During the past two decades several novel spoilage micro-organisms have emerged. Raw materials and products have been contaminated in increasing numbers of spoilage incidents causing widespread problems within the juice and beverage industry. This study investigates two such spoilage micro-organisms, A licyclobacillus acidoterrestris and Propionibacterium cyclohexanicum, both isolated from pasteurised contaminated fruit juice.
A variety of media were tested to determine which supported optimal growth of A. acidoterrestris with Orange Serum Agar providing consistently high plate counts. The presence of A. acidoterrestris in raw materials and shelf stable products was monitored and the effects on its growth and survival of temperature, headspace and movement of containers during storage were investigated. The survival of P. cyclohexanicum after pasteurisation was assessed and growth determined at a variety of temperatures. The survival of each bacterium was investigated in different fruit juices, when challenged by the preservatives sodium benzoate and potassium sorbate and the bacteriocin nisin and when grown in the same juice container and co-cultured on the same solid medium.
17% of samples tested were contaminated by A. acidoterrestris; however P. cyclohexanicum was not isolated from any sample. P. cyclohexanicum survived 10 minutes at temperatures of 4°C to 95°C and grew in orange, tomato and pineapple juice while A. acidoterrestris grew in all juices tested. A. acidoterrestris was inhibited by sodium benzoate (500ppm), potassium sorbate (500ppm) and nisin (51U/ml). P. cyclohexanicum, although not inhibited by nisin (1000IU/ml), was susceptible to sodium benzoate (500ppm) and potassium sorbate (l000ppm). I-Ieadspace, movement of containers and storage temperatures affected detection rates of A. acjdoterrestrjs. Co-cultures demonstrated that if found within the same enviromnent, both bacilli can survive and cause spoilage.
A. acidoterrestris is a world wide contaminant within the soft drinks industry and, considering the results of these studies P. cyclohexanicum with its heat resistance and tolerance to nisin may also emerge as a major spoilage microorganism