| 1. |
- Eriksson, Caj
(författare)
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Lipid oxidation catalysts and inhibitors in raw materials and processed foods
- 1982
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Ingår i: Food Chemistry. - : Elsevier BV. - 0308-8146 .- 1873-7072. ; 9:42006, s. 3-19
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Tidskriftsartikel (refereegranskat)abstract
- This paper is limited to those catalysts and lipid oxidation inhibitors which have been found to be present either in the raw food materials or in processed food as a result of its processing. Lipoxygenase and haemoproteins are very powerful lipid oxidation catalysts in many foods. Heat treatment usually inactivates lipoxygenase but can, under certain conditions, activate haemoproteins as non-enzymatic metal catalysts. Tocopherol, normally referred to as an antioxidant, can, under certain concentration conditions, shift to pro-oxidative properties. Even volatile lipid oxidation products have been shown to accelerate lipid oxidation. Inhibitors present in raw materials are found among proteins, amino acids and plant constituents such as flavonoids. Most spices and herbs have antioxidative properties, particularly in darkness. Some microorganisms in their normal metabolism inhibit lipid oxidation or the consequences thereof. Some enzymes, especially superoxide dismutase, are claimed to inhibit lipid oxidation. Among process-induced lipid oxidation inhibitors, Maillard reaction products are those most investigated, together with protein hydrolysates. Smoking generates antioxidative compounds. In most cases the mechanism of lipid oxidation inhibition is still unknown for these materials. © 1982.
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| 2. |
- Finglas, P M, et al.
(författare)
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Standardisation of HPLC techniques for the determination of naturally-occurring folates in food
- 1999
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Ingår i: Food Chemistry. - 0308-8146 .- 1873-7072. ; 64:2, s. 245-255
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this work was to evaluate current in-house HPLC procedures for the determination of naturally-occurring folates in food, and to identify problem areas for further improvement. Five intercomparison studies were completed over the period 1990-1997 in which nine participants from six countries took part. Through careful validations and detailed discussions held at evaluation meetings, possible biases and sources of systematic error have been identified and reduced. The use of ascorbic acid and nitrogen flushing during extraction, sample clean-up using strong anion exchange columns, spectrophometrically calibrated standards and fluorescence detection are all recommended. Both in-house hog kidney and human plasma deconjugase enzymes gave similar results to the circulated common hog kidney enzyme which was prepared from fresh pig's kidneys. The most consistently reported values were for 5-CH3H4-PteGlu, and to a lesser extent, for H(4)PteGlu. Four candidate reference materials (CRM 121, wholemeal flour; CRM 421, milk powder; CRM 485, lyophilised mixed vegetables, and CRM 487, lyophilised pig's liver) have been proposed with both indicative values (mean +/- uncertainty) for 5-CH3H4-PteGlu in CRM 421 (0.25; +/- 0.02 mg/kg) and CRM 485 (2.14; +/- 0.42 mg/kg), and information values (mean; range) for 5-CH3H4-PteGlu in CRh4 121 (0.04; 0.03-0.08 mg/kg) and CRM 487 (2.6; 1.9-3.8 mg/kg), Certified values are also given for total folate by microbiological assay: CRM 121 (0.50; +/- 0.07 mg/kg), CRM 421 (1.42; +/- 0.14 mg/kg), CRM 485 (3.15; 0.28 mg/kg), and CRM 487 (13.4; 1.3 mg/kg). Average recovery of 5-CH3H4-PteGlu, added prior to extraction and deconjugation, was 91% (84-95%) for the four CRMs. The average within- and between-laboratory variations were 6 and 15% for the determination of 5-CH3H4-PteGlu by HPLC, and 9 and 18% for the determination of total folate by microbiological assay. These CRMs will be used for quality control of folate measurements for nutritional labelling, and validation of new techniques. Further methodology work is required for the HPLC analyses of folate forms other than 5-CH3H4-PteGlu.
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| 3. |
- Hallberg, M.L., et al.
