Study of physicochemical, microbial and sensory properties of surimi produced from black mouth croaker (Atrobucca nibe) at freezing condition (-18ºC)

Black mouth croaker (Atrobucca nibe) is considered as a new valuable fish stock in the Oman Sea. In this study, surimi was manufactured from nonmarket size of the fish, manually and different cryoprotectant agents were added to the surimi. Finally changes in physiochemical, microbiological and sensory quality, characteristics of the surimi and kamaboko gel samples were assessed during 6 months at freezing storage (-18ºC). Surimi samples with the addition of Iranian tragacanth gum (TG), xanthan gum (XG), chitosan (CS) and whey protein concentrate (WPC) at 1% (w/w) were prepared to evaluate their impacts as a cryoprotectant on the surimi, individually. The results showed that the whiteness and lightness indexes in all surimi samples were gradually decreased during frozen storage. This trend of decreasing was more intensity in the control sample from 61.08±0.131 to 54.21±0.067 was recorded (p<0.05). Water holding capacity (WHC) in all treatments was decreased during 6 months. The lowest WHC (g/g) was obtained in the surimi without cryoprotectants and maximum WHC was measured in Tcs and Twpc samples, respectively (p<0.05). The lowest breaking force was calculated in Txg (166.00±22.627 g) and Tc (271.50±263.16 g) during 6 months at frozen storage, respectively (p<0.05), while Twpc treatment with slight variations showed the highest breaking force (p<0.05). Also, the lowest gel strength was obtained in Txg (68.22±6.740 g.cm) after 6 month of frozen storage (p<0.05). All Kamaboko surimi gels texture profile analysis parameters decreaced with increasing shelf life. This decreasing trend in the control sample was more severe. Floding results were reduced in all samples during storage (p<0.05). The best protective results probably were obtained in WPC, chitosan and commercial cryoprotectant agents, respectively due to protein stabilization of myofibrillar proteins and the protein-protein network structure, leading to the formation of surimi gel with strong textural properties during frozen conditions. The average number of surimi polygonal structures were significantly decreased (number per mm2) and their area were significantly increased (μm2) in all treatments (p<0.05). With increasing storage time, moisture, protein contents and pH were decreaced. Maximun TVB-N index was calculated in Tc (7.93±0.400 mg/100g) and Txg (7.88±0.477), respectively (p<0.05). TBRAs index was increased in all treatments during frozen storage, while this trend was reached in maximum value in Tc (p<0.05). Sensory evaluation of the fish finger quality characteristics (color, odor, texture and overall acceptability) preapare from frozen black mouth croaker surimi was decreaced during 6 month frozen storage. After the period of frozen storage the highest quality scores were measured in Twpc, Tcs and Tcc samples, respectively (p<0.05). In this study, coliform bacteria were not found in all treatments during frozen storage. The surimi sample containing chitosan showed lower mesophilic and psychrotropic bacteria (log cfu/g) than other treatments during frozen storage (p<0.05). Salt-soluble proteins extractions of all treatments were decreased during frozen storage. This decreacing trend was highest in Tcs (45.74±0.176%) and lowest in Tc treatments after 6 month of frozen storage (29.92±0.224%) (p<0.05). Although commercial cryoprotectant agents were successful in limiting the denaturation of proteins but sugar contents were not accepted for diabetics or those who disagree with the sweet taste and high calorie food. Hence, commercial cryoprotectant agents can be replaced with whey protein concentrate and chitosan at 1% level (w/w) consider that they were showed proper protection of the surimi myofibrillar proteins during storage.

The effect of Rosmarinus officinalis and Zataria multiflora extracts on the stability of poly unsaturated fatty acids in frozen silver carp minced

