Alicyclobacillus acidoterrestris: an increasing threat to the fruit juice industry?

Computational analysis of carboxylesterase genes and proteins in non-pathogenic food bacterium Alicyclobacillus acidocaldarius: insights from proteogenomics

Over recent years, Alicyclobacillus acidocaldarius, a Gram-positive nonpathogenic rod-shaped thermo-acid-tolerant bacterium, has posed numerous challenges for the fruit juice industry. However, the bacterium's unique characteristics, particularly its nonpathogenic and thermophilic capabilities, offer significant opportunities for genetic exploration by biotechnologists. This study presents the computational proteogenomics report on the carboxylesterase (CE) enzyme in A. acidocaldarius, shedding light on structural and evolutional of CEs from this bacterium. Our analysis revealed that the average molecular weight of CEs in A. acidocaldarius was 41 kDa, with an isoelectric point around 5. The amino acid composition favored negative amino acids over positive ones. The aliphatic index and hydropathicity were approximately 88 and - 0.15, respectively. While the protein sequence showed no disulfide bonds in the CEs' structure, the presence of Cys amino acids was observed in the structure of CEs. Phylogenetic analysis presented more than 99% similarity between CEs, indicating their close evolutionary relationship. By applying homology modeling, the 3-dimensional structural models of the carboxylesterase were constructed, which with the help of structural conservation and solvent accessibility analysis highlighted key residues and regions responsible for enzyme stability and conformation. The specific patterns presented the total solvent accessibility of less than 25 (Å2) was in considerable position as well as Gly residues were noticeably have high accessibility to solvent in all structures. Ala was the more frequent amino acids in the conserved-SASA of carboxylesterases. Furthermore, unsupervised agglomerative hierarchical clustering based on solvent accessibility feature successfully clustered and even distinguished this enzyme from proteases from the same genome. These findings contribute to a deeper understanding of the nonpathogenic A. acidocaldarius carboxylesterase and its potential applications in biotechnology. Additionally, structural analysis of CEs would help to address potential solutions in fruit juice industry with utilization of computational structural biology.

Application and potential of multifrequency ultrasound in juice industry: Comprehensive analysis of inactivation and germination of Alicyclobacillus acidoterrestris spores

The majority of acidic fruits are perishable owing to their high-water activity, which promotes microbial activity, thus exhibiting metabolic functions that cause spoilage. Along with sanitary practices, several treatments are used during processing and/or storage to inhibit the development of undesirable bacteria. To overcome the challenges caused by mild heat treatment, juice manufacturers have recently increased their involvement in developing novel non-thermal processing procedures. Ultrasonication alone or in combination with other hurdle technologies may be used to pasteurize processed fruit juices. Multifrequency ultrasound has gained popularity due to the fact that mono-frequency ultrasound has less impact on bacterial inactivation and bioactive compound enhancement of fruit juice. Here, we present and discuss the fundamental information and technological knowledge of how spoilage bacteria, specifically Alicyclobacillus acidoterrestris, assemble resistant spores and inactivate and germinate dormant spores in response to nutrient germinants and physical treatments such as heat and ultrasound. To the authors' knowledge, no prior review of ultrasonic inactivation and germination of A. acidoterrestris in fruit juice exists. Therefore, this article aims to provide a review of previously published research on the inactivation and germination of A. acidoterrestris in fruit juice by ultrasound and heat.

Fruit Juice Spoilage by Alicyclobacillus: Detection and Control Methods—A Comprehensive Review

Fruit juices have an important place in humans’ healthy diet. They are considered to be shelf stable products due to their low pH that prevents the growth of most bacteria. However thermo-acidophilic endospore forming bacteria of the genus Alicyclobacillus have the potential to cause spoilage of commercially pasteurized fruit juices. The flat sour type spoilage, with absence of gas production but presence of chemical spoilage compounds (mostly guaiacol) and the ability of Alicyclobacillus spores to survive after pasteurization and germinate under favorable conditions make them a major concern for the fruit juice industry worldwide. Their special characteristics and presence in the fruit juice industry has resulted in the development of many isolation and identification methods based on cell detection (plating methods, ELISA, flow cytometry), nucleic acid analysis (PCR, RAPD-PCR, ERIC-PCR, DGGE-PCR, RT-PCR, RFLP-PCR, IMS-PCR, qPCR, and 16S rRNA sequencing) and measurement of their metabolites (HPLC, GC, GC-MS, GC-O, GC-SPME, Electronic nose, and FTIR). Early detection is a big challenge that can reduce economic loss in the industry while the development of control methods targeting the inactivation of Alicyclobacillus is of paramount importance as well. This review includes a discussion of the various chemical (oxidants, natural compounds of microbial, animal and plant origin), physical (thermal pasteurization), and non-thermal (High Hydrostatic Pressure, High Pressure Homogenization, ultrasound, microwaves, UV-C light, irradiation, ohmic heating and Pulse Electric Field) treatments to control Alicyclobacillus growth in order to ensure the quality and the extended shelf life of fruit juices.

