Effects of gallotannin treatment on attachment, growth, and survival of Escherichia coli O157:H7 and Listeria monocytogenes on spinach and lettuce

Food-borne illness outbreaks are increasingly associated with fresh produce. Their high prevalence may reflect the lack of methods to effectively remove pathogenic bacteria from the surface of fruits and vegetables. This study evaluated the effect of antimicrobial gallotannins on attachment, growth, and survival of food-borne pathogens on green leafy vegetables. Spinach leaves and interior leaves of lettuce harboring high and low cell counts of background microbiota, respectively, were washed with tap water with and without added gallotannins. To account for the variability among organisms, green leafy vegetables were inoculated with strain cocktails of Escherichia coli O157:H7 and Listeria monocytogenes. Cell counts of L. monocytogenes were significantly reduced by the gallotannin treatment. Lower cell counts after storage for 8?days at 4?°C demonstrated antimicrobial effects of gallotannins retained on the surface of green leafy vegetables. Gallotannin treatments with 1?g/L did not inhibit E. coli O157:H7 but hindered their attachment to filter paper by up to 94?%. The addition of gallotannin-containing extracts from mango (Mangifera indica L.) kernels to the washing water did neither alter color nor texture of bagged fresh-cut products. In conclusion, gallotannin treatment significantly reduced surface contamination of green leafy vegetables with L. monocytogenes and reduced the attachment of cells of E. coli O157:H7.     

Effects of Bacillus coagulans as an adjunct starter culture on yogurt quality and storage

Bacillus coagulans has been widely studied for its probiotic properties. Therefore, identifying a strain that can be used as an adjunct starter culture for yogurt production would have commercial value. In this study, 30 B. coagulans strains were isolated from vegetable samples from 11 provinces or autonomous regions in China, and their pan-genomic and phylogenetic characteristics were analyzed. Phylogenetic analysis categorized 30 strains into 4 different subphylotypes, including subtype I (11 isolates), subtype II (7 isolates), subtype III (11 isolates), and subtype IV (1 isolate). Four B. coagulans strains (B. coagulans-70, B. coagulans-78, B. coagulans-79, and B. coagulans-100) were randomly selected from each subphylotype of the phylogenetic tree as adjunct starter cultures. Compared with the other tested strains, B. coagulans-70 showed the highest count in yogurt at the end of the manufacturing period. Comparative genome analysis indicated that the different bacterial levels of B. coagulans strains in yogurt may be associated with the abundance of genes related to carbohydrate transport and metabolism (e.g., sucrose utilization). Finally, differences in texture and volatile flavor compound profiles were observed between the yogurt samples. Compared with the other groups, the addition of B. coagulans-70 exerted a positive effect on the appearance and texture of yogurt products. Volatile analysis showed increased quantities of 2-heptanone, 2-nonanone, amyl alcohol, and 2-hydroxy-3-pentanone in the B. coagulans-70 group compared with control yogurts. These results above combined with the results of a sensory evaluation indicated that B. coagulans-70 is the most suitable strain for further use in functional dairy product development.     

Effect of blanching on the antioxidant properties of some tropical green leafy vegetables

Eight popularly consumed green leafy vegetables in Nigeria namely: Structium sparejanophora, Amarantus cruentus, Telfairia occidentalis, Baselia alba, Solanum macrocarpon, Corchorus olitorus, Vernonia amygdalina, and Ocimum gratissimum were blanched in hot water for 5 mins. The antioxidant properties of the fresh and blanched green leafy vegetables were subsequently determined. The total phenol, ascorbic acid and the antioxidant potentials as typified by reducing property and free radical scavenging activity was also determined. The results of the study revealed that blanching cause a significant (P<0.05) increase in the total phenol [fresh (0.1–0.3 g/100 g), blanched (0.2–0.6 g/100 g)] content of the green leafy vegetables except in Amarantus cruentus and Vernonia amygdalina where there was no change. Conversely, there was a significant (P<0.05) decrease in the vitamin C [fresh (43.5–148.0 mg/100 g), blanched (15.8–27.3 mg/100 g)], reducing property [fresh (0.5–1.5 absorbance), blanched (0.1–0.6 absorbance)] and free radical scavenging ability [fresh (20.0–51.4%), blanched (16.4–47.1%)] of the blanched green leafy vegetables except in Structium sparejanophora, where there was no change in the reducing property (0.6 absorbance) and free radical scavenging ability (59.8%) of the blanched vegetable. In view of this it could be concluded that blanching of vegetables though makes green leafy vegetables more palatable and less toxic, however it reduces their antioxidant properties drastically.     

