Shelf life extension of sliced wheat bread using either an ethanol emitter or an ethanol emitter combined with an oxygen absorber as alternatives to chemical preservatives

In the present study, the effect of active packaging [ethanol emitter (EE) or ethanol emitter combined with an oxygen absorber (EE + OA)] on shelf life extension of sliced wheat bread stored at 20 °C was investigated. Bread containing commercial preservatives (WP) and no preservatives (WOP) were taken as controls. Microbiological, physicochemical and sensory changes occurring in the product as a function of treatment and storage time were monitored for 30 days. Counts for yeasts and molds were 5.1, 3.8, 2.0 and 2.0 log cfu/g and for Bacillus cereus 4.7, 2.5, 2.3 and 2.0 log cfu/g for WOP, WP, EE and EE + OA treatments respectively after 30 days of storage. Initial pH 6.3 and 6.4, for WP and WOP samples remained fairly constant irrespective of specific treatment. Aroma quality deterioration during storage was due to the loss of volatile compounds and the formation of “off-flavors” through lipid oxidation. Neither the EE nor the EE + OA had an adverse effect on initial odor, taste and texture of bread. Based on sensory (texture) and microbiological data, shelf life was ca. 4 days for samples WOP; 6 days for samples WP; 24 days for samples containing the EE and at least 30 days for samples containing the EE + OA.     

γ-氨基丁酸对香蕉果实采后成熟的调控作用及其生理机制

香蕉是世界上最重要的水果之一,研究香蕉采后成熟与调控对香蕉品质形成及创新采后催熟技术具有重要意义。本实验室前期的研究结果发现Ma GAD1基因的表达与香蕉采后乙烯生物合成及果实成熟密切相关。本研究在此基础上,根据香蕉果实达到全黄并有黑色斑点期(YB)成熟度的天数为标准,筛选出Ma GAD1基因表达的诱导剂γ-氨基丁酸(GABA)能够促进香蕉果实采后成熟。生理学分析结果表明,外源GABA能够促使香蕉果实提前发生生理跃变。实时荧光定量PCR分析结果表明,外源GABA能够诱导Ma GAD1和Ma ACS1上调表达。因此,GABA通过诱导Ma GAD1和Ma ACS1上调表达及促进香蕉果实生理跃变,从而促进香蕉果实采后成熟。本研究不仅从理论上证明了GABA能够促进果实成熟,揭示了GABA促进果实成熟生理机制,并且从实际生产上为蕉催熟的应用提供了一种新方法。     

Evaluation of food protective property of five natural products using fresh-cut apple slice model

The present study evaluated the antioxidant (AA), antimicrobial and preservation effects of five plant derived natural products viz., Rosmarinic Acid (RA), p-Coumaric Acid (pCA), Trans-Cinnamic Acid (TCA), Hydroxyphenyllactic Acid (HPA) and Caffeic acid (CA) along with synthetic compounds (Ascorbic acid, gallic acid, citric acid and BHA) on fresh cut apple slices. Antimicrobial efficacy of these compounds against Bacillus licheniformis, Pseudomonas vulgaris, Shigella boydii, Salmonella typhi, Staphylococcus aureus, Listeria monocytogenes and Escherichia coli was found to be concentration dependent with the maximum inhibition observed at 500 microg mL(-1). A considerable AA potential of these compounds was observed in in vitro based assay system, with RA exhibiting significantly higher effect than the other compounds at 500 microg mL(-1). Furthermore the compounds at 500 microg mL(-1) significantly reduced the browning, maintained the acidic pH and restricted growth of L. monocytogenes even after 10 days of treatment. Ethanol accumulation in fresh cut apple slices increased significantly throughout the experimental period. Over all RA exhibited maximum effect in all the food preservation parameters studied suggesting that it has synchronized food protection effect and can be recommended as food additive.     