(författare)
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The relationship between lipid composition and oxidative stability of potato granules
- 1990
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Ingår i: Food Chemistry. - : Elsevier BV. - 0308-8146 .- 1873-7072. ; 38:3, s. 201-210
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Tidskriftsartikel (refereegranskat)abstract
- Lipid oxidation and changes in the lipid composition of potato granules during storage were studied. In particular, the possible rôle of the free fatty acids (FFA) in oxidation and storage stability was examined. Three potato granule materials which differed in FFA content were stored in darkness, in air at 25°C. The lipid oxidation was followed by gas chromatographic headspace analysis of volatile compounds and sensory evaluation was carried out after periods of 12 and 40 weeks of storage. The FFA were analysed by gas chromatography to determine fatty acid composition during storage. All three of the potato granule materials were markedly oxidized. However, the material containing the least original amount of FFA was the most rancid after only 12 weeks storage, according to both the sensory analysis and the content of hexanal. This shows that there was no connection between the original total amount of FFA and the oxidative stability of the potato granules. In the most highly oxidized material the FFA content decreased towards the end of the storage period, but in the other two materials, for which the rate of oxidation was lower, there was a slight increase of the polyunsaturated FFA (C18:2 + C18:3). This indicates that both simultaneous lipolysis and oxidation took place during storage. The fatty acid compositions within the lipid classes; neutral lipids, galactolipids, and phospholipids, were not found to change significantly during storage. © 1990.
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| 4. |
- Hansson, A., et al.
(författare)
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Effect of changes in pH on the release of flavour compounds from a soft drink-related model system
- 2001
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Ingår i: Food Chemistry. - 0308-8146 .- 1873-7072. ; 74:4, s. 429-435
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Tidskriftsartikel (refereegranskat)abstract
- Citric acid and phosphoric acid were added in variable amounts to a soft drink model system to show their effect on the release of six flavour compounds. High concentrations of the acids decreased the release of esters, probably because of the presence of large amounts of the dissociated form of the acids. However, the same amounts of added citric acid had no effect on flavour release when pH was regulated with sodium hydroxide. Changes in pH values achieved by adding hydrochloric acid also had no effect on flavour release. These results indicate that pH values used in soft drinks do not affect the release of flavour molecules. It is more likely the citric acid and the phosphoric acid, particularly their dissociated forms, which decrease the release of the esters. The other flavour compounds were not affected. Copyright © 2001 Elsevier Science Ltd.
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| 5. |
- Hansson, A., et al.
(författare)
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The effect of sugars and pectin on flavour release from a soft drink-related model system
- 2001
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Ingår i: Food Chemistry. - 0308-8146 .- 1873-7072. ; 72:3, s. 363-368
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Tidskriftsartikel (refereegranskat)abstract
- Three types of sugar and high-methoxyl pectin at different concentrations were added to a soft drink-related model system consisting of water and six flavour compounds. The addition of these ingredients contributes to changes in viscosity and water activity, which in turn affects the release of the flavour compounds to the gas phase above the soft drink. In the study, a higher concentration of sucrose and invert sugar increased the release of five flavour compounds, probably owing to a so-called 'salting-out' effect. Starch syrup at a concentration of 60% increased the amount of three of the flavour compounds released and would probably increase the release of more compounds at a higher concentration. When pectin was added to the system, it was seen that viscosity does not influence release of the flavour molecules, but that the kind of stabiliser used is more important. Copyright © 2001 Elsevier Science Ltd.
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| 6. |
- Jastrebova, Jelena, et al.
(författare)
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HPLC determination of folates in raw and processed beetroots
- 2003
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Ingår i: Food Chemistry. - 0308-8146 .- 1873-7072. ; 80:4, s. 579-588
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Tidskriftsartikel (refereegranskat)abstract
- A sensitive HPLC method with fluorescence detection and gradient elution has been developed for the determination of folates in vegetables. The method involved extraction of folates from food matrix by heat treatment, deconjugation of folate polyglutamates to monoglutamates by incubation with hog kidney conjugase and purification of food extracts by solid-phase extraction with strong-anion exchange cartridges. The chromatographic separation of folates was achieved on Zorbax SB C-8 column, which was found to be superior over conventional C-18 column in terms of selectivity and sensitivity. Validation of the method included linearity tests, the addition of standard folates for the determination of recovery, repeatability and stability tests. The method developed was applied to analysis of raw and processed beetroots; 5-methyltetrahydrofolate was found to be the main folate form in beetroots. Cultivar differences and growing conditions were found to have a pronounced effect on the folate content in beetroots. Processing resulted in considerable losses of folates, whereas losses during storage appeared to be moderate.
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| 7. |
- Lilja, Marianne, et al.
