Alyson Mitchell | University of California, Davis (original) (raw)

Papers by Alyson Mitchell

Metabolic Profiling of Flavonol Metabolites in Human Urine by Liquid Chromatography and Tandem Mass Spectrometry

Journal of Agricultural and Food Chemistry, Oct 1, 2004

Twenty-one flavonol metabolites have been identified by LC/ESI-MS/MS in human urine, including is... more Twenty-one flavonol metabolites have been identified by LC/ESI-MS/MS in human urine, including isomers, after the consumption of cooked onions. Metabolites identified include quercetin monoglucuronides, methyl quercetin monoglucuronides, a quercetin monoglucuronide sulfate, quercetin diglucuronides, a methyl quercetin diglucuronide, quercetin glucoside sulfates, methyl quercetin, quercetin, and kaempferol monoglucuronides. The fragmentation patterns of flavonol metabolites obtained by MS/MS were distinctive for some isomers, indicating that fragmentation patterns may be useful predictors of conjugation position. Two isomers of sulfate quercetin glucosides were also found in urine, suggesting that many of the quercetin glucosides in onion are absorbed intact and undergo metabolism to the sulfate conjugate. Additionally, the interindividual variation in urinary quercetin metabolite profiles was determined by comparing the relative level of six different quercetin metabolites excreted in the urine of healthy volunteers. The ranges of quercetin metabolites excreted were similar among volunteers, yet notable differences in the levels of metabolites among individuals were observed. This study demonstrates the potential of monitoring the range of quercetin metabolites to reveal information on interindividual biotransformation capacity in response to dietary manipulations and as a biomarker for flavonol consumption.

Organic fruit and vegetables

Elsevier eBooks, 2008

ACS food science & technology, Jan 25, 2022

The majority of commercial almonds grown in California undergo pasteurization using a validated p... more The majority of commercial almonds grown in California undergo pasteurization using a validated process such as moist heat exposure (MH) or fumigation with propylene oxide (PO) to reduce the potential of Salmonella bacteria contamination. Although these treatments are common, their effect on raw almond storage quality is not well understood. To address this, almonds were either pasteurized with MH and PO or left unpasteurized (control) and stored for 12 months under accelerated shelf life conditions. Lipid oxidation markers, headspace volatiles, and descriptive analysis were evaluated monthly. Significant differences were observed between treatments, with control samples expressing significantly higher levels of alcohols and organic acids and up to 3 times higher overall headspace volatile concentrations. At 8 months of storage, panelists distinguished the MH sample from the control sample with lower scores in rancidity-related attributes. MH > PO pasteurization decreases the rate of lipid oxidation during storage compared with controls, thereby increasing shelf life.

Journal of Agricultural and Food Chemistry, Jul 12, 2011

Acrylamide is a probable human carcinogen that is found in many roasted and baked foods. This pap... more Acrylamide is a probable human carcinogen that is found in many roasted and baked foods. This paper describes two sensitive and reliable LC-(ESI)MS/MS methods for the analysis of (1) acrylamide and (2) common acrylamide precursors (i.e., glucose, fructose, asparagine, and glutamine) in raw and roasted almonds. These methods were used to evaluate the impact of roasting temperatures (between 129 and 182°C) and times on acrylamide formation. Controlling the roasting temperature at or below 146°C resulted in acrylamide levels below 200 ppb at all roasting times evaluated. Six varieties of almonds collected in various regions of California over two harvest years and roasted at 138°C for 22 min had acrylamide levels ranging from 117 (5 μg/kg (Sonora) to 221 (95 μg/kg (Butte) with an average of 187 (71 μg/kg. A weak correlation between asparagine content in raw almonds and acrylamide formation was observed (R 2 = 0.6787). No statistical relationship was found between acrylamide formation and almond variety, orchard region, or harvest year. Stability studies on roasted almonds indicated that acrylamide levels decreased by 12.9À68.5% (average of 50.2%) after 3 days of storage at 60°C. Short-term elevated temperature storage may be another approach for mitigating acrylamide levels in roasted almonds.

