Multifunctionality of Rapeseed Meal Protein Isolates Prepared by Sequential Isoelectric Precipitation

Rapeseed meal is a by-product of the oil-producing industry with a currently underestimated application. Two protein isolates, PI_2.5–8.5 or PI_10.5–2.5, were obtained from industrial rapeseed meal after treatment with an aqueous ethanol solution. The alkaline-extracted proteins were sequentially precipitated by two different modes, from pH 10.5 to 2.5, and vice versa, from 2.5 to 8.5, with a step of 1 pH unit. The preparation approach influenced both the functional and antioxidant properties of the isolates. The PI_10.5–2.5 exhibited higher water and oil absorption capacities than PI_2.5–8.5, reaching 2.68 g H₂O/g sample and 2.36 g oil/g sample, respectively. The emulsion stability of the PI_2.5–8.5, evaluated after heating at 80 °C, was either 100% or close to 100% for all pH values studied (from 2 to 10), except for pH 6 where it reached 93.87%. For the PI_10.5–2.5, decreases in the emulsion stability were observed at pH 8 (85.71%) and pH 10 (53.15%). In the entire concentration range, the PI_10.5–2.5 exhibited a higher scavenging ability on 2,2-diphenyl-1-picryl hydrazyl (DPPH) and hydroxyl radicals than PI_2.5–8.5 as evaluated by DPPH and 2-deoxyribose assays, respectively. At the highest concentration studied, 1.0%, the neutralization of DPPH radicals by PI_10.5–2 reached half of that exhibited by synthetic antioxidant butylhydroxytoluene (82.65%). At the same concentration, the inhibition of hydroxyl radicals by PI_10.5–2 (71.25%) was close to that achieved by mannitol (75.62%), which was used as a positive control. Established antioxidant capacities add value to the protein isolates that can thus be used as both emulsifiers and antioxidants.

Preliminary Characterisation of Wastes Generated from the Rapeseed and Sunflower Protein Isolation Process and Their Valorisation in Delaying Oil Oxidation

Since rapeseed and sunflower meals are two of the most representative oilseed crops in the world, this study was focused on ethanol-wash solutes (EWS) obtained as wastes from the protein isolation process of rapeseed and sunflower meals. These meals have been previously valorised; however, the use of the EWS is unexplored. The present study is aimed at the characterisation of their phenolic profile, and antioxidant capacity for preventing lipid oxidation in rapeseed, sunflower, and soybean oil, which has been used as a reference oil. The sunflower EWS exhibited more total phenolic compounds (TPC) and antioxidant activity (119.39 ± 1.13 mg GA/g and 193.97 ± 9.77 mg TE/g, respectively) than the rapeseed one (103.44 ± 5.94 mg GA/g and 89.51 ± 3.17 mg TE/g). The phenolic identification showed hydroxybenzoic and protocatechuic acid in the rapeseed EWS, and pyrogallol and caffeic acid in the sunflower EWS, as the main representative phenols. Both EWS at 15% increased significantly (p < 0.05) the oxidative stability of the oils in the Rancimat equipment with values of antioxidant activity index (AAI) from 1.01 to 1.20, depending on the type of oil employed. In conclusion, the rapeseed and sunflower EWS showed great potential, and they could be used as a source of natural antioxidants within the food industry, replacing the synthetic ones, and promoting the circular economy since they are agro-food wastes.

