Alicyclobacillus acidoterrestris in fruit juices and its control by nisin

Summary The acid-tolerant and heat-resistant bacterium Alicyclobacillus acidoterrestris is a spoilage problem in pasteurized and heat-treated fruit juices. In this study it was shown to grow in orange juice, grapefruit juice and apple juice to produce detectable taint at levels of about 10⁴–10⁵ c.f.u. ml⁻¹. Decimal reduction times were determined at 80 °, 90 ° and 95 °C in each juice and confirmed the heat-resistant nature of the spores under normal juice pasteurization conditions. They also confirmed that heat sensitivity increased with decreasing pH but that this effect was less pronounced at higher temperatures. The organism was, however, sensitive to the bacteriocin food preservative nisin. The presence of nisin during heating decreased the D value by up to 40% and the MIC for nisin against spores at 25 °C was only 5 International Units (IU) ml⁻¹. The results indicate that use of nisin is a potentially useful way of controlling this organism in fruit juices and fruit juice-containing products.     

MICROBIOLOGICAL STATUS OF EGYPTIAN SALTED MEAT (BASTERMA) AND FRESH SAUSAGE

The microbiological quality of 125 samples of the most popular Egyptian meat products (75 Egyptian fresh sausage "EPS" and 50 basterma) was determined. The aerobic plate count (APC) and Lactobacillaceae count of basterma ranged from 1 × 10⁴ to 9 × 10⁶ CFU/g, respectively . Enterobacteriaceae, mold and yeast counts for basterma were similar (<1 × 10² CFU/g). Artificially contaminated slices of meat and garlic paste of basterma showed that the paste inhibited growth of Salmonella typhimurium. APC and Enterobacteriaceae counts of EFS ranged from 1.1 × 10⁴ to 1 × 10⁸ and from 1 × 10² to 1 × 10⁷ CFU/g, respectively. Nearly 26% and 29% of EFS were positive for Clostridium perfringens and coagulase-positive Staphylococcus aureus, respectively . Salmonella could not be detected in any examined samples. Bacteriologically, EFS might pose a potential health hazard, making it imperative to institute sanitary measures during its production and sale .; Accepted for Publication July 2, 1997     

REMOVAL OF SALMONELLA TYPHIMURIUM ATTACHED TO CHICKEN SKIN BY RINSING WITH TRISODIUM PHOSPHATE SOLUTION: SCANNING ELECTRON MICROSCOPIC EXAMINATION

The effect of trisodium phosphate (TSP) on Salmonella typhimurium attached to chicken skin was investigated by using scanning electron microscopy (SEM). Chicken drumsticks were inoculated with Salmonella typhimurium (2 × 10⁸ CFU/mL) for 30 min. Both inoculated and non-inoculated drumsticks were rinsed with 10% TSP solution at 10 or 50C for 15 s, and skin pieces were cut and fixed for SEM examination. For inoculated skins, a significant difference was noticed between TSP-rinsed and control skins (water-rinsed) at both temperatures. While control skins were covered with salmonellae (4 × 10⁵∼ 1 × 10⁶ CFU/cm²) and miscellaneous debris, TSP-rinsed skins, either at 10 or 50C, showed clean skin surfaces (<8×10³ CFU/cm²). For non-inoculated skins, it was difficult to see the difference in the number of attached bacteria due to their low numbers, however, water-rinsed skins still showed the debris on the surface. Above observations suggest that one of the major mechanisms of TSP on salmonellae reduction is detachment of contaminants from the skin surface.     

SHELF-LIFE OF FRESH FILLED PASTA. HAZARD ANALYSIS AND CRITICAL CONTROL POINTS OF THE MANUFACTURING PROCESS AND HOUSEHOLD PRACTICES