Effects of Holding Methods and Time on the Vitamin Contents of Five Tropical Leafy Vegetables

Five tropical leafy vegetables, Pterocarpus soyauxii (“oha”), Pterocarpus santalinodes (“nturukpa”), Gongronema latifolium (“utazi”), Corchorus olitorius (“ahihiara”) and Amaranthus hybridus (“green”) were held for four days at ambient condition using three different popular local methods used in the Southeastern states of Nigeria. Each leafy vegetable was divided into three lots. Lots I and II were unwrapped while lot III was wrapped with broad cocoyam leaves. The three lots were held under a shade. In addition, lot II was regularly taken outside to the open at nights where it was exposed to cool air and early morning dews. The vitamin contents of each leafy vegetable lot were analysed initially and on daily basis for four days. The beta carotene and ascorbic acid contents ranged respectively from 4.88 – 9.84 μg and 105.62 – 278.65 mg per 100 g of the leafy vegetable. The five leafy vegetables are fair sources of thiamin, riboflavin and niacin. There were losses in the vitamins as holding time increased, regardless of the holding method employed. The rate of loss of vitamins was highest in Lot I (the unwrapped leaves that were kept in a shade both day and night). The rate of loss of vitamins was lowest in Lot III (the wrapped leafy vegetables).     

Antioxidant activity and profiles of common vegetables in Singapore

Sixty-six types of vegetables commonly consumed in Singapore were analysed for their hydrophilic oxygen radical absorbance capacity (H-ORAC), total phenolic content (TPC), ascorbic acid (AA) and various lipophilic antioxidants. A single batch analysis of each vegetable showed that antioxidant composition and concentration varied widely across different vegetables. The vegetables with intense colours typically have high H-ORAC, TPC, AA, and carotenoid contents. Vegetables unique to the Asian market such as matrimony vine (Lycium chinense Miller), coriander, Chinese kale, water spinach and red chilli were consistently ranked high in H-ORAC, TPC, carotenoids and vitamin E levels. Based on consumption data, Chinese Singaporeans appear to have a higher intake of lutein, zeaxanthin, β-carotene, and tocopherols compared to the US population. Overall findings suggest that dark green leafy and brightly-coloured vegetables tend to contain high antioxidants. Our data are useful reference and substantiate many public health agencies’ recommendation to consume more vegetables, particularly the dark green leafy and brightly-coloured varieties.     

Aciduric, pH-Elevating Bacillus which Cause Noneffervescent Spoilage of Underprocessed Tomatoes

In the preliminary phase of this study, a selective isolation medium was developed. Using the new medium, 24 strains of Bacillus Spp. that elevate tomato juice pH were isolated from garden soil or natural vegetative materials. Two jars of home-canned, water-bathed tomatoes contained sporeformers which produced noneffervescent spoilage. All strains were morphologically and physiologically different from 2 flat-sour strains of B. coagulans and B. licheniformis strains, but similar to a previous isolate from home-canned, spoiled green beans that elevated pH. The new medium may have future applications in isolation and enumeration of other acidurics including yeast-like microorganisms.     

Carotenoid composition and retinol equivalent in plants of nutritional and medicinal importance: Efficacy of β-carotene from Chenopodiumalbum in retinol-deficient rats

This study aimed to (1) quantify carotenoids in leafy vegetables and plants of nutritional and medicinal importance, (2) evaluate retinol equivalent (RE) of provitamin-A carotenoids and (3) determine efficacy of β-carotene from Chenopodium album and to compare with retinol formed on feeding to retinol-deficient rats for 3 weeks. β-Carotene and lutein contents (mg/100 g dry weight) ranged from 1.5 to 120 and 11.7 to 185 (leafy greens) and 0.4 to 34.7 and 11.8 to 679 (medicinal plants) whereas, α-carotene ranged from 0.3 to 35.6 (leafy greens) and 0.1 to 15.7 (medicinal plants). RE values (mg%) ranged from 0.4 to 20 and 0.42 to 5.8 in leafy greens and medicinal plants. Efficacy of β-carotene (2400 μg/kg diet) from C. album in retinol-deficient rats revealed a 93.6% rise in plasma retinol levels from 0.53 to 8.4 μM. The plants analysed are a good source of retinol precursors and biologically active lutein; therefore can be exploited to meet carotenoid requirements.     