The purpose of this study, Evaluation the effect of Rosmarinus officinalis and Thymus vulgaris extracts on the stability of poly unsaturated fatty acids in frozen Silver carp minced. Treatments include: Treatment 1 - Control: frozen meat packaged in conventional Treatment 2: Frozen Silver carp minced+Thyme 300 mg/kg in normal packaging Treatment 3: Frozen Silver carp minced+Rosemary 200 mg/kg in normal packaging Treatment 4: Frozen Silver carp minced+Rosemary compound (100 mg/kg) and Thyme (100 mg/kg) in normal packaging After rapid freezing of samples in the spiral freezer by individual quick freezing method, to maintain the cold temperature (-18) °C were transferred. Sampling and measurements to determine the fatty acid profile of the zero phase beginning in the first month and then every ten days, and 15 days in the second month of the third month after the monthly test. Identifying, defining and measuring the fatty acid profile by gas chromatography was performed. In this study, levels of both saturated and unsaturated fatty acids in three experimental and one control were identified as follows: A: saturated fatty acids: Meristic C14: 0/Palmitic C16: 0/Hepta decaenoic C17: 0/Stearic C18: 0/Arashidic C20: 0/B:Mono unsaturated fatty acids: palmitoleic C16: 1-W7/Oleic C18: 1-W9/Gadoleic C20: 1-W9 C:Poly unsaturated fatty acids: Linoleic C18: 2-W6/α-Linolenic C18: 3-W3 D:High unsaturated fatty acids: Arachidonic C20: 4-W6 Eicosapentaenoic acid C20: 5-EPA/W3 Docosahexaenoic C22: 6-DHA/W3 Results of this study was to determine, Thyme and rosemary extracts containing silver carp minced stored in freezing conditions, Stability of different types of fatty acids, monounsaturated fatty acids, poly-unsaturated fatty acids, omega-3 and omega-6 fatty acids are. So that none of the fatty acids measured were not significant 100% increase or decrease, While changes in the fatty acid oxidation during storage time is minimized. The results obtained from the fatty acid profiles and indicators of their and statistical tests show that treatment with rosemary extract More stable during storage (-18) ° C In comparison with the control and other treatments are shown; And at relatively low compared to other treatments and control samples oleic acid and linoleic acid, palmitic more. According to studies,in Silver carp minced that containing rosemary extract, end of the storage period of six months. Were usable, so even rosemary extract the shelf-life examples to increase more than six months.

Application of whey protein incorporation with Cinnamon oil as a preservative in Huse huso fillet under chilled storage condition

Biodegradable protein-based film was developed by incorporating cinnamon essential oil (CEO) into whey protein concentrate (WPC) at level of 0.8% and 1.5% v/v. Then physical and mechanical properties of the films were evaluated. Adding CEO to the WPC matrix decreased the water vapour permeability of the films and water solubility. Films containing CEO showed significant antibacterial activity both gram-positive and gram-negative strains and exhibited significant inhibitory effect on the studied fungi. In continue, the effect of whey coating and whey coating incorporated with 1.5% CEO on quality and shelf life of Huso huso fillet during refregrated (4±1°C) storage period were also investigated. The control and treated fish samples were analyzed for microbiological (total viable count, psychrophilic counts), chemical (PV, TBA, FFA, pH, TVB-N), and sensory characteristics in 4-day intervals up of microbial, chmical and sensoy analyses indicated lower levels of PV, TBA, FFA, pH, TVB-N in coasted sampels and specially, those with CEO while were kept in refrigerator. Based on results, whey protein edible coating contain 1.5% cinnamon essential oil could enhance preserving ability Huso huso during storage cold.

Study of effect Rosmarinus officinalis oil and nisin on the growth of Streptococcus iniae in lab conditions and fillets of rainbow trout (Oncorhynchus mykiss)