Purification and Characterization of Plantaricin YKX and Assessment of Its Inhibitory Activity Against Alicyclobacillus spp

Consumers prefer natural over synthetic chemical preservatives on a food label. Therefore, it is crucial to ensure the safety and efficacy of such natural preservatives. The emergence of heat-resistant spore-forming Alicyclobacillus spp. has been associated with spoilage problems in the fruit juice industry. Herein, a bacteriocin-producing stain YKX was isolated from the traditional pickles in Hanzhong City, China, and it was identified as Lactobacillus plantarum by morphological, biochemical, physiological, and genotypic features. A stable bacteriocin, plantaricin YKX, was isolated, purified, and tested for its efficacy against Alicyclobacillus acidoterrestris. Plantaricin YKX is a 14-amino acid peptide (Lys-Tyr-Gly-Asn-Gly-Leu-Ser-Arg-Ile-Phe-Ser-Ala-Leu-Lys). Its minimal inhibitory concentrations (MICs) against the tested bacterial and fungal strains were ranged from 16 to 64 μg/mL. It is thermostable and active at pH 3-8. The flow cytometry data and microscopic observations suggested that plantaricin YKX can augment cell membrane permeability, induce potassium ion leakage and pore formation, and disrupt cell membranes. It also affects spore germination and guaiacol production of A. acidoterrestris, probably due to upregulation of the luxS gene linked to quorum sensing.

Viability, Sublethal Injury, and Release of Cellular Components From Alicyclobacillus acidoterrestris Spores and Cells After the Application of Physical Treatments, Natural Extracts, or Their Components

Alicyclobacillus acidoterrestris is a spoiling microorganism regarded as one of the most important causes of spoilage of fruit juices and acidic products. In this paper, four strains of A. acidoterrestris (type strain-DSM 3922; two wild strains isolated from soil-C8 and C24; wild strain isolated from a spoiled pear juice CB1) were treated through natural extracts/active compounds from essential oils (EOs), and physical treatments were used to assess their susceptibility and the presence of sublethal injury. The characterization of damage was also performed. The results suggest that it is possible to control A. acidoterrestris through alternative approaches, although the effect relied upon the age of spores. In addition to the mere antimicrobial effect, some treatments could cause a sublethal injury on spores. Lemon extract was the most effective treatment for both the antimicrobial effect and the sublethal injury, as evidenced by the release of proteins, and calcium dipicolinate [dipicolinic acid (DPA)] by fresh spores and only DPA (with an exception for C8) by old spores. A sublethal injury with protein release was also found for physical treatments [US (ultrasound) or heating]. For the first time, this paper reports on the existence of a sublethal injury for A. acidoterrestris, and this evidence could also be a challenge, because injured microorganisms could restore their metabolism, or an opportunity to design new preserving treatments.

Impact of Heating Rates on Alicyclobacillus acidoterrestris Heat Resistance under Non-Isothermal Treatments and Use of Mathematical Modelling to Optimize Orange Juice Processing

Alicyclobacillus acidoterrestris is a spoilage microorganism responsible for relevant product and economic losses in the beverage and juice industry. Spores of this microorganism can survive industrial heat treatments and cause spoilage during posterior storage. Therefore, an effective design of processing treatments requires an accurate understanding of the heat resistance of this microorganism. Considering that industrial treatments are dynamic; this understanding must include how the heat resistance of the microorganism is affected by the heating rate during the heating and cooling phases. The main objective of this study was to establish the effect of heating rates and complex thermal treatments on the inactivation kinetics of A. acidoterrestris. Isothermal experiments between 90 and 105 °C were carried out in a Mastia thermoresistometer, as well as four different dynamic treatments. Although most of the inactivation takes place during the holding phase, our results indicate the relevance of the heating phase for the effectiveness of the treatment. The thermal resistance of A. acidoterrestris is affected by the heating rate during the heating phase. Specifically, higher heating rates resulted in an increased microbial inactivation with respect to the one predicted based on isothermal experiments. These results provide novel information regarding the heat response of this microorganism, which can be valuable for the design of effective heat treatments to improve product safety and stability. Moreover, it highlights the need to incorporate experimental data based on dynamic treatments in process design, as heating rates can have a very significant effect on the thermal resistance of microorganisms.

