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The application of high hydrostatic pressure (HHP, 600 MPa, 8 min) on brined green asparagus and the changes in bacterial diversity after treatments and during storage at 4 °C (30 days) or 22 °C (10 days) were studied. HHP treatments reduced viable cell counts by 3.6 log cycles. The residual surviving population did not increase during storage at 4 °C. However, bacterial counts significantly increased at 22 °C by day 3, leading to rapid spoilage. The microbiota of green asparagus was composed mainly by Proteobacteria (mainly Pantoea and Pseudomonas), followed by Firmicutes (mainly Lactococcus and Enterococcus) and to a less extent Bacteroidetes and Actinobacteria. During chill storage of untreated asparagus, the relative abundance of Proteobacteria as well as Enterococcus and Lactococcus decreased while Lactobacillus increased. During storage of untreated asparagus at 22 °C, the abundance of Bacteroidetes decreased while Proteobacteria increased during late storage. The HHP treatment determined a reduction of the Proteobacteria both early after treatment and during chill storage. In the HHP treated samples stored at 22 °C, the relative abundance of Pseudomonas rapidly decreased at day 1, with an increase of Bacteroidetes. This was followed by a marked increase in Enterobacteriaceae (Escherichia) simultaneously with increase in viable counts and spoilage. Results from the study indicate that the effect of HHP treatments on the viability of microbial populations in foods also has an impact on the dynamics of microbial populations during the storage of the treated foods.

Food Research International Volume 89, 1 November 2016, Pages 790-796 Microbial diversity in pitted sweet cherries (Prunus avium L.) as affected by High-Hydrostatic Pressure treatment (Article) Toledo del Árbol, J.ab, Pérez Pulido, R.a, La Storia, A.b, Grande Burgos, M.J.a, Lucas, R.a, Ercolini, D.b, Gálvez, A.a a Área de Microbiología, Departamento de Ciencias de la Salud, Facultad de Ciencias Experimentales, Universidad de Jaén, Jaén, Spain b Department of Agricultural Sciences, Division of Microbiology, University of Naples Federico II, Via Università 100, Portici, Italy View references (42) Abstract Sweet cherries are a highly appreciated seasonal fruit rich in anthocyanins. The purpose of the present study was to determine the effect of High-Hydrostatic Pressure (HHP) processing on the microbiological quality and bacterial biodiversity of sweet cherries. Pitted cherries inoculated with their own epiphyte microbiota to simulate a worst-case scenario of contamination during preparation and processing were treated or not by HHP (600 MPa, 8 min) and stored at 4 °C for 60 days. HHP treatment reduced total viable counts by 4.65 log cycles. The surviving bacterial fraction did not increase significantly (p < 0.05) for the first 15 days of storage. Concentrations of yeasts and molds were reduced below detectable levels. Upon prolonged storage (60 days), microbial growth was observed. Bacterial biodiversity studied by high-throughput sequencing of the 16S rRNA gene revealed that Proteobacteria had highest relative abundance (88.70%) in the spiked cherries followed by Firmicutes (11.04%). Gluconobacter and Enterobacteriaceae together with Leuconostoc were the most abundant Operational Taxonomic Units (OTUs). Upon application of HHP treatment, 97.62% of OTUs from the surviving fraction belonged to Proteobacteria. The relative abundance of Enterobacteriaceae also decreased markedly while Acetobacteraceae (represented mainly by Gluconobacter) increased to 89.18%. Gluconobacter dominated during storage. Results from the present study provide insights on the microbiota of sweet cherries and the dynamics of the bacterial populations surviving HHP treatments that may be useful to improve the non-thermal preservation of cherries.

A cocktail of Leuconostoc mesenteroides, Leuconostoc gasicomitatum and Leuconostoc gelidum inoculated on autoclaved cherimoya pulp were treated by high hydrostatic pressure (HHP; 400, 500 or 600 MPa for 8 min) and with enterocin AS-48 (35 μg/g), singly or in combination. After treatments, samples were stored at 4 °C for 30 days or at 22 °C for 10 days. HHP treatments at 400 or 500 MPa reduced viable cell concentrations by 4.3 and 4.9 log cycles, respectively. No survivors were detected at 600 MPa. Bacteriocin addition in combination with HHP achieved an additional reduction of 0.6–0.9 log cycles after treatments at 400 or 500 MPa, and also reduced viable counts for most treatments during storage. In samples treated by HHP, regrowth of leuconostocs was delayed to days 15 (400 or 500 MPa) or 30 (600 MPa) of refrigeration storage, or day 3 at 22 °C (all treatments). Results from the study suggest that treatments at 600 MPa (8 min) can be useful to inactivate leuconostocs in cherimoya pulp.

Fermentation of caper berries is a traditional process relying on the indigenous microbiota. In this study, the application of Lactobacillus plantarum Lb9 isolated from spontaneous caper berry fermentation as starter culture was evaluated by means of culture-dependent and independent methods. The results obtained here indicated that L. plantarum Lb9 was able to carry on an accelerated lactic acid fermentation of caper berries, dominating the background microbiota present in the raw material until the end of fermentation even when fermentation broth was added with high salt concentration. Persistence of L. plantarum Lb9 in the starter-added fermentation was confirmed by RAPD-PCR of isolates from viable cell counting during the fermentation. TTGE analysis of the microbial community throughout fermentation process also indicated that lactobacilli were the predominant microbiota, and thus the microbial composition during the controlled fermentation was more homogeneous compared with spontaneous fermentations. Furthermore, the sensorial quality of the starter-added fermented capers was similar to the spontaneous fermented products. In conclusion, L. plantarum Lb9 was an adequate starter culture strain for caper berry fermentation prevailing over other bacteria present in the raw material. This fermentation ensured both the quality and safety of the end product.

Inactivation of Staphylococcus aureus strains by high hydrostatic pressure (HHP) treatments applied singly or in combination with natural antimicrobials (nisin, enterocin AS-48, cinnamon oil and clove oil) was investigated in rice pudding. Treatments at 600 MPa for 10 min reduced initial populations of staphylococci (7.9 log CFU/g) below detectable levels of 1 log CFU/g in the puddings. Treatments at 500 MPa for 5 min (achieving a 2.9-log reduction of viable counts) were investigated singly or in combination with nisin (200 and 500 IU/g), enterocin AS-48 (25 and 50 μg/g), cinnamon oil (0.2%, vol/wt) or clove oil (0.25% vol/wt). The combined treatment of enterocin AS-48 (50 μg/g) and HHP caused a non-significant reduction of 0.4–0.6 log cycles compared to HHP alone. Additional reductions of 0.87, 1.3 and 1.8 log cycles were recorded for the combined HHP treatments with nisin (500 IU/g), cinnamon oil (0.2%) and clove oil (0.25%), respectively. During refrigeration storage for one week, viable counts in puddings from combined treatments were significantly lower compared to the single HHP treatments, e.g. 1.5–2.7 log cycles for HHP-nisin (500 IU/g), 1.1–1.3 log cycles for HHP-AS-48 (50 μg/g) or approx. 1.5 log cycles for HHP-cinnamon oil (0.2%). These results suggest that the time and intensity of HHP treatments required for inactivation of S. aureus in puddings can be reduced when HHP is applied in combination with selected natural antimicrobials.