Changes In Sensory Properties Research Articles

Anti-listeria activity of Pediococcus pentosaceus BCC 3772 and application as starter culture for Nham, a traditional fermented pork sausage

Lactic acid bacteria forming bacteriocin active against Listeria monocytogenes were screened for potential use in controlling growth of L. monocytogenes in Nham, a Thai traditional fermented pork sausage. Based on the spot-on-lawn assay, Pediococcus pentosaceus BCC 3772 was found to produce the highest anti-listeria activity. Through a series of chromatographic techniques, Edman N-terminal sequencing and mass spectrometry, this anti-listeria compound showed a complete homology to pediocin PA-1/AcH. Inoculation of P. pentosaceus BCC 3772 in Nham caused a significant decrease of 3.2 log in population of spiked L. monocytogenes within 18–24 h of fermentation, in comparison with the initial count with no significant changes in sensory properties and consumer acceptability on the overall characteristics of the final fermented Nham products. These results indicate that the P. pentosaceus BCC 3772 should be useful as a functional starter culture for control of L. monocytogenes without compromising the unique quality of Nham.

Physicochemical, microbiological and sensory profiles of fermented milk containing probiotic strains isolated from kefir

A two-strain starter culture containing Lactobacillus plantarum CIDCA 83114, a potential probiotic strain isolated from kefir grains, and Streptococcus thermophilus CIDCA 321 was tested for the preparation of a fermented milk product. Kluyveromyces marxianus CIDCA 8154, a yeast with immunomodulatory properties was included to formulate a three-strain starter culture. Supernatants of enterohaemorragic Escherichia coli, shiga-toxin-producing strain, along with a two-strain or a three-strain starter culture were included in the medium of Vero-cell surface cultures. The results demonstrated that these combinations of microorganisms antagonize the cytopathic action of shiga toxins. The cell concentration of Lb. plantarum did not decrease during fermentation, indicating that the viability of this strain was not affected by low pH, nor did the number of viable bacteria change during 21 days of storage in either fermented products. The number of viable yeasts increases during fermentation and storage. Trained assessors analyzed the general acceptability of fresh fermented milks and considered both acceptable. The milk fermented with the two-strain starter culture was considered acceptable after two week of storage, while the product fermented with the three-strain starter culture remained acceptable for less than one week. The main changes in sensory attributes detected by the trained panel were in sour taste, milky taste and also in fermented attributes. The correlation between different sensory attributes and acceptability indicated that the panel was positively influenced by milky attributes (taste, odour, and flavour) as well as the intensity of flavour. In conclusion, the two-strain starter culture would be the more promising alternative for inclusion of that potential probiotic lactobacillus in a fermented milk product.

Qualidade física e sensorial da carne de cordeiros de três genótipos alimentados com rações formuladas com duas relações volumoso: concentrado

Objetivou-se avaliar os atributos sensoriais (dureza, odor, sabor, suculência e cor) e físicos (força de cisalhamento, perda por cocção e parâmetros de cor L*, a*, b*), além do conteúdo de ferro da carne de cordeiros dos grupos Santa Inês (SI), Dorper × Santa Inês (DP × SI) e Sem Padrão Racial Definido (SRD) terminados em confinamento com dietas formuladas com duas relações volumoso:concentrado (50:50 e 20:80). Foram utilizados 54 animais (18 de cada genótipo, com peso médio inicial de 23 kg e 150 dias de idade) abatidos com 36 kg de peso vivo. As dietas aplicadas favoreceram a diferenciação na cor da carne. A intensidade de brilho (L*) diferiu entre os grupos genéticos. Nos animais terminados com a dieta com alto nível de concentrado, a carne apresentou menores perdas por cocção. Observou-se a existência de correlação entre a intensidade de vermelho (a*) e a cor da carne in natura e entre a concentração de ferro dietético na carne e a intensidade de brilho (L*). A carne de cordeiros SI e SRD possui menor dureza e maior suculência à carne de cordeiros Dorper × Santa Inês. A relação volumoso:concentrado na dieta não promove modificações nos atributos sensoriais e parâmetros físicos da carne.

