Oxidative stability of solid foods with dispersed lipids

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.Kuluttajat haluavat uudenlaisia tuotteita, joissa on täysjyväviljaa ja jotka sisältävät paljon ravintokuitua. Tällaisten tuotteiden rasva on usein jakaantunut pieniksi pisaroiksi eli dispergoitunut. Kun se lisäksi sisältää runsaasti monityydyttymättömiä rasvahappoja, se hapettuu melko nopeasti. Tämä johtaa haju- ja makuvirheisiin, jotka huonontavat tuotteen laatua. Tässä työssä tutkittiin dispergoituneen rasvan hapettumiskestävyyttä kahta elintarvikemallia käyttäen. Ensimmäinen malli oli sumutuskuivattu emulsio, joka kuvaa esim. maitojauhetta ja keittojauheita. Työssä osoitettiin, että hapettuneen hajun muodostumiseen varastoinnin aikana vaikutti suuresti ilman suhteellinen kosteus. Se muutti veden määrää sumutuskuivatuissa tuotteissa, mikä johti jauheen rakenteen muutokseen. Nämä rakennemuutokset vaikuttavat hapen diffuusioon jauheeseen, millä on keskeinen merkitys rasvojen hapettumisessa. Ilman suhteellisen kosteuden hallinta varastoinnin aikana on siksi tärkeää elintarvikkeiden säilyvyyden kannalta. Työssä osoitettiin myös, että kosteuden aiheuttamat rakennemuutokset jauheissa vaikuttivat haihtuvien yhdisteiden vapautumiseen. Tämä on tärkeää ottaa huomioon, kun elintarvikkeiden rasvojen hapettumiskestävyyttä mitataan haihtuvien yhdisteiden avulla. Jos hapettumisessa syntyneet haihtuvat yhdisteet eivät vapaudu elintarvikkeesta, niitä ei myöskään pystytä mittaamaa käytössä olevilla tekniikoilla. Tällöin hapettumisen taso voidaan arvioida väärin. Toisena esimerkkimallina käytettiin kahta ekstruusiolla valmistettua viljatuotetta, jotka kuvaavat aamiaismuroja ja suolaisia välipaloja. Perusraaka-aineina käytettiin täysjyväkaurajauhoa ja ruisleseitä. Molemmissa viljatuotteissa rasvojen hapettumiskestävyys varastoinnin aikana riippui suuresti tuotteiden prosessointiolosuhteista. Kun ekstruusiolämpötila oli 70 °C, se riitti estämään kauran entsyymitoiminnan, joka muuten heikentää tuotteen säilymistä. Työssä voitiin myös osoittaa, että ekstruusiolämpötilaa voitiin nostaa ja vasta 130 °C:ssa ekstrudoitujen kauratuotteiden säilyvyys heikkeni. Näin korkea lämpötila edisti rasvojen kemiallista hapettumista. Ruisleseen ekstruusiossa puolestaan todettiin, että raaka-aineseoksen pieni vesipitoisuus (13 %) paransi tuotteen säilyvyyttä suurempaan vesipitoisuuden (30 %) verrattuna. Ekstruusiotutkimuksista voidaan yhteenvetona todeta, että seoksen pieni vesipitoisuus ja matala ekstruusiolämpötila paransivat tuotteen varastointikestävyyttä. Myös ruisleseiden partikkelikoon pienentäminen ja ekstruuderin syöttöruuvin nopeuden suurentaminen paransivat tuotteen säilyvyyttä. Tätä tietoa voidaan käyttää tulevaisuudessa kehitettäessä uusia täysjyvävilja- ja lesetuotteita

Enzyme-Assisted Extraction of Fish Oil from Whole Fish and by-Products of Baltic Herring (Clupea harengus membras)

