Nutritional quality evaluation of electron beam-irradiated lotus (Nelumbo nucifera) seeds

Nutritional and antinutritional qualities, and functional properties of raw and electron beam-irradiated (doses: 0, 2.5, 5, 7.5, 10, 15 and 30 kGy) lotus seeds were studied. Seeds were rich in protein, amino acids, unsaturated fatty acids and minerals, without heavy metal contamination. Irradiation of seeds revealed a decrease in crude protein and fibre, which was not significant at any of the doses. However, significant increase of ash (10 kGy onwards) and carbohydrates (at 30 kGy) were recorded after irradiation. Seed flours showed a significant dose-dependent decrease in water absorption capacity, while oil absorption capacity significantly increased from 10 kGy onwards (p < 0.05). Also, significant increase in protein solubility (5 kGy onwards) and foaming capacity (7.5 kGy onwards) with improvement in the least gelation capacity (5 kGy onwards) of seed flour (p < 0.05) was recorded after irradiation. Electron beam irradiation of seeds resulted in significant dose-dependent elevation of total phenolics and tannins, while phytic acid was eliminated at 5 kGy. Seeds of lotus can serve as food and minimise protein-energy malnutrition of economically weaker sections of the population in developing countries. The seed flours also possess great potential for development of new food products and formulations. As a physical method of preservation, electron beam irradiation was effective in the retention of the nutritional qualities of lotus seeds and is recommended for commercial exploitation.     

Free radicals in velvet bean seeds (Mucuna pruriens L. DC.) and their status after γ-irradiation and conventional processing

Free radicals in velvet bean seeds, a nutarceutically valued legume were examined by electron spin resonance (ESR) spectroscopy. The status of free radicals present naturally, after irradiation and conventional processing were recorded by entrapping small quantities of seed samples in potassium chloride powder in ESR quartz tubes. The ESR signal at g=2.0055(±0.0001) were more prominent in seed coat than cotyledon portion. Gamma irradiation of seeds (for hygienization and quarantine purposes) at different doses (0, 2.5, 5, 7.5, 10, 15 and 30 kGy) resulted in a dose-dependent increase of signal intensity at g=2.0055 in seed coat as well as in cotyledon. In seed coat, a weak triplet (satellite peak) accompanied the central line. This satellite peak (left line ‘g’) can be used as an authentic indication of radiation treatment of Mucuna seeds and can be employed as one of the detection methods for similarly irradiated legume seeds possessing prominent seed coat. In cotyledon, irradiation at high doses (15 and 30 kGy) showed a significant reduction of the ESR signals (P<0.05), which has been attributed to possible increase in free radical scavengers (particularly polyphenols). Some of the common processing practices such as microwave roasting, flame heating and pounding also generated free radicals similar to irradiation treatments. Results of the present study substantiate the suitability of employing ESR technique for detection of free radicals present naturally or produced after radiation and conventional processing. The results of this study might also be feasible for successful application of gamma irradiation of Mucuna seeds for quarantine purposes.     

Antioxidant properties of methanolic extracts from Agaricus blazei with various doses of γ-irradiation

Agaricus blazei Murrill (Agariaceae) was irradiated with gamma rays at doses of 2.5, 5, 10, 15 and 20 kGy and the antioxidant properties of its methanolic extracts were studied. At 7.5 and 10.0 mg/ml, antioxidant activities of methanolic extracts from 2.5 to 20 kGy γ-irradiated A. blazei were significantly higher than those of methanolic extract from the nonirradiated control. At 0.5-7.5 mg/ml, reducing powers of methanolic extracts from A. blazei with 2.5, 10, 15 and 20 kGy of irradiation and without irradiation were comparable. All methanolic extracts showed excellent scavenging abilities of 95.2-100.7% against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals at 0.5 mg/ml. With regard to the scavenging ability against hydroxyl radicals, unirradiated and γ-irradiated A. blazei were comparable. Total phenols were the major naturally occurring antioxidant components found in the range of 18.77-21.48 mg/g. All EC₅₀ values were below 10 mg/ml, except values in reducing power, scavenging ability against DPPH radicals and chelating ability against ferrous ions were below 1 mg/ml. That indicates the unirradiated and irradiated A. blazei were good in antioxidant properties. Summarily, up to 20 kGy of irradiation did not remarkably affect the amounts of total antioxidant components in A. blazei.     