Effect of water activity (aw) and irradiation on the shelf-life of fresh noodles

In this work, the effect of water activity (aw), irradiation and their combination on the preservation of fresh noodles was studied. Microbial growth, pH and sensory characteristics were investigated during 16 days' storage time under 37 °C. The combination of glycerol (3%), propylene glycol (2%), compound phosphate (0.4%) and salt (3%) was proved to be the most effective group which could reduce aw from 0.979 (control) to 0.900. Under this condition, the shelf-life of fresh noodles could be extended for more than 7 times. Moreover, a synergism between humectants and irradiation treatment was observed in relation to microorganism inhibition and shelf-life extension. For all the irradiated noodles, TPC (total plate count) did never exceed the selected deterioration threshold limit (106 CFU/g) during the entire observation period. When the irradiation dose was 4 kGy or higher, scarcely any bacteria proliferation was observed. Noodle samples irradiated at 4 kGy showed the best pH and sensory stability as the storage time increased. This paper presents an effective and low-cost method to prolong the shelf-life of fresh noodles, which can largely extend the store time of fresh noodles at room temperature, and does not produce any negative changes in sensory attributes. This method will be a new system for food preservation with lots of possible industrial applications. The results of this research also have implications for dumpling skins and other noodle types.

Influence of high pressure application on the nutritional, sensory and microbiological characteristics of sliced skin vacuum packed dry-cured ham. Effects along the storage period

Abstract The effect of high pressure processing at 600 MPa on sliced and vacuum packaged commercial dry-cured ham was determined by analyzing the induced color changes, the physicochemical characteristics, the microbiological count and the changes in sensory attributes and also its effect on lipid oxidation measured through TBARS (thiobarbituric reactive substances), antioxidant enzyme activities and the content of fatty acid from total, free and phospholipid fractions. This effect was also studied during 50 days refrigerated storage with different light conditions. The high pressure processing at 600 MPa modified the color of dry-cured ham producing an increase in lightness L*-parameter. Many sensory attributes were also modified resulting in an increase in hardness, chewiness, brightness, odor intensity and saltiness, while reducing color intensity. High pressure produced a reduction in the aerobic count. The oxidative stability of the pressurized dry-cured ham was not altered as observed from the absence of differences in fatty acid contents and antioxidant enzyme activities. Initially pressurization produced a decrease in TBARS levels, however this effect was not found after 50 days of refrigerated storage. Industrial relevance The application of high hydrostatic pressure (HHP) in food technology is a useful tool to combine a minimal processing that increases the shelf-life of the food products, maintaining their safety and nutritional properties and with minimal changes in flavor or taste. This processing technology is very important to increase the safety of the sliced foods which are prone to the microbiological deterioration, as cured meat products and cooked ham. Pressurization of sliced dry-cured ham at 600 MPa has been shown effective reducing spoilage associated microorganisms. The present study was carried out to evaluate the oxidative stability, nutritional quality, safety and sensory attributes of dry-cured ham pressurized at 600 MPa. This is very important because the hypothesis that HHP does not affect to sensorial characteristics needs to be confirmed in different kind of foods. Also, the possible causes of the observed effects should be explained by the study of physic–chemical parameters. In this way the oxidative stability is an important issue because some authors claimed that HHP can increase oxidation in food containing lipids.

Effect of vacuum and modified atmosphere packaging on the shelf life of rabbit meatEfecto del envasado al vacío y en atmósfera modificada en la vida útil de la carne de conejo

Rabbit hind legs were packaged under different modified atmospheres (Vacuum packaging (VP), 100% CO2 and a commercial gas blend) to determine an applicable packaging method for improving quality and durability of rabbit meat. The best atmosphere for preserving microbiological quality and extending shelf-life was 100% CO2 (5 weeks) followed by VP (between 3 and 4 weeks) and a commercial gas blend consisting of 35% CO2/35% O2/30% N2 (between 18 and 21 days). Reduction in acceptability was associated to exudate losses (100% CO2), “unspecific bad odours” (VP) and rancid off-odours (gas blend). The spoilage microflora in 100% CO2 and VP samples was dominated (up to 54%) by lactic acid bacteria (LAB). Under the gas blend atmosphere, Pseudomonas, LAB and Brochothrix thermosphacta accounted for 8.7%, 4.0%, and 2.4%, respectively. Among spoilage indicators, only extract-release volume significantly correlated (p < 0.05) with microbial changes. The 100% CO2 atmosphere was the best to increase the shelf-life and maintain the microbiological quality, with no significant changes in sensory properties.