Hazard Analysis and Critical Control Point (HACCP) approach was used to assess the safety of a fresh filling pasta (ricotta-filled ravioli) manufacturing plant in La Plata region, Argentina. Household practices like cooking and holding meals before serving were also evaluated. Samples of ricotta, main raw material of the filling, showed colony counts of Enterobacteriaceae total microorganisms, molds and yeasts of (5 × 10³-1 × 10⁵), (1x10⁵−1x10⁸) and 1 × 10⁵ CFU/g, respectively. E. coli was also detected in one out of five samples, suggesting a hazardous condition of this raw material. Salmonella spp. was not isolated from any of the dough samples tested. Ricotta filling showed high colony counts of mesophilic microorganisms (6 × 10⁶ CFU/g), Enterobacteriaceae (1 × 10⁵ - 1 × 10⁶ CFU/g), while E. Coli was detected in 20% of the samples. Counts of B. cereus, S. aureus were less than 1 × 10² CFU/g in the analyzed materials. In the finished product (ricotta-filled ravioli), the colony counts of mesophilic microorganisms and Enterobacteriaceae were 3 × 10⁸ and 8 × 10⁵ CFU/g, respectively. Critical Control Points found were cooking and holding time before serving. The implementation of suggested corrections allowed the microbial quality of the final product (ricotta-filled ravioli) to be improved considerably. The growth of total microbial counts during refrigerated storage (0, 4, 8 and 10C) were measured and the shelf-life of ricotta and ricotta-filled ravioli was calculated.     

EVALUATION OF BACTERIOLOGICAL QUALITY IN SELECTED COMMERCIAL INFANT FORMULAS AVAILABLE IN POLAND AND EGYPT

One hundred samples of commercial infant formula bought in shops in the Poznan region (Poland) and Cairo region (Egypt) were investigated. Samples were analyzed for aerobic plate counts (APC), total Bacillus cereus (TBC), and incidences of Bacillus spp. and coliforms. The mean APC and TBC did not show any important variation with country, being practically the same in products bought in Poland and Egypt. All commercial infant formula analyzed immediately after opening were of satisfactory bacteriological quality, exhibiting APC lower than 10⁴ CFU g⁻¹ (mean 4.9 × 10²) and TBC lower than 10³ CFU g⁻¹ (mean 1.1 × 10²). However, 60% of the examined fruit juice and ready-to-feed infant formula presented TBC above the recommendation safety limit after storage at 22C for 72 h and at 35C for 48 h. In most cases the mean log APC and TBC were highest (P > 0.05) for fruit juice and ready-to-feed infant formula stored at elevated temperature (35 ± 1C).     

Impact of nitrite on detection of Listeria monocytogenes in selected ready-to-eat (RTE) meat and seafood products

ABSTRACT:  The impact of sodium nitrite (NaNO₂) on detection and recovery of Listeria monocytogenes from select ready-to-eat (RTE) foods including smoked salmon, smoked ham, beef frankfurters, and beef bologna was assessed. Nitrite-containing (NC; 100 to 200 ppm NaNO₂) or nitrite-free (NF) foods were inoculated with a 5-strain cocktail of L. monocytogenes by immersion into Butterfield's buffer solution containing 5.4 to 7.4 × 10³ L. monocytogenes per milliliter. Inoculated products were vacuum-packaged and stored at 5 °C. A weekly comparative analysis was performed for presence of L. monocytogenes using 5 detection methods on products held at 5 °C for up to 8 wk. L. monocytogenes initially present at <100 CFU/g during the first 2 wk of storage increased throughout the study, attaining final populations of approximately 1 × 10⁴ to 1 × 10⁵ CFU/g. Lactic acid bacteria predominated throughout the study in all products. Exposure to NaNO₂ (100 to 200 ppm) resulted in 83% to 99% injury to the L. monocytogenes strains tested. The genetic-based BAX^® System (DuPont™ Qualicon, Wilmington, Del., U.S.A.) and modified USDA/FSIS methods detected 98% to 100% of Listeria -positive food samples and were consistently superior to and significantly different ( P < 0.05) from conventional cultural methods in recovering Listeria from NC samples. Data show that nitrite-induced injury adversely affects detection and recovery of L. monocytogenes from NC food, confirming earlier findings that nitrite-induced injury masks L. monocytogenes detection in NC RTE food products. Nitrite-injured Listeria can subsequently repair upon nitrite depletion and grow to high levels over extended refrigerated storage.     

INHIBITION OF STAPHYLOCOCCUS AUREUS AND BACILLUS CEREUS ON A VEGETARIAN FOOD TREATED WITH NISIN COMBINED WITH EITHER POTASSIUM SORBATE OR SODIUM BENZOATE

