Effect of different colored filters on photooxidation in pasteurized milk

The effect of different colored filters and atmospheres on photooxidation and quality in milk was studied. Pasteurized bovine milk (3.9% fat) was packed in 2 different atmospheres (air and N₂) and exposed to light for 20 h at 4°C under 8 transparent filters with different light transmission properties. The following transparent, noncolored, and colored filters based on polyethylene terephthalate (PET) were used: noncolored (PET), noncolored with 2 different UV-block regions, yellow, green, amber, orange, and red. Control samples were stored in darkness and in a carton. Sensory evaluation showed off flavors significantly increased in milk stored under all filters compared with the control samples. Variation in atmosphere resulted in significant differences in formation of rancid flavor in milk stored under different filters. Milk samples stored in N₂ underwent the most sensory deterioration under orange and red filters, whereas milk samples stored in air were most deteriorated under noncolored filters. According to the oxidation compounds measured by gas chromatography, milk samples stored under noncolored and orange filters were highly oxidized, whereas red, green, and amber filters offered better protection against photooxidation. Fluorescence spectroscopy was used to examine the degradation of photosensitizers (riboflavin, protoporphyrin, and chlorophyllic compounds) in the milk samples. Degradation of protoporphyrin and chlorophyllic compounds in N₂ correlated well with sensory properties related to photooxidation (R² = 0.75-0.95). The study indicates that protoporphyrin and chlorophyllic compounds were effective photosensitizers in milk. To avoid photooxidation in milk, it is therefore important to protect it against light from the UV spectrum as well as light from the entire visible region.     

Mechanisms and Factors for Edible Oil Oxidation

ABSTRACT: Edible oil is oxidized during processing and storage via autoxidation and photosensitized oxidation, in which triplet oxygen (³O₂) and singlet oxygen (¹O₂) react with the oil, respectively. Autoxidation of oils requires radical forms of acylglycerols, whereas photosensitized oxidation does not require lipid radicals since ¹O₂ reacts directly with double bonds. Lipid hydroperoxides formed by ³O₂ are conjugated dienes, whereas ¹O₂ produces both conjugated and nonconjugated dienes. The hydroperoxides are decomposed to produce off‐flavor compounds and the oil quality decreases. Autoxidation of oil is accelerated by the presence of free fatty acids, mono‐ and diacylglycerols, metals such as iron, and thermally oxidized compounds. Chlorophylls and phenolic compounds decrease the autoxidation of oil in the dark, and carotenoids, tocopherols, and phospholipids demonstrate both antioxidant and prooxidant activity depending on the oil system. In photosensitized oxidation chlorophyll acts as a photosensitizer for the formation of ¹O₂; however, carotenoids and tocopherols decrease the oxidation through ¹O₂ quenching. Temperature, light, oxygen concentration, oil processing, and fatty acid composition also affect the oxidative stability of edible oil.     

Quality of Sour Cream Packaged in Cups with Different Light Barrier Properties Measured by Fluorescence Spectroscopy and Sensory Analysis

ABSTRACT:  In this study, photooxidation of sour cream packaged in cups with different light barrier properties was investigated. The sour cream was light exposed for 36 h with a standard fluorescent light tube, simulating storage conditions in many Norwegian grocery stores. Three different cups were evaluated: a white cup, a cup with medium light barrier (LB), and a cup with high LB. The quality of the sour cream was evaluated by sensory analysis and front face fluorescence spectroscopy. The sour cream stored in white cups became very rancid during the light exposure, with a rancid flavor score of 7.8 on a scale from 1 to 9, where 9 is the highest intensity. Cups with high LB gave best protection against the light. The sensory assessors could not distinguish between sour cream stored in cups with high LB and sour cream stored in the dark. The rancid flavor intensity for the cups with medium LB was significantly different ( P  < 0.05) from both the white cup and the cup with high LB. The sensory flavor intensities indicated that with 36 h of light exposure, only a cup with high LB will protect the sour cream sufficiently. The fluorescence measurements corresponded well with the sensory analysis as the photosensitizers were somewhat degraded for sour cream stored in cups with medium LB and most degraded in the white cups. For the cups with high LB, the fluorescence peaks that originated from the photosensitizers were all intact.
PRACTICAL APPLICATION: Dairy products such as sour cream will develop off-odor and taste faults ("sunlight taste") in a few hours if exposed to sufficient fluorescent lightning in the grocery stores. A light barrier can be incorporated in the packaging material to protect the dairy products from the light. Our experiment showed that the incorporation of a black pigment into 1 of the 3 plastic layers in the cup for packaging of sour cream protected the sour cream from degradation when exposed to light.     

