Browsing by Subject "food Chemistry"

Sort by: Order: Results:

Now showing items 1-2 of 2
  • Chamlagain, Bhawani (Helsingin yliopisto, 2016)
    Vitamin B12 (later B12) intake is insufficient in developing countries, and globally, vegetarians and vegans are also at risk of B12 deficiency. Occurring naturally only in foods of animal origin, new affordable and sustainable dietary sources of B12 are needed to ensure sufficient intake. The only known food-grade producers of active B12, Propionibacterium freudenreichii strains, however, are yet to be exploited to enrich plant-based foods with B12. The B12 production capacity of P. freudenreichii depends on the strain, and the availability of the B12 lower ligand (5,6-dimethylbenzimidazole, DMBI) is a key factor for the production of active B12. Bread can be considered as a potential food for B12 fortification; yet the stability of in situ-produced B12 incorporated during breadmaking processes is not known. Current analytical methods such as the microbiological assay (MBA) lack the required specificity and the existing high-performance liquid chromatography (HPLC) methods are only capable of measuring higher B12 levels in fortified foods and supplements. The determination of active B12 in fermented foods, however, needs sensitive and selective methods. An ultra-HPLC (UHPLC) method was developed and validated to measure the active B12 contents. The identity of the B12 form was confirmed with an ion-trap or quadrupole time-of-flight mass spectrometry (MS). The B12 production capacity of 27 P. freudenreichii and 3 Propionibacterium acidipropionici strains was first studied in whey-based medium (WBM), and three of these P. freudenreichii strains were chosen to study B12 production in three aqueous cereal matrices prepared from malted barley (BM; 33% w/v), barley flour (BF; 6% w/v) and wheat aleurone (AM). Riboflavin (RF) and nicotinamide (NAM) as food-grade replacements for DMBI were investigated in WBM and cereal matrices. The stability of in situ-produced B12 and added cyanocobalamin (CNCbl) and hydroxocobalamin (OHCbl) during straight-dough, sponge-dough and sourdough breadmaking was studied. The developed UHPLC method employing an Acquity high-strength silica (HSS) T3 column showed excellent separation of active B12 from its analogues. A low limit of detection (0.075 ng/inj) enabled the measurement of the B12 levels in cell extracts directly and following immunoaffinity purification in extracts of fermented cereal matrices and B12-fortified baking samples. Analysis with UHPLC MS confirmed the production of active B12 by all 27 P. freudenreichii strains in WBM and 3 P. freudenreichii strains in cereal matrices. P. acidipropionici strains, however, produced an inactive form (pseudovitamin B12), thus making them unsuitable for active B12 fortification in foods. The level of B12 production in WBM varied considerably between the strains (0.45‒3.35 µg/mL), which increased up to 4-fold in 12 of the 27 P. freudenreichii strains following supplementation with RF and NAM. In many of these strains, the B12 yield was higher with RF and NAM co-supplementation than with DMBI. In cereal matrices without supplementation, the produced levels of active B12 (9‒37 ng/g) with P. freudenreichii strains were nutritionally significant. The B12 production increased many-fold, reaching up to 430 ng/g in BM, 39 ng/g in BF and 114 ng/g by adding cobalt (Co) and reached 712 ng/g in BM and 180 ng/g in AM with RF and NAM co-supplementation with Co. The incorporated in situ-produced B12 was retained during straight-dough breadmaking and the loss of 29% during sourdough baking was similar to the losses observed for relatively stable CNCbl. However, the added OHCbl decreased by 21%, 31% and 44% respectively in straight-dough, sponge-dough and sourdough breadmaking. These results showed that B12 produced in situ and incorporated during breadmaking was well retained in the bread prepared by the conventional breadmaking processes. This thesis shows that UHPLC combined with MS allows for the accurate identification and quantitation of low levels of active B12 in fermented food matrices (≥1 ng/g). P. freudenreichii strains could be utilised for in situ production of active B12 in cereal matrices and WBM. The availability of RF and NAM could considerably improve B12 production. The produced levels could easily fulfil the recommended dietary allowance set for B12 (e.g. 2‒2.4 µg/day for adults), and could be well retained in bread in the commonly used breadmaking processes.
