Saeed A. Hayek

Recent Application of Probiotics in Food and Agricultural Science

Probiotic foods are a group of functional foods with growing market shares and large commercial interest [1]. Probiotics are live microorganisms which when administered in adequate amounts confer a beneficial health benefit on the host [2]. Probiotics have been used for centuries in fermented dairy products. However, the potential applications of probiotics in nondairy food products and agriculture have not received formal recognition. In recent times, there has been an increased interest to food and agricultural applications of probiotics, the selection of new probiotic strains and the development of new application has gained much importance. The uses of probiotics have been shown to turn many health benefits to the human and to play a key role in normal digestive processes and in maintaining the animal’s health. The agricultural applications of probiotics with regard to animal, fish, and plants production have increased gradually. However, a number of uncertainties concerning technological, microbiological, and regulatory aspects exist [3].

The Microbiota Is Essential for the Generation of Black Tea Theaflavins-Derived Metabolites

Background Theaflavins including theaflavin (TF), theaflavin-3-gallate (TF3G), theaflavin-3′-gallate (TF3′G), and theaflavin-3,3′-digallate (TFDG), are the most important bioactive polyphenols in black tea. Because of their poor systemic bioavailability, it is still unclear how these compounds can exert their biological functions. The objective of this study is to identify the microbial metabolites of theaflavins in mice and in humans. Methods and Findings In the present study, we gavaged specific pathogen free (SPF) mice and germ free (GF) mice with 200 mg/kg TFDG and identified TF, TF3G, TF3′G, and gallic acid as the major fecal metabolites of TFDG in SPF mice. These metabolites were absent in TFDG- gavaged GF mice. The microbial bioconversion of TFDG, TF3G, and TF3′G was also investigated in vitro using fecal slurries collected from three healthy human subjects. Our results indicate that TFDG is metabolized to TF, TF3G, TF3′G, gallic acid, and pyrogallol by human microbiota. Moreover, both TF3G and TF3′G are metabolized to TF, gallic acid, and pyrogallol by human microbiota. Importantly, we observed interindividual differences on the metabolism rate of gallic acid to pyrogallol among the three human subjects. In addition, we demonstrated that Lactobacillus plantarum 299v and Bacillus subtilis have the capacity to metabolize TFDG. Conclusions The microbiota is important for the metabolism of theaflavins in both mice and humans. The in vivo functional impact of microbiota-generated theaflavins-derived metabolites is worthwhile of further study.

Antimicrobial Activity of Xoconostle Pears (Opuntia matudae) against Escherichia coli O157:H7 in Laboratory Medium.

The objective of this study was to investigate the antimicrobial activity of xoconostle pears (Opuntia matudae) against Escherichia coli O157:H7. Xoconostle pears were sliced, blended, and centrifuged. The supernatant was then filtered using a 0.45 μm filter to obtain direct extract. Direct extract of xoconostle pears was tested against four strains of E. coli O157:H7 in brain heart infusion (BHI) laboratory medium using growth over time and agar well diffusion assays. Our results showed that direct extract of xoconostle pears had a significant (P < 0.05) inhibitory effect at 4, 6, and 8% (v/v) concentrations and complete inhibitory effect at 10% (v/v) during 8 h of incubation at 37°C. Minimum inhibitory volume (MIV) was 400 μL mL−1 (v/v) and minimum lethal volume (MLV) was 650 μL mL−1 (v/v). The inhibitory effect of xoconostle pears found to be concentration dependent and not strain dependent. Thus, xoconostle pears extract has the potential to inhibit the growth of E. coli O157:H7 and could provide a natural means of controlling pathogenic contamination, thereby mitigating food safety risks.

Enzymatic activity of Lactobacillus reuteri grown in a sweet potato based medium with the addition of metal ions

The effect of metal ions on the enzymatic activity of Lactobacillus reuteri was studied. The enzymatic activity was determined spectrophotometrically using the corresponding substrate. In the control group, L. reuteri MF14-C, MM2-3, SD2112, and DSM20016 produced the highest α-glucosidase (40.06 ± 2.80 Glu U/mL), β-glucosidase (17.82 ± 1.45 Glu U/mL), acid phosphatase (20.55 ± 0.74 Ph U/mL), and phytase (0.90 ± 0.05 Ph U/mL) respectively. The addition of Mg2+ and Mn2+ led to enhance α-glucosidase produced by L. reuteri MM2-3 by 113.6% and 100.6% respectively. α-Glucosidase produced by MF14-C and CF2-7F was decrease in the presence of K+ by 65.8 and 69.4% respectively. β-Glucosidase activity of MM7 and SD2112 increased in the presence of Ca2+ (by 121.8 and 129.8%) and Fe2+ (by 143.9 and 126.7%) respectively. Acid phosphatase produced by L. reuteri CF2-7F and MM2-3 was enhanced in the presence of Mg2+, Ca2+ or Mn2+ by (94.7, 43.2, and 70.1%) and (63.1, 67.8, and 45.6%) respectively. On the other hand, Fe2+, K+, and Na+ caused only slight increase or decrease in acid phosphatase activity. Phytase produced by L. reuteri MM2-3 was increase in the presence of Mg2+ and Mn2+ by 51.0 and 74.5% respectively. Ca2+ enhanced phytase activity of MM2-3 and DSM20016 by 27.5 and 28.9% respectively. The addition of Na+ or Fe2+ decreased phytase activity of L. reuteri. On average, Mg2+ and Mn2+ followed by Ca2+ led to the highest enhancement of the tested enzymes. However, the effect of each metal ion on the enzymatic activity of L. reuteri was found to be a strain dependent. Therefore, a maximized level of a target enzyme could be achieved by selecting a combination of specific strain and specific metal ion.