Statistical Correlation of Quantitative Flavor Intensity Assessments and Individual Free Fatty Acid Measurements for Routine Detection and Prediction of Hydrolytic Rancidity Off-Flavors in Butter

A method for detecting and predicting hydrolytic rancidity off-flavors in butter has been developed by correlating quantitative sensory data with individual free fatty acid (FFA) concentrations (ppm) in butters using stepwise regression and discriminant analyses. An equation for indexing rancid flavor intensities in butter (Rancidity Score = 1.93163 + 0.01754 butyric acid + 0.00054 C₁₈ FFA congeners) gives Rancidity Scores for nonrancid, slightly rancid, and distinctly rancid butters between 1.00–2.80, 2.81–3.80, and 3.81–7.00, respectively. Hydrolytic rancidity off-flavors in butter are expressions of combinations of flavors in which rancid and goat-like flavors are principally caused by C₄ and C₆, and soapy and bitter flavors by C₁₀, and C₁₂ FFA.     

Determination of thermal oxidation and oxidation products of β-carotene in corn oil triacylglycerols

A reversed phase HPLC-DAD coupled to APCI-MS method is reported for the determination of the degradation of β-carotene and characterization of the oxidation products in corn oil. Corn oil containing β-carotene was oxidized in the Rancimat at 110 °C from 1 to 14 h. A significant degradation of β-carotene was observed in corn oil during accelerated thermal oxidation. A total of eight different oxidized products of β-carotene were identified, which includes 8′-apo-β-carotenal, 6′-apo-β-carotenal, 5,6-epoxy-8′-apo-β-carotenal, β-carotene-2,2′-dione, 13-Z-5,6,5′,6′-diepoxy-β-carotene, all-E-5,8-epoxy-β-carotene, all-E-5,6-epoxy-β-carotene, and 15-Z-5,6-epoxy-β-carotene. Corn oil triacylglycerols (TAGs) oxidation products were also identified using isocratic HPLC–ESI-MS. It was found that β-carotene promoted oxidation of TAGs especially at longer exposure times. For the first time two new classes of oxidized TAGs have been identified in corn oil, which were epidioxy bis-hydroperoxides and hydroxy bis-hydroperoxides. Other oxidation products of TAGs were mono-epoxides, mono-hydroperoxides, and epoxy hydroperoxides. It was found that complementing the HPLC-DAD method for β-carotene with ESI-MS method for TAGs oxidation provides a comprehensive set of analytical tools to characterize carotenoids and triacylglycerols oxidation and degradation in edible oils.     

QUENCHING MECHANISMS AND KINETICS OF CAROTENOIDS IN RIBOFLAVIN PHOTOSENSITIZED SINGLET OXYGEN OXIDATION OF VITAMIN D2

The oxidation of vitamin D₂ in a solution of 12% water, 88% acetone and 15 ppm ribqflavin under light or dark was studied by measuring the headspace oxygen. Ribofiavin accelerated the oxidation of vitamin D₂ by singlet oxygen under light, but did not affect vitamin D₂ oxidation under dark. Quenching mechanisms and kinetics within the range of 0–20 ppm β‐cawtene or fucoxanthin and with 0–80 ppm retinyl acetate or retinol on 15 ppm riboflavin photosensitized singlet oxygen oxidation of vitamin D₂ were also studied. The rate of singlet oxygen formation by 15 ppm riboflavin was 1.78 umole oxygen/mL headspace‐hour. The reaction rate constant of vitamin D₂ with singlet oxygen was 2.2 times 10⁷ M^?1A s^?1. The carotenoids minimized the oxidation of vitamin D₂ by quenching singlet oxygen. The total quenching rate constants of retinol, retinyl acetate, jucoxanthin and ft‐carotene were in the order of 1.22 times 10⁸, 5.98 times 10⁸, 1.78 times 10⁹ and 5.00 times 10⁹M^?1. s^?1 respectively, which suggests that as the number of double bonds of carotenoids increases, the quenching rate constant ofcarotenoid increases.     