Baltic herring (Clupea harengus membras) is one of the most abundant commercially caught fish species from the Baltic Sea. Despite the high content of fat and omega-3 fatty acids, the consumption of Baltic herring has decreased dramatically over the last four decades, mostly due to the small sizes and difficulty in processing. At the same time there is an increasing global demand for fish and fish oil rich in omega-3 fatty acids. This study aimed to investigate enzyme-assisted oil extraction as an environmentally friendly process for valorizing the underutilized fish species and by-products to high quality fish oil for human consumption. Three different commercially available proteolytic enzymes (Alcalase®, Neutrase® and Protamex®) and two treatment times (35 and 70 min) were investigated in the extraction of fish oil from whole fish and by-products from filleting of Baltic herring. The oil quality and stability were studied with peroxide- and p-anisidine value analyses, fatty acid analysis with GC-FID, and volatile compounds with HS-SPME-GC-MS. Overall, longer extraction times led to better oil yields but also increased oxidation of the oil. For whole fish, the highest oil yields were from the 70-min extractions with Neutrase and Protamex. Protamex extraction with 35 min resulted in the best fatty acid composition with the highest content of eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) but also increased oxidation compared to treatment with other enzymes. For by-products, the highest oil yield was obtained from the 70-min extraction with Protamex without significant differences in EPA and DHA contents among the oils extracted with different enzymes. Oxidation was lowest in the oil produced with 35-min treatment using Neutrase and Protamex. This study showed the potential of using proteolytic enzymes in the extraction of crude oil from Baltic herring and its by-products. However, further research is needed to optimize enzymatic processing of Baltic herring and its by-products to improve yield and quality of crude oil.</p

Effect of supercritical CO2 plant extract and berry press cakes on stability and consumer acceptance of frozen Baltic herring (Clupea harengus membras) mince

A promising way of processing Baltic herring, Clupea harengus membras, is turning the fish into boneless mince. However, Baltic herring is prone to lipid oxidation, which possesses a challenge for industrial applications. The aim of this work was to study the efficacy of press cakes from Finnish berries and a supercritical CO2 plant extract to limit lipid oxidation during frozen storage of Baltic herring mince and to determine the impact of these additions on consumer acceptance in a fish product. Peroxide value, formation of volatile oxidation products and loss of polyunsaturated fatty acids showed that the tested natural additives decreased oxidation to a greater or similar extent as conventional antioxidants during 10-month storage. While potential of berry press cakes and plant extracts as "green label antioxidants" was shown, consumer study indicated need for further research to reach both optimal antioxidative efficacy and sensory properties.Peer reviewe

Oxidative stability, oxidation pattern and α-tocopherol response of docosahexaenoic acid (DHA, 22:6n-3)-containing triacylglycerols and ethyl esters

DHA is most often used in supplements either in its triacylglycerol or ethyl ester form. Currently, there is only little published data on the differences in the oxidative stability and α-tocopherol response between the two lipid structures, as well as on the oxidation patterns of pure DHA. This study investigated the oxidative stability, α-tocopherol response and oxidation pattern of DHA incorporated in triacylglycerols and as ethyl esters with an untargeted approach after oxidation at 50 °C in the dark. Liquid and gas chromatographic methods with mass spectrometric detection and nuclear magnetic resonance spectroscopy were applied. DHA was more stable in triacylglycerols than as ethyl esters without α-tocopherol addition. With α-tocopherol added the opposite was observed. The oxidation products formed during triacylglycerol and ethyl ester oil oxidation were mostly similar, but also some structure-related differences were detected in both volatile and non-volatile oxidation products

Evaluation of the composition and oxidative status of omega-3 fatty acid supplements on the Finnish market using NMR and SPME-GC–MS in comparison with conventional methods

Previous studies disagree on the oxidative status of omega-3 supplements. The great deviation raises concerns about quality and the methods used to monitor it. This study investigated 49 omega-3 products for their fatty acid content, lipid class and oxidative status using official methods, gas and liquid chromatography with mass spectrometry and nuclear magnetic resonance spectroscopy. With minor deviations, omega-3 fatty acid content and lipid class of all products were as declared. 24% of studied products exceeded thresholds set by The Global Organization for EPA and DHA Omega-3s for peroxide and/or p-anisidine value suggesting a compromised oxidative status. However, peroxide and/or p-anisidine value were only suitable for detection of lipid oxidation in 90% or 73%, respectively, of the products. Analysis of volatile oxidation compounds can be an alternative method for p-anisidine value. Nuclear magnetic resonance spectroscopy was shown to be a rapid method for determination of oil type and lipid class.</p

Baltic herring (Clupea harengus membras) oil encapsulation by spray drying using a rice and whey protein blend as a coating material

