A comparison between E-beam irradiation and high pressure treatment for cold-smoked salmon sanitation: microbiological aspects

The effectiveness of electron beam irradiation and high pressure treatment for the sanitation of cold-smoked salmon from two points of view, microbial safety and shelf-life extension, was compared. From the response of L. monocytogenes INIA H66a to irradiation, a D value of 0.51 kGy was calculated. For samples stored at 5 °C, 1.5 kGy would be sufficient to attain a Food Safety Objective (FSO) of 2 log₁₀cfu/g L. monocytogenes for a 35-day shelf-life, whereas 3 kGy would be needed in the case of a temperature abuse (5 °C + 8 °C). Pressurization at 450 MPa for 5 min was considered to be an insufficient treatment, since the FSO of 2 log₁₀cfu/g L. monocytogenes was only attained for a shelf-life of 21 days at 5 °C. However, treatment at 450 MPa for 10 min achieved this FSO for samples held during 35 days at 5 °C, or during 21 days under temperature abuse (5 °C + 8 °C) conditions. Irradiation at 2 kGy kept the microbial population of smoked salmon below 6 log₁₀cfu/g after 35 days at 5 °C, with negligible or very light changes in its odor. Pressurization at 450 MPa for 5 min also kept the microbial population below 6 log₁₀cfu/g after 35 days at 5 °C and did not alter odor, but affected negatively the visual aspect of smoked salmon.     

Pulsed photostimulated- and thermo-luminescence investigations of γ ray-irradiated herbs

In this study, physical detection methods like pulsed photo-stimulated luminescence (PPSL) and thermoluminescence (TL) were investigated to indentify γ-ray irradiation treatment of some medicinal herbs. Dried herbal samples consisting of root, rhizome, cortex, fruit, seed, flower, spike, ramulus, folium and whole plant of nineteen different herbs were irradiated using a 60Co irradiator at 0–50 kGy. Fifteen non-irradiated control samples had photon counts (PCs) less than the lower threshold value (700 counts/60 s). The photon counts of four non-irradiated samples (roots of osterici, angelica gigas, liriope, and whole plant of taraxaci herba) were between the lower and upper threshold values (700–5000 counts/60 s). However, PCs of all the irradiated samples were found to be higher than the upper threshold value (5000 counts/60 s), clearly screening them out from the non-irradiated ones. Even after 12 weeks of storage PPSL signals of all irradiated samples were observed to be higher than the upper threshold value, making it possible to distinguish them from the non-irradiated control samples. The first TL glow curves (TL₁) for the non-irradiated samples were of very low intensity at about 250–300 °C. Irradiated samples (5–50 kGy) showed a higher peak at around 150–250 °C. TL ratios [ratio of the integrated areas of the first (TL₁) and second (TL₂) glow], measured after re-irradiation for the TL₁-tested samples at 1 kGy, were found to be less than 0.1 for the non-irradiated samples and higher than 0.1 for the irradiated ones. TL ratios for all irradiated samples measured after 12 weeks of storage under dark condition at (23 ± 2 °C) were apparent for distinguishing them from the non-irradiated controls.     

Quality of electron beam irradiation of blueberries (Vaccinium corymbosum L.) at medium dose levels (1.0-3.2 kGy)

We assessed the effect of electron beam irradiation of packaged fresh blueberries at doses greater than 1.0 kGy on the quality attributes of the fruits. Irradiation experiments were conducted using a 10 MeV (18 kW) linear accelerator with single beam fixture. Fruits were stored at 5 °C and 70.4% RH for 14 days and tested at days 0, 3, 7 and 14 for physico-chemical, textural, microstructural, and sensory characteristics. Control samples consisted of non-irradiated fruits. Irradiation at doses higher than 1.1 kGy did affect (P<0.05) the texture of blueberries as the fruits became considerably softer and less acceptable throughout storage. Only irradiation at 3.2 kGy affected the color of blueberries by the end of storage. Irradiation slightly reduced the respiration rates of the blueberries by the end of storage. In terms of overall quality, texture and aroma, only fruits exposed to 3.2 kGy were found unacceptable by the sensory panelists. Irradiation at the dose levels used in this study did not affect the density, pH, water activity, moisture content, acidity and juiciness of blueberries. Electron beam irradiation of blueberries up to 1.6 kGy is a feasible decontamination treatment that maintains the overall fruit quality attributes.     