Journal of Agricultural and Food Chemistry, Jan 12, 2019

Olives are inedible because of high levels of bitter phenolics (e.g., oleuropein) which are remov... more Olives are inedible because of high levels of bitter phenolics (e.g., oleuropein) which are removed during commercial olive processing. Current commercial processing methods are highly water-intensive, produce toxic wastewater, and are environmentally unsustainable. To address this, macroreticular polymeric resins were used to assist debittering and decrease water use. Amberlite resins XAD4, XAD16N, XAD7HP, and FPX66 were evaluated for the ability to adsorb bitter and/or highvalue phenolic compounds (i.e., oleuropein, ligstroside, oleuropein aglycone, ligstroside aglycone, oleocanthal, oleacein, and hydroxytyrosol) from whole olives during typical brine storage. All resins effectively adsorbed oleuropein and ligstroside. FPX66 reduced oleuropein in whole olives suspended in a 1.0% acetic acid brine to 0.635 mg/kg wet weight in 2.5 months with no further processing. This concentration is below levels measured in commercial California-style black ripe olives (0.975 mg/kg wet weight). Resins in storage brines effectively decrease levels of bitter phenolic compounds without additional lye processing. Excellent recoveries of high-value phenolic compounds are obtained from resins (e.g., 80.2 ± 3.3% to 89.4 ± 8.9% hydroxytyrosol).

Journal of Food Science, May 27, 2017

Acrylic acid, N-acetyl-glucosamine and glucosamine were investigated for their role in the format... more Acrylic acid, N-acetyl-glucosamine and glucosamine were investigated for their role in the formation of acrylamide in California-style black ripe olives [CBROs]. Levels of acrylic acid and glucosamine are reported for the first time in fresh (333.50 ± 21.88 and 243.59 ± 10.06 nmol/g, respectively) and in brine-stored olives (184.50 ± 6.02 and 165.88 ± 11.51 nmol/g, respectively). Acrylamide levels significantly increased when acrylic acid (35.2%), N-acetyl-glucosamine (29.9%), and glucosamine (124.0%) were added to olives prior to sterilization. However, isotope studies indicate these compounds do not contribute carbon and/or nitrogen atoms to acrylamide. The base-catalyzed degradation of glucosamine is demonstrated in olive pulp and a strong correlation (r 2 = 0.9513) between glucosamine in olives before sterilization and acrylamide formed in processed CBROs is observed. Treatment with sodium hydroxide (pH > 12) significantly reduces acrylamide levels over 1 to 5 d without impacting olive fruit texture.

Journal of Agricultural and Food Chemistry, Aug 2, 2019

Glucosinolates and their hydrolysis products were characterized in fresh and in in vitro gastric ... more Glucosinolates and their hydrolysis products were characterized in fresh and in in vitro gastric and intestinal digesta of Dinosaur kale (Brassica oleracea L var. palmifolia DC). In fresh kale, glucoraphanin, sinigrin, gluconapin, gluconasturtiin, glucoerucin, glucobrasscin, and 4-methoxylglucobrassicin were identified. After 120 min of gastric digestion, the levels of glucoraphanin, sinigrin, and gluconapin decreased, and no glucoerucin or glucobrasscin was detected. However, a concomitant increase in the glucosinolate hydrolysis products allyl nitrile, 3-butenyl isothiocyanate, phenylacetonitrile, and sulforaphane was observed. This trend continued through intestinal digestion. After 120 min, the levels of allyl nitrile, 3-butenyl isothiocyanate, phenylacetonitrile, and sulforaphane were 88.19 ± 5.85, 222.15 ± 30.26, 129.17 ± 17.57, and 13.71 ± 0.62 pmol/g fresh weight, respectively. Intestinal digesta were then applied to Caco-2 cell monolayers to assess the bioavailability. After 6 h of incubation, no glucosinolates were detected and the percentage of total cellular uptake of the glucosinolate hydrolysis products ranged from 29.35% (sulforaphane) to 46.60% (allyl nitrile).

