Fresh Button Mushrooms Research Articles

The Retention of Vitamin D2 and 25-Hydroxyvitamin D2 in Pulse UV-Irradiated Dried Button Mushrooms (Agaricus bisporus) after 12 Months of Storage.

Fresh mushrooms exposed to ultraviolet (UV) radiation prior to drying generate high concentrations of vitamin D2. The aim of this study was to determine the retention of D vitamers in mushrooms that were pulse UV irradiated, then air dried, and stored for up to 12 months. Fresh button mushrooms (A. bisporus) were exposed to pulsed UV radiation (dose 200 mJ/cm2, peak of 17.5 W/cm2), air dried and vacuum sealed before being stored in the dark at room temperature. After storage, samples were freeze dried and quantified for D vitamers using triple quadrupole mass spectrometry. After 3, 6 and 12 months of storage, there was 100% (11.0 ± 0.8 µg/g dry weight (DW), 93% (10.1 ± 0.6 µg/g DW) and 58% (5.5 ± 0.6 µg/g DW) retention of vitamin D2 and 88% (0.14 ± 0.01 µg/g DW), 71% (0.11 ± 0.01 µg/g DW) and 68% (0.1 ± 0.01 µg/g DW) retention of 25-hydroxyvitamin D2 (25(OH)D2), respectively. Compared to the irradiated dried mushrooms that were not stored, the D vitamer concentration was statistically significantly lower (p < 0.05) at 6 and 12 months for 25(OH)D2 and at 12 months for vitamin D2. Sufficient vitamin D2 (99 µg) remained after 12 months storage to provide at least 100% of daily dietary vitamin D requirements in a 20 g serving.

Button Mushroom - Potential Source of Vitamin D2 and Possibilities of Value Addition

Background: Despite, being known as the sunshine vitamin, there is a widespread deficiency of vitamin D. Mushrooms upon exposure to sunlight or UV radiations can synthesize vitamin D2 due to the presence of its precursor, ergosterol. The most common mushroom to be consumed worldwide is the button mushroom (Agaricus bisporus). These mushrooms possess a high nutritional value and have many therapeutic benefits. Objectives: This review aims to comprehend the potential of button mushrooms as a source of vitamin D2 and the possibilities of making value added products by incorporating button mushrooms. Conclusion: As button mushrooms are grown in dark chambers, they have negligible amounts of vitamin D2, however, on exposure to sunlight or UV B radiation, nutritionally significant vitamin D2 can be generated in fresh, whole, sliced or dried powder. The synthesis of vitamin D2 is largely dependent on the type of UV radiation, its intensity, temperature and exposed surface area. As fresh button mushrooms are highly perishable, they are often preserved in the form of jams, sauce, pickles and candy. Dried button mushroom powder finds utility in formulating nutrient enriched cakes, breads, biscuits, cookies, soup powders and composite flours. With the ever- increasing demand for novel health foods, vitamin D enhanced button mushroom and its powder can be used in various forms in the diet as a sustainable non-animal substitute to supplements and pills to tackle vitamin D deficiency.

Effect of air-drying on the generation of vitamin D2 and 25-hydroxyvitamin D2 by pulsed UV irradiation in button mushroom (Agaricus bisporus)

Fresh and dried mushrooms naturally generate vitamin D2 when exposed to ultraviolet (UV) radiation. Vitamin D2 and 25-hydroxyvitamin D2 (25(OH)D2) concentrations were compared in dried button mushrooms (Agaricus bisporus) exposed to pulsed UV radiation either before or after air-drying. A further aim was to assess the effect of air-drying on the generation of D vitamers. Fresh button mushrooms were irradiated (Irr) with a total of 200 mJ/cm2 pulsed UV radiation before (Irr/AD) or after (AD/Irr) being air-dried (AD). A third group of fresh button mushrooms was irradiated but not air-dried (Irr). Control mushrooms were fresh and untreated. The D vitamers were quantified in freeze-dried samples using triple quadrupole mass spectrometry. Irr/AD mushrooms had more than double the concentration of vitamin D2 than AD/Irr mushrooms (9.5 µg/g dry weight (dw) vs 4.6 µg/g dw). However, Irr mushrooms contained 6.3 µg/g dw. The concentration of 25(OH)D2 in Irr mushrooms was 0.05 μg/g dw, while 0.14 μg/g dw was detected in Irr/AD mushrooms. There was no detectable 25(OH)D2 in control mushrooms, nor in AD/Irr mushrooms. The sequence of irradiating and drying mushrooms was a key factor in generating vitamin D2.

