Formation of Volatile Compounds in Soy Flour by Singlet Oxygen Oxidation During Storage Under Light

ABSTRACT: Volatile compounds in soy flour stored under light and in the dark at 30 °C were studied by a combination of solid-phase microextraction-gas chromatography-mass spectrometry and sensory evaluation. As storage time increased from 0 to 6 d, the total volatile compounds in soy flour stored in the dark and under light increased by 60% and 300%, respectively. Dimethyl disulfide increased significantly under light, and 2-pentylfuran, 1-octene, and 2-heptenal were identified only in soy flour under light. This indicates that the singlet oxygen oxidation was taking place in soy flour stored under light. Sensory off-flavor scores were significantly higher in samples stored under light than in the dark.     

Impact of poly-lactic acid packaging material on semi-hard cheese

A study was performed in order to evaluate the impact of a poly-lactic acid (PLA) package relative to a polyester packaging material on quality of semi-hard cheese during light exposure and storage in the dark and when applying oxygen scavengers to the cheese packages. Migration of volatile compounds from PLA into the cheese was minute and well below any critical levels. Development of secondary lipid oxidation products and loss of riboflavin primarily took place when both oxygen and light were present. As more oxygen was present in the PLA packages than in the reference packages due to a higher oxygen transmission rate of PLA, a higher degree of lipid oxidation was noted in cheeses packaged in PLA. The degree of lipid oxidation was reduced when applying oxygen scavengers but to a lesser extent than when the products were stored in the dark. Riboflavin was degraded to the same extent in the PLA and the reference-packaged cheeses. The results indicate that dark storage/use of non-transparent materials and reduction of the water vapour transmission rate are recommended when using the present PLA for packaging of semi-hard cheeses in order to protect the products against both lipid oxidation and moisture loss.     

Chemical characteristics,oxidation and proteolysis in cheese produced from fresh or stored milk subjected to heat treatments

Cheese produced from fresh, stored or heat pretreated (65°C for 15 s) milk subjected to pasteurisation (72°C or 77°C for 15 s) was studied for chemical characteristics and proteolysis after 4 and 21 days of storage. Antioxidant activity was higher in cheese from fresh milk than in cheese from stored and heat pretreated milk. Malondialdehyde content as an index of lipid oxidation increased in cheese made with pretreated and preserved milk than in cheese made with fresh milk. Antioxidant activity and lipid oxidation were not significantly affected by pasteurisation temperature. Proteolysis increased during cheese maturation regardless of milk heat treatments.     

The evolution of chemical and microbiological properties of fresh goat milk cheese during its shelf life

This study investigated the changes in chemical and microbiological properties of fresh goat milk cheese stored in an open deck refrigerated display cabinet (6 ± 2°C) or in a dark cold room (4 ± 1°C). The effects of partial-vacuum packaging and fluorescent lighting were studied during the cheese shelf life (45 d) and 15 d after. Storage conditions did not affect the pH values (4.3), whereas a slight decrease in moisture (ca. 1%) and in water activity (<0.01 units) was recorded. Proteolysis monitored by Kjeldahl determination increased significantly during storage of all samples. The highest increase from 8.5 to 13.0% of soluble nitrogen (expressed as percentage of total nitrogen) was measured in cheese packaged in the presence of air and stored in a lighted cabinet. The proteolytic trend was also studied through capillary zone electrophoresis by monitoring the degradation of the main casein fractions and the formation of new peptides. In particular, 2 indices, based on peak area ratio of new-formed peptides and casein fractions were related to cheese age. Lipolysis, measured by solid-phase microextraction gas chromatography coupled to mass spectrometry of volatile fatty acids, was unaffected by air or light and did not proceed through storage. As expected, hexanal formed mainly in cheeses stored under light and packaged in air. Evaluation of sensorial quality, performed using a hedonic scale, showed significantly lower scores of cheeses kept under light compared with those kept in the dark, both at 45 and 60 d storage. Overall, the microbiological and chemical results suggested that the shelf life of soft goat milk cheese would be extended from 45 to 60 d. Such conclusion was supported also by the sensory quality evaluation.     