Characterisation of three starch degrading enzymes: thermostable β-amylase, maltotetraogenic and maltogenic α-amylases

White sesame seeds (Sesamum indicum L.) were studied with the purpose to evaluate γ-irradiation effect at 2.5, 5.0 and 10.0 kGy on lipid and fatty acid content, colour and protein allergenicity and to identify whether sesame oil was extracted from irradiated seeds by using High Resolution Nuclear Magnetic Resonance spectroscopy (HR-NMR). The fat decreased significantly, whereas triglyceride and phospholipid content was significantly decreased by the increase of irradiation dose. Monounsaturated and polyunsaturated fatty acids and unsaturated/saturated fatty acids ratio decreased. The presence of radiolytic decomposition products, shown by NMR, formed after a 2.5 kGy dose, confirmed that the lipid content decrease was a result of the irradiation process. The allergenicity of storage seed proteins was not significantly affected by irradiation up to 10.0 kGy. Colour parameter a^* increased after 5.0 kGy, while L^* values decreased significantly after 2.5 kGy. Conclusively, irradiation could be applied at doses <2.5 kGy while sustaining the sesame seed nutritional benefits.     

Effect of soaking and hydrothermal processing methods on the levels of antinutrients and in vitro protein digestibility of Bauhinia purpurea L. seeds

The effects of various domestic processing methods such as soaking, cooking and autoclaving on the levels of certain antinutritional factors and in vitro protein digestibility of seeds of Bauhinia purpurea L., an underutilised legume collected from South India, were investigated. The raw seeds were found to contain antinutritional factors like total free phenolics (2.75 g/100 g), tannins (2.35 g/100 g), phytic acid (692 mg/100 g) and flatulence factors, raffinose (0.54 g/100 g), stachyose (1.17 g/100 g) and verbascose (0.95 g/100 g). Soaking the seeds in distilled water caused maximum reduction in the phytic acid content (37%), whereas soaking in NaHCO₃ solution reduced significant levels of phenolics and tannins (72% and 78%, respectively). A reduction in the levels of oligosaccharides (raffinose by 63%, stachyose by 42% and verbascose by 79%) was observed during cooking. Of the attempted treatments, autoclaving appeared to be most effective in reducing levels of all the investigated antinutrients, except phytic acid, and also improved the in vitro protein digestibility of B. purpurea seeds.     

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 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.     

The effects of gamma-irradiation on the nucleotide degradation compounds in sea bass (Dicentrarchus labrax) stored in ice

The effects of two irradiation doses (2.5 and 5 kGy) on nucleotide breakdown compounds in sea bass stored in ice were investigated. Nucleotide degradation was slower in sea bass irradiated at 2.5 and 5 kGy than untreated samples. Irradiated samples had lower hypoxanthine and inosine content than the control group. Significant differences (p < 0.05) in K and related values were found between control groups and irradiated samples (2.5 and 5 kGy). H and G values showed a good correlation with storage time (r² ? 0.98) while linear regressions of K and Ki ranged from 0.95 and 0.93 to 0.98 and 0.97, respectively. A dose of 5 kGy seemed to be more effective than that of 2.5 kGy to reduce nucleotide breakdown in sea bass. The best linear correlation was obtained from G and H values; thus, they might be used as freshness indicators for non-irradiated and irradiated sea bass.     

Use of mild irradiation doses to control pathogenic bacteria on meat trimmings for production of patties aiming at provoking minimal changes in quality attributes

The objectives of the present work were to assess the use of moderate doses of gamma irradiation (2 to 5 kGy) and to reduce the risk of pathogen presence without altering the quality attributes of bovine trimmings and of patties made of irradiated trimmings. Microbiological indicators (coliforms, Pseudomonas spp and mesophilic aerobic counts), physicochemical indicators (pH, color and tiobarbituric acid) and sensory changes were evaluated during storage. 5 kGy irradiation doses slightly increased off flavors in patties. Two pathogenic markers (Listeria monocytogenes and Escherichia coli O157:H7) were inoculated at high or low loads to trimming samples which were subsequently irradiated and lethality curves were obtained. Provided that using irradiation doses ≤ 2.5 kGy are used, reductions of 2 log CFU/g of L. monocytogenes and 5 log CFU/g of E. coli O157:H7 are expected. It seems reasonable to suppose that irradiation can be successfully employed to improve the safety of frozen trimmings when initial pathogenic bacteria burdens are not extremely high.     

Effects of gamma irradiation on the development and reproduction of Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

The inhibitory effects of gamma irradiation were demonstrated on the development and reproduction including egg hatch, pupation, adult eclosion and oviposition of Plodia interpunctella. Failure of all these events increased with increasing doses from 0.1 to 1.0 kGy. However, the rates of developmental inhibition were different among three behavioral events. Egg hatch was almost completely inhibited by 0.5 kGy and higher doses. Pupation was completely inhibited by 0.25 kGy, but adult eclosion was not completely inhibited even by 1.0 kGy. In addition, different age groups within the egg and final larval stages differed in their susceptibility to 0.1 and 0.25 kGy doses; the rates of both hatching and pupation were lower when young individuals were irradiated. Fecundity and hatchability of eggs were greatly reduced when pupae were irradiated at 0.1 kGy and completely inhibited at 0.25 kGy and higher doses. This suggests that although some adults eclosed from pupae irradiated at 0.25 kGy and higher doses, they were not able to lay eggs. Our results suggest that irradiation at 0.5 kGy is appropriate for the inhibition of development and reproduction of P. interpunctella.     

