Resistance of Bacillus cereus and its enterotoxin genes in ready-to-eat foods to γ-irradiation

This study was investigated the resistance of Bacillus cereus ATCC 13752 and its enterotoxin coding genes in cereals, vegetables, and tryptic soy broth to γ-irradiation. Screening for enterotoxin coding genes, viability test, PCR analysis, measurement of DNA concentration, cellular constituents release, SEM, and antibiotic sensitivity tests were performed after irradiation at 0, 1.5, 3, 5, 7, 10, and 15 kGy. Thirty % of strains screened possessed all enterotoxins genes. At 10 kGy B. cereus viable cell count was reduced by 4 logCFU/mL. B. cereus in vegetables and broth demonstrated higher susceptibility than those in cereals. Enterotoxins coding genes could be identified in the γ-irradiated cells, antibiotic sensitivity profile was not affected. Concentration of DNA containing enterotoxin coding genes was reduced and release of cellular constituent was highest at 15 kGy. γ-Irradiation up to 10 kGy did not eliminate B. cereus neither affected their enterotoxins coding genes from ready-to-eat food.     

Effect of γ-irradiation on the sensory quality of moist beef biltong

Moist beef biltong (mean moisture content = 46.7% and a_w = 0.919) was vacuum packaged and irradiated to target doses of 0, 2, 4, 6, and 8 kGy. Thiobarbituric acid reactive substance (TBARS) measurements and sensory difference and hedonic tests were performed to determine the effect of γ-irradiation on the sensory quality of the biltong. TBARS values only increased significantly (P < 0.05) if biltong was irradiated to at least 8 kGy, indicating a low degree of lipid oxidation. This can be attributed to the low fat content (on average 1.53%) of the biltong used in this study, as well as irradiation under vacuum conditions. All irradiated samples could be discriminated (P < 0.05) from non-irradiated biltong, but none was rated as less acceptable. Dissipation of volatiles before tasting (by exposing the product to aerobic conditions before consumption), a low degree of lipid oxidation and liking of distinct ‘irradiation flavours’ possibly all attributed to the flavour of irradiated biltong not being regarded as unacceptable compared to controls. Biltong irradiated at 2 and 4 kGy was however liked significantly more (P < 0.05) than other samples, indicating that slight, non-oxidative irradiation-induced flavour changes may contribute to flavour development in the usually more bland moist beef biltong. Although lean moist beef biltong can thus be irradiated to doses up to 8 kGy without adversely affecting the sensory acceptability, low dose irradiation (4 kGy) is most feasible to optimise the sensory quality.     

Effect of ascorbic acid and protein concentration on the molecular weight profile of bovine serum albumin and β-lactoglobulin by γ-irradiation

The effects of ascorbic acid and protein concentration on the molecular weight size distribution of BSA and β-lactoglobulin were examined after irradiation of proteins at various doses. Gamma-irradiation of protein solutions caused disruption of the ordered structure of protein molecules resulting in degradation, cross-linking, and aggregation of the polypeptide chains. SDS–PAGE and gel permeation chromatography study showed that ascorbic acid protected the aggregation and degradation of proteins by scavenging oxygen radicals produced by irradiation and the effect of irradiation on protein conformation was more significant at lower concentrations of proteins.     

Influence of γ-irradiation on the reactive-oxygen metabolism of blueberry fruit during cold storage

To explore a safe, environmentally friendly, and efficient preservation technology for blueberry (Semen trigonellae), “Bluecrop” blueberry fruits were treated with different irradiation doses. During cold storage at 0 ± 5 °C, the decay rate, fruit firmness, and indices relating to respiration and reactive-oxygen metabolism were detected regularly. Results showed that irradiation treatment with 1.0 kGy to 2.5 kGy doses was able to inhibit the respiration intensity, ethylene production, and the improvement of lipoxygenase (LOX) activity, thus reducing the increase of malondialdehyde (MDA) content and the permeability of cell membranes. In addition, irradiation treatment can improve the activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) to eliminate, on a continual basis, the constantly generated superoxide anions (O₂⁻) and hydrogen peroxide (H₂O₂), keeping them at a low level: ultimately, this effectively guaranteed the storage quality and postponed the senescence process in the blueberry fruits. Meanwhile, those irradiated at 2.5 kGy presented optimal preservation effects as the respiration was inhibited to the utmost extent and the anti-oxidisation effect was enhanced. The results prove that the ⁶⁰Co γ-irradiation treatment at proper doses is an effective method of storing post-harvest blueberry fruits at low temperatures.     