  • Damerau, Annelie (Helsingin yliopisto, 2015)
    The consumption of whole grain foods high in fibre is of interest because of the health-promoting effects associated with dietary fibre. Therefore, there is interest in developing new fibre-rich cereal foods. However, these kinds of foods also contain polyunsaturated lipids, which are prone to oxidation. Further, lipids are dispersed in a heterogeneous matrix of starch, proteins and fibre, which increases their tendency to oxidize because of a large surface area and possible contact with prooxidants. The oxidation of lipids decreases nutritional quality and causes the formation of undesirable flavours. Knowledge of the oxidation behaviour of dispersed lipids in solid cereal foods, and of how factors like process parameters, structural features of the products and storage conditions affect lipid oxidation, is limited. In this thesis, the oxidative behaviour of foods with dispersed lipids was studied using two model systems. The first model system was a spray-dried emulsion containing sunflower oil encapsulated in a Na-caseinate-maltodextrin matrix, with either non-cross-linked or cross-linked proteins. The stability of the total and surface lipid fractions was determined during storage under different relative humidities (RHs). Further, the effect of RH on the amount of volatiles released from oxidized spray-dried emulsions was studied. The second model system consisted of extruded cereals produced from either whole grain oats or rye bran (coarse or fine) using different extrusion parameters. Their oxidative stability was studied during storage at 40 ºC, after milling and standardization to RH 33%. The primary oxidation was measured by peroxide values in the spray-dried emulsions and by losses of tocopherols and tocotrienols in the spray-dried emulsions and rye bran extrudates. Secondary oxidation was determined based on volatile secondary lipid oxidation products analysed by static head space (SHS-GC-FID) in the spray-dried emulsions and by head space solid-phase micro extraction (HS-SPME-GC-MS) in the extruded cereals. In addition to the oxidation parameters, enzymatic hydrolysis of lipids in the oat extrudates and the fatty acid composition of all models were studied by measuring the neutral lipid and fatty acid profiles, respectively. Increasing the RH improved the oxidative stability of both the total and surface lipid fractions of the stored spray-dried emulsions. This behaviour was mainly linked to the loss of individual powder particles upon caking and collapsing of the matrix at RH 75%. In addition, excess protein may have delayed oxidation via its radical scavenging activity. At RH 54%, cross-linking of the protein slightly improved the oxidative stability. The profiles of the volatile oxidation products from the spray-dried emulsions analysed by HS-SPME were also influenced by the RH. The effect was related to water-induced changes in hydrophilicity, structure and binding ability of the matrix, and to partitioning and solubility of the volatiles. The highest overall amount of volatiles released was obtained at water contents of 3.1% and 5.2% (RH 11% and 33%). The enzymatic hydrolysis of lipids in oats was effectively prevented by extrusion, even at the lowest temperature of 70 °C. The extrusion temperature could be increased to 110 °C without subjecting the lipids to non-enzymatic oxidation. However, by increasing the temperature to 130 °C, lipid oxidation was promoted, which also yielded losses of neutral lipids over time. In the case of the rye bran, the low water content (13% or 16%) in the extrusion of coarse or fine bran led to the most stable lipids during storage. The improved oxidative stability at low water contents in extrusion was connected with the higher formation of Maillard reaction products, which could have acted as antioxidants. The grinding of rye bran prior to extrusion caused a loss of tocols and increased the amounts of Maillard reaction products formed. The oxidative stability of the dispersed lipids was shown to be highly related to water induced physical changes in the matrix structure, which makes controlling the RH in the surrounding atmosphere an important factor in storage. Further, the RH affected the amount of volatile lipid oxidation products released, and this needs to be considered in determining lipid oxidation by HS-SPME. Extrusion was shown to inactivate lipases in oats. For the lipid stability in cereal extrudates, low temperature and low water content during extrusion were shown to be beneficial.