Moulds and yeasts in fresh and minimally processed vegetables, and sprouts

A limited survey of fresh and minimally processed vegetables, and sprouts was conducted in the Washington, DC area to determine if potentially toxigenic and pathogenic fungi were present in these commodities. Thirty-nine ready-to-eat salads, 29 whole fresh vegetables and 116 sprout samples (bean, alfalfa, broccoli, crunchy, garlic, spicy, onion, clover, lentil and multi-seed sprouts) were purchased from 13 local supermarkets and tested for yeast and mould counts as well as the presence of toxigenic moulds. Yeasts were the most prevalent organisms found in these samples, at levels ranging from less than 100 to 4.0x10(8) cfu/g. Mould counts generally ranged from less than 100 to 4.0x10(4) cfu/g. Two crunchy sprout samples, however, contained unusually high numbers of Penicillium (1.1x10(8) and 1.3x10(8) cfu/g), two alfalfa sprout samples contained Geotrichum populations about 10(6) cfu/g, and two alfalfa sprout samples had Cladosporium counts higher than 2.5x10(5) cfu/g. The most common moulds found in fresh and minimally processed vegetables were Cladosporium, Alternaria and Penicillium; less common was Geotrichum. The most frequently isolated moulds from sprouts were Alternaria, Cladosporium, Penicillium, and Phoma. Phoma was especially common in alfalfa sprouts. Fusarium, Rhizopus, Mucor, and Geotrichum were isolated less often.     

Microbial evaluation of minimally processed vegetables and sprouts produced in Seoul, Korea

The aim of this study was to evaluate the microbial quality of some minimally processed vegetables. A total of 345 samples of minimally processed vegetables were acquired at a department store, a local supermarket, and a restaurant in Seoul, Korea. Samples were tested for microorganism distributions and for the presence of pathogenic bacteria. The aerobic mesophilic counts ranged between 2.0 and 9.7 log CFU/g, with the highest count recorded from the sprouts. Counts of psychrotrophic microorganisms were as high as those of the mesophilic microorganisms. Total coliform populations between 1.0 and 8.8 log CFU/g were found in 98.3% of the samples. Microbiological counts for fresh-cut fruits were very low. Sprouts were highly contaminated with microorganisms and showed a high incidence of Escherichia coli and Clostridium perfringence. Salmonella species and Listeria monocytogenes were detected in 1.5 and 0.3% of samples, respectively. E. Coli O157:H7 and Yersinia enterocolitica were not detected in any of the samples.     

Survey of nitrate and nitrite contents of vegetables grown in Korea.

A scientific basis for the evaluation of the risk to public health arising from excessive dietary intake of nitrate in Korea is provided. The nitrate () and nitrite () contents of various vegetables (Chinese cabbage, radish, lettuce, spinach, soybean sprouts, onion, pumpkin, green onion, cucumber, potato, carrot, garlic, green pepper, cabbage and Allium tuberosum Roth known as Crown daisy) are reported. Six hundred samples of 15 vegetables cultivated during different seasons were analysed for nitrate and nitrite by ion chromatography and ultraviolet spectrophotometry, respectively. No significant variance in nitrate levels was found for most vegetables cultivated during the summer and winter harvests. The mean nitrates level was higher in A. tuberosum Roth (5150 mg kg(-1)) and spinach (4259 mg kg(-1)), intermediate in radish (1878 mg kg(-1)) and Chinese cabbage (1740 mg kg(-1)), and lower in onion (23 mg kg(-1)), soybean sprouts (56 mg kg(-1)) and green pepper (76 mg kg(-1)) compared with those in other vegetables. The average nitrite contents in various vegetables were about 0.6 mg kg(-1), and the values were not significantly different among most vegetables. It was observed that nitrate contents in vegetables varied depending on the type of vegetables and were similar to those in vegetables grown in other countries. From the results of our studies and other information from foreign sources, it can be concluded that it is not necessary to establish limits of nitrates contents of vegetables cultivated in Korea due to the co-presence of beneficial elements such as ascorbic acid and alpha-tocopherol which are known to inhibit the formation of nitrosamine.     

