The incidence and impact of microbial spoilage in the production of fruit and vegetable juices as reported by juice manufacturers

Microbiological quality of edible vegetable oils produced and marketed in Gondar City, Northwest Ethiopia

Edible oils are imported and produced in Ethiopia, notably in Gondar, and their production has expanded considerably in recent years. The expansion of locally produced edible vegetable oils with severe quality control, substandard edible oil production, and quality deterioration may contribute to the contamination of microbes, which may cause public health problems. This study determines the microbiological quality of edible vegetable oils being produced and marketed in Gondar City, Northwest Ethiopia, in 2021. A laboratory-based cross-sectional study design was conducted from May to July 2021 in Gondar City. A simple random sampling technique was used to collect 17 edible vegetable oil samples. Aseptically collected samples were analyzed in the microbiology lab room. The microbiological quality of vegetable oil was assessed using standard microbiological procedures and techniques. The collected data were entered into a Microsoft Excel 2016 spreadsheet and Stata Version 14. A non-parametric Kruskal-Wallis test was used to assess significant variation. Seventeen edible vegetable oil samples were examined and found to contain a varying number of bacteria, yeast, and molds. Staphylococcus aureus, Klebsiella Pneumoniae, and Pseudomonas aeruginosa were the identified bacteria, whereas Saccharomyces cerevisiae, Aspergillus niger, Aspergillus flavus, and Aspergillus fumigatus were the identified fungi. Total coliform and fecal coliform isolates were also identified in the oil samples. A level of microbial contamination that has public health importance was observed in some of the oil samples analyzed, and the isolated microorganisms indicate unhygienic handling, processing, and storage practices in the oil production and market sites. The introduction of strict rules, regulations, and updated manufacturing technologies and processes to ensure food safety and quality is needed.

Roles of polysaccharides-based nanomaterials in food preservation and extension of shelf-life of food products: A review

In food production sectors, food spoilage and contamination are major issues that threaten and negatively influence food standards and safety. Several physical, chemical, and biological methods are used to extend the shelf-life of food products, but they have their limitations. Henceforth, researchers and scientists resort to novel methods to resolve these existing issues. Nanomaterials-based extension of food shelf life has broad scope rendering a broad spectrum of activity including high antioxidant and antimicrobial activity. Numerous research investigations have been made to identify the possible roles of nanoparticles in food preservation. A wide range of nanomaterials via different approaches is ultimately applied for food preservation. Among them, chemically synthesized methods have several limitations, unlike biological synthesis. However, biological synthesis protocols are quite expensive and laborious. Predominant studies demonstrated that nanoparticles can protect fruits and vegetables by preventing microbial contamination. Though several nanomaterials designated for food preservation are available, detailed knowledge of the mechanism remains unclear. Hence, this review aims to highlight the various nanomaterials and their roles in increasing the shelf life of food products. Adding to the novel market trends, nano-packaging will open new frontiers and prospects for ensuring food safety and quality.

Effect of pre-harvest sanitizer treatments on Listeria survival, sensory quality and bacterial community dynamics on leafy green vegetables grown under commercial conditions

Leafy green vegetables (LGVs) have large surface areas and can be colonized by various microorganisms including pathogens. In this study, we investigated the effect of pre-harvest sanitizer treatments on the survival of inoculated proxy pathogen Listeria innocua ATCC 33090 and the natural microbial community of mizuna, rocket (arugula), red chard and spinach grown under commercial conditions. Electrolyzed water (e-water), peracetic acid (PAA), and 1-bromo-3-chloro-5-dimethylhydantoin (BCDMH) were tested against water controls. We also observed the subsequent sensorial changes of harvested, bagged LGV leaves over a period of 12 days within chill storage alongside the growth, diversity and structure of bacterial populations determined using 16S rRNA gene amplicon sequencing and total viable counts (TVC). Treatment with PAA resulted in the highest reductions of L. innocua (2.4-5.5 log units) compared to the other treatments (0.25-2.5 log units). On day 0 (24 h after sanitizer application), the TVC on sanitizer treated LGVs were significantly reduced compared to water controls, except for rocket. During storage at 4.5 (±0.5)°C sanitisers only hindered microbial growth on LGVs initially and did not influence final bacterial population levels, growth rates or changes in LGV sample colour, decay, odour and texture compared to water controls. Shelf-life was not extended nor was it reduced. The community structure on LGV types differed though a core set of bacterial amplicon sequence variants (ASV) were present across all samples. No significant differences were observed in bacterial diversity between sanitizer treatments, however sanitizer treated LGV samples had initially reduced diversity compared to water treated samples. The bacterial compositions observed at the end point of storage considerably differed from what was observed at initial point owing to the increase in abundance of specific bacterial taxa, mainly Pseudomonas spp., the abundance and growth responses differing between LGV types studied. This study provides a better understanding on the microbiology and sensory impact of pre-harvest applied sanitiser treatments on different LGVs destined for commercial food use.