EFFECT OF MILK PASTEURIZATION ON FLAVOR PROPERTIES OF SEVEN COMMERCIALLY AVAILABLE FRENCH CHEESE TYPES

ABSTRACT Previous research on matched pairs of experimental cheese showed that heat treatment of milk affected flavor properties. However, whether pasteurization has a generalized effect or whether the effect is specific to certain cheese varieties is not known. Experienced, highly trained sensory panelists developed flavor profiles for seven commercially available French cheeses (Brie, Coulommier, Camembert, Saint Nectaire, Muenster, Chèvre and Bleu) for which versions made from pasteurized or unpasteurized milk were commercially available. Raw‐milk cheese had stronger odor properties. Soft cheeses with white rind (Brie, Coulommier, Camembert and Saint Nectaire) as well as Chèvre and Bleu were affected similarly by heat treatment of milk, but the sensory characteristics of Muenster cheese did not follow the pattern of other cheeses. These results suggest that many, but not all, cheese types show similar changes in sensory attributes as a result of using pasteurized rather than raw milk. PRACTICAL APPLICATIONSThis study gives manufacturers and researchers information on flavor differences that exist between similar cheese types made from raw or pasteurized milk. Researchers and manufacturers can use that information in order to develop pasteurized‐milk cheese that has the traditional full‐flavored characteristics of its raw‐milk counterpart.

Chemical and sensory characterization of oxidative behavior in different wines

In wine making, the redox phenomena are responsible for profound changes in the wine’s chemical composition. Twenty wines set has been selected trying to cover a wide range of behaviors against to oxidation–reduction phenomenon. Free SO2 level was adjusted to the maximum level found to avoid its influence from the wine oxidative trend. Samples of this set of wines were submitted to extreme conditions during 1 month. Samples were taken in different days for sensorial and chemical analysis. It is proved that red wines oxidation velocity is much higher than white wines. Aldehydes were quantified by gas chromatography–negative ion mass spectrometry (GC–NCI–MS) using a previous derivatization procedure. In conclusion, it can be said that the speed at which the sensory characteristics of wine changes are loosely related to the production of relevant odor active aldehydes, particularly to levels of methional and phenylacetaldehyde. In general, red wines produce those aldehydes during oxidation at a much higher speed than white wines, which is in agreement with the observed changes in sensory properties. However, it was not possible to find good correlations between sensory changes and aldehyde production within the red or white subsets.

Flavour development during beef stock reduction

Abstract In beef stock, made of brisket, water and NaCl, reduction time was found to play a major role in development of volatile compounds and sensory characteristics. Nine stock reductions, made by varying concentration factor and reduction time (controlling power input from stove), were compared using dynamic headspace gas chromatography and a descriptive sensory analysis (n = 9). Aroma compounds could be classified into 5–6 groups, based on their concentration–time profiles. The initial flavour was found to be lost for both slow and fast reductions but, for fast reduction, insufficient time was left for development of new flavours. The decrease in volume alone, as often referred to in recipes, is accordingly not sufficient as the sole indication of flavour development. The observed changes in sensory properties, and changes in the underlying concentrations of chemical compounds during reduction, are discussed with regard to theoretical considerations about evaporation of volatile aroma compounds from the boiling two-phase (oil–water) liquid and heat-induced chemical reactions.

The effects of ionizing irradiation on Salmonella inoculated on almonds and changes in sensory properties

The goal of this study was to test the efficacy of irradiation on destroying Salmonella on raw almonds and evaluating the resultant sensory changes in the almonds. Raw almonds inoculated with various strains of Salmonella were irradiated at 5 dose levels up to 3 kGy and the D value was determined. The strain SEPT30 was the most resistant strain with a D value of 1.25 kGy indicating that a 4 log CFU/g reduction would require a dose of 5.0 kGy. Irradiation at 2.98 and 5.25 kGy induced significant sensory changes in almond nuts as manifested by intensity of chemical/metallic/rancid flavor ranked by a trained panel. A consumer panel found that samples treated with 5.25 kGy irradiation rendered the almonds unacceptable. Thus, irradiation by itself is unlikely to be a feasible method to eliminate Salmonella from raw almonds.