The effect of light on the vitamin B2 and the vitamin A content of cheese

Edam type cheese was exposed to sunlight at ambient temperature and to fluorescent light at 5 °C. The loss of vitamin B₂ (riboflavin) and vitamin A was monitored in both the surface and inner layers of the cheese and the results compared with control samples kept in the dark. The loss of riboflavin when exposed to sunlight was shown to be primarily a surface effect but losses of vitamin A were similar throughout the cheese. When exposed to fluorescent light at 5 °C and monitored at intervals for 10 days the loss of riboflavin was still greatest at the surface but a trend to lower values than the control was evident throughout the cheese. Vitamin A losses followed a different pattern in both sunlight and fluorescent light. There was a heavy initial loss throughout the cheese. Under fluorescent light this was followed by a period in which further loss was mainly in the surface layer. Vacuum packaging reduced the loss of riboflavin but had no effect on the loss of vitamin A.     

Effect of processing and storage of brined white (Nabulsi) cheese on fat and cholesterol oxidation

Brined white (Nabulsi) cheese was studied for cholesterol oxidation and for oxidative and hydrolytic rancidities during cheese processing, during storage in closed transparent and light‐protected glass jars at room temperature for 3, 6 and 9 months and during storage on an open tray exposed to atmospheric air and light for 1, 2 and 3 weeks. The peroxide value (PV), free fatty acid (FFA) content and 7‐ketocholesterol level were determined. The cheese processing steps (curd formation, salting and boiling in brine) had no significant effect on PV, FFAs and 7‐ketocholesterol. However, the storage conditions had a significant effect (p ≤ 0.5) on these parameters. Peroxides were not detected or were very low in the freshly boiled cheese, while the FFA content was 2.9 g kg^?1. The PV and FFA content increased to approximately 5 meq kg^?1 and 11 g kg^?1 respectively after 9 months of storage in transparent or light‐protected jars. The 7‐ketocholesterol level was 1.2 µg g^?1 in the freshly boiled cheese and reached maximum values of 2.3 and 5.2 µg g^?1 after 9 months of storage in light‐protected and transparent jars respectively. Cheese samples displayed on an open tray showed a higher increase in PV, FFAs and 7‐ketocholesterol than samples stored in closed jars, reaching values of 6.1 meq kg^?1, 6.8 g kg^?1 and 8.8 µg g^?1 respectively after 3 weeks of storage. © 2002 Society of Chemical Industry     

Light-induced changes in semi-hard cheese determined by fluorescence spectroscopy and chemometrics

The impact of modified atmosphere packaging and different storage conditions on light-induced oxidation of sliced Havarti cheese has been evaluated by fluorescence spectroscopy. Data were analyzed with principal component analysis (PCA) and 50–50 MANOVA showing effects of storage in light or dark, light source (yellow or white light), light intensity, residual oxygen level, headspace volume, and storage time. No effect of storage temperature was noted. The PCA gave three components. One of these indicated a decrease in riboflavin content, which was seen only for samples exposed to white light. Another component denoted the variation in spectra below 500 nm probably due to formation of fluorescent oxidation products. The third component described the variation above 600 nm, which is ascribed to photodegradation of porphyrins. The porphyrins were degraded with storage time for both light sources.     

Characteristics of Mackerel Mince Lipid Hydrolysis

The lipid hydrolysis products in minced mackerel stored under vacuum at 2–3°C for 15 days were free fatty acids (FFA) and 1,2-diglycerides (DG); no 1,3-DG br monoglycerides were obsrved, Lysophosphati-dylcholine fLPC and lvsoohosohatidvlethanolamine (LPE) increased and then ddcreased with time: Lysiphosphatidylserie was not observed. More FFA, 1,2-DG, LPC, and LPE were detected in dark muscle than in light muscle. The initial fatty acid composition, by GC, showed no significant differences (α-0.05) among whole, light and dark muscles. When the lipid extracts were separated into three fractions (1: mostly triglycerides; 2: mostly FFA, DG, and cholesterol; and 3: mostly phospholipid), the degree of unsaturation of the lipids in fraction 2 was between those in fraction 1 and 3 and increased with time. These findings support the possibility that fish lipid hydrolysis may affect fish wholesomeness.     