Detection of Alicyclobacillus spp. and Identification of Guaiacol Production Using the GENE-UP® PRO ACB, IFU Method No. 12, and Cosmo Bio Assays

Some species of Alicyclobacillus spoil beverages by producing guaiacol. Current culture-based methods detect the presence of Alicyclobacillus spp. and a subsequent peroxidase assay determines if the isolate can produce guaiacol. However, these methods are time-consuming and can yield false negatives due to differences in growth optima among species. The purpose of this study was to compare a RT-PCR-based method, the GENE-UP® PRO ACB assay, to the IFU Method No. 12 Enumeration and Enrichment methods. Ten species of Alicyclobacillus were detected using the tested RT-PCR assay, while A. dauci and A. kakegewensis were not detected using either IFU protocol. Low concentrations (1-10, 10-100, and 100-1,000 CFU/10 mL) of A. acidoterrestris, A. suci, and A. acidocaldarius were tested in five matrices. The proportion of positive samples identified using the tested RT-PCR assay (62/84) or the IFU Enrichment protocol (62/84) did not differ significantly from the proportion of inoculated samples (63/84). However, the IFU Enumeration method (32/84) detected statistically fewer positives. Additionally, methods identifying guaiacol production were compared. The proportion of correctly identified guaiacol producers using the tested RT-PCR assay (51/63) was not significantly different than those identified using the 3 h Cosmo Bio assay (54/63). Finally, four commercial samples of orange juice and sucrose solution were tested. Alicyclobacillus spp. were identified in all four samples using the IFU Enrichment method and in two samples using the tested RT-PCR assay. However, Alicyclobacillus was not detected in any sample using the IFU Enumeration method. Overall, this study showed consistent detection of Alicyclobacillus spp. using either the IFU Enrichment protocol or the tested RT-PCR assay, which both outperformed the IFU Enumeration protocol. Both the 3 h guaiacol bioassay and the tested RT-PCR assays consistently differentiated guaiacol-producing and nonproducing strains.

Potential of Syzygnium polyanthum as Natural Food Preservative: A Review

Food preservation is one of the strategies taken to maintain the level of public health. Oxidation activity and microbial contamination are the primary causes of food spoilage. For health reasons, people prefer natural preservatives over synthetic ones. Syzygnium polyanthum is widely spread throughout Asia and is utilized as a spice by the community. S. polyanthum has been found to be rich in phenols, hydroquinones, tannins, and flavonoids, which are potential antioxidants and antimicrobial agents. Consequently, S. polyanthum presents a tremendous opportunity as a natural preservative. This paper reviews recent articles about S. polyanthum dating back to the year 2000. This review summarizes the findings of natural compounds presented in S. polyanthum and their functional properties as antioxidants, antimicrobial agents, and natural preservatives in various types of food.

Thermosonication of Orange-Carrot Juice Blend: Overall Quality during Refrigerated Storage, and Sensory Acceptance

Ultrasound combined with high temperatures (thermosonication) is an alternative to thermal treatments applied for juice preservation purposes. Blend juices, such as orange-carrot juice, are an interesting option for consumers due to their diversity of unique flavors. The main aim of the present study is to investigate thermosonication's impact on the overall quality of an orange-carrot juice blend over 22-day storage at 7 °C, in comparison to thermal treatment. Sensory acceptance was assessed on the first storage day. The juice blend was prepared based on using 700 mL of orange juice and 300 g of carrot. The effect of ultrasound treatment at 40, 50, and 60 °C for 5 and 10 min, as well as of thermal treatment at 90 °C for 30 s, on the physicochemical, nutritional, and microbiological quality of the investigated orange-carrot juice blend was tested. Both the ultrasound and the thermal treatment could maintain pH, °Brix, total titratable acidity, total carotenoid content, total phenolic compounds, and the antioxidant capacity of untreated juice samples. All ultrasound treatments improved samples' brightness and hue value, and made the juice brighter and redder. Only ultrasound treatments at 50 °C/10 min and at 60 °C/10 min have significantly reduced total coliform counts at 35 °C. Thus, they were selected along with untreated juice for sensory analysis, whereas thermal treatment was used for comparison purposes. Thermosonication at 60 °C for 10 min recorded the lowest scores for juice flavor, taste, overall acceptance, and purchase intention. Thermal treatment and ultrasound at 60 °C for 5 min recorded similar scores. Minimal variations in quality parameters were observed over 22-day storage in all treatments. Thermosonication at 60 °C for 5 min has improved samples' microbiological safety and resulted in good sensorial acceptance. Although thermosonication has the potential to be used in orange-carrot juice processing, further investigations are necessary to enhance its microbial effect on this product.

Multi-Functional Potential of Lactic Acid Bacteria Strains and Antimicrobial Effects in Minimally Processed Pomegranate (Punica granatum L. cv Jolly Red) Arils

This study aimed to evaluate the antimicrobial activity of both cells, and cell-free supernatants (CFS) of 7 selected lactic acid bacteria (LAB) strains belonging to Limosilactobacillus fermentum (4 strains), Lacticaseibacillus paracasei (1 strain), Lacticaseibacillus rhamnosus (1 strain), and Enterococcus faecium (1 strain) species, against Listeria monocytogenes, Escherichia coli, Salmonella Typhimurium, Pseudomonas aeruginosa and Staphylococcus aureus, by both the agar-well diffusion and co-culture methods. In addition, probiotic and safety traits were also detected. Great variability was detected on antimicrobial effects, whereas all tested strains were found sensitive to most of the tested antibiotics, and without any DNase, gelatinase, or hemolytic activity. Moreover, strains showed excellent survival in acidic conditions and exhibited tolerance to pepsin and bile salts. Based on the in vitro results, the CFSs of two selected L. fermentum strains were applied, in a mixed solution, as bio-preservative into minimally processed pomegranate arils, inoculated with a cocktail of L. monocytogenes and E. coli. Samples, packaged in an ordinary atmosphere, were analyzed during refrigerated storage, for up to 12 days, for physicochemical (as weight loss, texture, color, pH, total soluble solids and organic acid content) and for microbiological traits. Results revealed the effectiveness of CFS, up to 12 days, in reducing weight loss and microbial growth, without any significant effect on texture, total soluble solid content and color, found comparable to the acid citric treatment, highlighting the multi-functional potential of selected probiotic strains.