Stability of sunflower and rapeseed oil-in-water emulsions supplemented with ethanol-treated rapeseed meal protein isolate

A protein isolate (ERPI) was prepared from ethanol-treated rapeseed meal and used as a stabilizing agent in sunflower and rapeseed oil-in-water emulsions. The aim of the current study was to explore the influence of protein and oil concentrations on initial stability of sunflower and rapeseed oil-in-water emulsions by evaluating Gibbs free energy (ΔG) and particle size distribution. The 7-day dynamics of emulsion stability was investigated by turbidity measurement as well. A 32 factorial design was applied to assess the significance of oil (5%, 10% and 15% w/w) and ERPI protein (0.25%, 0.5% and 1.0% w/w) addition on stability of the emulsions. The results demonstrated that the increase of oil concentrations from 5 to 15% positively influenced the initial stability of sunflower and rapeseed oil-in-water emulsions. In both oil types, ERPI protein supplementation at all levels resulted in significant differences in the stability of 5% and 10% oil emulsions but did not alter the initial stability of the emulsions prepared with either 15% sunflower or rapeseed oil. With a few exceptions, there was a good agreement between Gibbs free energy data and microstructural profiles of the emulsions. Overall, emulsions with all sunflower oil concentrations and 1.0% ERPI protein exhibited better initial and a 7-day stability dynamics compared to all rapeseed oil-based emulsions. The study demonstrated the potential of ethanol-treated rapeseed meal protein isolate to serve as an emulsifying agent in sunflower and rapeseed oil containing emulsions.

Foaming properties of acid-soluble protein-rich ingredient obtained from industrial rapeseed meal

The use of the rapeseed meal as a source for preparation of protein-rich ingredients for the food industry is an alternative to the current limited application as a feed additive. The aim of this study was to evaluate foaming properties of an acid-soluble protein-rich ingredient (ASP) obtained from industrial rapeseed meal as a co-product of a protein isolate. Foam capacity and stability over a period of 60 min were evaluated by using volumetric and image analyzing methods. The influence of NaCl at two boundary concentrations (0.03 and 0.25 M) was studied over a pH range from 2 to 10. The ASP exhibited high foamability (> 90%), not influenced by pH or salt addition. In contrast, foam stability, measured over a 60 min period, was pH and NaCl dependent. By the end of the observation period, the addition of 0.25 M NaCl reduced the foam volume by more than 70% at all pH values. After 30 min at pH values 4, 6 and 8, which are the most common for food products, the foams without NaCl retained 51, 38 and 41% of the initial foam volume, respectively. The results were in agreement with image analysis observations where microstructure of the foams with NaCl was more heterogeneous than that of the foams without salt addition. The high foamability and relatively high foam stability at pH from 4 to 8 without NaCl addition shows that ASP could be a potential alternative to plant proteins currently used as foaming agents in the food industry.

Pepsin-Assisted Transglutaminase Modification of Functional Properties of a Protein Isolate Obtained from Industrial Sunflower Meal

The utilization of industrial sunflower meal to produce protein-rich products for the food industry is an alternative approach for better and more efficient use of this agricultural by-product. Sunflower meal proteins possess specific functional properties, which however need improvement to broaden their potential as supplements for delivering high--quality products for human nutrition. The aim of the study is to evaluate the combined influence of low-degree pepsin hydrolysis and transglutaminase (TG) modification on industrial sunflower meal protein isolate functionality at pH=2 to 10. Three TG-modified pepsin hydrolysates with the degree of hydrolysis of 0.48, 0.71 and 1.72% were produced and named TG-PH1, TG-PH2 and TG-PH3, respectively. All three TG-modified pepsin hydrolysates exhibited improved solubility at pH between 3.5 and 5.5 as the highest was observed of TG-PH3 at protein isoelectric point (pI=4.5). Sunflower meal protein isolate and TG-modified sunflower meal protein isolate had greater solubility than the three TG-modified hydrolysates at pH<3 and >7. Significant improvement of foam making capacity (p<0.05) was achieved with all three TG-modified pepsin hydrolysates in the entire pH area studied. Pepsin hydrolysis of the protein isolate with the three degrees of hydrolysis did not improve foam stability. Improved thermal stability was observed with TG-PH3 up to 80 °C compared to the protein isolate (pH=7). At 90 °C, TG modification of the protein isolate alone resulted in the highest thermal stability. Pepsin hydrolysis followed by a treatment with TG could be used to produce sunflower protein isolates with improved solubility, foam making capacity and thermal stability for use in the food industry.