Quality changes in semi-hard cheese packaged in a poly(lactic acid) material

A study was performed in order to evaluate the influence of barrier properties of a poly(lactic acid) (PLA) relative to an amorphous poly(ethylene terephthalate)/polyethylene (APET/PE) packaging material on quality of Danbo cheese during light exposure and storage in the dark. Results showed that moisture loss from cheeses packaged in PLA was approximately 10 times higher than from the reference packages, but dry surface spots were not observed before 56 days of storage in the PLA packages. Secondary lipid oxidation products were primarily developed when both oxygen and light were present. During light exposure, lipid oxidation of cheeses packaged in PLA was rather limited for the first 56 days of storage, whereas lipid oxidation was almost negligible when the cheeses were protected from light during the 84 days of shelf life. The results indicate that the present PLA can be used for packaging of Danbo cheese for a shelf life maximum of 56 days in order to protect against both moisture loss and lipid oxidation.     

Riboflavin Photosensitized Singlet Oxygen Oxidation of Vitamin D

Samples containing various levels of vitamin D and riboflavin, with and without ascorbic acid or a-tocopherol were prepared in a model system. Samples were stored in the light or in the dark at 45®C for up to 8 h. Headspace oxygen was determined by gas chromatography with thermal conductivity detection. Oxidation of vitamin D was not observed in samples without riboflavin stored in the light nor in samples with riboflavin stored in the dark. Vitamin D with riboflavin was oxidized under light. α-Tocopherol quenched singlet oxygen at a rate of 2.52 × 10⁸ M^-1 sec^-1, whereas ascorbic acid quenched singlet oxygen at a rate of 2.23 × 10⁷ M^-1 sec^-1.     

Effect of irradiation, active and modified atmosphere packaging, container oxygen barrier and storage conditions on the physicochemical and sensory properties of raw unpeeled almond kernels (Prunus dulcis)

BACKGROUND: The present study investigated the effect of irradiation, active and modified atmosphere packaging, and storage conditions on quality retention of raw, whole, unpeeled almonds. Almond kernels were packaged in barrier and high‐barrier pouches, under N₂ or with an O₂ absorber and stored either under fluorescent lighting or in the dark at 20 °C for 12 months. Quality parameters monitored were peroxide value, hexanal content, colour, fatty acid composition and volatile compounds. Of the sensory attributes colour, texture, odour and taste were evaluated. RESULTS: Peroxide value and hexanal increased with dose of irradiation and storage time. Irradiation resulted in a decrease of polyunsaturated and monounsaturated fatty acids during storage with a parallel increase of saturated fatty acids. Volatile compounds were not affected by irradiation but increased with storage time indicating enhanced lipid oxidation. Colour parameters of samples remained unaffected immediately after irradiation. For samples packaged under a N₂, atmosphere L* and b* values decreased during storage with a parallel increase of value a* resulting to gradual product darkening especially in irradiated samples. CONCLUSION: Non‐irradiated almonds retained acceptable quality for ca. 12 months stored at 20 °C with the O₂ absorber irrespective of lighting conditions and packaging material oxygen barrier. The respective shelf life for samples irradiated at 1.0 kGy was 12 months packaged in PET‐SiOx//LDPE irrespective of lighting conditions and 12 months for samples irradiated at 3 kGy packaged in PET‐SiOx//LDPE stored in the dark. Copyright © 2010 Society of Chemical Industry     

Influence of PET and PET/PEN Blend Packaging on Ascorbic Acid and Color in Juices Exposed to Fluorescent and UV Light

ABSTRACT: Apple and orange juices packed in polyester bottles were stored in dark, intense fluorescent (1500 lux), and UV light conditions in temperature-controlled (22 °C) chambers and monitored more than 7 mo for ascorbic acid content and color changes. Polyester beverage bottles were made of polyethylene terephthalate (PET), or PET blended with 0.25%, 1%, and 4% polyethylene naphthalate (PEN). The cut-off wavelength ranged from 322 nm for PET to 373 nm for the 4% PEN/PET blend. Spectral irradiance, visible light intensity, and light distribution were evaluated in the light chambers and compared with supermarket display lighting and outdoor daylight conditions. Only the UV chamber and sunlight showed significant irradiance at wavelengths below 400 nm. Ascorbic acid (AA) degradation and concurrent color changes occurred in both juices during storage in all 3 lighting conditions and in all 4 bottle types. Zero-order reaction kinetics described the AA degradation rate for all treatments. Apple juice stored in UV had a significantly higher ( P < 0.05) AA degradation rate than juice stored in the dark or in fluorescent light. Under UV conditions, apple juice in PET/ PEN bottles had a lower AA degradation rate than the juice in PET bottles. AA degradation in orange juice was less affected by UV exposure than in apple juice. Both juices darkened over time when stored in dark and fluorescent conditions, whereas UV exposure caused some initial bleaching of color before darkening. The bleaching effect was reduced in apple juice stored in the PET/PEN bottles.     