Chlorophyllin-Based 405 nm Light Photodynamic Improved Fresh-Cut Pakchoi Quality at Postharvest and Inhibited the Formation of Biofilm

The aim of this study was to evaluate the effect of chlorophyllin-based photodynamic inactivation (Chl-PDI) on biofilm formation and fresh-cut pakchoi quality during storage. Firstly, Chl-based PDI reduced the amount of biofilm in an in vivo experiment and inactivated the food spoilage bacteria. Antibacterial mechanism analysis indicated that the bacterial extracellular polysaccharides and extracellular proteins were vulnerable targets for attacks by the Chl-based PDI. Then, the food spoilage microorganisms (Pseudomonas reinekei and Pseudomonas palleroniana) were inoculated onto the surface of fresh-cut pakchoi. We used chlorophyllin (1 × 10⁻⁵ mol/L) and 405 nm light (22.27 J/cm² per day) to investigate the effect of Chl-based PDI treatment on fresh-cut pakchoi quality during storage. The results showed that Chl-based PDI increased the visual quality and the content of chlorophyll, VC, total soluble solids, and SOD activity and decreased the occurrence of leaf yellowing and POD activity. These suggest that Chl-based PDI can be used for the preservation of fresh-cut pakchoi and has the potential to inhibit biofilm formation of food spoilage bacteria. It is of great significance for the effective processing and traditional vegetable preservation.

Purification and characterization of antifungal lipopeptide produced by Bacillus velezensis isolated from raw honey

Raw honey contains a diverse microbiota originating from honeybees, plants, and soil. Some gram-positive bacteria isolated from raw honey are known for their ability to produce secondary metabolites that have the potential to be exploited as antimicrobial agents. Currently, there is a high demand for natural, broad-spectrum, and eco-friendly bio-fungicides in the food industry. Naturally occurring antifungal products from food-isolated bacteria are ideal candidates for agricultural applications. To obtain novel antifungals from natural sources, we isolated bacteria from raw clover and orange blossom honey to evaluate their antifungal-producing potential. Two Bacillus velezensis isolates showed strong antifungal activity against food-isolated fungal strains. Antifungal compound production was optimized by adjusting the growth conditions of these bacterial isolates. Extracellular proteinaceous compounds were purified via ammonium sulfate precipitation, solid phase extraction, and RP-HPLC. Antifungal activity of purified products was confirmed by deferred overlay inhibition assay. Mass spectrometry (MS) was performed to determine the molecular weight of the isolated compounds. Whole genome sequencing (WGS) was conducted to predict secondary metabolite gene clusters encoded by the two antifungal-producing strains. Using MS and WGS data, we determined that the main antifungal compound produced by these two Bacillus velezensis isolates was iturin A, a lipopeptide exhibiting broad spectrum antifungal activity.

Susceptibility of Rosaceous Pome and Stone Fruits to Postharvest Rot by Paecilomyces niveus

Paecilomyces rot of apples is a postharvest disease caused by Paecilomyces niveus, a problematic spoiling agent of fruit juices and derivatives. Processing fruits infected with Paecilomyces rot can lead to juices contaminated with P. niveus ascospores. These ascospores are heat resistant and may survive food processing and germinate in finished products. Because the fungus produces the mycotoxin patulin, juice spoilage by P. niveus is an important health hazard. Little is known about the disease biology and control mechanisms of this recently described postharvest disease. The range of fruit products contaminated by P. niveus and patulin led us to hypothesize that the host range of Paecilomyces rot is broader than previously thought. Following Koch's postulates, we determined that multiple untested rosaceous fruits and popular apple cultivars are susceptible to Paecilomyces rot infection and that these infected fruits contain significant levels of patulin. We also observed that two closely related food spoiling fungi, Paecilomyces fulvus and Paecilomyces variotti, were unable to infect, cause symptoms in, or grow in wounded fruits. Therefore, we challenge the assumption that P. niveus spoilage inoculum is introduced to foods solely through environmental sources, and we show that other economically important rosaceous fruits, peaches, pears, sweet cherries, and sour cherries, are susceptible to infection and can also be sources of spoilage inoculum. Our results highlight the unique abilities of P. niveus to infect a variety of fruits, produce patulin, and form resistant spores capable of spoiling normally shelf-stable products.

Advancements in the Use of Fermented Fruit Juices by Lactic Acid Bacteria as Functional Foods: Prospects and Challenges of Lactiplantibacillus (Lpb.) plantarum subsp. plantarum Application

Lactic acid fermentation of fresh fruit juices is a low-cost and sustainable process, that aims to preserve and even enhance the organoleptic and nutritional features of the raw matrices and extend their shelf life. Selected Lactic Acid Bacteria (LAB) were evaluated in the fermentation of various fruit juices, leading in some cases to fruit beverages, with enhanced nutritional and sensorial characteristics. Among LAB, Lactiplantibacillus (Lpb.) plantarum subsp. plantarum strains are quite interesting, regarding their application in the fermentation of a broad range of plant-derived substrates, such as vegetables and fruit juices, since they have genome plasticity and high versatility and flexibility. L. plantarum exhibits a remarkable portfolio of enzymes that make it very important and multi-functional in fruit juice fermentations. Therefore, L. plantarum has the potential for the production of various bioactive compounds, which enhance the nutritional value and the shelf life of the final product. In addition, L. plantarum can positively modify the flavor of fruit juices, leading to higher content of desirable volatile compounds. All these features are sought in the frame of this review, aiming at the potential and challenges of L. plantarum applications in the fermentation of fruit juices.