Effect of irradiation on properties and storage stability of Som-fug produced from bigeye snapper

Effects of irradiation at different doses (0, 2 and 6 kilogray (kGy)) on the microbiological, chemical and physical properties of Som-fug, a Thai fermented fish mince, were investigated. Lactic acid bacteria (LAB), yeast and mould counts in samples irradiated at 6 kGy were not detectable throughout the storage of 30 days at 4 °C, whereas no growth was found in the sample irradiated at 2 kGy within the first 10 days. Generally, greater carbonyl contents of lipid and protein, as well as thiobarbituric acid-reactive substances (TBARS), were noticeable in the irradiated samples, than in the non-irradiated sample (p < 0.05). The carbonyl contents and TBARS increased with increasing storage time and the rate of increase was more pronounced in samples irradiated at higher dose (p < 0.05). With increasing storage time, Som-fug irradiated at 6 kGy showed greater decreases in hardness, adhesiveness, springiness and cohesiveness, than did non-irradiated samples and those irradiated at 2 kGy (p < 0.05). L^∗ value of all samples decreased, whereas a^∗ and b^∗ values increased throughout storage (p < 0.05). Lower acceptance in all attributes was observed in the samples irradiated at 6 kGy, than in other samples, particularly when storage time increased (p < 0.05). However, samples irradiated at 2 kGy showed no changes in acceptability within 20 days. The results revealed that irradiation at high dose (6 kGy) might induce lipid and protein oxidation, though the growth of microorganisms was inhibited. Therefore, the irradiation at low dose (2 kGy) could be used to control the overfermentation of Som-fug up to 20 days at 4 °C without adverse effects on quality and acceptability.     

Effect of integrated application of gamma irradiation and modified atmosphere packaging on physicochemical and microbiological properties of shiitake mushroom (Lentinus edodes)

Shiitake (Lentinula edodes) mushrooms were packed in biorientated polypropylene (BOPP) bags and exposed to different doses of gamma irradiation (1.0, 1.5, and 2.0 kGy) within the packaging, heat sealed and stored at 4 °C for 20 d. Of the three doses, 1.0 kGy was most effective in maintaining a high level of firmness. Samples treated with 1.0 kGy also exhibited smaller initial declines in soluble protein, higher increases in total sugar content and lower levels of malondialdehyde accumulation. Furthermore, 1.0 kGy promoted the accumulation of phenolics compound and showed higher antioxidant ability during storage. At higher doses, 2.0 kGy resulted in a higher microbial reduction, but showed negative effects on texture, chemical properties and functional components. All the gamma irradiation were effective in retarding mushroom sensory deterioration. Thus, application of gamma irradiation in combination with MAP can extend the storage life of shiitake mushroom up to 20 d.     

Effect of gamma irradiation on microbial load and quality characteristics of minced camel meat

The effect of gamma irradiation on microbial load, chemical and sensory characteristics of camel meat has been evaluated. Camel meat was irradiated at doses of 0, 2, 4 and 6 kGy of gamma irradiation. Irradiated and non-irradiated meat was kept in a refrigerator (1–4 °C). General composition and sensory evaluation of camel meat was done two days after irradiation, whereas, microbiological and chemical analysis was done immediately after irradiation and throughout the storage periods. The results indicated that all doses of gamma irradiation reduced the total mesophilic aerobic plate counts (TPCs) and total coliforms of camel meat. Thus, the microbiological shelf-life of camel meat was significantly extended from less than 2 weeks (control) to more than 6 weeks (samples irradiated with 2, 4 or 6 kGy). No significant differences in moisture, protein, fat, thiobarbituric acid (TBA) values, total acidity and fatty acids of camel meat were observed due to irradiation. There were slight effects of gamma irradiation in both total volatile basic nitrogen (VBN) and lipid oxidation values in camel meat. Sensory evaluation showed no significant differences between irradiated and non-irradiated camel meats.     