Preservation mechanism and flavor variation of postharvest button mushroom (Agaricus Bisporus) coated compounds of protocatechuic acid-CaCl2-NaCl-pullulan

To clarify preservation mechanism and flavor variation of postharvest button mushroom (Agaricus Bisporus) coated compounds of protocatechuic acid-CaCl2-NaCl-pullulan, the protocatechuic acid (118 mg/L)-CaCl2 (0.83%)-NaCl (0.55%)-pullulan (0.30%) composite preservative (CP) at the spray rate of 13:1 was used to coating on button mushroom and storage at 4 ± 1 °C. Compared to the negative control (NC) group, the respiration rate, browning degree, malondialdehyde (MDA) content, polyphenol oxidase (PPO), and total phenolic content of CP treatment decreased 26%, 27%, 25%, 26% and 37% respectively after 12days. On the contrary, the peroxidase (POD), catalase (CAT), phenylalanine ammonia-lyase (PAL) and total superoxide dismutase (T-SOD) of CP treatment increased 57%, 40%, 39% and 30% respectively. Further, button mushroom coated with CP maintained a higher content of soluble protein and nucleic acid, but lower content of free amino acid (FAA) than NC group. Characteristic flavor substance of button mushroom coated by CP, 3-octanone was higher than that in the NC group, but lower alkanes. Moreover, there was no significant difference in 3-octanone between the CP and fresh button mushroom. Hence, the CP treatment had improved postharvest button mushroom texture and flavors, and storage at 4 ± 1 °C, its shelf life is prolonged to 12 days after coated compounds of protocatechuic acid (118 mg/L)-CaCl2 (0.83%)-NaCl (0.55%)-pullulan (0.30%).

Maintaining Postharvest Quality of Fresh Button Mushrooms by Application of Hydrogen Peroxide and Antibrowning Agent Treatments

This experiment was conducted to study the effect of postharvest dipping of fresh button mushrooms (Agaricus bisporus) in hydrogen peroxide (H2O2) 5% alone or in combination with antibrowning agents (calcium chloride at 3 or 5%, ascorbic acid 3 or 5% and citric acid 2 or 4%) beside dipping in distilled water (control) to inhibition browning, had the lower level of microbial load and maintaining quality during storage for 12 days at 4 ± 1oC and 90 ± 2% relative humidity during two successive seasons of 2016 and 1017. Results showed that all studied treatments reduced weight loss percentage, browning index and Polyphenol oxidase activity, total bacteria counts, yeast and mold counts and maintaining of phenolic and flavonoids contents of fresh button mushrooms during cold storage comparing with untreated control. However, dipping button mushrooms in solution H2O2 5% + calcium chloride 5% was the most effective in this concern, which reducing browning, maintaining quality and inhibiting microbial counts for 12 days at 4 ± 1oC and 90 ± 2% relative humidity.

Optimization of button mushroom browning inhibition using response surface methodology

Post-harvest browning of fresh button mushroom (Agaricus bisporus), was inhibited by conducting a trial using three independent process variables viz. citric acid (0.1, 1.0 and 1.5%), aloe vera gel (50, 60 and 70%) and drying time (6, 7 and 8 h). Drying of harvested mushroom was done in a cabinet dryer at 60 ± 3oC. Response surface methodology was adopted for experimental design and optimization of process variables. Five minutes dip of mushroom in 60% aloe vera gel along with 1% citric acid and its subsequent drying at 60°C for 7 hours was found best in retaining the desirable traits viz. color, pH (6.52), TSS (6.38oBrix), ascorbic acid (6.92 mg/100g) and moisture content (12.16%). Results showed that the data were adequately fitted into second-order polynomial models developed by response surface methodology.

Optimization of Freeze-Drying Process Parameters for Qualitative Evaluation of Button Mushroom(Agaricus bisporus)Using Response Surface Methodology