Assessment of Spoilage Potential Posed by Alicyclobacillus spp. in Plant-Based Dairy Beverages Mixed with Fruit Juices during Storage

ABSTRACT

The scope of the present study was to assess the spoilage potential of different Alicyclobacillus spp. in commercial pasteurized (ambient-stable) plant-based dairy beverages mixed with fruit juices at different inoculation levels and storage temperatures. Different products (coconut and berry [CB]; almond, mango, and passionfruit [AMP]; and oat, strawberry, and banana [OSB]) were inoculated with 10 or 2 × 103 spores per mL of either Alicyclobacillus acidoterrestris, Alicyclobacillus fastidiosus, or Alicyclobacillus acidocaldarius strain composites, whereas noninoculated samples served as controls. Samples inoculated with A. acidoterrestris and A. fastidiosus were stored at 30 and 45°C, whereas A. acidocaldarius storage took place at 50°C for 240 days. Gas composition, Alicyclobacillus spp. populations, total viable counts, pH, water activity, color, and guaiacol off-taste were monitored. CB and AMP supported growth of A. acidoterrestris and A. fastidiosus, reaching populations of 4.0 to 5.0 log CFU/mL. In OSB, populations of A. fastidiosus remained close to the initial inoculation levels during storage at 30°C, whereas at 45°C, the populations declined <1 CFU/mL. A. acidocaldarius growth was supported in CB samples, but not in AMP and OSB samples, reaching ca. 3.0 log CFU/mL at 50°C, regardless of initial inoculum size. Total color change was increased during storage; however, the instrumentally recorded color changes were not macroscopically visible. Spoilage in terms of guaiacol off-taste was identified only in CB and AMP samples inoculated with A. acidoterrestris after 60 days at 30 and 45°C. The increased popularity of these products along with the scarcity of existing literature related to their spoilage by Alicyclobacillus spp., render the contribution of the findings and data of present study critical for assessing the significance of Alicyclobacillus spp. as a potential spoilage hazard in these products and for assisting in the design and implementation of effective mitigation strategies by the beverage industry.

HIGHLIGHTS

Short Wave Ultraviolet Light (UV-C) Effectiveness in the Inactivation of Bacterial Spores Inoculated in Turbid Suspensions and in Cloudy Apple Juice

Liquid foods might present interferences in their optical properties that can reduce the effectiveness of short-wave ultraviolet radiation (UV-C) treatments used for sterilization purposes. The effect of turbidity as UV-C interference factor against the inactivation of bacterial spores was analysed by using phosphate-buffered saline solutions (PBS) of different turbidity values (2000, 2500, and 3000 NTU) which were adjusted with the addition of apple fibre. These suspensions were inoculated with spores of Bacillus subtilis and Alicyclobacillus acidoterrestris. While higher UV-C doses increased the inactivation rates of spores, these were reduced when turbidity values increased; a dose of 28.7 J/mL allowed inactivation rates of B. subtilis spores of 3.96 Log in a 2000-NTU suspension compared with 2.81 Log achieved in the 3000-NTU one. Spores of B. subtilis were more UV-C-resistant than A. acidoterrestris. Cloudy apple juice inoculated with A. acidoterrestris spores was processed by UV-C at different doses in a single pass and with recirculation of the matrix through the reactor. Inactivation increased significantly with recirculation, surpassing 5 Log after 125 J/mL compared with 0.13 Log inactivation after a single-pass treatment at the same UV-C dose. UV-C treatments with recirculation affected the optical properties (absorption coefficient at 254 nm and turbidity) of juice and increased browning as UV-C doses became higher.

Microbes associated with fresh produce: Sources, types and methods to reduce spoilage and contamination

Global food security remains one of the most important challenges that needs to be addressed to ensure the increasing demand for food of the fast growing human population is satisfied. Fruits and vegetables comprise an essential component of a healthy balanced diet as they are the major source of both macro- and micronutrients. They are particularly important for communities in developing countries whose nutrition often relies solely on a plant-based diet. Recent advances in agriculture and food processing technologies have facilitated production of fresh, nutritious and safe food for consumers. However, despite the development of sophisticated chemical and physical methods of food and equipment disinfection, fresh-cut produce and fruit juice industry still faces significant economic losses due to microbial spoilage. Furthermore, fresh produce remains an important source of pathogens that have been causing outbreaks of human illness worldwide. This chapter characterizes common spoilage and human pathogenic microorganisms associated with fresh-cut produce and fruit juice products, and discusses the methods and technology that have been developed and utilized over the years to combat them. Substantial attention is given to highlight advantages and disadvantages of using these methods to reduce microbial spoilage and their efficacy to eliminate human pathogenic microbes associated with consumption of fresh-cut produce and fruit juice products.