纳塔生产中污染真菌的分离与控制

纳塔生产中真菌污染现象最普遍、危害最严重。从纳塔工厂的受污染发酵液、原料椰子水及环境中分离到58株酵母、17株霉菌。研究显示,产膜醭酵母,如假丝酵母(Candidaspp.)、毕赤酵母(Pichiaspp.)是引起污染的主要真菌,它们主要来源于大量带菌的原料椰子水,由于椰子水的不恰当处理而散布到环境中。向发酵液中添加2~3g/L脱氢醋酸钠或1.5~2g/L尼泊金丁酯,可以较好地抑制产膜醭酵母而不影响木醋杆菌的生长和纳塔的合成。      

Effects of Lactobacillus buchneri isolated from tropical maize silage on fermentation and aerobic stability of maize and sugarcane silages

This study was aimed to perform a screening of Lactobacillus buchneri strains from maize silage and use them as inoculant in maize and sugarcane silages. In all, 151 lactic acid bacteria (LAB) strains were isolated from whole‐plant maize silage, and their identification was based on the sequence analysis of 16S rDNA. In total, 15 strains were categorized to the L. buchneri group and eight of these were selected based on growth rate and fermentation pattern. The selected strains were evaluated on fermentation and aerobic stability of maize and sugarcane silages. For maize, the inoculated silages had lower pH and higher LAB population, but lower acetic acid concentration in comparison with the untreated control silage. For sugarcane silage, the strains 56.1, 56.4 and 40788 resulted in highest dry‐matter (DM) content and lowest DM losses. However, only the strain 40788 showed lowest counts of yeasts and moulds. Sugarcane silages inoculated with the strains 56.9, 56.26 and the untreated control silage showed highest concentrations of lactic acid and ethanol, besides the great DM losses. Even so, for both crops, the aerobic stability was not affected by inoculation. After air exposure, all silages increased temperature and had high population of yeast and moulds. Nevertheless, the strains 56.1 and 56.4 are promising for use as a silage inoculant.     

Fermentation of yam: microbiology and sensory evaluation of cooked fermented yam tissues

The microflora of white yam ( Dioscorea rotundata L.) slices fermented anaerobically in 1.5 percent brine for five days at room temperature were studied. The hydrolysis of the carbohydrate and the subsequent conversion of sugars and minerals by the fermenting microbes contributed much to the increased microbial load especially within the first 72 hours of fermentation. The organisms implicated in the fermentation include the species of Pediococcus, Lactobacillus and Pseudomonas, Bacillus subtilis and two other Gram negative coccal cells, yet to be identified. The decrease in microbial counts at the latter stage of fermentation was attributed to the high total acidity of the medium, which was about 2.67 times the initial value of 0.027% lactic acid. Meanwhile, the lactic acid bacteria increased continuously throughout the period of fermentation.     

Initial bacteria] numbers on lucerne prior to ensiling

Populations of lactic acid bacteria (LAB) on lucerne before and after havesting were extensively monitored over a two-year period and correlated with weather data, various wilting parameters and equipment used for harvest. The LAB on standing lucerne were below detectable levels (<10 colony forming units (CFU) g lucerne⁻¹). Immediately after mowing, low levels of LAB (51 CFU g⁻¹) were found on over half the samples. During wilting, the population of LAB generally increased. The amount of increase was affected primarily by the average air temperature during wilting, the length of wilting and the drying rate. The first two variables were positively correlated with bacterial growth whereas increased drying rate adversely affected LAB numbers. If the LAB numbers in the swath were below 100 CFU g⁻¹ prior to chopping, the forage harvester inoculated the chopped lucerne an level of 10² to 10⁴ CFU g⁻¹, depending on air temperature. Considering these factors, LAB counts on chopped lucerne could be predicted within one order of magnitude approximately 95% of the time.     