Reduction of nitrogen excretion and emission in poultry: A review for organic poultry

Organic poultry is an alternative to conventional poultry which is rapidly developing as a response to customers' demand for better food and a cleaner environment. Although organic poultry manure can partially be utilized by organic horticultural producers, litter accumulation as well as excessive nitrogen still remains a challenge to maintain environment pureness, animal, and human health. Compared to conventional poultry, diet formulation without nitrogen overloading in organic poultry is even more complicated due to specific standards and regulations which limit the application of some supplements and imposes specific criteria to the ingredients in use. This is especially valid for methionine provision which supplementation as a crystalline form is only temporarily allowed. This review is focused on the utilization of various protein sources in the preparation of a diet composed of 100% organic ingredients which meet the avian physiology need for methionine, while avoiding protein overload. The potential to use unconventional protein sources such as invertebrates and microbial proteins to achieve optimal amino acid provision is also discussed.

Assessment of a food microbiology senior undergraduate course as a potential food safety distance education course for poultry science majors

Distance education courses have become popular due to the increased number of commuter students as well as people already in the workforce who need further education for advancement within their careers. A graduate-level Web-based course entitled Special Topics-Poultry Food Safety Microbiology was developed from an existing senior undergraduate advanced food microbiology course in the Poultry Science Department at Texas A&M University. Conversion of standard lecture material into a distance education course can provide unique challenges to maintain comparable course content in an asynchronous manner. The overall objective for this course was to examine bacterial activities including ecology in food, animals, raw and processed meat, eggs, and human pathogenesis. Students were surveyed at the end of the class and the majority agreed that they would be willing to take the course as an online course, although they were not willing to pay an extra fee for an online course. The majority of students used the online version of the course as a supplement to the classroom rather than as a substitute.

Microbial inhibitory and radical scavenging activities of cold-pressed terpeneless Valencia orange (Citrus sinensis) oil in different dispersing agents

BACKGROUND

Due to their low solubility in water, oil-based bioactive compounds require dispersion in a surface-active agent or appropriate solvents to ensure maximum contact with microorganisms. These combinations, however, may change their physical and/or chemical characteristics and consequently alter the desired functionality. The objective of this study was to determine the impact of selected dispersing agents, ethanol, dimethyl sulfoxide (DMSO), and Tween-80, on cold-pressed terpeneless (CPT) Valencia orange oil to function as a free radical scavenger and an antimicrobial food additive.

RESULTS

When dissolved in ethanol or DMSO, the orange oil fraction had similar minimum inhibitory concentrations (MIC) for Listeria monocytogenes ATCC 19 115 (0.3% and 0.25% v/v respectively), which were significantly lower (P <or= 0.5) than the MIC for Salmonella typhimurium ATCC 14 028 (1% v/v). Both ethanol and DMSO oil dispersion systems exhibited an intermediate MIC (0.75% v/v) for Lactobacillus plantarum WCFS1. The orange oil (up to 3%) in an aqueous solution of 0.1% Tween-80 yielded no inhibitory activities against any of the test bacteria. However, the 1% natural orange oil dispersed in Tween-80 exhibited 56.86% 2,2-diphenyl-1-picryl hydrazyl (DPPH) radical inhibition versus 18.37% and 16.60% when the same level of orange oil was dissolved in DMSO or ethanol, respectively. At the same orange oil concentration, the oil/Tween-80 suspension yielded 57.92% neutralization of hydroxyl radicals. This represents 71.37% of the mannitol antioxidant activity, which was used as a positive control.

CONCLUSIONS

These findings suggest that Tween-80 is an appropriate dispersing agent only if the antioxidant functionality is desired. If both antimicrobial and antioxidant properties are needed, the CPT Valencia orange oil should be dispersed in either DMSO or ethanol.