Effectiveness of edible coatings combined with mild heat shocks on microbial spoilage and sensory quality of fresh cut broccoli (Brassica oleracea L.)

The use of edible coatings and mild heat shocks is proposed as postharvest treatments to prevent microbial deterioration of refrigerated broccoli. Minimally processed broccoli was coated with either chitosan or carboxymethyl-cellulose (CMC) combined or not with a previous application of a mild heat shock. The evolution of microbial populations (mesophilic, psycrotrophic, Enterobacteriaceae, molds and yeast, and lactic acid bacteria) was studied during 20 d of storage and fitted to Gompertz and logistic models. Results revealed that, at the end of the storage, chitosan coating significantly reduced all microbiological population counts, except lactic acid bacteria; while higher reduction was observed with chitosan coating combined with a heat shock treatment. A significant delay at the beginning of the exponential phase was observed for all the bacterial populations analyzed. On the other hand, CMC coating, with and without a previous thermal treatment, did not exert any antibacterial effect. Excellent agreement was found between experimental microbial counts and predicted values obtained from Gompertz and logistic models. Kinetic modeling was found to be valuable for prediction of microbiological shelf life of broccoli during storage. Results showed that the application of chitosan coating effectively maintained microbiological quality and extended shelf life of minimally processed broccoli. According to these results, the use of the edible chitosan coating alone or in combination with a heat mild shock appear to be a viable alternative for controlling microbiological growth and sensory attributes in minimally processed broccoli. PRACTICAL APPLICATION: The continuous consumer interest in high quality and food safety, combined with environmental concern has induced to the development and study of edible coatings that avoid the use of synthetic materials. The edible coatings, formed from generally recognized as safe materials, have the potential to reduce weight loss, respiration rate, and improve food appearance and integrity. It is one of the most effective methods to maintain food quality. On the other hand, heat treatments have been demonstrated to be effective as a nonchemical means of improving postharvest quality for a variety of horticultural products. The applications of mild heat shocks combined with edible coatings constitute an alternative for the natural preservation of crops for which the use of synthetic chemicals is objectionable.     

EFFECT OF CHLORINE TREATMENT ON CUT WATER CRESS AND ONION

Chlorine treatment was evaluated for cut vegetables to reduce microbial populations and improve keeping quality. Water cress and onion were selected because they are representative vegetables having high potential for processing into cut prepared products. Cut water cress had a high initial microbial contamintion of 10^7.5 cfu/g, while cut onion had only 10^1.7 cfu/g. The cut produce was treated by soaking in chlorine solutions of different concentrations at 25C for 1 min. Treatment with ≤100 ppm chlorine effectively reduced the microbial load of the produce without significant quality losses. High concentrations of chlorine resulted in greater microbial proliferation after 7 days, ascorbic acid destruction and significant color change in stored cut vegetables. The effectiveness of chlorine treatment was limited to short-term storage of precut vegetables, and did not provide extended shelf-life.     

The effect of packaging treatment on the storage quality of minimally processed bunched onions

Storage quality of minimally processed (MP) bunched onions, as affected by plastic film packaging, was investigated to determine the optimum packing method for this vegetable product. Five different packaging treatments, including two passive modified atmosphere packaging (MAP), two active MAP and a moderate vacuum packaging (MVP), were used for MP bunched onions. Quality attributes of the samples were evaluated periodically in terms of weight loss, colour, decay ratio, microbial counts and sensory properties during storage at 10 °C for 28 days. Various sealed‐packaging treatments did not significantly influence changes in colour of white stem and green leaf tissues, flesh weight loss and microbiological populations including mesophiles, psychrotrophs and lactic acid bacteria. However, sensory attributes and disease incidence were affected by packaging type. MVP with a gas‐permeable plastic film retained better quality bunched onions, with reduced microbial decay and visual sensory aspects, as compared with the other packages.     

