Production of Ergocalciferol (vitamin D2) and Related Sterols in Mushrooms with Exposure to Pulsed Ultraviolet Light
Open Access
- Author:
- Kalaras, Michael David
- Graduate Program:
- Food Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- January 04, 2012
- Committee Members:
- Ryan John Elias, Dissertation Advisor/Co-Advisor
Joshua D Lambert, Committee Member
Robert Bruce Beelman, Committee Member
Ali Demirci, Committee Member - Keywords:
- vitamin D
mushrooms
pulsed ultraviolet light - Abstract:
- Vitamin D status in humans worldwide presents itself as one the most important factors in human health. The classic bone diseases associated with vitamin D deficiency, rickets and osteomalacia, are still prevalent among certain subpopulations. In addition, modern research has found a putative link between vitamin D status and the risk of a host of diseases including various cancers, heart disease, stroke, diabetes, multiple sclerosis and rheumatoid arthritis, among others. Compounding the issue is the fact that in modern society, individuals spend less time exposed to sunlight due to various factors. Sunlight exposure is the main source of vitamin D, which is produced from the conversion of 7-dehydrocholesterol in the epidermis through UV irradiation. As such, the use of vitamin supplements and foods containing vitamin D are an important source. However, the number of foods that are sources of vitamin D is limited and more sources are needed. Mushrooms are an abundant source of ergosterol, which is the precursor to vitamin D2. Mushrooms have been shown to contain small amounts of vitamin D2 when grown in the wild. Furthermore, the vitamin D2 content of cultivated mushrooms has been shown to increase with exposure to artificial UV light. The use of conventional continuous UV systems has been shown to take on the order of minutes to hours of exposure to increase the vitamin D2 levels to a significant level. The main objective of this study was to investigate the use of pulsed UV (PUV) light as a rapid and predictable method for increasing the vitamin D2 content of mushrooms and mushroom products. A study was conducted to assess the effectiveness of a PUV system to increase the vitamin D2 content of a variety of mushrooms species (Agaricus bisporus, white and brown button mushrooms; Pleurotus ostreatus, oyster, and Lentinula edodes, shiitake) as well as several mushroom powders (Pleurotus eryngii, king oyster and Agaricus bisporus) and spent growing substrates containing mycelial biomass. Sliced white button mushrooms showed an increase from an initial level of 0 μg/g dw to 5.11 μg/g dw (325% DV/84g serving) after just one pulse. The PUV system generated 3 pulses per second, achieving an exposure time of less than one second with one pulse. Similar results were observed with brown button mushrooms, wherein vitamin D2 levels increased to 4.43 μg/g dw (362% DV/serving) with one pulse. Oyster mushrooms and shiitake contained higher initial levels of vitamin D2, 0.16 μg/g dw and 0.037 μg/g dw respectively, and the vitamin D2 content increased to 7.95 μg/g dw and 5.71 μg/g dw respectively after one pulse. All mushrooms tested had increasing levels of vitamin D2 with each additional pulse. The study also found that PUV was effective in increasing the vitamin D2 content of dried mushroom powders. With 4 pulses the vitamin D2 content of white button mushroom powder increased from near 0 to ca. 12 μg/g dw and increased with additional exposure of 16 total pulses to ca. 26 μg/g dw. Similar results were seen in king oyster mushroom powder with 10.4 μg/g dw and 23.0 μg/g dw vitamin D2 with 4 and 16 pulses, respectively. Spent mushroom substrate containing mycelial biomass contained lower levels of vitamin D2 (under 2 μg/g dw, with a maximum 16 pulses) when exposed to PUV. This study suggests that PUV is an effective and rapid means of increasing the vitamin D2 content of mushrooms and mushroom products with exposure times on the order of seconds. A dose-response study of the effect of PUV treatment on vitamin D2 content of Agaricus bisporus was conducted. In addition, factors influencing the conversion of ergosterol to vitamin D2 and effects of PUV on shelf life were also investigated. Fresh white button mushrooms were treated with PUV wherein vitamin D2 was found to rapidly increase to over 100% of the recommended dietary allowance (RDA) per serving following 3 pulses. Following 12 pulses, vitamin D2 levels began to approach a maximum concentration of 27 μg/g dw. A shelf life study of PUV-treated mushrooms was carried out, where it was observed that the vitamin D2 produced with 3 pulses dropped from 11.9 μg/g dw to 9.05 μg/g dw after 3 days of storage; however, vitamin D2 levels remained nearly constant after this point throughout the 11-day study. The effect of PUV treatment on sliced and whole mushrooms was also evaluated. Significantly more vitamin D2 was produced in sliced mushrooms than in whole mushrooms: 113% and 81% less for brown and white button mushrooms, respectively. Vitamin D2 production in brown compared to white button mushrooms were also examined, and it was observed that whole and sliced brown mushrooms exposed to PUV generated significantly less vitamin D2 than their white counterparts (33% and 21% less for whole and sliced, respectively). Finally, several quality attributes were assessed in PUV-treated mushrooms. No significant differences between control and PUV treated mushrooms were observed. These findings suggest that PUV treatment is a viable method for increasing the vitamin D2 content of fresh mushrooms without adversely affecting quality. The effect of PUV treatment of mushrooms on the production of photoproducts of ergosterol was investigated. In addition to vitamin D2, it is known that with UV exposure of ergosterol other products including previtamin D2, tachysterol2 and lumisterol2 are produced. White button mushrooms were sliced and treated in a single layer system with PUV irradiation increments from 0 to 60 pulses to determine the dose-response relationship between irradiation and photoproduct content. All photoproducts increased in a non-linear but dose-dependent manner as a function of increasing PUV irradiation. Vitamin D2 content approached a maximum value of ca. 124 μg/g dw with 60 pulses, and was observed to be the most abundant photoproduct with respect to yield. With 60 pulses, previtamin D2 content approached a maximum value of 44.6 μg/g dw, while lumisterol2 and tachysterol2 reached maximum levels of 30.5 μg/g dw and 24.7 μg/g dw, respectively. PUV has been shown to be an effective and rapid means of increasing the vitamin D2 content of mushrooms. Exposure times of approximately one second are more than sufficient to increase vitamin D2 to levels that are biologically significant. The shortest exposure time of any previous study using continuous UV regimes to achieve a level equivalent to 100% DV/serving was ca. 8 minutes. PUV treatment of mushrooms was also shown to have little to no effect on quality parameters as they relate to appearance and product quality. The presence of additional photoproducts of ergosterol in mushrooms was also demonstrated for the first time. These products may have some biological significance, which should be investigated in future studies. With the use of PUV, mushrooms can be a viable source of vitamin D2, which can aid in alleviating the persistent problem of vitamin D deficiency in humans.