Factors That Affect the Microbiological Stability of Chicha Morada during Its Production on an Industrial Scale: A Review

ABSTRACT

Chicha morada, also known as purple corn drink (PCD), is a traditional noncarbonated beverage commonly prepared at homes and restaurants in Peru. However, in recent years, it is being produced at an industrial scale aiming to extend its shelf life, expand its marketing, and make it known worldwide. Traditionally, this beverage, whose main component is purple corn (Zea mays L.), was made and consumed quickly and in some cases, stored under refrigeration until consumption, but never beyond 24 to 48 h. With its industrialization, factories are presented with challenges to design and provide adequate protection of the beverage, assuring its quality and safety. Although its production at an industrial level is similar to that of other noncarbonated drinks containing fruit juice, several processing factors could affect the microbiological stability desired for this beverage, such as the storage of the purple corn drink extract. In this document, a critical review of the production process (raw materials, production stages, and forms of commercialization) that can directly affect the contamination of the beverage is made. Recommendations are made for improving the control points in the industrial process and to avoid potential microbiological problems.

HIGHLIGHTS

Fabricating an anti-shrinking κ-carrageenan/sodium carboxymethyl starch film by incorporating carboxylated cellulose nanofibrils for fruit preservation

A stronger and dimension-stabilized film was obtained using κ-carrageenan and sodium carboxymethyl starch (CMS) with carboxylated cellulose nanocrystals (C-CNC) as a reinforcing agent and anti-shrinkage agent. C-CNC endowed the films with better mechanical properties as well as excellent dimensional stability. The film solutions showed shear thinning and acted as a pseudoplastic fluid. When C-CNC content was increased from 0% to 12%, the tensile strength and elongation at break of the films improved from 23.89 MPa to 38.37 MPa and 21.00% to 27.31%, respectively. The films maintained good thermal stability and barrier performance. The Zeta potential of the film suspension can reach below -30 mV, indicating C-CNC enhanced the electrostatic repulsion in the film-forming system, which favored the network structure more continuous and stable. By virtue of the excellent mechanical properties and dimensional stability, strawberries can be tightly wrapped without cracks by the coatings to delay the deterioration greatly. By comparing the weight loss rate, Vc, total soluble solid, hardness, titratable acid and pH, CCC12-coated strawberries were closer to fresh ones. Therefore, this study has developed a feasible, low-cost and green fruit coating that can be potentially utilized on a large-scale.

Alicyclobacillus mali sp. nov., Alicyclobacillus suci sp. nov. and Alicyclobacillus fructus sp. nov., thermoacidophilic sporeforming bacteria isolated from fruit beverages

Six thermo-acidophilic, spore-forming strains were isolated from a variety of juice products and were characterized genetically and phenotypically. According to 16S rRNA and rpoB gene phylogenetic analyses and average nucleotide identity comparisons against the species demarcation cutoff at <95 %, these six strains were determined to represent three novel species of Alicyclobacillus. The isolates were designated FSL-W10-0018^T, FSL-W10-0037, FSL-W10-0048, VF-FSL-W10-0049^T, FSL-W10-0057 and FSL-W10-0059^T. All six isolates were Gram-positive, motile, rod shaped, contained menaquinone 7 as the major respiratory quinone and had ω-cyclohexane C_17 : 0 as a major fatty acid. They were all able to grow aerobically in a range of acidic and moderate thermal conditions. Only isolates FSL-W10-0048 and VF-FSL-W10-0049^T were able to produce guaiacol. The following names are proposed for the three new species: Alicyclobacillus mali sp. nov. (type strain FSL-W10-0018^T =DSM 112016^T=NCIMB 15266^T); Alicyclobacillus suci sp. nov (VF-FSL-W10-0049^T=DSM 112017^T=NCIMB 15265^T); and Alicyclobacillus fructus sp. nov. (FSL-W10-0059^T=DSM 112018^T=NCIMB 15264^T).

Synthetic antimicrobial peptides control Penicillium digitatum infection in orange fruits

Fungal contamination is among the main reasons for food spoilage, affecting food safety and the economy. Among fungi, Penicillium digitatum is a major agent of this problem. Here, the in vitro activity of eight synthetic antimicrobial peptides was assessed against P. digitatum, and their action mechanisms were evaluated. All peptides were able to inhibit fungal growth. Furthermore, atomic force and fluorescence microscopies revealed that all peptides targeted the fungal membrane leading to pore formation, loss of internal content, and death. The induction of high levels of reactive oxygen species (ROS) was also a mechanism employed by some peptides. Interestingly, only three peptides (PepGAT, PepKAA, and Mo-CBP₃-PepI) effectively control P. digitatum colonization in orange fruits, at a concentration (50 µg mL^-1) 20-fold lower than the commercial food preservative (sodium propionate). Altogether, PepGAT, PepKAA, and Mo-CBP₃-PepI showed high biotechnological potential as new food preservatives to control food infection by P. digitatum.