The Role of Solid Support Bound Metal Chelators on System-Dependent Synergy and Antagonism with Nisin

Active packaging can enhance the performance of natural antimicrobials in controlling food spoilage and waste, while addressing consumer demands for cleaner labels. Yet, synergies are system dependent, with some conditions counterintuitively promoting antagonistic effects. In particular, metal chelators can improve performance of certain natural antimicrobials and have been incorporated in nonmigratory metal chelating active packaging technologies. However, the influence of chelating ligand chemistry on antimicrobial efficacy has not been investigated in microbial spoilage models. The effect of three commercial chelating resins on the growth of Alicyclobacillus acidoterrestris ATCC 49025, a thermoduric acidophilic spore-former, in growth media and apple juice was investigated. Dowex MAC-3, Chelex 100, and Lewatit TP260 were used as models for metal chelating active packaging containing carboxylic acid (CA), iminodiacetic acid (IDA), and aminomethylphosphonic acid (AMPA) ligands. Diameters (CA = 472.4 ± 117.2 μm, IDA = 132.93 ± 26.71 μm, and AMPA = 498.3 ± 29.24 μm), dissociation kinetics (CA = 6.44 ± 0.109, IDA = -0.977 ± 9.94, AMPA = 7.43 ± 0.193), and metal chelating capacities (CA = 1.16 × 10^-4 mol/g, IDA = 1.52 × 10^-3  mol/g, and AMPA = 4.67 × 10^-4 mol/g) were used to distinguish differences in antimicrobial efficacies. Growth of A. acidoterrestris in acidified Potato Dextrose Broth over 24 hr with chelating resins indicated early death phase for CA and IDA resins and bactericidal for AMPA resin. However, viability in commercial apple juice with the inclusion of nisin and chelating resins was variable, with IDA resin significantly (P < 0.05) increasing viability while the effect of CA and AMPA resins remained elusive. This work emphasizes the importance of biological repeatability and correct statistical modeling in identifying conditions under which the antimicrobial intervention of nisin in real food systems, such as acidic beverages and juices, are synergistic or antagonistic. PRACTICAL APPLICATION: New technologies to control microbial food spoilage and waste need to be explored to address consumers on-going demands for reducing additive use.  Solid support bound metal chelators can both promote and control microbial growth when used in conjunction with nisin, a natural antimicrobial.  This work explores how system conditions can render a given technology either synergistic or antagonistic, and highlights the importance of sufficient biological replicates in experimental design.

Continuous ohmic heating of commercially processed apple juice using five sequential electric fields results in rapid inactivation of Alicyclobacillus acidoterrestris spores

Spores of Alicyclobacillus acidoterrestris, a spoilage bacterium, cause problems for the apple juice industry because they are resistant to thermal treatment. Here, we examined the sporicidal effect of an ohmic heating (OH) system with five sequential electric fields and compared it with that of conventional heating. Apple juice product (50kg) inoculated with A. acidoterrestris spores were subjected to OH (electric field strength=26.7V/cm; frequency=25kHz) at 85-100°C for 30-90s. The effect of conventional heating was also examined under these conditions. OH treatment at 100°C for 30s resulted in total inactivation of the inoculum, with no recovery of viable cells (initial population=4.8-4.9logCFU/ml), whereas 3.6-4.9logCFU/ml of the spores survived conventional heating. OH did not alter the quality (°Brix, color, and pH) of commercial apple juice (p>0.05). These results suggest that the OH system is superior to conventional heating for rapid sterilization (30s) of apple juice to assure microbiological quality in the absence of chemical additives.