Does Feed Composition Affect Oxidation of Rainbow Trout (Oncorhynchus mykiss) during Frozen Storage?

Rainbow trout ( Oncorhynchus mykiss ) were fed a diet containing either fish oil or rapeseed oil and with or without 200 mg/kg carotenoid (either astaxanthin or canthaxanthin). A total of six diets were obtained: (1) fish oil/astaxanthin; (2) vegetable oil/astaxanthin; (3) fish oil/canthaxanthin; (4) vegetable oil/canthaxanthin; (5) fish oil/no pigment; and (6) vegetable oil/no pigment. The fish were slaughtered and stored in polyethylene bags individually as butterfly fillets for up to 22 months at -20 °C. The composition of the fish muscle at slaughter and during frozen storage was evaluated by sampling after 4, 8, 13, 18, and 22 months. The carotenoid content in the muscle was found to be approximately 9-10 mg/kg of fish for both carotenoids. Primary oxidation lipid products (peroxides) as well as secondary oxidation products (volatiles) were measured. In addition, the level of protein carbonyl groups and the content of tocopherols and carotenoids in the muscle were also measured. To estimate the overall changes in sensory properties of the different samples during storage, a trained sensory panel also evaluated the samples. Both the sensory panel and the chemical analysis revealed that in this investigation fish fed fish oil were slightly more oxidized than fish fed vegetable oil. Results showed that canthaxanthin effectively protected both protein and lipid against oxidation during frozen storage. In contrast, astaxanthin did not seem to have a clear and systematic effect. Results indicated that the feed composition influenced the fish muscle composition and subsequently the oxidative stability of the fish during frozen storage. Besides, other constituents in the feed might influence deposition of antioxidants in the tissue and consequently affect the oxidative stability of the muscle.

INFLUENCE OF STORAGE CONDITIONS ON SENSORY SHELF LIFE OF YERBA MATE

ABSTRACT Samples of yerba mate (YM) manufactured with natural and accelerated processes were stored under constant conditions of temperature (30 and 40C) and relative humidity (75 and 90% RH). Mold and yeast count and changes in sensory attributes, intensity of the flavor, bitterness and humidity flavor were studied. The end of shelf life was determined using the Weibull hazard method, calculated as the time at which 50% of the panelists find the product unacceptable. Conducted tests of acceptability carried out with habitual consumers of YM confirmed results obtained with the trained panel. Similar values of shelf life were found with the high humidity flavor descriptor and with results of acceptance–rejection test. Storage time to which off‐flavor was developed is analogous to the time of fast mold and yeast growth. The RH is the most important variable: sensory shelf life time of 32–44 days at 75% RH and 10–13 days at 90% RH were found at both temperatures of storage. PRACTICAL APPLICATIONSAn important contribution of the present work is the analysis of the influence of storage conditions on the quality loss of yerba mate (YM). Furthermore, the shelf life in unfavorable environmental conditions for the YM storage was determined. This is important because even though the Código Alimentario Argentino establishes an upper limit of moisture in YM, there are no systematic studies about the issue.In addition, sensory parameters of YM quality are associated to the consumer's habits and no standard sensory quality attributes are established. Nevertheless, the consumer expectation is satisfied by preservation of product sensory characteristics. In this sense, from the results of this study, it is possible to establish conditions of humidity and temperature of storage that guarantee the preservation of sensory quality of YM during their commercialization

Shelf life of linseeds and peanuts in relation to roasting

Changes in the oxidative status of peanuts and linseeds during storage were investigated by the ESR spin trapping technique with N-tert. butyl-α-phenylnitrone. It has proven to be a suitable method for the determination of the radical generating reactions in the very early stage of fat spoilage and deterioration reactions can still be detected, before changes in sensory properties are noticeable. Primarily, due to oxidative reactions of lipids, shelf life of peanuts and linseeds as well as their sensory quality decreases with storage time. Roasting has a controversial influence on the stability of linseeds and peanuts, respectively. Roasted linseeds became rancid more rapidly than fresh seeds. With increasing roasting temperature and time the oxidative stability of peanuts was improved and shelf life prolonged. This can be attributed to the formation of antioxidant Maillard reaction products. A correlation was found between the amount of deoxyosones as reactive Maillard reaction intermediates and shelf life of roasted nuts.

