Abstract
There is very little up to date information regarding apple microflora so in the current study we decided to address that issue and assess whether dominant fungi which reside in fruit might spoil apple juice. Microorganisms were isolated from apples of Koksa Górska harvested in the middle of October in 2016 and 2017. Identification of isolates was based on the sequencing of ribosomal DNA. Some isolates were characteristic for a particular year but in both years apple microflora was dominated by Aureobasidium pullulans. Based on phylogenetic analysis it was stated that only one isolate (LW81) was closely related to strains which are already described in available databases. All other isolates collected in the current study differed significantly from sequences stored in databases, tending to form a common cluster. It was possible to predict secondary structure of ITS2 region only for the isolate LW81, while we managed to establish the length and location of 5.8S gene in Rfam database for all sequences. A. pullulans is known exopolysaccharide producer so obtained microorganisms were tested for their ability to synthesise those substances on Czapek-Dox agar. The strain which proved to be the most significant exopolysaccharide producer (isolate LW14) was inoculated in the sterilised apple juice at three different initial cell number (100, 1000 and 10,000 cfu/ml) and subjected to pasteurisation. In all cases pasteurisation eliminated fungal growth effectively, therefore A. pullulans strains should not pose any risk to the quality of pasteurised apple juices.
Highlights
Knowledge about microbial species residing in raw materials, e.g. fruits or vegetables, is essential for predicting issues related to post-harvest losses or spoilage of fruit products, i.e. juices, jam, marmalades etc
We demonstrated that apple microflora is dominated by Aureobasidium pullulans strains
Our study was the first to demonstrate that C. railenensis might be present in apples—it was previously found on the fruit of an English oak (Isaeva et al 2009) or on the decayed wood in the evergreen forest (Ramírez and González 1984)
Summary
Knowledge about microbial species residing in raw materials, e.g. fruits or vegetables, is essential for predicting issues related to post-harvest losses or spoilage of fruit products, i.e. juices, jam, marmalades etc. When food manufacturers are aware of microorganisms which might deteriorate the quality of finished goods, they are able to select adequate food processing methods to provide the highest quality of their products, e.g. by adjusting parameters of thermal processing, introducing certain chemicals for washing and disinfection which are effective against fungi etc. Since apple is one of the most popular fruit in Poland, we decided to address identification of fungi residing in apple which might deteriorate the quality of apple-based products. Majority of the research was carried out before molecular methods became commonly available (Williams 1955; Pennycook and Newhook 1981; Bernier et al 1996). Most studies focused on changes of apple microflora during cold storage of harvested fruits
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