Microbiology of potatoes and potato products: a review

Effect of harvest-to-cooling delay and precooling on Kufri Jyoti (Solanum tuberosum) potato quality

Precooling is the rapid removal of field heat in harvested crops to preserve their quality and increase their shelf life. The following study was conducted to understand the importance of precooling and to optimize the precooling condition to extend the storage life of potatoes. Therefore, the study was divided into two components. In the first part, the Kufri Jyoti potatoes were subjected to field heat for 0-64 h, then were precooled for 48 h before sending to cold storage for 60 days. The results demonstrated that when the time delay was doubled, starch content (SC) decreased by 15.86%, reducing sugar content (RSC) increased by 32.71%, ascorbic acid content (AAC) decreased by 5.94% and total plate count (TPC) increased by 20.06%. Microstructural changes in potatoes due to the exposure to field heat were visible in SEM images. These results suggested a decrease in the quality of potatoes with an increase in time delay between harvest and cooling. In the second part of the study, the potatoes were precooled for 48 h at different temperatures (T) (6 °C, 8 °C, and 10 °C) and relative humidity (RH) (87%, 91%, and 95%), and their effect was studied on the same quality parameters after storage. Regression models were developed for each response, and models with non-significant lack of fit were selected for optimization. The analysis of the observations has shown that precooling aided in better quality retention of potatoes during cold storage.

Expression pattern of Stlhcb gene family in potato and effects of overexpression of Stcp24 gene on potato photosynthesis

Potato is one of the four staple food crops in the world. It has a wide range of cultivation, high yield, and high nutritional value. Enhancing the photosynthesis of potato is particularly important as it leads to an increase in the potato yield. The light-harvesting pigment-binding protein complex is very important for plant photosynthesis. We identified 12 Stlhcb gene family members from the potato variety "Atlantic" using transcriptome sequencing and bioinformatics. The proteins encoded by the Stlhcb gene family have between 3358 and 4852 atomic number, a relative molecular weight between 24060.16 and 34624.54 Da, and an isoelectric point between 4.99 and 8.65. The RT-qPCR results showed that the 12 Stlhcb genes were expressed in a tissue-specific and time-dependent fashion under low light. The relative expression of the Stlhcb genes in the leaves was significantly higher than that in the stems and roots, and the relative expression of these genes first increased and then decreased with the prolongation of light exposure time. The Stcp24 gene with the highest expression was cloned, and an expression vector was constructed. A subcellular localization analysis was performed in tobacco and an overexpression experiment was performed in potato using an Agrobacterium-mediated method. The subcellular localization analysis showed that the protein encoded by Stcp24 was located in chloroplasts as expected. Overexpression of Stcp24 in transgenic potato increased the yield of potatoes and the content of chlorophyll a and b; increased the net photosynthetic rate, transpiration rate, stomatal conductance, electron transport efficiency, and semi-saturated light intensity; and promoted photosynthesis and plant growth. This study provides a reference for the study of the function of the potato light-harvesting pigment-binding protein gene family. It lays a foundation for further study of the mechanism of the photosynthesis of potato, improvement of the light energy utilization of potato, and molecular breeding of potato.

Alternative proteins for meat and dairy replacers: Food safety and future trends

Traditionally, meat and dairy products have been important protein sources in the human diet. Consumers are eating more plant-based proteins, which is reflected in current market trends. Assessing how alternative proteins are processed and their impact on food safety helps realize market opportunities while ensuring food safety. In this review, an analysis of the food safety hazards, along with current industry trends and processing methods associated with alternative proteins for meat and dairy products for the European Union market is described. Understanding the effects of processing and safety alternative proteins is paramount to ensuring food safety and understanding the risks to consumers. However, the data here is limited. With the expected further increase in protein alternatives in consumers' diets, the risk of food allergens is apparent. The occurrence of processing contaminants in plant-based alternatives may occur, along with anti-nutritional compounds, which interfere with the absorption of nutrients. Further, typical food safety hazards related to the plant, the product itself, or processing are relevant. Although hazards in insects and seaweed are being addressed, other protein alternatives like cultured meat and SCPs warrant attention. Our findings can aid industry and governmental authorities in understanding current trends and prioritizing hazards for future monitoring.

Examples of potato epidermis endophytes and rhizosphere microbes that may be human pathogens contributing to potato peel colic

Potato tubers defend themselves against herbivores with endogenous secondary compounds such as solanine and scopolamine. They also recruit endophytes and members of the tuberosphere to repel herbivores. Many of these endophyte defence features are overcome by cooking, with some notable exceptions that have been identified by rDNA analysis of potato peel samples and may account for some previously unrecognised features of potato peel colic. This is relevant regarding the rather modern way of cooking, where the potato peel is left intact in food and consumed.

