Lilian M. Were

Encapsulation of nisin and lysozyme in liposomes enhances efficacy against Listeria monocytogenes.

The efficacy and stability against Listeria monocytogenes of nisin and lysozyme encapsulated in phospholipid liposomes was evaluated. Antimicrobial-containing liposomes were prepared by hydrating dried lipids with buffer containing nisin, nisin plus the fluorescence probe calcein, or calcein and lysozyme. Mixtures were then centrifuged and sonicated, and encapsulated liposomes were collected using size-exclusion chromatography. Antimicrobial concentration in liposomes was determined by bicinchoninic acid assay prior to determination of antimicrobial activity against strains of L. monocytogenes. When nisin was encapsulated in liposomes, protein concentrations of 0.39, 0.27, and 0.23 mg/ml for phosphatidylcholine (PC), PC-cholesterol (7:3), and PC-phosphatidylglycerol (PG)-cholesterol (5:2:3), respectively, were obtained. Encapsulation of nisin with calcein yielded protein concentrations of 0.35, 0.39, and 0.28 mg/ml for PC, PC-cholesterol, and PC-PG-cholesterol, respectively. Encapsulation of calcein with lysozyme resulted in protein concentrations of 0.43, 0.26, and 0.19 mg/ml for PC, PC-cholesterol, and PC-PG-cholesterol, respectively. Encapsulated nisin in 100% PC and PC-cholesterol liposomes inhibited bacterial growth by >2 log CFU/ml compared with free nisin. Growth inhibition with liposomal lysozyme was strain dependent, with greater inhibition observed for strains 310 and Scott A with PC-cholesterol and PC-PG-cholesterol liposomes. Inhibition of L. monocytogenes indicated the potential of liposomes to serve as delivery vehicles for antimicrobials in foods while improving stability of antimicrobials.

Inhibition of lipid oxidation in refrigerated and frozen salted raw minced chicken breasts with electron beam irradiated almond skin powder.

Antioxidant effects of electron beam irradiated almond skin powder (ASP) in raw minced chicken breasts (MCB) during refrigerated and frozen storage were studied. MCB samples were treated with BHT, non-irradiated ASP (0kGy), irradiated ASP (10kGy, 20kGy and 30kGy) and compared to MCB without antioxidants. Colour was determined on initial and final day of analysis while conjugated dienes (CD), peroxide values (POV), TBARS and hexanal content were evaluated periodically for 12 days of refrigerated storage and seven months of frozen storage. ASP addition lowered L* values compared to MCB without ASP or BHT. During refrigerated storage, MCB containing ASP had decreased formation of lipid oxidation products ranging from 0 to 66%, 7 to 24%, 0 to 37% and 4 to 71% reduction in POV, CD, TBARS and hexanal content, respectively, as compared to MCB without antioxidants over duration of study. A 15-65%, 3-25%, 14-50% and 28-82% reduction in POV, CD, TBARS and hexanal content, respectively, for frozen MCB was detected.

Effect of Maillard reaction products on oxidation products in ground chicken breast

Three amino acid-sugar solutions were adjusted to pH 8.0, heated and lyophilized prior to addition to ground chicken breast (GCB). GCB with no additives, GCB with 0.01% BHT, GCB with 0.1 or 0.2mg/g glucose heated with arginine, valine, or histidine were prepared. Thiobarbituric acid reactive substances (TBARS), volatiles determined by gas chromatography, and Hunter L*, a* and b* values were monitored over nine days. Multiple linear regression models were used to determine the effects of the studied factors on the corresponding outcome variables. a* values of GCB ranged from 1.60 to 4.90 over nine days of storage. While Maillard reaction products (MRP) lowered oxidation compared to control, no significant difference in TBARS between MRP solutions heated for 8 or 24h was found. Further, 0.1mg/g heated glucose-valine mixture decreased aldehydes up to 72.87%. Therefore, shelf-life of GCB could be extended using 0.1 or 0.2mg/g MRP.