Antioxidant properties of methanolic extracts from Antrodia camphorata with various doses of γ-irradiation

The mycelia of Antrodia camphorata (Chang & Chou) Wu, Ryvarden & Chang were irradiated with gamma rays at doses of 2.5, 5, 10, 15 and 20 kGy and the antioxidant properties of the methanolic extracts were studied. At 2.5 mg/ml, antioxidant activities of methanolic extracts from 10 to 20 kGy-irradiated mycelia were significantly higher than those of the non-irradiated control. Reducing powers of methanolic extracts from unirradiated and 0.5–7.5 kGy-irradiated mycelia were comparable except for the 20 kGy-irradiated mycelia. At 2.5 mg/ml, all methanolic extracts showed excellent scavenging abilities of 92.3–103% on DPPH radicals. Scavenging abilities of methanolic extracts from 2.5 to 20 kGy irradiated mycelia were better than that of the unirradiated control at 10 mg/ml. With irradiation at 5–20 kGy, mycelia possessed higher chelating ability on ferrous ions than did the unirradiated control. The EC₅₀ values were below 15 mg/ml, except for values of scavenging ability of the unirradiated control on hydroxyl radicals. Total phenols were the major naturally occurring antioxidant components found in the range of 13.0–15.5 mg/g. In summary, γ-irradiation not only maintained the antioxidant properties of mycelia but also enhanced the antioxidant properties to some extent.     

Effects of gamma irradiation on color characteristics and biological activities of extracts of Lonicera japonica (Japanese honeysuckle) with methanol and acetone

Effects of gamma irradiation on the color characteristic and biological activities of methanol and acetone extracts of Lonicera japonica (Japanese honeysuckle) irradiated at 0, 10, 20, and 30 kGy were investigated. Hunter color L^*- and a^*-value increased by irradiation in a dose-dependent manner, resulting in it being lighter than the nonirradiated, while Hunter color b^*-values decreased by irradiation (P<0.05). The extracts from L. japonica showed an inhibition effect against tyrosinase, xanthine oxidase and the nitrite scavenging ability. Tyrosinase inhibition effect of L. japonica was higher in the irradiated sample than the nonirradiated, and the effect was increased by irradiation doses. The L. japonica extracts had a higher inhibitory effect against xanthine oxidase, and the effect was not changed by irradiation. Nitrite scavenging activity was the highest in L. japonica extract at pH 1.2. The difference between solvents used was not detected. Thus, gamma irradiation may have no influence on the biological activities of the L. japonica extracts except for the tyrosinase inhibition effect when irradiated up to 30 kGy.     

Gamma irradiation of air-dried olive leaves: Effective decontamination and impact on the antioxidative properties and on phenolic compounds

Olive leaves are commercialized for their antioxidative value due to their valuable phenolic compounds. The present study aimed to evaluate the effect of gamma irradiation on microbial load, on antioxidative properties and on phenolic compounds of air-dried olive leaves. Irradiation was applied up to 25 kGy (5 kGy intervals) to powdered and intact samples. Total aerobic bacteria, yeast and mold, and lactic acid bacteria were counted after gamma irradiation. Decontamination was obtained at 20 kGy. The radioresistance of microbial population was high with D₁₀ values between 9.74 and 25.12 kGy. Besides, gamma irradiation up to 25 kGy was found to maintain the antioxidant capacity, molecular mass distribution of polyphenolics, total phenolics, ortho-diphenols, flavonoids, oleuropein, verbascoside and rutin contents.     

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.     

Changes to physicochemical properties and aroma of irradiated rice

Gamma-irradiation at dosages of 0.2-2.0 kGy controlled insects in packaged aromatic milled rice (KDML-105). However, it induced changes in physicochemical properties of the rice. Decreases in some pasting parameters, increases in water absorption and total solids in cooking water, and decreased cooked rice hardness showed that starch granules of milled rice were changed by irradiation. Alterations of the granular structure of starch were seen by scanning electron microscopy. These changes affected the texture of the cooked rice. In addition to an increase in yellowness (b-value) and an increase in lipid oxidation (TBA, thiobarbituric acid) and a decrease in volatile compounds (ACPY, 2-acetyl-1-pyrroline), irradiation contributed to changes in the colour and aroma of irradiated cooked rice. Gamma dosage had a significant positive correlation (P<0.01) with the b-value, pasting properties and a negative correlation with cooked rice hardness and ACPY content. Panelists responded to these changes with less perception of sensory qualities. Maximum doses of less than 1.0 kGy should be used to disinfest aromatic rice although when considered strictly on aroma, less than 0.5 kGy would be more suitable.     