First Report of a Foodborne Providencia alcalifaciens Outbreak in Kenya

Providencia alcalifaciens is an emerging bacterial pathogen known to cause acute gastroenteritis in children and travelers. In July 2013, P. alcalifaciens was isolated from four children appearing for diarrhea at Kiambu District Hospital (KDH) in Kenya. This study describes the outbreak investigation, which aimed to identify the source and mechanisms of infection. We identified seven primary and four secondary cases. Among primary cases were four mothers who had children and experienced mild diarrhea after eating mashed potatoes. The mothers reported feeding children after visiting the toilet and washing their hands without soap. P. alcalifaciens was detected from all secondary cases, and the isolates were found to be clonal by random amplified polymorphic DNA (RAPD) fingerprinting. Our study suggests that the outbreak was caused by P. alcalifaciens, although no fluid accumulation was observed in rabbit ileal loops. The vehicle of the outbreak was believed to be the mashed potato dish, but the source of P. alcalifaciens could not be confirmed. We found that lack of hygiene, inadequate food storage, and improper hand washing before food preparation was the likely cause of the current outbreak. This is the first report of a foodborne infection caused by P. alcalifaciens in Kenya.

Industrially processed vacuum-packed peeled Kennebec potatoes: process optimization, sensory evaluation, and consumer response

To optimize the processing and storage of Kennebec potatoes for sale in peeled, vacuum-packed ready-to-cook form, we studied the effects of blanching, various anti-browning solutions, and storage temperature. Unblanched potatoes pretreated with a mixture of 1% ascorbic acid and 0.5% citric acid, and stored at 2 °C, were found to have a shelf life of at least 1 mo without browning. Potatoes so treated differed sensorially from fresh potatoes, but were well received by consumers.

PRACTICAL APPLICATION

The process described here maintains the characteristics of fresh potato with all the amenities of a processed product.

Potential microbial risk factors related to soil amendments and irrigation water of potato crops

AIMS

This study assesses the potential microbial risk factors related to the use of soil amendments and irrigation water on potato crops, cultivated in one traditional and two intensive farms during two harvest seasons.

METHODS AND RESULTS

The natural microbiota and potentially pathogenic micro-organisms were evaluated in the soil amendment, irrigation water, soil and produce. Uncomposted amendments and residual and creek water samples showed the highest microbial counts. The microbial load of potatoes harvested in spring was similar among the tested farms despite the diverse microbial levels of Listeria spp. and faecal coliforms in the potential risk sources. However, differences in total coliform load of potato were found between farms cultivated in the autumn. Immunochromatographic rapid tests and the BAM's reference method (Bacteriological Analytical Manual; AOAC International) were used to detect Escherichia coli O157:H7 from the potential risk sources and produce. Confirmation of the positive results by polymerase chain reaction procedures showed that the immunochromatographic assay was not reliable as it led to false-positive results.

CONCLUSIONS

The potentially pathogenic micro-organisms of soil amendment, irrigation water and soil samples changed with the harvest seasons and the use of different agricultural practices. However, the microbial load of the produce was not always influenced by these risk sources. Improvements in environmental sample preparation are needed to avoid interferences in the use of immunochromatographic rapid tests.

SIGNIFICANCE AND IMPACT OF THE STUDY

The potential microbial risk sources of fresh produce should be regularly controlled using reliable detection methods to guarantee their microbial safety.

Prevalence and genetic diversity of Bacillus cereus in dried red pepper in Korea

Bacillus cereus is a foodborne spore-forming bacterial pathogen that is ubiquitous in the natural environment. Infections with this pathogen manifest as diarrheal or emetic types of food poisoning. In this study, 140 samples of dried red pepper purchased in Korea were assayed for the presence of B. cereus according to the U.S. Food and Drug Administration standard culture method. A multiplex PCR assay was developed for the rapid confirmation of B. cereus as an alternative to conventional biochemical confirmation tests. The genetic diversity of B. cereus isolates was investigated using a random amplified polymorphic DNA (RAPD) assay. B. cereus was found in 84.3% of the dried red pepper samples, with an average concentration of 1.9 x 10(4) CFU/g. B. cereus could be detected and distinguished from B. thuringiensis in the multiplex PCR assay by using the BCFW1 plus BCrevnew and the K3 plus K5 primer sets designed to detect the gyrB gene of B. cereus and B. thuringiensis and the cry gene of B. thuringiensis. A RAPD assay using the OPG 16 and MUP 3 primers was used to successfully distinguish among isolates, thus elucidating the genetic diversity of B. cereus isolates. The discriminating ability of the OPG 16 primer (142 types) was about threefold higher than that of MUP 3 (52 types) in the RAPD assay.