Use of Multi-response Modelling to Investigate Mechanisms of β-Carotene Degradation in Dried Orange-Fleshed Sweet Potato During Storage: from Carotenoids to Aroma Compounds

In order to give insight into β-carotene degradation mechanism during the storage of dried orange-fleshed sweet potato, and particularly into the role of isomers and norisoprenoids formation, multi-response kinetic modelling was applied. Determination of degradation compounds were carried out by HPLD-DAD and SPME-GC-MS as a function of time between 10 and 40 °C and at four water activities from 0.13 to 0.76. Kinetic modelling was developed assuming first-order reactions and by using mass balance. Eight compounds, namely, two isomers (9-cis- and 13-cis-β-carotene), two β-carotene epoxides (β-carotene 5,6 and 5,8 epoxide) and four volatile compounds (β-cyclocitral, β-ionone, 5,6-epoxy-β-ionone and dihydroactinidiolide), were integrated into two theoretical reaction schemes. The different models were discriminated according to goodness of fit to experimental data. This work showed that: (1) the formation of cis-isomers from β-carotene preceded oxidation, (2) β-cyclocitral arose directly from β-carotene scission while the other norisoprenoids resulted from β-carotene epoxide degradation, (3) cis-isomers were high reactive compounds. Temperature had a major influence on reaction rates k while water activities only impacted k at values under 0.51. Therefore, multi-response modelling is not only a tool to predict β-carotene degradation but a interesting way to select the appropriate degradation scheme based on the different options presented in literature.     

Light-induced quality changes in plain yoghurt packed in polylactate and polystyrene

The potential of using materials based on polylactate (PLA) for packaging of plain yoghurt has been demonstrated in the present study. Plain yoghurt (3.5% fat) was stored for 5 weeks in PLA or polystyrene (PS) cups under fluorescent light (3500 lux) or in darkness. Quality changes were studied by determination of color stability, formation of lipid hydroperoxides, development of volatile products (secondary oxidation products and release of styrene and lactate from the packaging materials) and degradation of ß-carotene, and riboflavin was determined. For light-exposed yoghurts, PLA was at least as effective in preventing color changes and formation of lipid hydroperoxides as PS. During storage under fluorescence light, concentrations of n-hexanal, n-heptanal, n-octanal, n-nonanal, 3-methyl-butanal, dimethyl disulfide, and 1-octen-3-ol were lower in yoghurts packed in PLA than in PS. Furthermore, losses of riboflavin and ß-carotene were less in light-exposed yoghurt packed in PLA than in PS. The amount of styrene in yoghurt stored in PS cups increased during storage, whereas lactate was not found in yoghurts stored in PLA. Practically no development of lipid hydroperoxides and secondary oxidation products or loss of riboflavin and ß-carotene were observed in yoghurts stored in darkness. Thus, it can be concluded that light exposure reduced the quality of plain yoghurt and that PLA provided a better protection against photo-degradation processes than PS.     

Effects of Chlorophyll and β-Carotene on the Oxidation Stability of Olive Oil

Virgin olive oil was purified by silicic acid column chromatography to remove non-triglyceride components. The effects of chlorophyll and β-carotene on the oxidation stability of purified olive oil were studied by a combination of measuring peroxide value and oxygen disappearance in the headspace of sample bottles by gas chromatography. Chlorophyll in the purified oil acted as a photosensitizer for singlet oxygen formation under light. β-carotene minimized lipid oxidation of purified oil under light storage by its light-filtering effect. Experiments clearly suggested that singlet oxygen was mainly responsible for the photooxidation of the oil containing chlorophyll.     

PACKAGING PRESERVATION OF β-CAROTENE IN SWEET POTATO FLAKES USING FLEXIBLE FILM AND AN OXYGEN ABSORBER

Sweet potato flakes are potentially an affordable, shelf-stable source of provitamin A β-carotene. Because β-carotene is susceptible to oxidative degradation, particularly in dehydrated food materials exposed to atmospheric oxygen, several packaging conditions were evaluated for enhancement of β-carotene retention in sweet potato flakes during storage. The flakes were packaged in either a polypropylene film (high oxygen permeability) with air headspace or a nylon laminate film (low oxygen permeability) with air headspace, under vacuum, or with an Ageless oxygen absorber sachet enclosed. Packaged flakes were stored in the dark at ambient laboratory temperature (～23C), and β-carotene content was determined at intervals from 0 to 210 day storage using reversed-phase liquid chromatography. Among the packaging conditions tested, β-carotene retention was enhanced incrementally as the apparent availability of oxygen was reduced (nylon > polypropylene; oxygen absorber > vacuum > air headspace). The combined use of oxygen absorbers and flexible oxygen barrier film gave excellent retention of β-carotene during the 210 day trial.     