Effects of riboflavin photosensitization on the changes of isoflavones in soymilk

Effects of riboflavin photosensitization on the distribution of isoflavones in commercially available soymilk were analyzed using high-performance liquid chromatography (HPLC). Total isoflavones (TI) in soymilk with riboflavin (1000 ppm, w/v) under light were significantly different from those stored in the dark for 24 h (P < 0.05), while TI in samples with 0 and 1000 ppm added riboflavin were not significant from each other in dark conditions (P > 0.05). To test the effects of the concentration of riboflavin on TI, soymilk was mixed with riboflavin to make 0, 100, 250, and 500 ppm (w/v) and stored under light at 25 degrees C for 24 h. TI in soymilk with 100 ppm riboflavin under light significantly decreased by 13.5% for 24 h (P < 0.05) compared to control samples and were not significantly different from those with 250 or 500 ppm samples (P > 0.05). Daidzin and genistin were predominant isoflavones in soymilk, and the rate of photo degradation of genistin was higher than that of daidzin for 24 h in soymilk under riboflavin photosensitization.     

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.     

Formation of ethyl carbamate in umeshu (plum liqueur)

Samples of umeshu, a Japanese plum liqueur made from unripe plums, shochu and crystal sugar, were stored under fluorescent light, in the dark and in the refrigerator. The amount of ethyl carbamate formed in umeshu exposed to light or room temperature was larger than that in the dark or at low temperature. The amount of ethyl carbamate formed in umeshu to which cyanide had been added was larger than that in the absence of added cyanide. Thus, the amount of ethyl carbamate formed in the umeshu was increased by not only light and higher temperature, but also cyanide. Samples of model alcoholic beverages were stored under various conditions using red, yellow and blue cellophanes. The amount of ethyl carbamate formed in the model alcoholic beverage with blue cellophane was larger than in the cases of red and yellow cellophanes. It was found that the amount of ethyl carbamate formed in the model alcoholic beverage was increased by light in the wavelength range of 375-475 nm.     

光对冷却肉脂肪氧化和色泽变化的影响

本文研究了不同光性质对脂肪氧化变化和色泽变化的影响。研究发现,选择照明光源(日光灯和白炽灯)时应根据贮存温度而定,在4±2℃温度下贮存时,两种光源对脂肪氧化程度影响之间不存在显著性差异(p>0.05),但日光灯照明可以延缓颜色发生变化,而在9±1℃温度下贮存时,采用白炽灯照明较适,可延缓脂肪氧化和变色发生。在4±2℃贮存温度下,采用日光灯照明时,光照强度低于750lux的情况下,光强大小对猪肉脂肪氧化和色泽变化的影响较小。在4±2℃贮存温度下,激发波长低于550nm的蓝光和绿光能明显加快猪肉脂肪氧化和变色。     

单色光照金枪鱼脂质和肌红蛋白氧化动力学研究

为探讨单色光照对金枪鱼生食产品脂质氧化和肌红蛋白(myoglobin,Mb)氧化的影响,优化其陈列展示光照条件,实验以大目金枪鱼(Thunnus obesus)赤身肉为研究对象,使用红、黄、绿和蓝4种单色LED(lightemitting diode)灯,以等功率、等光照强度和梯度光照强度3种方式施加光照,测定贮藏过程中金枪鱼肉硫代巴比妥酸反应产物值和高铁肌红蛋白含量变化。结果表明:贮藏期内,相较于暗室贮藏,单色光照显著促进了大目金枪鱼的脂质氧化,加速了Mb氧化;在相同光照强度下,单色光照的促氧化作用随波长减小而增大,但黄色光促氧化作用小于红色光;光照强度影响单色光促氧化作用,蓝色光和绿色光促氧化作用受光照强度的影响程度大于黄色光和红色光;脂质氧化和Mb氧化反应符合0级模式。因此,建议金枪鱼生食产品的陈列展示使用长波长的红、黄色光,避免短波长的绿、蓝色光。     

