Bacillus and Paenibacillus species associated with extended shelf life milk during processing and storage

Characterisation of spore formers associated with extended shelf life milk was performed by analysing the bacteriological quality of milk samples collected at various processing stages and during storage. Isolates were identified with MALDI‐TOF‐MS. Milk had spore counts <2 log₁₀ cfu/mL and 4 log₁₀ cfu/mL during processing and storage, respectively. Bacillus pumilus dominated the bacterial population. Bacterial species were inoculated into sterile milk for a shelf life study, and the population change was observed over 42 days at 7 °C. Although the extended shelf life milk process was effective in reducing bacterial counts and species diversity, the presence of Bacillus cereus shows a potential safety problem in extended shelf life milk.     

Occurrence,heat and antibiotic resistance profile of Bacillus cereus isolated from raw cow and processed milk in Mezam Division,Cameroon

Bacillus cereus is the aetiologic agent of two distinct forms of food poisoning: the diarrhoeal and emetic syndromes. Little data exist on the prevalence of B. cereus in raw milk and milk products sold in Cameroonian towns. This study was aimed at investigating the occurrence, heat and antibiotic resistance of B. cereus isolated from raw milk and selected milk products in Mezam division, Cameroon. Bacillus cereus was isolated by inoculating samples onto mannitol‐egg yolk‐polymyxin B agar. Isolates were characterised morphologically and biochemically. The occurrence of B. cereus in raw milk (8.22%) was less than that in milk powder (13.33%). Bacillus cereus was not isolated from fermented milk. There was no significant difference (P < 0.05) between the B. cereus load in raw milk (2.6 × 10³ cfu/mL) and milk powder (3.0 × 10² cfu/mL). All the isolates showed haemolysin activity and were sensitive to tetracycline, gentamicin, chloramphenicol and nalidixic acid, but resistant to penicillin, ampicillin and trimethoprim/sulphamethoxazole. The detection of drug‐resistant, haemolysin‐positive isolates should serve as a warning for an impending health hazard following consumption of untreated milk. Heat resistance of isolates was assessed by determining the decimal reduction time; D‐value (time to inactivate 90% of the B. cereus spores); and the heat sensitivity, z (temperature increase leads to a tenfold reduction in the D‐value). The values for D₁₀₀ ranged from 0.5 to 3.5 min, and z‐values ranged from 10.0 to 32.6 °C. These results could be used in the dairy industry to evaluate the importance of heat treatment on B. cereus inactivation and calculation of process efficiency.     

Comparative effect of different test methodologies on Bacillus coagulans spores inactivation kinetics in tomato pulp under isothermal conditions

Heat resistant micro‐organisms are an ongoing challenge to the food industry. Various factors may influence the heat resistance of micro‐organisms including type and strain; the environmental influences during cell and spore formations and during heat exposure; and the equipment and test tools used to perform the experimental process. In an attempt to analyse the influence of different test tools used on the heat inactivation processes, this study aimed to define the isothermal inactivation kinetics of Bacillus coagulans spores in tomato pulp at different temperatures and compare the inactivation of this bacterium when thermal death time (TDT) and capillary tube methods were used. Temperature ranges from 95 °C to 120 °C were studied, and inactivation kinetic parameters were estimated through the application of primary models. TDT inactivation curves consisted of shoulder and linear decline, while capillary method inactivation curves consisted of shoulder, linear decline and long tail. A secondary model was used to describe the influence of the temperature on spore inactivation parameters. The results showed test methods are at least as important in determining thermal processes as the micro‐organisms and media used.     

Effect of vacuum‐drying,hot air‐drying and freeze‐drying on polyphenols and antioxidant capacity of lemon (Citrus limon) pomace aqueous extracts

The aim of this study was to investigate the effect of freeze‐drying, hot air‐drying and vacuum‐drying at 70, 90 and 110 °C, on dried lemon pomace polyphenols and antioxidant capacity. The total phenolic content and antioxidant capacity were higher in lemon pomace dried by hot air or under vacuum than those dried by freeze‐drying and increased as the temperature increased. The highest total flavonoid content was recorded in the pomace dried under vacuum at 70 and 90 °C. Lemon pomace dried by freeze‐drying had the highest neohesperidin content, whereas pomace dried under vacuum at 70 °C had the highest rutin and p‐coumaric acid content. The highest gallic acid content was recorded in the pomace dried by hot air at 110 °C. The results of this study indicate that drying technique should be carefully selected according to the bioactive compounds aimed to be extracted.     

