Application of modified atmosphere packaging (gas flushing and active packaging) for extending the shelf life of Beauveria bassiana conidia at high temperatures

Shelf life determinations under non-refrigerated conditions, especially high temperature regimes characteristic of tropical/subtropical regions, deserve more attention. In this study, we investigated effects of modified atmosphere packaging (MAP) on longevity of conidia of Beauveria bassiana (Bb) strain GHA. Similar rates of conidial survival were observed after storage for 60 days at 50 °C in atmospheres of pure CO2, N2, H2, or He (49–51% viability), but few conidia (⩽2%) survived storage in O2-rich atmospheres. Viability of conidia stored in an atmosphere of 20% CO2/80% N2 decreased to <80% within 180 days at 40 °C and within 30 days at 50 °C but remained high (87%) after a 16-month storage period at 25 °C. O2 concentrations in the storage containers ranged from 0.3% at the start to as high as 12.4% at the end of experiments (due to container leakage). When active packaging (hermetically sealed packages with O2/moisture scavengers) was employed, shelf lives were substantially improved. Viabilities ⩾80% were consistently recorded after 6 months at 40 °C or 2 months at 50 °C when a dual O2/moisture absorber or a combination of sachets (dual O2 absorber/CO2 generator + desiccant) were used. Water activities (aw) supporting greatest survival were ⩽0.030, suggesting that optimal aw for long-term storage under anaerobic conditions is lower than determined in previous studies of storage in the presence of O2. Additionally, we have shown that actively packaged conidia with higher than desirable initial aw should be allowed an equilibration period at a moderate temperature before exposure to high storage temperatures. Active packaging of dried conidia (aw ⩽ 0.032) preserved 71% viability for 16 months at 40 °C and 63–65% for 3 months at 50 °C. To our knowledge, these are the longest survival times yet reported for Bb conidia under high-temperature conditions.