Effectiveness of combined preservation methods to extend the shelf life of Morcilla de Burgos

Morcilla de Burgos is the most famous blood sausage in Spain. However, while producers are interested in extending its shelf life, the consumer is increasingly demanding more natural food. This situation has led to the current search for new and mild preservation technologies. Two batches of four different products: control without any treatment, control with organic acid salts (CnOAS; a 3% mixture of potassium/sodium l-lactate), control with high hydrostatic pressure processing (CnHPP; 600 MPa–10 min), and a combination of both treatments (OAS + HPP), were carried out to evaluate any synergistic effect that occurs when combining OAS and HPP, and the influence of different preservative treatments on the spoilage bacterial population and their evolution. HPP (with or without addition of OAS) can be considered the most suitable method for preserving morcilla de Burgos as it does not produce negative changes in sensory attributes. No clear selective effect of different treatments on the composition of the spoilage bacteria was seen and similar spoilage patterns were observed independently of the preservation treatment used.

Meat quality of Argentinean “Camperos” chicken enhanced in omega-3 and omega-9 fatty acids

Five diets were assessed with the aim of increasing oleic fatty acid and omega-3 polyunsaturated fatty acid content in ‘campero’ poultry meat and evaluating their influence on sensory attributes. Animals from treatment 1 (T1) were confined and fed with corn/soybean diet; in T2, animals were fed with a corn/soybean mix with free access to pasture; T3 diet had high oleic sunflower seeds (HOSS) and linseeds with access to pasture; T4 diet was similar to T2 with free access to chicory instead of pasture and T5 diet was similar to T3 with free access to chicory instead of pasture. Linseeds and HOSS supplementation significantly increased the fatty acids profile, regardless of forage supply. T3 MUFA content was significantly higher than in the other treatments. Due to the high presence of omega-3 PUFA in linseeds and HOSS treatments (T3 and T5), meat omega-6/omega-3 ratio decreased from 9 to 4. The presence of off-flavours was not influenced by diets but there was an interaction between portion and storage conditions. ‘Poultry meat’ aroma was only influenced by the storage conditions, being slight after 4 months of freezing, while presence of off-aromas was affected by diets. We conclude that it is possible to produce ‘campero’ poultry meat with enhanced omega-3 and omega-9 content and a low omega-6/omega-3 ratio using diets based on linseed and HOSS, without any important change in sensory properties.

INFLUENCE OF SODIUM TRIPOLYPHOSPHATE (STP) TREATMENT AND COOKING TIME ON COOK LOSSES AND TEXTURAL PROPERTIES OF RED MEATS

ABSTRACT Sodium tripolyphosphates (STPs) are important functional additives used in meat products. STPs reduce cook losses and improve textural properties, especially by increasing the water‐holding capacity of proteins. However, increases in cooking time or temperature enhance meat proteins' denaturation, resulting in a reduced water‐holding capacity. The amount of STPs diffused into meats would play an important role for these changes. Therefore, the objectives of this research were to determine the effects of processing conditions (cooking time, STP concentration and dipping time) on cook losses and textural properties of red meats, and to relate these changes with diffused amount of STPs. For this purpose, meats (2 × 2 × 2 cm in size) were dipped in different concentrations of STP solutions (2, 4 and 6%) for 10, 20 and 30 min, and were cooked in boiling water for 5, 10 and 15 min. Cook losses were calculated from weight changes, and textural properties were determined by applying texture profile analysis to data obtained using Texture Analyzer TA‐XT2i (Stable Micro Systems, Godalming, Surrey, U.K.). STPs were found to decrease cook losses and hardness values. While an increase in STP concentration increased cohesiveness, increase in cooking time resulted in higher hardness, gumminess, chewiness and cook losses. An increase in dipping times also decreased the cook losses and hardness. The results showed that STP concentration, STP dipping and cooking times had significant effects on the changes of textural properties and cook losses of meats. These results may be used for further meat processing optimization studies if they get correlated with sensory data obtained at the same conditions. PRACTICAL APPLICATIONSCooking to assure safety of food products leads to changes in sensory attributes. The major changes occurring in meats are shrinkage, toughening of tissues, releasing of meat juice and color due to the effect of thermal treatment on proteins. Based on these, resulting cook losses for economical considerations and changes in textural properties affecting consumer satisfaction are widely recognized. Because the meat processing industry uses sodium tripolyphosphates (STPs) to improve textural properties and to reduce cook losses, the objective of this research was to determine the effects of STPs and cooking time on cook losses and textural properties of red meats. The results showed that STPs and cooking time affected the changes in cook losses and textural properties significantly. In addition to these results, an optimization study for decreasing cook losses while improving textural properties should be conducted where these changes are attributed to be significant for human perception using a sensory panel.

