Aflatoxigenic Aspergillus Section Flavi Strains and Diverse Molds Isolated from California Almonds

Almonds are an essential crop for the economy of California. However, mold and mycotoxin contamination of this commodity has a serious impact on food safety and international trade. The contamination levels of molds and the aflatoxigenic potential of <i>Aspergillus</i> section <i>Flavi</i> isolates were studied on almonds collected at a processing plant in California. The mean total fungal count for 80 samples was 1.0 × 10⁴ CFU/g, while 62 samples (77.5%) had a total mold count less than 1.0 × 10⁴ CFU/g. The most common fungal contaminants were <i>Aspergillus</i> section <i>Nigri</i> (100% of samples), followed by <i>Penicillium</i> (57.5%) and <i>Cladosporium</i> (52.5%) species. <i>Rhizopus</i>, <i>Fusarium</i> and <i>Alternaria</i> spp. were less frequent. A total of 26 <i>A</i>. section <i>Flavi</i> strains were identified, with most strains (23) belonging to the L morphotype of <i>A. flavus</i>. In addition, two S morphotypes of <i>A. flavus</i>, and one <i>A. tamarii</i> strain were observed. Other <i>Aspergillus</i> species, including <i>A. terreus</i> and <i>A. ochraceus</i> were rare. High Performance Liquid Chromatography (HPLC) analysis revealed that 9 out of 13 isolated <i>A. flavus</i> strains produced aflatoxin B₁ (AFB₁) on yeast extract sucrose media. The highest levels of AFB₁ were produced by two <i>A. flavus</i> isolates belonging to the S morphotype (78 and 260 µg/kg). Increasing temperatures and drought conditions may change the population dynamics of toxigenic mold strains on almonds, emphasizing the need to continue monitoring these fungal populations.