Utilization of Electron Beam Irradiated Almond Skin Powder as a Natural Antioxidant in Ground Top Round Beef

Defatted Carmel variety almond skin powder (ASP) irradiated at 0, 10, 20, and 30 kGy was mixed with ground top round beef at 0.5% (w/w) and stored at 4 degrees C. Color stability, peroxide values (PV), conjugated dienes (CD), thiobarbituric acid reactive species (TBARS), and hexanal were determined periodically over a 2-wk period. The L values were not affected by time or treatment. Initially, the redness (a value) was higher for both the negative control with no ASP (a value of 21.83) and positive control with 0.01% BHT (a value of 22.33) compared to samples that contained the ASP (a values from 17.70 to 20.17) on day 1. This decrease in redness was attributed to the presence of the ASP. Similar to day 1, the a values were not significantly different between the 2 controls over the duration of the study. All the samples with ASP exhibited lower lipid oxidation when compared to the negative control, with greatest oxidation retardation observed at 20 and 30 kGy. Over the treatment period, a 13% to 85% reduction in PV and a 40% to 80% reduction in TBARS were observed in the sample with 30 kGy ASP compared to the negative control. Generally, PV and TBARS of samples with ASP decreased with an increase in irradiation dose. While a difference due to irradiation dose was not observed in CD and hexanal content, the values were significantly lower (P < 0.05) than the controls over time. This study demonstrates that almond skin power could be used to extend the shelf life of refrigerated ground raw beef.

Capillary liquid chromatography–mass spectrometry for the rapid identification and quantification of almond flavonoids

A rapid negative ion ESI high-performance capillary liquid chromatography-mass spectrometry method was developed to identify and quantify flavonoids (e.g., flavanols, flavonols, flavanones and glycosides). Fifteen standards and two varieties of almond skin extract powder (Carmel and Nonpareil) were used to demonstrate the chromatographic separation, reproducibility and accuracy of the method that employed a 150 mm x 0.3 mm ChromXP 3C18-EP-120 column. All standards eluted in less than 10 min, providing a 9-12x reduction in analysis time compared to existing methods (90-120 min). However, isomers (e.g., catechin/epicatechin and galactosides/glucosides) were not resolved and, therefore, identified and quantified collectively. RSDs for retention time and peak area reproducibility (mass spectrometry data) were <0.5% and <5.0%, respectively. Peak area reproducibility was greatly improved (from a RSD>10%) after the implementation of a low-flow metal needle in the ESI source. Quantitation by mass spectrometry also afforded a % error less than 5% for most compounds.

Extraction, identification, and quantification of flavonoids and phenolic acids in electron beam-irradiated almond skin powder.

The effect of electron beam irradiation doses from 0 to 30 kGy on extraction yield and phenolic compounds was evaluated in almond skin phenolic extracts (ASPE). Total soluble phenols and distribution of phenolic compounds from acidified methanol ASPE and 52% methanol ASPE were quantified using Folin-Ciocalteau method, liquid chromatography with diode array and fluorescence detection, and negative ion electrospray-mass spectrometry. Electron beam irradiation increased extraction yield by as much as 23%, with the greatest increase observed in the acidified methanol ASPE. Irradiated samples extracted with acidified methanol also exhibited an increase in extractable phenols (Folin-Ciocalteau) and total HPLC-resolved phenolics at all irradiation doses. Samples extracted with 52% methanol exhibited an increase at 10 and 20 kGy, but a 31% decrease at 30 kGy. An increase in aglycones respective to their glycosides was not observed with irradiation. Therefore, the increase in phenolics was attributed to release of phenolics from their cellular matrix.

Effect of Coffee Filtrate, Methylglyoxal, Glyoxal, and Caffeine on Salmonella Typhimurium and S. Enteritidis Survival in Ground Chicken Breasts

The antimicrobial effect of roasted coffee filtrate (CF) and dicarbonyls on Salmonella Typhimurium and Salmonella Enteritidis in raw ground chicken breast meat (GCB) was investigated. Coffee was brewed and filtered before addition to GCB. Coffee filtrate with and without added caffeine, methylglyoxal, and/or glyoxal was added to GCB and then inoculated with Salmonella Typhimurium and Salmonella Enteritidis. Ground chicken samples were stomached with peptone water at days 1, 3, 5, and 7, plated on XLD agar with a TSA overlay, and Salmonella survivors were enumerated. CF alone gave less than a 1 Log reduction in all runs compared to control GCB with no treatment. Methylglyoxal (2.28 mg/g GCB) had the greatest antimicrobial effect against Salmonella Typhimurium and Salmonella Enteritidis in GCB with average Log reductions of 2.27 to 3.23, respectively, over the 7 d duration of the experiment compared to control GCB with no treatment. A 1 Log reduction was observed in GCB with CF, 0.93 mg glyoxal, and 1 mg caffeine/g chicken compared to the control and GCB with only CF. Heat-produced coffee compounds could potentially reduce Salmonella in retail ground chicken and chicken products.

