Influence of Storage Time and Color of Light on Photooxidation in Cheese

ARTICLE IN PRESS

International Dairy Journal 16 (2006) 1218–1226 www.elsevier.com/locate/idairyj

Inﬂuence of storage time and color of light on photooxidation in cheese: A study based on sensory analysis and ﬂuorescence spectroscopy

Jens Petter Wolda,Ã, Annette Veberga,b, Frank Lundbya, Asgeir Nikolai Nilsena, Johan Moanc

aMATFORSK—Norwegian Food Research Institute, Osloveien 1, 1430 A˚s, Norway bNorwegian University of Life Sciences, Department of Chemistry, Biotechnology and Food Science, P.O. Box 5036, 1432 A˚s, Norway cThe Norwegian Radium Hospital, Institute for Cancer Research, Department of Biophysics, Montebello 0310 Oslo, Norway

Received 19 January 2005; accepted 22 October 2005

Abstract

The sensitivity of front-face fluorescence spectroscopy to determine light-induced sensory changes in Jarlsberg cheese was elucidated. The cheese was exposed to white fluorescent light from 0 to 48 h, followed by fluorescence (380 nm excitation) and sensory analysis. Significant changes in sensory properties occurred after 4 h of exposure, while spectral changes could be measured after 30 min. Correlations between fluorescence spectra and sensory properties were generally high (E0.9). Sensory response to exposure to light of equal intensity, but of different colors was also investigated. Violet and white light resulted in the worse quality degradation, while green light gave least adverse effects. No significant (p40:05) sensory difference between exposure to red and blue light was observed. Photo- induced changes by red, orange, and yellow light are ascribed to light degradation of porphyrins and chlorins, while for violet, blue, and green light, the degradation of riboflavin is probably also involved. r 2005 Elsevier Ltd. All rights reserved.

Keywords: Photooxidation; Fluorescence spectroscopy; Sensory analysis; Cheese; Riboﬂavin; Porphyrin; Chlorophyll

1. Introduction sensitive compounds in the products (Skibsted, 2000). The Second is a rapid analytical method, which reflects the Today, consumers are demanding transparent packing, sensory perception of the consumer (Mortensen, Bertelsen, to better appraise the product prior to purchase. Further- Mortensen, & Stapelfeldt, 2004). more, environmental concerns have caused a reduction in The best way to protect dairy products is to exclude all the use of aluminum and metallized foils. These factors kinds of light exposure (Borlet, Sieber, & Bosset, 2001). have led to increased use of transparent packing materials Since that is not always compatible with market demands, within the entire food sector. However, packing of foods in one can try to avoid exposure to the most harmful transparent materials greatly increases the risk of light- wavelengths. In milk and dairy products, it has been induced oxidation. Milk and milk products are particularly generally accepted that riboflavin plays the major role as sensitive to light, and the photo-initiated reactions affect photosensitizer. Riboflavin absorbs light in the ultraviolet not only the sensory quality but may also lead to the (UV) region and up to about 500 nm (violet and blue), and formation of toxic compounds in certain products and to numerous studies indicate that the 400–500 nm region is the degradation of nutrients (Sattar and deMan, 1975). Efforts most harmful part of the visible spectral region with regard are therefore being made to design low-cost and effective to photooxidation in dairy products (Bosset, Gallmann, & packaging materials with minimal adverse effects. In order Sieber, 1993). Many of these studies (Bosset et al., 1993) to increase the efficiency of this work, there are two main used either light sources or packaging materials with rather needs. This is a thorough knowledge about the photo- broad spectral properties, where the spectral distribution has been described as, for instance, ‘‘cold’’ (much blue and ÃCorresponding author. Tel.: +47 64 97 01 00; fax: +47 64 97 03 33. violet light) and ‘‘warm’’ (much yellow, orange and red E-mail address: [email protected] (J.P. Wold). light). A clear trend has been that ‘‘cold’’ light is more