Analysis of flowering dynamics heritability in the perennial warm‐season grass Paspalum dilatatum

Understanding the flowering cycles of perennial warm‐season grass species may be very important to the design of management practices and breeding. However, developmental dynamics are not well understood. As most plant traits associated with flowering dynamics do not follow a normal distribution, the use of general linear models to describe and compare these variables might be misleading. The aims of this study were (i) to find a methodology to compare panicle accumulation curves and (ii) to estimate heritabilities for flowering curve attributes. Panicle counts were recorded during a complete flowering cycle on a diverse collection of dallisgrass (Paspalum dilatatum). We compared the efficiency of different linear mixed models based on whole plot or individual plant data; then, we adjusted nonlinear regression curves for individual plants to estimate several curve attributes and compared this approach to the area under the curve. Finally, we calculated the broad‐sense heritabilities of the estimated curve parameters. The following reproductive curve attributes were obtained: panicle production potential, panicle accumulation rate and days until 3, 5, 10 and 15 panicles. We found that monitoring individual plants is more efficient when studying flowering attributes. Significant differences among genotypes for several flowering cycle attributes were found. Heritabilities were very high for all flowering cycle initiation and duration attributes. We also showed that the number of days until the emergence of a given low number of panicles can be used as a highly heritable measure to characterize flowering cycles.     

Prediction of lactic acid bacterial numbers on lucerne

The numbers of lactic acid bacteria (LAB), as measured by Rogosa SL agar, on lucerne ( Medicago sativa ) chopped for ensiling were predicted using two methods. The first prediction method consisted of regression equations developed from two previous harvesting seasons and required inputs of wilting time between mowing and chopping, average wilting temperature and moisture content of the lucerne at chopping. The second method simulated the growth of LAB on the lucerne during wilting and needed similar inputs. The former method predicted LAB counts within one order of magnitude more than 95% of the time except for lucerne samples drier than 60% dry matter. The prediction of the simulation model had more variation than those of the regression equations, but the simulation model was applicable over a wider range of conditions. These results, together with earlier studies, provide a preliminary basis for determining when a silage inoculant containing LAB will be most beneficial.     

Influence of storage on chemical,microbial and consumer acceptability of a milk-like product made from melon seeds

The storage stability of melon milk at room (30 ± 2 ^°C)and refrigeration (10 ± 2 ^°C) temperatures was determined by analyzing changes in the chemical, microbial andsensory properties of the milk stored for 7 days. Theresults showed that at both storage temperatures, solublesolids and pH of the milk decreased while titratableacidity increased with storage. The standard plate countsincreased appreciably while coliforms were absent in themilk with storage at both storage temperatures. The overallacceptability score of the melon milk dropped duringstorage, the drop being faster at 30 ± 2 ^°C than at 10 ± 2 ^°C. The milk samples stored at 30 ± 2 ^°C and 10 ± 2 ^°C were acceptable only within one and three days, respectively; thereafter, theywere unacceptable.     

Aerobic stability of sugar-cane silage inoculated with tropical strains of lactic acid bacteria

Aerobic stability is an important feature in the evaluation of silages. The aims were to investigate the chemical and microbiological changes that occur in sugar-cane (Saccharum spp.) silage after aerobic exposure, to identify the major species of yeasts associated with the aerobic deterioration process and to select lactic acid bacteria (LAB) strains that can improve the aerobic stability of this silage. Fourteen wild LAB strains belonging to Lactobacillus plantarum, L. brevis and L. hilgardii were evaluated using experimental silos. Silage samples were collected at 0, 96 and 216 h after aerobic exposure to determinate the DM, WSC, pH, products of fermentation, to evaluate the silage temperatures and to identify yeast species associated with the aerobic deterioration of silage. The strains tested were able to modify the fermentative and chemical parameters and the diversity of yeasts species of silage after aerobic exposure. There was no association between the facultative or obligatory heterofermentative fermentation patterns and the increased aerobic stability of silage. Aerobic stability of sugar-cane silages was associated with high acetic acid and 1,2-propanediol concentrations. L. hilgardii UFLA SIL51 and UFLA SIL52 strains promoted an increase in aerobic stability of silage.     