Role of precursors on greening in crushed garlic (Allium sativum) bulbs, and its control with freeze-dried onion powder

BACKGROUND: Lachrymatory factor (LF) synthase in onion bulbs reacts with S‐1‐propenyl‐L ‐cysteine sulfoxide (1‐PeCSO), a key compound in garlic greening. In this study, freeze‐dried onion powder containing LF synthase was used in treatments to control garlic greening. Prior to the use of freeze‐dried onion powder to treat greening garlic bulbs, model reactions were conducted to confirm the reactivity of 1‐PeCSO in onion bulbs to garlic greening. RESULTS: While pink pigments were generated from 1‐PeCSO, green pigments were produced from the combination of 1‐PeCSO and S‐2‐propenyl‐L ‐cysteine sulfoxide (2‐PeCSO). However, pigments were formed in the systems containing 1‐PeCSO, amino acid and alliinase. Even non‐greening garlic bulbs stored at 20 °C turned green with the reaction of 200 g L^?1 1‐PeCSO; therefore 1‐PeCSO isolated from onion bulbs had the same role as 1‐PeCSO in garlic bulbs in terms of greening. Onion bulbs turned green after the addition of 600 g L^?1 2‐PeCSO. The addition of freeze‐dried onion powder inhibited garlic greening, and treatment with 15 g kg^?1 onion powder gave the best storage stability of crushed garlic bulbs. CONCLUSION: The addition of freeze‐dried onion powder inhibited the greening in crushed garlic bulbs, and treatment with 15 g kg^?1 onion powder gave the best storage stability of crushed garlic bulbs. Copyright © 2011 Society of Chemical Industry     

Radiation processing of minimally processed sprouts (dew gram and chick pea): effect on sensory,nutritional and microbiological quality

Sprouts have become an important part of the diet because of their nutritive value and low‐calorie content. The effect of radiation processing (1 and 2 kGy dose) on minimally processed dew gram and chick pea sprouts with respect to different quality parameters was studied over a storage period of 16 days at 8 °C. Radiation treatment and storage period did not have any significant effect on the sensory as well as nutritional qualities of irradiated dew gram and chick pea sprout. No significant change (P > 0.05) was observed in the colour and firmness of irradiated sprouts as compared to control samples. However, radiation processing resulted in significant reduction in aerobic plate counts (APC), coliform counts (CC), yeast and mould count (YMC) and staphylococci counts (SC). Radiation processing of dew gram and chick pea sprouts at 1 and 2 kGy extends the shelf life without affecting sensory and nutritional qualities.     

Evaluation of a pre-cut heat treatment as an alternative to chlorine in minimally processed shredded carrot

The effect of a pre-cut heat treatment (100 °C/45 s) as an alternative decontamination treatment to chlorinated-water (200 ppm active chlorine/1 min, 5 °C) was evaluated in minimally processed carrot (shredded). The quality of shredded carrots was studied just after minimal processing and during storage at 5 °C (10 days) by evaluating microbial (total mesophilic aerobic, yeast and moulds and lactic acid bacteria counts), physical–chemical (soluble solids content, pH, titratable acidity, whiteness index), physiological (peroxidase activity and headspace analysis) and sensorial attributes (colour, fresh-like appearance, aroma and general acceptance). The relationships between sensory perception of undesired changes, microbial contamination threshold, physico-chemical and physiological indices were investigated and compared between heat-treated and control samples. The use of heat in pre-cut carrot proved to be more efficient than chlorinated-water concerning microbial control (threshold concentration of 7 Log₁₀ cfu g^? 1), providing an acceptable fresh-like quality product during 10 days of storage (5 °C), which corresponds to a 3-day shelf-life extension compared to control samples. Heat-treated shredded carrot showed lower respiratory and POD activities than chlorinated samples suggesting that the use of heat provides a metabolic activity lowering effect besides the microbial effect which could be important to shelf-life extension of the fresh-cut product.Industrial relevanceIn minimally processed vegetables, namely in shredded carrot, chlorine solutions have been widely used by the industry for sanitization purposes. However, reduced microbiological efficiency allied to sensorial changes and eventual formation of carcinogenic chlorinated compounds pointed out the need for alternative decontamination methodologies. Also, the evermore conscious consumers are demanding minimization of the potentially negative impact of food processing on human health and the environment. From the practical experience of a fresh-cut industry directly involved in the R&D research project which supported this study, the marketability of minimally processed shredded carrot is limited due to rapid microbial growth and colour loss (decrease of orange intensity and/or whitening of the shreds). As a result, a pilot-plant scale study was performed, evaluating quality attributes of shredded carrot processed according to a clean pre-cut alternative decontamination process.     