American artisan cheese quality and spoilage: A survey of cheesemakers' concerns and needs

Production of artisan cheeses, including surface-ripened cheeses, has increased in the United States over the past 2 decades. Although many of these cheesemakers report unique quality and spoilage problems during production, a systematic assessment of the quality concerns facing this sector of specialty cheese production has not been conducted. Here we report the effects of microbial spoilage and quality issues on US artisan cheese production. In a survey of 61 cheesemakers, the most common issues reported were undesirable surface molds (71%) and incorrect or unexpected colors or pigments on rinds (54%). When asked, 18% of participants indicated that they were extremely concerned about quality and spoilage problems, and they indicated that their quality standards are frequently not met, either annually (39%) or monthly (33%). Although most of the respondents (62%) said that just 0 to 5% of their cheese was lost or rendered less valuable due to quality issues annually, a small number (7% combined) reported large losses of 20 to 30% or >30% of their product lost or rendered less valuable. Almost all respondents (95%) agreed that improved quality would reduce waste, increase profits, and improve production. The survey respondents indicated in open response questions that they want access to more online resources related to quality issues and digital forums to discuss issues with experts and peers when problems arise. These findings represent the first attempt to document and estimate the effect of quality and spoilage on the American artisan cheese industry. Future work should investigate what technologies, interventions, or information could reduce losses from these problems.

Categorisation of culturable bioaerosols in a fruit juice manufacturing facility

Bioaerosols are defined as aerosols that comprise particles of biological origin or activity that may affect living organisms through infectivity, allergenicity, toxicity, or through pharmacological or other processes. Interest in bioaerosol exposure has increased over the last few decades. Exposure to bioaerosols may cause three major problems in the food industry, namely: (i) contamination of food (spoilage); (ii) allergic reactions in individual consumers; or (iii) infection by means of pathogenic microorganisms present in the aerosol. The aim of this study was to characterise the culturable fraction of bioaerosols in the production environment of a fruit juice manufacturing facility and categorise isolates as harmful, innocuous or potentially beneficial to the industry, personnel and environment. Active sampling was used to collect representative samples of five areas in the facility during peak and off-peak seasons. Areas included the entrance, preparation and mixing area, between production lines, bottle dispersion and filling stations. Microbes were isolated and identified using 16S, 26S or ITS amplicon sequencing. High microbial counts and species diversity were detected in the facility. 239 bacteria, 41 yeasts and 43 moulds were isolated from the air in the production environment. Isolates were categorised into three main groups, namely 27 innocuous, 26 useful and 39 harmful bioaerosols. Harmful bioaerosols belonging to the genera Staphylococcus, Pseudomonas, Penicillium and Candida were present. Although innocuous and useful bioaerosols do not negatively influence human health their presence act as an indicator that an ideal environment exists for possible harmful bioaerosols to emerge.

Bacterial Spore Inactivation in Orange Juice and Orange Peel by Ultraviolet-C Light

Spore-forming bacteria are a great concern for fruit juice processors as they can resist the thermal pasteurization and the high hydrostatic pressure treatments that fruit juices receive during their processing, thus reducing their microbiological quality and safety. In this context, our objective was to evaluate the efficacy of Ultraviolet-C (UV-C) light at 254 nm on reducing bacterial spores of Alicyclobacillus acidoterrestris, Bacillus coagulans and Bacillus cereus at two stages of orange juice production. To simulate fruit disinfection before processing, the orange peel was artificially inoculated with each of the bacterial spores and submitted to UV-C light (97.8-100.1 W/m²) with treatment times between 3 s and 10 min. The obtained product, the orange juice, was also tested by exposing the artificially inoculated juice to UV-C light (100.9-107.9 W/m²) between 5 and 60 min. A three-minute treatment (18.0 kJ/m²) reduced spore numbers on orange peel around 2 log units, while more than 45 min (278.8 kJ/m²) were needed to achieve the same reduction in orange juice for all evaluated bacterial spores. As raw fruits are the main source of bacterial spores in fruit juices, reducing bacterial spores on fruit peels could help fruit juice processors to enhance the microbiological quality and safety of fruit juices.

Combined effect of water activity and pH on the growth of food-related ascospore-forming molds

Purpose

The contamination of raw materials, packaging, or processing environments by fungal ascospores is a real concern for food industries, where variable rates of spoilage can be reached in pasteurized acidic products such as fruit juices, fruit jams, or soft drinks. The aim of this work was to assess the combined effect of aw and pH on the growth of six isolates from three genera of ascospore-forming molds that may occur in raw materials and in food industrial environments, in order to determine the environmental conditions that prevent the spoilage of pasteurized foods and beverages.

Methods

Growth tests were carried out on 60-day-old ascospores from Aspergillus hiratsukae (≡Neosartorya hiratsukae), Aspergillus thermomutatus (≡Neosartorya pseudofischeri), Chaetomium flavoviride, Chaetomium globosum, Talaromyces bacillisporus, and Talaromyces trachyspermus. The tests were performed up to 90 days at 25 °C, using sucrose solutions at different aw (0.85, 0.88, 0.92, 0.95) and pH (3.20, 3.50, 3.80, 4.20, 4.60) values. Growth was characterized by fitting an ordinary logistic regression model to the collected growth data.

Results

The explained percentage of the growth/no growth models ranged between 81.0 and 99.3%: aw exerted the largest influence on the growth of all tested species, while pH was significant only for Chaetomium isolates. The minimum conditions for germination and growth were aw 0.92 and pH 3.50 or 3.80, respectively, for C. flavoviride (46 days) and C. globosum (39 days), aw 0.92 and pH 3.20 for T. trachyspermus (13 days), aw 0.88 and pH 3.20 for T. bacillisporus (39 days), and aw 0.88 and pH 3.20 for the two aspergilli (33 and 27 days, respectively, for A. hiratsukae and A. thermomutatus).

