TRANSFER OF NATURAL MICROORGANISMS FROM ORANGE FRUIT TO FRESH JUICE DURING EXTRACTION. EVOLUTION OF LACTIC ACID BACTERIA IN THE NATURAL MEDIUM

PEREZ MB, SAGUIR FM

Córdoba

Congreso; VI Congreso Argentino de Microbiología General.; 2009

In a previous work we compared the indigenous microflora on oranges peel purchased from local packinghouse and market. The microbial load on orange surfaces differed significantly, detecting the presence of lactic acid bacteria (LAB) only on the market fruits. In this work we investigated the capacity of transference of indigenous microflora from orange peel to fresh juice during extraction and the lactic acid microflora evolution in fresh juice during storage at 30°C under microaerophilic conditions. Oranges without any washing procedure were squeezed to obtain the juice under sterile conditions. Microbial flora transferred and the LAB evolution was analyzed by plating aliquots (diluted if necessary) on PCA, and MRS-agar pH 5 and added with 10 &mu;g/ml of pimaricin to inhibit yeasts growth (MRS-P) at different times during storage. MRS-P and PCA plates were incubated anaerobically and aerobically at 30 °C for 7 days before enumeration, respectively. LAB colonies by random selection were picked up from PCA and MRS-P plates and further characterized by phenotypic and genotypic methods.The microbial load on orange surfaces determined on PCA and MRS-P plates was 5.2 and 3.0 log cfu/ml, respectively. Majority of colonies on the PCA plates were small, corresponding to microorganism catalase positive as well as colonies belonging to Enterobacteriaceae and yeasts. On MRS-P, the colonies were mainly gram positive and catalase negative cells presumably identified as LAB. After extraction, the initial microbial counts in the fresh juice obtained in PCA and MRS-P media corresponded to 4,07 and 2,99 Log ufc/ml, respectively. At this time although LAB showed the highest transfer capacity, gram and catalase positive bacteria and yeasts were predominant in similar way as on fruit surface. At 72 h of fresh juice storage the counts became maximum increasing by about 4 log cycles, LAB mainly being isolated. From 191 colonies random selected LAB were identified accounting for 65% on the basis that they were Gram positive, catalase negative, non-spore forming, non-motile cells and exhibited a fermentative catabolism from glucose. The majority of them (64%) were homofermentative while only a few isolates were heterofermentative. Among homofermentative LAB isolates that did not produce ammonia from arginine the <i>Lactobacillus plantarum</i> species was mainly identified by specific PCR of specie. The results demonstrate the high capacity of transference of natural microflora of orange surfaces to fresh juice, especially of bacteria presumably identified as LAB. LAB became predominant microflora during fresh juice storage at abusive temperature under microaerophilic conditions. This fact, might be related with a better adaptation to natural juice and storage conditions and be able to initiate growth more rapidly than the predominant non-LAB  microflora from oranges peel.