Potential for development of an Escherichia coli-based biosensor for assessing bioavailable methionine: a review

Methionine is an essential amino acid for animals and is typically considered one of the first limiting amino acids in animal feed formulations. Methionine deficiency or excess in animal diets can lead to sub-optimal animal performance and increased environmental pollution, which necessitates its accurate quantification and proper dosage in animal rations. Animal bioassays are the current industry standard to quantify methionine bioavailability. However, animal-based assays are not only time consuming, but expensive and are becoming more scrutinized by governmental regulations. In addition, a variety of artifacts can hinder the variability and time efficacy of these assays. Microbiological assays, which are based on a microbial response to external supplementation of a particular nutrient such as methionine, appear to be attractive potential alternatives to the already established standards. They are rapid and inexpensive in vitro assays which are characterized with relatively accurate and consistent estimation of digestible methionine in feeds and feed ingredients. The current review discusses the potential to develop Escherichia coli-based microbial biosensors for methionine bioavailability quantification. Methionine biosynthesis and regulation pathways are overviewed in relation to genetic manipulation required for the generation of a respective methionine auxotroph that could be practical for a routine bioassay. A prospective utilization of Escherichia coli methionine biosensor would allow for inexpensive and rapid methionine quantification and ultimately enable timely assessment of nutritional profiles of feedstuffs.

Effect of soluble maillard reaction products on cadA expression in Salmonella typhimurium

The presence of Maillard reaction products (MRP) in foods and food components is due to the non-enzymatic reaction between protein and carbohydrate residues triggered by thermal steps during food processing. The objective of this study was to assess the effect of MRPs and increasing lysine concentrations on S. Typhimurium growth and the expression of cadA which may be an indirect determinant of Salmonella virulence response. Variations in lysine concentrations (from 0 to 0.5 mM) did not exert any effect either on the final optical density after 6-hour incubation or the growth rates of S. Typhimurium in media containing MRPs. In contrast to the reduced final absorbancy of the bacterial cultures grown with histidine and arginine MRPs supplementations (0.1%), growth rates, in general, remained unaltered by all MRPs at each lysine concentration when compared to the control (M9 pH 5.8, no MRPs added). The induction levels of cadA in media containing 0.1% MRPs were close to cadA induction in the reference media (M9, pH 5.8 and no MRPs) and did not exceed the corresponding values by more than approximately 30%. Although the observed negligible induction of cadA under these conditions complies with the concept of its potential "anti-virulence" function, additional studies involving various concentrations and more refined MRPs are needed.

Escherichia coli, an Intestinal Microorganism, as a Biosensor for Quantification of Amino Acid Bioavailability

In animal diets optimal amino acid quantities and balance among amino acids is of great nutritional importance. Essential amino acid deficiencies have negative impacts on animal physiology, most often expressed in sub-optimal body weight gains. Over supplementation of diets with amino acids is costly and can increase the nitrogen emissions from animals. Although in vivo animal assays for quantification of amino acid bioavailability are well established, Escherichia coli-based bioassays are viable potential alternatives in terms of accuracy, cost, and time input. E. coli inhabits the gastrointestinal tract and although more abundant in colon, a relatively high titer of E. coli can also be isolated from the small intestine, where primary absorption of amino acids and peptides occur. After feed proteins are digested, liberated amino acids and small peptides are assimilated by both the small intestine and E. coli. The similar pattern of uptake is a necessary prerequisite to establish E. coli cells as accurate amino acid biosensors. In fact, amino acid transporters in both intestinal and E. coli cells are stereospecific, delivering only the respective biological l-forms. The presence of free amino- and carboxyl groups is critical for amino acid and dipeptide transport in both biological subjects. Di-, tri- and tetrapeptides can enter enterocytes; likewise only di-, tri- and tetrapeptides support E. coli growth. These similarities in addition to the well known bacterial genetics make E. coli an optimal bioassay microorganism for the assessment of nutritionally available amino acids in feeds.

