Browsing by Subject "Food Science (Food Safety)"

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  • Kamlang-ek, Pimwalee (Helsingfors universitet, 2012)
    The literature survey reviewed principles of oxidation of edible oils, adverse effects of lipid oxidation and analysis of volatile oxidation products by SPME-GC-MS. The main aim of the experimental research was to study the influence of relative humidity (RH) on the release of volatile oxidation products from spray-dried emulsions with natural and cross-linked casein as emulsifier. The release of volatiles was determined by SPME-GC-MS. The sub aims were to study the effects of stabilization time at specific RHs, of temperature and agitation speed during the SPME extraction. The spray-dried emulsions were oxidised at 40oC in order to reach a certain level of oxidation. Next, the powders were stabilised under five RHs (0%, 11%, 33%, 54% and 75%) for one or two weeks in order to observe the effect of the RH and the stabilisation time on the release of volatiles. After adjusting the RHs, volatile compounds were analysed by SPME-GC-MS. The following SPME extraction conditions were tested: C1: temperature 40oC, agitation speed 250 rpm, C2: 50oC, 250 rpm, C3: 40oC, 500 rpm and C4: 50oC, 500 rpm. Identification of the compounds was carried out by matching their MS spectra with the NIST database. Altogether 45 volatiles released from the powders could be identified, and 18 of them were found in most samples. RH had an important effect on the release of volatiles from the encapsulated samples. The highest release was always observed at 11% and 33% RH, whereas the lowest release was found at 0% and/or 75% RH, depending on the SPME extraction conditions. The stabilisation time did not have a significant effect on the release of volatiles in most RHs. During the SPME extraction step, elevation of the temperature from 40oC to 50oC, as well as the agitation speed from 250 rpm to 500 rpm, facilitated higher release. However, the effect of temperature was greater than that of agitation speed. Although it was suspected that cross-linking of sodium-caseinate would enhance retention of volatiles, our experiment showed greater peak areas of most volatiles from the cross-linked samples than from the natural ones. By controlling the SPME parameters, it was possible to obtain repeatable volatile compound results. The SPME-GC-MS method applied in this study can be reliably used to analyse volatile oxidation products from spray-dried emulsions. Only at very low or high RH the release of volatiles may differ from samples stored at 11% -54% RH.
  • Yang, Yingying (Helsingfors universitet, 2013)
    The literature review presented the effects of the polyglutamate chain on the biological and nutritional properties of folates and the main methods used for folate assays, with a special emphasis on the approaches to studying intact polyglutamates. A brief introduction regarding safety aspects of folate fortification was also given. The aim of this study was to develop a UPLC-FLR/PDA method for simultaneous determination of polyglutamyl folate vitamers. Chromatographic conditions were optimised for the resolution of polyglutamyl 5-methyltetrahydrofolates and major naturally-occurring monoglutamates. Method validation was conducted for both the UPLC method and affinity chromatography. Applicability of the validated method was evaluated on lupin flour, faba bean flour, and dry yeast, which were subjected to preparatory treatments with and without deconjugation. In addition, the effects of the sequential modification of preparatory treatments on the folate content and composition were investigated by using both the UPLC method and Lactobacillus rhamnosus assay. A desirable separation of target polyglutamates and monoglutamates was successfully achieved on the BEH C18 UPLC column within 11 minutes. The optimised UPLC method showed satisfactory selectivity, linearity, and sensitivity for the determination of methylated polyglutamates in the femtomole range and monoglutamates in the picogram range. Affinity chromatography showed satisfactory recoveries for polyglutamyl 5-methyltetrahydrofolates, but not for 5-formyl polyglutamates. In all three selected foods, 5-methyltetrahydrofolate was the dominant folate vitamer. Meanwhile, the analysis of undeconjugated samples showed that in the intact methylated folate pools, pentaglutamate predominated in legume flours and heptaglutamate in dry yeast. In addition, different sequences of enzyme and purification pretreatments were found to significantly affect both the total measurable folates and the folate profiles. Our standard preparatory procedures comprising simultaneous treatments with amylase and conjugase, then protease and affinity purification resulted in the greatest yield of total folates, but UPLC analysis indicated incomplete deconjugation. However, a modification in which deconjugation was conducted as the last step enhanced hydrolysis efficiency.