Various amounts of nisin (0, 10³ and 5 × 10³ IU/g) in combination with either potassium sorbate (0, 2, and 3%) or sodium benzoate (0, 0.06 and 0.12%) were tested for effectiveness in inhibiting growth of Staphylococcus aureus C10 and Bacillus cereus B7 inoculated on a vegetarian food. The strains used were isolated from vegetarian foods obtained commercially in Taiwan, and the test food, spice and dried bean curd, was selected for the study based on ability to support the growth of these organisms. After treatment with a preservative combination, the surfaces of sterilized food samples were inoculated, samples were stored in vacuum or nonvacuum packages at either 4C or 30C, and at appropriate times, tested for microbial growth. Growth of both isolates was unaffected by vacuum-packaging treatment; however, a bacteriostatic effect was found at 4C. Data indicated that during the 14-day storage at 4C, vacuum-packaged samples treated with 5 × 10³ IU/g nisin and 0.12% sodium benzoate significantly (p < 0.05) decreased the counts of S. aureus C10 and B. cereus B7 by 2.61 and 3.02 log₁₀ CFU/g, respectively. In the vacuum-packaged samples treated with 5 × 10³ IU/g nisin and 3% potassium sorbate, counts for C10 and B7 were decreased by 2.35 and 2.64 log₁₀ CFU/g, respectively. Thus, the combined treatment extended the shelf-life of the vegetarian food .     

HYGIENIZATION OF INDIAN CHICKEN MEAT BY IONIZING RADIATION

Both fresh and frozen chicken meat were evaluated for microbiological status by screening for total bacterial counts and for the presence of pathogens like Enterobacteria , Bacillus cereus, coagulase positive Staphylococci and Salmonella spp. Most of the samples exhibited heavy bacterial contamination (1.2 × 10⁵ - 2.6 × 10⁶/g), mainly with Staphylococcus spp. (1.5 × 10⁴ - 2.8 × 10⁵/g). All the chicken samples also showed the presence of Salmonellae (3 × 10¹ - 2.1 × 10²/g). Among the different serotypes observed in chickens . S. typhimurium was common in fresh as well as frozen chicken. Radicidation at 2 kGy at cryogenic conditions (−40°C) was efficient in eliminating the natural pathogenic contamination of the poultry . Salmonella spp. viz. S. seftenberg and S. typhimurium differed in radiation sensitivity, the D₁₀ values in phosphate buffer (pH 7.2) being 0.25 kGy and 0.12 kGy, respectively. Chicken homogenate (10%) offered approximately 2-fold protection to these cells. Chicken samples artificially inoculated with a heavy inoculum (10⁸ cells/g) of these 2 serotypes required higher gamma radiation doses of 4–5 kGy. The findings suggested that a dose of 2 kGy is adequate for normally contaminated chicken samples, but for the heavily contaminated chicken a dose of 4–5 kGy, depending upon the predominating Salmonella serotype present, is required .     

QUANTITATIVE STUDIES OF PROTEOLYTIC AND LIPOLYTIC BACTERIA IN FROZEN MINCED BEEF AND HAMBURGER

Sixty frozen samples (30 hamburger patties and 30 minced meat) purchased from different retail markets in Ismailia, Egypt were examined for incidence of proteolytic and lipolytic bacteria. Mean values of proteolytic psychrophiles in the examined samples of hamburger and minced meat were 2×10⁵ and 6×10⁴, respectively. Lipolytic psychrophiles in hamburger were 8×10⁵ and 3×10⁵ in minced meat. Proteolytic mesophiles in hamburger and minced meat were 6×10⁵ and 5×10⁴, respectively. Mean values of lipolytic mesophiles were 5×10⁴ for hamburger and 5×10³ for minced meat. Proteolytic thermophiles in hamburger and minced meat were 3×10³ and 10³, respectively. Both proteolytic and lipolytic activities were exhibited by various bacteria that were identified.     

EFFECTS OF RAW MATERIALS AND PROCESS VARIABLES ON THE HEAT PENETRATION TIMES, FIRMNESS, AND PECTIC ENZYME ACTIVITY OF DICED TOMATOES (HALLEY BOS 3155 CV)

The effects of raw materials and process variables on the heat penetration times into diced tomatoes (Halley Bos 3155 cv) were evaluated. Variables included dice size (1.27 and 2.54 cm), maturity at harvest (red and red+2 weeks), and processing temperature (88 and 92C). Heat penetration times between dice sizes were significantly different, but not between maturities or processing temperatures. Tomatoes were also evaluated for firmness, pectin-methylesterase (PME) and polygalacturonase (PG) activities. Half-inch size diced tomatoes were processed at 88 and 92C, and evaluated for firmness using the shear-compression method. Firmness decreased to 60% of the initial raw firmness from 8.8 × 10⁵ to 5.3 × 10⁵ g-mm after 15 s at 88C, and to 50% from 8.8 × 10⁵ to 4.4 × 10⁵ g-mm after 15 s at 92C. Diced tomato firmness showed a slight firming trend after 150 s at both temperatures. PME was inactivated after 45 s, while 5% residual PG activity remained after 3 min.     