Ciprofloxacin-sensitive and ciprofloxacin-resistant Campylobacter jejuni are equally susceptible to natural orange oil-based antimicrobials

A total of 10 ciprofloxacin-sensitive (ciprofloxacin minimum inhibitory concentration, MIC < 0.5 micro g/ml) and 10 ciprofloxacin-resistant (MIC 16 to 32 micro g/ml) presumptive C. jejuni were further characterized and evaluated for their inhibition by natural orange oil fractions. Partial species identification was performed by using a hippuricase gene-based polymerase chain reaction (PCR) assay. One of the isolates appeared to be atypical and failed to hydrolyze hippurate. Of the ciprofloxacin-resistant C. jejuni isolates tested, six were found to have their quinolone resistance determined by a C --> T mutation in codon 86 of gyrA. Both groups of ciprofloxacin-sensitive and -resistant C. jejuni isolates were most susceptible to cold-pressed terpeneless Valencia orange oil (C4) which yielded inhibition zones from 44.0 +/- 1.4 to 80 +/- 0.0 mm. Less inhibitory responses were recorded for 5-fold concentrated Valencia orange oil (C3) and distilled d-limonene (C7) which exerted similar effects on both ciprofloxacin-sensitive and -resistant C. jejuni isolates. In general, ciprofloxacin-resistant and -sensitive C. jejuni isolates were equally susceptible to the respective orange oil fractions.

Induction of cadBA in an Escherichia coli lysine auxotroph transformed with a cad-gfp transcriptional fusion

CadBA functions as a part of overall Escherichia coli response to low extracellular pH. A gfpmut3 structural gene transcriptionally fused to the cadBA promoter (Pcad) was used as a reporter to monitor changes in intracellular lysine as a potential factor influencing cadBA induction. Different patterns of cadBA induction were observed in two E. coli strains with different lysine biosynthetic capabilities. In E. coli ZK126 (pJBA25-Pcad), a lysine prototroph, maximum levels of induction were detected 3 h after the transfer of bacterial cells under inducing conditions (pH 5.8; 3.4 microM extracellular lysine). The induction subsequently decreased until hour 7 after which no further change in expression was observed. However, in the lysine depleted strain E. coli ATCC 23812 (pJBA25-Pcad) which is an auxotroph for lysine, no decrease in cadBA expression was observed over time under the same induction conditions. Although no time dependent statistical differences in intracellular lysine were observed, bacterial cells depleted for no longer than 4 h (1.38 +/- 0.25 micromol lysine/g cell dry weight) exhibited more rapid induction of cadBA (after 3 h) and a lower maximum level of induction compared to cells with relatively lower intracellular lysine (approximately 1.08 micromol/g cell dry weight). For the latter, the detectable level of induction was delayed for 1 h but the maximum level of induction response was higher.

Campylobacter and Arcobacter species sensitivity to commercial orange oil fractions

Seven orange oil fractions were screened for their ability to inhibit the growth of selected Campylobacter and Arcobacter spp. using the standard agar-disk diffusion assay. Cold pressed (CP) terpeneless Valencia orange oil was found to be the most inhibitory to both Campylobacter jejuni and Campylobacter coli, exhibiting maximum zones of inhibition up to 80+/-0.0 mm. Five-fold concentrated Valencia oil and distilled d-limonene resulted in Campylobacter inhibition zones ranging from 11.0+/-1.4 to 44+/-1.4 mm against both C. jejuni and C. coli. No inhibition of Arcobacter spp. was detected by 6 out of 7 orange fractions except CP terpeneless Valencia orange oil which produced inhibition zones varying from 9.5+/-0.7 to 29+/-1.4 mm. Naturally occurring C. jejuni UAF 244 was isolated from a whole retail chicken, confirmed by hippuricase gene PCR assay, and used to determine antimicrobial capacities of the CP terpeneless Valencia orange oil and limonene when applied on chicken legs and thighs. The two types of chicken parts did not influence the antimicrobial strength of both orange fractions. While the observed reduction of C. jejuni cells attached to the skin varied approximately 1.5 to 2 logarithms compared to the control, the growth inhibition of the bacterial cells by limonene in the rinse increased by 6-fold and complete inhibition without recovery of detectable viable cells occurred when CP Valencia orange oil was applied. The study demonstrated the potential of the selected commercial orange oil fractions to serve as natural antimicrobials against C. jejuni, C. coli, and Arcobacter spp.

