White rot, a disease caused by the soil-borne fungus <i>Sclerotia cepivorum,</i> is a severe enemy of garlic and onion production in California, Oregon, and Washington<i>. </i>It is desirable to use sulfur-containing organic compounds to trigger sclerotia germination in the absence of a host to control the sclerotia. Previous research has shown that diallyl disulfide (DADS) can reduce fungus soil levels by 90 to 98 % in field trials.  However, soil incubation studies found that volatile organic sulfur compounds have strong interaction with the soil.  Depending on the types of soils, organic matter, and soil microorganisms, the sulfur compounds can bind to soil particles or be metabolized by microorganisms.  In either case, it reduces the efficiency of volatile sulfur compounds. This study was conducted to encapsulate commercial DADS and garlic oil with β-cyclodextrin (β-CD) to protect sulfur volatiles from reacting with soil and against oxidation, heat, light-induced degradation, and evaporation.  Also, volatile sulfur compounds' encapsulation may allow for slower release and increase their efficacy for sclerotia germination.  Inclusion complexes of DADS and garlic oil with β-cyclodextrin were prepared by the co-precipitation method with the DADA/garlic oil ratio β-cyclodextrin of 15:85 (w/w), which achieved the maximum inclusion efficiency of β-cyclodextrin. Oil analysis showed that the garlic oil was successfully encapsulated with greater than 90% powder recovery.  Encapsulated oil analysis also showed that the micro-encapsulation process did not change the chemical compounds, but their proportions were altered. Microencapsulated commercial DADS oil contained 63% diallyl disulfide, whereas the encapsulated garlic oil had 75% diallyl disulfide. Further research will study the release of volatile sulfur compounds from the encapsulation complex in different soils and its effects on sclerotia germination.

Encapsulation of garlic oil and diallyl disulfide with β-cyclodextrin for garlic white rot control

ACS Spring Meeting 2021

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