0958-6946/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.idairyj.2005.10.023 ARTICLE IN PRESS J.P. Wold et al. / International Dairy Journal 16 (2006) 1218–1226 1219 harmful than ‘‘warm’’ light, a valuable result, but rather of sensitivity of the method compared to sensory analysis has non-specific in terms of wavelength regions. More specific not been investigated. experiments have been performed, for instance, by The purpose of this work was to elucidate the sensitivity Lennartson and Lingnert (2000), who investigated expo- of fluorescence spectroscopy to photooxidation in cheese sure of mayonnaise to quite narrow spectral ranges of light and compare it with the evaluation by a trained sensory in the violet, green, yellow, and red region. Even more panel. This was done by analysis of Jarlsberg cheese (Swiss specific were Mortensen, Sørensen, Danielsen, and Stapel- like), which had been exposed to fluorescent white light in feldt (2003), who analyzed the effect of light exposure to 20 different time intervals from 0 to 48 h. Secondly, we Havarti cheese for the single wavelengths 366, 405, and investigated the exposure of the Gauda-like Norvegia 436 nm. Also, milk has been exposed to light of different cheese to different colors of light of equal intensity. colors by using sleeves and light sources with well-defined spectral properties (Hansen, Turner, & Aurand, 1975). It 2. Materials and methods was found that white fluorescent light was most harmful, inducing formation of off-favors after a few hours. Pink 2.1. Materials light retarded the oxidation process somewhat, while green light gave the best protection against the formation of off- 2.1.1. Storage time study flavors. Commercially packed rind-free Jarlsberg cheese (27% Although riboflavin does not act as a sensitizer for light fat, Swiss-like) was obtained from TINE (Klepp, Norway). wavelengths longer than 500 nm, Mortensen, Sørensen, The samples were 400 g portions packed in flow-packed and Stapelfeldt (2003) reported that exposure to yellow pouches of transparent laminate plastic film (OPA 12/ light (4550 nm) did indeed induce the formation of PE50; Wipak, Nastola, Finland). The headspace was a gas secondary oxidation products in cheese at the same level atmosphere with minimum of oxygen. All the cheese came as did white light. In a newly conducted work based on from the same batch in order to obtain homogeneous fluorescence spectroscopy, Wold et al. (2005) discovered samples. The products were brought directly to the that dairy products probably contain natural residues of institute and stored cool (4 1C) and in the dark approxi- different porphyrins and chlorophylls. These compounds mately 4 days prior to the experiments. are highly light sensitive and act as photosensitizers. The study showed that the photodegradation of these com- 2.1.2. Light color study pounds was closely correlated with changes in sensory Rind-free Norvegia cheese (Gauda like, 27% fat, 450 g attributes of the exposed cheese. It is well known that portions packed in commercial transparent laminate plastic porphyrins and chlorophyll initiate photooxidation in meat film, vacuum packed) was obtained from TINE (Klepp, and products containing vegetables (Bekbo¨ let, 1990), but Norway). All the cheese came from the same batch to they have traditionally not been associated with light- obtain a fairly homogeneous set of samples. The products induced oxidation in dairy products. The fact that there are were stored cool (4 1C) and in the dark 3 days prior to light natural stable occurrences of these tetrapyrroles in dairy exposure. products introduces some new aspects in the understanding of photooxidation in these foods, and how to optimize 2.2. Experimental design protection. The presence of porphyrins and chlorins was detected by 2.2.1. Storage time study use of front-face fluorescence spectroscopy, a rapid and very The cheeses were stored under fluorescent light for 20 sensitive method. Fluorescence spectroscopy has some different time periods: 0, 0.5, 1, 1.5, 2, 4, 6, 8, 10, 12, 14, 16, excellent advantages with regard to measurement of photo- 18, 21, 24, 27, 30, 36, 42, and 48 h. For each storage time, oxidation in dairy products. First of all, the method is rapid five cheeses were illuminated. Four of the cheeses were used and non-destructive, meaning that measurements can be for sensory analysis, while the last was used for fluores- done within a second, directly on the product. The method cence analysis. The storage design was performed in can instantly measure the photodegradation of riboflavin, duplicate. A total of 200 cheese samples were thus used porphyrins, and chlorins, probably the most important light in this experiment. sensitizers (Wold,Jørgensen,&Lundby,2002;Miquel, The cheeses were illuminated by a standard fluorescent Becker, Christensen, Frederiksen, & Haugaard, 2003; Wold tube (Osram L58W/21.840 Lumilux plus; Osram GmbH, et al., 2005), as well as some of the photo breakdown Mu¨ nchen, Germany). The tube is commonly used for products (Fox & Thayer, 1998; Juzenas, Iani, Bagdonas, displays in grocery stores. It emits light mainly in the Rotomskis, & Moan, 2001; Merzlyak et al., 1996; Rotoms- visible region and to a lesser extent in the UV region. The kis, Bagdonas, & Streckyte, 1996). This means that the initial cheese packages were positioned 10 cm from the tube process, which triggers photooxidation, probably can be (which is realistic compared with worst-case conditions in monitored directly in the intact product. Fluorescence grocery stores), exposing them to about 5.800 lx measured spectroscopy correlates well with sensory-assessed light- by a luxmeter (Lu-Ex 02 Digital-Luxmeter; Ecom Rolf induced off-flavors (Wold et al., 2002, 2004), but the degree Nied GmbH, Assamstadt, Germany). The transparent side ARTICLE IN PRESS 1220 J.P. Wold et al. / International Dairy Journal 16 (2006) 1218–1226