不同蔬菜对保加利亚乳杆菌生长的影响

为了说明发酵蔬菜制品中的浆水菜在发酵过程中发酵菌对原料蔬菜的选择性,以保加利亚乳杆菌(Lactobacillus bulgaricus)为菌种,以48种常见蔬菜为原料,按照浆水菜制作工艺,实验研究了菌体在添加不同蔬菜中的生长的情况。结果表明,添加白萝卜、黄瓜、山药、番茄、胡萝卜、小白菜、小青菜、油麦菜、芹菜、冬瓜等蔬菜的,保加利亚乳杆菌生长的很好,菌体浓度均可达到108cfu/mL以上;添加土豆、菠菜、海带、黄豆芽、油菜、芥菜、苦菊、芥蓝、茴香、菜花、莴笋、茄子、南瓜、西葫芦、苜蓿等蔬菜的,保加利亚乳杆菌有生长,菌体浓度在107cfu/mL左右;添加平菇、空心菜、生菜、大葱、蒜苔、青椒、大白菜、西兰花、茼蒿、韭菜、香椿、地瓜、紫薯、莲藕、娃娃菜、荷兰豆、苦瓜、紫甘蓝、丝瓜、冬笋、豇豆、香菜、洋葱等蔬菜的保加利亚乳杆菌没有生长。      

Physicochemical Properties,and Antioxidant and Antimicrobial Effects of Garlic and Onion Powder in Fresh Pork Belly and Loin during Refrigerated Storage

ABSTRACT: Pork loin and belly cuts were pumped to 110% of their original weight with solutions containing 5% of various ingredients (sodium ascorbate, garlic, and onion powder), and evaluated the physicochemical properties, and antioxidant and antimicrobial activities during refrigerated storage at 8 °C. The addition of garlic and onion powder tended to increase redness (a) and yellowness (b) in both the belly lean and loin with the exception of a few cases. Free fatty acid values in both pork belly and loin cuts were reduced with the addition of these ingredients, as compared to the control. Significant differences in peroxide values were observed in sodium ascorbate and garlic‐injected belly, and in sodium ascorbate and onion‐injected loin, as compared to the control. Thiobarbituric acid reactive substance values in the pork belly with garlic or onion powder were significantly lower than in the belly without these ingredients or with sodium ascorbate (P < 0.05). Total plate counts were lower in both the belly and loin containing garlic and onion powder, as compared to the control. In both the belly and loin cuts, the content of oxidative products (volatile compounds) was reduced with the addition of garlic and onion powder, particularly the aldehydes (hexanal). Overall, garlic and onion in enhanced meats showed an antioxidant activity as effective as that of sodium ascorbate and also an antimicrobial effect to inhibit the growth of total bacteria and Enterobacteriaceae.     

Influence of moderate heat pre-treatments on physical and chemical characteristics of kiwifruit slices

The effect of mild heat treatments, applied to whole kiwifruit, on physical characteristics and chemical composition of minimally processed fruit was studied. Fruits were subjected to heat treatments at 45 °C for 25 and 75 min, cooled for 24 h, minimally processed and stored at 4 °C for 12 days. Heat-treated fruits showed increased respiration rates in the first 2 days of storage. Samples colour was marginally affected either by heat treatments or by minimal processing. The application of heat treatments leads to an increment of slices firmness due to cross linking between demethylated galacturonic acid chains and endogenous calcium. An increment in sucrose, L-malic, citric, quinic and ascorbic acids was observed as a consequence of applied heat treatments. Heat treatment at 45 °C for 25 min applied to whole fruits allows quality retention of minimally processed fruit during 9 days at 4 °C.     