Effect of γ-irradiation on physical quality attributes and identification properties of different sauces

Gamma-irradiated (0, 1, and 10 kGy) ketchup (KTP), barbeque sauce (BBQ), and sweet chili sauce (SWC) were identified using photostimulated-luminescence (PSL) and thermoluminescence (TL) analysis and characterized for physical properties like Brix, consistency, and color. PSL-based screening showed negative results for all nonirradiated samples, while intermediated results were found for irradiated samples. Routine density separation method for mineral extraction provided better TL results; however, alkaline and acid hydrolysis could ease the process with acceptable results. A slight decrease in consistency of all the samples was observed. Brix of KTP remained unchanged, while increase of same was obvious in BBQ and SWC following irradiation. The Hunter L* value of the γ-irradiated sauces decreased except SWC samples, and the a* and b* values showed a general increase compared to the non-irradiated samples. The studied methods have potential to successfully identify and characterize the irradiated sauces for technical and regulatory requirements.     

Effect of γ-irradiation on the volatile oil constituents of turmeric (Curcuma longa)

The volatile essential oils from commercial samples of dry turmeric and samples γ-irradiated at a dose of 10 kGy were isolated using simultaneous distillation extraction technique and analyzed by GLC (Gas Liquid Chromatography) and gas chromatography/mass spectrometry (GC/MS). Some of the major compounds identified by GC/MS were α-phellandrene, p-cymene, 1:8cineol, β-caryophyllene, ar-curcumene, zingeberene, ß-sesquiphellandrene, nerolidol, turmerone, ar-turmerone, curlone and dehydrozingerone. No detectable differences were observed between the aroma impact compounds of the irradiated and commercial samples.     

Modification of bean starch by γ-irradiation: Effect on functional and morphological properties

Starches isolated from Red, White, Yellow and Black Kidney beans were treated by γ-irradiation doses of 5, 10 and 20 kGy. Physicochemical, morphological and pasting properties of irradiated bean starches were investigated. Microscopic observation under scanning electron microscope (SEM) showed that some of the bean starch granules were destroyed by γ-irradiation and the breakage was greater at a higher dose (20 kGy). Physicochemical properties differed significantly and showed strong dose-dependent relationship. Carboxyl content, solubility, water absorption capacity and transmittance increased, whereas swelling power, apparent amylose content, syneresis and pasting properties decreased upon the irradiation of kidney bean starch. Radiation doses were positively correlated with water absorption capacity and solubility index and negatively correlated with swelling index, peak viscosity, trough viscosity, breakdown and final viscosity. There were high positive correlations between pasting properties. X-ray diffraction pattern remained same upon irradiation but a decrease in crystallinity was observed with increasing irradiation dose.     

Effects of γ-irradiation on the biological activity of burdock (Arctium lappa L.) extracts

Burdock (Arctium lappa L.) extracts were prepared with different extraction methods, ethanol (70%, RT) and hot water (85°C for 3 hr, HT), and their biological activities were investigated after γ-irradiation (10 and 20 kGy). Color of the burdock extracts became brighter after application of irradiation regardless of the extraction system. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of the burdock extracts with RT and HT were 54.56 and 59.21% at 500 ppm, respectively, and the lipid oxidation of oil emulsion was delayed by addition of the extracts. The HT29 cancer cell viability was inhibited by burdock extracts with RT up to 52.45 at a 250 ppm level. The anti-mutagenicitiy against 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole and 2-nitrofluorene were also found. Results indicate that burdock extract possesses biological activities and RT showed an increasing trend in antixodiative activity and inhibition of cancer cell viability. Brighter color of the burdock extract after irradiation may improve industrial applicability.     

Effect of γ-irradiation on the antioxidant activity of turmeric (Curcuma longa L.) extracts

Effect of γ-irradiation (10KGy) on the antioxidant property of turmeric extracts was investigated. γ-irradiated as well as non-irradiated turmeric samples were subjected to successive solvent extraction using hexane, benzene, and 80% aq. methanol. Benzene extract, containing mainly curcuminoids were subjected to column fractionation in order to isolate the individual curcuminoids. The curcuminoid analogues as well as the above fractions were then tested for their antioxidant activity by measuring thiobarbituric acid value (TBAV) and peroxide value (PV) based on the air oxidation of linoleic acid. γ-irradiation at a dose of 10KGy did not affect the antioxidant activity of turmeric extracts studied.     