Journal of Agricultural and Food Chemistry, Jan 25, 2018

Monitoring oxidative flavor changes in almonds is possible only if the chemical and sensory profi... more Monitoring oxidative flavor changes in almonds is possible only if the chemical and sensory profile during roasting and storage is first established. Herein, almonds roasted at two different temperatures (115 and 152°C) were stored at 39°C for 0 to 12 months and were analyzed by headspace solid-phase microextraction gas chromatography−mass spectrometry, descriptive analysis, and consumer hedonic analysis. Volatile profiles, descriptive sensory profiles, and consumer hedonic scores were analyzed for predictive relationships. Descriptive attributes involving Roasted and Nutty as well as consumer liking were highest in fresh almonds, while flavors typically associated with oxidative rancidity such as Cardboard, Painty/Solvent, Soapy, and Total Oxidized increased during storage. Compounds most important for predicting rancidity-related attributes were lipid oxidation products, including pentanal, hexanal, heptanal, and octanal. Consumer liking was best predicted by similar compounds to those predicting Clean Nutty flavor, including Maillard reaction products such as 2-and 3-methylbutanal, 2-methylpyrazine, and 2,5-dimethylpyrazine.

Journal of Agricultural and Food Chemistry, Jul 18, 2016

Concealed damage (CD) is defined as a brown discoloration of the kernel interior (nutmeat) that a... more Concealed damage (CD) is defined as a brown discoloration of the kernel interior (nutmeat) that appears only after moderate to high heat treatment (e.g., blanching, drying, roasting, etc.). Raw almonds with CD have no visible defects before heat treatment. Currently, there are no screening methods available for detecting CD in raw almonds. Herein, the feasibility of using near-infrared (NIR) spectroscopy between 1125 and 2153 nm for the detection of CD in almonds is demonstrated. Almond kernels with CD have less NIR absorbance in the region related with oil, protein, and carbohydrates. With the use of partial least squares discriminant analysis (PLS-DA) and selection of specific wavelengths, three classification models were developed. The calibration models have false-positive and false-negative error rates ranging between 12.4 and 16.1% and between 10.6 and 17.2%, respectively. The percent error rates ranged between 8.2 and 9.2%. Second-derivative preprocessing of the selected wavelength resulted in the most robust predictive model.

Journal of Agricultural and Food Chemistry, Nov 11, 2014

Hexanal, peroxide value, and lipid hydroperoxides are common indicators of lipid oxidation in foo... more Hexanal, peroxide value, and lipid hydroperoxides are common indicators of lipid oxidation in food products. However, these markers are not always reliable as levels are dynamic and often can be detected only after significant oxidation has occurred. Changes in the volatile composition of light-and dark-roast almonds were evaluated during storage over 24 weeks at 25 or 35°C using headspace solid phase microextraction (HS-SPME) gas chromatography−mass spectrometry (GC-MS). Several volatile changes were identified in association with early oxidation events in roasted almonds. Hexenal decreased significantly during the first 6 weeks of storage and did not increase above initial levels until 20−24 weeks of storage depending upon the degree of roast. In contrast, levels of 1-heptanol and 1-octanol increased at 16−20 weeks, depending upon the degree of roast, and no initial losses were observed. Seventeen new compounds, absent in raw and freshly roasted almonds but detectable after 6 weeks of storage, were identified. Of these, 2-octanone, 2-nonanone, 3-octen-2-one, 2-decanone, (E)-2-decenal, 2,4-nonadienal, pentyl oxirane, and especially acetic acid increased significantly (that is, >10 ng/g). The degree of roasting did not correlate with the levels of these compounds. Significant decreases in roasting-related aroma volatiles such as 2-methylbutanal, 3-methylbutanal, furfural, 2-phenylacetaldehyde, 2,3-butanedione, 2-methylpyrazine, and 1-methylthio-2-propanol were observed by 4 weeks of storage independent of the degree of roast or storage conditions.

Journal of Agricultural and Food Chemistry, Feb 14, 2019

Understanding almond flavor, in terms of both sensory aspects and chemistry, is essential for pro... more Understanding almond flavor, in terms of both sensory aspects and chemistry, is essential for processors to maintain almond quality and to correctly identify acceptable or unacceptable product. This overview of the sensory and chemical characteristics of almond flavor discusses raw and heat-processed almonds, the volatile compounds generated upon heating, the aroma qualities associated with various odorants, and the use of descriptive sensory analysis for sweet almonds. Flavor development and off-flavors in almonds due to rancidity is also explored. The review examines the existing methods used to assess common nonvolatile as well as volatile indicators of lipid oxidation in almonds and the correlation of these indicators with consumer acceptance. Recent research on the relationship among volatile profile, rancidity indicators, and consumer acceptance is presented.