Bioactive components,ABTS radical scavenging capacity and physical stability of orange,yellow and purple sweet potato (Ipomoea batatas) powder processed by convection‐ or vacuum‐drying methods

This study aims to investigate the antioxidant properties and physical stability of convection‐ or vacuum‐dried orange, yellow and purple sweet potato (Ipomoea batatas) powder upon room temperature storage at different relative humidity (RH) of 33%, 43%, 54% and 75% for 25 days. Both convection and vacuum‐dried samples had lower total phenolic content (TPC), anthocyanin content and antioxidant activity compared to the fresh samples. Vacuum‐dried powder retained higher antioxidant activity than convection‐dried powder. Storage of the powder at high RH of 75% resulted in apparent clump formation, which was likely attributed to the decrease of glass transition temperature (T_g). In general, purple sweet potato powder contained the highest TPC (255.0 mg GAE 100 g DW^?1) and antioxidant activity (1924.0 μmol TEAC 100 g DW^?1), while orange powder had the highest beta‐carotene content (127.2 mg 100 g DW^?1). Vacuum‐dried sweet potato powder, which has relatively higher antioxidant activity, could be a potential functional ingredient or natural colourant for the food industry.     

Influence of temperature variations on growth,injury survival and inactivation of Listeria monocytogenes in goat milk samples at laboratory scale

Transmission of the thermo‐tolerant pathogen Listeria monocytogenes via contaminated milk and its products, can lead to serious food‐borne illness. In this study, the effects of selected temperatures on survival, percentage injury and inactivation of L. monocytogenes in goat milk samples collected from two different farms were evaluated. Low temperature ranges (0, 5, 10 °C) had a bacteriostatic effect; while at temperatures of 25 and 45 °C, this pathogen grew luxuriantly. However, growth was comparatively slow at 15 °C throughout a 12‐h stress period. Furthermore, a high temperature range (50, 55, 60 and 65 °C) resulted in the elimination of this pathogen within 4 h of stress. Results of Scanning Electron Microscopy showed morphological changes in the cells upon induction of stress temperatures.     

Effects of microwave and hot‐air drying methods on colour, β‐carotene and radical scavenging activity of apricots

The effects of drying by microwave and convective heating at 60 and 70 °C on colour change, degradation of β‐carotene and the 2,2‐diphenyl‐1‐picrylhydrazyl radical (DPPH) scavenging activity of apricots were evaluated. Microwave heating reduced significantly the drying time (up to 25%), if compared with convective one, also owing to the higher temperature reached during the last phase of the process, as monitored by infrared thermography. Colour changes of apricot surface, described with lightness and hue angle, in both drying methods followed a first‐order reaction (0.927 ≤ R² ≤ 0.996). The apricots dried by microwave were less affected by the darkening phenomena. The evolution of β‐carotene in fresh apricots (61.2 ± 5.6 mg kg^?1 d.w.) during the drying highlighted a wider decrease (about 50%) when microwave heating was employed for both the temperatures used. Radical scavenging activity increased (P < 0.05) in all dried samples except for hot‐air dried apricots at 60 °C.     

Stability of betacyanin from red pitahaya (Hylocereus polyrhizus) and its potential application as a natural colourant in milk

The effects of temperature (30, 50, 85 and 100 °C) treatment and 10 weeks of refrigerated storage (4 °C) on the betacyanin content and colour stability of betacyanins from red pitahaya (Hylocereus polyrhizus) were investigated and compared to red beet (Beta vulgaris; E‐162) which was used as a control. Temperature treatment at 50 and 85 °C caused a greater reduction in betacyanin content (BC) in E‐162 compared to red pitahaya by inducing changes in betacyanin profile. The 10 weeks of refrigerated storage at 4 °C induced colour changes in betacyanins from red pitahaya and E‐162. In milk, betacyanins from red pitahaya presented a lower loss of BC and total colour changes (ΔE*) compared to E‐162. The microbial onset in milk containing betacyanins from red pitahaya and E‐162 was delayed up to day 5 of refrigerated storage at 4 °C compared to day 3 in plain milk. Milk containing betacyanins from red pitahaya showed better colour acceptability (3.89 ± 1.89) compared to E‐162 (6.10 ± 1.71). Hence, betacyanins from red pitahaya may be a potential natural functional colourant to simulate strawberry colour in milk.     