(without any labels or emblems) of the packages was Research Corp., Acton, MA, USA) connected to a sensitive turned toward the light. Samples stored in the dark were charge-coupled device (CCD camera) (Roper Scientific placed in light-proof cases. Storage temperature for all NTE/CCD-1340/400-EMB; Roper Scientific, Trenton, NJ, samples was about 6 1C. USA). A cut-off filter at 400 nm (Melles Griot 03FCG049; Melles Griot, Rochester, NY, USA) was positioned in front 2.2.2. Light color study of the spectrograph slit to suppress excitation light reflected Commercial packages of Norvegia cheese were stored from the sample. Exposure time was 1 s for all spectroscopic under two broadband 575 W metal halide lamps (OSRAM measurements. The sample temperature was 16–19 1C. Two HMI 575 W/SE; Osram GmbH, Mu¨ nchen, Germany), spectra were collected from each sample, and the average was which have a relatively uniform emission spectrum in the used for further analysis. Spectrograph and detector were visible and near UV region. In addition to the transparent controlled by the software WinSpec, Version 1.4.3.4 commercial laminate plastic film package, the cheeses were (Roper Scientific). covered with plastic films with different spectral properties. Six different colored films manufactured by Rosco (Rosco, 2.4. Sensory analysis Stamford, CT, USA) were used, and the particular films used were: red (19 Super Fire red), orange (21 Super The sensory evaluation was performed by a sensory Golden amber), yellow (101 Yellow), green (89 Moss panel consisting of 11 selected assessors. A descriptive test green), blue (69 Super Brilliant blue), and violet (357 Royal (ISO, 1985) was carried out. Prior to the analysis, the panel Lavendel). These filters were chosen because of their well- was trained in the definition and intensities of the chosen defined and relatively narrow transmission bands in the attributes using cheeses with varying sensory properties visible spectral region. In addition to the colored filters, a (light exposed and non-exposed). The attributes used in UV filter (3114 UV Tough filter) was used to block UV both experiments are listed and defined in Table 1. The contributions transmitted through the red, orange, yellow, judges had long experience and were well trained so no and green filter. No UV block was used together with the references for the various attributed were used in these blue and violet filter, since some UV usually will specific experiments. Each assessor was served each cheese accompany these colors. Transmission properties of the sample on a cardboard plate. The serving order was color filters and of the UV block filter were measured by randomized according to sample and assessor. Water and Perkin Elmer Lambda 800 UV/VIS spectrophotometer crackers were provided to cleanse the palate between (Perkin Elmer, Norwalk, CT, USA). samples. A continuous non-structured scale was used for Eight different storage conditions were used: (1) storage the evaluation of sensory attributes ranging from the in the dark, or exposure through (2) red filter, (3) orange lowest intensity of each attribute (value 1.0) to the highest filter, (4) yellow filter, (5) green filter, (6) blue filter, (7) intensity (value 9.0). Each judge evaluated the samples at violet filter, and (8) transparent (the commercial plastic individual speed on a computer system for direct recording film, no color or UV filter). For each color, the cheese was of data (CSA, Compusense, Version 4.2; Guelph, Ont., exposed to a light intensity of approximately 2.0 W m2. Canada). The sensory scores for each sample of cheese To adjust to the same light intensity for each color, the were obtained by averaging the individual scores for the samples were placed at different distances from the 11 sub-samples. Forty samples were evaluated for the time light source. Light intensity was measured by a calib- storage experiment, so the measurements had to be carried rated spectrometer (Apogee Spektroradiometer; Apogee out over 2 days due to capacity limitation. In both Instruments Inc., Logan, UT, USA) and integrated in experiments, sub-samples were cut from the exposed the 300–800 nm region. All cheeses were exposed to light surface of the cheese and were about 4 4cm2 and 4 mm for 36 h. thick. Each judge replicated analysis of each sample. Two replicates were used in the storage time study, and three 2.3. Fluorescence measurements replicates were used in the light color study. Fluorescence emission spectra were measured directly on the illuminated surface of circular (D ¼ 5 cm) cut out 2.5. Data analysis samples of the cheese. An optical bench system optimized for measurement of rather large sample surfaces was used. Partial least-squares regression (PLSR; Martens & Næs, The samples were exposed to 380 nm excitation light, and 1989) was used for making a calibration between fluores- fluorescence emission spectra were recorded in the range cence and sensory-assessed attributes on the cheese. Full 400–750 nm. The excitation light was generated by a 300 W cross-validation was used for all models. This provided a Xenon light source (Oriel 6258; Oriel Corporation, Stratford, predicted value for each sample, yî, which was com- CT, USA) and passed through a 10 nm bandwidth pared with the reference sensory value, yi. Multivariate interference filter (Oriel 59920). The light was directed onto correlation coefficient (R) and the prediction error ex- the samples at an angle of about 451. The spectra were pressed as root mean square error of cross-validation collected by an imaging spectrograph (Acton SP-150; Acton (RMSECV) were used to evaluate the models. RMSECV ARTICLE IN PRESS J.P. Wold et al. / International Dairy Journal 16 (2006) 1218–1226 1221

