenol constituents in pomegranate products

The anti-oxidant content and potential health benefits associated with consuming pomegranate and pomegranate-containing products has lead to increased consumer demand for this crop resulting in it becoming a high value crop. The potential health benefits and high anti-oxidant content of this fruit is attributed to the polyphenolic compounds it contains, including the ubiquitous phenolic acids, gallic acid and ellagic acid, and punicalagin A and punicalagin B, two polyphenolics unique to this fruit. A rapid HPLC-UV method targeting these four metabolites requiring minimal sample cleanup and offering runtimes half as long as existing methods was established. Within day and inter-day run-to-run variability for the four metabolites ranged from 1.9% to 6.6% and 5.3% to 11.4%, respectively. Spike recovery percentages for gallic acid, punicalagin A, punicalagin B and ellagic acid were found to be 98.5%, 92.4%, 95.5%, and 96.5%, respectively. This method was applied to the evaluation of various pomegranate products, including commercial drinks, handmade juice, and marc extracts. This method may be readily used to verify the presence of pomegranate metabolites in juices, extracts, and other products.

Reduction of Salmonella Enteritidis Population Sizes on Almond Kernels with Infrared Heat

Catalytic infrared (IR) heating was investigated to determine its effect on Salmonella enterica serovar Enteritidis population sizes on raw almond kernels. Using a double-sided catalytic IR heating system, a radiation intensity of 5,458 W/m2 caused a fast temperature increase at the kernel surface and minimal temperature differences between the top and bottom kernel surfaces. Exposure of dry kernels to IR heat for 30, 35 and 45 s resulted in maximum kernel surface temperatures of 90, 102, and 113 degrees C, and when followed by immediate cooling at room temperature, yielded a 0.63-, 1.03-, and 1.51-log reduction in S. enterica population sizes, respectively. The most efficacious decontamination treatment consisted of IR exposure, followed by holding of the kernels at warm temperature for 60 min, which effected a greater than 7.5-log reduction in S. enterica on the kernels. During that treatment, the kernel surface temperature rose to 109 degrees C and gradually decreased to 80 degrees C. Similar IR and holding treatments with lower maximum kernel surface temperatures of 104 and 100 degrees C yielded reductions of 5.3 and 4.2 log CFU/g kernel, respectively. During these treatments, moisture loss from the kernels was minimal and did not exceed 1.06%. Macroscopic observations suggested that kernel quality was not compromised by the IR-holding combination treatment, as skin morphology, meat texture, and kernel color were indistinguishable from those of untreated kernels. Our studies indicate that IR heating technology is an effective dry pasteurization for raw almonds.

Enzymolysis kinetics and activities of ACE inhibitory peptides from wheat germ protein prepared with SFP ultrasound-assisted processing

There is a great demand for developing efficient enzymolysis methods in order to increase the enzymolysis efficiencies and activities of angiotensin converting enzyme (ACE) inhibitory peptides from wheat germ protein. The enzymolysis kinetics, ACE inhibitory activity of peptide and conversion rate of protein were studied using sweep frequency and pulsed (SFP) ultrasound-assisted enzymolysis and the results were compared with traditional enzymolysis. The studied factors were enzymolysis time and substrate concentration. By considering the activity of ACE inhibitory peptide and operation cost, the recommended conditions of SFP ultrasound-assisted enzymolysis were enzymolysis time of 120 min and substrate concentration of 24.0 g/L, which gave high conversion rates of protein (60.7%) and ACE inhibitory activity of peptide (65.9%). Compared to traditional enzymolysis, SFP ultrasound-assisted enzymolysis significantly increased the initial reaction rate (V) by 60.0% at substrate concentration of 24.0 g/L, increased the apparent breakdown rate constant (k(A)) by 66.7%, decreased the apparent constant (K(M)) by 6.9%, and raised the conversion rate of protein by 35.5% and ACE inhibitory activity of peptides by 35.6% under the recommended conditions. It has been concluded that SFP ultrasound can remarkably raise the enzymolysis efficiency and activity of ACE inhibitory peptides from wheat germ protein.

APPLICATION OF RADIOFREQUENCY POWER FOR NON-CHEMICAL DISINFESTATION OF ROUGH RICE WITH FULL RETENTION OF QUALITY ATTRIBUTES

The presence of insect pests in stored grains constitutes an undesirable condition leading to product losses, lesser quality, and reduced market value. Currently, to protect grains, the rice industry relies on insecticides and fumigants but many of these products are facing elimination (deregistration) due to health and environmental concerns. An alternative non-chemical disinfestation process is therefore needed. Radiofrequency (RF) power was selected as it can be applied to induce well-controlled, lethal thermal energy levels, rapidly, efficiently, and throughout the whole mass of grains with minimal physical and chemical changes. Natural and laboratory infested dried storage rough rice containing all life cycles of lesser grain borers (Rhyzopertha dominica) and Angoumois grain moths (Sitotroga cerealella) were used to evaluate the efficacy of RF power treatment. This study developed relationships between temperature and disinfestation effects that were used to optimize the processs disinfestation efficiency while operating at power and thermal load levels well tolerated by the commodity. Low-thermal load RF processing at 55°C to 60°C bulk rice temperatures for short times (5 min) resulted in >99% control of all biological stages of Sitotroga cerealella (grain moth). When higher thermal loads were applied using 50°C for Sitotroga cerealella with a 2-h tempering or 60°C for Rhyzopertha dominica with 1-h tempering, the treatment provided 100% control as indicated by the absence of emerging adults over a 120-d observation period. Under these processing conditions, no moisture losses or changes in milling quality were observed. An analysis of the potential of RF power for commercial disinfestation of grains is also included.