  • Chamlagain, Bhawani Shankar (Helsingfors universitet, 2011)
    Dynamics of raw milk associated bacteria during cold storage of raw milk and their antibiotic resistance was reviewed, with focus on psychrotrophic bacteria. This study aimed to investigate the significance of cold storage of raw milk on antibiotic-resistant bacterial population and analyse the antibiotic resistance of the Gram-negative antibiotic-resistant psychrotrophic bacteria isolated from the cold-stored raw milk samples. Twenty-four raw milk samples, six at a time, were obtained from lorries that collected milk from Finnish farms and were stored at 4°C/4 d, 6°C/3 d and 6°C/4 d. Antibiotics representing four classes of antibiotics (gentamicin, ceftazidime, levofloxacin and trimethoprim-sulfamethoxazole) were used to determine the antibiotic resistance of mesophilic and psychrotrophic bacteria during the storage period. A representative number of antibiotic-resistant Gram-negative isolates retrieved from the cold-stored raw milk samples were identified by the phenotypic API 20 NE system and a few isolates by the 16S rDNA gene sequencing. Some of the isolates were further evaluated for their antibiotic resistance by the ATB PSE 5 and HiComb system. The initial average mesophilic counts were found below 105 CFU/mL, suggesting that the raw milk samples were of good quality. However, the mesophilic and psychrotrophic population increased when stored at 4°C/4 d, 6°C/3 d and 6°C/4 d. Gentamicin- and levofloxacin-resistant bacteria increased moderately (P < 0.05) while there was a considerable rise (P < 0.05) of ceftazidime- and trimethoprim-sulfamethoxazole-resistant population during the cold storage. Of the 50.9 % (28) of resistant isolates (total 55) identified by API 20 NE, the majority were Sphingomonas paucimobilis (8), Pseudomonas putida (5), Sphingobacterium spiritivorum (3) and Acinetobacter baumanii (2). The analysis by ATB PSE 5 system suggested that 57.1% of the isolates (total 49) were multiresistant. This study showed that the dairy environment harbours multidrug-resistant Gramnegative psychrotrophic bacteria and the cold chain of raw milk storage amplifies the antibioticresistant psychrotrophic bacterial population.
  • Gürbüz, Göker (Helsingfors universitet, 2010)
    The literature review elucidates the mechanism of oxidation in proteins and amino acids and gives an overview of the detection and analysis of protein oxidation products as well as information about ?-lactoglobulin and studies carried out on modifications of this protein under certain conditions. The experimental research included the fractionation of the tryptic peptides of ?-lactoglobulin using preparative-HPLC-MS and monitoring the oxidation process of these peptides via reverse phase-HPLC-UV. Peptides chosen to be oxidized were selected with respect to their amino acid content which were susceptible to oxidation and fractionated according to their m/z values. These peptides were: IPAVFK (m/z 674), ALPMHIR (m/z 838), LIVTQTMK (m/z 934) and VLVLDTDYK (m/z 1066). Even though it was not possible to solely isolate the target peptides due to co-elution of various fractions, the percentages of target peptides in the samples were satisfactory to carry out the oxidation procedure. IPAVFK and VLVLDTDYK fractions were found to yield the oxidation products reviewed in literature, however, unoxidized peptides were still present in high amounts after 21 days of oxidation. The UV data at 260 and 280 nm enabled to monitor both the main peptides and the oxidation products due to the absorbance of aromatic side-chains these peptides possess. ALPMHIR and LIVTQTMK fractions were oxidatively consumed rapidly and oxidation products of these peptides were observed even on day 0. High rates of depletion of these peptides were acredited to the presence of His (H) and sulfur-containing side-chains of Met (M). In conclusion, selected peptides hold the potential to be utilized as marker peptides in ?-lactoglobulin oxidation.