Conclusions

Most of the spoiling mycetes tested were well-adapted to the formulations considered; therefore, foods strategies aiming to inhibit their growth should explore also the hurdle effect exerted by other factors (e.g., antioxidants, organic acids, oxygen levels).

Using extended Bigelow meta-regressions for modelling the effects of temperature, pH, °Brix on the inactivation of heat resistant moulds

The management of Heat Resistant Moulds (HRMs) is considered a great challenge for the juice fruit industry. Neosartorya, Byssochlamys and Talaromyces are three out of the main genera isolated from fruit juices that show great resistance to heat treatments. Several inactivation parameters can be found in the literature, however all of them were carried out in specific food matrices and using diverse inactivation methods. Thus, this meta-analysis study synthesizes the thermal resistance parameters of the three HRMs by adjusting extended Bigelow-based meta-regression models to data on inactivation experiments conducted in different liquid media. The meta-analytical data, extracted from publications between 1969 and 2017, was composed of decimal reduction time (D), inactivation method, temperature of inactivation, pH, °Brix, age of spores, and type of medium (model, juice, concentrates). Pooled D* values (D at 90 °C, pH 3.5 and 12° Brix) were estimated for B. fulva (1.95 min; 95% CI: 1.21-3.11 min), Talaromyces (4.03 min; 95% CI: 3.43-4.74 min), Neosartorya (0.5.35 min; 95% CI: 4.10-7.08 min), and B. nivea (10.32 min; 95% CI: 5.81-18.4 min). It was found that increasing the soluble solids in concentrates tends to cause a lower decrease in the heat resistance of Neosartorya and Talaromyces than increasing the soluble solids in model liquid or juices (p = 0.001; 0.012). In general, the screw-capped tubes and three neck round inactivation methods render higher D* values (p < 0.05) than the thermal death tubes, the polyethylene bag and the capillary methods. Spores of Talaromyces (overall z_pH = 7.56; 95% CI: 5.13-13.5) and Neosartorya (overall z_pH = 7.07; 95% CI: 5.04-10.8) appear to be more thermal sensitive to a decrease in medium pH than spores of Byssochlamys (overall z_pH = 4.34; 95% CI: 3.20-6.73). The meta-regression models presented in this study can be valuable for estimating pooled inactivation kinetic parameters to be used by the fruit juice industry in the management of thermal processes and in the determination of shelf-life.

Quantitative microbial spoilage risk assessment (QMSRA) of pasteurized strawberry purees by Aspergillus fischeri (teleomorph Neosartorya fischeri)

Aspergillus fischeri ascospores are known as potential spoilage microorganisms of pasteurized fruit products due to their high incidence in fruits, the ability to survive pasteurization and to grow in acidic conditions. This study aimed to develop a quantitative microbial spoilage risk assessment (QMSRA) model approach to estimate the spoilage risk of packaged strawberry purees due to A. fischeri under various scenarios regarding product formulation, processing and storage conditions. The development of the risk assessment comprised three steps: (1) initial contamination level of raw material by ascospores (N₀), (2) inactivation of ascospores during thermal processing (N_p) and (3) determination of the number of ascospores which are able to survive thermal processing and develop visible mycelia (D = 2 mm) during storage (N_f). Data of visible growth (t_v, days) comprised distributions previously obtained as function of water activity (a_w) (0.860-0.985), oxygen (0-21%), temperature (8-30 °C) and pasteurization (95-105 °C/15 s). The simulations were performed in triplicate with 100,000 iterations using the software R. The outcome "spoilage risk" was defined as the probability of having at least one ascospore (N_f) capable of forming visible colonies in 100 g-pack strawberry puree within the typical use-by dates. Overall, high probabilities of spoilage were estimated for purees pasteurized at milder treatments at 85 °C/15-60 s (67%) and 90 °C/15-60 s (≥40%) stored at ambient temperature (22 °C). The spoilage risk was only effectively reduced (0.02%) by increasing pasteurization conditions to 95 °C for at least 45 s. Moreover, the microbial stability of such purees, i.e., spoilage risk <0.001% (=less than 1 spoilage pack out of 10⁵ produced units) was predicted to occur for purees treated at 100 °C/15 s or stored at chilled conditions (≤8 °C) or at strict anaerobic conditions or produced as concentrates (a_w ≤ 0.860). Based on the outcomes obtained, a set of specifications for Heat-Resistant Moulds (HRMs) in raw material and pasteurized purees aimed to be used as an ingredient was suggested. Furthermore, the results can be used to support risk management decisions in identifying and quantifying the impact of possible interventions during formulation, processing and storage conditions of fruit purees to effectively reduce this risk.