Effects of storage condition and domestic cooking on the quality and nutrient content of African leafy vegetables (Cassia tora and Corchorus tridens)

BACKGROUND: The main objective of this research was to determine changes in nutrient content of two African leafy vegetables, Cassia tora and Corchorus tridens, on cooking and storage under different temperature conditions, i.e. room storage (20 °C), refrigerated storage (4 °C) and frozen storage (?18 °C). RESULTS: The leafy vegetables were analysed for moisture, colour (Hunter L, a, b), texture, total chlorophyll, ascorbic acid, dehydroascorbic acid and total phenolics. Results indicated that the degradation of ascorbic acid was highest as a result of frozen storage, followed by room temperature storage. The dehydroascorbic acid content was correspondingly high in frozen stored leafy vegetables, whereas it was undetectable in the room temperature and refrigerated stored materials. The total phenolic content of the leaves increased with storage time while the total chlorophyll content decreased under all storage conditions. Domestic cooking resulted in significant additional losses of ascorbic acid following storage under all temperature conditions, with only 1–10% retention in the leaves and 50–60% retention in the cooking water. The green colour of the leafy vegetables was retained best under refrigerated and frozen storage, while the peak force and toughness of the leaves increased upon storage under all conditions. The moisture content of the leafy vegetables did not show any significant difference on storage. CONCLUSION: This study is one of few to report nutrient content changes on the same raw material stored under various temperature conditions and cooked domestically. Refrigerated storage resulted in the highest retention of ascorbic acid and green colour in the leafy vegetables. Copyright © 2009 Society of Chemical Industry     

Impact of polyphenols from black tea and red wine/grape juice on a gut model microbiome

Food and beverage products derived from fruit and vegetables contain polyphenols, which have been associated with various health benefits. Polyphenols may influence health through direct uptake in the intestine but also upon interaction with the gut microbiota for example by modification of the microbial composition or by conversion of the polyphenols to further bioactive compounds. So far, there are limited studies of complex polyphenols on the human gut microbiota especially using modern molecular technologies. Most studies investigating effects of dietary polyphenols have focused on single molecules or bacterial strains. In the current study, an in vitro gut microbial ecosystem, namely simulator of the intestinal microbial ecosystem (SHIME), was challenged with either a black tea or a red wine grape extract (RWGE), both containing complex dietary polyphenol mixtures. Within the context of the model system, the effects of these interventions on both microbial numbers and composition as well as metabolite levels were assessed. Antimicrobial effects, largely confined to unculturable members of the ecosystem, were revealed by complementary microbiological techniques. Pyrosequencing analysis showed a shift in the Firmicutes:Bacteroidetes ratio for both interventions. Black tea stimulated Klebsiella, enterococci and Akkermansia and reduced bifidobacteria, B. coccoides, Anaeroglobus and Victivallis. RWGE promoted growth of Klebsiella, Alistipes, Cloacibacillus, Victivallis and Akkermansia while bifidobacteria, B. coccoides, Anaeroglobus, Subdoligranulum and Bacteroides were decreased.The study shows that these complex polyphenols in the context of a model system can modulate select members of the human gut microbiota. These members represent novel targets of polyphenol degrading or resistant microbes to be validated under physiological conditions in vivo and further investigated for polyphenol metabolism or resistance mechanisms.     