Fish are an important part of a healthy diet since they contain high quality protein, but typically present a low fat percent when compared to other meats. Fish is an extremely perishable food commodity. On the other hand, food borne diseases are still a major problem in the world, even in well-developed countries. The increasing incidence of food borne diseases coupled with the resultant social and economic implications means there is a constant striving to produce safer food and to develop new antimicrobial agents concerns over the safety of some chemical preservatives and negative consumer reactions to preservatives they perceive as chemical and artificial, have prompted on increased interest in more ‘‘naturalgreen’’ alternatives for the maintenance or extension of product shelf-life. Particular interest has focused on the potential applications of plant essential oils. However, to establish the usefulness of natural antimicrobial preservatives, they must be evaluated alone and in combination with other preservation factors to determine whether there are synergistic effects and multiple hurdles can be devised. In this study, were evaluated the effects of different concentrations of Rosmarinus officinalis and nisin and storage time (15 days) on growth of Streptococcus iniae GQ850377 in a lab conditions and a food model system (fillets of rainbow trout) in 4 and 8 °C. In addition, we also studied multi factorial effects of four different concentration of rosemary, three different concentrations of nisin, two different levels of pH in 3 temperature 4,15 and 37 °C on log% of S.iniae during 43 days in BHI broth. The results on growth of S. iniae were evaluated using SPSS 20.0 statistical software and analyzed the logarithm of total count of the bacterial by Tukey Test. Results were considered statistically significant when P<0.05. MIC and MBC values of rosemary and nisin were 0.03, 0.075 % and 5, 40 μg/mL, respectively. The growth of S. iniae was effected significantly (P<0.05) by rosemary and nisin and also combination of rosemary and nisin in 4 and 8 °C. Samples treated with 0.135 and 0.405 % of rosemary showed a significant decrease on the growth of the bacteria compared with control sample(P<0.05). The most ١٤٦ inhibitory effects were seen in samples treated with 0.135 and 0.405% of rosemary until 9 days after storage. Also, the synergism effects of rosemary and nisin on the growth rate of bacteria was significant (P<0.05) compared with untreated samples and samples treated with the rosemary or nisin, only. Synergistic effects was observed at concentration of 0.405% rosemary and 0.75 μg/mL nisin in both temprature. Results of this study showed that different concentration of rosemary a significant inhibitory effect (P<0.05) on log% of S. iniae, in BHI broth in pH 5.5 and 7 in 4,15 and 37 °C during 43 days. In concentration of 0% rosemary (control) in pH 5.5 and 7 and 37°C, log% were 1.099 and 3.15, whereas in concentration of 0.015% rosemary were -4/241 and 1.454, respectively. The use of essential oils may improve food safety and overall microbial quality. If essential oils were to be more widely applied as antibacterials in foods, the organoleptic impact would be important. In addition, it is recommended to apply essential oils or their compounds as part of a hurdle system and to use it as an antimicrobial component along with other preservation techniques. Thus essential of R. officinalis with high antibacterial activity selected in this study could be a potential source for inhibitory substances against some food-borne pathogens and they may be candidates for using in foods or food-processing systems.

Identification and measurement of fatty acids, amino acids in roe of tuna fish (Thunnus tonggol) and its TVB and peroxide value during cold storage

The first aim of this research was to identify fatty acids, amino acids composition of Thunnus tonggol roe and their changes during cold storage (-18'C). The second aim was to determine the changes of moisture, protein, fat and ash contents of the roe during one year cold storage (-18'C). 60 samples of longtail tuna (Thunnus tonggol) ovaries were randomly collected form Bandar-e-Abbas landings. The samples were frozen at-30'C and kept in cold store at -18'C for one year. According to a time table, the samples were examined for identification of fatty acids, amino acids, moisture, protein, fat, ash, peroxide and T.V.N. and their changes were evaluated during this time. The results showed that 26 fatty acids were identified. The unsaturated fatty acids (UFA) and saturated fatty acids (SFA) were 62.33 and 37.6%, respectively, in fresh roe. So that, DHA (C22:6) and oleic acid (C18:1) had high amounts (24.79 and 21.88%) among the UFA and palmitic acid (C16:0) was the most content (22.75%) among the SFA. The PUFA/SFA was 0.91. Also, 17 amino acids were identified that essential amino acids (EAA) and nonessential amino acids (NE) were 10478 and 7562 mg/100g, respectively, and E/NE was 1.38. Among the EAA and NE, lysine (2110mg/100g) and aspartic acid (1924 mg/100g) were the most contents. Also, results showed that moisture, ash, protein and fat contents were 72.74, 1.8, 19.88 and 4.53%, respectively, in fresh roe. The effects of freezing and cold storage on the roes showed that UFA and SFA contents have reached to 49.83 and 48.07%, respectively, at the end of cold storage. It indicated that these compounds change to each other during frozen storage. Also, n-3 and n-6 series of fatty acids were 32.75 and 1.61% in fresh roe. But their contents decreased to 22.96 and 1.25% at the end of period. Among the fatty acids, 22:6 and C16:0 had the most changes. The changes of fatty acids were significantly at 95% level except for C15:1, C18:3(n-3) and C20:4(n-6). All of the amino acids decreased in frozen storage and their changes were significantly (P<0.05). EAA was 7818 mg/100g and E/NE was 1.27 at the end of storage period. Among the amino acids, leucine and lysine had the most changes. Moisture, ash, protein and fat contents were 70.13, 1.82, 19.4 and 6.51%, respectively, at the end of storage period. The peroxide value and T.V.N. increased during storage. So that, their contents have reached to 5.86 mg/kg and 26.37 mg/100 g, respectively, at the end of frozen storage. The best shelf life of Thunnus tonggol roe was 6 or 7 months, because of lipid oxidation and increasing of peroxide.