Antibacterial and Antioxidant Activities of Essential Oils from Artemisia herba-alba Asso., Pelargonium capitatum radens and Laurus nobilis L.

Essential oils are natural antimicrobials that have the potential to provide a safer alternative to synthetic antimicrobials currently used in the food industry. Therefore, the aim of this study was to evaluate the antimicrobial and antioxidant activities of essential oils from white wormwood, rose-scented geranium and bay laurel against Salmonella typhimurium and Escherichia coli O157:H7 on fresh produce and to examine consumer acceptability of fresh produce treated with these essential oils. Our results showed that essential oil derived from rose-scented geranium exhibited the most effective antimicrobial activity at the same and similar minimum inhibition concentration levels (0.4%, v/v and 0.4% and 0.5%, v/v) respectively against Salmonella typhimurium and Escherichia coli O157:H7. All three essential oils showed antioxidant properties, with the highest activity occurring in bay laurel essential oil. In a sensory test, tomatoes, cantaloupe and spinach sprayed with 0.4% rose-scented geranium essential oil received higher scores by panelists. In conclusion, rose-scented geranium essential oil could be developed into a natural antimicrobial to prevent contamination of Salmonella typhimurium and Escherichia coli O157:H7 in fresh produce, plus this oil would provide additional health benefits due to the antioxidant properties of its residue.

Sweet Potatoes as a Basic Component in Developing a Medium for the Cultivation of Lactobacilli

A sweet potato medium (SPM) was formed with extract from baked sweet potatoes supplemented with 0, 4, or 8 g/L of each nitrogen source (beef extract, yeast extract, and proteose peptone #3) to form SPM1, SPM2, and SPM3 respectively. Lactobacilli MRS was used as control medium. Ten Lactobacillus strains containing an average of 2.34 ± 0.29 log CFU/mL were inoculated individually into batches of MRS, SPM1, SPM2, and SPM3. The growth patterns for the tested Lactobacillus strains growing in SPM2 and SPM3 were found to be similar to that in MRS. The average final population after 24 h of incubation in MRS, SPM2, and SPM3 reached 10.41 ± 0.35, 10.59 ± 0.27, and 10.72 ± 0.19 log CFU/mL respectively. SPM2 and SPM3 maintained higher pH values throughout the incubation period than MRS. These findings indicate that SPM2 can be a suitable medium for the growth of Lactobacillus and can provide an alternative at low-cost.

Enzymatic Activity of Lactobacillus Grown in a Sweet Potato Base Medium

The objective of this work was to study the enzymatic activity of Lactobacillus in a sweet potato-based medium (SPM). SPM was formed using an extract from baked sweet potatoes and supplemented with 4 g/L of each nitrogen source (beef extract, yeast extract, and proteose peptone #3). Lactobacillus strains were grown in SPM and MRS for 16 h at 37 °C and then plated to determine the final bacterial populations. The strains were screened spectrophotometrically for α-glucosidase, β-glucosidase, acid phosphatase, and phytase using the corresponding substrate. Our results showed no significant (p > 0.05) differences in the final bacterial populations of Lactobacillus strains grown in SPM and MRS. All Lactobacillus strains, except L. reuteri, showed similar α-glucosidase and β-glucosidase activity in SPM and MRS. L. reuteri showed lower α-glucosidase and higher β-glucosidase activity in SPM compared to MRS. Acid phosphatase activity of Lactobacillus in SPM was similar to that in MRS except for L. reuteri SD2112 having higher acid phosphatase in SPM than MRS. In regard to phytase, all strains showed higher activity in SPM than MRS. Strains of L. reuteri showed the highest enzymatic activity of α-glucosidase, acid phosphatase, and phytase whereas L. delbrueckii subsp. bulgaricus SR35 showed the highest β-glucosidase activity. Thus, the growth of Lactobacillus in a SPM could result in enhanced or comparable level of enzymatic activity while showing similar growth compared to MRS.