Button mushroom cubes of constant cross-sectional area (0.75 cm × 1.5 cm) and varying thickness (2 mm, 5 mm, and 8 mm) were freeze-dried. Pressure (0.04, 0.07, and 0.10 mbar), primary drying temperature (−2°C, −5°C, and −8°C), and secondary drying temperature (25°C, 28°C, and 31°C) were taken as drying parameters. The protein, ascorbic acid, and antioxidant contents were taken as quality estimates for freeze-dried mushrooms. It was observed that the secondary drying temperature affected the protein (p&lt;0.05) and antioxidant content (p&lt;0.01) significantly, whereas all three freeze-drying parameters affected the ascorbic acid content with higher effect due to temperature parameters (p&lt;0.01) as compared to pressure (p&lt;0.05). The optimized values for protein, ascorbic acid, and antioxidant content obtained using response surface methodology were7.28±0.56 mg/g,26.92±0.87 mg/100 g, and8.60±0.44 mg/g, respectively, as compared to8.43±0.21 mg/g,28.00±0.53 mg/100 g, and9.10±0.10 mg/g, respectively, for fresh button mushrooms. The optimum values for process variables were obtained as 0.09 mbar, 0.36 cm, and −7.53°C and 25.03°C for pressure, sample thickness, and primary and secondary drying temperatures, respectively.

Evaluation of the potential use of probiotic strain Lactobacillus plantarum 299v in lactic fermentation of button mushroom fruiting bodies.

The available literature does not provide data on the application of probiotic strains in mushroom processing. The aim of the study was to evaluate the potential to use the L. plantarum 299v strain with documented probiotic properties in the process of lactic fermentation of button mushroom fruiting bodies (Agaricus bisporus). Fresh button mushroom fruiting bodies and cultures of lactic acid bacteria L. plantarum Ib and a probiotic strain L. plantarum 299v were the material analysed. Sensory evaluation was performed with a 5-point scale, an instrumental method of colour measurement based on the CIA L*a*b* scale, total phenolic compounds were determined with the Folin method, antioxidant properties were assayed with the DPPH radical test, and reducing power was determined using the FRAP method. After a week-long lactic fermentation, the pH value in the samples declined to a level of 3.6 (L. plantarum Ib) and 3.75 (L. plantarum 299v); these values persisted or decreased slightly during the period of maturation of the fermented samples under refrigeration. Fermented mushrooms were assigned high grades in the organoleptic evaluation. The colour analysis revealed significant changes in the values of the L*a*b* parameters in the fermented product, in comparison with fresh mushrooms. Blanching contributed to a significant decrease in the content of total phenolic compounds in the mushroom fruiting bodies and to a decline in antioxidant activity. Mushrooms fermented with the probiotic strain were characterised by higher phenolic compound content and higher antioxidant activity. L. plantarum 299v strain with documented probiotic properties can be applied in fermentation of button mushroom fruiting bodies. Products obtained with the use of both strains were characterised by good sensory properties. The type of strain used in the lactic fermentation of mushroom fruiting bodies had an effect on the phenolic compound content and antioxidant properties of the final product.

Suppression of Cell Wall Degrading Enzymes and their Encoding Genes in Button Mushrooms (Agaricus bisporus) by CaCl2 and Citric Acid.

Fresh button mushrooms (Agaricus bisporus) were harvested and treated with a solution of 1.5% CaCl2+0.5% citric acid and stored for 16days at 12°C. The effects of this treatment on firmness, weight, color, cell wall compositions (cellulose and chitin) and cell wall degrading enzymes (cel1ulase, beta-1, 3 glucanase, chitinase and phenylalanine ammonialyase) were investigated during post-harvest storage. The expressions of major genes (Cel1, Glu1, Chi1 and PAL1) involved in cell wall degradation during post-harvest storage were also monitored. The results revealed that the post-harvest chemical treatment maintained better firmness, weight, color and inhibited cellulase, beta-1, 3 glucanase, chitinase and phenylalanine ammonialyase activities. These findings showed that the down-regulation of cell wall degrading enzymes is a possible mechanism that delays the softening of button mushrooms by the application of combined chemical treatment.

Effects of high CO2 in-package treatment on flavor, quality and antioxidant activity of button mushroom (Agaricus bisporus) during postharvest storage

Button mushroom (Agaricus bisporus) is marketed for its good flavor and health benefits. However, the shelf life of fresh button mushroom is limited and quality is lost rapidly during storage. In this study, button mushrooms were treated with high CO2 (95%–100%) at the time of sealing of the packages and the packages were ventilated after 0, 12, 24 and 48h by puncturing the film at four corners. Results showed that 12h high CO2 treatment had a significant effect in reducing browning index (BI) and maintaining flavor of button mushroom during storage. In addition, the malonaldehyde (MDA) content was significantly inhibited while catalase (CAT) and peroxidase (POD) activities were significantly promoted by high CO2 treatment. High CO2 treatment increased antioxidant ability of button mushroom, which in turn maintained the flavor, quality and consumer acceptance of button mushroom during postharvest storage.