Irradiation and storage effects on some properties of potato starch and use of thermoluminescence for identification of irradiated tubers

The effect on properties of starch isolated from Ajax and Diamant potatoes freshly harvested and irradiated immediately after harvest and after two weeks with 0.05, 0.10, 0.15, and 0.20 kGy were reported. Changes due to postirradiation storage up to six months at two different conditions (5 C, 90±2% RH and 20 C, 79±5% RH) were also studied. Swelling power (SP) slightly decreased or remained unchanged with different irradiation dose, but the effect of timing of irradiation after harvest was significant. Doses of 0.2 and 0.15 kGy significantly (p≤0.05) increased solubility, particularly at 90 C solubility temperature compared to lower doses. Decrease in viscosity with increasing dose immediately after irradiation was observed in both varieties but was more pronounced in Diamant. However, changes were dependent on variety, irradiation dose, timing of irradiation, and postirradiation storage conditions. Viscoamylograph test showed that 0.2 kGy significantly (p≤0.05) increased transmission temperature (TT) and temperature at maximum viscosity (TMV), but decreased the maximum viscosity immidiately after irradiation. The same trend was established during the post-irradiation storage time, particularly in Ajax starch, regardless of timing of irradiation or storage conditions. Thermoluminescence (TL) glow curves exhibited qualitative differences between irradiated and unirradiated tubers during the entire storage period, but dose estimation could not be determined.     

The quantitative assessment of Listeria monocytogenes growth in a laboratory ensiling system allowing limited aerobic spoilage

Listeria monocytogenes contamination is associated with silage that has been subjected to aerobic deterioration. A laboratory ensiling system based on plastic tube silos, which permit aerobic spoilage to take place in a controlled manner, is described. This system gives a high degree of consistency between replicates. Parameters measured over a 90-d ensiling period were pH, L. monocytogenes and Enterobacteriaceae counts and percentage spoilage. The system may be suitable for assessing the effectiveness of additives on parameters, such as aerobic spoilage and L. monocytogenes , which are not easily measurable in field studies. The study confirmed the relationship between the presence of Listeria spp. and Enterobacteriaceae in aerobically spoiled silage, showing that the latter group of bacteria may be useful as indicators of the potential risk of L. monocytogenes contamination of silage.     

Fermented Milk–Starch and Milk–Inulin Products as Vehicles for Lactic Acid Bacteria

Formulations using cassava starch or inulin plus milk were fermented with three different lactic acid bacteria (LAB) strains: Lactobacillus plantarum D34, Lactobacillus sp. SLH6, and Streptococcus thermophilus ST4. Growth and acidification were followed in 3% powdered milk (M3), 3% milk–6% starch (M3-S6), and 3% milk–6% inulin (M3-In6). D34 and SLH6 growth was enhanced by starch in M3-S6, when compared to the count (CFU/ml) obtained in M3. Growth of all strains was promoted by inulin. All fermented products showed LAB counts of 8.0 log or higher. Carbohydrate utilization was in agreement with growth and acidification results. The highest increase in CFU in rat feces was observed in M3-S6 fermented with ST4; the D34 fermented product also increased CFU but SLH6 did not, either with starch or inulin. This suggests that ST4 and D34 strains provide a good choice to ferment the proposed formulations in order to obtain a marked improvement of natural intestinal flora.     