Table 1 Deﬁnition of each sensory attribute, and indication of which experiments were used (two right columns)

Attribute Description Time storage study Light color study

Sun odor Related to oxidized proteins. Training reference—milk exposed to sun X X Acidic odor Odor of fruity acids, fresh/acid/sweet odor X X Packaging odor Odor of cardboard and plastic packaging material X Grass odor Intensity of grass odor X Stearin odor Intensity of stearin odor X Paint odor Intensity of paint odor X Oxidized odor Intensity of all rancid odors (grass, hay, stearin and paint flavor) X X Sun flavor Related to oxidized proteins. Training reference—milk exposed to sun X X Acidic flavor Flavor of fruity acids, fresh/acid/sweet flavor X X Packaging flavor Flavor of cardboard and plastic packaging material X Grass flavor Flavor of green grass X Stearin flavor Flavor of stearin X Paint flavor Flavor of paint X Oxidized flavor Intensity of all rancid flavors (grass, hay, stearin and paint flavor) X X Whiteness Scale from no whiteness (black)–to all white X was defined as 7 vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi sun odor u oxidized odor u XN t 1 acidic flavor RMSECV ¼ ðy y^ Þ2, 6 N i i i¼1 5 where i denotes the samples from 1 to N. Data analyses were performed with the software The Unscrambler, Version 7.5 (Camo AS, Oslo, Norway). 4 Significance testing of the sensory analysis with respect

to time was performed by one-sided Dunnett’s multiple Sensory scores 3 comparisons with the samples stored in the dark as control. Significance testing of the sensory analysis with respect to 2 light of different colors was performed by Tukey honestly significantly different all-pairwise comparisons test. Sig- 1 nificance testing was carried out with the software Statistix 010203040 8.0 (Analytical Software, Tallahassee, FL, USA). Storage time (h)