Efficacy of Different Washing Treatments on Quality of Button Mushrooms (A.bisporus)

To enhance the quality and to obtain a better colour, fresh button mushrooms were given washing treatments with different chemical solutions of different concentration for 10 minutes and stored under refrigerated conditions to check their shelf life. The chemicals used were citric acid (0.5%, 1.5%, 2.5%), H2O2 (1.5%, 2.5%, 3.5%) and EDTA (2%, 4%, 6%). Of all the treatments used, 2.5% citric acid was found to be the most effective in controlling weight loss, maturity index and microbial growth for up to a period of 12 days and was found to be highly acceptable according to the scores after sensory evaluation. With the advancement in storage period, significant difference in the color values (L*, a* and b*) and browning index was observed and an increase in weight loss, maturity index and microbial growth of mushrooms was observed.

Effect of PLA/PCL/cinnamaldehyde antimicrobial packaging on physicochemical and microbial quality of button mushroom (Agaricus bisporus)

The effect of biobased poly(lactic acid) (PLA)/poly(ɛ-caprolactone) (PCL) blend films with different cinnamaldehyde contents (0, 3, and 9wt%) on the physicochemical and microbial quality of button mushrooms (Agaricus bisporus) stored at 4±1°C for 16 days was investigated. The low-density polyethylene (LDPE) film was used as the control. The microbial levels and physicochemical properties such as weight loss, firmness, total soluble solids, O2 and CO2 concentrations, microbiological quality, color, and sensory quality of mushrooms were measured. Although the highest weight loss (3.08%) was observed in the PLA/PCL/C9 treatment at the end of storage, it was still lower than 5%. Mushrooms packaged in the PLA/PCL/cinnamaldehyde blend films were significantly (p<0.05) firmer than those packaged in the control and PLA/PCL film. The CO2 level inside the PLA/PCL film with cinnamaldehyde was lower than those inside the control and PLA/PCL film, but the O2 level was similar in all packages. The PLA/PCL/C9 film was more effective in reducing microbial counts and preserving the color of mushrooms than the other three films. The overall acceptability of mushrooms packaged in the PLA/PCL/C9 film still remained good and within limit of marketability after 12d of storage. The results suggested that the PLA/PCL/C9 film with higher water vapor permeability could be used to maintain the quality of fresh button mushroom and extend its postharvest life.

Effect of exogenous glycine betaine on qualities of button mushrooms (Agaricus bisporus) during postharvest storage

In order to extend the storage life of button mushrooms (Agaricus bisporus), glycine betaine (GB) treatment was introduced and its effect on the quality and physiological characteristics of button mushrooms during storage was evaluated in the present work. Fresh button mushrooms were soaked with GB solutions of different concentrations and then stored at low temperature (2 °C) for 12 days. The variations of weight loss rate, percent open caps and color of mushrooms were investigated. Physiological characteristics were evaluated during storage, including respiration rate, polyphenol content, malondialdehyde accumulation as well as activities of polyphenol oxidase enzyme (PPO) and antioxidant enzymes. Membrane permeability and microstructure was also analyzed by electrical conductivity and scanning eletron microscope (SEM) measurement. The results showed that the button mushrooms treated with GB kept a lower level of weight loss and respiration rate, the cap opening and browning were also inhibited. Meanwhile, treated samples maintained high content of polyphenol and ascorbic acid and showed better integrity of cell membrane structure. In addition, GB inhibited PPO activity and improved activities of antioxidant enzymes such as SOD, POD and CAT during storage period. The results of treatment group with 2 mM GB were significantly better with other treatment groups (p < 0.05), which was determined to be the suitable treatment concentration of GB to extend the storage life of button mushrooms.

Enhancing stability of essential oils by microencapsulation for preservation of button mushroom during postharvest.

Fresh button mushrooms (Agaricus bisporus L.) are sensitive to browning, water loss, and microbial attack. The short shelf-life of mushrooms is an impediment to the distribution and marketing of the fresh product. Essential oils outstand as an alternative to chemical preservatives and their use in foods meets the demands of consumers for natural products. To resolve controlled release of oil and increase in antioxidant and antimicrobial activities, the oil was incorporated into microcapsules. Effects of microcapsulated thyme (Thymus vulgaris L.) and rosemary (Rosmarinus officinalis L.) on quality of fresh button mushroom were compared. Physicochemical qualities were evaluated during 15 days of storage at 4 ± 0.5°C. All treatments prevented product weight loss and decrease in polyphenoloxidase and peroxidase activities during storage. Color and firmness, microbiological analysis, and total phenolic content caused the least change. With use of microencapsulated oils, mushrooms were within acceptable limits during 10 days of storage. Microencapsulated rosemary oil produced the highest beneficial effects and has potential to improve quality of button mushrooms and extend shelf-life.