As popular coating material for encapsulation like milk proteins and maltodextrin do not fully mask unpleasant fish flavors, rice and whey protein blend was tested to aid the use of Baltic herring (BH) oil in functional foods. Particle size and morphology of emulsions (7.5% whey protein, 7.5% rice protein, 15% BH oil and water) produced at pH 3, 6 or 8 with one or two step homogenization and resulting powders were characterized together with fatty acid composition, volatile compounds and oxidative stability. The use of rice and whey proteins lead to stable emulsions with bimodal size distribution and large dispersion (0.05-100 mu m). Emulsion's pH affected powder particle sizes, with pH 3 resulting in powders with biggest particle sizes. Morphology of powders showed spherical shape with porous structure. Emulsions with pH 6.5 produced powders with the highest induction periods (1.59-1.73 h) and low content of volatile compounds

Effect of supercritical CO2 plant extract and berry press cakes on stability and consumer acceptance of frozen Baltic herring (Clupea harengus membras) mince

A promising way of processing Baltic herring, Clupea harengus membras, is turning the fish into boneless mince. However, Baltic herring is prone to lipid oxidation, which possesses a challenge for industrial applications. The aim of this work was to study the efficacy of press cakes from Finnish berries and a supercritical CO2 plant extract to limit lipid oxidation during frozen storage of Baltic herring mince and to determine the impact of these additions on consumer acceptance in a fish product. Peroxide value, formation of volatile oxidation products and loss of polyunsaturated fatty acids showed that the tested natural additives decreased oxidation to a greater or similar extent as conventional antioxidants during 10-month storage. While potential of berry press cakes and plant extracts as“green label antioxidants”was shown, consumer study indicated need for further research to reach both optimal antioxidative efficacy and sensory properties</p

Baltic herring (Clupea harengus membras) protein isolate produced using the pH-shift process and its application in food models

In this study, protein isolate was prepared from Baltic herring (Clupea harengus membras) using alkaline pH-shift process. The aim of this research was to characterize the protein isolate and to study its potential in food models. A special focus was placed on characterization of odour profile and volatile compounds contributing to the odour profile of the protein isolate using gas chromatography - olfactometry. 2,3-Pentanedione, hexanal, 4(Z)-heptenal, 2,4(E,E)-nonadienal, and three compounds tentatively identified as 1,5(E)-octadien-3-ol, 1,5(Z)-octadien-3-ol, and 1,5(Z)-octadien-3-one were the most important odour-contributing compounds in the protein isolate (Nasal Impact Factor 83-100%, intensity 2.6-3.3 on a scale 0–4). 2-Methylpropanal, 2- and 3-methylbutanal, and three unknown compounds were less intense in the protein isolate than in the raw material, which might have contributed to the lower intensity of fishiness observed for the protein isolate (2.2 vs 3.3 on a scale 0–4). Surimi-type gels prepared from the Baltic herring protein isolate had texture properties (hardness and cohesiveness) similar to those of commercial products. Due to the abundancy of dark muscle tissue in Baltic herring, the protein isolate had a significantly lower whiteness (W=63) compared to the commercial surimi products (W=80–83). Increasing the solubilisation or precipitation pH did not improve the whiteness, but resulted in significantly softer, less cohesive, and less chewy gels. The findings of this study indicate that alkaline-based pH-shift processing is a potential way to increase the food application of Baltic herring.</p

Quality of Protein Isolates and Hydrolysates from Baltic Herring (Clupea harengus membras) and Roach (Rutilus rutilus) Produced by pH-Shift Processes and Enzymatic Hydrolysis

Fractionation is a potential way to valorize under-utilized fishes, but the quality of the resulting fractions is crucial in terms of their applicability. The aim of this work was to study the quality of protein isolates and hydrolysates extracted from roach (Rutilus rutilus) and Baltic herring (Clupea harengus membras) using either pH shift or enzymatic hydrolysis. The amino acid composition of protein isolates and hydrolysates mostly complied with the nutritional requirements for adults, but protein isolates produced using pH shift showed higher essential to non-essential amino acid ratios compared with enzymatically produced hydrolysates, 0.84-0.85 vs. 0.65-0.70, respectively. Enzymatically produced protein hydrolysates had a lower total lipid content, lower proportion of phospholipids, and exhibited lower degrees of protein and lipid oxidation compared with pH-shift-produced isolates. These findings suggest enzymatic hydrolysis to be more promising from a lipid oxidation perspective while the pH-shift method ranked higher from a nutrient perspective. However, due to the different applications of protein isolates and hydrolysates produced using pH shift or enzymatic hydrolysis, respectively, the further optimization of both studied methods is recommended