Stability of lipids and fatty acids in frozen and gamma irradiated Patagonian toothfish (Dissostichus eleginoides) from the Southwestern Atlantic

Patagonian toothfish were captured in the Southwestern Atlantic Ocean (FAO Zone N° 41). The fatty acid profile of total lipids and the triacylglycerol and phospholipid content of control and irradiated samples (1 and 5 kGy) stored at −18 °C were analyzed at 0 and 293 days post irradiation. The fatty acids are mainly monounsaturated acids (47 g/100 g total fatty acids), the most abundant one being oleic acid (18:1 n-9). This is followed in order of abundance by saturated fatty acids (26 g/100 g total fatty acids), consisting mainly of palmitic acid (16:0). Polyunsaturated fatty acids were less abundant (17 g/100 g total fatty acids) and consisted mainly of eicosapentaeonic (20:5 n-3) and docosahexaenoic (22:6 n-3) acids. Triacylglycerol content was 563.07 mg/mL oil, whereas phospholipids were 11.21 mg/mL oil. Gamma irradiation did not significantly affect the fatty acid profile or triacylglycerol and phospholipid content of P. toothfish stored for 293 days at −18 °C. The results suggest that the species exhibits a marked stability when subjected to irradiation and prolonged storage in the frozen state.     

Effect of gamma and electron beam irradiation on the survival of pathogens inoculated into salted, seasoned, and fermented oyster

The objective of this study was to identify the efficacy of gamma and electron beam irradiation of the food-borne pathogens including 3-strain cocktail of Listeria monocytogenes (ATCC 19114, 19115, and 19111), Staphylococcus aureus (ATCC 6538, 25923, and 29213), and Vibrio parahaemolyticus (ATCC 17802, 33844, and 27969) in salted, seasoned, and fermented oyster (oyster Jeotkal, 8% salt), commercially available in the market. Irradiation (0, 0.5, 1, 2, and 5 kGy) significantly reduced the initial microbial level not only immediately after irradiation but also during storage at 10 °C for 4 weeks (P ≤ 0.05). No viable cell was detected at 5 kGy of irradiation at a detection limit of 10¹ CFU/g. Gamma irradiation was more effective than electron beam irradiation, and yielded D₁₀ values of 0.60, 0.71, and 0.29 kGy for L. monocytogenes, S. aureus, and V. parahaemolyticus, and those of electron beam irradiation were 0.69, 0.94, and 0.29 kGy, respectively. V. parahaemolyticus was most sensitive to irradiation and storage among all pathogens tested. Sensory quality was not affected by irradiation treatment. Results suggest that a low dose irradiation can improve the microbial quality and reduce the risk by the food-borne pathogens of oyster Jeotkal, which has limited alternative sterilization methods due to the temperature sensitivity of food products.     

Changes in physicochemical and sensory-properties of irradiated rice during storage

Milled aromatic rice (KDML-105) was γ-irradiated at doses of 0, 0.2, 0.5 and 1.0 kGy. Changes in physicochemical and sensory properties were recorded during subsequent storage in polyethylene bags at ambient temperature for 1 year. Similar trends were observed in both irradiated and non-irradiated samples. Insignificant changes in yellowness and total solids in cooking water were observed during storage of irradiated rice compared with those of naturally-aged rice. Irradiated rice showed less increase in Rapid Visco Analyzer (RVA) setback, greater reduction of RVA breakdown, and softer texture than non-irradiated rice. It also had a softer but slimy texture, off odour and inferior taste compared with the non-irradiated sample. Based on overall acceptability to panelists preferring fresh rice, non-irradiated rice could be stored for more than 1 year while rice irradiated at 0.2, 0.5 and 1.0 kGy had shelf lives of 9, 7 and 2 months, respectively.     

Antioxidative activity of carnosine in gamma irradiated ground beef and beef patties