Oxidative stability of cream cheese stored in thermoformed trays as affected by packaging material,drawing depth and light

The oxidative stability of cream cheese stored in thermoformed trays made of amorphous polyethylene terephtalate (A-PET)/polyethylene (PE), polystyrene (PS)/Ethylene-vinylalcohol copolymer (EVOH)/PE and Polypropylene (PP)/PE with different depth (25, 50 and 70 mm) and colour (black, white and transparent) was studied by sensory evaluation and gas chromatographic analysis of volatile compounds. The polymer combination had an important effect on sensory scores of both sunlight and acidulous flavour in cream cheese stored in the dark for 2, 4 and 6 months. Cream cheese stored in trays made of A-PET/PE had higher acidulous flavour and lower content of hexanal and 2-nonanone. Only small differences were observed between PS/EVOH/PE and PP/PE despite the great diversity of oxygen transmission rates. The drawing depth of the packages had no significant effect on oxidative stability of cream cheese, irrespective of storage in the dark or under illumination. The colour of the examined packaging material had a pronounced effect on photoxidative changes in cream cheese.     

Oxidative Changes of Heat-Sterilized Meat in Trays

We studied oxidative changes of ground pork meat filled into plastic or aluminum trays, sterilized at 121 or 131°C and stored up to 56 days at 20 or 37°C in the dark or exposed to light, respectively. Sterilization temperature did not influence either thiobarbituric acid reactive substances (TBARS) of the samples or ethane concentrations in headspace of trays. An increase of storage temperature from 20 to 37°C increased TBARS and ethane concentrations regardless of filling method and packaging material. No changes in double-bond indices were observed. Nitrogen flushing in combination with light protection reduced lipid oxidation up to 85–95%     

Retail lighting and packaging influence consumer acceptance of fluid milk

Little is known about the effect of retail light-emitting diode (LED) exposure on consumer acceptance of milk. The study objective was to determine effects of fluorescent and LED lighting under retail storage conditions on consumer acceptance of milk. Consumer acceptance of milk stored under retail conditions was determined through sensory evaluation (2 studies; n = 150+ each) and analytical measures (dissolved oxygen, secondary oxidation products, riboflavin retention). Study 1 evaluated milk stored in high-density polyethylene (HDPE) packages for 4 h under LED light (960 lx). Commercially available HDPE package treatments included translucent HDPE (most commonly used), white HDPE [low concentration (1.3%) TiO₂], and yellow HDPE; in addition, HDPE with a higher TiO₂ concentration (high white; 4.9% TiO₂) and a foil-wrapped translucent HDPE (control) were tested. Translucent and control packages also were tested under fluorescent light. Study 2 evaluated polyethylene terephthalate (PET) packages for 4 h under fluorescent and LED light (1,460 lx). The PET packaging included 2 treatments (medium, 4.0% TiO₂; high, 6.6% TiO₂) as well as translucent HDPE (exposed to fluorescent), clear PET (fluorescent and LED), and light-protected control. Overall mean acceptability of milk ranged from “like slightly” to “like moderately” with significantly lower acceptability for milk exposed to fluorescent light. Milk in HDPE and PET packages had comparable overall acceptability scores when exposed to LED light. Only the fluorescent light condition (both PET and HDPE) diminished overall acceptability. Fluorescent light exposure negatively influenced flavor with significant penalty (2.0–2.5 integers) to overall acceptability of milk in translucent HDPE and clear PET. The LED also diminished aftertaste of milk packaged in translucent HDPE. Changes in dissolved oxygen content, as an indication of oxidation, supported the observed differences in consumer acceptance of milk stored under fluorescent and LED light. Consumers like the flavor of fresh milk, which can be protected by selecting appropriate packaging that blocks detrimental light wavelengths.