Phoebe Qi - Academia.edu (original) (raw)

Papers by Phoebe Qi

Nanoscale, 2020

Flagella-templated Au nanowires were fabricated and demonstrated superior electrocatalytic activi... more Flagella-templated Au nanowires were fabricated and demonstrated superior electrocatalytic activity in the inhibition of bacterial growth by plant secondary metabolites.

Food Control, Jun 1, 2023

Journal of Dispersion Science and Technology, Jul 16, 2020

Some proteins will function as flocculants to clear water of suspended particles. Prior work has ... more Some proteins will function as flocculants to clear water of suspended particles. Prior work has shown that covalent methylation of a protein's carboxyl groups can enhance that protein's flocculant activity; this effect is usually attributed to the reduction in negative charges on the protein. We present results generated using four proteins which show that much of the flocculant activity enhancement occurs in a very short time at the beginning of the methylation reaction, before most of the carboxyl groups have been methylated. A variety of techniques are used to show that the methylation reaction has unintended effects on protein structure and aggregation, and that these effects may play an important role in enhancing protein flocculant activity. The observed enhancement in flocculant activity results from both charge and structural modification.

Separation and Purification Technology, 2022

Applied Biochemistry and Biotechnology, 2017

Lignin accounts for 15-35% of dry biomass materials. Therefore, developing valueadded co-products... more Lignin accounts for 15-35% of dry biomass materials. Therefore, developing valueadded co-products from lignin residues is increasingly important to improve the economic viability of biofuel production from biomass resources. The main objective of this work was to study the lignin extracts from corn stover residue obtained from a new and improved process for bioethanol production. Extraction conditions that favored high lignin yield were optimized, and antioxidant and antimicrobial activities of the resulting lignin were investigated. Potential estrogenic toxicity of lignin extracts was also evaluated. The corn stover was pretreated by low-moisture anhydrous ammonia (LMAA) and then subjected to enzymatic hydrolysis using cellulase and hemicellulase. The residues were then added with sodium hydroxide and extracted for different temperatures and times for enhancing lignin yield and the bioactivities. The optimal extraction conditions using 4% (w/v) sodium hydroxide were determined to be 50°C, 120 min, and 1:8 (w:v), the ratio between corn stover solids and extracting liquid. Under the optimal condition, 33.92 g of lignin yield per 100 g of corn stover residue was obtained.

Journal of Dispersion Science and Technology, 2020

Journal of Dairy Science, Jul 1, 2023

Consumers' growing interest in fermented dairy foods necessitates research on a wide array of lac... more Consumers' growing interest in fermented dairy foods necessitates research on a wide array of lactic acid bacterial strains to be explored and used. This study aimed to investigate the differences in the proteolytic capacity of Lactobacillus helveticus strains B1929 and ATCC 15009 on the fermentation of commercial ultrapasteurized (UHT) skim milk and reconstituted nonfat dried milk powder (at a comparable protein concentration, 4%). The antihypertensive properties of the fermented milk, measured by angiotensin-I-converting enzyme inhibitory (ACE-I) activity, were compared. The B1929 strain lowered the pH of the milk to 4.13 ± 0.09 at 37°C after 24 h, whereas ATCC 15009 needed 48 h to drop the pH to 4.70 ± 0.18 at 37°C. Two soluble protein fractions, one (CFS1) obtained after fermentation (acidic conditions) and the other (CFS2) after the neutralization (pH 6.70) of the pellet from CFS1 separation, were analyzed for d-/l-lactic acid production, protein concentration, the degree of protein hydrolysis, and ACE-I activity. The CFS1 fractions, dominated by whey proteins, demonstrated a greater degree of protein hydrolysis (7.9%) than CFS2. On the other hand, CFS2, mainly casein proteins, showed a higher level of ACE-I activity (33.8%) than CFS1. Significant differences were also found in the d-and l-lactic acid produced by the UHT milk between the 2 strains. These results attest that milk casein proteins possessed more detectable ACE-I activity than whey fractions, even without a measurable degree of hydrolysis. Findings from this study suggest that careful consideration must be given when selecting the bacterial strain and milk substrate for fermentation.