3. Results and discussion Fig. 1. Sensory scores for sun odor, oxidized odor and acidic flavor measured on Jarlsberg cheese after light exposure from 0 to 48 h. The time of storage and colored light studies are presented and discussed separately with a common about 8 to 10 h, respectively, of exposure. Paint flavor, discussion at the end. which is a marker for progressed oxidation, increased slower and a significant change was noted first after 21 h. 3.1. Time storage study No significant differences were found for whiteness and grass flavor. The rather rapid changes in sensory properties 3.1.1. Sensory analysis have been observed in similar studies on cheese. Morten- The sensory analysis revealed significant changes over sen, Sørensen, Danielsen, et al. (2003) and Mortensen, the storage period. Samples exposed up to 48 h were Sørensen, & Stapelfeldt (2003) reported odor changes in described by the panel as clearly oxidized. Fig. 1 shows the sliced Havarti cheese already after 4 to 6 h of exposure to average sensory scores for the properties acidic flavor, sun soft white fluorescent light, as well as to the specific odor, and oxidized odor up to 48 h of exposure. Although wavelengths 405 and 436 nm. Significant flavor changes in the panel used a scale from 1 to 9, no samples were scored milk after exposure to fluorescent light were observed after higher than 7 for any attribute. Table 2 summarizes at 2–6 h (deMan, 1978; Hansen et al., 1975; Whited, approximately what storage time the different sensory Hammond, Chapman, & Boor, 2002). attributes became significantly different from the control (cheese stored in the dark). A significant reduction in 3.1.2. Fluorescence analysis acidity (marker for freshness) was noticed already after 4 h Fig. 2 shows the fluorescence spectra from cheese from of light exposure. A significant formation of oxidized flavor some of the 20 different storage times. The spectra can be and odor and sun flavor and odor were registered after divided into three characteristic spectral regions. The ARTICLE IN PRESS 1222 J.P. Wold et al. / International Dairy Journal 16 (2006) 1218–1226

Table 2 Storage times (h) when sensory-assessed attributes of Jarlsberg cheese became signiﬁcantly different (a ¼ 0:05) from control samples (stored in the dark)

Sensory property Acidic Oxidized Sun Paint Stearin Package Grass Whitenessa

Flavor 4 10 10 21 8 14 NS NS Odor 4 8 10 16 8 10 NS NS

aWhiteness is not a ﬂavor or odor, but refers to visual appearance. NS indicates no signiﬁcant difference.