Impact of packaging and storage conditions on colour and β-carotene retention of pasteurised mango purée

The effects of light and oxygen on β-carotene, vitamin A value, and colour stability of mango purée during storage were evaluated. Non-aseptic production at a pilot-plant scale, involving continuous high-temperature-short-time (HTST) heating, caused significant 13-cis-β-carotene formation, resulting in a pro-vitamin A retention of 82.3–89.6%, while peroxidase (POD) activity was reduced to residual levels of 0.4–2.6% in the pasteurised purée. Since oxygen removal from the package headspace by flushing with superheated steam or N₂ marginally affected β-carotene stability during storage, hot-filling was most crucial for exhausting the air. Irrespective of the packaging material, pro-vitamin A loss during storage was chiefly caused by oxidative degradation of β-carotene. Additional photo- isomerisation under exposure to light became manifest in the relative increase in 9-cis-β-carotene with associated decline in the 13-cis isomer portion. Despite photoisomerisation, pro-vitamin A retention was up to 90.9% in bottled purée after 168 days of light-exposed storage, with deaeration of the purée resulting from hot-filling. Marked colour loss mainly caused by accumulation of brown oxidation products was monitored by a rising degree of discolouration (Dd). Although additional headspace deaeration of cans and bottles improved colour retention, dissolved residual oxygen and other reactive compounds provoked browning and β-carotene degradation. As regards pro-vitamin A and colour, headspace minimisation was much more effective than its deaeration. Due to smaller headspace volumes, bottling proved superior to canning under the prevailing conditions, irrespective of light-exposed storage.     

Quenching Mechanism of β-Carotene on the Chlorophyll Sensitized Photooxidation of Soybean Oil

The effects of 0, 5, 10, and 20 ppm β-carotene on the oxidation of 0.033, 0.066, 0.165, 0.330, or 0.660M soybean oil in methylene chloride containing 4 ppm chlorophyll have been studied by measuring headspace oxygen depletion in gas-tight sample bottles during 24 hr of light storage. The oxygen depletion was measured by a thermal conductivity gas chromatograph. The rate of singlet oxygen formation in soybean oil by 4 ppm chlorophyll was 0.17 μmoles O₂/mL head-space during first 24 hr of storage. The quenching mechanism study of g-carotene on the chlorophyll sensitized photooxidation of soybean oil showed that g-carotene minimized the oxidation of soybean oil by quenching singlet oxygen. p-carotene did not quench chlorophy11.     

Non-stationary drying of carrot: Effect on product quality

This paper presents the results of studies concerning the quality of food materials like vegetables subjected to convective drying in non-stationary conditions. The effect of different frequencies and amplitudes of the periodically changeable drying air temperature on the quality of dried carrot (Daucus carota L.) has been investigated. The indicators of the quality such as the color change, the water activity and the retention of β-carotene were analyzed. The slices of carrot root were used as the material for experimental tests. It has been shown that the non-stationary drying carried out in a prescribed variable air temperature significantly minimized the unfavorable effects in color changes, β-carotene degradation, and decay phenomena.     

Kinetic study on the singlet oxygen quenching activity of nordihydroguaiaretic acid (NDGA) using methylene blue sensitized photooxidation of α-terpinene

Singlet oxygen is highly reactive and can therefore induce rapid oxidation of a range of biological molecules, causing cell damages. The effects of nordihydroguaiaretic acid (NDGA) on the photochemical singlet oxygen oxidation of α-terpinene in methanol were studied. NDGA showed strong protective activity on the singlet oxygen oxidation of α-terpinene in methanol in a dose dependent manner. The protective activity of NDGA was considerably higher than that of butylated hydroxytoluene and 1,4-diazabicyclo[2.2.2]octane. Total singlet oxygen quenching rate constant (k _r +k _q ) of NDGA was determined by a steady state kinetic equation. The total singlet oxygen quenching rate constant of NDGA was 9.81×10⁷ M^?1 sec^?1. The result showed that NDGA possessed strong singlet oxygen quenching activity, indicating its potential for the protection of molecules, cells and nutrients from the highly reactive singlet oxygen. To the best of our knowledge, this is the first report on the singlet oxygen quenching rate constant of NDGA.     

Lipid Oxidation and Sensory Analysis of Cooked Pork and Turkey Stored under Modified Atmospheres

Precooked pork and turkey were stored at 4°C for 18 hr and at - 20°C for 3 months in vacuum and in atmospheres of air, carbon dioxide, and nitrogen. For both short-term refrigerated storage and long-term frozen storage, vacuum-packaging of precooked turkey and pork resulted in more meaty and less warmed-over flavor and aroma than the other packaging treatments. Samples stored in carbon dioxide and nitrogen atmospheres were less “oxidized” as indicated by sensory scores and TBA values than those stored in air but were more “oxidized” than vacuum-packaged meat. Warmed-over and rancid flavor and aroma scores correlated highly and consistently with TBA values, but inconsistently with the less sensitive fluorescence method. Vacuum-packaged turkey was darker and redder than other samples after frozen storage.     