In vitro fermentation response of laying hen cecal bacteria to combinations of fructooligosaccharide prebiotics with alfalfa or a layer ration

The objective of this in vitro study was to evaluate the effects of combining a prebiotic with alfalfa on fermentation by laying hen cecal bacteria. Cecal contents from laying hens were diluted to a 1:3,000 concentration with an anaerobic dilution solution and added to serum tubes filled with ground alfalfa or a layer ration with or without fructooligosaccharide (FOS) prebiotic. Samples were processed in an anaerobic hood, pressurized by using a pressure manifold, and incubated at 37 degrees C. Volatile fatty acid (VFA) and lactic acid concentrations were quantified at 6 and 24 h of substrate fermentation. In this study, fermentation of alfalfa resulted in greater production of acetate, VFA, and lactic acid compared with the layer ration. Although with a relative inconsistency in data between trials, the amendment of FOS to both alfalfa and the layer ration appeared to further increase fermentation as demonstrated by overall higher propionate, butyrate, VFA, and lactic acid concentrations. The effect was more pronounced after 24 h of fermentation, implying time constraints for the optimal production of fermentation products in the chicken gastrointestinal tract. These data indicate that in vitro cecal fermentation can be enhanced by the addition of FOS.

The influence of a fructooligosaccharide prebiotic combined with alfalfa molt diets on the gastrointestinal tract fermentation, Salmonella enteritidis infection, and intestinal shedding in laying hens

Molting is a natural process, which birds undergo to rejuvenate their reproductive organs. The US poultry egg production industry has used feed withdrawal to effectively induce molt; however, susceptibility of Salmonella Enteritidis has encouraged the development of alternative methods. Previous research conducted in our laboratory showed that alfalfa is effective at molt induction and provides equivalent postmolt production numbers and quality when compared with feed withdrawal. In the attempt to further increase the efficacy of alfalfa molt diet and decrease the chicken susceptibility to Salmonella Enteritidis during molt, fructooligosaccharide (FOS) was added to a combination of 90% alfalfa and 10% layer ration in 2 levels (0.750 and 0.375%). Ovary and liver colonization by Salmonella Enteritidis in 3 and 2 of the 4 trials, respectively, were reduced (P <or= 0.05) in hens fed FOS-containing diets compared with hens subjected to feed withdrawal. Significant decreases in ce-cal Salmonella Enteritidis counts were also observed in 2 of the 4 trials. In 3 of the 4 trials, the same diets did not affect (P > 0.05) the production of cecal total volatile fatty acids when compared with hens undergoing feed withdrawal. However, in all 3 alfalfa molt diets, the concentrations of lactic acid were greater (P <or= 0.05) than hens with feed withdrawal, but no differences (P > 0.05) were observed among hens fed alfalfa combined with FOS and hens fed alfalfa/layer ration without FOS. Overall, given the similarities between hens fed 0.750% FOS (H) and 0.375% FOS (L), molt diets combined with the lower level of FOS should be sufficient.