Development of a Polyclonal Antibody-Based Sandwich Enzyme-Linked Immunosorbent Assay for the Detection of Spores of Alicyclobacillus acidoterrestris in Various Fruit Juices

A polyclonal rabbit antibody-based sandwich ELISA for the rapid and specific detection of spores of Alicyclobacillus acidoterrestris was established. The reactivity of the antisera with spores was confirmed by immunofluorescence. For a thorough evaluation of the ELISA, 61 strains and isolates of Alicyclobacillus spp. were characterized regarding their guaiacol production ability and genetic variability. The ELISA was highly sensitive, the detection limits were isolate-dependent and ranged from 2.1 × 10(3) - 3.8 × 10(4) spores/mL, except for one isolate, for which a slightly lower sensitivity (5 × 10(5) spores/mL) was observed. Inclusivity tests revealed that the ELISA reacts with all tested A. acidoterrestris, while no cross-reactions with spores of 30 strains of Bacillus spp. and Clostridium spp. were observed. Further on, the assay applicability was tested with orange, apple (clear and unfiltered), tomato, pink grapefruit, pear, and white grape juices. Juices were inoculated with 1 or 10 spores/mL of A. acidoterrestris. After enrichment for 48 h, the established ELISA enabled the reliable and reproducible detection of contaminated samples. The enriched samples could be applied directly to the assay, underlining the robustness of the developed ELISA method.

Genotypic and Phenotypic Heterogeneity in Alicyclobacillus acidoterrestris: A Contribution to Species Characterization

Alicyclobacillus acidoterrestris is the main cause of most spoilage problems in fruit juices and acidic products. Since soil borne species often contaminate fruit juices and do not need strict extreme requirements for survival, it is a great concern to investigate whether and how soil species could evolve from their ecological niches in microbial community to new environments as fruit juices. In this study, 23 isolates of thermo-acidophilic, spore-forming bacteria from soil were characterized by cultural and molecular methods. In addition, 2 strains isolated from a spoilage incident in pear juice were typed. Strains phenotyping showed that they could be grouped into 3 different clusters, and some isolates showed identical or quite similar patterns. Analyzing pH and temperature ranges for growth, the majority of strains were able to grow at values described for many species of Alicyclobacillus. Qualitative utilization of lysine, arginine and indole production from tryptophan revealed, for the first time, deamination of lysine and decarboxylation of arginine. Resistance to 5% NaCl as well as the ability to hydrolyze starch and gelatin, nitrate reduction, catalase and oxidase activities confirmed literature evidences. Examining of 16S rRNA, showed that isolates were divided into three blocks represented by effectively soil species and strains that are moving from soil to other possible growing source characterized by parameters that could strongly influence bacterial survival. RAPD PCR technique evidenced a great variability in banding patterns and, although it was not possible to obtain genotypically well-distinguished groups, it was feasible to appreciate genetic similarity between some strains. In conclusion, the investigation of a microbial community entails a combination of metagenomic and classic culture-dependent approaches to expand our knowledge about Alicyclobacillus and to look for new subspecies.

Alicyclobacillus spp.: New Insights on Ecology and Preserving Food Quality through New Approaches

Alicyclobacillus spp. includes spore-forming and thermo-acidophilic microorganisms, usually recovered from soil, acidic drinks, orchards and equipment from juice producers. The description of the genus is generally based on the presence of ω-fatty acids in the membrane, although some newly described species do not possess them. The genus includes different species and sub-species, but A. acidoterrestris is generally regarded as the most important spoiler for acidic drinks and juices. The main goal of this review is a focus on the ecology of the genus, mainly on the species A. acidoterrestris, with a special emphasis on the different phenotypic properties and genetic traits, along with the correlation among them and with the primary source of isolation. Finally, the last section of the review reports on some alternative approaches to heat treatments (natural compounds and other chemical treatments) to control and/or reduce the contamination of food by Alicyclobacillus.

Food Targeting: A Real-Time PCR Assay Targeting 16S rDNA for Direct Quantification of Alicyclobacillus spp. Spores after Aptamer-Based Enrichment

Spore-forming Alicyclobacillus spp. are able to form metabolites that induce even in small amounts an antiseptical or medicinal off-flavor in fruit juices. Microbial contaminations could occur by endospores, which overcame the pasteurization process. The current detection method for Alicyclobacillus spp. can take up to 1 week because of microbiological enrichment. In a previous study, DNA aptamers were selected and characterized for an aptamer-driven rapid enrichment of Alicyclobacillus spp. spores from orange juice by magnetic separation. In the present work, a direct quantification assay for Alicyclobacillus spp. spores was developed to complete the two-step approach of enrichment and detection. After mechanical treatment of the spores, the isolated DNA was quantified in a real-time PCR-assay targeting 16S rDNA. The assay was evaluated by the performance requirements of the European Network of Genetically Modified Organisms Laboratories (ENGL). Hence, the presented method is applicable for direct spore detection from orange juice in connection with an enrichment step.