Magnetic field hydrocooling system: Effect of field intensities on the cooling characteristics of three different leavy vegetables

The physiological changes occurring during postharvest of leafy vegetables affect quality. To address this, several cooling technologies that utilize physical fields like magnetic fields (MFs) have been proposed. The application of MFs in the cooling of leafy vegetables however remains a substantial controversy among the food engineers. Therefore, the effectiveness should be clarified by experiments. In the current study, the effect of MFs (at 534.1 mT, 458.0 mT, and 396.8 mT) on hydrocooling process of three different leafy vegetables including jute mallow, fluted pumpkin, and bitter leaf was investigated by using a specially designed hydrocooling system facilitated with magnetic field (also known as magnetic field hydrocooling; MFHC) generated from a Neodymium permanent magnet. The investigation included the comparison of the cooling curves, physiological loss in weight (PLW), microbial loads, and observation of microstructures. Based on the results of the experiment, it was observed that the weak magnetic fields provided significant improvement on the hydrocooling technique as well as the quality of hydrocooled vegetables. The MFHC assisted by Neodymium magnet (at 396.8 mT) provided higher cooling rate (at P ≤ 0.05) when compared with conventional room cooling, reduced microbial loads significantly from 8.40 × 10⁵ to 5.86 × 10⁵ CFU/ml, 7.03 × 10⁵ to 5.89 × 10⁵ CFU/ml and 6.00 × 10⁵ to 4.0 × 10⁵ CFU/ml (at P ≤ 0.05) for jute mallow, fluted pumpkin and bitter leaf respectively. In addition, hydrocooling-assisted by magnetic field (at 396.8 mT) is more effective in the preservation of the microstructures. The study indicates that the MFHC technology enhances cooling process and preserves the leafy vegetables, thus pose great potential in the food industry.Practical applicationsLeafy vegetables deteriorate faster after harvest; hence, there is a need to cool them in order to extend their shelf-life. MFHC technique has great potentials in preservation of leaves, with the advantage of minimum quality loss due to reduction in cooling time and microbial activities. Currently, innovative studies have been carried out on the use of MFHC technique to improve the cooling process and achieve better quality preservation. However, the findings presented in this work can provide detail insights on the quality of some leafy vegetables that were cooled by MFHC, and give some guidance for further developments of MFHC technology.     

Nutritional and sensory evaluation of Atriplex triangularis leaves

Leaves of Atriplex triangularis (AT), a highly salt-tolerant plant, were evaluated for nutritional and sensory characteristics. Samples of frozen AT, along with commercial brands of spinach and mustard green, were analyzed for proximate composition, ascorbic acid and vitamin A. Several minerals were determined on dried samples of AT and spinach. Sensory evaluations of these vegetables were conducted. On the basis of the nutritional analysis and the sensory evaluation, AT leaves have good potential for use as a green leafy vegetable.     

The evaluation of electrolysed water as an agent for reducing micro-organisms on vegetables

The efficacy of electrolysed oxidizing water in reducing micro‐organisms on vegetables was evaluated. Formation of brown spots on leafy and fruit vegetables could be avoided when they were soaked in acidic electrolysed oxidizing (AC) water for less than 9 and 15 min, respectively. Soaking in alkaline electrolysed (AK) water for 30 min did not affect the appearance of the vegetables. The effectiveness of water or AK water on aerobic plate count (APC) reduction was limited (0.5 log CFU g^?1). However, soaking in AC water alone effectively reduced APC values of leafy vegetables and fruit vegetables by 1.0–1.5 log CFU g^?1. Soaking in AC water followed by AK water further reduced APC by 0.5 and 0.7 log CFU g^?1 on leafy cabbage and green pepper, respectively. Continuous changing of electrolysed water with either shaking or ultrasonication can effectively reduce APC by 2–2.5 log CFU g^?1. Electrolysed oxidizing water was significantly more effective than water in eliminating micro‐organisms on vegetables.     

Quality evaluation of probiotic pasta produced with Bacillus coagulans GBI-30

Nowadays, the production of non-dairy and heat-treated probiotic foods has been gaining high interest. With this aim, due to its spore-forming ability Bacillus coagulans has been widely used in research studies. In this study, probiotic pasta production was accomplished with the addition of Bacillus coagulans GBI-30 spores into semolina. Samples were packed in zip-lock bag and stored at room temperature for 6 months. The microbiological characteristics, cooking behavior, texture, color and sensory attributes of pasta samples were investigated at 0 and 6 months of storage. Results showed that B. coagulans GBI-30 count of pasta samples decreased from 7.20 to 6.08 log CFU/g during cooking and storage showed statistically significant effect on B. coagulans GBI-30 count. At the end of the cooking in boiling (100 °C) distilled water for 8 min, B. coagulans GBI-30 did not negatively affect the sensorial quality of pasta according to the sensory panel of 7 experts. Therefore, it was concluded that the pasta can be considered as a probiotic product after 6 months of storage at room temperature due to the fact that B. coagulans GBI-30 count was above 6 log CFU/g.     