Effects of initial air removal methods on microorganisms and characteristics of fermented plant beverages

The effects of 3 different methods for removing the initial air on the properties of fermented plant beverages produced from phom-nang seaweed (Gracilaria fisheri) and wild forest noni (Morinda coreia Ham.) were investigated. Only method M which covered the space above the fermentation liquid with a water filled plastic bag produced no surface film of yeast, had the highest acidity and also antibacterial activity from both plants after 90 days of fermentation. However, the yeast count still exceeded the standard guidelines for plant beverages. The fermented beverage from wild forest noni showed more antibacterial activity against 3 of 4 pathogenic bacteria tested than that from the phomnang seaweed, probably for its higher levels of acidity and ethanol content. Lactic Acid Bacteria (LAB) isolated from the fermentation samples from days 1-5 using the method M from both fermented plant beverages were Leuconostoc mesenteroides supsp. mesenteroides and Leu. mesenteroides subsp. dextranicum while presence of Lactobacilus plantarum was only recorded at days 4-5 in the wild forest noni beverage. From days 6-14 the isolates were Lactobacillus plantarum, Lactobacillus fermentum and Lactobacillus brevis from wild forest noni beverage, whereas only L. brevis was not detected in the seaweed beverage. During days 21-45 both beverages had a similar LAB population of L. plantarum and L. brevis while L. coryniformis was only found in the wild forest noni beverage. Between days 60-90 in both plant beverages only L. plantarum and Lactobacillius sp. were detected.     

Influence of harvest date of primary growth on microbial flora of grass herbages and haylage, and on fermentation and aerobic stability of haylage conserved in laboratory silos

The influence of harvest date of the primary growth of grass herbages on the microbial flora of herbage pre-conservation and haylage post-conservation was studied along with fermentation variables and aerobic stability of haylage. The primary growths of two grass swards, one intensely (Int) and one extensively (Ext) managed, were cut at three different harvest dates (May, June, August) and ensiled in laboratory silos for 120 d. Later harvest dates resulted in increased counts of yeast, mould and enterobacteria in the pre-conserved herbage ( P  <   0·001). Counts of lactic acid bacteria (LAB) ( P  <   0·001) and number of mould species ( P  <   0·001) were highest in the pre-conserved herbage harvested in August. Later harvest dates resulted in higher yeast ( P  <   0·001) and LAB ( P  <   0·001) counts in the haylage while counts of enterobacteria decreased ( P  <   0·001). Clostridial spore counts were unaffected by harvest date both in herbage and haylage. The haylage harvested in August had the lowest pH and the lowest concentration of ethanol but the concentration of lactic acid was in general low. Aerobic stability was longer ( P  <   0·01) for haylage from herbage harvested in August compared with haylage from herbage harvested in May and June. Sward type had less influence than harvest date on microbial variables in herbage and haylage and on fermentation variables of haylage, and did not influence the aerobic stability of haylage.     

茶多酚对冰藏大黄鱼品质及微生物的影响

采用生物保鲜剂茶多酚对大黄鱼进行浸泡处理,研究了大黄鱼在冰藏保鲜过程中品质及微生物的变化。通过测定感官评分值、菌落总数、p H值、挥发性盐基氮(TVB-N值)及硫代巴比妥酸值(TBA值),评价大黄鱼在冰藏过程中品质变化,同时采用16 S r DNA克隆文库及限制性内切酶片段长度多态性(RFLP)技术对大黄鱼在冰藏条件下的腐败菌进行分析。结果表明,在冰藏过程中,茶多酚处理组的菌落总数、p H值、TVB-N值、TBA值均低于对照组,感官评分值优于对照组,大黄鱼在冰藏条件下货架期由12~16 d延长至20~24 d,茶多酚处理组保鲜效果较好。新鲜大黄鱼细菌种类比较丰富,达15种类型,而腐败后细菌种类明显减少,在腐败末期,对照组(20 d)的细菌种类有8种,其中假单胞菌属(Pseudomonas)和希瓦氏菌(Shewanella)为主要腐败菌,所占比例分别为43.7%和39.6%。而茶多酚处理组(24 d)细菌种类较对照组更少,其腐败菌主要为假单胞菌属(Pseudomonas),占细菌总量的76.8%。     

Quality and shelf life of calcium-enriched wholemeal bread stored in a modified atmosphere