The effect of sterilizing doses of γ-irradiation on the molecular weight and emulsification properties of gum arabic

Experiments were performed on raw, kibbled and spray-dried gum arabic. Microbiological tests showed that following a radiation dose of 10 kGy the contaminating micro-organisms were effectively inactivated. The average molecular weight of kibbled and spray dried gum arabic was shown by viscosity measurements to be somewhat reduced as the result of γ-irradiation. No significant radiation-induced changes in the molecular weight of raw gum arabic could be detected. The yields of radiolytically produced strand breaks (breaks/100 eV of radiation absorbed) have been calculated for spray-dried [G(strand breaks) = 4.1 × 10⁻¹] and for kibbled [G(strand breaks) = 2.9 × 10⁻¹]. Gel permeation chromatography confirmed this order of radiation stability and indicated that gum arabic consists of at least three major components, the larger molecular weight fraction appearing to be the more radiation sensitive. There was no measurable change in the total hexuronic acid content (20%) of any of the samples on γ-irradiation. Finally, measurements showed no adverse effect of γ-irradiation, even up to doses of 30 kGy, on the ability of the gum arabic to stabilize emulsions. The extent of chemical change induced by irradiation with sterilizing doses has no practical adverse significance and demonstrates that this technique is suitable for processing raw gum arabic samples.     

Effect of γ-irradiation on antioxidant activity of black pepper (Piper nigrum L.)

Antioxidant activity and EPR investigations of irradiated ground black pepper (Piper nigrum L.) were evaluated. The black pepper was exposed to γ-irradiation at doses from 5 to 30 kGy. The effect of irradiation on antioxidant properties of black pepper extracts was investigated by radical-scavenging effect on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals, by determination of reducing power and content of thiobarbituric acid-reactive substances. Some significant changes were observed in creation of thiobarbituric acid-reactive substances (TBARS). Difference between non-irradiated and irradiated samples at the legal European limit dose of 10 kGy reached, on average, 23% and, at the Food and Drug Administration (FDA) 30 kGy limit, 33%. Irradiation affected significantly the DPPH radical-scavenging activity and reducing power of ground black pepper extracts. The γ-radiation treatment of ground black pepper samples observed by EPR, resulted in the production of three paramagnetic species (GI–GIII) characterized by different origin, thermal behaviour and stability. The axially symmetric EPR resonances, GI and GII, were assigned to the carbohydrate radical structures. The spin Hamiltonian parameters of GIII possessed the characteristic features of “cellulosic” radical species. The EPR measurements, performed 20 weeks after the radiation process, confirmed that temperature increase from 298 to 353 K, caused significant decrease of integral EPR signal intensity for γ-irradiated samples (∼40%), compared to the reference (non-irradiated) ground black pepper, where only 13% drop was found. Significant correlation between EPR and thiobarbituric acid methods was assessed by study of antioxidant activity changes in relation to irradiation doses and also in the case of spice storage, between EPR and reducing power methods.     

Moisture-mediated effects of γ-irradiation on antioxidant properties of mung bean (Vigna radiate L.) cultivars

The present investigation is the very first report about the effect of γ-irradiation along with moisture on antioxidant properties of mung bean. Mung bean cultivars were conditioned to moisture level of 10 (control), 12, and 14% and treated with different doses of γ-irradiation (1.0, 2.5, and 5.0 kGy). The total phenolic content (TPC) decreased upon very low (1 kGy) and low dose (2.5 kGy) of γ-irradiation while significantly increased upon further increase in dose (5 kGy) at 10% moisture. However, γ-irradiation (1 and 2.5 kGy) at 12% moisture increased the TPC by 8 and 9%, respectively, and at 5 kGy dose lowered by 15% as compared to control. Antioxidant activity (AOA) was decreased by 10% (1 kGy and 10% moisture) and increased by 13% (5 kGy and 10%) while significantly increased at all doses (at 12%) by 106%. Total flavonoids content and reducing power also affected significantly upon γ-irradiation at various moisture.Industrial relevanceThe present investigation is the first report revealing the impacts of moisture-mediated γ-irradiation of mung bean. Since γ-irradiation is a popular method for safe storage of food including legumes and cereals, the moisture content between 10 and 14% was considered safe for grain storage. But γ-irradiation of mung bean at these levels of moisture significantly changed the antioxidant potential. By selecting suitable moisture content and dose of γ-irradiation, the antioxidant potential of mung bean may be improved to get the maximum health benefit. Therefore, the legume processing industry can utilize these combinations (moisture and dose of irradiation) to improve the antioxidant properties of mung bean.     