Food Chemistry, Nov 1, 2020

We investigated changes in the chemical composition of WPI as a result of heating (60°C, 72 h) wi... more We investigated changes in the chemical composition of WPI as a result of heating (60°C, 72 h) with SBP in solution (pH 6.75). The concentration of WPI was kept at a constant (3%), whereas the level of SBP was varied at 1, 1.5, and 3%. The reaction products were examined using the Ellman's reagent, ninhydrin assay, and gel electrophoresis. The results demonstrated that the losses of the free sulfhydryl (-SH) and primary amine (-NH 2) contents in WPI were less severe compared to those occurring in the dry-state at similar conditions (mass ratio, temperature, and reaction duration). The mixtures were used as emulsifiers in an O/W emulsion system at pH 3.20 and 6.75 and showed an improved ability to stabilize the average size of the droplets than WPI alone at acidic pH. The mixtures at higher levels of SBP, ≥ 1.5%, however, adversely affected the emulsion stability at neutral pH.

Food Hydrocolloids, Jun 1, 2017

It has been shown previously that reacting whey protein isolate (WPI) with sugar beet pectin (SBP... more It has been shown previously that reacting whey protein isolate (WPI) with sugar beet pectin (SBP) through a Maillard type reaction in a dry-state led to noticeable improvement in the physical, chemical and functional properties of the end products. Studies on the changes in the molecular structure of whey protein as a result of the reaction were carried out in this work to provide a molecular understanding of these observed improvements. The effect of interacting and conjugating with SBP on the apparent secondary structure of WPI was examined by far-UV circular dichroism (CD) spectroscopy and followed by spectral deconvolution. Results showed that the structure of WPI, especially the antiparallel b-sheet element, was preserved by reacting with SBP at the weight ratios of WPI:SBP ¼ 3:1, 2:1, and 1:1. The analysis of difference UV-VIS spectra indicated significant changes occurred in the molecular electronic states of both WPI and the feruloyl moieties of SBP. Initial Maillard reaction products were detected in the form of the FRET complexes with WPI as the donor, and SBP, the acceptor by the studies of the steady-state fluorescence and the lifetime of the excited states. The tertiary structural contacts in WPI, probed by the intrinsic Trp fluorescence, were disrupted significantly upon reacting with SBP at an equal ratio (1:1). The thermal stability of WPI, however, at both secondary and tertiary structural levels, was greatly improved by the dry-heating induced reaction with SBP at all levels. The thermal stability of the feruloyl groups of SBP was also enhanced by reacting with WPI. Furthermore, the fluorescence lifetime studies definitively identified the distinctive advanced Maillard reaction end products (AMREPs) formed between WPI and SBP at varying ratios.

Food Hydrocolloids, Aug 1, 2017

Mention of trade names or commercial products in this publication is solely for the purpose of pr... more Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer.

Food Hydrocolloids, Aug 1, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Foods that are rich in protein and other micronutrients such as bioactives and vitamins but low i... more Foods that are rich in protein and other micronutrients such as bioactives and vitamins but low in sugar and fat may help mitigate the global obesity epidemic. Specialty ingredients can be fabricated to possess specific functions such as encapsulating bioactives through controlled assembly of protein and polysaccharide molecules. One of the most commonly used methods of combining proteins and polysaccharides into functional biopolymer particles is based on electrostatic attraction between oppositely charged groups under appropriate conditions(concentration, pH, ionic strength, and temperature etc.). In this work, interactions betweenβ-lactoglobulin(β-LG), a major milk protein, and sugar beet pectin(SBP), one of the most versatile polysaccharides, were investigated using online multi-detection High Performance Size Exclusion Chromatography(HPSEC) at neutral pH. The hydrodynamic properties of various interacting polymeric fractions were characterized in detail. Results showed that alt...

Food Chemistry, 2020

Food Hydrocolloids, 2018

We investigate changes in the molecular structures of whey proteins (WPI) caused by heat-induced ... more We investigate changes in the molecular structures of whey proteins (WPI) caused by heat-induced interaction and reaction with varying concentrations of sugar beet pectin (SBP) in aqueous solution at neutral pH. The resulting complexes were examined using circular dichroism (CD) and steady-state and time-resolved fluorescence spectroscopic techniques. Far-UV CD spectroscopy combined with spectral deconvolution revealed noticeable reduction (up to 5%) in the amount of antiparallel b-sheet element of WPI upon interacting with SBP. Analyses from the UV-VIS and steady-state fluorescence spectroscopies showed changes in the molecular electronic states of both WPI and the feruloyl moieties of SBP upon heat-induced interaction and conjugation. The tertiary structural contacts in WPI, studied by the intrinsic Trp fluorescence, were also disrupted in the presence of SBP in the form of FRET (Fluorescence Resonance Energy Transfer) complexes, most noticeably at a high level of SBP (3%), contrasting to the results from dry-heating. The thermal stability of WPI, at both secondary and tertiary structural levels, did not increase considerably by interacting and conjugating with SBP, especially at an equal concentration of SBP (3%). However, the stability of feruloyl groups of SBP saw moderate improvement and was less pronounced than that of the dry-state reactions. Published by Elsevier Ltd. * Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer.