The activity of carnosine as a natural antioxidant in gamma irradiated ground beef and beef patties was studied. Samples of ground beef, in the absence and presence of 0.5% or 1.0% carnosine, as well as raw and cooked beef patties prepared with 1.5% salt (NaCl), in the absence and presence of 0.5% or 1.0% carnosine, were gamma irradiated at doses of 0, 2, and 4 kGy. The extent of oxidation in irradiated and non-irradiated samples of ground beef and raw beef patties was then determined during refrigerated (4 ± 1 °C) and frozen (−18 °C) storage, while determined for cooked beef patties during refrigerated storage only. Moreover, the determination of metmyoglobin (MetMb) accumulation and sensory evaluation for the visual color were carried out for samples of ground beef and raw patties. The results indicated that salt or salt and cooking accelerated the oxidative processes and significantly increased the peroxide value (PV) and thiobarbituric acid reactive substances (TBARS) in the prepared non-irradiated samples. However, salt slowed down the accumulation of MetMb in raw patties. Irradiation treatments and storage in the absence of carnosine significantly (P < 0.05) increased the PV and TBARS in samples, at higher rates in salted or salted and cooked beef. Moreover, irradiation and storage significantly (P < 0.05) increased the formation of MetMb in ground beef and raw patties in the absence of carnosine. Addition of carnosine significantly (P < 0.05) reduced the oxidative processes and MetMb formation (proportionally to the used concentration) in samples post-irradiation and during storage. Furthermore, carnosine exerted significant efficacy in maintaining an acceptable visual red color post-irradiation and during storage of ground beef and raw patties. These results demonstrate that carnosine can be successfully used as a natural antioxidant to increase the oxidative stability in gamma irradiated raw and cooked meat products.     

Greek dry-salted olives: Monitoring the dry-salting process and subsequent physico-chemical and microbiological profile during storage under different packing conditions at 4 and 20 °C

Naturally black olives cv. Thassos were processed in dry salt according to industrial procedure by uniformly dispersing 40 kg of coarse salt in 100 kg freshly harvested olives. Dry-salting process was monitored by measuring selected physico-chemical (weight loss, NaCl content, pH, a_w, reducing sugars) and microbiological parameters (total viable counts, lactic acid bacteria, enterobacteria, yeasts, pseudomonads). Total weight loss amounted to 21 g/100 g after 80 days of dry-salting. Salt content in the fruits increased to 7.4 g/100 g followed by a decrease in water activity from 0.98 to 0.76. The pH did not change significantly presenting a slight decrease from 5.25 to 4.92. The initial microflora of the fruits comprised of lactic acid bacteria (4.1 log₁₀ cfu/g), yeasts (5.7 log₁₀ cfu/g), enterobacteria (3.7 log₁₀ cfu/g ) and pseudomonads (4.0 log₁₀ cfu/g). In the end of dry-salting, no microbial groups were enumerated apart from yeasts, due to the low water activity of the product. After dry-salting, olives were packed in HDPE bags under air (control samples) and 100 ml/100 ml CO₂. Another lot of fruits was dipped in 1 g/100 ml solution of potassium sorbate for 10 min prior to packing in the same bags under aerobic conditions. All packages were stored at 4 and 20 °C for a period of 180 days. During storage, the microbial flora comprised of yeasts, while no lactic acid bacteria, enterobacteria, pseudomonads or Staphylococcus aureus were detected as the low water activity/high salt content does not favour their growth. At 4 °C, the population of yeasts declined steadily throughout storage, but to a different extend depending on the packing treatment. At 20 °C, only potassium sorbate was effective in suppressing yeast growth. All packing treatments prevented fungal growth at both storage temperatures, apart from the samples stored in air. The pH, a_w and salt content did not change significantly throughout storage.     

Modelling the effect of gamma irradiation on the inactivation and growth kinetics of psychrotrophic bacteria in squid rings during refrigerated storage. Shelf-life predictions

Psychrotrophic bacteria behaviour, when gamma irradiation is applied with shelf-life extension purposes to a fresh squid product, was modelled. In this regard, the effect of gamma irradiation at 0, 1.8, 3.3 and 5.8 kGy on psychrotrophic microorganisms in vacuum-packed squid (Illex argentinus) rings was analysed during storage at 4–5 °C. First-order kinetics satisfactorily described the radio-induced inactivation of the initial psychrotrophs population. The growth of surviving bacteria during storage was fitted to two empirical models: modified Gompertz model and a polynomial expression dependent on irradiation dose and storage time. In turn, the influence of irradiation dose on kinetic parameters of Gompertz model was described by second order polynomials. Both proposed models satisfactorily described the behaviour of psychrotrophs as affected by gamma irradiation, allowing accurate shelf-life predictions for doses up to 5.3 kGy. Considering the predictions accuracy, complete Gompertz model was preferred and model validation was done for irradiation at 4.8 kGy.     