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 γ-irradiation on the quality changes of fresh noodles prepared from wheat cultivated with N-fertilization treatments

Quality changes of fresh noodles prepared from wheat cultivated with N-fertilization treatments, followed by γ-irradiation were investigated. The protein content of the KPS60 was the highest of all treated samples, and protein contents of wheat cultivated with N-fertilizer was increased. γ-Irradiation did not affect the protein contents of the samples. However, the water holding capacity and resistant starch contents was increased by irradiation. The dry gluten and wet gluten contents of samples were further increased by γ-irradiation. The pasting properties were influenced by γ-irradiation but not N-fertilization. The hardness of noodles made with irradiated wheat flour was decreased, but the degree of decrease was small compared with that of viscosity. The gumminess and chewiness of noodles made with irradiated flour having higher protein content and WG showed also higher score. Thus, treatment of wheat flour with N-fertilization and γ-irradiation may improve the quality of Korean-style noodles during storage.     

Effect of ozonation and γ-irradiation on post-harvest decontamination of mussels (Mytillus galloprovincialis) containing diarrhetic shellfish toxins

Contamination of shellfish with diarrhetic shellfish poisoning (DSP) toxins readily occurs during algal blooms. Such phenomena raise important public health concerns and thus comprise a constant challenge to shellfish farmers, the seafood industry and health services, considering the increasing occurrence of toxic episodes around the world. To avoid the detrimental effects of such episodes, research has focused on the use of various detoxification methodologies that should be rapid, efficient, easy to apply, and will not alter the quality and sensory properties of shellfish. In the present study, both ozonation (15 mg kg(-1) for 6 h) and γ-irradiation (6 kGy) were utilised in order to reduce the toxin content of contaminated shucked mussels, collected during the DSP episodes of 2007 and 2009 in Greece. DSP toxicity was monitored using the mouse bioassay (MBA) whilst the determination of toxin content of the okadaic acid (OA) group (both free and esterified forms) was carried out by LC/MS/MS analysis. Toxin reduction using γ-irradiation was in the range of 12-36%, 8-53% and 10-41% for free OA, OA esters and total OA, respectively. The appearance and texture of irradiated mussels deteriorated, pointing to a low potential for commercial use of this method. Ozonation of mussels resulted in toxin reduction in the range of 6-100%, 25-83% and 21-66% for free OA, OA esters and total OA, respectively. Reduction of OA content was substantially higher in homogenised mussel tissue compared with that of whole shucked mussels. In addition, differences detected with regard to quality parameters (TBA, sensory attributes) between ozonated and control mussels were not considerable. Even though varying percentage reductions in OA and its derivatives were achieved using ozonation under specific experimental conditions tested, it is postulated that upon optimisation ozonation may have the potential for post-harvest commercial DSP detoxification of shucked mussels.     

Effect of ozonation and γ-irradiation on post-harvest decontamination of mussels (Mytillus galloprovincialis) containing diarrhetic shellfish toxins