PROCESSING OF YOGURT-BASED PRODUCTS WITH PULSED ELECTRIC FIELDS: MICROBIAL, SENSORY AND PHYSICAL EVALUATIONS

Yogurt-based products similar to a dairy pudding dessert were formulated and processed by mild heat and pulsed electric fields (PEF) to investigate the effects of combined mild heat and PEF treatment on the microbial stability and quality of high viscosity foods. Commercial plain low fat yogurt was mixed with fruit jelly and corn syrup and processed by mild heat treatment at 60C for 30 s and 30 kV/cm electric field strength for 32 μs total treatment time using OSU-2C pilot plant scale PEF system. Control and processed products were aseptically packaged and stored at 4 and 22C. Mild heat combined with PEF treatment significantly decreased the total viable aerobic bacteria and total mold and yeast of yogurt-based products during storage at both 4 and 22C (P ≤ 0.05). Mild heat treatment alone without any PEF treatment did not prevent the growth of microorganisms in yogurt-based products. Sensory evaluation indicated that there was no significant difference between the control and processed products (P ≤ 0.05). Color, pH and °Brix were not significantly affected by mild heat and PEF processing conditions.     

切割果蔬的微生物及其生物控制

切割果蔬由于其食用方便、营养丰富、清沽卫生等特点近年来受到人们的广泛关注。然而，实际生产中的许多问题，如褐变、失色、脱水、微生物污染等限制了切割果蔬加工业的进一步发展。微生物是影响切割果蔬质置与安全的重要冈素。本文分析了切割果蔬中微生物的来源、构成、生物膜形成以及切割果蔬生产过程对微生物的影响。同时对微生物的快速检测技术和切割果蔬的生物控制方法进行了综述，以期对切割果蔬加工业提供一定的理论基础。     

Physicochemical and Microbiological Quality of Sous-Vide-Processed Carrots and Brussels Sprouts

Physical properties, microbiological quality and volatile compounds of sous-vide-processed carrots and Brussels sprouts were analysed after 1, 5 and 10 days of refrigerated storage. Similar analyses were performed on raw and steamed carrots and Brussels sprout for comparison. Sous-vide carrots were firmer than steamed and firmness increased during storage. Similar values of colour indices were obtained for both steamed and sous-vide carrots, which also showed an increase of redness and colour saturation during storage. Aerobic and anaerobic counts of raw carrots were significantly reduced both by steaming and sous-vide procedures at values lower than 1 log cfu/g; these values were maintained until the end of storage. Among volatiles, terpenes were better preserved in sous-vide than steamed carrots, but all volatile fractions were significantly affected during storage. Steamed Brussels sprouts were softer and greener than sous-vide-processed ones, but softening and loss of green of the latter increased under vacuum storage. Microbiological counts of raw products were more efficiently reduced by sous-vide procedures than steaming. Higher amounts of nitriles and terpenes were shown in sous-vide vegetables in comparison to steamed, whereas thiocyanates and isothiocyanates occurred in lower quantities. Volatiles were not affected during 5 days of storage.     

模拟条件下香辛类蔬菜对N-二甲基亚硝胺形成的影响

研究采用体外模拟条件及亚硝化反应体系,探究大葱、生姜、大蒜、洋葱4种香辛类蔬菜的冻干粉及其可溶性组分干粉对N-二甲基亚硝胺(N-nitrosodimethylamine,NDMA)形成的影响。结果表明:香辛类蔬菜的种类和添加量、亚硝化反应体系的温度、时间等都对NDMA的形成表现出不同程度的促进或抑制作用。在模拟温度(腌制(4±1)℃、室温(25±1)℃、低温加工(80±1)℃)条件下,大葱粉、洋葱粉及生姜粉均明显促进NDMA形成(P0.05),且80℃时促进率最大;同一温度条件下,随反应时间延长,大葱粉和洋葱粉对NDMA形成的促进作用明显增强(P0.05),生姜粉对NDMA形成没有显著影响(P0.05);在同一温度同一反应时间内,随香辛类蔬菜粉添加量增加,对NDMA形成的促进作用显著增强(P0.05)。但在4℃或25℃时,大蒜粉及生姜水溶性组分干粉对NDMA形成表现为抑制作用,其中生姜水溶性组分干粉抑制作用较弱(10%);在80℃时大蒜粉表现为促进NDMA的形成。实验说明4类香辛类蔬菜在模拟条件下对NDMA的形成未能起到抑制作用。     

Matrix effects on the antimicrobial capacity of silver based nanocomposite absorbing materials