THE EFFECT OF AEROBIC MESOPHILIC MICROFLORAL LEVELS ON THE ISOLATION OF INOCULATED LISTERIA MONOCYTOGENES STRAIN LM82 FROM SELECTED FOODS

The effect of aerobic mesophilic microfloral concentration on the isolation of Listeria monocytogenes LM82 was studied in 31 (18 cheeses and 7 noncheese) retail foods having standard plate counts of 10¹ to 10⁸ colony forming units (CFU)/g. Foods were spiked with L. monocytogenes and enriched at 30°C for 24 h in a selective enrichment broth used in a U.S. Food and Drug Administration method. Inoculum levels for isolation on modified McBride agar ranged from 0.1 to > 5 × 10³ with a geometric mean value of 5 inoculated CFU/g or 1.4 CFU/g. Pure Enterococcus (Streptococcus) faecalis ( 0 to 6 × 10⁶ inoculated CFU/mL ) in the absence of food matrix had no effect on the enrichment of L. monocytogenes. Ease of isolation of LM82 was independent of the food microflora concentration both generally and in the specific food type of 9 Brie cheeses. Competition, when it occurs, therefore, may be due to specific bacterial competitors rather than bacterial numbers .     

MICROBIOLOGICAL QUALITY OF TRADITIONAL MARKET CURED FISH IN TANZANIA

The microbiological quality of six varieties of retail market traditionally cured fish in Morogoro, Tanzania was investigated over a five-month period. The fish were contaminated with bacteria and molds at levels of: total aerobes, 10⁶ - 1.7 × 10⁷ c.f.u/g; faecal coliforms, 1.1 × 10¹ - 2.5 × 10³ MPN/g; faecal streptococci, 1.4 × 10¹ - 1.3 × 10³ MPN/g; Staphylococcus aureus, 1.3 × 10³ - 8.6 × 10³ c.f.u/g; Aspergillus flavus group, 2.1 × 10¹ - 2 × 10² c.f.u/g of fish. Of faecal coliform, 45% of the isolates were Escherichia coli. Twenty-five percent of the S. aureus isolates were coagulase positive. Sixteen percent of A. flavus isolates were aflatoxigenic. Aflatoxin contamination ranged from O to 18.5 μg/kg of fish. Insect infestation by Dermestes spp. and mites was observed. The results of this preliminary study emphasize the importance of proper processing and handling offish in the tropics in order to safeguard public health .     

APPLICATION OF CHLORINE TO REDUCE POPULATIONS OF ESCHERICHIA COLI ON BEEF

The effects of chlorine against 2 strains of E. coli attached to the surface of beef carcass tissue (BCT) were examined using a model carcass washer. Lean and adipose BCT with approximately 5 log ₁₀ CFU/cm ² E. coli bacteria were spray-treated with water and sodium hypochlorite (NaOCl) to give chlorine concentrations of 50, 100, 250, 500, or 800ppm, incubated for 24 h, 4C, and E. coli populations enumerated. Spray treatments with water did significantly (P < 0.05) reduce the bacterial populations of either organism attached to lean or adipose BCT, as compared to populations of controls; however, reductions were less than 0.60 log ₁₀ CFU/cm ². Treatments with 500 and 800 ppm chlorine against E. coli ATCC 25922 attached to BCT resulted in the greatest reductions of 1.22 and 1.28 log ₁₀ CFU/cm ², respectively. At 800 ppm chlorine , E. coli O157:H7 ATCC 43895 attached to BCT was reduced by 1.04 log ₁₀ CFU/cm ², whereas spray treatments with 50, 100, 250, and 500 ppm chlorine resulted in reductions of < 1 log ₁₀ CFU/cm ². Spray treatments with chlorine from sodium hypochlorite solutions reduced populations of E. coli, however, these reductions were not sufficient to completely inactivate the bacteria attached to red meat .     