Quality evaluation of mozzarella cheese made from buffalo milk by using paneer booti (Withania coagulans) and calf rennet

This systematic research was conducted to assess the suitability of Withania coagulans for the preparation of mozzarella cheese from buffalo milk. The extract of dried berries of paneer booti (W. coagulans) was prepared in three buffers separately viz. Tris‐HCl, phosphate, NaCl and appropriate concentration of crude extracts were tested for their milk coagulating activity. NaCl solution with 0.85% strength was found to be suitable for milk coagulation without any objectionable taste and flavour. The results revealed that 15 μL crude enzyme extract per mL of milk was the optimum concentration for coagulation while 4.25 and 37 °C were the best levels of pH and incubation temperature for coagulation respectively. Mozzarella cheese prepared from crude enzyme extract was compared with the cheese prepared by calf rennet using acidification process. There was a nonsignificant difference among all tested parameters of both the coagulants. These findings support the suitability of an aqueous extract of W. coagulans for the commercial preparation of different types of mozzarella cheeses.     

Thermal Death Determination: Design and Evaluation of a Thermoresistometer

The design and performance of a thermoresistometer (TR-SC) are described. This instrument has a high heating (5.7°C/sec) and cooling rate and can be used to determine spore survival curves at temperatures up to UHT range. Spores can be heated in homogenized foods under constant monitoring of pH ± 0.001 u. pH) and stable temperatures (± 0.1°C). D, values can be determined to 0.008 min. This method takes less time and effort than by capillaries. The fit of D_t values to thermal death time curves (TDT) curves is better by the TR-SC than by the capillary method. Survival and TDT curves for Bacillus licheniformis Bacillus coagulans and Bacillus subtilis were determined in homogenized foods and in McIlvaine buffer at tempertures up to the UHT range.     

Formation and dispersal of biofilms in dairy substrates

The formation and dispersion of biofilms in the dairy industry is a problem because it increases cross‐contamination, affecting the shelf life of the products and their safety. The objective of this study was to evaluate the influence of different dairy substrates (cows’ milk and whey protein) on the formation and dispersion of Enterococcus faecalis, Listeria monocytogenes, Staphylococcus aureus and Bacillus cereus in two biofilm systems (mono‐species and multi‐species) on stainless steel at 25 °C. The dominant behaviour of E. faecalis occurred in most of the tests on mono‐species and multi‐species biofilms. A greater dispersion of biofilm cells was observed in skimmed milk.     

Changes in bioactive compounds and antioxidant activity during convective drying of murta (Ugni molinae T.) berries

Murta (Ugni molinae T.) berries were air‐dried at five temperatures (40, 50, 60, 70 and 80 °C), and the changes in β‐carotene, phenolic acids, total phenolic and flavonoid contents and antioxidant capacities (DPPH and ORAC) were investigated. The berries showed a high content of β‐carotene, which decreased during drying temperature between 40 °C and 80 °C. Free and bound phenolic acids were also determined, showing gallic acid to be the prevalent phenolic acid. Total phenolic and flavonoid contents in the dried berries showed a higher decrease at lower temperature due to longer drying time. The radical‐scavenging activity also showed higher antioxidant activity at higher drying temperatures (70–80 °C) than at lower drying temperatures (40–50 °C). Total phenolic content (TPC) and flavonoids showed good correlation with antioxidant capacity. Murta berries proved to be an excellent source of antioxidants and bioactive compounds and are therefore a potential ingredient for new functional food products.     

Behaviour of Listeria monocytogenes and Staphylococcus aureus in sliced,vacuum-packaged raw milk cheese stored at two different temperatures and time periods

The behaviour of Listeria monocytogenes and Staphylococcus aureus in raw milk cheese slices packaged under vacuum was evaluated. Artificially contaminated 80-day ripened cheese was portioned, vacuum packaged, and then stored for 28 days at 4 °C and for 56 days at 10 °C. Bacterial counts were obtained before vacuum packaging and then weekly during storage. At the end of ripening, the initial L. monocytogenes count was 4.46 ± 0.89 log cfu g⁻¹; weekly bacterial counts remained substantially unchanged in the samples stored at 4 °C but decreased to 3.54 ± 1.54 log cfu g⁻¹ in those stored at 10 °C. The initial S. aureus count before vacuum packaging was 3.60 ± 0.78 log cfu g⁻¹; it then gradually decreased to 2.60 ± 1.32 log cfu g⁻¹ in the samples stored at 4 °C and to about 1.9 log cfu g⁻¹ in those stored at 10 °C.     