Presence and significance of Bacillus cereus in dehydrated potato products

Dehydrated potato contains Bacillus cereus at a prevalences of 10 to 40% and at numbers usually less than 10(3) CFU g(-1). B. cereus in dehydrated potato is likely to be present as spores that are able to survive drying of the raw vegetable and may represent a significant inoculum in the reconstituted (rehydrated) product where conditions favor germination of, and outgrowth from, spores. Holding rehydrated mashed potato alone, or as part of another product (e.g., potato-topped pie), at temperatures above 10 degrees C and below 60 degrees C may allow growth of vegetative B. cereus. Levels exceeding 10(4) CFU g(-1) are considered hazardous to human health and may be reached within a few hours if stored inappropriately between these temperatures. Foods incorporating mashed potato prepared from dehydrated potato flakes have been implicated in B. cereus foodborne illness. This review is a summary of the information available concerning the prevalence and numbers of B. cereus in dehydrated potato flakes and the rate at which growth might occur in the rehydrated product.

Microflora of minimally processed frozen vegetables sold in Gaborone, Botswana

Two hundred samples of minimally processed, frozen, and prepacked potato chips, peas, corn, and a variety of combined vegetables from supermarkets in Gaborone, Botswana, were examined microbiologically. Determination of aerobic mesophilic plate count, aerobic psychrotrophic plate count, lactic acid bacteria, yeasts and molds, coliforms, Listeria spp., and Staphylococcus aureus were done. Chips had the lowest mean log values for all of the microorganisms enumerated except yeasts and molds. The mean log values for single vegetables ranged from 3.6 to 9.1, 3.4 to 8.9, 2.9 to 5.6, and 2.1 to 6.5 log CFU/ g aerobic mesophilic plate count, aerobic psychrotrophic plate count, lactic acid bacteria, and yeasts and molds, respectively. The microbial profiles of peas and corn were almost similar (P < 0.001). The mean values for combined vegetables were clustered within 4.6 and 5.4 and 4.2 and 5.2 log CFU/g aerobic mesophilic plate count and aerobic psychrotrophic plate count, respectively. All of the vegetables had a coliform population distribution ranging from 0 to < 10(4) most probable number per g. The predominant gram-negative bacteria isolated included members of Enterobacteriaceae and Pseudomonaceae (86.2%). Escherichia coli was not detected in all of the samples. The organisms isolated included those responsible for spoilage in frozen vegetables, namely Pseudomonas, Klebsiella, Corynebacterium, lactic acid bacteria, and Flavobacterium. The predominant lactic acid bacteria were Lactobacillus spp. (55.9%). Other spoilage organisms were yeasts, and Cryptococcus spp. (55.4%) was predominant. Pathogens, namely Listeria monocytogenes, were also isolated at a rate of 2 to 10%, of which 4% was from corn, 2% each from peas and country crop, and 10% from stir-fry. Bacillus cereus was also isolated and accounted for 7.7% of the microorganisms from corn. S. aureus was isolated from all of the vegetables. Enterotoxigenic strains were from corn, peas, mixed vegetables, and stir-fry, and all of them produced enterotoxin A. In addition, the isolates from stir-fry vegetables also produced enterotoxins B and C. The study reveals the presence of pathogens and emerging opportunistic pathogens in the ready-to-use or ready-to-eat vegetables. If E. coli is the only indicator for safety and acceptability, consumers may be exposed to foodborne diseases. Inclusion of other groups as indicator organisms is suggested. Retailers are urged to invest in standby generators to maintain the cold chain.

Presence and growth of Bacillus cereus in dehydrated potato flakes and hot-held, ready-to-eat potato products purchased in New Zealand