DETECTION OF STAPHYLOCOCCUS AUREUS PRODUCTS IN FOODS USING ENZYME LINKED IMMUNOSORBENT ASSAY AND SPECTROPHOTOMETRIC THERMONUCLEASE ASSAY

The comparative sensitivity of an enzyme linked immunosorbent assay (ELISA) using four different antistaphylococcal antisera and a spectrophotometric assay for thermonuclease were determined using cheese and ravioli samples seeded with strains of Staphylococcus aureus and S. epidermidis. The ELISA used antisera to enterotoxin A, enterotoxin B, S. aureus strains 14609 (human), and UNH-570 (bovine). The 570 ELISA and spectrophotometric thermonuclease assay were of comparable sensitivity and detected seeded culture in concentrations as low as 2 × 10⁷ CFU/g of cheese. A simple two hour method for extracting thermonuclease from foods was 50% efficient when as little as 50 ng of purified enzyme was seeded per g of cheese. Analyses of 43 commercial cheeses for viable S. aureus found five (12%) positive with 3 × 10⁴ CFU/g of cheese being the highest counts detected. All samples were negative by ELISA and thermonuclease assay. A simple screening procedure for demonstration of S. aureus contamination of foods is discussed.     

Singlet Oxygen Oxidation Rates of ∝-, γ-, and δ-Tocopherols

ABSTRACT:  The reaction rate constants of 5 × 10⁻⁴ M, 10 × 10⁻⁴ M, and 20 × 10⁻⁴ M α-, γ-, and δ-tocopherols with singlet oxygen in methylene chloride containing 1 × 10⁻⁵ M chlorophyll under light at 25 °C for 60 min were studied. The oxidation of tocopherols determined by a spectrophotometric method showed that the losses of 20 × 10⁻⁴ M α-, γ-, and δ-tocopherols after 60 min under light were 21%, 16%, and 9%, respectively. The degradation of α-, γ-, and δ-tocopherols was undetectable in the absence of chlorophyll under light or in the presence of chlorophyll in dark. The losses of tocopherols under light were mainly due to singlet oxygen oxidation. The degradation rates of 20 × 10⁻⁴ M α-, γ-, and δ-tocopherols were 6.6 ×10⁻⁶ M/min, 5.0 × 10⁻⁶ M/min, and 2.9 × 10⁻⁶ M/min, respectively. The reaction rates between α-, γ-, or δ-tocopherol and singlet oxygen were 4.1 ×10⁶/M s, 3.3 × 10⁶/M s, and 1.4 × 10⁶/M s, respectively. The singlet oxygen oxidation rate of δ-tocopherol was significantly lower than α- or γ-tocopherol at α= 0.05. As the electron density in the chromanol ring of tocopherol increased, the singlet oxygen oxidation was increased.     

EFFECT OF SEVERAL EXPERIMENTAL PARAMETERS ON COMBINATION OF RED KIDNEY BEAN (PHASEOLUS VULGARIS) α-AMYLASE INHIBITOR WITH PORCINE PANCREATIC α-AMYLASE

Purified red kidney bean (Phaseolus vulgaris) amylase inhibitor forms a 1:1 stoichiometric complex with porcine pancreatic α-amylase leading to complete loss of enzyme activity on starch. Rate of complex formation is pH dependent and is maximal at pH 5. The rate constants for complex formation, as measured by loss of amylase activity, were 2.85 × 10⁴ M^-1 sec^-1 at pH 6.9 (ionic strength of 0.918) and 2.55 × 10⁵ M^-1 sec^-1 at pH 5 at 30°C. At pH 6.9, rate of complex formation was 4.8 times faster at 0.918 ionic strength as compared with the rate at 0.138 ionic strength. At 30°C, pH 6.9 and ionic strength of 0.168 the dissociation constant of the enzyme-inhibitor complex was determined to be 3.5 × 10^-11 M. The rate constant for dissociation of the complex was calculated to be 8.7 × 10^-8 sec^-1 under the same conditions. The rate constant for complex formation, at ionic strength of 0.168, was 1.1 × 10⁴ M^-1 sec^-1 at 37⁰ and 9.77 × 10² M^-1 sec^-1 at 25.7°C. The calculated activation energy for complex formation is 39.5 kcal/mole suggesting a rate-controlling conformational change. Oxidation of the carbohydrate moiety of the glycoprotein inhibitor caused complete loss of activity. Maltose, a competitive inhibitor of α-amylase, bound as readily to the enzyme-inhibitor complex as to free α-amylase. Trypsinized α-amylase, although still able to bind to Sephadex, did not bind inhibitor. The experiments with maltose and trypsinized amylase suggest the inhibitor may not bind at the active site of α-amylase.     