50000 Table 3 0 Correlations between fluorescence spectra and sensory attributes assessed 0.5 from Jarlsberg cheese stored from 0 to 48 ha 2 40000 4 10 Sensory attribute LV R RMSEP 24 48 30000 Acidic odor 1 0.90 0.50 Acidic flavor 1 0.90 0.50 Sun odor 3 0.88 0.32 20000 Sun flavor 3 0.87 0.34 Oxidized odor 1 0.88 0.65 Oxidized flavor 1 0.87 0.71 10000 LV: number of latent variables; R: multivariate correlation; RMSEP: root mean square error of prediction. Fluorescence emission intensity (counts) 0 aCalibration models are based on partial least-squares regression. 450 500 550 600 650 700 750 Wavelength (nm) Herbert, 2001). However, the emission intensity for vitamin Fig. 2. Fluorescence spectra from Jarlsberg cheese after exposure to A for excitation at 380 nm is expected to be negligible. fluorescent light from 0 to 48 h. Numbers referring to the different curves indicate sample exposure time in hours. It is obvious from the spectra that riboflavin began to be degraded as soon as the cheese was illuminated. A significant decrease in fluorescence around 530 nm was prominent and broad peak around 530 nm is attributed to measured already after half an hour. There was a gradual riboflavin. This was suggested by Wold et al. (2002), and decrease with time, and the lowest intensities were verified by Miquel Becker et al. (2003). The next interesting consequently measured for cheese stored in 42 and 48 h. region is 600–750 nm. In this region, there are at least five Since the light degradation of riboflavin is considered to be different peaks, which have been tentatively identified by responsible for the initiation of oxidation processes in dairy Wold et al. (2005) as hematoporphyrin (Hp) at 620 nm and products, the direct measurement of this breakdown should protoporphyrin at 635 and 705 nm, while the double peak intuitively enable early measurement of light-induced at 661 and 672 nm probably can be ascribed to chlorophyll, oxidation. In the region from 600 to 750 nm, there was a type b and a, respectively. These compounds seem to clear decrease of fluorescence with time at the double peak appear more or less in all dairy products, they are all light at 661 and 672 nm. The smaller protoporphyrin peaks at sensitive and act as light sensitizers. In accordance to Wold 635 and 705 nm seemed to disappear after about 4 h of et al. (2005), they play a significant role in the initiation of exposure, while the peak at 620 nm, probably related to photooxidation in cheese. The third region from 410 to Hp, seemed to be formed at the same time. Hp has an 480 nm shows some change with time; however, the main absorption peak close to 620 nm, and it has been observed chromophores responsible for the signals are not certain. that the emission peak decreases for higher concentrations This region typically shows fluorescence from stable of Hp because of self-absorption (Yamashita, Nomura, oxidation products formed by aldehydes and amino acids Kobayashi, Sato, & Aizawa, 1984). In this case, when the (Kikugawa & Beppu, 1987). This is also a region where concentration presumably decreases with light exposure, lumichrome, a breakdown product from riboflavin, ex- the emission peak can increase. The degradation rate of hibits fluorescence at typically 444–479 nm (Fox & Thayer, riboflavin and chlorophyll was closely correlated. This is 1998). Riboflavin, beta-carotenoid, chlorophyll, and por- reasonable, since the cheese was exposed to white phyrin compounds all absorb in this region, which means fluorescent light, which contains wavelengths degrading that photodegradation of these pigments might introduce both riboflavin and chlorophyll. changes in the fluorescence spectra due to more or less re- In Table 3 the fluorescence spectra are correlated with absorption of the fluorescence by these compounds. the sensory properties using PLSR. Correlations between Finally, vitamin A, which is also light sensitive, has a 0.87 and 0.90 are satisfactory, since we are dealing with fluorescence emission maximum around 411 nm (Christen- early oxidation. Fig. 3 shows predicted versus measured sen, Povlsen, & Sørensen, 2003; Dufour, Devaux, & values for acidic and oxidized odor. Based on these data, ARTICLE IN PRESS J.P. Wold et al. / International Dairy Journal 16 (2006) 1218–1226 1223

7 7 6 6

5 5

4 4

3 3

2 2 Predicted acidic odor

1 Predicted oxidized odor 1

0 0 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 Measured acidic odor Measured oxidized odor

Fig. 3. Predicted versus measured acidic odor (R ¼ 0:90), and oxidized odor (R ¼ 0:87) by calibration model based on ﬂuorescence spectra.

the sensitivity and accuracy of front-face fluorescence is a 100 substitute for sensory panel; accordingly, the method could enable more efficient studies of light-induced oxidation in 80 cheese, and most probably in other dairy products as well. Additional work with sensory analysis and fluorescence spectroscopy with other products would have to be 60 conducted to confirm this hypothesis. The close relation between fluorescence and sensory measured photooxidation has been indicated earlier by Mortensen, Sørensen, 40