Enhancement of Antioxidant Properties and Increase of Content of Vitamin D2 and Non-volatile Components in Fresh Button Mushroom, Agaricus bisporus (Higher Basidiomycetes) by γ-irradiation

Agaricus bisporus is a popular culinary-medicinal mushroom in Taiwan, and γ-irradiation could extend its shelf life. Our objective was to study the content of vitamin D2 and the taste components and antioxidant properties of ethanolic extracts from A. bisporus with various doses of γ-irradiation. After irradiation, the vitamin D2 content of 5-10 kGy irradiated mushrooms was in the range of 5.22-7.90 µg/g, higher than that of the unirradiated control (2.24 µg/g). For all treatments, the total content of soluble sugars and polyols ranged from 113 to 142 mg/g, and the monosodium glutamate-like components ranged from 6.57 to 13.50 mg/g, among which the 2.5 kGy irradiated sample has the highest content of flavor 5'-nucleotide. About antioxidant properties, 10 kGy irradiated samples exhibited lower EC50 values than did other samples. EC50 values were less than 5 mg/mL for ethanolic extracts. Total phenols were the major antioxidant components and the total content was 13.24-22.78 mg gallic acid equivalents/g. Based on the results obtained, γ-irradiation could be used to improve the vitamin D2 content and intensity of umami taste in fresh mushrooms. In addition, γ-irradiation not only maintained the antioxidant properties of mushrooms but also enhanced the antioxidant properties to some extent.

Bioactive compounds from discarded mushroom beds

Discarded dried button, dried oyster, and fresh button mushroom beds were examined for their bioactive compounds and industrial enzymes. Levels of reducing sugars and total sugars were high in all mushroom beds. Carboxymethyl cellulase activity was higher (920 µg/mL) in the dried oyster mushroom bed extract. Schizophyllum commune, Fomitopsis feei, Trametes gibbosa, and Trametes elegans were grown on direct mushroom bed extract, 0.2% glucose-containing mushroom bed extract, and common production medium for determination of growth and lignolytic activities. Since lignolytic activities were high with the direct mushroom bed extract, this medium was further diluted to 1:1 and 1:2 ratios and again tested for growth and lignolytic activities with F. feei, T. gibbosa, and T. elegans. It was determined that the 1:1 ratio gave good results for all these organisms. The button mushroom bed extract was concentrated using a rotary evaporator and compared for growth and lignolytic enzymes with dried powder extract using F. feei, T. gibbosa, and T. elegans. Growth was high with these 3 organisms in the dried powder extract, but lignin peroxidase activity was the highest with the rotary evaporator extract using T. gibbosa. The results indicate that these waste mushroom bed extracts can be used as cost-effective media for the growth of microorganisms and for the production of bioactive compounds and industrial enzymes.

Effects of Postharvest Pulsed UV Light Treatment of White Button Mushrooms (Agaricus bisporus) on Vitamin D2 Content and Quality Attributes

Pulsed UV light (PUV) was investigated as a means to rapidly increase vitamin D(2) (D(2)) content in fresh button mushrooms (Agaricus bisporus). D(2) was found to increase to over 100% RDA/serving following 3 pulses (1 s). Following 12 pulses, D(2) began to approach a maximum concentration of 27 μg/g DW. The D(2) produced with 3 pulses decreased from 11.9 to 9.05 μg/g DW after 3 days of storage; however, D(2) levels remained nearly constant after this point throughout an 11-day shelf life study. PUV treated sliced mushrooms produced significantly more D(2) than whole mushrooms, and it was also observed that brown buttons generated significantly less D(2) than white buttons. Several quality attributes were assessed, and no significant differences between control and PUV treated mushrooms were observed. These findings suggest that PUV treatment is a viable method for rapidly increasing the D(2) content of fresh mushrooms without adversely affecting quality parameters.