Potato products prepared from dehydrated potato flakes have been implicated in foodborne illness incidents involving Bacillus cereus intoxications. B. cereus can survive as spores in potato flakes and can germinate and multiply in the rehydrated product. This study assessed the frequency and concentration of B. cereus in dehydrated potato flakes and hot-held, ready-to-eat mashed potato products. Of 50 packets of potato flakes tested, eight contained greater than 100 CFU/g B. cereus (maximum 370 CFU/g). The temperature of the potato portion of 44 hot-held food products was measured immediately after purchase, and 86% were below the safe hot-holding temperature of 60 degrees C. The potato portions were subsequently tested for B. cereus. Only two of the potato portions contained B. cereus at greater than 100 CFU/g, a potato-topped pastry (1000 CFU/g) and a container of potato and gravy (120 CFU/g). To assess multiplication of B. cereus in this food, we held rehydrated potato flakes with naturally occurring B. cereus at 37, 42, and 50 degrees C and tested them over 6 h. By 6 h, the number of B. cereus in potato stored at 37 degrees C had exceeded 10(3) CFU/g, was greater than 10(4) CFU/g at 50 degrees C, and was close to 10(6) CFU/g at 42 degrees C. Growth data were compared to predictions from the U.S. Department of Agriculture Pathogen Modeling Program (PMP 7.0). The PMP predictions were found to simulate the measured growth better at 42 degrees C than at 37 degrees C. Hot-held potato products should be safe for consumption if held at 60 degrees C or above or discarded within 2 h.

Prevalence of Clostridium species and behaviour of Clostridium botulinum in gnocchi, a REPFED of italian origin

Sales and consumption of refrigerated processed foods of extended durability (REPFEDs) have increased many-fold in Europe over the last 10 years. The safety and quality of these convenient ready-to-eat foods relies on a combination of mild heat treatment and refrigerated storage, sometimes in combination with other hurdles such as mild preservative factors. The major hazard to the microbiological safety of these foods is Clostridium botulinum. This paper reports on the prevalence and behaviour of proteolytic C. botulinum and non-proteolytic C. botulinum in gnocchi, a potato-based REPFED of Italian origin. Attempts to isolate proteolytic C. botulinum and non-proteolytic C. botulinum from gnocchi and its ingredients were unsuccessful. Based on assessment of the adequacy of the methods used, it was estimated that for proteolytic C. botulinum there was < 25 spores/kg of gnocchi and < 70 spores/kg of ingredients. The total anaerobic microbial load of gnocchi and its ingredients was low, with an estimated 1 MPN/g in processed gnocchi. Most of the anaerobic flora was facultatively anaerobic. A few obligately anaerobic bacteria were isolated from gnocchi and its ingredients and belonged to different Clostridium species. The protection factor, number of decimal reductions in the probability of toxigenesis from a single spore, was determined for eight different gnocchi formulations by challenge test studies. For all gnocchi stored at 8 degrees C (as recommended by the manufacturer) or 12 degrees C (mild temperature abuse), growth and toxin production were not detected in 75 days. The protection factor was >4.2 for proteolytic C. botulinum, and >6.2 for non-proteolytic C. botulinum. When inoculated packs were stored at 20 degrees C (severe temperature abuse), toxin production in 75 days was prevented by the inclusion of 0.09% (w/w) sorbic acid (protection factors as above), however in the absence of sorbic acid the packs became toxic before the end of the intended shelf-life and the protection factors were lower. Providing sorbic acid (0.09% w/w) is included in the gnocchi, the safety margin would seem to be very large with respect to the foodborne botulism hazard.

Effective use of nisin to control Bacillus and Clostridium spoilage of a pasteurized mashed potato product

Heat-resistant spore-forming bacteria such as Bacillus and Clostridium can survive and grow in cooked potato products. This situation represents both a public health problem and an economic problem. The natural food preservative nisin is used in heat-treated foods to prevent the growth of such bacteria. A cocktail of Clostridium sporogenes and Clostridium tyrobutyricum spores was inoculated into cooked mashed potatoes, which were vacuum packed, pasteurized, and incubated at 8 and 25 degrees C. The shelf life of the mashed potatoes at 25 degrees C was extended by at least 58 days with the addition 6.25 microg of nisin per g. At 8 degrees C, in control samples not containing nisin, the natural contaminant Bacillus grew, but the inoculated Clostridium strains did not until the temperature was raised to 20 degrees C after 39 days. No bacterial growth occurred in nisin-containing samples. The shelf life of the mashed potatoes was extended by at least 30 days with 6.25 microg of nisin per g. In trials involving a cocktail of Bacillus cereus and Bacillus subtilis strains, 6.25 microg of nisin per g extended the shelf life of mashed potato samples that were not vacuum packed by at least 27 days at 8 degrees C. At 25 degrees C, 25 microg of nisin per g extended shelf life by a similar period. Shelf life extension was also observed at lower nisin levels. Microbiological analysis of the mashed potato ingredients showed that a high spore level was associated with the onion powder. It is emphasized that the preservative and the ingredients must be well mixed to ensure good nisin efficacy. Nisin remained at effective levels after pasteurization, and good retention was observed throughout the shelf life of the mashed potatoes.