Food Hydrocolloids, 2017

Food Hydrocolloids, 2021

Abstract We investigated the molecular properties of interacting complexes and conjugates formed ... more Abstract We investigated the molecular properties of interacting complexes and conjugates formed between α-lactalbumin (αLA) and SBP using a multi-detection (UV, dRI, MALLS, and DPV) HPSEC. Dry-heating reactions were conducted at the mass ratios 1:0, 5:1, 3:1, 2:1, 1:1, and 0:1 αLA:SBP under controlled conditions (60 °C, 79% RH, 72 h). The in-depth physicochemical analysis showed that the association levels were 32, 37, 47, and 61% αLA and 18, 24, 30, and 42% SBP for 5:1, 3:1, 2:1, and 1:1 αLA:SBP, respectively. The stoichiometry was estimated to be 233, 121, 90, and 45 αLA per SBP. Studies of the solution mixtures (3:1) demonstrated that αLA formed complexes with all sized SBP at pH ~ 6.50 through local charge-charge and hydrophobic interactions with stoichiometry ~110:1. Furthermore, the complexes and conjugates did not change the conformation of SBP considerably, i.e., compact spheres, random coils, and rigid rods but increased the molecular chains' stiffness.

PLOS ONE, 2022

Olive leaf extract (OLE) has been increasingly recognized as a natural and effective antimicrobia... more Olive leaf extract (OLE) has been increasingly recognized as a natural and effective antimicrobial against a host of foodborne pathogens. This study attempts to predict the minimum inhibitory concentration (MIC) of OLE against Listeria monocytogenes F2365 by utilizing the asymptotic deceleration point (PDA) in a logistic model (LM), namely MIC-PDA. The experimental data obtained from the inhibitory rate (IR) versus OLE concentration against L. monocytogenes were sufficiently fitted (R2 = 0.88957). Five significant critical points were derived by taking the multi-order derivatives of the LM function: the inflection point (PI), the maximum acceleration point (PAM), the maximum deceleration point (PDM), the absolute acceleration point (PAA), and the asymptotic deceleration point (PDA). The PDA ([OLE] = 37.055 mg/mL) was employed to approximate the MIC-PDA. This MIC value was decreased by over 42% compared to the experimental MIC of 64.0 mg/mL, obtained using the conventional 2-fold dil...

Whey protein concentrates (WPC) and isolates (WPI), comprised mainly of β-lactoglobulin (β-LG), α... more Whey protein concentrates (WPC) and isolates (WPI), comprised mainly of β-lactoglobulin (β-LG), α-lactalbumin (α-LA) and casein glycomacropeptide (GMP), are added to foods to boost nutritional and functional properties. Supercritical carbon dioxide (SCO 2) has been shown to effectively fractionate WPC and WPI to obtain enriched fractions of α-LA and β-LG, thus creating new whey ingredients that exploit the properties of the individual component proteins. In this study, we used SCO 2 to further fractionate WPI via acid precipitation of α-LA, β-LG and the minor whey proteins to obtain GMP-enriched solutions. The process was optimized and α-LA precipitation maximized at low pH and a temperature (T) ≥65 °C, where β-LG with 84% purity and GMP with 58% purity were obtained, after ultrafiltration and diafiltration to separate β-LG from the GMP solution. At 70 °C, β-LG also precipitated with α-LA, leaving a GMP-rich solution with up to 94% purity after ultrafiltration. The different protein fractions produced with the SCO 2 process will permit the design of new foods and beverages to target specific nutritional needs.

Research and development on films and coatings made from various agricultural proteins has been c... more Research and development on films and coatings made from various agricultural proteins has been conducted over the past 20 years, but is of heightened interest, due to the demand for environmentally-friendly, renewable replacements for petroleumbased polymeric materials and plastics. To address this demand, films and coatings have been made from renewable resources, such as casein, whey, soy, corn zein, collagen, wheat gluten, keratin and egg albumen. Those made from agricultural proteins create new outlets for agricultural products, byproducts and waste streams, all of which can positively impact the economics of food processes. Due to casein's ability to form water-resistant films, it was used for hundreds of years in paints and coatings (Gettens and Stout 1984). In the late nineteenth century, casein was converted into a hard plastic material by cross-linking it with formaldehyde. A patent for this technology was issued to Adolf Spitteler in Bavaria (Brother 1940), and it was...