(författare)
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Liberation of free fatty acids during production of potato granules
- 1989
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Ingår i: Food Chemistry. - : Elsevier BV. - 0308-8146 .- 1873-7072. ; 34:1, s. 15-23
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Tidskriftsartikel (refereegranskat)abstract
- The amount of free fatty acids and their composition were studied during an add-back process of potato granules. Samples were taken at several different stages in the production, from raw tubers to final potato granules. Lipids were extracted and lipid classes separated by liquid chromatography. Free fatty acids were separated from the neutral lipid fraction by high performance liquid chromatography (HPLC). The fatty acid composition was analysed by gas chromatography (GC). The amount of free fatty acid increased in the first stages of the process and rose to its highest level in the samples from the steam-cooking step. During further processing the amounts of free fatty acids slowly decreased. Since enzymatic hydrolysis is one explanation for liberation of fatty acids, lipase activity was measured by a spectrofluorimetric method in the raw tubers, blanched slices and steam-cooked slices. After the blanching step, some enzyme activity was found but after steam-cooking there was none. © 1989.
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| 8. |
- Lilja, Marianne, et al.
(författare)
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Lipid changes during the production of potato granules
- 1989
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Ingår i: Food Chemistry. - 0308-8146 .- 1873-7072. ; 31:4, s. 267-277
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Tidskriftsartikel (refereegranskat)abstract
- Potato granules were produced by an add-back-process. The lipid composition of the potato tubers and the final potato granules were assessed in order to study the influence of the process. The extracted lipids were fractionated into three major classes, neutral lipids, galacto-lipids and phospholipids, on a silicic acid column. The free fatty acids were separated from the neutral lipids by high performance liquid chromatography (HPLC). The fatty acid composition of the three lipid classes as well as the free fatty acid fraction was analysed by gas chromatography. No changes could be observed in the galactolipids and the phospholipids but the free fatty acid content was found to be about ten times higher in potato granules than in the potato tubers. © 1989.
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| 9. |
- Solomon, O., et al.
(författare)
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Effect of oxygen and fluorescent light on the quality of orange juice during storage at 8°C
- 1995
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Ingår i: Food Chemistry. - 0308-8146 .- 1873-7072. ; 53:4, s. 363-368
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Tidskriftsartikel (refereegranskat)abstract
- The effect of oxygen and light exposure and the combination of these two parameters on the retention of ascorbic acid, occurrence of non-enzymatic browning and the formation of 5-hydroxymethyl-2-furfuraldehyde (HMF) and furfural was investigated in orange juice stored at 8°C for 52 days. Orange juice, reconstituted and HTST-pasteurised, was stored in glass containers, covered on the sides with aluminium foil and sealed on the top with packaging materials, i.e. glass, polyethylene and paper carton. having different light transmission and oxygen permeation characteristics. The ascorbic acid content was significantly affected by the level of dissolved oxygen in the juice, but no effect of light could be observed under the conditions of this study. Browning increased during the first 3 weeks of storage in all samples and was over the whole period of storage significantly correlated to the level of dissolved oxygen, but the effect of light was insignificant. HMF and furfural content did not increase significantly in any of the samples during the 52-day storage at 8°C. © 1995.
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| 10. |
- Strålsjö, Lena, et al.
(författare)
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Evaluation of a radioprotein-binding assay (RPBA) for folate analysis in berries and milk
- 2002
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Ingår i: Food Chemistry. - 0308-8146 .- 1873-7072. ; 79:4, s. 525-534
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Tidskriftsartikel (refereegranskat)abstract
- This study aimed to optimise a commercial radioprotein-binding assay (RPBA), routinely used for clinical samples, for folate quantification in foods containing mainly 5-CH3-H(4)folate. The assay was modified using external calibration with 5-CH3-H(4)folate in a lower concentration range diluted in food extraction buffer, rather than the buffer with human serum albumin (HSA) provided by the kit. We evaluated the modified RBPA on some selected food products; milk, whey powder, rose hips, strawberries and European certified reference materials (CRM 421, 485) and the adjustments did not affect the assay negatively. Performance parameters included control of selectivity, absence of matrix effects, recoveries of 94-113%, precision of 1-6 CV% (intra-assay) and 5-9 CV% (inter-assay). Folate concentrations in berries and milk, obtained by the modified RPBA were also compared with other quantification methods such as HPLC and MA. The optimised RPBA was found to be a quick and inexpensive complement to HPLC methods, reliable for folate quantification in foods such as milk and berries that contain mainly 5-CH3-H(4)folate. (C) 2002 Elsevier Science Ltd. All rights reserved.
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