Effect of Co γ-irradiation on postharvest quality and selected enzyme activities of Pleurotus nebrodensis

Freshly harvested Pleurotus nebrodensis fruit bodies were exposed to four different doses (0.8-2.0 kGy) of ⁶⁰Co γ-irradiation and various physiological changes associated with postharvest deterioration, as well as the activities of selected enzymes (proteinase, polyphenoloxidase, superoxide dismutase, catalase) thought to play a role in the process of deterioration, were monitored during 22 days of subsequent storage at 4 °C and 65-70% relative humidity. An irradiation dose of 1.2 kGy significantly delayed (by 6-9 days) the onset of fruit body softening, splitting and browning compared with non-irradiated controls and test samples subjected to lower or higher irradiation doses. Irradiation with 1.2 and 1.6 kGy also had a positive effect on other indicators of mushroom tissue senescence, resulting in smaller decreases in soluble protein levels and more protracted increases in proteinase activity. Peak levels of polyphenoloxidase activity, widely recognized as causing postharvest browning of mushroom tissue, were also significantly lower (P < 0.05) in fruit bodies exposed to 1.2 kGy compared with non-irradiated controls. Our data increase our understanding of the effects of γ-irradiation on the biochemical changes associated with postharvest deterioration in P. nebrodensis, and improve the prospects of more targeted strategies for extending the shelf life of both this and other mushrooms.     

Effects of carbon monoxide-modified atmosphere packaging and irradiation on E. coli K12 survival and raw beef quality

The objective of this study was to evaluate the combined effects of irradiation and carbon monoxide in modified atmosphere packaging (CO-MAP) on total plate counts, Escherichia coli K12, color, and odor of fresh beef during refrigerated storage. Beef was packaged aerobically or in CO-MAP, and irradiated at 0, 0.5, 1.0, 1.5 or 2.0 kGy then held at 4 °C for 28 days. Raw beef odor decreased and acid/sour, rancid and grassy odors increased starting on day 14. Initially, no difference existed for visual green color scores due to gas atmosphere. After 14 days of storage, aerobically packaged beef was greener and less red than CO-MAP packaged beef. The a∗ value of CO-MAP packaged beef was higher than that of aerobically packaged beef. Red color of CO-MAP packaged samples decreased slightly in some irradiated samples after 14 days of storage. On day 0 and thereafter, no coliforms were detect after irradiation at 1.5 or 2.0 kGy regardless of packaging format. These findings suggest that CO-MAP could be used to preserve beef color irradiated at doses sufficient to reduce microbial loads to safe levels during 28 days of storage.     

Fate of Staphylococcus aureus in cheese treated by ultrahigh pressure homogenization and high hydrostatic pressure

We evaluated the influence of ultrahigh pressure homogenization (UHPH) treatment applied to milk containing Staphylococcus aureus CECT 976 before cheese making, and the benefit of applying a further high hydrostatic pressure (HHP) treatment to cheese. The evolution of Staph. aureus counts during 30 d of storage at 8°C and the formation of staphylococcal enterotoxins were also assessed. Milk containing approximately 7.3 log₁₀ cfu/mL of Staph. aureus was pressurized using a 2-valve UHPH machine, applying 330 and 30 MPa at the primary and the secondary homogenizing valves, respectively. Milk inlet temperatures (T_in) of 6 and 20°C were assayed. Milk was used to elaborate soft-curd cheeses (UHPH cheese), some of which were additionally submitted to 10-min HHP treatments of 400 MPa at 20°C (UHPH+HHP cheese). Counts of Staph. aureus were measured on d 1 (24 h after manufacture or immediately after HHP treatment) and after 2, 15, and 30 d of ripening at 8°C. Counts of control cheeses not pressure-treated were approximately 8.5 log₁₀ cfu/g showing no significant decreases during storage. In cheeses made from UHPH treated milk at T_in of 6°C, counts of Staph. aureus were 5.0 ± 0.3 log₁₀ cfu/g at d 1; they decreased significantly to 2.8 ± 0.2 log₁₀ cfu/g on d 15, and were below the detection limit (1 log₁₀ cfu/g) after 30 d of storage. The use of an additional HHP treatment had a synergistic effect, increasing reductions up to 7.0 ± 0.3 log₁₀ cfu/g from d 1. However, for both UHPH and UHPH+HHP cheeses in the 6°C T_in samples, viable Staph. aureus cells were still recovered. For samples of the 20°C T_in group, complete inactivation of Staph. aureus was reached after 15 d of storage for both UHPH and UHPH+HHP cheese. Staphylococcal enterotoxins were found in controls but not in UHPH or UHPH+HHP treated samples. This study shows a new approach for significantly improving cheese safety by means of using UHPH or its combination with HHP.     