Effect of Metal Ions on the Enzymatic Activity of Lactobacillus reuteri Growing in a Sweet Potato Medium

The objective of this study was to determine the effect of metal ions on α-glucosidase, β-glucosidase, acid phosphatase, and phytase activity of L. reuteri. In the control group, L. reuteri MF14-C, MM2-3, SD2112, and DSM20016 produced the highest α-glucosidase (40.06 ± 2.80 Glu U/mL), β-glucosidase (17.82 ± 1.45 Glu U/mL), acid phosphatase (20.55 ± 0.74 Ph U/mL), and phytase (0.90 ± 0.05 Ph U/mL) respectively. The addition of Mg2+ and Mn2+ led to an increase in α-glucosidase activity of L. reuteri MM2-3 by 23.46 and 20.77 Glu U/mL respectively. The β-glucosidase activity of MM7 and SD2112 increased in the presence of Ca2+ by 9.65 and 9.85 and Fe2+ by 11.4 and 9.62 Glu U/mL respectively. Acid phosphatase produced by L. reuteri CF2-7F and MM2-3 increased in the presence of Mg2+, Ca2+, and Mn2+ by 13.53, 6.17, and 10.01 and 5.54, 5.92, and 3.98 Ph U/mL respectively. Phytase produced by L. reuteri MM2-3 increased in the presence of Mg2+ and Mn2+ by 0.26 and 0.38 Ph U/mL respectively. On average, Mg2+ and Mn2+ followed by Ca2+ led to the highest enhancement of tested enzymes. The effect of metal ions on the enzymatic activity of L. reuteri was found to be strain dependent. Thus, the enzymatic activity of L. reuteri could be enhanced by the addition of metal ions, with the specific selection of metal ions being necessary to maximize the level of the target enzyme.

Using Sweet Potatoes as a Basic Component to Develop a Medium for the Cultivation of Lactobacilli

Sweet potatoes (Ipomoea batatas) were investigated as a basic component to develop a medium for the cultivation of lactobacilli. Extract from baked sweet potatoes was used to form a sweet potato medium (SPM) which was supplemented with 0, 4, or 8 g/L of each nitrogen source (beef extract, yeast extract, and proteose peptone #3) to develop SPM1, SPM2, and SPM3, respectively. The growth of Lactobacillus in SPM was compared to lactobacilli MRS. Low inoculums’ levels (2–2.5 log CFU/mL) were used to investigate the suitability of SPM to support the growth of Lactobacillus. Lactobacillus strains were individually inoculated into batches of MRS, SPM1, SPM2, and SPM3 then incubated at 37 °C. The growth of Lactobacillus was monitored using turbidity (OD at 610 nm), bacterial population (log CFU/mL), and pH values. Our results showed no significant differences (p < 0.05) in the maximum specific growth rates (μ max) of Lactobacillus strains growing in MRS, SPM2, and SPM3. After 24 h on incubation, Lactobacillus strains grown in SPM2, SPM3, and MRS reached averages of 10.59 ± 0.27, 10.72 ± 0.19, and 10.41 ± 0.35 log CFU/mL, respectively. Slower growth rates were observed in SPM1 with 1.57 ± 0.55 log CFU/mL less of bacterial populations than MRS. SPM2 and SPM3 maintained higher pH values throughout the incubation period compared to MRS. Therefore, these findings indicated that SPM2, containing 12 g/L of nitrogen sources, is suitable for the growth of Lactobacillus, and SPM2 could be used as an alternative low-cost medium.

Interaction Between Bifidobacterium and Medical Drugs

Probiotics are live microorganisms which when administered in adequate amounts confer beneficial health benefits to the host. However, commonly consumed medical drugs may interact with probiotic bacteria and influence their viability and functionality. The objective of this study was to determine the impact of commonly administered medical drugs on the survival of Bifidobacterium. Five strains of Bifidobacterium (B. breve, B. longum, B. infantis, B. adolescentis, and B. bifidium) were individually grown in MRS broth at 37 °C for next day use. One tablet of commonly used medical drug (Aleve, Aspirin, Tylenol, Hydro, Lisinopril, Metformin, Metoprolol, or Glipizide) was completely dissolved into batches of 9 mL MRS broth then samples were inoculated with 1 mL of overnight grown cultures. Samples were incubated at 37 °C for 2 h and bacterial populations were determined immediately after exposure to medical drugs and after 2 h of incubation. Our result showed a decrease in bifidobacteria population by an average of 3.0 ± 0.25 log CFU/mL in the presence of tested drugs. Arthritis drug (Aleve, Aspirin, and Tylenol) showed higher killing effect on bifidobacteria compared to other tested drugs. These findings suggested that intake of common medical drugs may decrease the viability of probiotic bacteria and may reflect their contribution to human health. The intake of probiotic dietary supplements and functional foods may reduce the negative effect of medical drugs on probiotics.