Calcium-enriched wholemeal bread packed in a modified atmosphere (60% CO₂, 40% N₂), was examined for stability and microbiological changes throughout 32-day storage. The product was still acceptable after 24 days at 20 ± 1 °C. At this time no microbiological changes were observed; however, there was a continuous decline in sensory quality, mainly due to deterioration of the texture. Crumb hardness increased, whereas its springiness and cohesiveness decreased. These observations were accompanied by physical and chemical changes characterized by a steady increase in acidity and a sharp decrease in blue value, especially at the beginning of storage. The first microbiological changes occurred only after 27 days of storage and were due to the growth of moulds and amylase-negative Gram-positive cocci, cocci-bacillus or bacillus. The principal component analysis showed that nearly 86% of the variance in ten considered variables could be represented by two new variables: PC1, defined by eating quality and physicochemical attributes, and PC2 defined mainly by chewiness. Three groups of stored bread were identified on the score plot. The first group, fresh and 3-day stored bread, was characterized by low hardness and sourness; the second, bread stored from six to twenty days, scored lower for overall sensory quality, low springiness, cohesiveness and blue value; and the third group, the product during the final stages of storage, exhibited a clear increase in chewiness and hardness and showed the first indications of microbial deterioration.     

Synergism between potassium sorbate dips and brief exposure to high CO2 or O2 at curing temperature for the control of citrus postharvest green and blue molds

Synergistic effects and very effective control of citrus postharvest green and blue molds, caused by Penicillium digitatum and Penicillium italicum, respectively, were observed on artificially inoculated ‘Valencia’ oranges and ‘Clemenules’ and ‘Ortanique’ mandarins after a potassium sorbate (PS) treatment was followed by 2 days of storage in atmospheres of elevated CO₂ or O₂ at a curing temperature. A combined treatment consisting of 60-s dips in aqueous solutions of 3% PS heated to 62 °C was followed by 48-h exposure to air, 15 kPa CO₂ or 30 kPa O₂ at 33 °C. Control treatment was a 60-s water dip at 20 °C followed by 24-h exposure to air at 20 °C. Synergism was observed on citrus fruit either incubated at 20 °C for up to 22 days, simulating direct commercialization, or stored at 5 °C for up to 45 days, simulating commercial cold storage. This research offers potential new tools to the citrus industry for implementation of nonpolluting integrated postharvest disease management programs, especially devoted to high added value organic markets or export markets with zero residue tolerance.     

Internalisation of microbes in vegetables: microbial load of Ghanaian vegetables and the relationship with different water sources of irrigation

The occurrence of pathogens in the internal parts of vegetables is usually associated with irrigation water or contaminated soil and could pose risk to consumers as the internalised pathogens are unaffected by external washing. This study was carried out to assess the rate of internalisation of microbes in common Ghanaian vegetables. Standard microbiological methods were employed in microbial enumeration of vegetables collected at the market and farm levels, as well as irrigation water and soil samples. The overall mean counts of vegetables were 4.0 x 10(3) cfu g(-1); 8.1 x 10(2) cfu g(-1); 2.0 x 10(2) cfu g(-1); 3.5 x 10(2) cfu g(-1) for total bacteria, coliform counts, faecal coliform counts and yeast counts, respectively. The rate of internalisation of coliforms in vegetables irrigated with stream/well water was 2.7 times higher than those irrigated with pipe water. The mean coliform counts (4.7 x 10(7) cfu g(-1)) and faecal coliform counts (1.8 x 10(6) cfu g(-1)) of soil samples were similar to those of stream water suggesting both sources exerted similar contamination rates on the vegetables. Generally, there were no significant variations between the rates of internalisation of microbes at the market and farm levels at p < 05, indicating that internalisation of microbes in the vegetables mainly occurred at the farm level. The study has shown that microbial contamination of vegetables in Ghana is not limited to the external surface, but internal vegetable parts could harbour high microbial loads and pose risk to consumers. Safety practices associated with the commodity should therefore not be limited to external washing only. There is the additional need of heating vegetables to eliminate microbes both externally and internally before consumption.