Evaluation of Different Biomass Materials as Feedstock for Fermentable Sugar Production

Saline crops and autoclaved municipal organic solid wastes were evaluated for their potential to be used as feedstock for fermentable sugar production through dilute acid pretreatment and enzymatic hydrolysis. The saline crops included two woods, athel (Tamarix aphylla L) and eucalyptus (Eucalyptus camaldulensis), and two grasses, Jose tall wheatgrass (Agropyron elongatum), and creeping wild rye (Leymus triticoides). Each of the biomass materials was first treated with dilute sulfuric acid under selected conditions (acid concentration =1.4% (w/w), temperature =165°C, and time =8 min) and then treated with the enzymes (cellulases and β-glucosidase). The chemical composition (cellulose, hemicellulose, and lignin contents) of each biomass material and the yield of total and different types of sugars after the acid and enzyme treatment were determined. The results showed that among the saline crops evaluated, the two grasses (creeping wild rye and Jose tall wheatgrass) had the highest glucose yield (87% of total cellulose hydrolyzed) and fastest reaction rate during the enzyme treatment. The autoclaved municipal organic solid wastes showed reasonable glucose yield (64%). Of the two wood species evaluated, Athel has higher glucose yield (60% conversion of cellulose) than eucalyptus (38% conversion of cellulose).

Pretreatment of defatted wheat germ proteins (by-products of flour mill industry) using ultrasonic horn and bath reactors: Effect on structure and preparation of ACE-inhibitory peptides

The ultrasonic horn and bath reactors were compared based on production of angiotensin-converting-enzyme (ACE) inhibitory peptides from defatted wheat germ proteins (DWGP). The DWGP was sonicated before hydrolysis by Alcalase. Degree of hydrolysis, ACE-inhibitory activity, surface hydrophobicity, fluorescence intensity, free sulfhydryl (SH), and disulfide bond (SS) were determined. The highest ACE-inhibitory activity of DWGP hydrolysate was obtained at power intensity of 191.1 W/cm(2) for 10 min in the ultrasonic horn reactor. The fixed frequency of 33 kHz and the sweep frequency of 40±2 kHz resulted in the maximum ACE-inhibitory activity. The combined irradiation of dual fixed frequency (24/68 kHz) produced significant increase in ACE-inhibitory activity compared with single frequency (33 kHz). The ultrasonic probe resulted in significant higher ACE-inhibitory activity compared with ultrasonic bath operating at single or dual fixed and sweep frequencies. The changes in conformation of the DWGP due to sonication were confirmed by the changes in fluorescence intensity, surface hydrophobicity, SHf and SS contents and they were found in conformity with the ACE-inhibitory activity in case of the ultrasonic horn reactor but not in bath reactor.

Extract of Phenolics From Pomegranate Peels

The effects of different solvents, temperature conditions, solvent-solid ratios and particle sizes on solid-solvent extraction of the total phenolics, proanthocyanidins and flavonoids herein also referred to as antioxidant from pomegran- ate marc peel (PMP) was studied. Water, methanol, ethanol, acetone, and ethyl acetate extraction efficiencies at extraction times of 0.17 to 10 min, extraction temperatures of 25 to 95°C, ratios of solvent/solid of 5:1 to 50:1 and particle sizes of 10 to 40 mesh were evaluated. At 40 °C, solvent/solid ratio of 15:1, extraction time of 240 min and particle size of 40 mesh, methanol gave the highest extract yield of the total phenolics (8.26%), followed by water (5.90%), ethanol (1.55%), acetone (0.37%), and ethyl acetate (0.18%), respectively. However, at an extraction temperature of 95°C, the total phe- nolics extract yield with water was 11.15% for particle size of 40 mesh, solvent/solid ratio of 15:1, and extraction time of 2 min. Despite the lowest extract yield at extraction temperature of 40 °C, solvent/solid ratio of 15:1, extraction time of 240 min and particle size of 40 mesh, ethyl acetate extraction gave the highest content of the total phenolics (20.24%), proanthocyanidins (2.65%) and flavonoids (3.92%) in the extract. The DPPH antioxidant activity of extracts had a linear relationship with the total phenolics content in the extracts (R 2 =0.9779). This study revealed that water extraction, which has the economic and safety merits, can be used as an environmentally friendly method for producing antioxidants from the PMP.