Anti-Listeria monocytogenes activity of heat-treated lyophilized pomegranate juice in media and in ground top round beef.

Heat treatment can affect antimicrobial activity of plant by-products by altering phenolic content and composition and forming melanoidins. The antilisterial efficacy of heat-treated and unheated lyophilized pomegranate juice (LPJ) was determined. The LPJ was heated at 100 degrees C for 0, 30, 60, or 120 min and added at 2% (wt/wt) to ground top round beef, which was then cooked and inoculated with individual L. monocytogenes strains. Samples of meat stored at 5 degrees C were taken at days 1, 8, 14, and 21 and plated onto Oxford medium for enumeration of bacteria. The MIC of LPJ was determined, and agar well diffusion assays were conducted. Against five L. monocytogenes strains, LPJ had a MIC of 1.50 to 1.75% (wt/vol) and 16.8- to 20.0-mm zones of inhibition. In general, no significant differences in L. monocytogenes levels between the various treatments, including the commercial sodium lactate-sodium diacetate combination, were detected at days 1 and 8. The LPJ (0, 30, 60, and 120 min of heating) significantly inhibited growth of all five L. monocytogenes strains in refrigerated ground cooked beef by 1.80 to 4.61 log CFU/g at day 21. Heating did not negatively impact LPJ antilisterial activity. Addition of LPJ lowered pH values by 0.3 units. The L*, a*, and b* values of cooked ground beef with LPJ changed during the study by 3.4 to 4.43, 0.44 to 0.8, and 0.57 to 1.36 units, respectively, compared with the control. This is the first investigation to confirm pomegranates antilisterial activity in vitro and in ground beef.

Chlorogenic Acid Oxidation-Induced Greening of Sunflower Butter Cookies as a Function of Different Sweeteners and Storage Conditions

Sunflower butter use as an allergen-free alternative to tree and legume nut butter in baking is limited by chlorogenic acid induced greening that occurs at alkaline pH. Limited information is available on controlling this greening in a food matrix. This study examined how different liquid sweeteners and relative humidity influenced greening of sunflower butter cookies. Doughs had similar initial pH (7.52-7.66) which increased to 8.44-9.13 after baking as ranked: xylitol>maple syrup>corn syrup>honey>agave syrup. Cookies made with maple syrup had the highest moisture and greening corresponding with lowest free chlorogenic acid. The % greening followed the same trend as greening intensity, and was positively correlated (r=0.9101) with chlorogenic-lysine adduct content. Our findings provide an ingredient solution to controlling greening, as results demonstrate that greening can be promoted with high relative humidity storage, and use of high moisture and pH ingredients. Unwanted greening can be inhibited by simply changing the liquid sweetener.

Lipid and protein antioxidant capacity of dried Agaricus bisporus in salted cooked ground beef

Dried Agaricus bisporus powder (DAB)s antioxidant capacity was tested in refrigerated cooked ground beef (CGB) containing 0, 1 or 1.5% NaCl. Lipid and protein oxidation products were monitored over time and correlated with changes in phenolic content. On day 16, 88-94% lower malondialdehyde (MDA) was found in CGB with DAB compared to control (1.15mg MDA/kg samples). Volatile aldehydes were up to 99% lower on day 16 in CGB with DAB than controls. In unsalted CGB, thiols dropped by 82% in control compared to <60% in CGB with DAB. On day 16, tryptophan fluorescence decline in unsalted control was higher (28%) than that in CGB with rosemary or DAB (2.4-5.5%) while Schiff bases declined in control and CGB+1% DAB, but increased in CGB+2% and 4% DAB. DABs extension of shelf life was concentration dependent. Phenolic compounds had moderate to strong negative correlations with MDA up to day 10 indicating a possible role of DAB phenolics in preventing malondialdehyde production.