Effects of UV-C treatment on inactivation of Escherichia coli O157:H7, microbial loads, and quality of button mushrooms

This study investigated the effects of ultraviolet-C (UV-C) light applied to both sides of mushrooms on microbial loads and product quality during storage for 21 d at 4 °C. Microflora populations, color, antioxidant activity, total phenolics, and ascorbic acid were measured at 1, 7, 14 and 21 d of storage. Additionally, the inactivation of Escherichia coli O157:H7 by UV-C was determined. Results showed that UV-C doses of 0.45–3.15 kJ m −2 resulted in 0.67–1.13 log CFU g −1 reduction of E. coli O157:H7 inoculated on mushroom cap surfaces. UV-C radiation also reduced total aerobic plate counts by 0.63–0.89 log CFU g −1 on the surface of mushrooms. Although mushrooms treated with UV-C had more severe browning with increasing dosage after initial treatment, the control mushrooms also browned as indicted by lower L* and higher a* values after 21 d of storage at 4 °C. In addition, the UV-C treatments apparently inhibited lesion development on the mushroom surface. During the first 7 d, irradiated mushrooms had lower antioxidant activity, total phenolics, and ascorbic acid content compared to non-radiated samples. However, irradiated mushrooms reached similar amounts of these nutrients as the control after 14 d of storage at 4 °C. In summary, UV-C radiation could potentially be used for sanitizing fresh button mushrooms and extending shelf-life.

Accumulation of Lignin and Malondialdehyde in Relation to Quality Changes of Button Mushrooms (Agaricus bisporus) Stored in Modified Atmosphere

Whole fresh button mushrooms (Agaricus bisporus) were stored in unsealed bags in two types of modified atmosphere packaging (MAP), namely, active and passive, at 4 °C. The packaging film was 0.04 mm low-density polyethylene and the gas composition of the active MAP was 12% O(2), 2.5% CO(2) and 85.5% N(2). Firmness of Mushroom showed a positive correlation with the accumulation of lignin in the tissue. On the other hand, changes of malondialdehyde content with storage time were proportional to the evolution of browning. The button mushrooms in control treatment developed severe browning at the end of the 15-day storage, while the mushrooms of both active and passive MAP treatments browned slightly. MAP treatments could not inhibit phenylalanine ammonia lyase activity; however, it can reduce the lignification process by the inhibition of peroxidase (POD) activity and the accumulation of lignin. Correlation between the cinnamyl alcohol dehydrogenase activity and lignin accumulation was not obvious. Our results suggested that an increase in the firmness of mushrooms during senescence may be a consequence of tissue lignification, a process associated with increase in POD activity. Both active and passive MAPs were useful for the conservation of tenderness and whiteness in button mushrooms.

Vitamin D2 Formation and Bioavailability from Agaricus bisporus Button Mushrooms Treated with Ultraviolet Irradiation

Agaricus bisporus mushrooms contain an abundance of ergosterol, which on exposure to UV irradiation is converted to vitamin D2. The present study evaluated the effects UV-C irradiation on vitamin D2 formation and its bioavailability in rats. Fresh button mushrooms were exposed to UV-C irradiation at mean intensities of 0.403, 0.316, and 0.256 mW/cm(2) from respective distances of 30, 40, and 50 cm for periods ranging from 2.5 to 60 min. Vitamin D2 and ergosterol were measured by HPLC-MS/MS. The stability and retention of vitamin D2 were assessed including the extent of discoloration during storage at 4 degrees C or at room temperature. Exposure to UV-C irradiation at 0.403 mW/cm(2) intensity from 30 cm distance resulted in a time-dependent increase in vitamin D2 concentrations that was significantly higher than those produced at intensities of 0.316 and 0.256 mW/cm(2) from distances of 40 and 50 cm, respectively. Furthermore, the concentrations of vitamin D2 produced after exposure to UV-C irradiation doses of 0.125 and 0.25 J/cm(2) for, 2.5, 5, and 10 min were 6.6, 15.6, and 23.1 microg/g solids, equivalent to 40.6, 95.4, and 141 microg/serving, respectively. The data showed a high rate of conversion from ergosterol to vitamin D2 at short treatment time, which is required by the mushroom industry. The stability of vitamin D2 remained unchanged during storage at 4 degrees C and at room temperature over 8 days (P = 0.36), indicating no degradation of vitamin D2. By visual assessment or using a chromometer, no significant discoloration of irradiated mushrooms, as measured by the degree of "whiteness", was observed when stored at 4 degrees C compared to that observed with mushrooms stored at room temperature over an 8 day period (P < 0.007). Vitamin D2 was well absorbed and metabolized as evidenced by the serum response of 25-hydroxyvitamin D in rats fed the irradiated mushrooms. Taken together, the data suggest that commercial production of button mushrooms enriched with vitamin D2 for improving consumer health may be practical.