Journal of Agricultural and Food Chemistry, Oct 20, 2011

A sensitive and reliable LC-(ESI)MS/MS method was developed and validated for the simultaneous an... more A sensitive and reliable LC-(ESI)MS/MS method was developed and validated for the simultaneous analysis of five common advanced glycation endproducts (AGEs) after enzymatic digestion in raw and roasted almonds. AGEs included carboxymethyl-lysine (CML), carboxyethyl-lysine (CEL), pyralline (Pyr), argpyrimidine (Arg-p), and pentosidine (Pento-s). This method allows accurate quantitation of free and AGEÀprotein adducts of target AGEs. Results indicate that CML and CEL are found in both raw and roasted almonds. Pyr was identified for the first time in roasted almonds and accounted for 64.4% of free plus bound measured AGEs. Arg-p and Pento-s were below the limit of detection in all almond samples tested. Free AGEs accounted for 1.3À26.8% of free plus bound measured AGEs, indicating that protein-bound forms predominate. The roasting process significantly increased CML, CEL, and Pyr formation, but no significant correlation was observed between these AGEs and roasting temperature.

Robust UHPLC-(ESI+)-MS/MS Method for Simultaneous Analysis of Glucoraphanin, Sulforaphane, and Sulforaphane Metabolites in Biological Samples

ACS food science & technology, Jul 6, 2023

Lipid Oxidation and Volatile Compounds of Almonds as Affected by Gaseous Chlorine Dioxide Treatment to Reduce Salmonella Populations

Journal of Agricultural and Food Chemistry, Mar 22, 2023

Journal of Food Quality, Aug 13, 2018

Olives are one of the oldest food products in human civilization. Over the centuries, numerous me... more Olives are one of the oldest food products in human civilization. Over the centuries, numerous methods have been developed to transform olives from a bitter drupe into an edible fruit. Methods of processing table olives rely on the acid, base, and/or enzymatic hydrolysis of bitter phenolic compounds naturally present in the fruit into nonbitter hydrolysis products. Today, there are three primary methods of commercial table olive processing: the Greek, Spanish, and Californian methods, in addition to several Artisanal methods. is review focuses on the technological, microbiological, chemical, and sensory aspects of table olive processing and the inherent bene ts and drawbacks of each method. e table olive industry is facing challenges of environmental sustainability and increased consumer demand for healthier products. Herein, we examine current research on novel technologies that aim to address these issues.

Biochemistry, Apr 28, 1998

Mass spectrometric analysis of proteolysis products of haloenol lactone-modified glutathione S-tr... more Mass spectrometric analysis of proteolysis products of haloenol lactone-modified glutathione S-transferase isozyme mGSTP1 indicates that the haloenol lactone 3-cinnamyl-5(E)-bromomethylidenetetrahydro-2-furanone is covalently attached to the protein at Cys-47. Comparisons of the extent of adduct formation with losses in enzymatic activity indicate that mGSTP1 exhibits greatest reactivity toward the haloenol lactone, followed by mGSTM1 and mGSTA3. Activities of mGSTP1 and mGSTM1 decrease in inverse proportion to haloenol lactone concentration, whereas modification had no apparent effect on catalytic activity of mGSTA3. Decreases in activity agree with the extent of protein modification observed in ESI mass spectra for mGSTP1 and mGSTM1 but not for mGSTA3. Kinetic studies employing recombinant human proteins with replacement of cysteine by serine at Cys-47 and Cys-101 indicate that rapid inactivation (t 1/2) 2 min) occurs only when residue 47 is cysteine. Mass spectra of C47S-hGSTP1 incubated with haloenol lactone demonstrate covalent attachment of a haloenol lactone-glutathione conjugate and suggest that an ester forms between the lactone and Ser-47. Therefore, we propose that initial opening of the lactone ring is promoted by Cys-47 through thioester formation between the lactone carbonyl and the Cys-47 sulfhydryl. Enol-keto tautomerization and enzyme-mediated hydrolytic cleavage of the thioester produces a reactive R-bromoketone which reacts a second time with Cys-47 and inactivates the enzyme. These results suggest that Pi class GSTs have thioesterase activity and that haloenol lactone inactivation occurs through an enzyme-mediated process.