Foodborne Salmonella ecology in the avian gastrointestinal tract

Foodborne Salmonella continues to be a major cause of salmonellosis with Salmonella Enteritidis and S. Typhimurium considered to be responsible for most of the infections. Investigation of outbreaks and sporadic cases has indicated that food vehicles such as poultry and poultry by-products including raw and uncooked eggs are among the most common sources of Salmonella infections. The dissemination and infection of the avian intestinal tract remain somewhat unclear. In vitro incubation of Salmonella with mammalian tissue culture cells has shown that invasion into epithelial cells is complex and involves several genetic loci and host factors. Several genes are required for the intestinal phase of Salmonella invasion and are located on Salmonella pathogenicity island 1 (SPI 1). Salmonella pathogenesis in the gastrointestinal (GI) tract and the effects of environmental stimuli on gene expression influence bacterial colonization and invasion. Furthermore, significant parameters of Salmonella including growth physiology, nutrient availability, pH, and energy status are considered contributing factors in the GI tract ecology. Approaches for limiting Salmonella colonization have been primarily based on the microbial ecology of the intestinal tract. In vitro studies have shown that the toxic effects of short chain fatty acids (SCFA) to some Enterobacteriaceae, including Salmonella, have resulted in a reduction in population. In addition, it has been established that native intestinal microorganisms such as Lactobacilli provide protective mechanisms against Salmonella in the ceca. A clear understanding of the key factors involved in Salmonella colonization in the avian GI tract has the potential to lead to better approach for more effective control of this foodborne pathogen.

Effects of Maillard reaction products on hilA expression in Salmonella typhimurium

Salmonella is a foodborne pathogen causing severe gastroenteritis. Three types of Maillard reaction products (MRP) generated by heat sterilization of D-glucose and L-lysine, L-histidine, and L-arginine were studied at 2 different levels of supplementation (0.5% and 1.0%) for their influence on growth and virulence of Salmonella. Two methods, namely, real-time polymerase chain reaction (RT-PCR) and a beta-galactosidase gene fusion assay, were used to determine the expression of hilA, a regulatory gene for Salmonella pathogenicity. Neither the type of MRP nor their quantities up to 1.0% affected the growth rates of S. Typhimurium EE658 (P > 0.05). When determined by beta-galactosidase assay, lysine MRP in both levels of supplementation were not found to have any effect on the hilA expression compared to the control. The addition of histidine and arginine MRP to M9 media (0.5%) increased by 2-fold hilA induction and up to 6-fold at the higher level (1%) supplementation of these compounds. Although somewhat inconsistent, RT-PCR analyses of hilA expression confirmed the greater induction effect of arginine MRP on hilA compared to lysine MRP. In contrast to beta-galactosidase assay results, however, lysine MRP were found to increase hilA expression compared to the control in both supplementation levels in all trials. The potential of MRP serving as a bacterial virulence modulator may be a factor to be considered in food thermal processing when assessing Salmonella risk for causing foodborne disease.

Extracellular antimutagenic activities of selected probiotic Bifidobacterium and Lactobacillus spp. as a function of growth phase

The capabilities of selected strains from genera Lactobacillus and Bifidobacterium to produce extracellular bioactive compounds with antimutagenic properties against benzo[a]pyrene (BaP) and sodium azide (SA) were tested as a function of growth phase. The bacterial supernatants from exponential and stationary phases were characterized with different patterns of antimutagenic activity against the two mutagens. All lactobacilli exhibited either no effect or low antimutagenicity against BaP during exponential growth. Higher antimutagenic activities of lactobacilli supernatants were observed in the stationary phase against SA as well. An exception was Lactobacillus sakei 23K which expressed a relatively low percent of inhibition of mutagenesis (PI = 28.14 +/- 7.41) in the exponential phase and no antimutagenic activity in the stationary phase. Of the bifidobacteria, only Bifidobacterium adoleascentis ATCC 15703 exhibited higher antimutagenecity against BaP in the exponential phase. The same bacterial supernatants however, did not possess any antimutagenicity against SA in either the exponential or stationary phases. B. bifidum ATCC 11863 did not express any significant differences in its activity against either BaP or SA in the exponential or stationary phases. Only B. breve ATCC 15700 expressed a high antimutagenic effect against SA in the stationary phase but exhibited no effect during exponential growth. Overall, bacterial antimutagenic responses were associated with growth phase and type of mutagen.