  • Wan, Xing (Helsingfors universitet, 2012)
    Class IIa (pediocin-like) bacteriocins are a major group of bacteriocins produced by lactic acid bacteria (LAB) characterised by their antilisterial activity. As a protective LAB strain for meat products, Leuconostoc carnosum 4010 kills Listeria by producing two class IIa bacteriocins, the well characterised leucocin A (LeuA) and the less studied leucocin C (LecC). Although the amino acid sequence of the secreted LecC has been published, the genes required for its production remain unknown. The aims of this study were to characterise the genes needed for LecC production and to express the lecC gene in Lactococcus lactis. The lecC gene was localised by Southern blot in a large plasmid different from the one harbouring LeuA genes in Ln. carnosum 4010 genome. Five genes in two operons were identified mainly by PCR-based methods and sequencing, namely, the structural gene (lecC) with a 72-bp signal sequence, the immunity gene (lecI) encoding a 97-aa immunity protein, two genes lecTS for an ABC transporter and the gene lecX for an accessory protein. The immunity function of LecI was demonstrated by expressing the lecI gene in LecC sensitive Listeria monocytogenes. Compared to the wild type, LecI-producing Listeria was more tolerant to LecC, thus corroborating the immunity function of LecI. For heterologous expression of LecC, the lecC gene was fused to the lactococcal usp45 signal sequence in the nisin-selectable and nisin-inducible food-grade secretion vector pLEB690. Consequently, bioactive LecC was secreted efficiently by the recombinant Lc. lactis. In conclusion, novel genes for the production of LecC in Ln. carnosum 4010 were identified. The findings indicate that LecC is produced by a dedicated system independent of LeuA. The successful production of functional LecC in Lc. lactis offers an attractive approach for the future application of bacteriocins in food production.
  • Hou, Yaxi (Helsingfors universitet, 2014)
    Non-digestible oligosaccharides possess important physicochemical and physiological properties. They have gained great attention because of their potential prebiotic properties. The oligosaccharides have wide food industrial applications as dietary fibers, sweeteners, humectants, and possible weight controlling agents. In this thesis, cloned Weissella confusa VTT E-90392 dextransucrase was used to catalyze the synthesis of oligosaccharides (acceptor products) by acceptor reaction, when sucrose was the glucosyl unit donor. Maltose acceptor reaction was selected to analyze the effects of the concentrations of sucrose and maltose, as well as the dosages of dextransucrase on maltose acceptor products. Other acceptor reactions were also evaluated, with primary lactose and cellobiose acceptor products being purified and partially characterized by MS/MS. Concentrations of sucrose and maltose, as well as their interactions were the most important factors regarding isomalto-oligosaccharides production. The production of overall oligosaccharides could be increased by increasing sucrose and maltose concentrations. Lactose, cellobiose, other disaccharides and trisaccharides could be acceptors for W. consufa dextransucrase. In combination with the structures from previous publications, 2-a-Dglucopyranosyl-cellobiose and 2-a-D-glucopyranosyl-lactose were probably the primary products for cellobiose and lactose, although one trisaccharide synthesized by lactose acceptor reaction remains unknown. In order to verify the characterization, NMR spectroscopic analysis is needed for further study. In conclusion, W. consufa dextransucrase is capable of catalyzing oligosaccharides synthesis, and acceptor reactions would be promising methods in producing prebiotic oligosaccharides.