Danielsen, et al. (2003) and Wold et al. (2002, 2005). Transmission (%) Since fluorescence detects the photodegradation of the 20 various light sensitizers, it is reasonable that the method is able to measure early oxidation. Although the relation between light-sensitizer breakdown and sensory changes 0 300 400 500 600 700 800 900 appears to be linear, we must assume that the photo- Wavelength (nm) chemical oxidation processes are more complex. Fig. 4. Light transmission properties (percent transmitted light per 3.2. Light color study wavelength) of the colored filters used in the color exposure experiment. The spectral curves in the plot are colored in accordance with the colored 3.2.1. Transmission properties of colored films filters. Spectrum corresponding to the filter used to block UV is in black. The transmission properties of the UV block and the colored films are shown in Fig. 4. Note that the yellow and orange filters were not pure yellow and orange, they did acidic odor also transmit red light. Since the total transmitted intensity 7 sun odor of each filter was equal, the amount of red light transmitted oxidized odor by the yellow filter was much less than that of the red filter. 6 Note also that the UV block had a sharp cut-off at about 400 nm, blocking the UV contributions from the green, 5 yellow, orange, and red filters. 4 3.2.2. Sensory analysis

The sensory panel noted large differences between Sensory scores 3 samples stored under the different conditions. Fig. 5 shows the average sensory responses for three of the sensory 2 attributes: acidic odor, sun odor, and oxidized odor.

Although the panel used a scale from 1 to 9, no samples 1 were scored higher than 7 for any attribute. Table 4 shows dark green yellow orange red blue white violet the significant differences among the various storage Color of exposure light conditions. Cheese stored in the dark had a distinct acidic Fig. 5. Sensory scores measured on Norvegia cheese exposed to light of flavor (sign of freshness) and low scores for oxidized and seven different colors and darkness for acidic odor, sun odor and oxidized sun odors and sun flavors, while cheese exposed to violet odor. ARTICLE IN PRESS 1224 J.P. Wold et al. / International Dairy Journal 16 (2006) 1218–1226

Table 4 Signiﬁcant differences in sensory responses to different storage conditionsa Storage condition color of light Acidic odor Acidic flavor Oxidized odor Oxidized flavor Sun odor Sun flavor Violet 1.2 1.2 6.7 6.4 6.6 6.5 White 1.3 1.5 5.7 6.1 6.2 6.3 Blue 2.1 2.1 4.8 4.8 5.4 5.6 Red 2.4 2.8 4.0 3.7 4.8 4.8 Orange 3.4 3.8 2.9 2.8 4.3 4.1 Yellow 3.6 3.7 3.2 3.2 4.1 4.0 Green 3.7 4.0 2.8 2.8 3.7 3.6

Dark 6.1 6.2 1.4 1.3 1.8 1.8

aVertical lines cover groups of storage conditions in which the means are not signiﬁcantly (a ¼ 0:05) different from each other. Numbers indicate average sensory score for each storage condition.

and white light (transparent film) was mostly oxidized. 60000 There was also a significant sensory deterioration for cheese covered by blue, green, yellow, orange, and red 50000 filters. It is notable that the sensory response for red light was not significantly different from that of blue light for 40000 any of the sensory attributes, indicating that red light indeed induced photooxidation, although it is not absorbed 30000 by riboflavin. Overall, the green filter seemed to give the minimal adverse affects with regard to photooxidation. 20000 Hansen et al. (1975), who evaluated the effect of light exposure from differently colored light on oxidation in 10000 milk, also found that green and yellow light in general had the least adverse effect. They found that pink light was Fluorescence emission intensity (counts) 0 slightly worse, while white fluorescent light gave the most 450 500 550 600 650 700 750 rapid formation of off-flavors. A related result has been Wavelength (nm) reported for Havarti cheese, where both white light, which degrade riboflavin, and yellow light, which does not harm Fig. 6. Fluorescence spectra from Norvegia cheese samples stored under light of different colors. Colors of the spectra refer to the light filter used riboflavin, both induced the formation of secondary for each storage condition (see Fig. 1). Spectrum from cheese stored in the oxidation products (Mortensen, Sørensen, & Stapelfeldt, dark is black. Spectrum from cheese with transparent filter is gray. 2003).