Physicochemical,thermal and pasting properties of starch separated from γ-irradiated and stored potatoes

The morphological, thermal and pasting properties of starch separated from potatoes of three varieties (Kufri Chandramukhi, Kufri Jyoti and Kufri Chipsona-2), treated either with CIPC (isopropyl N-(3 chlorophenyl) carbamate) or γ-irradiation (Co⁶⁰, 0.1 and 0.5 kGy) and subsequently stored at 8, 12 and 16 °C for 90 days, were studied. Scanning electron microscopy (SEM) showed the presence of oval and irregular shaped starch granules with a diameter range of 15–16 μm. Mean granule size of starch separated from potatoes stored at 12 °C ranged from 18–25 μm and irradiation treatment resulted in an increase in the proportion of small size granules. The irradiation of potatoes with 0.5 kGy resulted in starch with significantly lower peak-, trough- and breakdown-viscosity as compared to starch from potatoes treated with either CIPC or 0.1 kGy irradiation. The irradiation of potatoes with 0.5 kGy caused a significant increase in setback and pasting temperature. Pasting temperature of starch was observed to vary with the storage temperature. Starch separated from potatoes stored at higher temperature showed lower pasting temperature and vice versa. The starch from potatoes stored at 8 °C showed higher peak-, trough- and breakdown-viscosity and lower setback. Peak viscosity increased and swelling volume decreased with increase in storage temperature. FTIR spectra showed that the starch from irradiated potatoes displayed a significant decrease in the intensity of the C–H stretch region between 2800 and 3000 cm⁻¹, which was observed to be irradiation dose-dependent, and higher with 0.5 than 0.1 kGy. However, a slight broadening of O–H stretch (3000–3600 cm⁻¹) in starches from irradiated potatoes was observed. The spectral changes caused by γ-irradiation were apparent in the O–H stretch (3000–3600 cm⁻¹), C–H stretch (2800–3000 cm⁻¹) and bending mode of water (1600–1800 cm⁻¹).     

Gamma irradiation of cowpea (Vigna unguiculata L. Walp) flours and pastes: Effects on functional,thermal and molecular properties of isolated proteins

In a previous study irradiation of cowpea flours and pastes at medium (10 kGy) and high (50 kGy) doses resulted in significant changes in protein-related functional properties. To understand some of the effects of gamma irradiation on cowpea proteins in particular, we isolated proteins from cowpea flours (FPC) and pastes (PPC) treated with gamma irradiation at 2, 10, and 50 kGy and analyzed their functional, thermal and molecular properties. Nitrogen solubility index of both FPC and PPC decreased, whereas oil absorption and emulsion capacities increased significantly with increasing irradiation dose. Differential scanning calorimetry showed decreases in transition temperatures (T_d) and enthalpies (ΔH), indicating a progressive denaturation of cowpea proteins with increasing irradiation. Size exclusion HPLC revealed increases in protein molecular weights, probably due to protein–protein cross-linking with irradiation in a dose-dependent manner. Reducing SDS-PAGE of FPC and PPC samples seems to suggest that the contribution of disulphide bonds to irradiation-induced cowpea protein–protein cross-linking is small.     

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.     

Use of low dose e-beam irradiation to reduce E. coli O157:H7, non-O157 (VTEC) E. coli and Salmonella viability on meat surfaces

This study determined the extent that irradiation of fresh beef surfaces with an absorbed dose of 1 kGy electron (e-) beam irradiation might reduce the viability of mixtures of O157 and non-O157 verotoxigenic Escherichia coli (VTEC) and Salmonella. These were grouped together based on similar resistances to irradiation and inoculated on beef surfaces (outside flat and inside round, top and bottom muscle cuts), and then e-beam irradiated. Salmonella serovars were most resistant to 1 kGy treatment, showing a reduction of ≤ 1.9 log CFU/g. This treatment reduced the viability of two groups of non-O157 E. coli mixtures by ≤ 4.5 and ≤ 3.9 log CFU/g. Log reductions of ≤ 4.0 log CFU/g were observed for E. coli O157:H7 cocktails. Since under normal processing conditions the levels of these pathogens on beef carcasses would be lower than the lethality caused by the treatment used, irradiation at 1 kGy would be expected to eliminate the hazard represented by VTEC E. coli.