Hierarchically structured nanocarbon electrodes for flexible solid lithium batteries

The ever increasing demand for storage of electrical energy in portable electronic devices and electric vehicles is driving technological improvements in rechargeable batteries. Lithium (Li) batteries have many advantages over other rechargeable battery technologies, including high specific energy and energy density, operation over a wide range of temperatures (-40 to 70. °C) and a low self-discharge rate, which translates into a long shelf-life (~10 years) [1]. However, upon release of the first generation of rechargeable Li batteries, explosions related to the shorting of the circuit through Li dendrites bridging the anode and cathode were observed. As a result, Li metal batteries today are generally relegated to non-rechargeable primary battery applications, because the dendritic growth of Li is associated with the charging and discharging process. However, there still remain significant advantages in realizing rechargeable secondary batteries based on Li metal anodes because they possess superior electrical conductivity, higher specific energy and lower heat generation due to lower internal resistance. One of the most practical solutions is to use a solid polymer electrolyte to act as a physical barrier against dendrite growth. This may enable the use of Li metal once again in rechargeable secondary batteries [2]. Here we report a flexible and solid Li battery using a polymer electrolyte with a hierarchical and highly porous nanocarbon electrode comprising aligned multiwalled carbon nanotubes (CNTs) and carbon nanohorns (CNHs). Electrodes with high specific surface area are realized through the combination of CNHs with CNTs and provide a significant performance enhancement to the solid Li battery performance. © 2013 Elsevier Ltd.

Plasmid biology of natural Lactococcus lactis strains and molecular mechanisms of bacteriophage-host interaction

Lacticin 3147, enterocin AS-48, lacticin 481, variacin, and sakacin P are bacteriocins offering promising perspectives in terms of preservation and shelf-life extension of food products and should find commercial application in the near future. The studies detailing their characterization and bio-preservative applications are reviewed. Transcriptomic analyses showed a cell wall-targeted response of Lactococcus lactis IL1403 during the early stages of infection with the lytic bacteriophage c2, which is probably orchestrated by a number of membrane stress proteins and involves D-alanylation of membrane lipoteichoic acids, restoration of the physiological proton motive force disrupted following bacteriophage infection, and energy conservation. Sequencing of the eight plasmids of L. lactis subsp. cremoris DPC3758 from raw milk cheese revealed three anti-phage restriction/modification (R/M) systems, immunity/resistance to nisin, lacticin 481, cadmium and copper, and six conjugative/mobilization regions. A food-grade derivative strain with enhanced bacteriophage resistance was generated via stacking of R/M plasmids. Sequencing and functional analysis of the four plasmids of L. lactis subsp. lactis biovar. diacetylactis DPC3901 from raw milk cheese revealed genes novel to Lactococcus and typical of bacteria associated with plants, in addition to genes associated with plant-derived lactococcal strains. The functionality of a novel high-affinity regulated system for cobalt uptake was demonstrated. The bacteriophage resistant and bacteriocin-producing plasmid pMRC01 places a metabolic burden on lactococcal hosts resulting in lowered growth rates and increased cell permeability and autolysis. The magnitude of these effects is strain dependent but not related to bacteriocin production. Starters’ acidification capacity is not significantly affected. Transcriptomic analyses showed that pMRC01 abortive infection (Abi) system is probably subjected to a complex regulatory control by Rgg-like ORF51 and CopG-like ORF58 proteins. These regulators are suggested to modulate the activity of the putative Abi effectors ORF50 and ORF49 exhibiting topology and functional similarities to the Rex system aborting bacteriophage λ lytic growth.