Journal of Agricultural and Food Chemistry, Mar 21, 2017

In almonds, there is no standard method for detecting oxidative changes and little data correlati... more In almonds, there is no standard method for detecting oxidative changes and little data correlating consumer perception with chemical markers of rancidity. To address this, we measured peroxide values (PV), free fatty acid values (FFAs), conjugated dienes, tocopherols, headspace volatiles, and consumer hedonic response in light roasted (LR) and dark roasted (DR) almonds stored under conditions that promote rancidity development over 12 months. Results demonstrate that, although rancidity develops at different rates in LR and DR almonds, consumer liking was not significantly different between LR and DR almonds. Average hedonic ratings of almonds were found to fall below a designated acceptable score of 5 ("neither like nor dislike") by 6 months of storage. This did not correspond with recommended industry rejection standard of PV < 5 mequiv peroxide/kg oil and FFA < 1.5% oleic. FFAs remain well below <1.5% oleic during storage, indicating that FFAs are not a good marker of rancidity in roasted almonds stored in low humidity environments. Regression of consumer liking to concentration of rancidity indicators revealed that selected headspace volatiles, including heptanal, octanal, nonanal, 2-octenal, 2-heptanone, 2pentylfuran, hexanal, and pentanal, had a better correlation with liking than did nonvolatile indicators.

Biochemical Journal, Jul 1, 1997

Cytosolic glutathione S-transferase (GST) isoenzymes from brain, heart, lung, liver, kidney and g... more Cytosolic glutathione S-transferase (GST) isoenzymes from brain, heart, lung, liver, kidney and gonads of male and female CD-1 mice were identified and quantified with a combination of affinity purification, electrospray ionization MS, Edman microsequencing, Western blot analysis and reverse-phase HPLC. The three principal hepatic GST subunits, mGSTA3 (25 271 Da), mGSTP1 (23 478 Da), and mGSTM1 (25 839 Da), were isolated from liver, lung, kidney, testes and female heart, whereas brain, ovaries and male heart contained mGSTM1 and mGSTP1. Additional isoenzymes were detected in tissues, including mu class subunits mGSTM2 (25 580 Da) and mGSTM3 (25 570 Da), an N-terminally blocked Alpha subunit (25 480 Da) assigned as mGSTA4, and proteins of molecular masses 25 490, 22 540, 24 493, 24 378 and 25 383 Da. Distinct gender differences in expression of GST subunits were observed for liver, heart,

Food Chemistry, May 1, 2014

A robust HS-SPME and GC/MS method was developed for analyzing the composition of volatiles in raw... more A robust HS-SPME and GC/MS method was developed for analyzing the composition of volatiles in raw and dry-roasted almonds. Almonds were analyzed directly as ground almonds extracted at room temperature. In total, 58 volatiles were identified in raw and roasted almonds. Straight chain aldehydes and alcohols demonstrated significant but minimal increases, while the levels of branch-chain aldehydes, alcohols, heterocyclic and sulfur containing compounds increased significantly (500-fold) in response to roasting (p < 0.05). Benzaldehyde decreased from 2934.6 ± 272.5 ng/g (raw almonds) to 315.8 ± 70.0 ng/g (averaged across the roasting treatments evaluated i.e. 28, 33 and 38 min at 138°C) after roasting. Pyrazines were detected in only the roasted almonds, with the exception of 2,5-dimethylpyrazine, which was also found in raw almonds. The concentration of most alcohols increased in the roasted samples with the exception of 2-methyl-1-propanol, 3-methyl-1-butanol and 2-phenylethyl alcohol, which decreased 68%, 80%, and 86%, respectively.