Physiological alterations involved in inactivation of autochthonous spoilage bacteria in orange juice caused by Citrus essential oils and mild heat

This study investigated physiological alterations involved in the inactivation of Levilactobacillus (L.) brevis and Leuconostoc (Lc.) mesenteroides in orange juice caused by Citrus lemon essential oil (CLEO) and C. reticulata essential oil (CREO) alone and combined with mild heat treatment (MHT). Damage in DNA, membrane integrity, membrane potential, metabolic and efflux activity of bacterial cells were measured after exposure (6 and 12 min) to CLEO or CREO (0.5 μL/mL) and/or MHT (54 °C) using flow cytometry. Limonene was the major constituent in CLEO (66.4%) and CREO (89.4%). The size of the damaged cell subpopulations increased (p < 0.05) after longer exposure time and varied with the tested essential oil and/or bacterial isolate. After exposure to CLEO and CREO alone, the cell subpopulations with damage in measured physiological functions were in a range of 19.6-66.8% and 23.8-75.9%, respectively. Exposure to CREO resulted in larger Lc. mesenteroides cell subpopulations (35.4-68.7%) with damaged DNA, permeabilized and depolarized membrane and compromised metabolic or efflux activity compared to L. brevis (23.8-58.0%). In contrast, exposure to CLEO led to higher damaged L. brevis cell subpopulations (35.1-77%) compared to Lc. mesenteroides (25.3-36.6%). Exposure to combined treatments (CLEO or CREO and MHT) affected the measured physiological functions in almost the entire L. brevis and Lc. mesenteroides cell population (up to 99%), although the damage extension on each isolate varied with tested essential oil. Results show that inactivation of L. brevis and Lc. mesenteroides cells caused by CLEO and CREO alone and combined with MHT in orange juice involves a multi-target action, which causes DNA damage, altered permeability and depolarization of membrane and compromised metabolic and efflux activities.

Yeast biofilm in food realms: occurrence and control

In natural environments, microorganisms form microbial aggregates called biofilms able to adhere to a multitude of different surfaces. Yeasts make no exception to this rule, being able to form biofilms in a plethora of environmental niches. In food realms, yeast biofilms may cause major problems due to their alterative activities. In addition, yeast biofilms are tenacious structures difficult to eradicate or treat with the current arsenal of antifungal agents. Thus, much effort is being made to develop novel approaches to prevent and disrupt yeast biofilms, for example through the use of natural antimicrobials or small molecules with both inhibiting and dispersing properties. The aim of this review is to provide a synopsis of the most recent literature on yeast biofilms regarding: (i) biofilm formation mechanisms; (ii) occurrence in food and in food-related environments; and (iii) inhibition and dispersal using natural compounds, in particular.

Innovative Hurdle Technologies for the Preservation of Functional Fruit Juices

Functional nutrition, which includes the consumption of fruit juices, has become the field of interest for those seeking a healthy lifestyle. Functional nutrition is also of great interest to the food industry, with the aims of improving human health and providing economic prosperity in a sustainable manner. The functional food sector is the most profitable part of the food industry, with a fast-growing market resulting from new sociodemographic trends (e.g., longer life expectancy, higher standard of living, better health care), which often includes sustainable concepts of food production. Therefore, the demand for hurdle technology in the food industry is growing, along with the consumption of minimally processed foods, not only because this approach inactivates microorganisms in food, but because it can also prolong the shelf life of food products. To preserve food products such as fruit juices, the hurdle technology approach often uses non-thermal methods as alternatives to pasteurization, which can cause a decrease in the nutritional value and quality of the food. Non-thermal technologies are often combined with different hurdles, such as antimicrobial additives, thermal treatment, and ultraviolet or pulsed light, to achieve synergistic effects and overall quality improvements in (functional) juices. Hence, hurdle technology could be a promising approach for the preservation of fruit juices due to its efficiency and low impact on juice quality and characteristics, although all processing parameters still require optimization.

Microbial Contamination, an Increasing Threat to the Consumption of Fresh Fruits and Vegetables in Today's World

Microbes are found all over the globe with some few exceptions, including sterilized surfaces. They include normal flora that is nonpathogenic, which contribute to the larger percentage, and pathogenic species which are few. Hence, the activities of humans cannot be completely separated from microbes. Thus, many pathogenic microbes have found their way into fresh fruits and vegetables which are a great source of a healthy diet for humans. The growing demand for fresh fruits and vegetables has necessitated larger production. The larger production of vegetables within the shortest possible time to meet the growing demand has placed them at a higher risk of contamination with the pathogenic microbes, making the safety of consumers uncertain. Study of sources of contamination and type of pathogenic etiological agents isolated from fresh fruits and vegetables includes Bacillus cereus, Campylobacter jejuni, Clostridium botulinum, E. coli O157: H7, Listeria monocytogenes, Salmonella spp., Shigella, Staphylococcus, and Vibrio cholera. Several measures have proven to be effective in controlling contamination of microbes and they include the establishment of surveillance systems to monitor the production chain and thoroughly washing vegetables with vinegar water. Saltwater and other washing techniques are effective but caution should be taken to make sure one does not use one cycle of water for washing all vegetables. The consumption of fresh fruits and vegetables is still encouraged by this review but significant measures must be taken to check the safety of these products before consumption.

Development of the Saltatory Rolling Circle Amplification Assay for Rapid and Visual Detection of Alicyclobacillus acidoterrestris in Apple Juice

A novel nucleic acid isothermal amplification method based on saltatory rolling circle amplification (SRCA) for rapid and visual detection of Alicyclobacillus acidoterrestris in apple juice was established. Fourteen A. acidoterrestris strains and 44 non-A. acidoterrestris strains were used to confirm the specificity. The sensitivity of SRCA was 4.5 × 10¹ CFU/mL by observing the white precipitate with the naked eye, while it was 4.5 × 10⁰ CFU/mL by fluorescence visualization. The detection limit of SRCA in artificially inoculated apple juice was 7.1 × 10¹ and 7.1 × 10⁰ CFU/mL via visualization of the white precipitate and fluorescence, respectively. Compared with the traditional PCR method, SRCA exhibited at least a 100-fold higher sensitivity and 100-fold lower detection limit. Seventy samples were investigated for A. acidoterrestris contamination, and the results showed 100% sensitivity, 97.01% specificity, and 97.14% accuracy compared with those by the conventional microbiological cultivation method. Overall, this method is a potentially useful tool for visual and rapid detection of A. acidoterrestris.