Effects of γ-irradiation on Listeria monocytogenes population,colour, texture and sensory properties of Feta cheese during cold storage

Feta, a white brine cheese, was produced and contaminated with Listeria monocytogenes. Contamination occurred either at the beginning (pre-process contamination) or at the end of Feta manufacturing (post-process contamination). In the first case the milk was contaminated with 10³ cfu/ml, and 2 months later, in the final product, the L. monocytogenes population was approximately 10⁵ cfu/g. In the second case, the brine (NaCl, 7% w/v), in which the Feta was packaged, was contaminated with 10³ cfu/ml. Contaminated Feta samples were vacuum-packaged and exposed to irradiation doses of 1.0, 2.5 and 4.7 kGy and stored at 4 °C for a month. In the pre-process contaminated samples none of the irradiation doses eliminated L. monocytogenes; however the highest dose reduced the viable population to a level which is in compliance with EC regulations. In the post-process contamination, the 2.5 kGy and 4.7 kGy doses reduced L. monocytogenes counts below the detection limit. Irradiation had no effect on the texture of Feta. Irradiation at 4.7 kGy increased Feta's redness and decreased its yellowness and lightness. Sensorial analyses showed that at the 4.7 kGy dose, the aroma profile of Feta was temporarily affected, since it was restored after 30 days of cold storage.     

Effect of gamma irradiation on fungal load, chemical and sensory characteristics of walnuts (Juglans regia L.)

Walnuts of the Baladi variety were treated with 0, 0.5, 1.0, 1.5 and 2.0 kGy of gamma irradiation. The irradiated and unirradiated nuts were stored at room temperature (15-18°C) and 50-70% r.h. Fungal load, proximate composition (moisture, protein, fat and ash contents), chemical changes and sensory properties of nuts were evaluated immediately after irradiation and after 12 months of storage. The results indicated that gamma irradiation reduced fungal load. The doses applied did not cause any significant change in proximate composition of walnuts. Gamma irradiation increased total acidity and decreased iodide value and volatile basic nitrogen (VBN) immediately after treatment. After 12 months of storage, gamma irradiation decreased total acidity and peroxide value and increased iodide value and VBN. No significant differences were observed between irradiated and nonirradiated samples in flavor and aroma immediately after irradiation. After 12 months of storage, higher doses (1.5 and 2.0 kGy) had a negative effect on sensory characteristics.     

Effect of gamma radiation and cold storage on chemical and organoleptic properties and microbiological status of liquid egg white and yolk

This investigation aims to establish a feasible radiation dose for treating liquid egg white (LEW) and yolk (LEY) at room temperature to improve their microbial safety. Samples of LEW and LEY were subjected to gamma irradiation doses of 0,1,2,3 and 4 kGy at room temperature followed by storage at 4 ± 1 °C. Then the effects of irradiation and cold storage on proximate composition, pH, soluble protein and free sulfhydryl content (SH) were determined for LEW and LEY in addition to the contents of total carotenoids in LEY. Moreover, free fatty acids (FFA) and peroxide value (PV) were determined for lipids of LEY.The microbial safety of LEW and LEY was established during storage throughout the enumeration of the total plate count, enterobacteriaceae, Staphylococcus aureus as well as the detection of Salmonella. The effects of irradiation at 3 kGy dose, which was enough for improving the microbial safety of samples, on amino acid composition of LEW and LEY and fatty acid profiles of LEY lipids were studied. In addition, sensory evaluation was carried out for liquid and scrambled egg white and egg yolk samples. The results showed that gamma irradiation and refrigerated storage had no significant effects on proximate composition and pH of liquid egg samples, while significantly decreased the contents of total carotenoids in LEY samples. Furthermore, gamma irradiation had no significant effects on protein solubility and the contents of free SH in LEW, while induced significant slight decreases in protein solubility and the contents of free SH in LEY. Cold storage, however, showed no significant effects on protein solubility and free SH in all liquid egg samples. FFA contents and PV of LEY lipids significantly increased post irradiation treatments and during storage, but the observed values were relatively low and acceptable. In addition, gamma irradiation at 3 kGy dose had no significant effects neither on the amino acid composition of LEW and LEY nor on fatty acid profiles of LEY lipids. The sensory preference did not alter neither for the liquid egg samples nor for scrambled egg samples that prepared from irradiated liquid egg products. Finally, gamma irradiation at 3 kGy dose appeared to be the optimum for treating LEW and LEY at room temperature followed by cold storage at 4 ± 1 °C.     