Assessment of Different Packaging Structures in the Stability of Frozen Fresh Brazilian Toscana Sausage

The aim of this work was to evaluate the effect of different package conditions on the characteristics of Toscana fresh sausage stored for 150?days under freezing. The analyses of lipid oxidation, moisture, pH, acidity, water activity, and counting of psychotrophic microorganisms were carried out along with the storage time for each package (low-density polyethylene with and without vacuum and oxygen permeability of 500?cm³ O₂/m² day atm at 23 ??C; nylon polyester with and without vacuum and permeability of 100?cm³ O₂/m² day atm at 23 ??C; and formal copolymer of ethylene and vinyl alcohol with and without vacuum and oxygen permeability of 5?cm³ O₂/m² day atm at 23 ??C). Results showed that from 60?days of storage, the samples stored using polyethylene without vacuum and nylon 100?cm³ O₂/m² day atm, without vacuum, presented a slight rancidity flavor, statistically different (p?<?0.05) from the other tested ones. After 151?days of storage, a relationship between 2-thiobarbituric acid reactive substances analysis and sensory characteristics could be observed. In this case, the packages without application of vacuum presented higher values in the sensory and oxidative rancidity analyses, configuring flavor of slight to moderate rancidity.     

LIPID-AUTOXIDATION-LIMITED SHELF-LIFE OF NIXTAMALIZED INSTANT CORN MASA

Consumers often report the presence of off-flavors and off-odors characteristic of lipid oxidation in commercial dry instant corn masa, but the extent of this problem is unknown. The lipid oxidation states of two common brands of nixtamalized instant corn masa produced in Mexico were evaluated during 23-weeks of storage at 15, 25, 35, 45, and 55C. Lipid autoxidation was evaluated by determining peroxide values (PV) and conjugated dienoic acids (CD) of extracted lipids, and sensory analyses of flours and tortillas made from stored flours. Increased storage time significantly increased lipid oxidation (P < 0.001). Similarly, increased storage temperature significantly decreased the time to reach rancid flavor thresholds. The Q₁₀ values for flours and tortillas were 1.58 and 1.75, respectively. The shelf-lives of instant corn masa were 5.8 months when stored at 25C and only 2 months at 45C.     

Measurement of lipid oxidation and porphyrins in high oxygen modified atmosphere and vacuum-packed minced turkey and pork meat by fluorescence spectra and images

This paper illustrates that fluorescence spectroscopy and imaging can be used to measure the extent and distribution of lipid oxidation in meat. Minced turkey thighs and pork semimembranosus muscles were stored for 7 and 12 days at 4°C in high oxygen (O(2)) modified atmosphere packages and vacuum. Turkey meat packed in high O(2) atmosphere was oxidised already after 7 days of storage. The sensory rancid odour score was 4.7 (on a scale from 1 to 9) and the TBARS value was 1.86mg MDA/kg. There was also an increase in fluorescence emission intensity in the 410-550nm region, which arises from lipid oxidation products. The combination of unsaturated fatty acids and access to O(2) resulted in lipid oxidation gradients in the turkey meat samples, and these gradients were clearly visualised by fluorescence images. In comparison, pork meat was more stable against lipid oxidation, with TBARS values <0.2mg MDA/kg and no development of fluorescent lipid oxidation products was detected. The fluorescence spectra measured in the present experiment suggest that turkey thighs and pork semimembranosus muscle in addition to protoporphyrin also have a natural content of Zn protoporphyrin. The porphyrin content was higher in pork meat than in turkey meat. It increased during storage time when the meat was packed in vacuum, and it decreased with O(2) availability. The distribution of porphyrins in the meat was visualised by fluorescence imaging.     

食品中脂类物质的1O2氧化及控制方法

脂类食品中存在的天然色素通常是潜在的光敏剂,可以通过光敏反应Type II途径将基态氧激发并转变为单线态氧（singlet oxygen,1O2）。1O2是一种亲电性、非自由基的激发态氧分子,具有活化能低、反应活性高的特点,可以快速引发脂类物质氧化,并最终导致其氧化劣变。本文查阅并分析了国内外本领域的最新研究成果,对脂类食品中1O2的形成途径、光敏氧化机理及甘油三酯和植物甾醇等常见脂类物质的光敏氧化进行了深入阐述,并从光敏剂和三线态氧的脱除与控制、1O2淬灭、光源选择等方面总结了食品中脂类物质光敏氧化控制的最新研究进展,以期为深入研究食品中脂类物质的光敏氧化及抑制技术提供理论依据。