3.2.3. Fluorescence analysis respectively. The strong degradation of these photosensi- Fig. 6 shows the fluorescence spectra from cheese at the tizers by red light probably explains the formation of off- eight different storage conditions. There were obvious flavors induced by ‘‘warm’’ colors like red, orange, and differences in the spectra of light-exposed cheese depending yellow. So, in addition to the well-known riboflavin on the color filters. There was a clear decrease in the initiated oxidation, there are probably substantial con- riboflavin peak at 530 nm for violet and blue and white tributions from porphyrin- and chlorin-initiated oxidation. light, consistent with the absorption region for riboflavin. While riboflavin absorbs light in the UV region and up to Light from the green filter degraded riboflavin to a less about 500 nm, chlorins and porphyrins generally absorbs extent because only a fraction of the green light was within light throughout the entire visible part of the spectrum, but its absorption band. Red, orange, and yellow light had, as most strongly in the 350–450 nm region and in the red expected, little or no influence on riboflavin. In the region (630–670 nm). Since the absorption regions are the 600–750 nm region, all colors apparently degraded the most harmful, it is apparent that the green–yellow light in protoporphyrin peaks at 635 and 705 nm. The chlorophyll the 500–600 nm region presumably gives the least adverse peaks at 661 and 672 nm were degraded most effectively by effects. red light, but also by violet, blue, and orange light. The Wold et al. (2005) showed that the spectral signals from porphyrin peak at 620 nm was most effectively degraded by porphyrins and chlorophylls correlated well with sensory violet and blue light. The results resemble those reported properties. Models were made based on the three spectral by Wold et al. (2005). Protoporphyrin and chlorophyll regions 410–480, 480–600 and 600–750 nm, in order to have absorption peaks at approximately 630 and 660 nm, elucidate the information content within each region. The ARTICLE IN PRESS J.P. Wold et al. / International Dairy Journal 16 (2006) 1218–1226 1225

Table 5 Correlations between ﬂuorescence spectra and sensory-assessed attributes based on partial least-squares (PLS) regressiona

Sensory property Whole spectrum 410–480 nm 480–600 nm 600–750 nm

LVb R LV R LV R LV R

Oxidized odor 4 0.95 2 0.95 1 0.89 4 0.95 Sun odor 2 0.94 3 0.91 2 0.86 1 0.94 Acidic ﬂavor 5 0.96 4 0.90 1 0.79 3 0.92

aRegression models were based on the whole spectrum as well as some specific spectral regions. bLV: number of PLS factors used in the model; R: correlation coefficient. results showed that variation in the pure riboflavin region Acknowledgements at 480–600 nm explained the variation in sensory perceived oxidized odor well, but less of sun and acidic flavor. The We would like to thank TINE Norwegian Dairies for 410–480 nm variation was also most closely related to providing the cheese, and the Norwegian Research Council oxidized flavor, but little of the two other attributes. The for partial funding of this study. porphyrin region correlated highly with all sensory attributes. Table 5 shows that much the same is the case References for this experiment. The riboflavin region (480–600 nm) correlates quite well with the sensory properties, but not as Bekbo¨ let, M. (1990). Light effects on food. Journal of Food Protection, well as the two other regions. The close correlation with the 53(5), 430–440. 410–480 nm region was slightly surprising; however, the Borlet, F., Sieber, R., & Bosset, J. O. (2001). Photo-oxidation and regression coefficients (not shown) indicate an important photoprotection of foods, with particular reference to dairy products. An update of a review article (1993–2000). Sciences des Aliments, 21(6), peak around 420 nm, which might be related to the 571–590. degradation of chlorophyll. Bosset, J. O., Gallmann, P. U., & Sieber, R. (1993). Influence of light transmittance of packaging materials on the shelf-life of milk and dairy 4. Conclusion products—A review. In M. Mathlouthi (Ed.), Food packaging and preservation (pp. 222–268). London, UK: Blackie Academic & Prof. Christensen, J., Povlsen, V. T., & Sørensen, J. (2003). 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