Microbiological stabilization of Aloe vera (Aloe barbadensis Miller) gel by high hydrostatic pressure treatment.

The effect of high hydrostatic pressure (HHP) treatment (300, 400 and 500 MPa for 1 and 3 min at 20 °C) on the microbiological shelf-life and microbiota composition of Aloe vera gel during 90 days of storage at 4 °C was investigated. Aerobic mesophilic and psychrotrophic bacteria, as well as moulds and yeasts, were enumerated after HHP treatment and through cold storage. Randomly selected isolates from the count plates were identified by standard methods and the API identification system. Results showed that HHP treatment at or over 400 MPa for 3 min were effective to keep the microbial counts to undetectable levels during the whole storage period, and consequently the microbiological shelf-life of A. vera gel was extended for more than 90 days at 4 °C. The microbiota in the untreated A. vera gel was dominated by Gram-negative bacteria (mostly Rahnella aquatilis) and yeasts (mostly Rhodotorula mucilaginosa). In contrast, Gram-positive bacteria tentatively identified as Arthrobacter spp. and Micrococcus/Kocuria spp. were the predominant microorganisms in samples pressurized at 300 MPa for 1 and 3 min, while Bacillus megaterium predominating in samples treated at 400 MPa for 1 min. At 400 MPa for 3 min and above, the microbial growth was completely suppressed during at least 90 days; however, viable spore-formers were detected by enrichment.