The formulation, testing and stability of 16% fat cream liqueurs

Cream liqueurs manufactured by a one-step process, where alcohol was added before homogenisation, were more stable than those processed by a two -step process which involved addition of alcohol after homogenisation. Using the one-step process, it was possible to produce creaming-stable liqueurs by using one pass through a homogeniser (27.6 MPa) equipped with "liquid whirl" valves. Test procedures to characterise cream liqueurs and to predict shelf life were studied in detail. A turbidity test proved simple, rapid and sensitive for characterising particle size and homogenisation efficiency. Prediction of age thickening/gelation in cream liqueurs during incubation at 45 °C depended on the age of the sample when incubated. Samples that gelled at 45 °C may not do so at ambient temperature. Commercial cream liqueurs were similar in gross chemical composition, and unlike experimentally produced liqueurs, these did not exhibit either age-gelation at ambient or elevated temperatures. Solutions of commercial sodium caseinates from different sources varied in their calcium sensitivity. When incorporated into cream liqueurs, caseinates influenced the rate of viscosity increase, coalescence and, possibly, gelation during incubated storage. Mild heat and alcohol treatment modified the properties of caseinate used to stabilise non-alcoholic emulsions, while the presence of alcohol in emulsions was important in preventing clustering of globules. The response to added trisodium citrate varied. In many cases, addition of the recommended level (0.18%) did not prevent gelation. Addition of small amounts of NaOH with 0.18 % trisodium citrate before homogenisation was beneficial. The stage at which citrate was added during processing was critical to the degree of viscosity increase (as opposed to gelation) in the product during 45 °C incubation. The component responsible for age-gelation was present in the milk-solids non fat portion of the cream and variations in the creams used were important in the age-gelation phenomenon Results indicated that, in addition to possibly Ca++, the micellar casein portion of serum may play a role in gelation. The role of the low molecular weight surfactants, sodium stearoyl lactylate and monodiglycerides in preventing gelation, was influenced by the presence of trisodium citrate. Clustering of fat globules and age-gelation were inhibited when 0.18 % citrate was included. Inclusion of sodium stearoyl lactylate, but not monodiglycerides, reduced the extent of viscosity increase at 45 °C in citrate containing liqueurs.

Cellular and in-vitro models to assess antioxidant activities of seaweed extracts and the potential use of the extracts as ingredients

Seaweeds contain a range of antioxidant compounds such as polyphenols, carotenoids, sulphated polysaccharides and vitamins and have the potential to be used as ingredients in neutraceuticals. The antioxidant activity of crude 60% methanol extracts prepared from five Irish seaweeds, Ascophyllum nodosum, Laminaria hyperborea, Pelvetia canaliculata, Fucus vesiculosus and Fucus serratus were examined using in-vitro assays and a cell model system to determine the antioxidant activity of the extracts and their ability to protect against H2O2 and tert-BOOH-induced DNA damage and alterations in cellular antioxidant status in the human adenocarcinoma, Caco-2 cell line. To optimise the extraction of antioxidant compounds from seaweeds, an accelerated solvent extraction (ASE®) was used in combination with food grade solvents. The antioxidant activity of these extracts against H2O2 and tert-BOOH-induced DNA damage and alterations in cellular antioxidant status was also assessed. Extracts that exhibited the highest antioxidant activity, A. nodosum (100% water and 80% ethanol extracts) and F. vesiculosus (60% ethanol extract) were selected as ingredients for incorporation into fluid milk and yogurt at concentrations of 0.25% and 0.5%. The addition of the seaweed extracts to milk and yogurt did not affect the pH or shelf-life properties of the products. Seaweed addition did however significantly influence the colour properties of the milk and yogurt. Yellowness values were significantly higher in yogurts containing F. vesiculosus at both concentrations and A. nodosum (80% ethanol) at the 0.5% concentration. In milk, the F. vesiculosus (60% ethanol) and A. nodosum (80% ethanol) at both the 0.25% and the 0.5% concentrations had higher greenness and yellowness values than the milk containing A. nodosum (100% water). Sensory analysis revealed that appearance and flavour governed the overall acceptability of yogurts with the control yogurt, and yogurts containing A. nodosum (100% water) were the most preferred samples by panellists. However, in the milk trial the perception of a fishy taste was the determining factor in the negative perception of milk. The unsupplemented control and the milk containing A. nodosum (100% water) at a concentration of 0.5% were the most overall accepted milk samples by the sensory panellists. The antioxidant activity of the extracts in milk and yogurt remained stable during storage as determined by the in-vitro assays. Seaweed supplemented milk and yogurt were also subjected to an in-vitro digestion procedure which mimics the human digestive system. The milk and yogurt samples and their digestates were added to Caco-2 cells to investigate their antioxidant potential however neither the undigested or digested samples protected against H2O2-induced DNA damage in Caco-2 cells.