Effect of high-pressure processing on reduction of Listeria monocytogenes in packaged Queso Fresco

The effect of high-hydrostatic-pressure processing (HPP) on the survival of a 5-strain rifampicin-resistant cocktail of Listeria monocytogenes in Queso Fresco (QF) was evaluated as a postpackaging intervention. Queso Fresco was made using pasteurized, homogenized milk, and was starter-free and not pressed. In phase 1, QF slices (12.7 × 7.6 × 1 cm), weighing from 52 to 66 g, were surface inoculated with L. monocytogenes (ca. 5.0 log₁₀ cfu/g) and individually double vacuum packaged. The slices were then warmed to either 20 or 40°C and HPP treated at 200, 400, and 600 MPa for hold times of 5, 10, 15, or 20 min. Treatment at 600 MPa was most effective in reducing L. monocytogenes to below the detection level of 0.91 log₁₀ cfu/g at all hold times and temperatures. High-hydrostatic-pressure processing at 40°C, 400 MPa, and hold time ≥15 min was effective but resulted in wheying-off and textural changes. In phase 2, L. monocytogenes was inoculated either on the slices (ca. 5.0 log₁₀ cfu/g; ON) or in the curds (ca. 7.0 log₁₀ cfu/g; IN) before the cheese block was formed and sliced. The slices were treated at 20°C and 600 MPa at hold times of 3, 10, and 20 min, and then stored at 4 and 10°C for 60 d. For both treatments, L. monocytogenes became less resistant to pressure as hold time increased, with greater percentages of injured cells at 3 and 10 min than at 20 min, at which the lethality of the process increased. For the IN treatment, with hold times of 3 and 10 min, growth of L. monocytogenes increased the first week of storage, but was delayed for 1 wk, with a hold time of 20 min. Longer lag times in growth of L. monocytogenes during storage at 4°C were observed for the ON treatment at hold times of 10 and 20 min, indicating that the IN treatment may have provided a more protective environment with less injury to the cells than the ON treatment. Similarly, HPP treatment for 10 min followed by storage at 4°C was the best method for suppressing the growth of the endogenous microflora with bacterial counts remaining below the level of detection for 2 out of the 3 QF samples for up to 84 d. Lag times in growth were not observed during storage of QF at 10°C. Although HPP reduced L. monocytogenes immediately after processing, a second preservation technique is necessary to control growth of L. monocytogenes during cold storage. However, the results also showed that HPP would be effective for slowing the growth of microorganisms that can shorten the shelf life of QF.     

The comparative effect of steaming and irradiation on the physicochemical and microbiological properties of dried red pepper (Capsicum annum L.)

The comparative effects of steaming and gamma irradiation on the physicochemical and microbiological properties of dried red pepper (Capsicum annum L.) were investigated during post-treatment storage at refrigerated (4 ± 2 °C) and room (20 ± 2 °C) (RT) temperatures for 6 months. Whole dried peppers were either steamed, hot air-dried and processed into powder form or powderised, packed in PE bags and gamma-irradiated at 10 kGy. The commercial steam treatment led to a 1- to 2-log reduction in the initial microbial load (10⁶ CFU/g) accompanied with changes in spice as indicated by low Hunter’s colour values and reduced sensory scores in RT-stored samples. However, irradiation resulted in a 5-log reduction with minimal effects on the physicochemical properties, except for the decreased content of capsanthin in the irradiated samples. The functional components of spices were not apparently affected by both treatments. The refrigerated storage following irradiation is recommendable for powdered red pepper to minimise physicochemical changes.