Real-Time PCR Assay for Detection and Enumeration ofHanseniasporaSpecies from Wine and Juice

<i>Hanseniaspora</i> species (anamorph <i>Kloeckera</i> sp.) are common yeast constituents on grapes and often dominate in the early stages of wine fermentations. Growth of <i>Hanseniaspora</i> sp. in must has been linked to changes in sensory attributes of wine and is proposed as a factor in stuck and sluggish fermentations. A real-time quantitative polymerase chain reaction (PCR) assay was developed to rapidly profile <i>Hanseniaspora</i> sp. populations. The assay allows direct enumeration of <i>Hanseniaspora</i> sp. populations in either must or wine and is not impacted by high concentrations of <i>Saccharomyces cerevisiae</i> DNA. The development of this assay will enable high throughput surveys of must samples to better explore the relationship between early <i>Hanseniaspora</i> sp. populations and the ensuing wine fermentation or sensory changes.

A bioreactor model system specifically designed for Tetrahymena growth and cholesterol removal from milk

This work describes the configuration and operation of a bioreactor system especially designed for Tetrahymena cultivation and its use for milk improvement, particularly cholesterol elimination by the action of this cell. An advantage of the proposed method is the re-use of the growth medium; thus, the medium is used twice to provide two batches of Tetrahymena biomass without the need of further inoculation. This makes the procedure of producing the cell biomass faster and more economical. Cells are concentrated in the culture vessels by sedimentation at room temperature and then transferred to milk suspensions, where they can further grow for at least one generation with the benefit of reducing steeply cholesterol level. Milk treated according to this process is separated from the biomass by centrifugation. Under these conditions, less than 5% of the cells remain in the milk, and cholesterol elimination amounts to 75 +/- 10% of that initially present. No changes in sensorial properties of the milk, such as clotting or butyric odor, were observed as a result of this treatment. In addition, the bioreactor allows the aseptic recovery of the spent growth medium, which contains diverse enzymes of interest, and the cell pellets, to exploit particular lipids like phosphonolipids, abundant poly-unsaturated fatty acids and co-enzyme Q(8).

Dry-cured ham quality and acceptability as affected by the preservation system used for retail sale

Dry-cured ham cuts and slices were stored at 4 ± 2 °C for 8 months under vacuum and modified atmosphere (20% CO 2 + 80% N 2), respectively. Instrumental colour and texture, pH, non-protein nitrogen, total volatile basic nitrogen, acidity, lipid oxidation, sensory profile and consumer acceptability and purchase satisfaction were measured throughout storage. The overall quality of vacuum-packaged dry-cured ham cuts showed limited changes. Significant changes of sensory attributes involved only loss of flavour. The overall acceptability assessed by both trained and consumer panels did not decrease significantly throughout storage and the willingness to purchase remained above 50%. Conversely, modified-atmosphere-packaged ham slices had intense and extensive changes affecting sensory quality, particularly in visual appearance, flavour loss, off-flavour formation, saltiness and rancidity. Some of these changes were related to oxidation caused by low pH due to the presence of carbon dioxide in the protective atmosphere. Acceptability was significantly lower from the 4th month of storage and willingness to purchase fell below 50% at the same time.

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

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 (≈0.9). 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 ( p > 0.05 ) 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.