A cad-gfpmut3 plasmid construct in Escherichia coli for gene induction-based quantification of lysine in acid hydrolysates of feedstuffs

AIMS

To generate an inducible plasmid-borne cad-gfpmut3 transcriptional fusion and develop a method for quantification of total lysine.

METHODS AND RESULTS

The cad-gfpmut3 transcriptional fusion was constructed by cloning the cad promoter (Pcad) upstream of a promotorless gfpmut3 located on a high-copy plasmid. The construct was electroporated into Escherichia coli ZK126 and the transformed strain was subsequently used to quantify lysine in feed ingredients. Lysine standard curves based on gene induction of the bacterial cells were used for estimating acid hydrolysate lysine concentrations in four feed ingredients. Except for sorghum, no substantial differences were observed when the data for lysine in soybean (2 x 49 +/- 0 x 37%), cottonseed (1 x 82 +/- 0 x 15%), and meat and bone meal (2 x 31 +/- 0 x 24%) generated by the newly developed construct were compared with previously published data.

CONCLUSIONS

Using the cad-gfpmut3 fusion, feed derived lysine induction was measured easily and accurately, and could be a useful tool for the estimation of lysine in acid hydrolysates of feed ingredients.

SIGNIFICANCE AND IMPACT OF THE STUDY

The described approach for lysine quantification in feed ingredients represents a cost- and time-efficient method offering rapid and accurate lysine quantification of multiple samples.

Quantification of total and bioavailable lysine in feed protein sources by a whole-cell green fluorescent protein growth-based Escherichia coli biosensor

Using a fluorescent whole-cell Escherichia coli biosensor previously developed in our laboratory, we determined total and bioavailable lysine in four feed ingredients (soybean, cottonseed, meat and bone meal, and sorghum) and three complete feeds (chick starter and finisher, and swine starter). The same feed sources were analyzed for total lysine by high performance liquid chromatography (HPLC) and bioavailable lysine by chick bioassay. No significant differences were found between bioavailable lysine estimates for soybean, cottonseed, meat and bone meal, chick starter and finisher, and swine starter obtained by the fluorescent E. coli biosensor and chick bioassay. Except for sorghum, the E. coli biosensor estimates for total lysine were highly comparable to those obtained by HPLC. Comparisons were also conducted between conventionally performed optical density-based and the newly developed fluorescence-based lysine assay. The lack of significant differences in data obtained for total and bioavailable lysine by both detection modes indicated reliance and accuracy of the fluorescent E. coli biosensor. Overall results suggest that the microbial assay based on green fluorescent protein fluorescence represents a promising alternative method for lysine quantification.

In vitro anaerobic incubation of Salmonella enterica serotype Typhimurium and laying hen cecal bacteria in poultry feed substrates and a fructooligosaccharide prebiotic

The objective of this study was to investigate the effect of combining a prebiotic with poultry feeds on the growth of Salmonella enterica serotype Typhimurium (ST) in an in vitro cecal fermentation system. Cecal contents from three laying hens were pooled and diluted to a 1:3000 concentration in an anaerobic dilution solution. The cecal dilution was added to sterile test tubes filled with alfalfa and layer ration with and without fructooligosaccharide (FOS). Two controls containing cecal dilutions and anaerobic dilution solution were used. The samples were processed in the anaerobic hood and incubated at 37 degrees C. Samples were inoculated with Salmonella at 0 and 24h after in vitro cecal fermentation and plated at 0 and 24h after inoculation with ST. Plates were incubated for 24h and colony forming units (CFU) enumerated. The samples immediately inoculated with ST without prior cecal fermentation did not significantly lower ST counts 24h later. However, samples pre-incubated for 24h with cecal microflora prior to ST inoculation exhibited reduced ST CFU by approximately 2 logarithms, with the most dramatic decreases seen in alfalfa and layer ration combined with FOS. The addition of FOS to feed substrate diets in combination with cecal contents acted in a synergistic manner to decrease ST growth only after ST was introduced to 24h cecal incubations.