Contamination of shellfish with diarrhetic shellfish poisoning (DSP) toxins readily occurs during algal blooms. Such phenomena raise important public health concerns and thus comprise a constant challenge to shellfish farmers, the seafood industry and health services, considering the increasing occurrence of toxic episodes around the world. To avoid the detrimental effects of such episodes, research has focused on the use of various detoxification methodologies that should be rapid, efficient, easy to apply, and will not alter the quality and sensory properties of shellfish. In the present study, both ozonation (15?mg?kg^?1 for 6?h) and γ-irradiation (6 kGy) were utilised in order to reduce the toxin content of contaminated shucked mussels, collected during the DSP episodes of 2007 and 2009 in Greece. DSP toxicity was monitored using the mouse bioassay (MBA) whilst the determination of toxin content of the okadaic acid (OA) group (both free and esterified forms) was carried out by LC/MS/MS analysis. Toxin reduction using γ-irradiation was in the range of 12–36%, 8–53% and 10–41% for free OA, OA esters and total OA, respectively. The appearance and texture of irradiated mussels deteriorated, pointing to a low potential for commercial use of this method. Ozonation of mussels resulted in toxin reduction in the range of 6–100%, 25–83% and 21–66% for free OA, OA esters and total OA, respectively. Reduction of OA content was substantially higher in homogenised mussel tissue compared with that of whole shucked mussels. In addition, differences detected with regard to quality parameters (TBA, sensory attributes) between ozonated and control mussels were not considerable. Even though varying percentage reductions in OA and its derivatives were achieved using ozonation under specific experimental conditions tested, it is postulated that upon optimisation ozonation may have the potential for post-harvest commercial DSP detoxification of shucked mussels.     

Influence of γ-irradiation on antioxidant,thermal and rheological properties of native and irradiated whole grain millet flours

Millets of different types like Barnyard (Echinochloa utilis), Finger (Eleusine coracana), Foxtail (Setaria italic), Kodo (Paspalum setaceum) Little (Panicum sumatrense), Pearl (Pennisetum glaucum) and Proso millets (Penicum miliaceum) are staple foods for Indian and African diets. The germination, fungal and microbial contamination leads to postharvest losses mainly due to poor warehouse storage in Asia and Africa. Six millet varieties conditioned at 12% and 14% moisture content and irradiated at a dosage of 2.5 and 5 kGy and then milled into flours. The flour was analysed for composition, antioxidant and the rheological and thermal properties. Pearl, Proso, Finger Kodo at 12% moisture contents showed significant (P ≤ 0.05) increase in Phenolic contents at 2.5 kGy level of irradiation treatments compared with native and 5% irradiation treatment level. The DPPH activity showed an interesting results (42.77–72.65%) with wide variation and a mixed trend of high and low results with irradiation. Thermal transition temperatures showed that the irradiation decreased the transition temperatures primarily due to loss of the crystalline and amorphous starch structure due to radiation that lead to rapid water uptake and shorter time to reach peak viscosity. We are further studying the application of the irradiated flours in different food products to understand the influence of irradiation on nutritional, sensory and functional properties in cereal-based products.     

Impact of γ-irradiation,CIPC treatment,and storage conditions on physicochemical and nutritional properties of potato starches

In the present study, three potato varieties were treated with chlorpropham (CIPC, 35 ppm), γ-irradiated (0.1 kGy) and stored for up to 5 months at 8 °C, and the physicochemical properties and in vitro starch digestibility of native and cooked starches were investigated. Sprouting was found to be satisfactorily suppressed by γ-irradiation and CIPC treatment. However, irradiation increased total free glucose content in two potato varieties, and decreased the thermal transition and pasting temperature of starch. The crystallinity of starch in irradiated potatoes decreased significantly (p ? 0.05) which may explain its decreased resistant starch content. Sprout inhibiting treatments and storage had no effect on in vitro starch digestibility in cooked starches, but cooling cooked starch significantly (p ? 0.05) increased its resistant starch content.     

Effect of γ-irradiation on the physicochemical and sensory properties of cashew nuts (Anacardium occidentale L.)

The present study evaluated cashew nuts' quality as a function of γ-irradiation dose in order to determine dose levels causing minimal undesirable changes to the product. Physicochemical (colour, peroxide value, hexanal content, fatty acid composition, volatile compounds) and sensory (colour, texture, odor, taste) properties of cashew nuts were determined after irradiation at doses up to 7 kGy. Results showed a five-fold increase in peroxide value (PV) and a two-fold increase in hexanal content after irradiation at a dose of 7 kGy. Of the fatty acids determined, stearic acid concentration increased while oleic acid decreased with irradiation dose. PUFA were unaffected by irradiation. Volatile compounds such as aldehydes, ketones and alcohols increased after irradiation indicating enhanced lipid oxidation. Colour parameter a∗ increased (p < 0.05) at doses >3 kGy while colour parameters L∗ and b∗ remained unaffected by irradiation. Sensory analysis showed that cashew nuts remained organoleptically acceptable at doses <3 kGy.