Effect of using mycotoxin-detoxifying agents in dairy cattle feed on natural whey starter biodiversity

Natural whey cultures (NWC) are undefined multiple-strain bacterial starter communities that can be affected by even small changes along the entire dairy chain. We applied a multidisciplinary approach to investigate how the addition of 2 mycotoxin-detoxifying agents [sodium smectite and lignocellulose-based material (B1); leonardite and betaine (B2)] to cow diets modified the microbiota of the NWC in manufacture of a Grana-like cheese. Microbiological and flow cytometry analyses showed that the content and viability of lactic acid bacteria (LAB) and the total whey microbiota were not affected by the detoxifying agents, and Streptococcus thermophilus, Lactobacillus helveticus, and Limosilactobacillus fermentum were the dominant taxa. Random amplified polymorphic DNA-PCR fingerprinting and metagenomic analysis highlighted differences in the bacterial community of the NWC and in the relative abundance of Bacteroidetes that increased when B1 and B2 were included in the diet. Two of 6 St. thermophilus biotypes were detected only in control samples; conversely, none of the Lb. helveticus biotypes found in control samples were isolated from B1 and B2. In vitro tests showed that the 2 binders did not significantly affect the development of St. thermophilus, but they stimulated the growth of Lb. helveticus strains recovered only from B1 and B2 NWC. The addition of binders in cow feed can affect the LAB biotypes present in NWC.     

Simple quantitative analysis of Escherichia coli K-12 internalized in baby spinach using Fourier Transform Infrared spectroscopy

Bacterial contamination continues to be a serious concern for food safety. Although washing fresh produce helps in reducing pathogen levels, pathogen internalization often limits the effectiveness of washing. When pathogens internalize in leafy vegetables, the method of identification and quantitative measurement would be called into question. This study was aimed to use Fourier Transform Infrared (FTIR) spectroscopy integrated with an attenuated total reflectance kit for quantification of Escherichia coli K-12 internalized in baby spinach. The bacteria were inoculated into vascular and intracellar tissues of spinach leaves by syringe injection and the distribution of internalized E. coli K-12 cells was confirmed under scanning electron microscopy (SEM). FTIR measurement following the preparation of bacterial suspension from spinach leaves with high speed pulverizing enabled to detect the absorbance peaks in the amide II region between 1590 and 1490 cm⁻¹ as a fingerprint for the microbes. It was found that the estimated concentrations of E. coli K-12 agreed well with the concentrations determined by plate counting with R² values of 0.98 and 0.97 in peptone water and spinach extracts, respectively. The results demonstrated that FTIR can identify and quantify E. coli K-12 in baby spinach extracts at a limit of detection of approximately 100 CFU/mL in 5 min. The developed method is expected to be suitable for the analysis of pathogenic E. coli strains and other bacterial species in fresh vegetables.     

An exopolysaccharide from a probiotic: Biosynthesis dynamics,composition and emulsifying activity

An exopolysaccharide (EPS) was isolated from Bacillus coagulans RK-02. Time course accumulation of EPS was studied with respect to biomass growth. The probiotic bacterium produces an EPS during exponential and stationary growth phases. Growth kinetics of the producer organism was characterized. The probiotic bacterium exhibited high affinity for the growth limiting substrate and hence grows at a higher specific growth rate. Based on HPLC and FTIR analyses, the EPS was found to be heteropolymer composed of galactose, mannose, fucose, glucose and glucosamine. The EPS showed significant emulsifying activities in different vegetable oils/hydrocarbon substrates. To the best of our knowledge, this is the first report on a bacterial EPS with fucose as a constituent sugar and also the first report on an EPS from B. coagulans.     