RADIATION STERILIZATION OF SPICES FOR HOSPITAL FOOD SERVICES AND PATIENT CARE

A survey of the commercial spices used by food services in a typical hospital environment revealed high contamination with microorganisms, i.e., 10⁴ to 10⁷ counts per gram. The predominant microorganisms were as followed (in colony counts/gram): (1) heat-resistant bacterial spores in black pepper, 1 × 10⁷; thyme, 2 × 10⁶; anise, 7 × 10⁴; curry powder, 4 × 10⁵; poultry seasoning, 8 × 10⁴; pickling spice, cardamom, and cumin, 1.5–3 × 10⁴; (2) mixed populations of vegetative cells and bacterial spores in cumin, 1 × 10⁶; (3) molds in cream of tartar, 2 × 10⁴. Sterility of food may be important in a hospital setting, especially in the care of immunocompromised patients. To eliminate the organisms, we recommend radiation treatment, accompanied by appropriate microbiological quality control. On the basis of radiation survival data, the composite natural flora would be reduced to the level of "commercial sterility" (defined as less than 10 organisms per gram((Kiss 1982) by the following minimum radiation doses (in kGy): black pepper, 13; thyme, 13; cumin, 12; anise, 10; curry, 7.3; pickling spice, 7; poultry seasoning, 6; cardamom, 9.4; cream of tartar, 4. For practical purposes, two dose levels can be recommended for treatment of spices in the hospital environment, low = 6–10 kGy and high = 10–15 kGy.     

CHANGES IN PARBOILED ROUGH RICE CAUSED BY IMPROPER DRYING AND MICROBIAL INFECTION

Molds and bacteria contaminate parboiled rough rice when it is improperly dried or while awaiting drying due to humid rainy weather. When IR 20 parboiled rough rice was not dried for 7 days due to humid weather molds increased to 2.45 × 10⁷ per gram from 6 × 10⁴ per gram and bacteria increased to 75.9 × 10⁶ per gram from 5.1 × 10⁶ per gram observed initially. The milled rice yield decreased to 60.1% from 72.2% and the head rice yield decreased to 55.0% from 98.8% due to infection. The resultant bran contained only 12.1% oil compared to 31.9% in normally dried and milted paddy with about 40.0% free fatty acids in oil. The infection induced breakdown changes increased the levels of sugars, amino acids and polyphenols in grains which might cause kernel discolouration in the associated heat development during infection.     

Development of a Meat-Like Process Flavoring from Soybean-Based Enzyme-Hydrolyzed Vegetable Protein (E-HVP)

ABSTRACT: Response surface methodology (RSM) was used to develop a meat-like process flavoring agent from enzyme-hydrolyzed vegetable protein (E-HVP). Five factors were evaluated: pH (3.6 to 8.4), temperature (51 to 99 °C), heating period (0.3 to 2.7 h), amount of ribose (0 to 1 × KHmol) and amount of cysteine (0 to 1 × 10 ³mol). Sensory analysis limited to aroma in terms of overall liking and intensity of specific aroma attributes was investigated. The aroma attributes measured included bean-like, potato-like, Brussels sprouts-like, molasses-like, chicken-like, beef-like, egg-like, roasted and apple sauce-like). Based on the fitted surfaces and consumer test data (overall liking), the optimum reaction conditions for production of a meat-like flavoring were pH 6,99 °C reaction temperature, 1.5 h heating time, 5 × 10⁻⁴ mol of ribose and 5 × 10⁻⁴ mol of cysteine.     

Influence of pre-treatments on microbial load of stored dehydrated onion slices

Onions slices were pre-treated in potassium meta-bisulphite (KMS) and sodium chloride with different concentration levels to study the microbial load of tray and greenhouse-dried onion slices up to 6 months of storage. Data were analysed as per procedure of one-way classified anova using DMRT of AgRes statistical package for bacteria, yeast, fungi and Lactobacilli . Results revealed that in almost all samples, permissible levels of bacteria [18.33 × 10¹ colony-forming units (CFU) per gram], yeast (ND), fungi (0.5 × 10¹ CFU g⁻¹) and Lactobacilli (0.25 × 10¹ CFU g⁻¹) were observed after 5 months of storage. All the samples were also found to be free from Escherichia coli and no Mac Conkey growth was noticed. Onion slices pre-treated in 0.25% and 0.50% KMS and dried in tray and greenhouse, respectively, were found best after 6 months of storage period.