Cereal products for specific dietary requirements. Evaluation and improvement of technological and nutritional properties of gluten free raw materials and end products

Coeliac disease is one of the most common food intolerances worldwide and at present the gluten free diet remains the only suitable treatment. A market overview conducted as part of this thesis on nutritional and sensory quality of commercially available gluten free breads and pasta showed that improvements are necessary. Many products show strong off-flavors, poor mouthfeel and reduced shelf-life. Since the life-long avoidance of the cereal protein gluten means a major change to the diet, it is important to also consider the nutritional value of products intending to replace staple foods such as bread or pasta. This thesis addresses this issue by characterising available gluten free cereal and pseudocereal flours to facilitate a better raw material choice. It was observed that especially quinoa, buckwheat and teff are high in essential nutrients, such as protein, minerals and folate. In addition the potential of functional ingredients such as inulin, β-glucan, HPMC and xanthan to improve loaf quality were evaluated. Results show that these ingredients can increase loaf volume and reduce crumb hardness as well as rate of staling but that the effect diverges strongly depending on the bread formulation used. Furthermore, fresh egg pasta formulations based on teff and oat flour were developed. The resulting products were characterised regarding sensory and textural properties as well as in vitro digestibility. Scanning electron and confocal laser scanning microscopy was used throughout the thesis to visualise structural changes occurring during baking and pasta making

Development and assessment of new sensor systems in food packaging applications

The use of optical sensor technology for non-invasive determination of key quality pack parameters improved package/product quality. This technology can be used for optimization of packaging processes, improvement of product shelf-life and maintenance of quality. In recent years, there has been a major focus on O2 and CO2 sensor development as these are key gases used in modified atmosphere packaging (MAP) of food. The first and second experimental chapters (chapter 2 and 3) describe the development of O2, pH and CO2 solid state sensors and its (potential) use for food packaging applications. A dual-analyte sensor for dissolved O2 and pH with one bi-functional reporter dye (meso-substituted Pd- or Ptporphyrin) embedded in plasticized PVC membrane was developed in chapter 2. The developed CO2 sensor in chapter 3 was comprised of a phosphorescent reporter dye Pt(II)- tetrakis(pentafluorophenyl) porphyrin (PtTFPP) and a colourimetric pH indicator α-naphtholphthalein (NP) incorporated in a plastic matrix together with a phase transfer agent tetraoctyl- or cetyltrimethylammonium hydroxide (TOA-OH or CTA-OH). The third experimental chapter, chapter 4, described the development of liquid O2 sensors for rapid microbiological determination which are important for improvement and assurance of food safety systems. This automated screening assay produced characteristic profiles with a sharp increase in fluorescence above the baseline level at a certain threshold time (TT) which can be correlated with their initial microbial load and was applied to various raw fish and horticultural samples. Chapter 5, the fourth experimental chapter, reported upon the successful application of developed O2 and CO2 sensors for quality assessment of MAP mushrooms during storage for 7 days at 4°C.

Fundamental studies of sourdoughs fermented with Weissella cibaria and Lactobacillus plantarum: influence on baking characteristics, sensory profiles and in vitro starch digestibility of gluten-free breads