Survival of probiotic bacteria in a whey cheese vector submitted to environmental conditions prevailing in the gastrointestinal tract

Various foods may be used to deliver probiotic bacteria into the gastrointestinal tract; one such example is Requeijão, a Portuguese whey cheese. Survival and stability of Bifidobacterium animalis strains BLC-1, Bb-12, and Bo, Lactobacillus acidophilus strains LAC-1 and Ki, L. paracasei ssp. paracasei strain LCS-1 and L. brevis strain LMG 6906 inoculated into Requeijão, when exposed to simulated gastrointestinal tract conditions, were assessed. Homogenates of inoculated whey cheese in 0.85% (w/v) sterile saline water were exposed to a solution of hydrochloric acid (pH 2.5–3.0) and pepsin (1000 units mL^–1) at 37 °C, and then to 0.3% (w/v) bile salts after 60 or 120 min of acid exposure. All bacterial strains retained their initial viable cell numbers. Bifidobacterium animalis strains Bb-12 and Bo, and L. brevis strain LMG 6906 exhibited the highest viable cell numbers when exposed to bile salts, whereas the other strains had variable death rates.     

Evaluation of antioxidant potential in selected green leafy vegetables

Green leafy vegetables represent a class of underexploited plants that are stipulated to be rich sources of natural antioxidants. A fundamental study of free radical-scavenging activity in four plant species, namely Trigonella foenum-graecum, Centella asiatica, Sauropus androgynus and Pisonia alba, was carried out by measuring the ability of methanol extracts of these plants to scavenge radicals generated by in vitro systems and by their ability to inhibit lipid peroxidation. The levels of non-enzymatic antioxidants were also determined by standard spectrophotometric methods. Correlation and regression analysis established a positive correlation between some of these antioxidants and the in vitro free radical-scavenging activity of the plant extracts. The conclusions drawn from the study indicate that in vivo studies, isolation and analysis of individual bioactive components will reveal the crucial role that these plants may play in several therapeutic formulations.     

Determination of mineral element composition of Ayoyo,Baobab and Dandelion vegetable green leaves in Ghana using instrumental neutron activation analysis

The present investigation was undertaken to determine the nutritional compositions (mineral elements) of three green leafy vegetable; Dandelion (Taraxacum Officinale), Ayoyo (Corchorus Olitorius) and Baobab (Adasonia Digitata). The ultimate goal is to improve nutrition and health by advocating for increased consumption of indigenous green leafy vegetables with an objective to increasing public acceptance, awareness and utilization. The mineral elements were determined using instrumental neutron activation analysis, over 20 elements were detected. However, 14 mineral elements were quantitatively evaluated on the basis of k₀-method and relative comparator method. The leaves were characterized with high concentration of Mg, Ca, Cl and K, and substantive amount of Mn, Fe, Zn, Cu and I. The composition of the mineral elements and its respective percent contribution to Recommended Dietary Allowance/Adequate Intake (RDA/AI) for various life groups indicates that reasonable consumption of any of the three green leafy vegetable can contribute substantive amount of daily nutritional requirement for minor nutrients like; I, Cu, Zn, Mn, and Fe as well as major nutritional (Mg, Ca, Cl and K) needs for all life groups. Each of the leaves was also characterize with high K/Na ratios. Tolerable upper intake levels (UL) analysis also showed no significant abuse for the mineral elements determined. Other potential toxic elements (As, Cd and Hg) and non-nutritional minerals (Br, V, Al and Ba) were either not detected or were found in low concentrations.     

Carotenoid and chlorophyll composition of commonly consumed leafy vegetables in Mediterranean countries

Major chloroplast pigments in five leafy vegetables (chicory-Cichorium intybus, cv. ‘Anivip’ and cv. ‘Monivip’, dandelion-Taraxacum officinale, garden rocket-Eruca sativa and wild rocket-Diplotaxis tenuifolia), commonly consumed in Mediterranean countries, have been separated by high-performance liquid chromatography (HPLC) on a reversed-phase column. Three classes of pigments were identified and quantified: xanthophylls (oxygenated carotenoids), carotenes (hydrocarbon carotenoids) and chlorophylls. The contents of the pigments in the analysed leafy vegetables varied significantly. The results indicated that selected leafy vegetables were moderately rich in xanthophylls, primarily lutein (3.87–7.44 mg/100 g fwt). Other xanthophylls were detected in relatively small quantities. The provitamin A carotenoids (α- and β-carotene) were also detected, but α-carotene were not present in chicory cultivars and in dandelion. The ratio of chlorophyll a/b varied from 2.44 to 2.67 depending on the species. The highest content of all the analysed constituents was found in the garden rocket.