Emerging preservation techniques for controlling spoilage and pathogenic microorganisms in fruit juices

Fruit juices are important commodities in the global market providing vast possibilities for new value added products to meet consumer demand for convenience, nutrition, and health. Fruit juices are spoiled primarily due to proliferation of acid tolerant and osmophilic microflora. There is also risk of food borne microbial infections which is associated with the consumption of fruit juices. In order to reduce the incidence of outbreaks, fruit juices are preserved by various techniques. Thermal pasteurization is used commercially by fruit juice industries for the preservation of fruit juices but results in losses of essential nutrients and changes in physicochemical and organoleptic properties. Nonthermal pasteurization methods such as high hydrostatic pressure, pulsed electric field, and ultrasound and irradiations have also been employed in fruit juices to overcome the negative effects of thermal pasteurization. Some of these techniques have already been commercialized. Some are still in research or pilot scale. Apart from these emerging techniques, preservatives from natural sources have also shown considerable promise for use in some food products. In this review article, spoilage, pathogenic microflora, and food borne outbreaks associated with fruit juices of last two decades are given in one section. In other sections various prevention methods to control the growth of spoilage and pathogenic microflora to increase the shelf life of fruit juices are discussed.

Inactivation of Alicyclobacillus acidoterrestris spores in apple and orange juice concentrates by gamma irradiation

The objective of this study was to evaluate the effect of different concentrations of reconstituted apple and orange juice on reduction of Alicyclobacillus acidoterrestris spores by gamma irradiation. Spores of A. acidoterrestris were inoculated into three concentrations of apple (18, 36, and 72 °Brix) and orange (11, 33, and 66 °Brix) juice and subjected to five radiation doses (1, 3, 5, 7, and 10 kGy). No significant reductions (P > 0.05) in spores were observed after the 1-kGy treatment for all apple and orange concentrations. Spores in 18, 36, and 72 °Brix apple juice concentrates subjected to 10 kGy were reduced to 4.34, 3.9, and 3.84 log CFU/ml, respectively. Similar results were observed for orange juice. When 10 kGy was applied to 11 °Brix orange juice, populations of spores were reduced by 5 log CFU/ml. The reduction of spores in 33 and 66 °Brix orange juice concentrates exposed to 10-kGy gamma irradiation was 4.54 and 3.85 log CFU/ml, respectively. Juice concentration did not affect (P > 0.05) the number of surviving A. acidoterrestris spores from the same kGy treatment. Gamma irradiation treatment did not change the pH or water activity of the juice (P > 0.05).

Alicyclobacillus contamination in the production line of kiwi products in China

Alicyclobacillus are spoilage microbes of many juice products, but contamination of kiwi products by Alicyclobacillus is seldom reported. This study aims to investigate the whole production line of kiwi products in China to assess the potential risk of their contamination. A total of 401 samples from 18 commercial products, 1 processing plant and 16 raw material orchards were tested, and 76 samples were positive, from which 76 strains of microbes were isolated and identified as 4 species of Alicyclobacillus, including Alicyclobacillus acidoterrestris, Alicyclobacillus contaminans, Alicyclobacillus herbarius and Alicyclobacillus cycloheptanicus, and another 9 strains as 3 species of Bacillus by sequencing of their 16S rDNA. Through phylogenetic tree construction and RAPD-PCR amplification, it was found that there exist genotypic diversities to some extent among these isolates. Four test strains (each from one species of the 4 Alicyclobacillus species isolated in this study) could spoil pH adjusted kiwi fruit juice and some commercial kiwi fruit products with producing guaiacol (11-34 ppb).

Electronic Nose for Microbiological Quality Control of Food Products

Electronic noses (ENs) have recently emerged as valuable candidates in various areas of food quality control and traceability, including microbial contamination diagnosis. In this paper, the EN technology for microbiological screening of food products is reviewed. Four paradigmatic and diverse case studies are presented: (a)Alicyclobacillusspp. spoilage of fruit juices, (b) early detection of microbial contamination in processed tomatoes, (c) screening of fungal and fumonisin contamination of maize grains, and (d) fungal contamination on green coffee beans. Despite many successful results, the high intrinsic variability of food samples together with persisting limits of the sensor technology still impairs ENs trustful applications at the industrial scale. Both advantages and drawbacks of sensor technology in food quality control are discussed. Finally, recent trends and future directions are illustrated.