The application of sourdough can improve texture, structure, nutritional value, staling rate and shelf life of wheat and gluten-free breads. These quality improvements are associated with the formation of organic acids, exopolysaccharides (EPS), aroma or antifungal compounds. Initially, the suitability of two lactic acid bacteria strains to serve as sourdough starters for buckwheat, oat, quinoa, sorghum and flours was investigated. Wheat flour was chosen as a reference. The obligate heterofermentative lactic acid bacterium (LAB) Weissella cibaria MG1 (Wc) formed the EPS dextran (a α-1,6-glucan) from sucrose in situ with a molecular size of 106 to 107 kDa. EPS formation in all breads was analysed using size exclusion chromatography and highest amounts were formed in buckwheat (4 g/ kg) and quinoa sourdough (3 g/ kg). The facultative heterofermentative Lactobacillus plantarum FST1.7 (Lp) was identified as strong acidifier and was chosen due to its ubiquitous presence in gluten-free as well as wheat sourdoughs (Vogelmann et al. 2009). Both Wc and Lp, showed highest total titratable acids in buckwheat (16.8 ml; 26.0 ml), teff (16.2 ml; 24.5 ml) and quinoa sourdoughs (26.4 ml; 35.3 ml) correlating with higher amounts of fermentable sugars and higher buffering capacities. Sourdough incorporation reduced the crumb hardness after five days of storage in buckwheat (Wc -111%), teff (Wc -39%) and wheat (Wc -206%; Lp -118%) sourdough breads. The rate of staling (N/ day) was reduced in buckwheat (Ctrl 8 N; Wc 3 N; Lp 6 N), teff (Ctrl 13 N; Wc 9 N; Lp 10 N) and wheat (Ctrl 5 N; Wc 1 N; Lp 2 N) sourdough breads. Bread dough softening upon Wc and Lp sourdough incorporation accounted for increased crumb porosity in buckwheat (+10.4%; +4.7), teff (+8.1%; +8.3%) and wheat sourdough breads (+8.7%; +6.4%). Weissella cibaria MG1 sourdough improved the aroma quality of wheat bread but had no impact on aroma of gluten-free breads. Microbial shelf life however, was not prolonged in any of the breads regardless of the starter culture used. Due to the high prevalence of insulin-dependent diabetes mellitus particular amongst coeliac patients, glycaemic control is of great (Berti et al. 2004). The in vitro starch digestibility of gluten-free breads with and without sourdough addition was analysed to predict the GI (pGI). Sourdough can decrease starch hydrolysis in vitro, due to formation of resistant starch and organic acids. Predicted GI of gluten-free control breads were significantly lower than for the reference white wheat bread (GI=100). Starch granule size was investigated with scanning electron microscopy and was significantly smaller in quinoa flour (<2 μm). This resulted in higher enzymatic susceptibility and hence higher pGI for quinoa bread (95). Lowest hydrolysis indexes for sorghum and teff control breads (72 and 74, respectively) correlate with higher gelatinisation peak temperatures (69°C and 71°C, respectively). Levels of resistant starch were not increased by addition of Weissella cibaria MG1 (weak acidifier) or Lactobacillus plantarum FST1.7 (strong acidifier). The pGI was significantly decreased for both wheat sourdough breads (Wc 85; Lp 76). Lactic acid can promote starch interactions with gluten hence decreasing starch susceptibility (Östman et al. 2002). For most gluten-free breads, the pGI was increased upon sourdough addition. Only sorghum and teff Lp sourdough breads (69 and 68, respectively) had significantly decreased pGI. Results suggest that the increase of starch hydrolysis in gluten-free breads was related to mechanism other than presence of organic acids and formation of resistant starch.

“Green preservatives” – combating fungi in the food industry by applying antifungal lactic acid bacteria

Fungal spoilage is the most common type of microbial spoilage in food leading to significant economical and health problems throughout the world. Fermentation by lactic acid bacteria (LAB) is one of the oldest and most economical methods of producing and preserving food. Thus, LAB can be seen as an interesting tool in the development of novel bio-preservatives for food industry. The overall objective of this study was to demonstrate, that LAB can be used as a natural way to improve the shelf-life and safety of a wide range of food products. In the first part of the thesis, 116 LAB isolates were screened for their antifungal activity against four Aspergillus and Penicillium spp. commonly found in food. Approximately 83% of them showed antifungal activity, but only 1% showed a broad range antifungal activity against all tested fungi. The second approach was to apply LAB antifungal strains in production of food products with extended shelf-life. L. reuteri R29 strain was identified as having strong antifungal activity in vitro, as well as in sourdough bread against Aspergillus niger, Fusarium culmorum and Penicillium expansum. The ability of the strain to produce bread of good quality was also determined using standard baking tests. Another strain, L. amylovorus DSM19280, was also identified as having strong antifungal activity in vitro and in vivo. The strain was used as an adjunct culture in a Cheddar cheese model system and demonstrated the inhibition of P. expansum. Significantly, its presence had no detectable negative impact on cheese quality as determined by analysis of moisture, salt, pH, and primary and secondary proteolysis. L. brevis PS1 a further strain identified during the screening as very antifungal, showed activity in vitro against common Fusarium spp. and was used in the production of a novel functional wortbased alcohol-free beverage. Challenge tests performed with F. culmorum confirmed the effectiveness of the antifungal strain in vivo. The shelf-life of the beverage was extended significantly when compared to not inoculated wort sample. A range of antifungal compounds were identified for the 4 LAB strains, namely L. reuteri ee1p, L. reuteri R29, L. brevis PS1 and L. amylovorous DSM20531. The identification of the compounds was based on liquid chromatography interfaced to the mass spectrometer and PDA detector