  • Xu, Maonian (Helsingfors universitet, 2013)
    A review of the literature emphasised the significance of protein oxidation, which can lead to such modifications as the loss of essential amino acids and protein cross-links, and may bring about adverse effects on human nutrition and protein functionality. As the globulin fraction constitutes the predominant storage protein in oats, oxidation of oat globulin is in great need of attention and understanding. Oat globulin-containing oil-in-water emulsions were used as a food model. Thus, the objectives of the present work include the oxidation of oat proteins as well as lipid oxidation in prepared food emulsions together with a commercial oat protein-containing cream, and the possible antioxidant activities of berry phenolics (i.e. ellagitannins) towards protein oxidation. Oat globulin was extracted with a cold isolation buffer preceded by the removal of water-soluble impurities. Oxidation took place in darkness by placing the emulsion and cream samples in an oven with continuous stirring and a constant temperature at 37 oC. Sampling for lipid and protein oxidation measurements was carried out at day 0, 3 6 and 9. During the 9-day oxidation, no hexanal was detected in any oat protein-containing samples except for the ones without oat proteins, which were measured by headspace gas chromatography. The development of protein oxidation in prepared emulsions could not be revealed by the proposed loss of tryptophan fluorescence, as the tryptophan fluorescence actually increased and then decreased in the current study as opposed to continuous decrease as indicated in references, but carbonyl and dityrosine formation reflected the progression of protein oxidation. However, the same fluorescence techniques as in prepared emulsions ended up with contradictory fluorescence results in cream samples due to syneresis of oat creams during oxidation. In conclusion, fluorescence spectroscopy is a promising technique to investigate protein oxidation in food emulsions using carbonyl and dityrosine formation as oxidation markers.
  • Zeng, Xin (Helsingfors universitet, 2014)
    The literature review part describes a whey protein, ?-lactalbumin (ALA) and its oxidation, aronia (Aronia melanocarpa) procyanidins including their chemistry and analysis, as well as interactions between protein and plant phenolics. The aim of the thesis was to study the oxidation of tryptic peptides of ALA with and without procyanidins. Fractions containing both procyanidin dimers and trimers were collected from aronia juice proanthocyanidins with preparative-HPLC thereafter identified and quantified with UHPLC and NP-HPLC. ALA was digested by modified trypsin and the subsequent peptides were fractionated with preparative-HPLC. The selected peptides were WLAHKALC (m/z 936) and LDQWLCEK (m/z 1034), containing specific amino acids prone to oxidation. The oxidation of peptides with and without procyanidins was catalysed by ascorbic acid, H2O2 and FeCl3, and lasted for 14 days. Oxidation was monitored with LC-MS using samples collected on days 0, 1, 7 and 14. For peptide-phenolic interaction studies, peptide WLAHKALC (m/z 936) was incubated with procyanidin B2 standard (dimer) and peptide LDQWLCEK (m/z 1034) with aronia procyanidin dimers and trimers with a 10:1 ratio. Dimeric and trimeric procyanidins exhibited antioxidant activity towards selected peptides. Possible interaction products were not detected. For further investigations of interaction, higher concentration and ratio of peptides and procyanidins as well as expanding the MS detection range are recommended. Intensive research of oxidation products of ALA peptides is needed to accomplish a thorough understanding of the oxidation and other interaction reactions of ALA peptides with other food constituents.
  • Liu, Chang (Helsingfors universitet, 2015)
    The literature review related to faba bean proteins, the mechanism of protein oxidation and detection methods for protein oxidation as well as the relationship between lipid and protein oxidation. Native faba bean, faba bean treated by oven and microwave, as well as soy protein isolate were used as materials. The materials differed in their lipoxygenase activity. Oil-in-water emulsions were made of 10% purified (removal of antioxidants) rapeseed oil and 3% water soluble proteins that were extracted from flour samples. The emulsions were prepared by homogenizing using microfludizer. Oxidation took place in the oven at 37 °C in the dark with constant stirring by magnet stirrers. Sampling for measurements was carried out on day 0, 1, 4 and 7 from each replicate. Oxidative stability of was monitored by following lipid oxidation as formation of conjugated dienes and hexanal, and by following protein oxidation by measuring loss of tryptophan, formation of carbonyls and dityrosine through fluorescence detections both in the lipid phase and in the continuous phase. In this study, the degree of protein oxidation was generally consistent with corresponding lipid oxidation. Generally, the degree of protein oxidation in lipid phase of emulsions was higher than that in continuous phase, although the protein content was far less in the lipid phase. Both results implied co-oxidative relationship between lipid and protein oxidation. In addition, the results showed that thermal treatment or microwave irradiation can not only result in retarding or decreasing lipid oxidation by lowing lipoxygenase (LOX) activity, but also affect protein oxidation via lipid oxidation and the conformational changes of proteins.