Effect of different storage conditions on coagulating properties and cheese quality of Withania coagulans extract

The effects of different storage conditions on the coagulating properties of extracts of Withania coagulans berries were investigated in terms of coagulation time, pH and quality attributes of cheese prepared from buffalo milk. The extracts were stored under different conditions, viz. room temperature (27 ± 3 °C), refrigerated storage (4 °C), frozen storage (?20 °C) and lyophilisation. The milk‐coagulating activity of the plant extracts was measured on a fortnightly basis for a period of 5 months. There was a nonsignificant change in pH and the milk coagulating properties of the lyophilised extract. Physiochemical analysis revealed that cheese prepared with lyophilised extract retained the highest content of ash (2.3%), fat (23.8%), total solids (48.7%) and crude protein (22.7%), and resulted in the highest cheese yield (17.6%) compared to other tested treatments. Thus, it is concluded that lyophilisation has good potential for storage of vegetable extract coagulants.     

Effect of Infrared Blanching on Enzyme Activity and Retention of β‐Carotene and Vitamin C in Dried Mango

The objectives of this work were to evaluate infrared (IR) dry blanching in comparison with conventional water blanching prior to hot air drying of mango to inactivate polyphenol oxidase (PPO) and ascorbic acid oxidase (AAO) enzymes, and to study its effect on color change and retention of vitamin C and β‐carotene. Mango cylinders were blanched under similar temperature–time conditions either by IR heating or by immersion in a water bath during 2 min at 90 °C (high‐temperature‐short‐time—HTST) or for 10 min at 65 °C (low‐temperature‐long‐time—LTLT). After blanching mango was hot air dried at 70 °C. PPO was completely inactivated during the blanching treatments, but AAO had a moderate remaining activity after LTLT treatment (～30%) and a low remaining activity after HTST treatment (9% to 15%). A higher retention of vitamin C was observed in mango subjected to IR dry blanching, 88.3 ± 1.0% (HTST) and 69.2 ± 2.9% (LTLT), compared with water blanching, 61.4 ± 5.3% (HTST) and 50.7 ± 9.6% (LTLT). All‐trans‐β‐carotene retention was significantly higher in water blanched dried mango, 93.2 ± 5.2% (LTLT) and 91.4 ± 5.1% (HTST), compared with IR dry blanched, 73.6 ± 3.6% (LTLT) and 76.9 ± 2.9% (HTST). Increased levels of 13‐cis‐β‐carotene isomer were detected only in IR dry blanched mango, and the corresponding dried mango also had a slightly darker color. IR blanching of mango prior to drying can improve the retention of vitamin C, but not the retention of carotenoids, which showed to be more dependent on the temperature than the blanching process. A reduction of drying time was observed in LTLT IR‐blanching mango.     

Effect of thermosonication in a batch system on the survival of spore‐forming bacteria

Thermosonication may help reduce bacteria counts responsible for spoilage in dairy products. Vegetative cells and spores of Geobacillus stearothermophilus, Anoxybacillus flavithermus and Bacillus subtilis (spores only) were treated with either heat alone or thermosonication in a batch system from 0 to 120 s in tryptic soy broth and 2% fat milk at 72 and 73 °C. D‐values for vegetative cells were calculated and were reduced after thermosonication. Maximum reduction in vegetative cells after thermosonication was 1 log after 30–45 s and for spores was ≤0.2 log after 120 s, which may not influence dairy product quality in scale‐up systems.     

Evaluation of the stability of Bacillus coagulans MTCC 5856 during processing and storage of functional foods

The study was aimed to find out the stability of Bacillus coagulans MTCC 5856 in functional foods during processing and storage. B. coagulans MTCC 5856 was found to be stable during baking and storage at frozen conditions of banana muffins (92% viability) and waffles (86% viability) upto 12 months. After brewing coffee at 90 °C for 2 min, there was 87% viability and retained 66% viability even after maintaining temperature at 77 °C for 4.0 h. It showed over 95% viability in chocolate fudge frosting, hot fudge toppings, peanut butter, strawberry preserve and vegetable oil at room temperature upto 12 months. It was found to be stable in apple juice upto 6 months at refrigerated condition and concentrated glucose syrup at 4 ± 3 and 25 ± 2 °C upto 24 months. B. coagulans MTCC 5856 showed promising stability during processing and storage of functional foods and could be an excellent probiotic ingredient to use in various food applications.     