Isolation and characterisation of antifungal compounds from lactic acid bacteria and their application in wheat and gluten-free bread

As part of the “free-from” trend, biopreservation for bread products has increasingly become important to prevent spoilage since artificial preservatives are more and more rejected by consumers. A literature review conducted as part of this thesis revealed that the evaluation of more suitable antifungal strains of lactic acid bacteria (LAB) is important. Moreover, increasing the knowledge about the origin of the antifungal effect is fundamental for further enhancement of biopreservation. This thesis addresses the investigation of Lactobacillus amylovorus DSM19280, Lb. brevis R2: and Lb. reuteri R29 for biopreservation using in vitro trials and in situ sourdough fermentations of quinoa, rice and wheat flours as biopreservatives in breads. Their contribution to quality and shelf life extension on bread was compared and related to their metabolic activity and substrate features. Moreover, the quantity of antifungal carboxylic acids produced during sourdough fermentation was analysed. Overall a specific profile of antifungal compounds was found in the sourdough samples which were strain and substrate dependently different. The best preservative effect in quinoa sourdough and wheat sourdough bread was achieved when Lb. amylovorus DSM19280 fermented sourdough was used. However, the concentration of the antifungal compounds found in these biopreservatives were much lower when compared with Lb. reuteri R29 as the highest producer. Nevertheless, the artificial application of the highest concentration of these antifungal compounds in chemically acidified wheat sourdough bread succeeded in a longer shelf life than achieved only by acidifying the dough. This evidences their partial contribution to the antifungal activity and their synergy. Additionally, a HRGC/MS method for the identification and quantification of the antifungal active compounds cyclo(Leu-Pro), cyclo(Pro-Pro), cyclo(Met-Pro) and cyclo(Phe-Pro) was successfully developed by using stable isotope dilutions assays with the deuterated counterparts. It was observed that the concentrations of cyclo(Leu-Pro), cyclo(Pro-Pro), and cyclo(Phe-Pro) increased only moderately in MRS-broth and wort fermentation by the activity of the selected microorganism, whereas the concentration of cyclo(Met-Pro) stayed unchanged.

Studies on the texture, functionality, rheology and sensory properties of Cheddar and Mozzarella cheeses

The effect of fortification of skim milk powder and sodium caseinate on Cheddar cheeses was investigated. SMP fortification led to decreased moisture, increased yield, higher numbers of NSLAB and reduced proteolysis. The functional and texture properties were also affected by SMP addition and formed a harder, less meltable cheese than the control. NaCn fortification led to increased moisture, increased yield, decreased proteolysis and higher numbers of NSLAB. The functional and textural properties were affected by fortification with NaCn and formed a softer cheese that had similar or less melt than the control. Reducing the lactose:casein ratio of Mozzarella cheese by using ultrafiltration led to higher pH, lower insoluble calcium, lower lactose, galactose and lactic acid levels in the cheese. The texture and functional properties of the cheese was affected by varying the lactose:casein ratio and formed a harder cheese that had similar melt to the control later in ripening. The flavour and bake properties were also affected by decreased lactose:casein ratio; the cheeses had lower acid flavour and blister colour than the control cheese. Varying the ratio of αs1:β-casein in Cheddar cheese affected the texture and functionality of the cheese but did not affect insoluble calcium, proteolysis or pH. Increasing the ratio of αs1:β-casein led to cheese with lower meltability and higher hardness without adverse effects on flavour. Using camel chymosin in Mozzarella cheese instead of calf chymosin resulted in cheese with lower proteolysis, higher softening point, higher hardness and lower blister quantity. The texture and functional properties that determine the shelf life of Mozzarella were maintained for a longer ripening period than when using calf chymosin therefore increasing the window of functionality of Mozzarella. In summary, the results of the trials in this thesis show means of altering the texture, functional, rheology and sensory properties of Mozzarella and Cheddar cheeses.