Fungistatic effect of guayule resin against dairy product fungi

Defects caused by undesirable molds may appear during the cheese-making process. To avoid this, the cheese industry currently uses authorized synthetic compounds to control them, but consumers are increasingly inclined towards foods made up of more natural ingredients and are rejecting those that contain chemical compounds in their formulation. In this work, different guayule (Parthenium argentatum) resin fractions were assayed against two molds, Penicillium verrucosum and Aspergillus flavus, that cause alterations in the dairy industry which entail serious economic losses and could produce mycotoxins. Reverse phase-flash chromatography technique (Biotage Sfär C18D-Duo 100A- 30 µm cartridge, flow 50 ml/min, 60:40 acetonitrile:water to 100% acetonitrile in 25 min) was used to fractionate the guayule resin in three different fractions. The most polar one (F1_gCD) was mainly composed of polar guayulins C and D, fraction F2_aA by argentatin A and, finally, fraction F3_gAB by apolar guayulins A and B. PDA plates containing the different fractions at 5 and 10 mg/ml concentration, previously diluted with acetone, were produced. The two molds (10 µl of a suspension between 1 to 5?105 conidia/mL) were inoculated in a 1 cm diameter disk filter previously placed in the center of the fortified plates. Plates of PDA medium with acetone and plates with the inoculum alone were used as controls. After an incubation period of 9 days (25 ºC), the results of each plate were analyzed with the Countermat flash equipment (IUL S.A., Barcelona, Spain) to obtain a precise image of each one. The diameter of the growth zones was determined using ImageJ v1.52a software. Contrary to what was expected, guayulins C and D showed fungistatic activity, an activity that was not shown by guayulins A and B, nor by argentatin A. After 9 days of incubation, fraction F1_gCD had reduced between 40-50% the molds growth in comparison with the controls. Less resistance to guayulins effect was observed in the genus Penicillium than in the genus Aspergillus. Results were more visible at concentrations of 10 mg/mL. Tests should be carried out with the isolated pure compounds to determine their potential industrial application since the activity shown as an enriched fraction was moderate