Understanding spoilage microbial community and spoilage mechanisms in foods of animal origin

The increasing global population has resulted in increased demand for food. Goods quality and safe food is required for healthy living. However, food spoilage has resulted in food insecurity in different regions of the world. Spoilage of food occurs when the quality of food deteriorates from its original organoleptic properties observed at the time of processing. Food spoilage results in huge economic losses to both producers (farmers) and consumers. Factors such as storage temperature, pH, water availability, presence of spoilage microorganisms including bacteria and fungi, initial microbial load (total viable count-TVC), and processing influence the rate of food spoilage. This article reviews the spoilage microbiota and spoilage mechanisms in meat and dairy products and seafood. Understanding food spoilage mechanisms will assist in the development of robust technologies for the prevention of food spoilage and waste.

Tetranitrile-anthracene as a probe for fluorescence detection of viscosity in fluid drinks via aggregation-induced emission

An AIE-based fluorescent probe was developed for monitoring the viscosity change during the spoilage process of fluid drinks.

Fungal food spoilage of supermarkets' displayed fruits

Background and Aim:

Post-harvest fungal infection of fruits and vegetables is mainly caused by fungal pathogens that can be harmful to both human and animals as they produce mycotoxins, post-harvest diseases in fruits and vegetables are a serious problem that results in the loss of a large percentage of crops reaching 50% in some fruits. This study aims at screening the post-purchasing shelf-life of four highly consumed fruits and vegetables and at identifying the fungal strains behind their spoilage in Qatar.

Materials and Methods:

Fruits and vegetables were collected from the market to study their post-purchasing shelf-life and to identify the fungal types involved in samples rotting. Factors that affect samples’ shelf-life were also analyzed.

Results:

A total of 73 fungal isolates were isolated and identified, with the highest percentage of Penicillium (21.9%) followed by Rhizopus (17.8%). Interestingly, many mycotoxins producing and diseases inducing fungi were identified in this study; this includes Rhizopus, Aspergillus, Penicillium, Alternaria, Fusarium, Cladosporium, Botrytis, Geotrichum, and Colletotrichum. Statistical analysis shows that different fruits have significantly different shelf-life and different predispositions for spoilage. In many cases, a strong relationship was shown between the fungal types isolated and the country of origin of the fruit. Finally, the price of the commodity did not have a significant effect on its contamination level nor did the market from which the sample was purchased. This indicates that the fruit displaying methods in Qatar do not affect their contamination level.

Conclusion:

The study is among the first reports about fungal types involved in fruits and vegetables rotting in Qatar and it highlights the strong link between spoiling fungi and their country of origin.

Control of Autochthonous Spoilage Lactic Acid Bacteria in Apple and Orange Juices by Sensorially Accepted Doses of Citrus Spp. Essential Oils Combined with Mild Heat Treatments

This study assessed the compromised acceptance threshold (CAT) and rejection threshold (RT) of Citrus lemon (CLEO) and Citrus reticulata essential oil (CREO) in apple and orange juices. The efficacy of CLEO and CREO concentrations below the RT were evaluated alone and combined with mild heat treatment (MHT) (54 °C, up to 12 min) to inactivate the autochthonous spoilage bacteria Lactobacillus brevis, Lactobacillus plantarum, and Leuconostoc mesenteroides in apple and orange juices. The CAT of CLEO and CREO varied from 0.15 to 0.17 μL/mL in orange and apple juices. The RT of CLEO was approximately 0.58 μL/mL in apple and orange juices, and the RT of CREO was 0.68 μL/mL in both juices. When CLEO and CREO were assayed alone, the highest concentration (0.50 μL/mL) decreased counts of all strains approximately 2 log₁₀ CFU/mL after 12 min of exposure to 54 °C. All concentrations of CLEO or CREO in combination with MHT acted synergistically against L. brevis, L. plantarum, and L. mesenteroides. Decreases in counts varied with the strain, CLEO and CREO concentrations, juice type, and exposure time to the combined treatment. CREO was more effective than CLEO in combination with MHT against the strains in apple and orange juices. Effective combinations of CLEO or CREO with MHT to control the autochthonous spoilage bacteria did not compromise the quality parameters (°Brix, pH, and titratable acidity) that characterize unsweetened juices. These results indicate CLEO or CREO at concentrations below the sensory RT in combination with MHT as a feasible technology to control autochthonous spoilage bacteria in fresh fruit juices. PRACTICAL APPLICATION: The present study provides novel information concerning the efficacy of sensorially accepted doses of CLEO and CREO combined with MHT against autochthonous spoilers in fruit juice. The valuable synergistic effects that can be observed when combining CLEO and CREO with MHT reveal a feasible preservation technology and alternative to traditional treatments that are successful because they help reduce treatment intensity, thereby avoiding adverse effects on the sensory, physicochemical, and nutritional properties of these products.

Fungal Spoilage in Food Processing

Food processing, packaging, and formulation strategies are often specifically designed to inhibit or control microbial growth to prevent spoilage. Some of the most restrictive strategies rely solely or on combinations of pH reduction, preservatives, water activity limitation, control of oxygen tension, thermal processing, and hermetic packaging. In concert, these strategies are used to inactivate potential spoilage microorganisms or inhibit their growth. However, for select microbes that can overcome these controls, the lack of competition from additional background microbiota helps facilitate their propagation.