Incidence and characterisation of aerobic spore‐forming bacteria originating from dairy milk in Tunisia

The purpose of this study was to evaluate the incidence and characterisation of aerobic spore‐forming bacteria originating from dairy milk in Tunisia. The distribution of Bacillus species in raw milk, pasteurised milk and UHT milk were 47.5%, 27.5% and 25%, respectively. Seven Bacillus species, including Bacillus pumilus (10%), Bacillus subtilis (12.5%), Brevibacillus brevis (10%), Bacillus cereus (22.5%), Bacillus sphaericus (7.5%), Bacillus licheniformis (12.5%) and Bacillus sporothermodurans (25%) were identified in different milk samples. Bacillus cereus was predominant in raw and pasteurised milk. Although B. sporothermodurans was the predominant sporogenous micro‐organism in UHT milk, B. cereus, B. sphaericus and B. licheniformis were also present. This study showed that there is a high degree of diversity, both phenotypic and genotypic, among Bacillus isolates from Tunisian milk and the persistence of spoilage risk in UHT milk.     

Thermal Inactivation Kinetics of Tulane Virus in Cell‐Culture Medium and Spinach

Human noroviruses (HNoVs) cause significant gastrointestinal disease outbreaks worldwide. Tulane virus (TV) is a cultivable HNoV surrogate widely used to determine control measures against HNoVs. The objective of this study was to determine the heat inactivation kinetics (D‐ and z‐values) of TV in cell‐culture media and on spiked homogenized spinach using the first‐order and Weibull models. TV in cell‐culture media at approximately 7 log PFU/mL (PFU—plaque forming unit) in 2‐mL glass vials was heated at 52, 54, and 56 °C for up to 10 min in a circulating water bath. Survivors were enumerated using confluent host LLC‐MK2 cells in six‐well plates by plaque assay. Data from three replicate treatments assayed in duplicate were analyzed statistically. D‐values by the first‐order model for TV in cell‐culture media at 52, 54, and 56 °C were 4.59 ± 0.05, 2.91 ± 0.05, and 1.74 ± 0.07 min, respectively, with a z‐value of 9.09 ± 0.01 °C (R² = 0.997). The Weibull model showed t_d = 1 values of 2.53 ± 0.08, 1.99 ± 0.10, and 0.57 ± 0.64 min, respectively, at the same temperatures. The D‐values for TV in spinach were 7.94 ± 0.21, 4.09 ± 0.04, and 1.43 ± 0.02 min and the z‐value was 10.74 ± 0.01 °C (R² = 0.98) by the first‐order model and 4.89 ± 0.02, 3.21 ± 0.45, and 0.25 ± 0.38 min for the Weibull model at 50, 54, and 58 °C, respectively. In comparison to previously reported results for the cultivable HNoV surrogate, murine norovirus ‐1, TV in cell‐culture media and spiked on spinach homogenates showed lower D‐ and z‐values. TV may not be an ideal HNoV surrogate for heat inactivation studies in cell‐culture media or homogenized spinach in vacuum bags.     

Inactivation of Bacillus cereus Spores on Red Chili Peppers Using a Combined Treatment of Aqueous Chlorine Dioxide and Hot‐Air Drying

The effect of a combined treatment using aqueous chlorine dioxide (ClO₂) and hot‐air drying to inactivate Bacillus cereus spores on red chili peppers was evaluated. Ten washed and dried pepper samples, each comprising half of a single pepper (Capsicum annuum L.), were inoculated with B. cereus spore suspension. The inoculated samples were washed with sodium hypochlorite (NaOCl; 50, 100, or 200 μg/mL) or ClO₂ (50, 100, or 200 μg/mL) solution for 1 min and then air‐dried (25 ± 1 °C, 47 ± 1% relative humidity), which was followed by drying with hot air at 55 °C for up to 48 h. The spore populations on the samples were enumerated and their a_w and chromaticity values were measured. The spore numbers immediately after treatment with NaOCl and ClO₂ were not significantly different. A more rapid reduction in spore numbers was observed in the samples treated with ClO₂ than those treated with NaOCl during drying. A combined treatment of ClO₂ and hot‐air drying significantly reduced the spore populations to below the detection limit (1.7 log CFU/sample). B. cereus spores on chili peppers were successfully inactivated by washing with ClO₂ solution followed by hot‐air drying whereas the pepper color was maintained.