The suitability of cellulose/silver nanocomposites to decrease the microbial loads in absorbent materials was studied during the shelf-life of minimally processed foods. Cellulose/silver nanocomposites were synthesised by means of reduction by UV/heat of silver nitrate adsorbed on fluff pulp cellulose fibres. Minimally processed fruits and meat products were packaged in trays containing commercial absorbent pads or silver loaded absorbers, and stored during 10 days at 4 °C. The synthesised antimicrobial nanocomposites were useful to control the population of spoilage-related microorganisms in absorbent pads, being particularly effective in contact with low-protein food products. In contact with silver loaded absorbers, counts of total viable microorganisms and yeasts and moulds were reduced up to 99.9% in juices from kiwi fruit and melon; in drip from poultry and beef meat, microbial loads (total viable counts, lactic acid bacteria) were constantly 90% below the controls. Consequently, silver based absorbent materials could be especially designed to improve hygienic conditions during the manipulation and storage of minimally processed fruit cuts and meat products, but matrix effects must be taken into account.     

Storage behaviour of minimally processed pumpkin (Cucurbita maxima) under modified atmosphere packaging conditions

 Minimally processed vegetables in fresh, ready-to-cook form are gaining the confidence of both the trader and the consumer. This has led to a need to develop technology for increasing shelf life while maintaining the microbial, nutritional and sensory quality of minimally processed vegetables. This investigation was carried out on pumpkin in minimally processed form, packed in different polymeric film bags of varying permeabilities, creating an active equilibrium modified atmosphere within the package for the extention of storage life. It was observed that minimally processed pumpkin, which has a high respiratory rate at room temperature (155.7 mg CO₂/kg/h) could be stored for a period of 25 days at 5±2  °C under modified atmosphere packaging conditions with a minimum physiological loss in weight of 0.06% and marginally low changes in biochemical constituents, such as vitamin C, total soluble solids, moisture, carotenoids and titrable acidity, enabling the retention of near-fresh quality. The microbial loads of mesophilic aerobes and coliforms, which were log 5.5 and log 4.3 were less than threshold level. There was no growth of yeasts and moulds or mesophilic spore formers at the end of the storage period. Received: 24 January 2000 / Revised version: 4 April 2000     

Shelf‐life extension of fresh‐like ready‐to‐use pear cubes

Minimally processed fruit and vegetables are generally more perishable than the original raw materials due to the injury stresses during preparation that greatly increase tissue respiration and lead to deterioration through various biochemical pathways. In this paper, the effects of low intensity blanching treatments on enzymatic and microbiological stability on the fresh‐like quality of ready‐to‐use pear cubes has been evaluated. Blanching treatments as well as packaging were carried out both in aseptic and in non‐aseptic conditions. The combination of low intensity blanching with superficial enzymatic treatments has been carried out. The results confirm that the combination of a mild heat treatment (3 min at 95 °C) under aseptic conditions is enough to enhance the stability of this minimally processed product with an acceptable reduction in the texture. The superficial treatment with lysozyme did not result in an improvement in the stability of the blanched pear cubes during storage under refrigerated conditions. © 1999 Society of Chemical Industry     

Comparison of four commercial DNA extraction kits for PCR detection of Listeria monocytogenes, Salmonella, Escherichia coli O157:H7, and Staphylococcus aureus in fresh, minimally processed vegetables

Four commercial DNA extraction methods, PrepMan Ultra (Applied Biosystems), InstaGene Matrix (BioRad), DNeasy Tissue kit (Qiagen), and UltraClean (MoBio), were tested for PCR detection of Listeria monocytogenes, Escherichia coli O157: H7, Salmonella, and Staphylococcus aureus in fresh, minimally processed vegetables. For comparative purposes, sensitivity assays with specific PCRs were carried out after DNA extraction with the four methods in green pepper, broccoli, and onion artificially inoculated with the four pathogens separately. As confirmed by statistical analysis, the DNeasy Tissue kit rendered the highest sensitivity values in the three matrices assayed for Salmonella, L. monocytogenes, and E. coli O157:H7 and in onion for S. aureus. Despite being the most expensive of the methods compared, the DNeasy Tissue Kit can be successfully applied for any of the four most commonly studied pathogens, thus saving time and overall reducing the cost of the analysis.